Fast idle...

Well she's on the road now. Took her out for a bit, then took my son for a spin on it.

After he got off, I putted around for a bit more. I pulled into a parking lot because it seemed like it wasnt running right - lo and behold I had the choke on. After switching it off it reved smoother and ran great. I just have to get those exhaust gaskets put on (ordered them locally today) and I'm good to go.

After a while of blasting around the engine started wanting to keep a very high idle - around 4k. In gear it behaved a little better, but I didnt even need throttle to maintain speed. Is my idle set too high? Or what else could it be?


Could the exhaust leaks (at the manifold) have anything to do with it?

How do your plugs look after riding around a bit? High idle can be caused by a lean condition, which could be caused by your missing exhaust gaskets (too much exhaust airflow). Your plugs will tell you if it's lean.

All four are dry - 3 look like they're on the lean side and one looks sooty. I'm not sure to what extent one header is leaking compared to another, but here's the pic



They are in order from left (1) to right (4)

I believe a sooty spark plug in cylinder #2 indicates a bad petcock.

Well I have no other indication of a bad petcock. When I take off the lines I can shake the tank around and no fuel comes out.

High idle is most likely a leak somewhere. I would check to ensure that all four vacuum ports are capped. I would then check the seat on the carb assembly for leaks. I would then look at the throttle cable. Should have VISIBLE slack when you bend over and look at the cable as it enters the bellcrank. Also, there is an idle adjust knob that could have gotten knocked around. Only a TINY little difference in the amount the throttle butterflies are open will change the idle speed dramatically. Try turning the idle screw down some... plastic knob, etc.

Yeah, what wiredgeorge said!

It is not your exhaust gaskets

Just want to reiterate what these other two said...I've had high idle problems on two occasions with my 750-4. The first was I routed the throttle cable wrong and it was kind of pinched, kept looking for vacuum leaks until I checked for slack at the carb end of the cable and realized there wasn't any. The second was a small split in my vacuum line to #4 carb. Wouldn't show up at first, but when the rubber softened, it would open up. My 400 had the same problem with the petcock vacuum line.

Good luck!

Just make sure that the carbs are FREE of anything but good fresh gas. Throttle stuck open in rush hour last month, 70mph in stop and go traffic is a butt puckerer! Turns out there was some dried gooey gas in carbs 1 and 2 (from a badly cleaned gas tank) See pic below. Recleaned everything, did the POR15 tank liner and now it runs like new, except for that oil leak, but that's not the subject here.... might be worth taking the carbs off and taking a look at the slides, make sure there's nothing in there sticking, like dried gooey gas, preventing the normal return of the throttle assembly. Just my own experience.