XT250 hard to start & jetting/kickstarter issue?

I got the newly rebuilt, big-bored 1983 XT250 engine running this morning. This motor has a larger piston, medium race cam, a Mikuni 34mm carb and stock ignition. I have three issues I'd like input on.

1. It wouldn't start by kicking it, even with the choke on. Each time I would kick it, at the bottom of the kickstarter travel, the engine felt like it would lightly backfire, forcing the kickstarter back into my foot a little. I ended up taking out the plug, injecting some raw fuel into the combustion chamber, putting the plug back in and then it would fire and run after 2-3 solid kicks. Only once I was able to kickstart it withoult manually injecting fuel: that was after 4-5 kicks with the choke on and then turning it off and kicking some more.

2. After it is running, it wants to surge at idle/low rpm. It seem "wheezy". It feels like it is lean at idle and low in the transition. I didn't rev it past about 4000 rpm or so, but once it got above 2500 rpm? the jetting seemed better. I played with the air screw (from 1-3 turns out) but it didn't seem to help. I'm thinking I need to install a larger idle jet and then work with the air screw. I haven't started reading the plug yet, as the engine has a total of about 8-10 minutes of low rpm run time on it. Once there are 2-3 more heat cycles on it and it's more broken in, I'll start reading the plug.

3. I stalled the engine while turning and couldn't kickstart it. About the 5th kick and there was a popping sound and the kickstarter wouldn't move at all. I removed the right side case and there were three starter gear teeth broken off. I'm wondering if this make of motor had a weak spot in this area or did the "backfiring" cause the breakage? Any ideas on what would cause the gear teeth to break. I've got a buddy with a spare gear I can get and I'll buy a spare off eBay but I don't want to break another.

Any advice for these problems would be greatly appreciated.


Is the automatic decompressor working like it should?


It seems to be. When the kickstarter first starts to move down, the decompressor lever opens and then when it gets to about 1/2-2/3 down it closes again.

A friend, Bob, has a parts motor that I got the kickstarter gear out of. I got it to run after again manually priming it. It feels lean everywhere and backfires a lot, even under mild acceleration. I tried to rev it once but it just hesitated, surged slowly and backfired occasionally. This either seems like a carb that is too lean everywhere or an ignition that is too far advanced everywhere.

Here's a pic of a new spark plug with about 10 minutes of run time on it. It has a whitish ring around the electrode and porcelain. That with the constant backfiring indicate too lean of a mixture to me. What do you think? What about the backfiring? That could be caused by too lean of a mixture....

Would an ignition that is too advanced cause both of these problems as well? It is mechanically set at the factory but I could "elongate" the mounting holes to retard it a few degrees.

Nearly every time I kick it, it will pop backwards into my foot. Sometimes mildly, sometimes more forcefully. I'm sure that's what broke the kickstarter gear.




Today, at lunch, I checked to make sure the floats were right-side-up, replaced the "30" pilot jet with a "40" and raised the needle two positions. This made the bike startable without manual priming, didn't backfire once and idle noticably better. I then played with the air screw and got the idle decent but not trustworthy. It was also smoking a little (too rich). Transition was much better and it would rev higher now. After about 10 minutes of running on the stand (revving & idling) the plug was darkened. I will try a "35" pilot jet and the needle down one position next. I'll also put a timing light on it and see if that needs adjustment. It's getting closer.....


I put a timing light on the motor tonight and it is firing at about 45* BTDC.....

I don't understand how this can be, the flywheel is keyed, the stator plate bolts on with round holes (no adjustment), and the trigger coil bolts to the stator plate with round holes (no adjustment). The only idea I have is that I got the trigger coil leads swapped but I'm guessing this wouldn't matter.

Could it be a fried ignition module?

Any help would be greatly appreciated. This seems to be the whole problem.



sounds like wrong cdi on the bike. does your buddy have a good 250 one? that one might be from a 350 or 500. i know they wrk as we have a xt200 one on a 86 xt350 atm. runs and pulls great too.

main, thanks for the suggestion.

