Full speed power loss

[BrandonG]

My 66cc BB kit runs great, until 32 mph. It loses power and slows to maybe 27 then picks back up, cruises around 32 for a few seconds and repeats.

I searched this alot and found many people have the same problem, but the general solution was that gas wasnt getting to the engine. I dont have the stock tank, its one off an old lawn mower, run through a ball valve and a new fuel filter. The tank is behind the seat and lower than stock, but my best guess is 5" above the bottom of tank and where fuel goes in the NT carb. That should be enough pressure right? There is a part where the fuel line goes up, but if I shorten the line the angle will interfere with the choke lever. Would the way the line is run cause the problem? The choke is off and Im runnin 32:1 mix. Its a new-ish sparkplug, and I think it looks good, but I posted a pic and would love to hear advice on that.

Today After a 3 mile mostly wide open ride I parked it and noticed the fuel line was bubbling a bunch of small bubbles going up the 4" of gas before hitting the air bubble in the line. This bubbling went on for like 5 minutes. Does this mean the float bowl was empty? I cant imagine that there isnt enough fuel getting through. Wouldnt the float valve be the most restricting part? I havent heard of anyone complaining of that though.


Cant wait to hear what advice ya'll have!

 

[headtrama]

The spark plug looks okay, The air bubbles in your line are most likely from air getting in the line from a loose connection. How old is your fuel line is it hard if so change it. To get all the air out of your fuel line after you replace it open the drain screw on your float bowl. Let the fuel run out of the bowl until all the air is gone. I have had a motor slow down at full throttle. After jetting it every way and never correcting the problem I changed the magneto and it went away.

 

[BrandonG]

The fuel line is 3 months old. I have hose clamps on all the connections on the line and the air bubble was gone yesterday after I rode and it hasnt done the bubbling since. So no bubbles now, but still slowing at full speed. My magneto got wet and I put a new one on last week

Also, I tried giving a slight choke when it bogs (to see if it was a lean condition at WOT) but that didnt help any.

 

[biknut]

If you're running a 44T sprocket you're not going to get more than about 32 mph out of it. That's already over revving it. If that's not your problem start at square one.

First remove the fuel line from the carb. With the gas cap in place open the petcock, and see that fuel flows out like a fire hose. If yes, then fuel supply is no problem. Bubbles in the fuel line mean nothing. Fuel line going uphill doesn't hurt anything as long as the fuel level in the tank is higher than the highest point of the fuel line.

Assumeing all that is good. What jet are you using? Your plug looks a little rich to me. Try a 68 jet, with the needle clip in the next to top position. Next try a 66 jet if it still doesn't rev out all the way.

Keep an eye on the spark plug. I recommend getting a NGK B6HS, and a BP6HS. Try both, and use the one that works best. The difference is the BP is extended tip. Some motors like them better.

As always, make sure there's no intake, or exhaust leaks. Any leaks will show up as oil leaks.

 

[BrandonG]

Ive gotten it to 34 on flat ground, 35 on a slight hill. Im fine with 30 if it would not cut down to 25 so often.

Fuel flows like a waterfall. Alot better than the stock system.

Its the stock jet that came with the NT carb, but I dont know what size that is.

Ill try a bigger jet and those plugs and let ya know.

No leaks!

 

[2door]

How many miles/gallons of fuel has your engine accrued? High end bogging can be a sign of an engine that is not fully broken in yet. They require anywhere from two to three hundred miles to get the rings seated properly. If this is a fairly new engine I wouldn't worry about going over 30 for a while.

Actually, your 32 mph would be enviable by many. 25 to 30 is considered about tops for many stock engines with a 44T sprocket.

Tom

 

[BrandonG]

3 1/2 gallons through, no clue on the miles. Definitely not 525 (3.5 gal x the supposed 150mpg! Id doubt even 350 miles)

Maybe Ill give it another gallon or two to see if it fixes itself

 

[biknut]

Its the stock jet that came with the NT carb, but I dont know what size that is.

Ill try a bigger jet and those plugs and let ya know.

No leaks!

The stock jet is about a 70. Most of the time you'll need to go down in jet size. I've found 66-68 to be about right in my motors.

 

[bigdbeach]

Well I had a head stud back out of the lower end a few days ago and she has not been the same since. I took some advice from some people on here and made new head studs today at work and while I had the head off I "lapped" the head, cleaned the burn marks off the gasket with Scotch Brite pad. Put it back together and still not the same power on WOT as before. Can some one point me in the right direction please?