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PostPosted: Sun Apr 08, 2018 4:35 pm 
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On the street

Joined: Thu Aug 03, 2017 1:30 pm
Posts: 49
Location: Essex, England
Country: United Kingdom
Bikes owned: GT 250 1975
This is a continuation of a previous problem, that just doesn't seem to want to be fixed!

Previously we could get the bike to tick over, would rev up fine, but die under load. Now if you give it some beans it will go, not great, but it goes, if you try to pull away slowly it doesn't want to know!

The engine has been rebuilt, a new right hand carb, lots of other work done to it by Tom from on here

So any ideas are most welcome?

Thanks

Trev


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PostPosted: Sun Apr 08, 2018 6:25 pm 
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Moto GP
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Joined: Mon Dec 13, 2010 4:32 pm
Posts: 3278
Location: southwestern Pennsylvania
Country: USA
Bikes owned: 69 T350 thru 75 GT750
See Service Bulletin GT-30 for the variations in timing GT250As.
http://www.ozebook.com/compendium/techbuls/SerBulletin%20GT%20027-33.pdf

_________________
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
09 Triumph Bonneville SE


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PostPosted: Mon Apr 09, 2018 1:29 am 
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On the street

Joined: Thu Aug 03, 2017 1:30 pm
Posts: 49
Location: Essex, England
Country: United Kingdom
Bikes owned: GT 250 1975
jabcb wrote:
See Service Bulletin GT-30 for the variations in timing GT250As.
http://www.ozebook.com/compendium/techbuls/SerBulletin%20GT%20027-33.pdf



Thanks, i shall have a read 8)

Any further help or advice that anyone might have, please send it my way :?: :up: :clap:


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PostPosted: Mon Apr 09, 2018 3:56 am 
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Joined: Mon Dec 01, 2008 2:52 am
Posts: 1163
Location: Manchester, UK
First, is it firing evenly on both cylinders or is it missing a bit on one pot? Make sure the contact breaker point faces are clean and residue-free (contact cleaner or brake cleaner with some clean white paper works well).

Is the fuel tap flowing enough fuel? Is the vac pipe connected between the tap and the carbs?

Are you using a good battery? Don't worry too much about the charging system at this point - a good freshly-charged battery will give you a couple of hours running even if the charging system is duff (my GT380 ran total-loss for a few years quite happily). Put the battery on charge until you get 15V at the terminals, then fit it to the bike and see if that helps.

As Jabcb posted, check the timing -- do NOT use the marks on the flywheel to set your timing, as Suzi never changed the marks from the L/M to the A models, despite the fact that the recommended timing settings changed quite a lot for the A/B models, because of the revised porting. You need to use a dial gauge to set it properly and accurately.

Have you done a compression test? As it's been rebuilt, it should be at least 130psi in each cylinder (engine warm or hot, throttle held wide open, after 6 or 7 hard kicks in quick succession).

Are the exhausts and baffles clear? It's not enough just to clean the baffles, the exhausts will be FULL of oily crud and baked-on carbon. Bash them on the seams with a rubber mallet, poke stuff up them, etc.

Keep going, you'll get there :up:

_________________
1976 GT380 - wounded by me, and sold on
2006 SV650S. It's got cams, and valves, and stuff


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PostPosted: Mon Apr 09, 2018 4:07 am 
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On the street

Joined: Thu Aug 03, 2017 1:30 pm
Posts: 49
Location: Essex, England
Country: United Kingdom
Bikes owned: GT 250 1975
Craig380 wrote:
First, is it firing evenly on both cylinders or is it missing a bit on one pot? Make sure the contact breaker point faces are clean and residue-free (contact cleaner or brake cleaner with some clean white paper works well). No it is not firing evenly on both pots,but also it currently have an electronic ignition fitted, which might be a bit suspect to be honest, i have another other post about a new electronic ignition

Is the fuel tap flowing enough fuel? Is the vac pipe connected between the tap and the carbs? I would say that fuel is getting through, if it's enough is a another question?

