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RM80 has fuel in exhaust pipe & crank. Help

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I have a 1994 RM80 that my boy was riding and died. He tried to start it and fired up but only went about 100 feet before it died again. I have had many issues trying to get the bike jetted correct because no matter what I did to the bike it always had a bad bog when you cracked open the throttle. I was running a 210MJ 30PJ and stock needle in 4th position. After I pulled the plug it was soaked in gas, so I cleaned it and reinstalled it. I tried to start the bike again and it made a lil sputter but no go. After about 10 kicks I pulled the plug and it was soaked again. The bike has never fouled a plug the entire time I owned it. I checked the spark and it was bright blue. I did a compression test and it measured at 140psi. I started to pull parts to do a leak down test and fuel poured out of the expansion chamber. The float height is set correct and does not leak gas. I also noticed that the crank case is now full of fuel as well. How could this happen after only a few kicks? I drained all the gas out of the expansion chamber and crank case, changed the oil and put the bike back together. I tried to kick the bike again about 15 times and no luck. The exhaust and crank was once again full of raw fuel. I pulled the top end off and the piston looked a lil scarred but the cylinder, which is bored out to 49.50mm, looks good all around. What would cause the bike to all of a sudden flood it self out? I rebuilt the carb in the process to hopefully solve the fuel problem but no go as well. If any one has some input I would appreciate it.

Thanks!

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Wow interesting case and for sure something isn't right. I would go back to the carb for starters and check everything and set the float height.

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I double checked the float height per the manual and it was correct. I also installed new reeds a few months back. I just ordered a new top end and figured I might as well replace it since I got it apart.

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I'd check to make sure the float needle is seating correctly and not allowing gas to continue to flow.

Beyond that, if the carb seems to be working correctly it must be an ignition problem. Start with trying a fresh plug. It's possible that there's a bad connection somewhere, like the plug lead.

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I'd check to make sure the float needle is seating correctly and not allowing gas to continue to flow.

Beyond that, if the carb seems to be working correctly it must be an ignition problem. Start with trying a fresh plug. It's possible that there's a bad connection somewhere, like the plug lead.

Bingo!!!!combo of stuck float/float needle and I would be willing to guess your reeds are shot too.

My son races a 07/08 rm85L super mini so I work on them all the time.

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Could a 3 month old set of reeds need replacing already? They still look new and are flush against the reed cage.

Nope it isn't the reeds.

What plug are you running in that bike?

I find it very disturbing that the crankcase is loaded with fuel, but the carb isn't overflowing.

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Ditto. Either a vent is clogged, or it isn't firing right. Maybe the timing got knocked out of whack?

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The plug is a NGK BR10EG and the crank case vent hose had a lil crap in it but not clogged.

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The plug is a NGK BR10EG and the crank case vent hose had a lil crap in it but not clogged.

I think that plug is supposed to be BR9EG.

UA meant the carb hoses I believe.

Uncle Alpo also might be on to something with the timing. The keyway could be sheered or twisted. I've seen that a dozen times with lawn mowers.

But the crankcase filled with fuel is bugging me...... It could be that the plug is so loaded from using to cool a plug that it's building up!

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I just looked it up.. they do call for a 10 which seems a little cold to me but thats what they want. However, has the bike been modified in anyway? Like in anyway that would increase compression... because then you would want a hotter plug.

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Yeah, sorry, the carb vent hoses. I'd look at the vents themselves, just be safe.

If the timing is way off, the engine could suck fuel in and not fire it.

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The bike has a 2mm over bore from stock but other than that he bike is all stock. The carb vent hoses are a lil old and hard but there seems to be nothing clogged in them. Do you think I should try and go with a hotter plug? I will check the timing and keyway next.

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If it calls for a BR10 then use that.

Dig into the timing a bit and see what you have there to work with. Also the coil or stator could be bad. I know it gives a nice blue spark now, but what about at 3000 rpm?

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Ok this may be a dumb one but I fixed a friends LT80 quad that was doing the same exact thing....He had the fuel hose from the gas tank hooked to the wrong port on the carburator...sure the bowl was filling with gas but wasnt going through the needle and seat. try opening the fuel petcock to let the carb fill with gas then shut it. that should prevent it from flooding out...You should be able to start it then and run it for a few seconds at least or longer.

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Check the float needle or just get a new one. Had this with a bike just recently and even 'adjusted perfect', the bowl was still overflowing and putting the needle up to high to stop overflow yet enough to run was too lean and too low and 'run good' would end with gas flowing out the overflow.

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Just a follow up with the RM80. I replaced the top end, honed the cylinder and put new reeds in. The little yellow machine fired after the third kick and after the heat cycles, shes a little screamer. I'm now going to let the wife ride this since I already went out and bought a 04 KTM 85 for a grand. Thanks to everyone that chimed in and for all the helpful information.

Felix

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Just a follow up with the RM80. I replaced the top end, honed the cylinder and put new reeds in. The little yellow machine fired after the third kick and after the heat cycles, shes a little screamer. I'm now going to let the wife ride this since I already went out and bought a 04 KTM 85 for a grand. Thanks to everyone that chimed in and for all the helpful information.

Felix

Glad you got it fixed.:thumbsup:

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