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PostPosted: Sat Aug 12, 2017 12:37 pm 
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On the street

Joined: Wed Aug 10, 2016 1:38 pm
Posts: 30
Country: United States
Bikes owned: 71 T500 Titan
I finally got a pretty good response from my carb tuning. I struggled for weeks with getting anything above 3/4 throttle. It looked to be over rich every time I checked everything, but I was stuck with the Idea that it had to be richer than stock due to using Uni filters and expansion chambers, and the weird thing is that I was wrong, and now I don't know why. The timing is set where it should be, but it could be off a few degrees.


So here is the set up I cobbled together.

.010 over pistons
No porting
Expansion chambers
Uni sponge filters
Powerdynamo ignition
B77HC plugs

Stock t500 carbs:
30 idle jet
5FP-8 needle- 2nd Notch from top
150 main jet

I am going to fiddle a little bit with the needle valve/ float height, but for the most part, I actually have a powerband here, and it doesn't choke itself off at WOT.

So my question to you all is why would it have to be so lean. I welded together the expansion chambers myself from the Swarbricks kit, and though I am no welde, I doubt I added an obstruction so bad in there that it would be flowing less air than stock. UNI filters may be crap. Timing may be off. Spark looks good to the normal eye.

Any ideas why this would be? So I can have a direction for my tinkering?

Thanks all.


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PostPosted: Sat Aug 12, 2017 3:42 pm 
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Road race school
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Joined: Wed Jan 18, 2012 8:01 pm
Posts: 865
Location: North of Albany, NY
Country: USA
Bikes owned: T500R (now), T500M (30 yrs ago)
Well, you are just about back to stock jetting, except for a leaner Jet Needle clip setting. I'll assume they are stock, early modle carbs (no external vent/overflow lines).

-- What Needle Jets are installed - P4 or P5? Suzuki was all over the place in their tech bulletin, even having a P4 in one carb, P5 in the other, for at least one year. The P5 is good for one, maybe two clip settings, richer than the P4. On my bike (71 T500 w/'73 engine, stock air box and exhaust) I had to use shims to find a happy place between clip position 2 and 3 with a P4 Needle Jet. I have a 150 Main, but think I will bump it up to 152.5, as I haven't been getting the power I should at WOT.

-- Perhaps your pod filters aren't as free flowing as you think. You may want to try a less dense foam.

-- Pods with hard plates behind them have been problematic to some folks with 2-stroke engines. There isn't the smooth vacuum you find on a 4-stroke engine. A bit of pulsing takes place, and may echo off pods with a hard plate across from the carb's intake bell.


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PostPosted: Sun Aug 13, 2017 8:53 am 
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On the street

Joined: Wed Aug 10, 2016 1:38 pm
Posts: 30
Country: United States
Bikes owned: 71 T500 Titan
Thanks for the reply. And I know that is where I ended, up and that is what is bothering me. It is nice to ride, but it is bugging me why it would be so lean. I do have early carbs. they are teh stock carbs from 70-71.

Stock needle jets- 188 series P-5s ( I had gotten the closest I could new jets for that series which were P-8s but they were way to rich and bogged it out.)

These Unis do have a hard plate inthe back, and it is only 2-3 inches from the inlet on the carb too. That is a good point.


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PostPosted: Sun Aug 13, 2017 2:54 pm 
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To the on ramp

Joined: Wed Jul 10, 2013 12:04 pm
Posts: 332
Country: England, UK
Bikes owned: FZ50, GP100, RG125 Gamma, GT380, Bandit 1200S
Try putting the stock airbox back on with standard carb settings. If that fixes everything then you know that your problem is with either the jetting or the air filters.
If it does NOT fix everything then you may have dirt in your carbs or (far less likely) ignition problem or other problem.
Is your oil pump correctly adjusted?
Are your crank seals ok?
Are your crankcase halves sealed well with the correct type of sealant?
Are the plug gaps correctly set?
Can you hear a head gasket leak?
Do you have good compression?
Do you have any trouble starting it?


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PostPosted: Sun Aug 13, 2017 3:19 pm 
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Road race school
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Joined: Wed Jan 18, 2012 8:01 pm
Posts: 865
Location: North of Albany, NY
Country: USA
Bikes owned: T500R (now), T500M (30 yrs ago)
With the P-5, the clip position is not unreasonable (for a stock motor).

sportston's input is correct, but I would, at this point, make sure that the Uni's aren't either too restrictive, or the back plates are causing an issue. Popping the stock airbox (if you have it) would be a good check, even if you need to punch a few holes in a filthy paper filter to let some air through.


