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72 Suzuki ts90, runs 15 seconds,fouls the plug with gas

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Ron K

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I have been a small engine mechanic for 40 years and this one has me stumped. Engine starts with enriching lever on,runs for a few seconds,slide the lever off,engine idles decent,rev it up a few times and then it quits with a gas fouled plug.I have rebuilt the carb and and set the float to factory specs,float is good,replaced the enriching plug with a new one and properly adjusted cable.Used a Keyster carb kit,new jets etc. Bike ran just like this when I got it.So that is why I did the carb first. Then I replaced the right side crankshaft seal as I though maybe oil from the trans was getting by a bit. Ran the same. Compression was a wee bit low so I replaced the piston and rings with new gaskets. Runs the same.Oil pump is hooked up and working. I pulled the bottom engine crankcase drain screw and some fuel came out,enough to wet your hand. The transmission oil is not getting into the crankcase area,I left the bottom plug out for 2 days and nothing came out. I tried several different plugs and it still runs the same. I have examined the inside of the carb numerous times....it looks perfect...I wish I had another carb to try. It is a Mikuni VM19 series. The damn thing starts with a clean plug,runs for 15 seconds or so and gas fouls it right out. I am perplexed.....Oh yea,ignition is great and timing is spot on. No restrictions on air inlet either.

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Ron K

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Have you tried to source another carb? Turn the petcock off and disconnect the inlet hose @ the carb then start the bike. This will ensure no float / fuel level variance.

I cannot find a nos carb, I tried running it with just the fuel in the carb and no hose on it but it runs out of fuel too quickly....I have the proper size pilot jet in it as well as the proper size main jet and I played with all positions of the slide needle...same thing...runs for a wee bit and gas fouls the plug....The reason I am so adamant about getting this bike running is my very first motorcycle was a 72 ts90j...I rode it to high school all the time...it is a sentimental thing...however,I am still at a loss now as to what to do...

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Ron K

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Have you tried running the mixture screw way out? I'd also back the idle screw off so as to keep the bike on the pilot circuit.

Todays update: Double checked everything in the carb,closed up the plug gap to .018. Started the bike,it fouled the plug again,,,replaced the plug with another NGK B8hs gapped at .018...It started and I adjusted the pilot air screw out to 1 3/4 turns and it stayed running ,I did not touch the throttle...It ran for about 5 minutes before I gingerly twisted the throttle a few times...It got warmed up real good.I tried to ride it but it does not want to accept a load on the engine very well. I now want to double check the points and reset the timing.....we will see what happens then....

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Grand Master

FORMA MOTO

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You keep saying it 'fouls the plug with gas'....not sure what you mean by that.

 

If it is only gas fouled, you should be able to burn off the gas with a lighter, and use the plug again

 

Are you sure you just don't have a stator that is failing; no spark after a few minutes?

 

If you have points, file them flat, and replace the condensor.

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Ron K

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You keep saying it 'fouls the plug with gas'....not sure what you mean by that.

 

If it is only gas fouled, you should be able to burn off the gas with a lighter, and use the plug again

 

Are you sure you just don't have a stator that is failing; no spark after a few minutes?

 

If you have points, file them flat, and replace the condensor.                                                                       Real simple,engine quits and ya remove the plug and it is wet with gas,I burn them clean with  a propane torch to dry them out.....Like I said,I will yank the flywheel and check out the whole ignition system one more time.

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  • 6 years later...
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csutton5

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Has anyone found a solution to this problem? I have a 71 Ts90 with the exact same issue and It's driving me up the wall. Word for word what Ron has done with the same result. I'm stumped, any advice would be greatly appreciated. 

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csutton5

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10 minutes ago, highmarker said:

The carb venting has to be outside the housing the carb lives in, I'd look at that or any open vents on the carb.  Make sure the RV is timed right also if you had it apart.

I didn't have the rotary valve apart but I have not looked over the venting. Like Ron says, the bike runs like a top, idles fine, revs fine, for about 15 seconds then starts sputtering, engine rpm will not increase, and dies with a wet fouled plug. I can put a fresh one in and it starts right up and does the same thing. 

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Grand Master

CRF2eR

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In 1975 I was in college and right behind the school were hills with trails that went for miles. 

I bought a stripped down Suzuki ts90 from a classmate for $50 bucks that would run good for a short time then crap out. 

This drove me crazy until I finally replaced the condenser in the ignition system. It would heat up and short out. When it cooled off, it would work normal for a short while again. A new $4 part fixed it. 

Randy 

ps. I went through alot of sparkplugs before I discovered the problem. 

 

Edited by CRF2eR
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csutton5

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3 minutes ago, CRF2eR said:

In 1975 I was in college and right behind the school were hills with trails that went for miles. 

I bought a stripped down Suzuki ts90 from a classmate for $50 bucks that would run good for a short time then crap out. 

This drove me crazy until I finally replaced the condenser in the ignition system. It would heat up and short out. When it cooled off, it would work normal for a short while again. A new $4 part fixed it. 

Randy 

ps. I went through alot of sparkplugs before I discovered the problem. 

 

Thanks Randy, I thought the exact same thing. Condenser is brand new. Still has the same issue. 

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