Idle problems - Too low on Startup, too high when warmed up

I have an 81 650 Maxim that I just bought 2 weeks ago. I'm a complete noob to bikes and engines as a whole, so I'm hoping this makes sense.

The bike can be difficult to start with the choke all the way out. Once the bike is warmed up and I'm driving down the road (choke in) :wink: I come to a stop and pull the clutch in, the RPMs shoot up to 3-4000. To the point I have to let the clutch out a little to drop the RPMs.

If I start tinkering with idle adjustment screw (ie lower the idle), I'm worried that I won't be able to start it at all.

I plan to rebuild the carbs over the winter, but I'm not sure this is realated.

Will the carb rebuild solve this issue? Is there anything I can do in the meantime?

 

A good clean up and a sync job and you should be good to go

 

back the center idle speed screw out. Make the idle nice with the mix screws and sync, then repeat. Mine had a similar problem. Also, I (so far) have not had to and it doesn't want to start on full choke. About half is all she needs and she fires after about half a rotation.

 

Re: Idle problems - Too low on Startup, too high when warmed

I'm having the same sort of problem with my Seca. I've had good results by syncing the carbs. It's not perfect yet. It hangs up around 1500 rpm and will drop back down to 1100 after a few seconds, but it was doing the same as yours. I suspect I need to clean the carbs more thoroughly, but adjusting the balance made the biggest difference.

 

clean them carbs up(always a pre requisite to any XJ)
bench sync
then do a vac sync
then start doing some chops(adjusting mixture screws as you go to give them a "nice summer tan")
once all steps are complete get that bike up to opporating temp and set idle to 1050 plus or minus 50 rpms

please note, if there is a vaccum leak it will need to be repaired to tune the bike.

 

Re: Idle problems - Too low on Startup, too high when warmed

Your idle increasing when hot is because the mixture is too lean. This can be from an air leak or dirty carburetors.

I'd get a can of starting fluid and squirt a bit around the carburetor holders (manifolds) and butterfly shafts before I pulled the carbs. If the engine revs you'll know in advance that you need shaft seals or carb holders and can order them with your other parts.