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Author Topic: Help with Pilot Jet and Idling LT250R  (Read 2233 times)

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Help with Pilot Jet and Idling LT250R
« on: May 13, 2015, 08:25:10 pm »
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!

http://chirb.it/A35qMr
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Re: Help with Pilot Jet and Idling LT250R
« Reply #1 on: May 13, 2015, 11:34:21 pm »
Quote from: tcgravy on May 13, 2015, 08:25:10 pm
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!

http://chirb.it/A35qMr


1/4 throttle is not pilot circuit.  1/4 throttle is needle jet and slide cutaway.  The pilot jet functions from closed throttle to full throttle but it's effects are minimal at 1/4 throttle opening.   Check your reed petals.  If your petals are ok your needle jet and or needle is probably worn out allowing too much fuel at 1/4 throttle

Plug chops at partial throttle are a waste of time and will not tell you anything especially when the engine is rich enough to miss-fire.  Your ears are telling you it is miss-firing and the plug will remain white for the 1st 10 minutes or so when it is running rich enough to miss-fire.  Tune it so that it runs good and forget about trying to read the plug!!!!!!!!
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Re: Help with Pilot Jet and Idling LT250R
« Reply #2 on: May 14, 2015, 06:12:00 am »
I had similar problem with my two lt250r, i fix the problem replacing the needle jet ( the hole )  it was worn out , and at the same time i replaces the jet needle ( needle ) .

a worn out needle jet that cannot be see with eye. created a rich condition that can be compensated with idle air screw at idle  . but the rich condition occur until 1/4 throttle.  that i cannot compensated with the needle.

Carl, Irecacer, Carl point me to this problem and he was right.
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88 Lt250r.
79 Lawnboy 21" ;-P

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Re: Help with Pilot Jet and Idling LT250R
« Reply #3 on: May 14, 2015, 05:29:22 pm »
Reeds are good for sure.

As for the needle jet being worn out and causing a rich condition i will have to re-check this.....looked at it when cleaning the carb to male sure it was stock but didnt think to check it for wear. What will the "worn out" part of it look like? Will i be able to see it with the naked eye?

Thanks for the input guys   
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Re: Help with Pilot Jet and Idling LT250R
« Reply #4 on: May 14, 2015, 08:57:20 pm »
Quote from: tcgravy on May 14, 2015, 05:29:22 pm
Reeds are good for sure.

As for the needle jet being worn out and causing a rich condition i will have to re-check this.....looked at it when cleaning the carb to male sure it was stock but didnt think to check it for wear. What will the "worn out" part of it look like? Will i be able to see it with the naked eye?

Thanks for the input guys   

No you cannot see .0002" of ware.  One increment of needle jet size is about .0002"  You cannot see .0200" with is 100 steps richer.  It will not hurt to put a new one in and see if that fixes the problem.
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Re: Help with Pilot Jet and Idling LT250R
« Reply #5 on: May 15, 2015, 10:30:48 pm »
Yes I think you are right. I went all the way down to a 22.5 pilot jet and it is still rich at idle.

New needle jet is on order...only $14 from local shop. Thanks for your help and input I will try to remember to let you know how it goes. Thanks.
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Re: Help with Pilot Jet and Idling LT250R
« Reply #6 on: May 18, 2015, 07:26:18 am »
Yes, definitely lets us know if it fixes your problem. 

It could help others with the same problem.   +k2
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Re: Help with Pilot Jet and Idling LT250R
« Reply #7 on: May 20, 2015, 09:41:17 am »
i will gues that the O-rings in the choke circuit have been comprimised. or some airleak.
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1992 SUZUKI LT250R
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Re: Help with Pilot Jet and Idling LT250R
« Reply #8 on: May 28, 2015, 06:22:51 pm »
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!
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Re: Help with Pilot Jet and Idling LT250R
« Reply #9 on: May 29, 2015, 10:29:50 am »
Nice , you should thank carl, iceracer ...  +k2
I currently have  have similar problem with my tmx 38 carburetor, i have to lower the needle jet size .
Most people like me before don't know that the needle jet can worn out...
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88 Lt250r.
79 Lawnboy 21" ;-P

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Re: Help with Pilot Jet and Idling LT250R
« Reply #10 on: May 29, 2015, 11:27:49 am »
Yes, thanks to Carl and Iceracer!!!

What's your setup on the TMX 38?? I actually have a TM38 carb laying around from an old YZ250 and I am debating trying it on the LT250R. Have any suggestions?

What's your jetting at and have you noticed a performance gain at all?
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