Big Bore Kit Install

Joseph Besko /

Hey so I just installed an 80cc big bore kit on my moped and it seems to be running great. I have noticed that the exhaust has turned blue. I read that it could be from running lean. The plug seems to be good but I'm wondering if it's normal for the color on a new build for the first ride. Or if I should look into tuning for more fuel.

Re: Big Bore Kit Install

Terbo Speghetti /

What kind of engine? And what did you do besides install the kit? I hope you upjetted your carburetor, and even if you did, you've still got tuning to do.

Have you read Fred's Guide and/or the performance wiki articles?

Re: Big Bore Kit Install

Tri-ped Dave O.D.B. /

Blue is from heat often caused by lean but sometimes other things. The oil is in the fuel, so if lean, you are starving for oil as well and will toast your new kit in no time. Check the plug color first. If you get her tuned nicely on the mixture and it is still hot, reduce the compression a tad. You can do this by adding a thicker head gasket or a thicker base gasket whichever seems to make it run better.

Re: Big Bore Kit Install

Think about it.......

A bigger bore will mean that at each suction stroke more air will be pulled in.

You will have to re-jet to get the air/fuel mixture correct.

Get a selection of larger jets. Start with the biggest one and work your way down to the point that the plug color looks correct.

Re: Big Bore Kit Install

Joseph Besko /

139QMB, I also put on a 20mm carb, and new exhaust. I put a #90 jet in there. Like I said the plug looks good maybe a bit dry so I will look into fine tuning the carb a bit better or do you suggest i go up a jet and try that.

Re: Big Bore Kit Install

♣Slew Foot♣ /


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