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PostPosted: Tue Nov 01, 2016 7:07 pm 
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Location: New Hampshire
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Bikes owned: Suz, Yam, Honda, Kaw.
Has anyone enlarged the Pilot Bypass hole to enrich just off idle performance?

The VM larger carbs have two pilot holes. The one closest to the engine (pilot hole) and the one just behind the slide (bypass). The pilot hole diameter in carb body is usually smaller than bypass hole. If you have a "regularly" slide the bypass hole is typically blocked by slide during idle and only the pilot hole is feeding needed fuel mixture. In fact it is stated at this time the bypass hole is working in reverse actually feeding air to lean the pilot hole mixture. Now as you begin to lift round slide the bypass hole transitions to feeding additional fuel along with the now richer pilot hole, until the jet needle can kick in as slide is lifted even more.

If you are rich at idle, but lean as you just crack slide open it would seem that enlarging the bypass passage would help. I think if you enlarge bypass hole you have to turn in the pilot air screw for example since the larger bypass hole will be feeding even more air to pilot hole when slide is all the way down idling.

Now I have seen round slides shave a small notch/window right in front of the bypass. This being the case I would think the bypass is always supply fuel even when slide is closed... never transitioning from an air supply for pilot outlet.

One could change the slide cut richer, but think that would affect a wider range of throttle. These pilot holes seem to come into play between 0 to 1/8 (1/16) slide travel?

Anyone ever do this enlarge bypass hole or get a notched round slide?

Update: I suppose I should verify their sizes in case they have eroded or have become pitted. ... just a tad larger on bypass?

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Current Bikes
74 GT250 (T350 upgrade),
76 GT250 (T350 upgrade),
71 T350,
70 T350,
74 GT380,
75 T500,
73 GT550,
75 GT750,
72 Yamaha DS7 (R5 upgrade),
77 Yamaha RD400,


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PostPosted: Tue Nov 08, 2016 7:17 pm 
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Location: New Hampshire
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Bikes owned: Suz, Yam, Honda, Kaw.
This post reflects the challenges of a street rider versus racer: Trying to get cruising power at small throttle position. The bigger the engine the more you are small throttle pilot circuit and if you are like me want to get the most out of this without always giving more than needle throttle.

Recently, I put a new crank in my 73 GT550 and fresh top end :up: . It was a cold day when I ran it (<40F) last and what started this post for me. Just off idle (1/16 - 1/8 throttle most) it pinged like crazy . Full closed throttle it won't ping and idles well. Every where else in throttle pos an drpm very good. When around 80F outside no ping, but you know it is on the hairy edge at this spot. If you reduce compression (stock or less) it will go away, some, but still lean and suspect it would show up if a cold day and riding at this throttle pos and trying to get rpms.

The only issue is this one spot just off idle!!! :evil: To me this is where the pilot bypass is to supply fuel before needle jet can take over. I think it is more this than slide cut that come in just after pilot hole is done.

I did not find anything about bypass versus pilot hole sizing ratio. Nor the notch in the slide (also there is the opposite of the slot called a stake or something that looks to keep bypass covered longer?) Whatever, no information other than at idle you should be using Pilot hole only and as you begin to open throttle valve those bypass holes are critical and must supply fuel until the needle /jet can kick. I think this is what’ important for my situation.

I did find some better carb manual that talk about this area.

http://www.lunadesign.org/images/gixxer ... Manual.pdf
http://www.performanceoriented.com/special-procedures/
http://www.dansmc.com/MC_repaircourse.htm
http://bmwmotorcycletech.info/dellorto_manual.pdf
Holley, Rochester, etc

You find more on this pilot hole versus bypass hole(s) stuff with butterfly throttle (good stuff :up: ). Same thing though.

If you look at the early GT550 versus later GT550, they both have 1.4mm bypass but, the early has 0.5mm pilot hole (27.5 jet) and later has 0.8mm (25 jet) :idea:

What I have gleaned so far reading:
If you’re idle stop screw has the round slide lifted too much to hold idle you may be using the bypass supply too soon. So when you open throttle more there is no more bypass supply to add and you are lean as more air comes but before l needle/jet kicks in fuel mix. That sounds like it to me?
I suppose if there was a slide height distance range to check for when idling I could tell if too high. Also, if you are too high slide at idle, your pilot Air Screw has little or no affect . Now I have seen this before and now may understand a possible reason for this. Have this with the GT550, air screw does little. I think the VM bypass uses the fuel from pilot jet directly and nothing to do with air from pilot air screw like pilot hole.

