Well I'm stumped. I have just put a used bottom end on my mc21 as the last one had a worn crank, seals and bearings. Now for some strange reason the lower cylinder is sucking air into the exhaust while idling. It has a little putt every now and then with a bit of smoke coming out but that's it. When I give it a little throttle around 2500rpm it gets a bit better but the exhaust gas seems colder than the top cylinder. At around 5000rpm it heats right up and appears to be good.
The top cylinder is running great, no complaints at all.
I have cleaned the carbies, rebuilt the reed cages, swapped the coils over and had a good general look over to eventually find nothing out of the ordinary.
Any advice or idea would be great as I can't think of a single thing to try now. Don't hold back, I'm willing to try anything.
Carbies have already been cleaned and balanced, ignition checked and ok. I have sprayed aero-start all over the engine whilst running and that had no effect aswell. All air solenoid assembly has been cleaned and checked.
Today I removed the airbox and ran the bike for a few minutes just to see if there was anything out of the ordinary. I did notice a small amount of fuel being expelled out the carby throat on the lower cylinder while giving a little throttle. At idle there was only a sucking effect. At this point the exhaust is still sucking.
It would appear that there is only one place for the air/fuel mixture and air from the exhaust to be going. I guess it's time to break out the old leak down tester.
You would think the cylinders would work as a team but NO, one has to get greedy!!!
I get to pull another motor apart. Who likes riding bikes anyway.
The center crank seal almost holds 2 psi for 1.57 seconds.
All 3 crank seals failed miserably but the center one is by far the worst. It is passing air from bottom to top cylinder way faster than top to bottom.
I guess that's what you get when you buy a bottom end from the worlds most popular auction site.
Almost time to give up on the bike and concentrate on the rx4.
Keep note the center crank seal will leak air from right to left (bottom to top cyl) within hours after the engine has been shut down. This is normal. With the engine running, the 2t oil will seal it completely.
All primary chEcks were done with the engine running. Seals are gone ( all 3). Please excuse the short posts as seq where I live are experiencing the worst floods in 35 years.
A couple more sets of red traffic lights and I wouldn't have made it home to bid at all!!! By the time I got the computer on there was about 5 minutes left.
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