Fuel Leaking from Carburetor Air Filter??

usermeister said:

Well, I'm new here and this is my first post. I found this thread by searching for 'leaking carb' and might have an interesting story to share. Maybe someone will find it useful.

I have a Skyhawk GT5 66cc engine which I purchased recently and have been riding for a couple of days. Yesterday engine started to get coughs and today it turned off. I noticed that the carburator was leaking fuel. It would only leak when fuel valve was completely open.

Since the engine has gone through about 30 miles it somehow seemed unlikely that it could be caused by junk in fuel. Spark plug was also cleaned. It was even replaced with another one when I was taking the spark plug out while defflooding the engine.

Afterwards I took apart the carburator and noticed that mainjet was unscrewed and dropped in a bowl. Being a noob, I wondered whether it was supposed to be like that, but concluded that it wasn't. So I screewed it up, assembled everything back together and... it solved the problem. So I guess the lesson is: check everything related.

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yeah that'll do it.

The main jet loosening or falling out happens a good bit, the jet on my CNS/2 backed out a few rounds once but I noticed the change in engine performance and checked it before it fell out. You will learn over time what to check more often on your bike.

allen standley said:

Curious... Is this an NT carb or other.

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Yes, it is an NT Carb. I have a 64mm jet, and it still 4 strokes.
I also have a high flow filter from SBP.

30 mi-You're basically running a new engine. It was fine for a while, Then flooding, then found jet in bowl, fixed it, now you're 4 stroking. I run NT's with 63 and 64 jets, run just perfect 65ft above sea level. I'ld put up with 4 stroking for a while if the bike will run ok. They run better after time and use. Get thru your breakin mix. assuming your running rich oil mix.

Yeah...Somebody - anybody else chime in.

Hey Allen the first post is over two years old, placidscene has fuel blowback from his air filter. It could be his float level is a little high, I still get some blowback on both of mine at times. This is the results of a induction system without reed valves.

Thanks Greg! The older I get the more other people find me talking to myself.

Ive already bent the tines down on the needle arm in the float bowl also. I also checked to see if the float is floating. It is. ?
I have put plenty of miles on the engine to be passed break in on it.
Did you notice the pic of the fuel stain under the spark plug also?
I think I will put a new head on it, and see if that could cause the issues I am having. It looks like it is leaking through the spark plug hole. I have a hard time threading the plug without cross threading it, so I think I must have damaged the threads at some point.
Any not so expensive aftermarket heads that you would recomend?

By the way, Greg, I checked out your public profile. Do you make your own CDI?
Do you think they work better than the stock ones?

I have built a couple of cdi's , to educate myself on the working aspects of the ignition system. A lot of members have spent a lot of time developing cdi's that adjust the timing, I built the basic design. Back to your bike, like I said earlier both of my bikes get some blowback. If you get the jetting just right it should help.

Greg58 said:

like I said earlier both of my bikes get some blowback..

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I missed that in your earlier post.
I am currently running a 64 jet, should I go smaller in increments of 1 or 2?

It all depends on spark plug color, the link below should help.


http://motorbicycling.com/showthread.php?t=24873

The other day, I checked the spark plug color, it looked good to me.
I put was running an NGK bh6. The fuel on the head indicated to me that it was leaking through the spark plug threads. The metal seal on the spark plug looked buggered a little, so I put in another plug that I had. It is a NGK bh7.
I cant remember if the bh7 is a hotter, or a cooler plug than the 6.
I cleaned up the fuel on the head and on the chain guard so that I could see if it continued spitting fuel out of the plug hole and the carberator air filter, and went for a ride. It seemed to be four stroking still, to I pulled over and moved the needle to the leanest setting. It had been in the second leanest setting. Then I went for a 30 mile ride.
It seemed to be four stroking less, but it also seemed to have a little less bottom end power, and a little less high end revs.
There is however less blow back from the carburetor, and no new fuel on the head from the spark plug.
The plug color on both plugs looks good to me, so why does my engine sound like a jackhammer at full throttle? It will get to the top end and sounds great, but then the sound changes dramatically to a four stroking sound.

In the picture the plug on the right is the BH7 that I am currently running, and the plug on the left is the BH6 that was leaking.
You can tell that the BH6 has run rich, but if you look at the tip, it looks good.