So I am thinking it is a better idea to enlarge my pilot hole from 0.5mm to 0.8mm and use the 25 pilot. Which may be the issue with early GT550 versus later? I should be able to idle with a lower slide height and allow the bypass to kick in later as slide opens, before needle jet.

What do you think?

_________________
Current Bikes
74 GT250 (T350 upgrade),
76 GT250 (T350 upgrade),
71 T350,
70 T350,
74 GT380,
75 T500,
73 GT550,
75 GT750,
72 Yamaha DS7 (R5 upgrade),
77 Yamaha RD400,


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PostPosted: Thu Nov 10, 2016 10:27 am 
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Joined: Tue Mar 10, 2015 12:35 pm
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Location: Wales
Country: WALES
Bikes owned: suzuki gt 550j
I have a 1972 GT550 and was having similar problems to you pinking but only going up steep hills. This was in all types of weather, we sometimes get over 40 C. In summer and -12 in winter. I cured my problem by going up a size pilot jet from 27.5 to 30. No more pinking but mpg has suffered a little. I understand what you are saying about the pilot bypass but surely the carb slide is always going to be uncovered at idle due to the throttle stop screw? I always balance my carbs with the slides on the bottom and then turn the throttle stop screws in about 3 turns in which equates to the 1100 rpm for tickover. This of course keeps the slides off the pilot bypass all the time surely? I am interested in the outcome of your experiment as i was worried about plug colour being a little towards lean and not the chocolate brown i would prefer. I have raised the NJ clip to position 2 to richen the mixture. The bike starts and runs extremely well its just the plug colour i wasnt happy with. I have my airscrews 1 1\2 turns out but you are right when you say they seem to have little effect! I will be interested in the outcome

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PostPosted: Sat Nov 12, 2016 11:18 am 
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Joined: Tue May 18, 2010 5:38 pm
Posts: 1350
Location: New Hampshire
Country: USA
Bikes owned: Suz, Yam, Honda, Kaw.
I have two extra sets of carbs, but up here in New Hampshire biking season is just about over (snowmobiles coming out). But drilling pilot/bypass holes will either work or ruin them... probably the latter why looking for someone who has been here, but else I'll give it a go next season.

I like the slide notch idea too. A gent on here (forget who now but could search) in UK I think, has a set of very late GT550 carbs with slides that have the notched window. He was going to measure notch.. but it's not easy taking a slide out of those ganged carbs!

I am also looking at 2.0 slides ... I have a box (somewhere) of Yamaha DS7 slides. They should fit

But I think it's pilot circuit bypass so cut would be the right answer, but who knows I am in the right circuit

At the moment my GT550 is not a cold day bike for sure and I had raised compression some so that will need to go back if I can't fix that spot. Maybe squish heads would help, but still I am very sure that "spot" is too lean. every where else the bike is fine. but for street riding that "spot" is very popular :x

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Current Bikes
74 GT250 (T350 upgrade),
76 GT250 (T350 upgrade),
71 T350,
70 T350,
74 GT380,
75 T500,
73 GT550,
75 GT750,
72 Yamaha DS7 (R5 upgrade),
77 Yamaha RD400,


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PostPosted: Wed Nov 23, 2016 5:52 am 
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Joined: Tue Oct 14, 2008 6:47 pm
Posts: 1690
Location: Blythewood, SC, USA
My GT750 has 34mm VMs on it. When I got them they had 3.0 slides in them. It never pinged, but it did not like to come off idle without revving up quite a bit. I lived with it for years, and finally bit the bullet and replaced the slides with 2.5s. WHAT A DIFFERENCE!!! It picks up off idle easily and runs better through the whole range. I don't have any experience with modifying bypass holes, but it does sound as if you are too lean just as the slide moves, which is what I was experiencing. Good luck.



Lane

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Too many bikes, too much time, ENOUGH SPACE, FINALLY! Never enough money.........


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PostPosted: Thu Jan 05, 2017 6:23 pm 
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Location: New Hampshire
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Bikes owned: Suz, Yam, Honda, Kaw.
Vintageman wrote:
I am also looking at 2.0 slides ... I have a box (somewhere) of Yamaha DS7 slides. They should fit


They don't directly fit. Yam DS7's have the "Narrow" Guide Pin Groove type where the GT550 is the "Wide" type. Next the DS7 is a "Short" height Throttle Valve and GT550 is the "Tall" type.

