Sporadic high idle while approaching/at stop sign

Got the 83 750 Maxim...

First off, this problem seems to be linked to a hose that comes out of my tank and is hooked up to carb 2's vacuum input nub. When I take that hose out of my petcock it quits doing the high idle thing. If I put a piece of tape over the hose it will start doing it again. However, it seems like it shouldn't be that way. Any ideas?

 

Sorry to say that hose is not your high idle problem.

The hose is the supply to the vacuum operated fuel shut off valve.

If your valve is working properly and you take that hose off you also turned off the fuel supply, but the bike will continue to run with the fuel in the float bowls.

If you leave the hose open you basically shut down cly # 2 from running properly, therefore your idle goes down.

Sporadic idle problems could be dirty carbs, carb sync problems, or carb shaft seal o-rings needing replacing, just to name a few.

 

ok.... weird thing is that my bike runs fine without it plugged in. Runs like ass with it in the tank. I went 120 miles with it out. I know for sure my carbs are super clean. Nick, could you think of anything else or any other reason why that would be the case or explain to me how it still runs and consumes fuel? I am pretty new to bikes, however, I have successfully cleaned my carbs twice very well. Man... I just don't like the idea of having that hose wide open to natures little crap that could get sucked into it.

 

1) Your petcock has issues. Fuel should not flow in ON or RES without the engine vacuum applied. In my case it was the rubber disk with 5 holes that goes behind the fuel valve. $8 at my local dealer.

2) You're probably rich on #2. Letting the extra air in is leaning it back out for you.

With the bad petcock I'd think a stuck float or needle/seat problem would drain the fuel tank into the oil while parked. The rich condition is probably something else.

 

If the bike runs better with the hose "open", I would suspect a rich mixture. The vacuum is produced by the downward motion of the piston. The hose allows air to enter at the intake port after the fuel/air mixture set by the carbs. So it is leaning the mixture out. Main thing your bike needs is a colortune and carb sync. I think your problems will be answered by that.

 

where can you buy a colortune kit?

 

Here is one link. Someone here found a US source that I don't have a link for.
http://www.carbtune.com/colortune.html

 

http://www.eastwoodco.com/jump.jsp?item ... pe=PRODUCT Is one I found in usa

 

stupid question but... what size spark plugs does the xj750 have? Is it an 18mm?

 

14mm