Powerband issues

[Jbducati]

My compression is 179psi. It has awesome Low end up to about half throttle. It's ported by someone before I bought it and I have a uni one the back of the carb with about 3 or 4 inches of pipe in-between each other. But doesn't hit powerband in 3rd to 6th unless it wants to which is half the times I try. Ive been through 230, 290 up to 330 in size 10 incriments. I'm pissed please help.

-John-

 

[94fiveohvert]

what octane fuel are you running? you've checked the reeds, the exhaust to make sure it isn't restricted, the plug. Also what is the needle set at?

 

[myusername]

with 179psi compression, i believe you need to be running race gas or at least a mix. are you running a stock carb on that motor? if so, thats probably part of your problem. i dont know that you can get 179psi of compression without doing some serious motor work.

 

[2smoker85]

is the motor detonating? if the motor is making pinging sounds u need to up the octane and start running race fuel. vp110 is the choice of most. what carb size? carb will restrict if the motor is ported heavily and needs more, say like a 34mm or bigger, depends on mods. what exhaust are u running with the port work? tell us everything u know about this bike so we can help.

 

[Jbducati]

Needles at 1.5 turns. It's sounds like it knocking at idle. Like if there was no wrist pin bearing. Some saved the head A LOT there's no lip at the end of the combustion chamber at all. I was thinking of ccing it. Can I try two copper head gaskets? Or a spacer under the jug?

 

[Larry's Shee]

What does plug look like? look close for little blobs of aluminum. Do a comp test.

 

[roadkill]

Needles at 1.5 turns. It's sounds like it knocking at idle. Like if there was no wrist pin bearing. Some saved the head A LOT there's no lip at the end of the combustion chamber at all. I was thinking of ccing it. Can I try two copper head gaskets? Or a spacer under the jug?

do you have any engine modifications like an aftermarket pipe or anything?

 

[Jbducati]

No aluminum on the plug. Did a comp test 179 psi. Stock pipe and silencer I think. Just have porting and filter. I'd love to just put a stock jug back on.

 

[jlsparky7]

Ewww, stock pipe with 179 pounds? wow...

 

[Jbducati]

This how I bought it I just want it to run good enough to beat the crap out of...I got it for 350$

 

[cole454]

Maybe talk to one of the builders here and see if they can cut your head in a little to lessen the compression to make it more usable for you.

 

[Jbducati]

Yeah that's why I was wondering if I could stack head gaskets maybe just two

 

[Outlawed Genetics]

simple answer. no, adding base gaskets messes with port timing and i doubt you'd get a seal on 2 head gaskets..

 

[2smoker85]

def not 2 head gaskets, 2 base gaskets can be used but u will more apt to have an air leak,and throw off the port timing. u need to understand if it was ported it was set up a certain way, we need some pics. what u need to do is have ur head modified or run race gas which gets expensive so ur best bet is to spend the money and get ur head modded which if u want pics i got some of what a builder did for me, but i had my whole motor done.

 

[Luni]

Wow... 179 compression is ALOT. Stockish range is 125-140ish depending on where you live (the higher in elevation you go, the less compression youll have).

If I were you, Id do a test. Id go to my local parts store and buy myself a bottle of NOS brand octane booster. (Its like 10-12 bucks a bottle), and use half that in a tank of gas.

That will raise your 91 up to around 93ish. If you have 93 octane where you live, it should put you around 94.5ish which is better than 93 for sure.

First rule of business should also be to get yourself a decent pipe. On that type of compression Id run a Toomey or something meaner. An FMF would help, but that thing wants to breathe.

Then Id do something about the carb. Id consider at least upgrading to a 28-30mm carb. If you dont have an aftermarket air filter installed, get one.

And for jetting, if youre on the stock carb, for the type of compression youre at, you need to have a pretty fat jet on there, but the pipe is really screwing you. Id guess in the realm of ~300 main to start. Maybe more.

Your pipe is too small for your porting. Your head is too aggressively cut too, you definately have to run higher octane fuel.

 

[Jbducati]

Im gunna chock my head up in a lathe at work and start cutting. I'll just keep ccing it. I read somewhere here that every thou you shave is one psi and one cc. Does anyone know stock cc amount?

 

[blasterdemon7]

Simple fix. Send it to Ken O'Conner.