GT250 left cylinder issues

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jabcb
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Re: GT250 left cylinder issues

Post by jabcb »

Making headway…

A good, but expensive battery. You should use a battery charger/tender that is labeled for use with lithium batteries. Should also use a rectifier/regulator that is compatible with lithium batteries.

The alternator output specs for stock bikes are here: https://ozebook.com/compendium/suzi/suzidata1.htm
See page 17, #s for stock T250/GT250 with an old-school non-sealed battery & stock lighting.
The GT250 should start charging by 2k rpm. Voltage should rise with increasing rpms.

Your aftermarket coils might have different primary resistance. Don’t know what you did with the lighting load. That will affect the rpm your bike starts charging.

The voltage doesn’t vary with rpm — this has me wondering.
Some T250/T350/T500 will not start without a battery, some will start & run badly, and some will start & run fine.
(Some years ago I disconnected a T350 battery when adjusting the points. Got interrupted by something. Forgot to reconnect the battery. Bike started & ran fine but then burned out the lights.)

Do your lights work without the engine running? (Am thinking maybe you have a wiring issue, or ???)

for 1&3) It’s fairly common for the oil pump lever to stay partially open with the throttle closed when the engine is not running. It is fine if it returns when the engine is running.

for 2) the slide cutout faces the air cleaner. Remove the air filters & look in the carb to verify. This is a common mistake.
While you are at it — visually check to see if the slides operate in unison. Do they fully open at the same time? Do they work smoothly?
BAS (Bike Acquisition Syndrome) - too many bikes but have room for more

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GT750 2x75
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Yellow02Z06
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Suzuki 2-Strokes: 1974 GT250

Re: GT250 left cylinder issues

Post by Yellow02Z06 »

jabcb wrote: Thu Mar 03, 2022 10:29 am Making headway…

A good, but expensive battery. You should use a battery charger/tender that is labeled for use with lithium batteries. Should also use a rectifier/regulator that is compatible with lithium batteries.

The alternator output specs for stock bikes are here: https://ozebook.com/compendium/suzi/suzidata1.htm
See page 17, #s for stock T250/GT250 with an old-school non-sealed battery & stock lighting.
The GT250 should start charging by 2k rpm. Voltage should rise with increasing rpms.

Your aftermarket coils might have different primary resistance. Don’t know what you did with the lighting load. That will affect the rpm your bike starts charging.

The voltage doesn’t vary with rpm — this has me wondering.
Some T250/T350/T500 will not start without a battery, some will start & run badly, and some will start & run fine.
(Some years ago I disconnected a T350 battery when adjusting the points. Got interrupted by something. Forgot to reconnect the battery. Bike started & ran fine but then burned out the lights.)

Do your lights work without the engine running? (Am thinking maybe you have a wiring issue, or ???)

for 1&3) It’s fairly common for the oil pump lever to stay partially open with the throttle closed when the engine is not running. It is fine if it returns when the engine is running.

for 2) the slide cutout faces the air cleaner. Remove the air filters & look in the carb to verify. This is a common mistake.
While you are at it — visually check to see if the slides operate in unison. Do they fully open at the same time? Do they work smoothly?
Have proper lithium specific charger.

Lighting works when not running.

Now one of the new aftermkt coils failed looks like manufacturing defect in terms of plug wire connection….these coils are no where near as good quality as typical OE coils but old ones were bad after 50 years and OE quality replacements do not seem to be out there…

Replacement on way…

I am again getting hopeful though that Inhave solved problem….anxious to test but have to wait for coil…
74 CL200 scrambled
75 GT250 cafe
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85 RZ 350
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jabcb
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Suzuki 2-Strokes: 69 T350 thru 75 GT750
Location: southwestern Pennsylvania

Re: GT250 left cylinder issues

Post by jabcb »

What coils are you using?

While you are waiting could be a good time to look into a rectifier/regulator that is compatible with your lithium battery.
BAS (Bike Acquisition Syndrome) - too many bikes but have room for more

Suzuki:
GT750 2x75
GT550 72 & 75
GT380 72
T500 69 project & 73 project
T350 69 & 71
Honda 85 CB650SC & 86 CB700SC
09 Triumph Bonneville SE
Yellow02Z06
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Suzuki 2-Strokes: 1974 GT250

Re: GT250 left cylinder issues

Post by Yellow02Z06 »

jabcb wrote: Fri Mar 04, 2022 10:13 am What coils are you using?