Are you using a good battery? Don't worry too much about the charging system at this point - a good freshly-charged battery will give you a couple of hours running even if the charging system is duff (my GT380 ran total-loss for a few years quite happily). Put the battery on charge until you get 15V at the terminals, then fit it to the bike and see if that helps. Yes it is a good battery

As Jabcb posted, check the timing -- do NOT use the marks on the flywheel to set your timing, as Suzi never changed the marks from the L/M to the A models, despite the fact that the recommended timing settings changed quite a lot for the A/B models, because of the revised porting. You need to use a dial gauge to set it properly and accurately. Ok, I will need to get a dial gauge, are they expensive?

Have you done a compression test? As it's been rebuilt, it should be at least 130psi in each cylinder (engine warm or hot, throttle held wide open, after 6 or 7 hard kicks in quick succession). I haven't but Tom (Sporton) my have done?

Are the exhausts and baffles clear? It's not enough just to clean the baffles, the exhausts will be FULL of oily crud and baked-on carbon. Bash them on the seams with a rubber mallet, poke stuff up them, etc. Will need to take a look at them

Keep going, you'll get there :up:


The major problem is, it's my mates bike, and he now lives 2 hours away from me, so getting to look at it is not very frequent! but as you say we will continue to battle on!

and thanks for the reply :up: 8)


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PostPosted: Mon Apr 09, 2018 1:52 pm 
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Road race school

Joined: Wed Jul 10, 2013 12:04 pm
Posts: 847
Country: England, UK
Bikes owned: FZ50, GP100, RG125 Gamma, GT380, Bandit 1200S
Craig380 wrote:
First, is it firing evenly on both cylinders or is it missing a bit on one pot?
No. Right pot is worse.
Is the fuel tap flowing enough fuel? Yes. It had the fuel tap stripped, carefully cleaned and new inline fuel filters and fuel lines fitted.
Is the vac pipe connected between the tap and the carbs? Yes and it too is quality new pipe

Are you using a good battery? Yes. Voltage was fine

As Jabcb posted, check the timing -- do NOT use the marks on the flywheel to set your timing, as Suzi never changed the marks from the L/M to the A models, despite the fact that the recommended timing settings changed quite a lot for the A/B models, because of the revised porting. You need to use a dial gauge to set it properly and accurately.
Good point. I didn't know that Suzuki made that bodge! I used a bright strobe light and flywheel marks as the manual suggested

Have you done a compression test? Yes. They were fine. The bores are not scored or worn and the pistons and rings don't look old or show signs of blow-by.

Are the exhausts and baffles clear? It's not enough just to clean the baffles, the exhausts will be FULL of oily crud and baked-on carbon. Bash them on the seams with a rubber mallet, poke stuff up them, etc. Baffles are clear but clogged pipes was one of the outside chance possibles I mentioned to him. I simply ran out of time to do any more. I wonder if it would be a good idea to run up the road without pipes on just to test it.

Also had carbs ultrasonic cleaned and reconned. Float levels set very carefully. New plugs. Plug caps swapped with no effect. Coils swapped with no effect. New quality earth wires run to engine and chassis from negative of battery. Inlet leak found so replaced inlet stub and now no signs of inlet leaks. New air filter fitted. Crankcase leak was found, so split cases and replaced broken bolt and resealed using 3-bond. Head gasket leaked, so head and barrel was skimmed and squish-band recut. Obviously new gaskets fitted. Crank was reconned by Chris Applebee. New gearshaft and bearing fitted to replace damaged old one. Oil dam missing so installed s/hand one. Neutral brake spring and plunger missing, so installed s/hand one. Oil lines bled and leaking oil tank pipe replaced.

Keep going, you'll get there :up: I agree!


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PostPosted: Thu Apr 12, 2018 4:50 pm 
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Joined: Tue May 18, 2010 5:38 pm
Posts: 1413
Location: New Hampshire
Country: USA
Bikes owned: Suz, Yam, Honda, Kaw.
I had a real hard time with a gt250A once upon a time(s)

Was it a running bike before you did project?

Post a video of it running!

How hard is it to stick the points back on?

Micron wrote:
Crank was reconned by Chris Applebee


What was done exactly?

I don't think 20 degrees vs 24 degrees is enough of a difference to cause what you describe, but should sort that out.

