85-91 Yamaha 9.9 will not idle when hot?

[Lee Strong]

I cleaned out all the gummy deposits I could see from the carb, it started right up (HOOHA!) and idled just fine. I gradually revved it up, got it warm, and then it stalled when returned to idle (HMMMM?) Restarted with acceleration, but it is hard to start warm, and will not idle warm!!!<br /><br />Illustrations in the Clymer manual show this is a 1985-91 model, with a bimetal vacuum switching valve(BVSV) instead of the electrothermal valves shown on later models. I guess this is an older enrichment system active only when cold, right? When warm, it should cut out, and some other idle circuit must take over, but which one? There is no plainly marked 'idle jet' !?!<br /><br />Any ideas how to troubleshoot this?<br /><br />Thanks, Lee

 

[12Footer]

Re: 85-91 Yamaha 9.9 will not idle when hot?

It sounds like an air leak, as you explained. So the problem could be the carb/intake gasket (often re-used but flatten-out when bolted up).<br />They will never re-seal a second time like they did the first. You can make a new one from bulk gasket material,and a pair of scissors,using the old one as a pattern.<br />Also,I sugjest a compression check.<br />The recirculation valve,tees,and hoses should be inspected for leaks. It's not important that the engine be recirculating to idle ok,but the loss of vacumm from a holy hose or somethin is.