Of course with effort and custom fabricating they could be made to work.

1) Narrow/Wide Guide Pin -> Fab a new guide pin or enlarge the Slide's Guide slot
2) Short versus Tall -> Use the shorter Carb Caps (e.g. from DS7)... but suspect stock throttle cable would be too long to lift slide. Get different throttle cable (H1 Kawa triple?) or make a tall adjusting screw in cap.

Good thing is you have both a left and right Idle groove position, hold jet needle at proper height and a 2.0 cut.

I am frustrated just cant find a round slide 2.0 cut that fits directly.... Am I wrong? Any other motorcycle may have the slide I need?

Do you know of any one in USA who could machine (has before) a large slot into the DS7 round slide?

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Current Bikes
74 GT250 (T350 upgrade),
76 GT250 (T350 upgrade),
71 T350,
70 T350,
74 GT380,
75 T500,
73 GT550,
75 GT750,
72 Yamaha DS7 (R5 upgrade),
77 Yamaha RD400,


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PostPosted: Thu Jan 05, 2017 7:07 pm 
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Joined: Mon Nov 03, 2008 10:47 am
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Location: Illinois
You should be able to machine (file) 0.5mm or more off the front section of your slides to reduce the cutaway. You may have to file the cutaway at a shallower angle but that's probably not necessary.

Throttle stop (idle screw) will need to be adjusted a little to let the slide close.

I had to change a set of Mikuni slides many years ago and took and angle grinder to them. Job done in 5 minutes and a huge improvement in slow speed pickup. YMMV


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PostPosted: Fri Jan 06, 2017 1:57 am 
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Joined: Thu Feb 16, 2012 11:50 am
Posts: 1916
Location: The Republic of South Yorkshire
Country: England
Bikes owned: GT550s GT750 GSX1400 and lots of spares
On my GT550A I always use 'super' fuel. I tried 'standard' with ethanol and it runs poor at low/mid throttle.
Better fuel, better running at all throttle/rpms.
It is tuned and has skimmed heads, mind.


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PostPosted: Fri Jan 06, 2017 11:36 pm 
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Location: New Hampshire
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Bikes owned: Suz, Yam, Honda, Kaw.
Alan H (et al),

Yes I understand that low octane fuel, increased static compression or dynamic compression ( e.g. from chambers) etc. can cause this detonation.

What is interesting, with these early GT550s, it happens only at one fixed throttle position, everywhere else is perfect … so clearly it can be fixed with proper jetting… no need to reduce compression to stock, remove chambers, reduce timing or run race gas.

This problem throttle position is very popular for street riding where much of our easy street cruising resides: Between pilot progression circuit to beginning of main circuit point. Solving this would make me happy and others may be able to leverage this joy.

I can induce this problem spot in just two ways: when I come down from larger throttle position, hard pull , and over 5000 RPM. Next I back off this smaller problem throttle position waiting for RPM to drop. Until RPMs drop it pings. If I simply remember (a terrible burden) to back all the way off throttle to pilot stop , no issue while RPMs settle down. This tells me idle is not jetted lean.

I can also make it happen if I open the throttle to this problem spot, hold, and let the RPMs climb high with light engine load. Once above 5000 rpm it happens again. All I need to do is open the throttle a tad more and it is perfect but damn I like doing this lazy aggressive type riding and should not have to put up with this f’upped throttle position. Tired of thinking about avoiding this problem throttle position, not enjoyable

I am look for a long 2.0 cut throttle valve with Large guide groove and left and right idle stop adjustment (don't exist?) or ideas of how fab one using a good starting point

I think this will fix “The” spot if it's at 1/8 throttle maybe not if 1/16 position? I am not sure if the position the issue occurs is at 1/16 or 1/8 throttle... it is one very narrow spot though and it should be possible for me to measure this, but my method to measure needs to be little more exact. I think the best cure really depends with accuracy where the spot is and thus how to fix this fixable jetting issue in the best manner: slide cut or pilot progression hole (AKA Pilot Bypass hole)

I see that most Kawasaki H1’s used 2.0 cut, not sure if they have the large guide groove or narrow. Does anyone have a H1 slide and can check?


Unfortunately, The H1 slide throttle stop is different than GT550 and controlled by rod to cap. I think my spare GT250/T250 caps will… so maybe this is an option.

Trying the UFO (one for Banshee may work on GT550?), may prove to be more work than I want to start with… so would like to try a 2.0 Cut first. Again very frustrating I can’t find one that fits.