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PostPosted: Tue Aug 15, 2017 7:28 am 
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On the street
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Joined: Tue Aug 01, 2017 11:48 am
Posts: 28
Location: Brighton, MI USA
Country: US
Bikes owned: ts250m
If you are relying on your plug reading to determine rich/lean there are a few things to bear in mind.
1) The heat range of the plug and type will affect the color of the insulator. A hot plug will read lighter than a cold plug.
2) The oil/fuel ratio and type of oil can affect the color of the insulator. This is more applicable to pre-mix only or pre-mix plus CCI than only CCI alone. Bean oil will look richer than synthetic.
3) To get an ideal main jet plug reading you should do a WOT run in top gear (going slightly uphill would be ideal but level ground is OK, downhill is not good) at least 30 seconds to a minute then pull in the clutch and kill the engine. Coast to a stop and do your plug reading. That way you are seeing ONLY the main jet effects. Use the same technique at 1/2 - 3/4 throttle for the jet needle clip position.
4) Ideally, you should be tuning for the altitude at which you are typically riding and the type of fuel you typically use. If all you can get is 10% ethanol (like in my case) then you might as well tune for it.

One more just my own 2 cents worth. In general, I like to tune two cycles just short of too rich with the factory recommended standard plug (if running high compression heads I'll go to a one step colder plug) and use both plug readings and the feel of the engine to determine the jetting.

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Currently - 75 TS250, 02 Kaw ZX-6R
Previously - 70 T350, 71 TS250, 72 GT380, 72 TS125, 72 TS250, 75 Yam YZ360B, 72 GT380 diy cafe racer, 80 GS750, 73 TS185, 82 GS1100


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PostPosted: Wed Aug 16, 2017 10:49 pm 
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On the street

Joined: Wed Aug 10, 2016 1:38 pm
Posts: 30
Country: United States
Bikes owned: 71 T500 Titan
Sportston. All of those would lead to an over-lean condition not overly rich. That is what is bothering me.
Starts fine, idles fine. cranks and case halves were fine. Head gasket may be a problem at some point, but it seemed like it was sealing fine. compression wasn't optimal when I started, but I intended to recheck after the rings set in. If i remember correctly there were both sides just under 120, or just over maybe.

Also, no air box to try. And Oiler is set correctly. I am not doing plug chops yet to determine lean/rich as up to this point it has all been over rich as I am working my way down. Above the current settings, the bike would bog itself out above 1/2 throttle. I started at the pretty standard 2 steps up on jetting for expansion chambers and filters, but it again choked itself to death above 1/2 throttle. Plugs completely wet at that point.

Update though. I cut the back plate out of the UNIs that i used. glued in some filter sponge, and it obviously changed a lot as far as the mixture goes. I havent had a chance to rejet to see where I end up now. But at this point I have a whole spectrum of jets, so I am going to go back to 125 mains and see how that is.


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PostPosted: Thu Aug 17, 2017 6:58 am 
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Road race school
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Joined: Wed Jan 18, 2012 8:01 pm
Posts: 865
Location: North of Albany, NY
Country: USA
Bikes owned: T500R (now), T500M (30 yrs ago)
Sharky wrote:
But at this point I have a whole spectrum of jets, so I am going to go back to 125 mains and see how that is.


125 ??? That is 10 steps leaner than stock.

With better air flow, you would wish to go richer.


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PostPosted: Thu Aug 17, 2017 12:33 pm 
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On the street

Joined: Wed Aug 10, 2016 1:38 pm
Posts: 30
Country: United States
Bikes owned: 71 T500 Titan
152.5 - I wasn't thinking when typing.


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PostPosted: Thu Aug 17, 2017 1:04 pm 
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Road race school
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Joined: Wed Jan 18, 2012 8:01 pm
Posts: 865
Location: North of Albany, NY
Country: USA
Bikes owned: T500R (now), T500M (30 yrs ago)
OK. Back on the same page. :up:

In fact, I just finished putting the 152.5 mains back on my bike. waiting for my wife to finish speaking with her mom, we'll have something to eat, and then take the bike out to see how she feels about more fuel at WOT. 8)

If I only got $1 for each time I've pulled the carbs, and made an adjustment... :roll:


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PostPosted: Sat Aug 19, 2017 10:40 am 
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On the street

Joined: Wed Aug 10, 2016 1:38 pm
Posts: 30
Country: United States
Bikes owned: 71 T500 Titan
Same boat. Cutting the backing plate out of the cheap UNIs really made a difference. 152.5 didn't do it lastnight. Trying 155s today.

For future reference these: Not so good for the Titan.

http://www.oldbikebarn.com/uni-pod-filter-kit-kawasaki-77-83-kz550-650.html


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PostPosted: Sat Aug 19, 2017 12:16 pm 
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Joined: Mon Dec 13, 2010 4:32 pm
Posts: 2878
Location: southwestern Pennsylvania
Country: USA
Bikes owned: 69 T350 thru 75 GT750
ConnerVT wrote:
Well, you are just about back to stock jetting, except for a leaner Jet Needle clip setting. I'll assume they are stock, early modle carbs (no external vent/overflow lines).

-- What Needle Jets are installed - P4 or P5? Suzuki was all over the place in their tech bulletin, even having a P4 in one carb, P5 in the other, for at least one year. The P5 is good for one, maybe two clip settings, richer than the P4. On my bike (71 T500 w/'73 engine, stock air box and exhaust) I had to use shims to find a happy place between clip position 2 and 3 with a P4 Needle Jet. I have a 150 Main, but think I will bump it up to 152.5, as I haven't been getting the power I should at WOT.

-- Perhaps your pod filters aren't as free flowing as you think. You may want to try a less dense foam.

