1989 LT250R

Will not idle, does not run well at all in pilot circuit. Starts relatively easy. Runs OK once you get into the needle and the main. Bone stock engine, freshly rebuilt top end and all seals. DG Pipe. Stock Carb. Stock airbox, no lid. Stock jetting... 30 pilot & 240 main.

Tried these things first:
- Cleaned Carb, went through everything, works as it should
- Set float level to stock setting per manual
- Went through stator, coil, & plug cap...spark is bright blue
- Compression good 150 psi

Then tried changing pilot. Have tried 27.5, 30, 35, and 37.5 with no luck (seems to run like crap on pilot circuit with all of these). Have done multiple plug chops on pilot circuit at 1/4 throttle. All show no carbon color on base ring of plug but it is very wet/oily so plug is hard to read.

Below is a link to an audio recording of it running.... at first at 1/4 throttle and then some acceleration. PLEASE HELP!

Link to Audio File - LT250R Engine Miss

 

How is your air screw set? Listening to your clip, it initially sounded good at idle. The needle takes over pretty early in the powerband. It sounds like it is falling on its face once you give it some throttle. Stock motor and stock jetting with an aftermarket pipe, hmmm. I would think you need to go up on the main a couple sizes and see how she runs there. Maybe one size over on the pilot, but sometimes stock is OK in the warmer months.

You are well off the pilot circuit by 1/4 throttle...

 

Thanks for listening.

Tried air screw at various positions (all in and checking out in 1/2 turn increments all the way to 3 turns out) with all pilot sizes.

As for idle you said it sounded good but that whole beginning is at maybe 1/8 throttle (I have to hold throttle open a bit just to keep it running).

I tried going up one size on the main, but it runs much worse there just a rich sputter on anything past half throttle.

 

Ok, sounds like the main is good, but if you have one size down from your starting point i would try that too. On the air screw anything past 2.5 turns out and you generally need to go up on the pilot. Have you checked the clip position on the needle? I would put it back to stock if it has been changed and see if it gets any better. My other thought is to check the choke mechanism for proper function.

 

Yes needle, needle jet, and cutaway are all stock and clip is on 3rd position. As for air screw, yes, thats why I have been attempting so many different pilot jets hoping one would fix the idle issue and pilot circuit.

As for choke this seems to work fine as well (moving choke lever definitely delivers more fuel).

 

Pics of spark plug after plug chop at 1/4 throttle.....

No carbon/burn color on base ring but plenty wet (seems like oil but I am not sure what this means).




https://m.flickr.com/#/photos/132255...5/17417407355/

 

What pre mix ratio are you running? Type of oil? The stock recommendation was 24:1, but that tends to be to much oil for modern pre mix. Want to try draining the old gas from tank and carb? Mix up a gallon of fresh with some quality pre mix maybe? I usually am at 40:1 with klotz or bel ray.

 

Running 32:1 with citgo sea and snow 2 stroke oil

All this is with fresh gas, less than a week old, i drained tank in offseason and just mixed recently

I am thinking (hoping) I am just rich on the pilot jet and that coming down helps.......remember its bad at 1/4 throttle yes but it wont idle at all either

 

Replaced needle jet (the hole) and voila... my idle has returned! That was definitely the problem, idle circuit is back and engine runs better throughout the entire rpm range.

Back to a 30 pilot jet (stock) and happy as can be. Thanks a ton everybody!