I have a 1978 Yamaha xs650. It won’t accelerate past 4k and it starts making a crackling noise. Too lean?
March 31st, 2010 | Articles | 6 Comments »
Mitch asked:
I had to leave the bike sit for about 6 weeks. Before riding I also changed the oil to a new, synthetic brand. The first time riding it I noticed slight problems at higher RPMs on the highway and when I drove it home it was much worse. When I get to about 4-5k it won’t let me accelerate and just makes a crackling sound. I had to drive 50 mph all the way home. I don’t know if this is because of the oil or because I let it sit. It sat without fuel the whole time I was gone. It also makes a crackling noise on deceleration.
I checked the plugs and the left plug had a little carbon build-up but a whitish tip; the right plug was mostly whitish. I plan on cleaning the carburetors this weekend. I’ve had a problem with gas coming out of my vacuum petcocks for a while but this other problem is new.
I just overhauled the top end – all new. I just passed the break in period, hence the oil change. I’d like to learn how to fix this myself, so hopefully there isn’t too much wrong with it. The overhaul killed me over how much they charged for labor. I really want to learn how to fix anything myself. Please help.
I appreciate any advice.
I had to leave the bike sit for about 6 weeks. Before riding I also changed the oil to a new, synthetic brand. The first time riding it I noticed slight problems at higher RPMs on the highway and when I drove it home it was much worse. When I get to about 4-5k it won’t let me accelerate and just makes a crackling sound. I had to drive 50 mph all the way home. I don’t know if this is because of the oil or because I let it sit. It sat without fuel the whole time I was gone. It also makes a crackling noise on deceleration.
I checked the plugs and the left plug had a little carbon build-up but a whitish tip; the right plug was mostly whitish. I plan on cleaning the carburetors this weekend. I’ve had a problem with gas coming out of my vacuum petcocks for a while but this other problem is new.
I just overhauled the top end – all new. I just passed the break in period, hence the oil change. I’d like to learn how to fix this myself, so hopefully there isn’t too much wrong with it. The overhaul killed me over how much they charged for labor. I really want to learn how to fix anything myself. Please help.
I appreciate any advice.
Thank you
I also wanted to mention that after it warms up it has a high idle.
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First, go back to a regular, conventional motor oil. 10W40, 20W50 etc. Your bike was not designed to run with these newer type oils in it. I have always used conventional motor oil in all my bikes and still do. I have never had a problem. the older machines just seem to perform better with it.
The carb and petcock issue should be simple enough to fix on your own. As for the labor charge for a rebuild, what were you expecting? the average rate in a shop is $70/hour. It takes 10 hours to remove everything that has to be moved, removed and to get the engine out of the frame, and torn down. So there is $700 right there, now the engine is sitting in pieces on a bench, do you want it fixed? Parts are additional, and be thankful the 650 sold in the numbers it did, otherwise you would still be searching for parts. Then it takes another 10 hours to reassemble the engine put it back in the bike and reconnect everything, so another $700 there, plus the parts. Now the shop costs come in for 3-4 qrts of oil, a new filter, the new air filter etc.
yep not enough gas
you should also check and see if your throttle bodies have no tears and they move up and down freely. oil has absolutley nothing to do with your problem!
now listen to me
your gonna have to take them carbs off!
engine can stay right there in the bike!
on the idle jet screws turn them 2 &1/2 turns counter clockwise. if these still have the metal plugs on them? you need to drill and extract them off for access to the screws. Now take the card float bowls off inside you will see brass screws with numbers (main jets) like k100 or 150 they have a small hole in them get yourself a bottle of compressed carb cleaner stick the straw in them and blast away do these for all the holes you see do it to where the fuel enters as well also removes the floats and blast the spray into those holes. If this does not fix your problem you might want to go up 1 or 2 sizes bigger on the main jets. you just need a flathead screwdriver to remove and replace them. make sure fuel leaves the fuel tank dont need clogs
Before you go tearing into things or needlessly changing oil check some simple items first. it does sound like a lean condition. Fuel tank cap venting? good fuel flow from the petcock? Rust or scale evidence in a fuel sample? Check these simple items first. Post your question to a brand specific board. You’ll find lots of genuine expertise.
Check your distributor points and rotor. The rotor thingie is springy so it can do the spark advance. Make sure the points are clean and the rotor thingie is springy.
If your bike still has points, make sure the point gap is correct (probably .014-.016 inch). Too close means not enough time for the ignition coil to become fully saturated (with electricity) and that means weak spark. The faster the engine runs the less saturation time anyway, so that’s where I’d start. Incidently, make sure your feeler gauge is completely clean and oil free. After adjusting the points, close them and draw a piece of heavy paper through them to clean them up.
You are definitely running lean. Either the float bowls are not getting enough fuel or you have an air leak. Those vacuum petcocks are notorious for not working right, turn it to the “prime” position to see if that helps. If you have an inline filter check that as well. The intake manifolds are prone to cracking when they age so check them out, they are available from mikes xs. Check your vacuum lines for cracks too.