I don’t think the later GT550 has this issue. The only difference I see as noted earlier is the pilot hole is larger on the latter. To me that would affect throttle position 0 to 1/16, not where I think the issue is. If I up the pilot jet size it quickly gets too rich for example setting at traffic light or just off idle. Increasing Pilot jet size helps problem spot, but doesn’t fully fix it and now I have induced a worse issue at idle/just off Idle which was fine before.

But maybe the later GT550 has it fixed and the Pilot hole is too small on early bike. Both bikes are the same, at Idle air box shouldn’t matter? Why: maybe the issue is due to the fact I have to raise the slides too high to achieve Idle at closed throttle. Thus, I am pulling fuel not from just the Pilot hole but also the progression (Bypass) hole just to idle. So as I lift throttle to 1/16 -1/8 there is no progression fuel supply left and thus run lean until main circuit can start to contribute the engines need.

So if 2.0 Cut is not the best fix. My next guess is to copy the later GT550 carb and enlarge Pilot hole (not Bypass hole).

If you have a butterfly throttle valve you can see when at idle stop setting if you are too wide exposing some of the progression supply holes where you should not. Not so easy for me to tell with slide type carb.

Long reply, I am sure this can be fixed with just jetting,

_________________
Current Bikes
74 GT250 (T350 upgrade),
76 GT250 (T350 upgrade),
71 T350,
70 T350,
74 GT380,
75 T500,
73 GT550,
75 GT750,
72 Yamaha DS7 (R5 upgrade),
77 Yamaha RD400,


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PostPosted: Fri Jan 06, 2017 11:36 pm 
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Joined: Tue May 18, 2010 5:38 pm
Posts: 1350
Location: New Hampshire
Country: USA
Bikes owned: Suz, Yam, Honda, Kaw.
Alan H (et al),

Yes I understand that low octane fuel, increased static compression or dynamic compression ( e.g. from chambers) etc. can cause this detonation.

What is interesting, with these early GT550s, it happens only at one fixed throttle position, everywhere else is perfect … so clearly it can be fixed with proper jetting… no need to reduce compression to stock, remove chambers, reduce timing or run race gas.

This problem throttle position is very popular for street riding where much of our easy street cruising resides: Between pilot progression circuit to beginning of main circuit point. Solving this would make me happy and others may be able to leverage this joy.

I can induce this problem spot in just two ways: when I come down from larger throttle position, hard pull , and over 5000 RPM. Next I back off this smaller problem throttle position waiting for RPM to drop. Until RPMs drop it pings. If I simply remember (a terrible burden) to back all the way off throttle to pilot stop , no issue while RPMs settle down. This tells me idle is not jetted lean.

I can also make it happen if I open the throttle to this problem spot, hold, and let the RPMs climb high with light engine load. Once above 5000 rpm it happens again. All I need to do is open the throttle a tad more and it is perfect but damn I like doing this lazy aggressive type riding and should not have to put up with this f’upped throttle position. Tired of thinking about avoiding this problem throttle position, not enjoyable

I am look for a long 2.0 cut throttle valve with Large guide groove and left and right idle stop adjustment (don't exist?) or ideas of how fab one using a good starting point

I think this will fix “The” spot if it's at 1/8 throttle maybe not if 1/16 position? I am not sure if the position the issue occurs is at 1/16 or 1/8 throttle... it is one very narrow spot though and it should be possible for me to measure this, but my method to measure needs to be little more exact. I think the best cure really depends with accuracy where the spot is and thus how to fix this fixable jetting issue in the best manner: slide cut or pilot progression hole (AKA Pilot Bypass hole)

I see that most Kawasaki H1’s used 2.0 cut, not sure if they have the large guide groove or narrow. Does anyone have a H1 slide and can check?


Unfortunately, The H1 slide throttle stop is different than GT550 and controlled by rod to cap. I think my spare GT250/T250 caps will… so maybe this is an option.

Trying the UFO (one for Banshee may work on GT550?), may prove to be more work than I want to start with… so would like to try a 2.0 Cut first. Again very frustrating I can’t find one that fits.

I don’t think the later GT550 has this issue. The only difference I see as noted earlier is the pilot hole is larger on the latter. To me that would affect throttle position 0 to 1/16, not where I think the issue is. If I up the pilot jet size it quickly gets too rich for example setting at traffic light or just off idle. Increasing Pilot jet size helps problem spot, but doesn’t fully fix it and now I have induced a worse issue at idle/just off Idle which was fine before.