Tonight I borrowed a buddy's CDI unit off of his running bike and we swapped it into mine. I kicked and kicked and it never even popped..... We took the plug out and there was no spark. We traced out the wiring to make sure connections were right and tried again. No spark. We then put my CDI back on and no spark.....:p

I'm slightly concerned that the bike fire melted some insulation somewhere and now that we've moved the wires they are now shorted out. I'll also test the coil primary and secondary tomorrow.

This is getting to be a real headache. I thought swapping CDI units would reveal the problem, as it ran last night for about 10 minutes before I shut it off.

I'm tempted just to order replacement parts (CDI unit & coil) off of ebay and "start over".:ride:

Well, I've narrowed the problem down considerably. It is not a jetting issue, it is an ignition timing issue.

Tonight, after work, I picked up my friend and his TT250 and took it to my shop. I've checked the Yamaha microfiche that the TT250 and XT250 use the same flywheel, stator plate, ignition coil, trigger coil, CDI unit and spark coil. We warmed up his bike and checked the ignition timing. It was operating correctly.

Here's what we did:

1. We swapped my spark coil onto his bike. It ran correctly. Coil good.

2. We swapped my CDI unit onto his bike. It ran correctly. CDI unit good.

3. We swapped both my spark coil and CDI unit onto his bike. It ran correctly. Verified coil & CDI unit good.

4. I checked the ignition coil resistance. It was within limits per the Yamaha manual. Ignition coil good.

5. I checked the trigger coil resistance. It was within limits per the Yamaha manual. Trigger coil good.

6. I then swapped my spark coil and CDI back onto my bike. It still sparks at about 45* BTDC.

Here are my thoughts on possible problems.

1. Accidentally swapped the trigger coil wires (white/red & white/green). Would this cause an advanced timing condition?

2. Accidentally swapped the ignition coil wires (red & brown). Would this cause an advanced timing condition?

3. I've accidentally used the lighting coil wires and hooked them to the CDI unit (highly unlikely as I spent a lot of time tracing the wires and was very careful to avoid this).

4. Trigger magnet is screwed up??? Highly unlikely.

I could pick up a stator plate and wiring harnes. That surely would solve this problem.

Please, any real advice would be appreciated.



Duggy, have you checked your flywheel? Maybe it sheared the key? I had that happen on a KLX 300 I was doing some work to.

Yes, both my friend and I verified multiple times that the piston is at TDC when the mark shows "T".


This morning I rolled the dice and swapped the white/red and white/green wires. I used a cordless drill to spin it over to check the timing: it's right on. One kick and it runs like a top!!!!!!!!!!! I'd also switched back to the jetting that Sudco had sent me. It started first kick when warm and runs well. Lots of bark, grunt and low end. Throttle response seems good, just a little tuning on the idle and then I'll break it in. Can't wait.

Thanks for all the advice.


That's great news Doug! Enjoy that thing. :p

Outstanding project Duggy!

That exhaust pipe is what really makes it a Frankenbike, in my opinion (not saying that in a "bad" context)

That's a seriously sweet bike!


My '81 XT 250 is having almost exactly the same problem. Newly rebuilt carb and all. You switched the wht/red and wht/green wires between themselves at both ends, before the CDI and after, or what?

I'm pretty puzzled with mine.

Since I'd cut all the wires as they exited the case/grommet I got them backwards there. They were correct at the top connectors. Once I swapped the top connectors, everything was fine. Try a timing light. If the coil fires way before it should, try swapping the white/red and white/green.

I might try that. Mine will start sometimes but even then it will pop a little, is not very responsive to throttle, and idles badly and dies. To the best of my knowledge its a timing issue, but who knows, could also be wiring.

What cam did you use and where can i buy one, also what larger piston did you use, OEM oversize or the Dr 350 piston way , also stock or high comp piston? Thanks , I just bought an 81' or 82' made july of 81'.

Hobocop: I would at least check your timing and if it's off, try the wire swap. It didn't seem to hurt anything on my bike.

Dudlyscrf: If you read my Frankenbike thread you will find out what I used (Megacycle cam and a Warrior 350 84mm 10.5:1 piston & Warrior 350 sleeve). I ordered my cam directly from Megacycle and the piston/sleeve off of eBay.

Hobocop: I would at least check your timing and if it's off, try the wire swap. It didn't seem to hurt anything on my bike.

I tried it with no luck. I suspect its probably timing, then.

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