If you don't have dial gauge, but have Vernier Calibers with a tail, you can extend the tail into cylinder to do measurement

I have timed many bikes via Rotor marks and no mechanical problem all very accurate. Unless key way or crank spun

Since the crank was torn down it would be good to verify back together OK and checking rotor timing mark to actual piston/crank position with gauge in cylinder will sort that out. And, if you find rotor timing marks are off significantly something else is wrong in my experience


swap carbs (even if left and right carbs I think can be rigged for testing?)


Is the top end noisy? Rattling more than it should.

Can you shake either end of crankshaft (bad bearing)

If the crank is off, it quickly makes piston wears the cast iron liner. Take off exhaust, raise pistons to see if liner has lost all it hone marks. I think intake side takes it the worst, bit check both

What else

Oh, With carbs off. place you hand over each intake and kick it over. You should feel sharp suction and both equal.

Is transmission binding, Disengage clutch to test maybe?

Kick it over by hand short quick moves as piston is up stroke compressing, If good piston/ring fit it should feel smooth and bouncy/ springy. no air leaking past rings... no binding. Use kicker by hand get a good feel as you try each piston


good timing, Sharp long blue spark arc
Carb (check float height with hose level) Mikuni Jets all. Stock Airbox



Oh what was wrong with my Gt250A. First time too much fuel due to me trying to do airbox swap. Starting new jetting choices rich on an oil injection only system is not safe as they say... fuel washes oil away... mix a little oil in tank if you are doing a complete new carb intake setup

another time crank shaft Rod/big end out off spec (after about just a few hundred miles of use) causing piston to slam against cylinder liner intake side. Piston really no wear, but liner wore out. Top end noisy (Yes air cooled two strokes are, but should not be that loud)

Not sure if this helps at all, but it brings back some awful memories.

Good new is once you sort things out... It is a freaking little rev rocket with no torque below 4K RPM. I couldn't drive mine slow

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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 (Daytona Cyls),


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PostPosted: Thu Apr 12, 2018 6:04 pm 
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Moto GP
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Joined: Mon Nov 03, 2008 10:47 am
Posts: 6016
Location: Illinois
At this stage it sounds like jetting or crank seals.

Pull the carbs again and remove jets. Blow through one drilling in the carb body with a can of carb cleaner and then repeat on the other side and compare flow. It's a little subjective, but a clog will quickly reveal itself if one is very different to the other.

If the pilot jets are not new, replace them with new genuine Mikuni jets and do teh same flow test comparison. Make sure they are the correct design of pilot jets. There are at least 2 designs that look the same from a few feet away but flow very differently. I think yours are VM22-210.

On the ignition side, measure resistance on the coils - primary and secondary and then measure the caps -or just replace them and avoid that step.

If you have a compression tester, test both sides, plugs out, fuel and ignition off and throttles wide open. Kick til the reading stops rising and report back. A compression tester can be loaned form Autozone or other auto stores.

Next I would do a leakdown test. You don't need a full service Motion Pro tester. a simple one from Economycycle will probably fit. You may need different size plugs but they are cheap and you get them from the plumbing section of your local ACE HArdware or Lowes or whichever.

Also check that both throttle slides are rising smoothy together and in synch.

20 or 40 degrees of ignition timing would work to get it running but get it right for hard running.


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PostPosted: Tue Apr 17, 2018 1:55 am 
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On the street

Joined: Thu Aug 03, 2017 1:30 pm
Posts: 49
Location: Essex, England
Country: United Kingdom
Bikes owned: GT 250 1975
Thanks Vintageman,
I have added my comments below :up:

Vintageman wrote:
I had a real hard time with a gt250A once upon a time(s)

Was it a running bike before you did project? Not well hence the original stip down

Post a video of it running! That may have to wait, as the bike is some two hours away from me, sorry

How hard is it to stick the points back on? very, it never came with them

Micron wrote:
Crank was reconned by Chris Applebee


What was done exactly? new bearings and seals

I don't think 20 degrees vs 24 degrees is enough of a difference to cause what you describe, but should sort that out. I don't remember mentioning this?