But maybe the later GT550 has it fixed and the Pilot hole is too small on early bike. Both bikes are the same, at Idle air box shouldn’t matter? Why: maybe the issue is due to the fact I have to raise the slides too high to achieve Idle at closed throttle. Thus, I am pulling fuel not from just the Pilot hole but also the progression (Bypass) hole just to idle. So as I lift throttle to 1/16 -1/8 there is no progression fuel supply left and thus run lean until main circuit can start to contribute the engines need.

So if 2.0 Cut is not the best fix. My next guess is to copy the later GT550 carb and enlarge Pilot hole (not Bypass hole).

If you have a butterfly throttle valve you can see when at idle stop setting if you are too wide exposing some of the progression supply holes where you should not. Not so easy for me to tell with slide type carb.

Long reply, I am sure this can be fixed with just jetting,

_________________
Current Bikes
74 GT250 (T350 upgrade),
76 GT250 (T350 upgrade),
71 T350,
70 T350,
74 GT380,
75 T500,
73 GT550,
75 GT750,
72 Yamaha DS7 (R5 upgrade),
77 Yamaha RD400,


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PostPosted: Sat Jan 07, 2017 11:19 am 
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Joined: Mon Nov 03, 2008 10:47 am
Posts: 5809
Location: Illinois
tz375 wrote:
You should be able to machine (file) 0.5mm or more off the front section of your slides to reduce the cutaway. You may have to file the cutaway at a shallower angle but that's probably not necessary.

Throttle stop (idle screw) will need to be adjusted a little to let the slide close.

..



What he said. Just file the front of the slides by 0.5mm and try. If it helps but needs more, rinse and repeat.


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PostPosted: Sat Jan 07, 2017 1:20 pm 
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Joined: Tue May 18, 2010 5:38 pm
Posts: 1350
Location: New Hampshire
Country: USA
Bikes owned: Suz, Yam, Honda, Kaw.
Tz375, thanks for re-pointing that out. I did missed it first time and only saw Alan H

I also think that advice is in one of the links I added earlier too. I have tried this front file trick in the past in and didn't work out and thus avoided this option until now. Thanks for the poke on this and I am agreeing with you as what to do

I don't think it was too high idle problem as you mentioned about idle stop but a good point and easy to fix.

Let's think...it also changes the reference position of the jet needle to needle jet. Lowers it by .5 mm for example in this case. but that may be a good thing since the angle cut effects this area (making it richer) cancelling dropping the needle makes it leaner.

I must say I am very happy with my needle setting and finally get good mpg and runs perfect. OK maybe a little work here sorting out a new needle position or not. Would be the case if I found a 2.0 cut slide.

They sell shims, but every time I use them it makes the needle clip press against the needle retainer mechanism and the needle wont float about and center itself in the needle jet. Know what I mean? I have not had luck with shims and maybe not doing it right (another post maybe)

Now .5 mm in my case difference in needle jet may be a moot point

tz375 wrote:
the cutaway at a shallower angle but that's probably not necessary.
:?:

The other issue if I recall taking off from front in a level manner actually reaches over some into the cut angle so .5 off front will be more like a 0.6 less cut slide. so if I want .5mm affect maybe I go 0.4 or 0.45mm All trivial,

so yes to make a .5mm less cut I could reduce front by .5mm, maybe make the idle stop screw have a skinnier tip angle if needed. adjust needle pos if needle. Since I am not going to find a 2.0 cut slide this is worth a test and easy as you say

I have some spare slides to test.


I don't think the slide cut is the correct spot, but might be close enough and fixes my complaint.

_________________
Current Bikes
74 GT250 (T350 upgrade),
76 GT250 (T350 upgrade),
71 T350,
70 T350,
74 GT380,
75 T500,
73 GT550,
75 GT750,
72 Yamaha DS7 (R5 upgrade),
77 Yamaha RD400,


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PostPosted: Sat Jan 07, 2017 1:20 pm 
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Joined: Tue May 18, 2010 5:38 pm
Posts: 1350
Location: New Hampshire
Country: USA
Bikes owned: Suz, Yam, Honda, Kaw.
Tz375, thanks for re-pointing that out. I did missed it first time and only saw Alan H's reply

I also think that advice is in one of the links I added earlier too. I have tried this front file trick in the past (maybe going too much like 1.0mm where .5mm is OK) and didn't work out and thus automatically avoided this option until just now. Thanks for the poke on this and I am agreeing with you as what to do

I don't think it was too high idle problem as you mentioned about idle stop but a good point and kind of easy to fix.