-- Pods with hard plates behind them have been problematic to some folks with 2-stroke engines. There isn't the smooth vacuum you find on a 4-stroke engine. A bit of pulsing takes place, and may echo off pods with a hard plate across from the carb's intake bell.

Would K&N tapered angled pods eliminate the echo problem?
They look like:
Image

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BAS (Bike Acquisition Syndrome) - too many bikes but have room for more

Suzuki:
GT750 2x75
GT550 72 project & 75
GT380 72
T500 73 project
T350 69, 71 & 72 project
T250 72
Honda 85 CB650SC & 86 CB700SC
Yamaha 75 XS650
09 Triumph Bonneville SE


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PostPosted: Sat Aug 19, 2017 12:45 pm 
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Road race school
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Joined: Wed Jan 18, 2012 8:01 pm
Posts: 865
Location: North of Albany, NY
Country: USA
Bikes owned: T500R (now), T500M (30 yrs ago)
I really have no practical, first hand experience with putting pods on the Suzuki 2-stroke. Just what I have gleamed from here (and other sources on the web), and an understanding of how the engine and carbs behave. Quite a few folks have had issues with pods on these bikes. I know that there is a fairly choppy airflow through these carbs.

The issue could be there isn't enough volume at the intake bell side of the carb (the area inside the foam), or that the hard cap across from the bell reflects back the any pulse from the carb. The air box (with its boot) is a significantly larger volume, and being it joins both carbs, helps even out any turbulence or pressure differences (after all, these carbs work on the difference in pressure on one side to the other).

All theoretical ideas at this point, but then, isn't that what custom engineering is all about? :wink:


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PostPosted: Sat Aug 19, 2017 3:47 pm 
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To the on ramp

Joined: Wed Jul 10, 2013 12:04 pm
Posts: 332
Country: England, UK
Bikes owned: FZ50, GP100, RG125 Gamma, GT380, Bandit 1200S
Unless you have rolling road and gas analyser it is hard to set up jetting correctly for pod filters. 2-strokes don't like them and even 4-strokes will usually give you more power with a larger box on the intake.
They are a waste of time. The main problem with them is that they do not smooth the pulses out sufficiently. Manufacturers spend lots of expert time and money on trying to smooth out the pulses, as it will give more power and efficiency. They make bigger airboxes, reed valves, disc valves, induction chambers and try all kinds of methods to do this. One of the worse things you can do is to remove the airbox, especially on a 2-stroke. Make it bigger and you are heading in the right direction, but make it smaller or remove it entirely and you are making things worse for no reason. It might give you a teeny bit more mid-range but will seriously effect your top end.
If you wish to improve your engine's breathing capabilities, I suggest you put a standard, or larger than standard, airbox on, fit a high-quality foam filter inside it and put jetting back to standard or very close to standard size (unless you have a modified engine).

Also make sure you have;-
1. inline fuel filters fitted (essential!)
2. carbs have been blown out on a high-pressure airline thoroughly after fitting the filters
3. if you have points and condensors make sure they are adjusted and in good order (Replace if in doubt)
4. set the timing accurately
5. check that your plug leads are not corroded where they join the plug caps
6. check there are no cracks in the plug caps
7. check there are no cracks in the plugs porcelain
Good luck!


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PostPosted: Sat Aug 19, 2017 6:23 pm 
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Road race school
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Joined: Wed Jan 18, 2012 8:01 pm
Posts: 865
Location: North of Albany, NY
Country: USA
Bikes owned: T500R (now), T500M (30 yrs ago)
Agree with you on the air box. But customs have been doing it for some time, so the trick is mitigating the problems that come with putting a small foam sock on the intake bell of the carb, and calling it a day. Bigger is likely better - the more volume should dampen the bad effects (be it a larger foam filter, a runner between the carb and filter, some sort of "H" boot to connect the two carb bells together). That said, if it is an otherwise stock looking bike, find an air box.

Agree mostly with many of the other things you said.

Also make sure you have;-
1. inline fuel filters fitted (essential!)

- Not a big fan of inline filters. Much better to clean/prepare your fuel tank/system properly.

2. carbs have been blown out on a high-pressure airline thoroughly after fitting the filters
- Never use compressed air on an assembled Mikuni carb. It is very easy to damage the floats. With really gunked up bodies and brass, I prefer to soak in a carb dip, then flush everything with the jet nozzle from my garden hose.

3. if you have points and condensors make sure they are adjusted and in good order (Replace if in doubt)
4. set the timing accurately

- OP said he has an aftermarket ignition. I haven't seen timing to be super critical on the T500, until you are really fine tuning it. In fact, if someone was saying they were losing power at high RPM, I would first look to battery voltage before timing issues. I also recommend that folks don't change out their condensor unless they know there is an issue with it. Too many new dodgy ones one the market these days.

5. check that your plug leads are not corroded where they join the plug caps
6. check there are no cracks in the plug caps
7. check there are no cracks in the plugs porcelain

- A good recommendation for everyone. Worth the few bucks to buy new plug caps, cut back the plug wire a 1/2" or so, and put those new caps on. Stock 45+ year old coils can use all of the help they can get.


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