1981 XJ 550 Seca Throttle Hangs then comes downs

Hey Everyone,

I bought a project XJ 550 and am almost done restoring it minus the paint, think I will leave that original.

It had been sitting for 29 years with gas in it.. so you can probably understand that state everything was in. So I cleaned it all up, carbs, gas tank etc are now spotless. The bike would not idle.. so changed the coils... problem solved.

The issue I am now faced with is when I give the bike some throttle, it hangs on a particular RPM for a few seconds then comes back down. I thought it could be an air leak some where but I cant find one! Any ideas?

Thanks

 

Valves in spec vacuum synch done. Pretty common out of synch symptom.

 

A hanging idle is usually a sign of a lean burn. Assuming the carbs were completely and thoroughly cleaned (Church of Clean clean), then you could check all 4 air nipples on the carb boots, including the hose on cylinder 2 leading to the fuel petcock. also check for air leaks at the carb boots using either unlit propane or quick start fluid with the bike running.

Hopefully the idle circuits are clean and the tiny passages near the top of the butterfly valves are not partially clogged. Some of the smaller passages in these mikuni carbs are very difficult to get clean - 29 years worth of varnish is a lot.

 

Carbs are in total sync, mixture screw is 3 turns out so I definitely don't think its running lean.

My Carbs I am sure are spotless I spent over a week cleaning them and re cleaning them.. even went as far as to put them on another bike.

Ill try the starter fluid trick and see if the engine speeds up, I'll also check the valve clearance.

Thanks for the assistance so far!

 

the linkages are all clear and free?

 

Yes they are.

 

valves and wet float set carbs

 

Yep.

Get the valves in spec.

Accurately wet-set your float levels, Mikunis are especially fussy about this.

Then do a good, careful running vac sync with the YICS blocked and the bike fully warmed up.