81 XJ650 Maxim - Carburetor, mixture/fouling problem

Just aquired this bike and took it over to a local shop to have carbs looked at because it was idling rough and fouling plugs after it's been run for awhile.

I was told the Hitachi carbs are notorious for problems. Says the shaft/bore for the butterfly valve is worn/loose and lets in air when bike heats up. Also the intake manifolds are old and show cracks which may also contribute to more air entering. Recommendation was to swap out the entire carb rack for some Mikuni's or Keihin's along with replacing all the rubber manifolds and gaskets from the engine to the airbox....were talking roughly $1400!

I noticed that the part on the carb that is "leaking" is a nylon bushing. Any possibility of doing a cheaper fix on the problem besides swapping out all the carburetors?

 

1st., welcome!

2nd., put your location and bike on your profile/signature so we know what you have.

3rd., we have a member that specializes in XJ parts. He has the carburetor holders (intake manifolds) and butterfly shaft seals. That's his advertisement blinking at the top of the screen.

I don't know that Hitachis are any more problematic than any other carburetor. Certainly cheaper to fix them up than to successfully adapt something else.

The problems you describe would make the bike run lean. Lean doesn't foul plugs. You've either got different or more issues.

 

$1400 dollars sounds like a lot of money to me. But it is relative to what your able to do. If your mechanically minded and have the tools, then it's fun and to some degree theraputic. My son bought an 1980 XJ650 earlier this summer, his first bike. I tried to convince him against buying it as I told him a 30 yr old bike will give you problems.. While he is a quick learner, I generally do all the vehicle and house repairs, and I knew little to nothing about bikes. The bike quite after three weeks, and I was left to fix it...with lots of research and help from this site, I now have the bike running real well and don't want to part with it..

He bought the bike for $1200, but I have invested about $600 to fix it... Not a win win for me. But it has been a real fun project and I have learned tons. He has already bought a newer bike, so I have decided to keep the XJ. My pointis is this, if your at alll mechanical, willing to do some research and take suggestions, I think you can do better then $1400 and come out with a much better understanding of how these machines work...

I now dream carbs, I've taken them off about 30 times, and can take one apart in my sleep... It's been a blast ... Now onto brakes as they were still original. Another addiction - my wife is getting concerned.

 

riverrebel,

welcome.

Gary

 

After reading this, I slapped my head and said you're right. I'm now thinking it could be the fuel enrichment system (aka choke) since it smokes a lot when I increase the throttle. Seems logical since it really loads up and fouls the plugs after running it for awhile. Any suggestions? Thanks for your help

 

Why do you think that's related to the choke?

And no, the hitchais are actually more user friendly than the mikunis... though the mikunis seem to have a bit more of an edge on performance.

First off, how far out are your idle mixture screws?

What shape is your air filter in?

Go read the thread "brainstorming issues that affect mpg" or whatever it is called that's active right now in either xjcht or general... basically every possible cause of running rich is discussed there, right down to weak battery giving a weaker spark giving less complete combustion. You should get some ideas there.