Bogging at full throttle

GoldenMotor.com

callahoochy

New Member
Aug 5, 2010
14
0
0
DC area
My motor regularly bogs and sputters at full throttle.

Bike's mods history:
1) pre-build, tech help at King's had me add the little spark plug bushing to the end of the throttle cable outside the carb to add some tension - it was a bit slack from the factory. And had me place the C/E clip centered.
2) upgraded to HP air filter - seemed a bit quicker after that.
3) drilled out both intake and exhaust manifolds from round to elliptical to sorta match the ports on the cylinder head. That made the bike a bit quicker, and quieter, not faster (and I'm not interested in faster - just want uphill torque).
4) Upgraded plug and wire; that seemed to make it run smoother.

I baby'd my new engine for two tankfuls, never cranking the throttle hard. The engine has, over the summer, developed more quickness, but it always bogs and sputters after being at full throttle for half a minute, as if it is getting more gas than it can use. And though it runs pretty good on flat ground, I'm disappointed in the uphill power.

I don't have a clear technical understanding of what the carb C/E clip does; mine is centered.

Sidenote: Does ambient air temperature affect power? Yesterday was the first chilly day, and it seemed to have less power than in warmer temps.

Thanks in advance to all the vets who chime in regularly and know their stuff! - but especially Pablo at SBP who has given me more time and attention than I suspect he really has to give to one customer.
 

bairdco

a guy who makes cool bikes
Aug 18, 2009
6,537
264
63
living the dream in southern california
i've had this problem before, too. seemed to me that it was running out of gas. like it was using it faster than it could flow. i changed out the petcock to a real one from a tecumseh lawnmower (had to tap the tank threads to 1/8 NPT (pipe thread.) and added a real fuel line.

no more problems.
 

WildAlaskan

New Member
Sep 30, 2010
578
0
0
alaska
yeah i got the same feelings the fuel is being burned faster than it can be replenished i am not going to worry about it casue it keeps my going at a safer speed
 

callahoochy

New Member
Aug 5, 2010
14
0
0
DC area
Bairdco... "had to tap the tank threads to 1/8 NPT"... makes a lot of sense.

thanks for the suggestions. They are much appreciated. While I still have little understanding of what the pin in the carburetor does, I moved the E clip to the 2nd from top position; bike has more uphill grunt, smoother but not faster top end, so, exactly what I was looking for.
 

bairdco

a guy who makes cool bikes
Aug 18, 2009
6,537
264
63
living the dream in southern california
what i meant (in case you were being sarcastic) is the threads for the stock petcock on the tank are regular straight cut threads. "NPT" stands for "National Pipe Thread."

it's like a tapered thread, so you can't screw something all the way through it. as an example, a regular nut can screw all the way down onto a bolt, but with an NPT thread, it'll only go so far before it gets stuck.

pretty much every petcock besides our cheap bikes uses an NPT thread, and they rarely leak.

so if you wanted to put a better petcock in the tank, you would need a 1/8" NPT tap, and re-thread the tank.

simple, really.

on a side note, the bike i'm building now, i'm going to make a custom tank for. last night, i finished up the engine install and wanted to take it for a test ride so i slapped the kit tank on, filled it fulla gas, and the brand new "upgrade" petcock that comes with the kit leaked like a MF'r, so i had to grab my gas can, drain it all back out, clean all the gas off the bike, and install another one. i hate those stupid tanks.
 

callahoochy

New Member
Aug 5, 2010
14
0
0
DC area
Thanks again, and no, I was not being sarcastic. There needs to be a font specifically for sarcastic to end this ambiguity so often a problem with emails and posts!

I moved my pin from 3rd to 2nd position and it runs better. Still would like more low end torque for uphill, but I think my motor is running better than average, so I'll stop messing with it at this point.