While you are waiting could be a good time to look into a rectifier/regulator that is compatible with your lithium battery.
I ordered the coils from Rex’s - they appear to b a fairly std aftermarket coil, but unclear the brand. Rex’s sent me a new one. I installed, and bike is having same issues….and further investigation showing strange behavior…I was hopeful the oil pump adjustment was the fix but it was not….I was taking one coil wire off again at a time…and at one point right cylinder did not fire and left did….opposite of normal problem….but the strange thing that hooking up a timing light when engine running shows signal in spark plug wires both and static rest (spark plugs out, turn over engine by hand) always shows spark…

All I can think of is that somehow not getting strong spark in both, while running….but again not sure

Maybe Lithium battery is root…wiring diagram to me shows alternator charges battery which then fires plugs, so maybe it not giving enough voltage when running but voltage at least at battery is showing good when running…it’s a strange one for sure….

By the way that annual in one book does not have GT250 as a model in it….
74 CL200 scrambled
75 GT250 cafe
71 A7 Avenger 350
85 RZ 350
77 XS400 “No XS”
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karl pa
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Re: GT250 left cylinder issues

Post by karl pa »

Just went through the post from beginning, I see you replaced coils,one condenser,plugs and caps, but didn't see anything about replacing points or second condenser.
I am also confused, at one point you say plugs are showing rich, another point you say the left plug is clean, another point you say the left plug is wet.
At some point you need to do a leak down test to check crank seals. Compression test shows top end condition, it has no bearing on crank seals and bottom end. I know you said it ran good before, but crank seals can let go while riding, and you said it let go suddenly and hasn't run good since. So it would be good to rule them out of the issue.
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Re: GT250 left cylinder issues

Post by Yellow02Z06 »

karl pa wrote: Sun Mar 06, 2022 8:14 am Just went through the post from beginning, I see you replaced coils,one condenser,plugs and caps, but didn't see anything about replacing points or second condenser.
I am also confused, at one point you say plugs are showing rich, another point you say the left plug is clean, another point you say the left plug is wet.
At some point you need to do a leak down test to check crank seals. Compression test shows top end condition, it has no bearing on crank seals and bottom end. I know you said it ran good before, but crank seals can let go while riding, and you said it let go suddenly and hasn't run good since. So it would be good to rule them out of the issue.
Thks Karl for taking the time…actually I did just replace second condensor….have not replaces points…I bought them, but one appears to be used which I did not realize, so decided against putting both in…the existing ones seem clean and functional….

Regarding the plugs, to clarify left has been wet and when one wipes it off, it’s clean…in general since the beginning the left cylinder has never gotten hot as measured by exhaust pipe temp…

So most recently as I was saying it has gotten more confusing, as left has starting heating up, firing, but then right stopped….I know this by taking plug wires on and off one at a time, while it’s running.

It will always show a spark on both cylinder when plugs out, just testing for spark. it always shows spark with a timing light flashing on both cylinders.

Yet it is clear that it is often running on one cylinder most of the time the right.

So I think it’s related to somehow not getting strong spark in running conditions especially at mid to high rpm, I really do not think it’s fuel related as that left plug is usually wet, and unburned fuel will conme from left pipe…

And further maybe it’s Lithium battery or stator or regulator related….

And yes you are right I should do a leakdown at some point, I have a friend with the setup

I generally do all my own work and have been through a lot and come out other end successfully on a number of old bikes, but this one is really strange and frustrating….
74 CL200 scrambled
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85 RZ 350
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Re: GT250 left cylinder issues

Post by karl pa »

Yellow02Z06 wrote: Sun Mar 06, 2022 11:00 am And further maybe it’s Lithium battery or stator or regulator related….
The stator and regulator only comes into play with charging issues, and you said it shows 13.2 volts which should be fine for ignition.
I agree with jabcb that you should go with proper regulator/rectifier to save your battery from overcharge, I also agree with jabcb your voltage should vary at different rpm. Most stock charging systems will go as high as 16-17 volts at high rpm, which is way to high for modern batteries.
When I check voltage, I install a temporary volt meter so I can see voltage as I ride.
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Re: GT250 left cylinder issues

