what cyl pressure should be?/?

K you motor heads ...
I got a 76 900 motor it is cranking at 110psi +/- 5 psi...not sure what the cams are degree'd at yet...all I know is that they are supposed to be yosh stg. III cams...they do say POP Y on them.

what should it be....supposed to be a new wiesco 1015 kit in it.

This all started with carb jetting. I have a early set of keihin 31's( with the ticklers)....when I got the bike to Edmonton...it was running super rich...so I'm ththinkin'...ok elevation change....2000+ feet here only 600' in Thunder bay.
It had 110 mains and 60 pilots....
I change the mains to 100's and can't get pilots.
So I end up talking with a guy named Mark from M3 racing...they run cb 750's and he tells me that he runs 120 mains and 60 pilots ....and that he thinks that there is something else causing the rich condition.
So I pulled the valve cover...did a compression check( I know leak down...my tester is in T bay)
and thats what I have for numbers.
seems low to me...but I'm no expert
chime in and let me know what you think.

Also where can a guy get a positive piston stop.

Well Ben,

All the big boys have been here, and no takers so far. For whatever it's worth, I'll give it a shot. I would think with the 10:1 pistons & cams, MIN. compression should be around the stock numbers. I do not know the opening and closing points, of the intake cam or it's timing? With those numbers, I would take a better guess. Everything is a guess, until the motor is rebuilt and tested.

I would think that a 110 psi is very low, for any piston or cam set up.(or at least, for any street set up)

Off the top of my head, I would think in the range of 150-180 psi.

NOTE- Once you hit appx. 200psi, you will be sucking cannel water, as far as, pump gas goes. You may get + or -a couple of pounds, but not much more.

I don't know very much about those carbs, I would try Marty (screen name "promod") he's a good guy and may just have, your answers. I know he uses them on his 1045 motor, maybe he used them on his old 1015?

PS- If you ever get any info on those cams, I would sure like to have it. I have been chasing those specs, for a long time.

PSS- As for the postive stop, ask Jay at APE. Or Star Racing. I have seen a few companies that still sell them. If nothing else, make one out of an old spark plug and a bolt with the head cut off.

That is the best, I can tell you................John

hey john i just got off the phone with ben and we where bouncing some ideas off each other about the compression problem with 10.25-1 pistons i would expect between 160 and 180 psi my self.as far as those carbs go they sound lean to me just the way the problem is being described going to marty about them is a real good idea because in order to get a little motor like his to go as quick as he did he obviously knew something trick.

Thanks Guys...I will give Marty a shout and see what he says...
maybe there is turbo pistons in there LOL.
As soon as I get the piston stop I will see where the cams are degree'd...I have my suspisions that is what the problem is.
The guy who put the new wiesco kit in changed the cam timing #'s "to be more streetable#
so that is the only thing that has changed...
the dyno sheet I have staes that the cyl pressure was 195# across the board...and made just shy of 110 hp
so we will see what the degree numbers are now and go from there.While we are on it...what do you guys think they should be....I was thinkin' 105int-107ext

Ben,

I would want to know what the suggested lobe center, was from Pops? Where did he say they should be? Then make your timing changes. That would help to cut down on the guess work.

kzz1p wrote:

Ben,

I would want to know what the suggested lobe center, was from Pops? Where did he say they should be? Then make your timing changes. That would help to cut down on the guess work.

yes I am trying to find that info...no luck as of yet though

on my big cam's that i just put in i went 108.5 on the intake and 109 on the exhaust

irishwill wrote:

kzz1p wrote:

Ben,

I would want to know what the suggested lobe center, was from Pops? Where did he say they should be? Then make your timing changes. That would help to cut down on the guess work.

yes I am trying to find that info...no luck as of yet though

Have you tried Yosh ? I don't even know if they will tell you. I have one more place for you to try, I will let you know tomorrow.

ben i just looked thru a bunch of info i have and you know i can't find any info on yosh cam's at all but i'll keep looking

Ben

Just thinking off the top of my head. Isn't the stage III the bonneville grind? If so, I think megacycle cams??? now has a copy grind of that cam.(I think it was them) I saw it in an old megacycle catalog add.

I am not sure but I think it is something like 300* duration and .410" lift????? If I am right, it has big balls to run long distance. I don't think they used it on the banked tracks? It's not what you call a real streetable cam, hence the 31mm carbs.

I could be wrong on this..........

I'm gonna go measure the lift...and see if I cant find any more idenifying marks.
I have a reciept for yosh "bonne" cams so I think you are on the right track the bill is from 1980...but there is another one from '83 that says yosh stg III cams that went in at the same time as the original yosh 1015 kit.

the intake is like a .405 measured...I never got to the duration... need a wheel.