Hello:

I recently purchased a used 1987 Quadrunner that needed lots of work. I have since rebuilt both the front and back ends including new wheel bearings, axles, u-joints, and front differential. Also have cleaned and rebuilt the carburetor (new jets, needle, gaskets, etc.), redone the front engine mount, and cleaned the fuel system including petcock, and all hoses. I have completely drained the fuel system and put in fresh fuel. Oil and filter have been changed. Valves have been adjusted to spec. Spark is good. Air box and filter have been totally cleaned. Compression is good -- around 155.

The problem is this: It will only idle when the choke is on. If I rev it up with the choke on there is a phenomenal amount of thick white smoke that comes out from the exhaust--so bad that I can't do it in the garage. If I take the choke off, it stalls (at any RPM). I also notice that if I try to rev it and then slowly take the choke off, it makes a sort of hissing/coughing "tssss" sound before it stalls. When it makes this hissing noise, there doesn't seem to be any discharge out the back end of the carburetor other than a slight puff of fog/mist--barely noticeable. I have tried adjusting the mixture screw to spec, and doesn't help. Even with the screw completely closed, it still is running incredibly rich. I have done all of this with the airbox off so I know that it is getting air. There any no leaks in the exhaust system at the manifold--there are at the exhaust pipe/muffle juncture, but this shouldn't affect it.

Any help would be much appreciated--not sure what to try next. A clogged passage in the carb? Fuel pump? Too much fuel seems to be the issue, so I'm not sure that it's that.

Regards,

Brendan

 

Take ur plug out, if its.black then its rich. White, then its lean

 

I put in a new plug and it is turning shiny black. Feels sticky.

 

Hello everyone:

Since I made my first post, I did a bunch more work on the quad and have been unable to find the problem. I did a complete top end rebuild including reboring the cylinder, new piston and rings, new intake valve, valve guide seals, and refinishing the valve seats. All new gaskets and everything cleaned up. The valves and cylinder were done by a professional. I've cleaned the carburetor multiple times, including soaking it in the nasty/smelly carb cleaner, and using compressed air. I've put in a new used wiring harness. I swapped my CDI box and ignition coil onto a fully functioning 1988 quadrunner and both performed well on the other machine. I have polished and cleaned most of the electrical connections.

The performance improvement from all of this work has been a big reduction in the amount of smoke in the exhaust. The problem of the gasping/hissing carburetor when trying to open the throttle is still happening. Basically the machine has no power and I can't rev it up. Any ideas?

 

Did you actually rebuild the carburetor with a kit? I had some carburetor problems awhile back and I did a full rebuild of the carburetor with a kit. New jets, needles and what have you. Its very inexpesive. Another thing to consider is maybe the float is making contact to the side of the bowl or improperly adjusted float height.

 

Hi:

Yes, I rebuilt the carb--new jets, needle, etc. Also doubled checked float level and it is within spec. Will check to see if the float is catching on the side of the bowl.

-Brendan

 

Another thought would be maybe to check to see if your stator is producing or the pickup for the CDI is working properly. You can check the resistence via the manual specs. Only three things make it run, fuel spark and compression. You know its getting fuel, and you rebuilt the top end so It has compression. I think your at a point that its just trouble shooting now.

 

I think you're carburetor isn't working right, whether it's a set-up issue or a defective part.

 

Dog Walker:

You called that one. I finally figured out what the problem was--an aftermarket needle jet made by Shindy. I thought Shindy was a good brand, however I am beginning to reconsider. As soon as I swapped in the OEM needle jet, everything was fine.

-Brendan