What is wrong with my weber ?
 

Hello All !
i have a small problem with my adjustment of weber ...
at 3200 rpm ,i have pop in my carb. my engine is running great at idle and 3500 rpm and more...it is a 2.7 liter with 60 idles jets and
135 main jets, ventury 34mm, i think my timing is good,
do you think my weber is too lean at the beging of main stage...?
or i mist some other adjustments,
Thanks
Raynald

Sounds like partially plugged idle jet; unscrew 'em, blow 'em out, reinstall. Takes 10 minutes. Happens to mine all the time.

May be is a little lean. My webers do the same when they are out of calibration.

I'd agree with David,....its likely a clogged idle jet or two.


David,...........................I must tell you that this doesn't need to be a regular occurrance,...:) With proper air and fuel filtering, its a VERY rare event.

Here are few suggestion for keeping Weber's (and any other carburetor) trouble free:

1) Make sure the tank is absolutely rust free and the in-tank filters are clear

2) Use a fuel filter that removes debris down to 1 micron. I use a Racor 110A.

3) Throughly clean the air cleaner housing(s) and use a layer of grease on the rubber ends of the air filter element(s). This keeps dust out.

4) Replace or eliminate the sound proofing pad between the cabin & the engine compartment. When they are old, they sluff off tiny particles that always find their way into the flow bowls, and thus into the idle passages.

nice tip steve on sound pad. when i gave up fussing and handed car over to mechainic he took one look at my crumbling engine sound pad and said "that's the culprit". crap falling off everywhere. removal plus rebuild and i am tight for 1.5 years.

Thanks
is this possible my carb are not good balance over 3000 rpm ?
Raynald

Not sure I know what you mean by that. I'm in agreement with the others, check you idle jets. I assume the car runs smoother when you're deeper into the gas pedal. There's been a lot of threads about this lately with both webers and zeniths. Mine had a clogged jet on one cylinder so it was terrible at part throttle but fine at full throttle when you're pulling primaily from the main circuit. I like the adjustment instructions in the Hayne's manual best for sychronizing and adjusting the carbs.

hmmm.. I bought five 2 micron spin on filters for the 120 model. I guess I'll be ok. I didn't know 1 micron was available? meanwhile I have it in my head that the routine is 10 microns...

I'd say 10 microns would be sufficent since that's about 0.0004 inches or 0.01 mm. My idle jets for example are 0.62mm or 620 microns! I'd think a 0.1 micron filter is a little extreme. Having said that however my tank probably has a little rust, the internal filter has never been changed and I use a generic filter. Still I think my clogged idle jet was caused by varnished gas due to winter storage or debris left from rebuilding the carbs. Heck it could have even been something in the fuel line after the filter for all I know.

Hello All
today i do your recommendations, i removed all idles jets and check all no problem there... i do a mixture ajustment and all have reaction of turn and all is Ok at 3 turns and haft out, my idle is stable...
my problem is at 3200 rpm i have a pop on high-way in carb...
at this RPM it running on the main circuit ?

Raynald

hello
i check my plugs all is the same color cofee-moka...
what is the next step...?

The pop on the highway, how far down is the gas pedal? Also how did you check the jets? I usually check them with the appropriate sized pin drill but a thin piece of wire also works. My guess is you're still mostly using the idle circuit on the highway, how does it do at full throttle, any pops then?

Christian
it is hapening only in highway at around 100 KM./H. when i try to accelarate i hear a pop in weber, my pedal is in meedle and after the pop i have a good accelaration, in city i don't saw the problem,
i saw the springs around the mixtures screws is not very tight my screws is moving by side after 3 turns and a hafts out !!! is this normal ?
can this afect my adjusment ?
Thanks

maybe check the accelerator pump flow.

Yep, check those accelerator pumps. It should squirt fuel even with small movements of the butterflies. Those screws do seem a little loose, but without seeing them I can't say for sure. I'd be tempted to try a 61-63 idle jet and turn those screws in a little. Take one of the screws out and check the o-ring on it, if they are missing or broken you'll pull air past them and cause the car to run lean and the screws to be loose. Have you adjusted the accelerator pump linkage?

Thanks,
i rebult my weber 2 years ago and i have adjust my pump ,if i remenber i have 6 cc of gas on each bank,
but i think my mixture screws is too out , it will be a good idea to orders bigger idles jets and turn more in my screws i can move it side by side.
and i will check for the carb balance at 3200 rpm,
Raynald

Good news !!
i make progress ! i have check the carb balance at 3000 rpm and everything is fine ! i have old mains jets of 105 and i drill it a little more of my new 135 (estimation of 145 or 150) and i try it to night and no popping at 3200 rpm...
i will try it tomorrow with a long run !
i hope i will have resolve my problem...
Thanks
Raynald

Raynald, please do report your findings after you drive it. Based on the description that the engine pulls well at higher revs and greater throttle openings, I wouldn't necessarily think that the main jets need to be larger. Your description sounds like the pop occurs when the throttles are transitioning more into the main jets which does seem like an accelerator pump issue. Might be worth it to check their discharge again just to be sure...? Did this popping issue just occur or has it been doing it all along?

By the way, I was looking at the pics of your car on your link and it looks incredible. You did a really nice job restoring it! Are the black paddle Fuchs in some of the pics 7" & 8" X 16's? and what's up with that exhaust...what is it?

Hello Bob,
i will recheck my accelerator pump again to be sure ! but my english is not perfect i can not explain perfectly my problem,when i stay at 3200 rpm on hightway it is poping some time, not when i do acceleration
it is like my weber are too lean at the begin of the main stage...
my fuchs are 7 and 8 X 15 inchs i restaured ... a lot of sand-paper... and time and the muffler is Dansk i brought it from jasper a pelican member

That sound a lot like the idle jets to me, try one or two sizes bigger and see what happens. I really don't know why they call them idle jets, they should correctly be called part throttle jets.

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

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.

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!

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

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.

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.

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.

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.

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. ;)

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.

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.

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.

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.