What is wrong with my weber ?

[Raynald]

Hello Bob and Christian,
i want to report to you my today run without popping carb !
i drive two hours and trying to run around 3200 to 3400 rpm and i hear nothing...
but i will change my idle jets in futur to reduice the 3 1/2 turn out ...
and see what will happens, i will have my other mains jets for testing with the new idles jets,
my car running great today and i want to be ready for running in Maine in a few weeks for vacation...
Thanks to All of You again for your great advices !
Raynald

[1974carrera]

Great news, Raynald!! It's always a good time when you work on your webers and then the engine runs better than ever. Have fun driving.

[A Quiet Boom]

Glad to here it. As great as modern fuel injection is it just doesn't compare to the "romance" or throttle response of individual runner carbs. I've got my Zenith's tuned to idle around 500rpm and pull from about 1000 in every gear. My throttle response is necksnappingly quick! I think I'd only realistically think about EFI for a turbo engine (which I am contemplating for my '73 tub) On the other hand a 46mm PMO-ed 3.6 with an early fan would make a hell of a sleeper!

[911pcars]

Now that Raynald has the problem cured, I thought I'd offer this.

Not only should you verify the idle jets are not clogged, one should also squirt some carb cleaner into the idle passage and make sure they're open.

Well, better late than never.

Sherwood

[RoninLB]

Originally posted by A Quiet Boom
On the other hand a 46mm PMO-ed 3.6 with an early fan would make a hell of a sleeper!

that will be my next engine when I blow this one up..

and guys, I'm tweaking new PMOs with 55 idle jets right now before getting this thing on the road.. the spitting described by Ray is somewhat my issue now. I just got 60s in the mail. The boss says that's it's unusual for me to get spitting thru the rpm band. My personal confirmation that I need 60s is the high EGTs while tuning in my garage. It's noticeably higher than reving the old CIS for that length of time. So anyway, I'll work on putting this car on the road and drive it a little with the 55s to give his comment some consideration before changing to the 60s. I'm ready to do the 60 right now but I'm trying to be patient.. naturally I've been thru all other outside variables.. I'm betting I'll be doing the 60s eventually.. whatever.

[RoninLB]

Originally posted by RoninLB

, I'll work on putting this car on the road and drive it a little with the 55s

thanks be to Ray for bringing a lotta talent to this thread.. just in case I need help, So, just did a couple of miles in second gear around town, ng. all EGTs were about 300-400deg hotter than the stock CIS. Generally there was no consistancy between each one.. meaning the spread was sometimes briefly 400deg and mostly 150-250deg. that's a confirm 'cause the computer gives max differential evey 3sec among all 6egts I had no interest in going further on the ride.
Maybe why it's excessively poping on 55s may have something to do with timing the cams to the early E-cam spec at maximum advance, not the second generation lower specs .
[ RS dizzy mech advance at 8/ 35 ]

I shall return.

[A Quiet Boom]

Ron,

Are you saying you suspect the timing and not the fuel mixture? FWIW I'm running the MSD timing computer with both the mechanical and vacuum advances locked out on my car. My total timing of 34 degrees is in by 3500rpms, I believe initial advance is set at 14 degrees. This timing curve is somewhat agressive but I suffer no detonation trouble with 93 octane.

[RoninLB]

Originally posted by A Quiet Boom
Ron,

Are you saying you suspect the timing and not the fuel mixture?

not the ignition timing. I think the cam timing may be a slight contributing factor. The E-cam timing sometimes becomes a bit of confusion when it's written about as to the specific years. Even B Anderson admits to this. The cam will sometimes have 2 specs listed as in Wayne's rebuild book on p207. The 1968 specs advance is 3.0-3.3. The 1972-73 spec is 2.7-3-1. So I timed to the max earlier spec of a hair shy of 3.3, [I beleve because I can't find my written during-task notes]. The difference isn't a big deal but I was wondering that if it is lean on fuel, on the edge, with the 55s that the slight advance to the earlier spec may have worsened a bad situation. I don't have enough cam experience to make an educated call on that one. So my thought is an educated question. And I have no thoughts of retarding the cam to maybe save gas $ by using the later spec. I want the max advance, I believe, to compensate for chain wear and maybe lowering where the torque curve is placed in the rpm band..
whatever.

[A Quiet Boom]

OK, I get it now. To answer your question, probably not. In fact advancing the cam might even create a touch more vacuum than straight up or retarded. And yes you want to run that cam advanced particularily on the street. The only time I've ever run a cam retarded was on a drag car in an attempt to bleed off some low RPM torque to help launch the car with less wheelspin. The E-spec cam (which I had in my 2.0) has a decent vacuum signal. I ran mine advanced as well after I repaired a blown head gasket on that motor and the change required only minor tweaking of the mixture, no jet change. Without knowing the size of the idle air jet for webers vs. zeniths this is a stab in the dark but I'm running 0.62 on my zenith's with stock SC cams in a 3.0, the signal from a E-cam should be weaker than an SC grind and therefore require a touch more jet. Again I don't know how close the idle circuits are to one another between the two brands but I'd be willing to bet they're not two different. Try those .60's and let us know. I'll be sure to enjoy my trip and take care of my back.

[A Quiet Boom]

While we're on the subject BTW, any idea how much the 911 chain stretches at speed? I remember reading years ago about Ford's 427 SOHC motor and how they had to set the cams advanced just so they'd be straight up in the higher RPM range, than motor had a huge amount of timing chain and apparently could lose as much as 6 degrees cam timing once warmed up and revving. All chains stretch from thermal expansion (as well as wear of course) and I just wonder how much it move the cam events on a 911.

[RoninLB]

Originally posted by A Quiet Boom
OK, I get it now. To answer your question, probably not. In fact advancing the cam might even create a touch more vacuum than straight up or retarded. And yes you want to run that cam advanced particularily on the street.

this is a stab in the dark but I'm running 0.62 on my zenith's with stock SC cams in a 3.0, the signal from a E-cam should be weaker than an SC grind and therefore require a touch more jet. Again I don't know how close the idle circuits are to one another between the two brands but I'd be willing to bet they're not two different. Try those .60's and let us know.

thanks for the confirm on the timing.

hmmm. I gotta get an available jet size chart. I thought it went from .60 to .65.. and for trivia, 8.5 compression.

[RoninLB]

Originally posted by A Quiet Boom
While we're on the subject BTW, any idea how much the 911 chain stretches at speed?

nope.
and the issue of "stretch" has turned into some dogmatic responses that chains don't stretch on previous threads.. and the amount of stretch was never mentioned, only the amount of wear.

[A Quiet Boom]

Ron,

Since I'm using Zenith's my jets are hand drilled and thus 0.62mm, hope that clears it up. As for chains, they like any other metal expand when they get hot and therefore "stretch". The problem is so does the block.