I have a 91 trailboss 250 that has been sitting for 2 years. I cleaned the carb and still can't get the damn thing started. Someone told me the crankcase seal may be bad. Would this make starting the atv difficult? If so, why? Does it draw a vacuum? Next question, how hard would this be to replace? Thanks in advance.

 

Yes IIRC the fuel is drawn into the cylinder by vacuum created by the piston. So, a leaky crank seal could cause your problem. However,,,, have you replaced the spark plug, fuel filter, and fuel? Also, make sure that you're getting spark. Do these things and post your results before tearing into the engine.

I have a 95 300 that ran fine but had a major leak at the bowl of the carb. I removed it only to find that the screws had backed out. So, I tore it down, cleaned, and reassembled. It took a little while to get it running again after reinstalling it.

O, do you smell fuel in your air box?

 

Thanks for your time and reply, Sam.

Yes, I have checked for spark, good. Fuel filter seems to be ok and the fuel is good. It will almost start but ultimately..... nothing. This thing is about to drive me crazy!

At this point, I smell fuel everywhere! I have good vacuum where the carb attaches to the crankcase but who knows!

Replacing the crankcase seal, how big of a job is this? Thanks a million.

 

Can't help you on the seal replacement,,, haven't had to go that far into mine yet. Are you choking it? I have to choke mine when it's cold (first start of the day) but only until it "hits" once. Then flip the choke off and it usually starts fine.

Are you certain that you have the mixture screw & idle speed screws set correctly or,, at least in the ball park? Not sure which carb you have but my Mikuni (sp?) seems to like about 2 turns out on the mixture. Can't remember where I have the idle speed,,, had to fiddle with it too many times.

Also, I had to replace/clean & dry the plug several times while trying to get mine restarted after the carb clean. Do you smell gas in the exhaust pipe? And, does the plug look wet when you pull it after trying to crank? If so, you're getting fuel and maybe fouling the plug out.

 

Do a compression check too. If it's below 90, the top end may need to be rebuilt.

 

And welcome to the forums SKC405. [img]i/expressions/face-icon-small-smile.gif[/img]

 

AHH, didn't see your edit about the fuel smell. Sounds like your just flooded. The thing I've noticed about 2 stroke engines is,,, once they're flooded,,, it's a PITA to get them fired because the gas will evaporate but the oil tends to hang around on the plug.

Try pulling the plug and drying it off,,, I used my air compressor and hit it with 80 psi until it looked good & dry. Then connect the plug to the plug wire, but don't reinstall in into the head. Instead hang it off to the side of the engine and make sure it's grounded. Turn the gas switch off so you won't draw any more fuel into the engine. Then hit the starter switch for a few seconds. Check to ensure that the plug is sparking. If so,,, good. Continue to turn the engine over for a few seconds at a time. This will help dry out the cylinder & combustion chamber to prevent immediately fouling the plug when you reinstall it. NOW install the plug, leave the gas off and try to start it. Hopefully it will hit. Then turn the fuel on and try again. You may have to pull the choke in momentarily to "prime" the carb.

I had to go through the sequence about 3 times to get mine started. Turns out I had the idle speed screw too far out. This nearly cut off all air flow the the carb and probably caused it to draw too much fuel.

 

<div class="FTQUOTE"><begin quote>Originally posted by: Scootergptx

Do a compression check too. If it's below 90, the top end may need to be rebuilt.</end quote></div>

I thought 115 was the minimum for the 2 strokes,,, are the older ones different?

 

Thanks again, everybody. I don't have anything to check compression with here but I'll try to get that done tonight.

 

Factory should be about 120. On a older one, 100 is not unusual.

SKC, check and see if maybe a local auto parts store like Auto Zone or someone rents a compression checker. Or if you plan on keeping the quad, it might not be a bad investment.