If you don't have dial gauge, but have Vernier Calibers with a tail, you can extend the tail into cylinder to do measurement I have purchased a dial gauge, so will use it next time i'm there

I have timed many bikes via Rotor marks and no mechanical problem all very accurate. Unless key way or crank spun

Since the crank was torn down it would be good to verify back together OK and checking rotor timing mark to actual piston/crank position with gauge in cylinder will sort that out. And, if you find rotor timing marks are off significantly something else is wrong in my experience Will need to do this


swap carbs (even if left and right carbs I think can be rigged for testing?)


Is the top end noisy? Rattling more than it should. Not particually

Can you shake either end of crankshaft (bad bearing) hopefully not, as the bearing are new, and the bike hasn't really moved much since

If the crank is off, it quickly makes piston wears the cast iron liner. Take off exhaust, raise pistons to see if liner has lost all it hone marks. I think intake side takes it the worst, bit check both

What else

Oh, With carbs off. place you hand over each intake and kick it over. You should feel sharp suction and both equal. I will try the other stuff first, including new ignition

Is transmission binding, Disengage clutch to test maybe? Doesn't appear to be

Kick it over by hand short quick moves as piston is up stroke compressing, If good piston/ring fit it should feel smooth and bouncy/ springy. no air leaking past rings... no binding. Use kicker by hand get a good feel as you try each piston


good timing, Sharp long blue spark arc Sparks appear to be ok, not sure if they are long sparks
Carb (check float height with hose level) Mikuni Jets all. Stock Airbox



Oh what was wrong with my Gt250A. First time too much fuel due to me trying to do airbox swap. Starting new jetting choices rich on an oil injection only system is not safe as they say... fuel washes oil away... mix a little oil in tank if you are doing a complete new carb intake setup

another time crank shaft Rod/big end out off spec (after about just a few hundred miles of use) causing piston to slam against cylinder liner intake side. Piston really no wear, but liner wore out. Top end noisy (Yes air cooled two strokes are, but should not be that loud)

Not sure if this helps at all, but it brings back some awful memories.

Good new is once you sort things out... It is a freaking little rev rocket with no torque below 4K RPM. I couldn't drive mine slow


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PostPosted: Tue Apr 17, 2018 2:00 am 
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On the street

Joined: Thu Aug 03, 2017 1:30 pm
Posts: 49
Location: Essex, England
Country: United Kingdom
Bikes owned: GT 250 1975
Hi tz,

Again thank you for the continued support, I have added my comments below :shock: :D

tz375 wrote:
At this stage it sounds like jetting or crank seals.

Pull the carbs again and remove jets. Blow through one drilling in the carb body with a can of carb cleaner and then repeat on the other side and compare flow. It's a little subjective, but a clog will quickly reveal itself if one is very different to the other. The right one is brand new, the left has been ultrasonically cleaned

If the pilot jets are not new, replace them with new genuine Mikuni jets and do teh same flow test comparison. Make sure they are the correct design of pilot jets. There are at least 2 designs that look the same from a few feet away but flow very differently. I think yours are VM22-210. I believe the left hand jets have been replaced, but Sporton will know more, as he did the carb work, the right one is new

On the ignition side, measure resistance on the coils - primary and secondary and then measure the caps -or just replace them and avoid that step. Caps are new, coils have been replaced before, but I will check the resistance

If you have a compression tester, test both sides, plugs out, fuel and ignition off and throttles wide open. Kick til the reading stops rising and report back. A compression tester can be loaned form Autozone or other auto stores. Compression has been check again by Sporton, and he reports them to be good

Next I would do a leakdown test. You don't need a full service Motion Pro tester. a simple one from Economycycle will probably fit. You may need different size plugs but they are cheap and you get them from the plumbing section of your local ACE HArdware or Lowes or whichever. Not sure what a leakdown test is

Also check that both throttle slides are rising smoothy together and in synch. Yes they are

20 or 40 degrees of ignition timing would work to get it running but get it right for hard running. Again, I don't remember mentioning anything about this?


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PostPosted: Tue Apr 17, 2018 3:52 pm 
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Road race school

Joined: Wed Jul 10, 2013 12:04 pm
Posts: 847
Country: England, UK
Bikes owned: FZ50, GP100, RG125 Gamma, GT380, Bandit 1200S
Yes both carbs had new jets and needles. Complete recon kits installed, both carefully and properly.
Crankcases were opened cleaned and resealed using 3-bond. So should be no leaks from them.
If new ignition system is fitted and it still runs like poo, it must be the exhausts. Its the only thing left.


