Author Topic: 1990 Lt250r Fresh rebuild now fouling plugs (Read 879 times)

Redman · « **on:** September 14, 2014, 04:20:18 pm »

Fresh bored .20 over, constantly fouling plugs. Before rebuild, never fouled a plug in years, running 32:1 with klotz oil,has stock needle and needle jet, down 3 notches in the needle, 250 main jet, don't understand why it fouls plugs, help please!!

MotorGeek - Jerry Hall · « **Reply #1 on:** September 14, 2014, 05:11:54 pm »

Quote from: Redman on September 14, 2014, 04:20:18 pm

Fresh bored .20 over, constantly fouling plugs. Before rebuild, never fouled a plug in years, running 32:1 with klotz oil,has stock needle and needle jet, down 3 notches in the needle, 250 main jet, don't understand why it fouls plugs, help please!!

Does it run good without any miss-firing at partial throttle?

Does it run good at wide open throttle and high RPM?

What spark plug are you running

Redman · « **Reply #2 on:** September 14, 2014, 07:30:58 pm »

Quote from: MotorGeek on September 14, 2014, 05:11:54 pm

Quote from: Redman on September 14, 2014, 04:20:18 pm
Fresh bored .20 over, constantly fouling plugs. Before rebuild, never fouled a plug in years, running 32:1 with klotz oil,has stock needle and needle jet, down 3 notches in the needle, 250 main jet, don't understand why it fouls plugs, help please!!

Does it run good without any miss-firing at partial throttle?

Does it run good at wide open throttle and high RPM?

What spark plug are you running

Redman · « **Reply #3 on:** September 14, 2014, 07:41:21 pm »

doesnt misfire at partial throttle, wide open is good with fresh plug, after running awile half hour or so when i open it up it doesnt want to pull strong breaks up and ends up fouling the plug and dies using ngk br8es and tried br8eg

MotorGeek - Jerry Hall · « **Reply #4 on:** September 14, 2014, 09:12:11 pm »

A lot of two strokes need to be opened every few minutes or so to keep the spark plug burned off. If you go 30 minutes or so without opening it up, it may foul the spark plug when using the recommended heat range.

Installing a heat range one step hotter would probably cure the spark plug fouling problem if you are going to go 30 minutes without opening it up. There is a danger of causing pre-ignition when using a hotter spark plug when you open it up for too many seconds at a time especially if the engine is up to normal operating temperature.

Also set your spark plug gap to .018" to .020".

Redman · « **Reply #5 on:** September 15, 2014, 04:31:42 am »

thanks ,i do open it up thru out the 1/2 hour many times im sorry i didnt explain that,but after the 1/2 hour or so when i open it up it fouls out. i run it the same way i use to and the plug use to have a nice brown color to it but now after the rebuild it is always black and wet and smokes alot more than before. the guy that rebuilt it said the 1 crank seal was pushed out and could have been leaning it out. could it have been that way a long time and the jetting was always rich and the pushed out seal compensated for the rich mixture ? or does boring the cylinder out 20 thousands change the fuel/air mixture ?

MotorGeek - Jerry Hall · « **Reply #6 on:** September 15, 2014, 06:30:32 am »

Quote from: Redman on September 15, 2014, 04:31:42 am

thanks ,i do open it up thru out the 1/2 hour many times im sorry i didnt explain that,but after the 1/2 hour or so when i open it up it fouls out. i run it the same way i use to and the plug use to have a nice brown color to it but now after the rebuild it is always black and wet and smokes alot more than before. the guy that rebuilt it said the 1 crank seal was pushed out and could have been leaning it out. could it have been that way a long time and the jetting was always rich and the pushed out seal compensated for the rich mixture ? or does boring the cylinder out 20 thousands change the fuel/air mixture ?

The crank seal on the transmission side may also be pushed out allowing the engine to be consuming transmission oil. It is time to do a pressure test on the engine.

Boring the engine .020" will not change the jetting. A plugged up spark arrestor will make the jetting act rich. A dirty air filter can make the jetting act rich. A broken reed petal will make the jetting act rich.

Pushed out crank seals are usually the result of a carburetor flooding the crankcase. If the crankcase is full of fuel when it is pushed or kick started, it will often break a reed or push the seals out of the case.

Redman · « **Reply #7 on:** September 15, 2014, 07:34:51 am »

Thanks for all the info maybe the arrester is pluged, all the seals and gasket are new . I will check the reeds to ,do you think a 250 main jet is to big?

MotorGeek - Jerry Hall · « **Reply #8 on:** September 15, 2014, 03:08:39 pm »

I would still pressure check the engine. Recently I had a gasket set that came with crank seals. One of the crank seals was wrong. The ID of one of the seal was about .5mm larger than the crank journal.

I noticed the problem when I installed the crank. The crank seemed too rotate too freely. It did not have the customary drag a new seal has. Closer inspection revealed the seal was very close to but not touching the journal

Redman · « **Reply #9 on:** September 15, 2014, 07:21:13 pm »

thanks for all the info

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Author Topic: 1990 Lt250r Fresh rebuild now fouling plugs (Read 879 times)

Redman

1990 Lt250r Fresh rebuild now fouling plugs

MotorGeek - Jerry Hall

Re: 1990 Lt250r Fresh rebuild now fouling plugs

Redman

Re: 1990 Lt250r Fresh rebuild now fouling plugs

Redman

Re: 1990 Lt250r Fresh rebuild now fouling plugs

MotorGeek - Jerry Hall

Re: 1990 Lt250r Fresh rebuild now fouling plugs

Redman

Re: 1990 Lt250r Fresh rebuild now fouling plugs

MotorGeek - Jerry Hall

Re: 1990 Lt250r Fresh rebuild now fouling plugs

Redman

Re: 1990 Lt250r Fresh rebuild now fouling plugs

MotorGeek - Jerry Hall

Re: 1990 Lt250r Fresh rebuild now fouling plugs

Redman

Re: 1990 Lt250r Fresh rebuild now fouling plugs

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