GT250 left cylinder issues

[Yellow02Z06]

Lithium batteries are very picky about voltage. They are very easy to ruin too.
You absolutely need to upgrade to a modern rectifier/regulator. You also should use charger that is recommended for lithium batteries.

The T250/T350/GT250 tend to run on only one cylinder with a flat battery. The meager alternator has trouble charging up a dead battery & running the bike at the same time.
Try using fully charged battery.

Thks jab, yes staring to think this is my issue, only wierd thing is I do get spark when plugs are out…maybe not sparking after running….and I have been trying after fully charging it….BUT it is the smallest AntiGravity battery (AG401) you can get….

So I am either going to hook up a big battery (but I have no place to put it now) or try the Colortune to see if it’s firing or just get a bigger AntiGravity

PS to your point I did find the R mark! Thks for the help

[jabcb]

Check you battery voltage.

Are you using the original wiring?

The alternator has charging coils & lighting coils. The lighting coils are switched on & off by the switch that turns the lights on & off. So the output sort of matches the load. And Suzuki was able to get away without a voltage regulator.

We used a small AGM battery on our GT250 cafe build. It’s hidden in the bump on the rear of the cafe seat. Works fine.


ignore this if it’s too geeky technical….
When the points close, the current builds up a magnetic field in the coil’s core. When the points open, the field collapses & causes a spark.
The dwell time is the time period that the current builds up the magnetic field. The strength of the spark depends on the dwell time.
The coil has a limit were it cannot fire the plug if the dwell time is to short.

When you test the plug outside of the motor, the dwell time is something like a second or more.
At 2,000 rpm, the plug fires about 30 times a second, and the dwell time is about 0.015 seconds.
So you could get a nice spark when testing it, and no spark with the motor running.

[Yellow02Z06]

Check you battery voltage.

Are you using the original wiring?

The alternator has charging coils & lighting coils. The lighting coils are switched on & off by the switch that turns the lights on & off. So the output sort of matches the load. And Suzuki was able to get away without a voltage regulator.

We used a small AGM battery on our GT250 cafe build. It’s hidden in the bump on the rear of the cafe seat. Works fine.


ignore this if it’s too geeky technical….
When the points close, the current builds up a magnetic field in the coil’s core. When the points open, the field collapses & causes a spark.
The dwell time is the time period that the current builds up the magnetic field. The strength of the spark depends on the dwell time.
The coil has a limit were it cannot fire the plug if the dwell time is to short.

When you test the plug outside of the motor, the dwell time is something like a second or more.
At 2,000 rpm, the plug fires about 30 times a second, and the dwell time is about 0.015 seconds.
So you could get a nice spark when testing it, and no spark with the motor running.

Thks Jab, I am not getting email notifications (I’ll see if I can fix) so sorry for delayed response to your continued and highly appreciated help.

I am using original wiring, but have no horn or turn signals hooked up and don’t plan to…have no brake and taillight but will…

I have been checking voltage at battery and it’s good after charging, and at start, but does go down after the brief test rides I have done. I have gone ahead and ordered a bigger more powerful lithium-ion battery which will mean I have redo my bracketry - but I may have charging issues.

Very interesting info re dwell, did not know that…I studied and worked in engineering and finance, and am technical, and love to know and learn detail so not too geeky at all….

So my next steps:
1) check carb fuel level with gauge(incoming)
2) change out battery and bracketry for bigger Li batt (incoming)
3) see if problem solved (doubt it)
4) try to see if sparking institutes with my buddy’s colortune
5) tbd

[Yellow02Z06]

Well I did some more work but still not running right.

1) Changed out Lithium Battery for more powerful one
2) Checked compression 150 psi on right 148 on left and that is with a compression tester with a hose (some psi loss with hose I understand)
3) Started it and checked spark by using timing strobe light it’s is firing the strobe light at both low and high rpm so I figure it’s firing in cylinder
4) Rode it - still down on power I’m less convinced left cylinder is dead outright but it’s still not running nearly as strong as it has before, it seems very doggy and won’t run past 6000rpm
4) left cylinder still way cooler than right….temp at exhaust near flange is about 110 on left but 160 on right after running a little, on exhaust flange itself it’s about 300 on left and 190 on right
5) Left plug still very/too clean/ unburned has some wet oil/fuel on it, but wipes off clean
6) Right plug looks a lot better, more like a typical correct running to a little rich/2 strokes look

Not sure where to got from here honestly…I suppose carburetion can be off somehow, but just as I said rebuilt them….

Any other input is appreciated

[jabcb]

So right drops from 190 at flange to 160 near the flange. Reasonable numbers.
I’ve measured the exhaust headers on several good running Suzuki with a HarborFreight device & got numbers like 150.

