is your bike losing power at top speed?

[biknut]

Ball valves are my favorite design so far.

Has anyone had an issue with their gas cap resulting in poor fuel delivery? I had this happen to me and it took along time to diagnose. I guess the vent got plugged somehow but when I would loosen the cap while riding my bogging went away. Makes sense that if the fuel that leaves the tank isnt replaced by air then it simply wont come out. Just an experience of mine.

Not very many. Only about 5,785,439 people. And that's just on this site.

 

[Goat Herder]

I don't disagree with 2 ither. How ever on my morini it would die sometimes at wide open throttle. Not enough flow was there.


On my china the cheezy filter fell apart on the valve in the tank. Which subsequently a tiny fleck of whatever got into the valve it did not flow well. Cleaned it out on four occasions. Threw it away after that no more drama.

I never did like there valves on the china. I had some that leaked. I had the filters fall apart on them just for staring at them never even had to touch them. I had them show up in the kit all ready broken.

The valve I switched too will not clog and I never put a filter on it just a in line filter later down the line.

When you have a motor that runs perfect all the way to full blown RPM.s and then cut out well that is something to consider.

I am free from china motors right now life is good! Had leaking gas caps on the china kit tanks all of them ...never was a vent issue ether. Don't get fooled that easy lol. Biknut Your not revving that China motor of yours hard enough? Mine were to perform top notch red line! I was the fasted over grown kid on the block.


A float bowl set too low will do it too..

Originally By 2 Door :

Think of it this way: Fill your fuel tank then open the petcock and drain the tank back into a can. Time how long it takes to empty the tank. Now fill the tank again and go for a ride using the advertised gas milage of most 2 stroke kits, 100+ mpg (probably more like 80). Run your tank dry and time your ride from start to stop. I will guarantee that the ride will last a lot longer than it took to drain the tank. Even with 3/16" line. I can't imagine that even a modified pocketbike motor would require more than the amount of fuel that could flow through a 3/16" line. That's a lot of fuel. Just for comparison, you can successfully feed a 300 hp small block Chevy with a 3/8" line and never starve for fuel at highway cruising speeds; and it has seven more cylinders

 

[happycheapskate]

re: chevy with 3/8 gas line. True, but if the petcock or filter clogs, or the gas tank doesn't vent, it might not work well. Think of a 5 gallon water cooler with no vent. Pour pour pour pour.....burp...trickle trickle, pour pour etc.

 

[motorbike57]

YEP. that did it. I made pretty aggressive mods to my cylinder and piston. I ramped the top of the piston at the exhaust and transfer ports, skirted the piston at the intake port, cleaned up the transfer ports, widened the intake and exhaust port, shaved the roof of the exhaust port, shaved the bottom of the intake port, etc.. etc.. I had already ported the cylinder and ramped the piston, but very mildly. took it apart and got really aggressive with the dremel. put it all back together and it ran great up to WOT where it died. I read this post and I got rid of the in line filter and used 1/4" clear plastic hose and clamps from advance auto parts. Ran it again and NO LOSS OF POWER AT WOT !!! except for some 4stroking. oh, Im also running an RT carb. So then, I installed my jaguar ignition and dialed it in to the right advance/retard curve and it now runs like a BEAST. before changing out the hose, I was driving myself nuts playing with different jets. nothing worked. it didn't dawn on me that the opened up engine needed more fuel. only problem now is I'm sure my gas mileage is gonna suck. so what. its a trade off - more speed = more fuel. love it.

 

[Slogger]

I had a kit petcock that wouldn't stop off the gas. I took it apart and the rubber piece inside was crumbling, gas leaking by it. The rubber bits were sometimes fouling the needle and seat in the carb, too.
I think the stock ones are big enough (until they start to rot) since so many bikes reach top speed just fine using them. I would still replace it, though, just because of its leaks, crumbling and dirt production.
I used a SBP one, and it flows gobs of gas and shuts off tight. It took some gorilla torque to thread in, so it is not technically a direct replacement, but can work once forced into place.

 

[crassius]

if that is the petcock that has a twist valve rather than the one with the lever valve, the twist type uses a pipe thread that does not need to be all the way in to seal - when it gets hard to turn, it's in

 

[Davezilla]

Yup... the pipe thread on the original petcock aren't tapered like American pipe threads and the bung in the tank should be re tapped with an not tap to put the small taper in the threads, European pipe threads aren't tapered but the thread pitch is the same for this size so a quick thread chase with the right sized npt tap will remedy this problem, then once the new petcock is snugged down it shouldn't leak, you can use a little thread paste on the threads if it does seep a little once snugged down. I try to avoid Teflon tape here since it can break off and get into the carb, and if I do have to use thread tape, I always make sure the tape isn't applied to the first few threads to be sure none of it ends up in the carb later.

 

[crassius]

for lever type petcocks, I use a 1/2 inch bit to counter sink & smooth the tank just a tad, then add a nitrite o-ring onto the petcock - makes a nice seal & allows a bit more room to adjust lever to good position