Post by Yellow02Z06 »

karl pa wrote: Sun Mar 06, 2022 11:38 am [quote=Yellow02Z06 post_id=178750 time=<a href="tel:1646586002">1646586002</a> user_id=15320]
And further maybe it’s Lithium battery or stator or regulator related….
The stator and regulator only comes into play with charging issues, and you said it shows 13.2 volts which should be fine for ignition.
I agree with jabcb that you should go with proper regulator/rectifier to save your battery from overcharge.
[/quote]

OK well that all makes sense, it’s just with the spark plug on left side being wet and unburned fuel coming out, it’s sure looks like it’s getting fuel….I guess I can look at / clean carbs again….unless either of you guys have other ideas
74 CL200 scrambled
75 GT250 cafe
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85 RZ 350
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Re: GT250 left cylinder issues

Post by dollydog »

this one just came to me as i was refurbing an alternator stator. i couldn't find this fault for ages and it was the same symptoms as yours. where the black and the white wire - from the points/condensors - go through the little hole in the stator and out the other side. got it? well one of my wires had chafed and it was earthing out, not all the time, but enough to cause one side to run, then not. i found it when i actually took the stator off to change it. i put some heat shrink over it, right down inside the hole, shrank it, replaced it and never had a problem with that engine again. i tried everything before then, as you have, until i found that :D
cheers, dd.
p.s. if it isn't that, at least it can be crossed off the list :up:
GTS250 road registered. TS250 engine, Ramair frame.
GT250 big bang road registered. Both pistons fire the same time. USD forks.
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Yellow02Z06
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Re: GT250 left cylinder issues

Post by Yellow02Z06 »

dollydog wrote: Mon Mar 07, 2022 4:40 pm this one just came to me as i was refurbing an alternator stator. i couldn't find this fault for ages and it was the same symptoms as yours. where the black and the white wire - from the points/condensors - go through the little hole in the stator and out the other side. got it? well one of my wires had chafed and it was earthing out, not all the time, but enough to cause one side to run, then not. i found it when i actually took the stator off to change it. i put some heat shrink over it, right down inside the hole, shrank it, replaced it and never had a problem with that engine again. i tried everything before then, as you have, until i found that :D
cheers, dd.
p.s. if it isn't that, at least it can be crossed off the list :up:
Now that a good one! I’ll ck - only in vintage motorcycles does crap like that happen, but when you find it - it’s exciting! Thks
74 CL200 scrambled
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71 A7 Avenger 350
85 RZ 350
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73 H1 500 Aubergine
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Re: GT250 left cylinder issues

Post by Yellow02Z06 »

I finally f%#*king fixed it!!!

So i took the carbs back off and noticed that the left side main/jet emulsion tube assembly was moving/loose….I looked at a parts diagram and noted that there is a washer in between the jet and tube. I think it may have been missing when I got the bike, but luckily I had two of them in a rebuild kit i had, installed them, reinstalled carbs, and voila!

Both cylinders firing, similar exhaust temps, revs well, rode it a bit feels pretty damn strong (froze my ass off!)

Thks for all the help guys….weird one but I learned more about the bike, found and fixed some other issues, and got some maintenance /new parts in through this

I will see about getting a posting service so i can share some pics….
74 CL200 scrambled
75 GT250 cafe
71 A7 Avenger 350
85 RZ 350
77 XS400 “No XS”
73 H1 500 Aubergine
87 GSX-R750
85 GPz900R Ninja GWB
83 CB1100F
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Re: GT250 left cylinder issues

Post by karl pa »

:up: Good to hear, many times it is a small thing that can be hard to find but can drive you nuts :wth:
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Re: GT250 left cylinder issues

Post by Yellow02Z06 »

74 CL200 scrambled
75 GT250 cafe
71 A7 Avenger 350
85 RZ 350
77 XS400 “No XS”
73 H1 500 Aubergine
87 GSX-R750
85 GPz900R Ninja GWB
83 CB1100F
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Re: GT250 left cylinder issues

Post by badgereng »

Nice looking bike. :clap:

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Re: GT250 left cylinder issues

Post by badgereng »

Nice looking bike. :clap:

Pete
FS1E
RD250 E
CB750 K6
CBX B
CB900 FD
CBR1000 FD
CBR600 FV
CBR600 F1
CBR600 RR
FZ1-S Fazer
Z1000 SX

Z1000 SX Tourer
GT380L

Current - 1981 Honda CX500 & 2023 Kawasaki Z1000SX Ninja
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