Let's (over) :wink: think...it also changes the reference position height of the jet needle to needle jet. Lowers it by .5 mm for example in this case. but that may be a good thing since the angle cut effects this area (making it richer) cancelling dropping the needle .5mm which makes which it leaner. I may have more work re-tuning needle height even if I had gone with a true 2.0 cut slide.

I must say I am very happy with my needle setting on GT550 and finally get good mpg and runs perfect here. OK maybe a little work here sorting out a new needle position or not.

Bit off topic: They sell shims, but every time I use them it makes the needle clip press against the needle retainer mechanism and thus the needle wont float about and center itself in the needle jet. Runs real bad .. Do you know what I mean? I have not had luck with shims and maybe not doing it right (another post maybe)


tz375 wrote:
the cutaway at a shallower angle but that's probably not necessary.
:?:

The other issue if I recall taking off from front in a level manner actually reaches over some into the cut angle so .5 off front will be more like a 0.6 less cut slide. so if I want .5mm affect maybe I go 0.4 or 0.45mm All trivial,

I have some spare slides to get modded and ready to try this Spring (too cold now in New Hampsire)

Also to Alan H's point.

I do think I will restore head back (or closer to) stock static compression and that does help. And, since I don't run high octane gas (not possible these days just by pulling up to a gas pump unfortunately, if that pump shares one hose for all grades... and you only want to top off gas tank. Even if you select 93 octane... and if the guy before bought 87 you'll get a large slug of 87)

My point keeping this post going is there is clearly IMO a lean spot in jetting from day one with this bike and any performance mods can expose this very quickly.

Thanks

_________________
Current Bikes
74 GT250 (T350 upgrade),
76 GT250 (T350 upgrade),
71 T350,
70 T350,
74 GT380,
75 T500,
73 GT550,
75 GT750,
72 Yamaha DS7 (R5 upgrade),
77 Yamaha RD400,


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PostPosted: Mon Jan 09, 2017 5:10 pm 
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Joined: Sat Jul 31, 2010 5:53 am
Posts: 119
Location: Cleveland
Country: USA
Bikes owned: GT750
Vintageman wrote:
Alan H (et al),

Does anyone have a H1 slide and can check?






Groove is .080
S3's and s2's had 2.0 slides as well


Image

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'79 KZ650SR w/162hp Polaris XC700 Snowmobile Engine Dragbike
'73 GT750
'74 H2 750
'90 GSXR 1100
'75 H1 500
'76 KH400
'76 RD400
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PostPosted: Sun Jun 11, 2017 9:26 am 
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Joined: Tue May 18, 2010 5:38 pm
Posts: 1350
Location: New Hampshire
Country: USA
Bikes owned: Suz, Yam, Honda, Kaw.
Never did nothing with these VM carbs (I do think it is too lean at cross over from pilot to needle jet circuit even stock bike).

I reduced compression (back to stock but my ex ports are raised about 1.5 - 1.75mm ... so a little less than stock I suppose). I knew this helped but didn't fully rid the pinging as post explained. But this year I switched from Bassani 3-3 chambers ( they look to be similar dimensions as the Jemcos as well) to Ocelott's 3-3 chambers. This fully cured the issue that made me hate :evil: to ride this bike mildly aggressive.

The Bassani's see to have a max peak boost affect at lower RPM (5K-6K RPM) so with my driving style explained in this post, every time I backed off throttle after a >5K rpm pull the chambers were raising cylinder compression. Ping! Ping! Ping! if back throttle off 1/16 - 1/8 open.

The Ocellot's total tune length is 8 inches shorter :wth: . Running the numbers (via Bell's book) my RPM Peaks boost should have shifted up 750-1000 rpm. It did 8) . And since the GT550 is tuned for bottom and midrange I can't "feel" where I lost anything down here.

So i gave up on carb idea to provide more fuel to cool things down at this carb lean spot under higher compression... It sure sucked and glad it's gone and hope forever.

It has been many years since I ran my stock pipes, but do recall I had same problem ( i think others have complained as well here to) and would have had to figure something out and this is where I was heading. Sorry I did not follow though to see if this would have worked.

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Current Bikes
74 GT250 (T350 upgrade),
76 GT250 (T350 upgrade),
71 T350,
70 T350,
74 GT380,
75 T500,
73 GT550,
75 GT750,
72 Yamaha DS7 (R5 upgrade),
77 Yamaha RD400,


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