First real CB500 problem

[LoserShoes]

I'll vote for blocked exhaust too. Probably got mufflers full of mouse nest. Might want to pull the headlight and check the wires there, my wifes XJ 650 that sat for 15 years had quite a bit of mouse damage to the wiring in there where a mouse built a nest and made a meal of the insulation.

Steve

[81xsproject]

I will look into the exhaust. By the way new airfilter, airbox is spotless, and chokes work properly as they are actually butterfly CHOKE mechanisms instead of enrichers. This is SO wierd

[Geezer]

Try taking the gas cap off and then run it to see if the problem changes.

Geezer

[81xsproject]

yeah, I tried the gas cap the first time around when I still thought it might be fuel starvation. I finally got a real hint from the bike yesterday. I think it may be something mechanical after all. I ran it for maybe 20-30 seconds and like always, it started to bog down like it does just before it dies. I gave it some throttle trying to force it to keep running. This lasted for maybe another 5 seconds then it came to a very abrupt halt like always. Except this time I immediately tried to kick start it. I couldn't get it to budge. For about 15 seconds it was all locked up. I am not sure what it means, but it is a better clue. I always thought that the way it died was so hard it was more than the usual fuel, air, and spark problems. Any ideas what could be happening?

I am pretty sure the oil pump works because there is this stupid oil port plug that is held in by the stator cover. If you kick the engine over or hit the starter with that cover off, it will shoot out from oil pressure and then oil pours out all over the floor.

[LoserShoes]

It's either seized or a cylinder is filled with fuel. Pull the plugs and try to crank it, stand clear of the plug holes, they can squirt gas big time.

My bet is that the cylinders will have to come off.

Steve

[81xsproject]

I have pulled the plugs, not full of fuel. The bike did sit for 25 years, so problems with the cylinder walls is not to far out.

[TomB]

I once had the valve timing out on an old Triumph (long story) that far that the block heated up that quick it locked up in a hurry.

I pulled the motor down and found the slightest mark on the piston and nothing on the cylinder so I rebuilt it all, adjusted the valve timing and it ran like a dream.

I now go through everything before pulling a motor down, but think Steve (losershoes) is right

[81xsproject]

Well, I bought a cylinder hone today. I hope I don't end up using it.

[81xsproject]

Update, there was concern on the SHOC site that oil wasn't getting to the head. So, I checked it and it is. I decided, the hell with it, I didn't buy that cylinder hone for nothing. I am in the process of removing the head. I have never honed cylinders out before. Anything I need to know?

[TomB]

Slow RPM and plenty of coolant, (diesel, kerosene)

And old clothes, it gets messy

[81xsproject]

Well, I need to get some new rings for the pistons as some broke while trying to free them from there rusted position. While doing research on my options, I found out that the only difference between the 500's and the 550's were the jugs and pistons. So, I already got some 550 pistons and am keeping my eye out for a good deal on the jugs. Like a factory big bore

[TomB]

Can you rebore the 500 cylinder block out to 550, at least that way you'll have new bores.

If you find 550 cylinders they might be worn or are the 550 pistons oversize and you plan to rebore any you get.

[LoserShoes]

Check and see what it costs to bore your 500 cylinders, haven't done a MC for a while, but last time I did a car block, I think it was $8 per hole. And you have a nice new straight bore.

Steve

[81xsproject]

Everything I have heard for MC rebores is around $40 a hole. I plan on using the 550 cylinders and pistons and hopefully the set I just bought will be in good enough condition to just hone and go if they look decent. If boring weren't so expensive, I could have got a 555 kit off of ebay that, with everything, was still cheaper than 4 sets of rings.

[chopwatchagot]

I had almost exactly the same problem on a 1971 CB 500 I aquired a couple of years ago. The bike had sat for about 12 years. It had been parked with about a half tank of gas. By the time I got it the gas had turned to the consistancy of frozen honey. I got it cleaned out, rebuilt the carbs and yadda,yadda,yadda got the bike running. Ran for just a little bit then seemed to starve for fuel and die. I'ld wait about half a minute and then it would start again. I finally figured out that the fuel tank vent was clogged causing a vacuum as the engine sucked the fuel out of the carbs. Once I cleaned the vent in the cap the problem was solved.