GT250 left cylinder issues

[Yellow02Z06]

I bought the bike about 6 months ago it was running quite well, just needed front brake rebuilt, but I also decided to mod it quite a bit into a cafe racer…see pic….I like it…anyway though after all the work, first test ride was running well, then one cylinder went cold, lost power….

It was sparking, so I pulled the carbs, they were clogged mess…rebuilt them…got it back together….still low on power on left side, seemed to be firing, got some exhaust smoke, but temp on exhaust way lower than right…

The right plug looks totally clean as if not firing at all, still getting spark…carbs slides are working right, opening full….

Checked timing it appears good, only strange thing is there is only an L mark, which matches to left cylinder and left points….the right side points are clearly 180 degrees away, but there is no mark…i wonder how one is supposed to ensure those are correct? I think they are because that cylinder works well but it’s strange?

I do know I’m getting spark so somehow my most likely issue is fuel in left, but fuel is going thru line and is present in float bowl, and float height if anything is set to allow enough fuel not too little…so I while I think I have a fuel,problem I not sure why…

[karl pa]

so I pulled the carbs, they were clogged mess…rebuilt them

When you say you rebuilt them, did you replace jets or just clean them? most aftermarket rebuild kits can give trouble.
Does the left side fire when choke is applied? Did you get every carb passage clean? they can be difficult to get completely clear, I blow carb cleaner and compressed air through every passage to make sure there clear.

[Yellow02Z06]

Hi Karl Thks for your response.

In terms of the carb, I actually sourced new carb bodies as mine had destroyed stuck pilot jets…the bodies I got were very nice, and clean…I blew thru the main jet and pilot jet passages, and (what I think is) the choke pickup tube, they all flowed. Actually the only new parts I used were pilot jets from Jets R Us…everything else was cleaned by soaking in Yamalube then cleaning further with carb cleaner…I have not tested firing with choke on…presumably if it runs that way I have bad air leak? I suppose I could shoot stater fluid down there to see if it perks, to verify my problem is fuel…This is my first GT, but AI do have 2 other street 2 strokes (H1, and A7 Avenger) and 5 other bikes so I have cleaned a lot of carbs…

[karl pa]

If it runs with choke it can be an issue with the pilot circuit, or air leak

[Yellow02Z06]

It’s strange as I get smoke from the pipe and I swear I hear a “brap” like it’s firing but it’s a cold smoke, the pipe is nowhere near as hot as right, and the plug is still like new, no sign of burn.

So I took carbs back off, tried to keep upright so I could see how much gas was in float bowl and it was lower in the left non firing cylinder…however I was at 13-14mm float height as measured from the casting the main sits in per spec….the firing side was more like 15 so I put them both at 15+ hopefully this will solve it…I will reassemble and see tomorrow….only problem…snow coming…I want to ride this little thing and call it done

[jabcb]

Usually setting the float level works out fine. But sometimes it doesn’t. In those cases setting the fuel level can solve the problem.
Makes sense because the goal of setting the float level is to get the correct fuel level.
There are some forum posts about it. Here is one:
viewtopic.php?f=9&t=13872&p=172459&hili ... ol#p172459

I usually don’t bother with it. Typically I’ve found that the fuel level is reasonably good after carefully setting the float level. But a few years ago I had a carb that wasn’t even close — worked fine after I set the fuel level.


All of the T250/T350/GT250 stators I’ve seen in person & in pics have both L & R timing marks.

The GT250 choke mechanism is in the left carb. It serves both carbs. The choke jet is in the bottom of the left float bowl. So the choke doesn’t work if you swap float bowls.

Visually check to make sure the slides are synchronized & that the cutouts are facing the air cleaner. If you swap slides, you’ll never get the bike to run correctly.

I would not be surprised if it turns out to be an ignition problem.

[Yellow02Z06]

Thks Jab for detailed response…yes I was kind of trying to set fuel level by observing where it was when I took off bowls again…about to go out to garage and kick and test…reassembled last night…I will look real hard again for that R cylinder mark on stator….maybe I overlooked thru some oil or dirt…hope it’s not ignition but I have been through this process enough on other old bikes enough to know it often takes a while going through everything to get them sorted…by the way I keep trying to add pics to posts and or my signature…no luck any idea if site permission required or maybe it my iPad/browser?

