CB175 starts and revs up really high

[link55nyc]

I recently got a 175 that has been sitting for a while, but is in otherwise great condition. I fixed all the other issues, but now I'm having carb problems. I can only start it with the choke open unless it's warm, then it can be started in almost any position. Once it starts, it revs up to 7-8K RPM real fast. I can close the choke to control the RPM and it idles fine with the choke just barely open. The throttle does almost nothing, but sometimes it actually cuts the engine.

I have cleaned the carbs twice now. The jets were pretty gummed up, so I soaked them in carb cleaner and blew them out with my compressor and they look clear now. What else should I check? The needles look OK, but I'm by no means a carb expert.

 

[tobiism]

I'd bet money on an intake leak. Check your carb boots and all connections of the carb to the head. That unwanted, unregulated intake of air is whats causing your engine rev so high.

 

[chrisf]

That's exactly what I was thinking. It could be as easy as the diaphram slipping out of its key or as bad as a diaphram boot tear.

--Chris

 

[link55nyc]

I just cleaned the carbs again, including the plastic pieces connecting to the engine. I boiled all the internal parts in lemon juice and soda blasted the external parts, then blew it all out with an air gun. Everything seems very clean, the needle moves freely, and all the jets are OK.

There don't appear to be any cracks or leaks in anything. With the choke nearly closed all the way, I can get an idle around 4-5K RPM with some throttle response now.

I recently took the head off to have a HeliCoil put in one of the spark plug holes. Could there be a leak somewhere else?

I also tried running one cylinder at a time with no difference. Does that lend to the idea of a leak elsewhere?

 

[link55nyc]

I'm an idiot. I never thoroughly checked the throttle cable. Where the main cable splits into two there is a plastic housing. The main cable had popped out just enough to keep it suck open a bit.

Now I just have to adjust the idle and I should be in business. At least I have really clean carbs now.

 

[tobiism]

Sweet. Glad to know its fixed.