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PostPosted: Tue Apr 17, 2018 8:43 pm 
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Moto GP
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Posts: 6016
Location: Illinois
Hold it right there. Did you say you fitted carb kits with needles and jets from the kits? If so please find the old needles and needle jets and buy new genuine Mikuni mains and pilot jets and report back. Carb kits are notorious for not being to stock OEM dimensions and are frequently worse than stock worn jets!

When all that was going on, were the pipes removed and cleaned? or were the baffles removed and cleaned at least? I once rebuilt a motor and stuffed paper towels in the exhaust ports to keep bugs and dust out. Then I fitted teh pipes and fired it up and of course those wads of paper were now completely stuck down inside the pipes. You didn't do anything that silly did you?


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PostPosted: Wed Apr 18, 2018 12:54 am 
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On the street

Joined: Thu Aug 03, 2017 1:30 pm
Posts: 49
Location: Essex, England
Country: United Kingdom
Bikes owned: GT 250 1975
Thanks for all the replies, I think that I need to do one thing at a time, so I will get the electronic ignition sorted first and go from there.
Please watch this space!


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PostPosted: Wed Apr 18, 2018 3:14 am 
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Road race school

Joined: Wed Jul 10, 2013 12:04 pm
Posts: 847
Country: England, UK
Bikes owned: FZ50, GP100, RG125 Gamma, GT380, Bandit 1200S
The carb recon kits were of reasonable quality and the correct sizes. The old jets were damaged and worn so are useless. If it were a problem with jet dimensions it would not effect only the right cylinder, it would effect both as they both had identical jets.
I didn't put anything down the exhausts. I did remove the baffles to check them and the baffles are clear and not badly coked up. However that does not rule out the possibility of the insides of the exhausts being clogged.
However, I did notice that the ignition rotor didn't line up with one of the optic sensors very well due to badly manufactured ignition system. Which is why I suggested getting a new electronic ignition of better quality.


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PostPosted: Thu Apr 19, 2018 12:13 pm 
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Joined: Tue May 18, 2010 5:38 pm
Posts: 1413
Location: New Hampshire
Country: USA
Bikes owned: Suz, Yam, Honda, Kaw.
Micron wrote:
I think that I need to do one thing at a time, so I will get the electronic ignition sorted first and go from there.
Please watch this space!

+1

Carb rebuild kits.

Main Jet, Pilot Jet - just buy Mikuni: They are inexpensive, why take a chance a try some no-name or second source brand.

Float Needle Valve: Buy OEM (more expensive), should be available. You can just buy the needle itself if your clever. The aftermarket will work but usually requires you to bend the float tab too much and more than you should.

Did you verify float height?


Needle Jet. No kit gives you this. I think it's 172 series and obsolete from Mikuni (please verify this). Many times (due to age -oxidation) the needle jet is bad inside where it meters about jet needle. Oh it may say the 169 series is a direct cross. It is not. It sets 1mm lower in carb body. If you take this option I would lower the Jet Needle one clip position leaner to make up fact 169 set lower. Shimming it up can cause aligning issue with air passage in carb body.

Better is use the 18x series Mikuni needle jet. by x I think it is either x=2 or x = 8: 182 or 188 series... I forget. This needle jet is the same dimensions everywhere as the 172. But, It take a Hex jet instead of Round main jet. You can cross the round size jet to hex and use hex. Or as I do ( when making stock bike) use the round and it will cross thread it's way in easy, re-thread it and hold well.


Jet Needle. This may be obsolete. Check eBay for needle or spare carb parts. If yours is bad, your only option may be aftermarket like Keyster ( their Y series). I have seen and heard claims that this is one item not copied very exactly. Also a bike may have changed jet needle over time and you get the wrong one. GT250A, I think has remained the same jet needle series since early T250 turned into GT250 and into the A and B models (verify this please)


OEM Bowl gaskets...only way to go for many aftermarket ones don't fit well or material fails and leaks.

_________________
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 (Daytona Cyls),


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