[Alan H]

The added files must be less than 240k, or you'll have to stash them elsewhere and link to them.

[Yellow02Z06]

Thks Alan H, I tried using small attachments, but last one was listed at only 27k, still did not take….I’ll try again…PS I love the (I think) George Carlin quote in your signature

[Yellow02Z06]

Typically I’ve found that the fuel level is reasonably good after carefully setting the float level. But a few years ago I had a carb that wasn’t even close — worked fine after I set the fuel level.

If you swap slides, you’ll never get the bike to run correctly.

I would not be surprised if it turns out to be an ignition problem.

Well I reset float level and left still acting same,(slides are correct, unlike other carbs I’ve seen they r pokeyoked ie they can’t go in backwards) ie seems sort of to be firing in that exhaust and noise comes out, but it’s still about 90degrees at exhaust near head where other side is at least 175, and the smoke coming out is cold and plug is clean as a whistle but still gives spark when tested. It is weird….

I guess I can order one of those fuel level testers…

Other notes
1) I did put in a small lithium battery as part of my cafe redo of the bike
2) Bike seemed to b running strong when I bought it and on first test post cafe build, but lost the left cylinder fire/power at end of ride, and then I got into carbs, etc
3) I do note the pilot jet is way high and it would take a high fuel level to get there..
4) strange also I sprayed some starter fluid in back of left carb while running at slightly open throttle and no reaction….if it was fuel problem I would think I should have gotten some noticeable firing….

[karl pa]

unlike other carbs I’ve seen they r pokeyoked ie they can’t go in backwards

They can't go in that carb backwards, but if you put the right slide in the left carb and left slide in the right carb, then the slides are backward. notch toward engine instead of airbox. It happens often with the twins.
If you sprayed starting fluid in carb with no change, then I agree with jabcb it is ignition or something more sinister.

[Yellow02Z06]

If you sprayed starting fluid in carb with no change, then I agree with jabcb it is ignition or something more sinister.

Well it’s sparking (at least with spark plug out of engine for test) and the timing is correct. I ordered one of those fuel level gauges anyway and I had a thought, my buddy has colortune plugs, don’t know if correct size, but that could show probly if at least still sparking under compression / installed…the caps are very tight to the ram air but seem to be clicking onto plugs…any other ideas are welcome and thks

[karl pa]

If the plug caps are close to the ram air cover, be sure you aren't losing spark by jumping to ram air cover.
You said you installed a small lithium battery, does it have enough power to run the ignition ? these bikes tend to lose a cylinder when power gets to low.
Is the crank seal behind alternator intact? You said the left plug looks clean, If the center seal is bad the plug would be oil covered, but if the left seal is bad, it could be sucking to much air and not pulling the fuel charge into the cylinder.
But I would think the starting fluid would have still fired.

[Yellow02Z06]

If the plug caps are close to the ram air cover, be sure you aren't losing spark by jumping to ram air cover.
You said you installed a small lithium battery, does it have enough power to run the ignition ? these bikes tend to lose a cylinder when power gets to low.
Is the crank seal behind alternator intact? You said the left plug looks clean, If the center seal is bad the plug would be oil covered, but if the left seal is bad, it could be sucking to much air and not pulling the fuel charge into the cylinder.
But I would think the starting fluid would have still fired.

Yeah the plug caps basically touch (the rubber does) the ram air cover, it both left and right do, and it has run properly ie both cylinders with it that way….that being said on other bikes I've replaced the fairly cheaply made stock caps with good NGK caps and new wires…may do same here at some point…

I am starting to think the battery could be part of the trouble if not the cause…I bought basically the smallest one I could get as I was all caught up in my redesign (sure wish I could post a pic!). I may have to see if I can test with one of my other full size batteries (it’s a drag spent a ton of time getting this all set up with custom brackets oil tank etc!) or see if I can get a more powerful battery in same size…also it did lose charge on one short test ride

Not sure about the crank seal….but like AI said it was running right when AI bought and in first test ride for a while…

I did find the R mark in the rotor after all, and I rechecked timing statically and L was retarded a bit - gonna restart in morning but I doubt the timing was it….

Thks again for all the help!

[jabcb]

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.