Carb tuning - Suzuki JR50 - Resolved

[Terry Olson]

I'm having trouble getting my son's '86 Suzuki JR50 running right. I'm sure the problem is fuel delivery. I replaced the carb (Mikuni) and can get it to run pretty well when the choke is partially open, but not fully opened. While running it with the choke off (fully open) it won't idle and bogs when I give it throttle. Choke it a bit and it runs fine, but choke it too much and it's boggy again.

These symptoms make me think it's too lean but I've had the mixture screw everywhere from fully opened to nearly closed and can't alleviate these symptoms. There are only two adjustments on the carb - idle speed and idle mixture. I've played with both and see no other adjustments that can be made.

I checked from the tank to the carb and don't find any obstructions. I also find that I can run it at high RPM for a while so I don't think it's a fuel starvation problem.

I replaced the carb because I thought I had a vacuum leak where the carb meets the "intake", which is really just a pipe. There's a plastic sleeve in there that can't be bought separately and I wasn't confident in the float either (not to mention that there is no rebuild kit available for this carb anymore). I removed the intake and found the gasket where it meets the cylinder looks good, but I sealed it on both sides with RTV just to make sure.

Still the same symptoms. What am I missing?

 

[Bob_VT]

Re: Carb tuning - Suzuki JR50

Re: Carb tuning - Suzuki JR50

Is that an oil injected model? It may be getting a heavy shot of oil.... my first item would be a new plug. They are plug hungry motors. That is almost the cheapest and quickest fix.

 

[Terry Olson]

Re: Carb tuning - Suzuki JR50

Re: Carb tuning - Suzuki JR50

I'll check the injection - disconnect it momentarily and see what that does for me. I should have mentioned that I replaced the plug and don't have even 10 minutes run time on it - but - I can't get the correct plug (the one the book calls for anyway) so I replaced it with what was in there before. We've run it maybe 100 hours on that type of plug so I know it works although it may not be the optimum plug for this application.

 

[Bob_VT]

Re: Carb tuning - Suzuki JR50

Re: Carb tuning - Suzuki JR50

Mix up some pre-mix and feed it to the carb through a seperate line. I would NOT run straight gas for any reason. Those bearings are tiny and will cook quick. The other "common" error is in the cdi ignition.

I only run NGK's in the 2 stroke bikes.

 

[Terry Olson]

Re: Carb tuning - Suzuki JR50 - Resolved

I played with the mixture settings some more and got it running right. I was thinking I was too lean because of the off-idle stumble or bog and slightly choking it brought it around. I leaned it way out and got it running like new.

So - I wasn't too lean, I was too rich. I leaned it way out when I was playing with the mixture before but didn't find the same result for some reason. Who knows - there's a bit of inexplainable magic in every engine - or I just don't know enough about what I'm doing.

Either way - I'm good to go. Thanks for the advice Bob.

 

[Bob_VT]

Re: Carb tuning - Suzuki JR50 - Resolved

Sound great.... just got back from dinner w/the wife and I was thinking SeaFoam may help clean that carb fuel system and would also help the cylinder.

 

[Terry Olson]

Re: Carb tuning - Suzuki JR50 - Resolved

I'm a regular Seafoam user. Already did that, but that goes without saying in my garage (3 cans on the shelf out there at the moment).

Thanks again.