But let drops from 300 on the flange to 110 near the flange. Suspect & deserving of investigation.

[jabcb]

For the cafe build, did you get rid of the stock vacuum petcock?
Check for air leaks on the left intake.

[Yellow02Z06]

So right drops from 190 at flange to 160 near the flange. Reasonable numbers.
I’ve measured the exhaust headers on several good running Suzuki with a HarborFreight device & got numbers like 150.

But let drops from 300 on the flange to 110 near the flange. Suspect & deserving of investigation.

I reversed the on flange numbers: correctly stated left is 160 on flange 110 off it, right is 300 on flange 190 off it….so left side is much colder….and left is also reading the wet unburned plug….

[Yellow02Z06]

For the cafe build, did you get rid of the stock vacuum petcock?
Check for air leaks on the left intake.

If there is a vacuum petcock stock, my bike must have an aftermarket petcock because it’s not vacuum….

I will check for air leaks on left but don’t think that’s it as that I think gets you more air and lean condition and I think if anything I’m rich on left….but I’ll check for sure

[jabcb]

The left carb has a vacuum port that operates the stock vacuum petcock. Make sure that the port is properly sealed.

[Yellow02Z06]

The left carb has a vacuum port that operates the stock vacuum petcock. Make sure that the port is properly sealed.

Yes good point and yes properly sealed

[Yellow02Z06]

Well I am absolutely sure both cylinders are firing now (just started it up with left only spark plug wire hooked up - doh!) and i have a bigger Lithium battery now (was able to exchange) that is holding a strong charge well….but left cylinder not getting as hot as right still…

I still top out at about 6K and therefore not getting all the power I need mostly probably due to left cylinder I have a couple of things I’m doing

1) Going to hotter, NGK brand plug, I kind of lazily used on range colder plug Autolite crossover that I had bought for my triple
2) Jetting….plugs look rich (the one on the left cylinder is actually we’re) got some jets off Amazon which of course they are cheap chinese mismarked etc.(was tempted by the quick ship) returned those and got some from Jets R Us on the way

[Yellow02Z06]

Update:
1) changed main jets to 110 fron the stock i think 112.5 that i had
2) went to correct, hot end of range B8ES (i think, writing this without bike in front of me)
3) removed and inspected baffles, left one had very wet packing, removed oacking from both - thought this may have been a key issue

So I test rode bike this in warm spurts we had between rain and cold

Seems to run better but still wont pull past an indicated 6-6500 (honestly not 100% confident in tach as it audibly sounds like higher rpm after tach stops at 6k)

I dont beleive i am getting the listed 30hp

I have an XS400 with listed 36 hp and a CL200 w listed 17 hp so I thinkI know what 30hp should feel like and 6-6500 is not redline either

I rechecked timing its correct but i did not see much advance happenning but then did not see a mexhanism and a local friend told me there indeed is no advance mechanism

Although i though i was rich maybe im lean - stock unpacked exhaust and foam filters plugs dont look lean but i do have more airflow than stock again per my buddy so i guess ill try going the opposite way to a bigger jet

Any more input is welcome u guys have been great

[karl pa]

I rechecked timing its correct but i do not see much advance happening -

Suzuki GT's have no timing advance. Are you checking timing with a timing light or a dial indicator?
The timing is to be set with a dial indicator on the GT's, not a timing light, the marks are not always exact, this is why you are to measure piston degree before TDC.
From what I found, the 74-75 GT250 should spark at 2.93 mm before TDC. The way I do it is set the piston where it should be using dial indicator, then compare the timing marks, you can now use a timing light to set the marks where they were when you set the piston by measuring.
If you are using foam air filters and not stock airbox, you will probably need to go up on main jets, I heard of guys needing to go up 4 sizes on mains due to increased air flow.
Also, do not trust the tach., I have some that go up to a point, then actually start going down even though you can tell engine speed is increasing.
A side note, both my 250's will keep up with my brothers Yamaha XS400

[Yellow02Z06]

Thks Karl all that makes sense I am using strobe timing light I dont have a dial indicator but i guess i need one anyway….I have my second order of richer jets (what a drag it is paying $10 to have $12 worth of jets shipped twice!)
on order….the tach is used and off another Suzuki too….searched hard for ine with Suzuki on the face and only had neutral and high beam lights so its perfect for my build aside from the fact that it may need a rebuild

[karl pa]

You can get away without a dial indicator, I have used a caliper already. you just need someway of measuring and setting the piston 2.93 mm before TDC
Sometimes the marks are that close you can use a timing light with the marks, but the smaller bikes are more affected by the timing off a little than the bigger bikes.