421 not reving out

[sheeban]

Hey guys Ive got a 421 cub that i have been having problems pulling threw the gear. Off the bottom and threw the mid range seems perfect and hits hard like it should it just seems like i am hitting a rev limiter on the top end. When I first built this motor I had T6s and figured that was the problem but now with small bore shears it still does the same thing. I am running 39mm Pwks with 272 mains and does not seem to fat. My elevation is about 4200, timing is plus 4, and run Av gas. Where should i look next oh and compression is 160 on both sides.

[okbeast]

I didn't know PWK jets went up to 272? I'm running the same setup with 35 pwk's and have 155 mains. You're quite a bit higher in elevation so I'm thinking maybe a 165 would work.

 

Or do 39 pwk's take different jets

[BANSHEE HP]

272 is not a jet for a pwk or mikuni carbs that i know of, but if for some reason that is the jet size then your waaaay fat and thats why your not reving out btwn 155-170 is about whered u be...im running a 155 same motor but a pwm carb lil diff then pwk

[pr0blumz]

You're jetted too fat. Try a 165 and go from there.

[sheeban]

Woops sorry i ment 172 but i have worked down to a 165 and still have the same effect on the top end maybe i need to go way lower.

[okbeast]

I wouldn't think you'd need too much lower. Do your plugs look ok if you ride it in the rpm's that it's not blubbering on? Do they come out oily or really wet?

[Pasi S.]

You could have fouled plugs if you have ride it too rich. Put new plugs in and try it again with those smaller mains.

[Paul M]

I was running 152 or 155 in my 39 pwks on a cub at sea level

[sheeban]

OK guys well I will go down a ways slowly on the main and get new plugs even though the ones in it i just replaced. Are you guys running the CEL needles or the stockers that came with the Pwks?

[Paul M]

OK guys well I will go down a ways slowly on the main and get new plugs even though the ones in it i just replaced. Are you guys running the CEL needles or the stockers that came with the Pwks?

 

 

Mine were CEL some guys run the dgh I would throw some 158s in with the clip in the middle make a short pass and see if it gets better ! what gears are you running ? is this on a hard flat surface or a hill ?

Edited April 21, 2010 by Paul M

[sheeban]

Mine were CEL some guys run the dgh I would throw some 158s in with the clip in the middle make a short pass and see if it gets better ! what gears are you running ? is this on a hard flat surface or a hill ?

Im running stock gears it does not seem to matter if im on a hill or not it does the same thing. It almost seems like an ignition problem but i need to jet down first to rule that out will post back. Thanks for the advice.

[okbeast]

Pull one of your plugs out and have someone kick it over real hard and see if it's getting good spark. Helps if it's dark too.

[locogato11283]

160 mains. 48 pilot. needle in the middle. bump timing to +7.

[sheeban]

160 mains. 48 pilot. needle in the middle. bump timing to +7.

Well i tried 158 mains needels are on the middel clip timing is +4 and no change same sputter on top end i was worried about +7 but i wll give it a try loco. Jeff mentioned not to run it to hard at plus 7 but i will see if that gets rid of the probelm.