Weber Idle Adjustment Problem - Page 2 - Alfa Romeo Bulletin Board & Forums
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post #16 of 76 (permalink) Old 09-14-2018, 05:24 PM
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I agree with Gordon, 200's are bigger than you need and the bigger the valve the less tolerance you have for higher fuel pressure.

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post #17 of 76 (permalink) Old 09-21-2018, 03:00 PM
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I drove the car last weekend and it was bogging down on acceleration.
I pulled the carbs off on Sunday and blew carb cleaner through all the accelerator circuits and again through the idle circuits.
I also changed my accelerator jets from 45's to 35's and made sure their passages weren't blocked.
I read that these provide a longer duration stream that helps in transition.
Added a new fuel filter too.
A quick road test and it seems to be all good now.

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Last edited by 1978alfa; 09-24-2018 at 10:12 AM.
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post #18 of 76 (permalink) Old 10-16-2018, 03:49 PM
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Hi folks, can now update with findings for my vehicle as well.

After a long saga, I pulled both Webers and the intake manifold and did a full detail of the carbs and ensured various passages were clean, along with some basic tinkering (following Gordon's advice carefully to avoid a mishap). A detailed cleaning of both barrels and the edges of both butterflies of accumulated gunk improved the closure of the butterflies. Next, the intake manifold got a once over including a new brake booster vacuum hose as the old one was dry and cracked slightly at the intake connection. My conclusion is that this is the root cause of the slightly lower vacuum reading from that offending carb barrel. Everything put back on with mostly new hardware and full isolator mounts instead of those billet mounts with simple o-rings.

Unfortunately this did not fully solve the issue! Moving to the ignition system, which I should have done before everything else, I found that cyl. 4 was not firing at all and traced it back to a faulty Marelli distributor. Having had put so much effort in at this point, I decided a 123ignition programmable dizzy was the obvious next gift to myself. That got cyl. 4 firing and we are now in the tuning/tweaking stage.
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post #19 of 76 (permalink) Old 10-16-2018, 04:03 PM
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(It's always the ignition on those stupid Webers that cause the BIG problems!)
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post #20 of 76 (permalink) Old 10-16-2018, 05:15 PM
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@ zuker81.
Chasing problems like this can get extremely frustrating but it is very rewarding when it gets sorted!

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post #21 of 76 (permalink) Old 12-08-2018, 02:28 PM
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Hey folks, need some additional advice here. It seems I got ignition sorted, yet still having problems with cyl #4. When fully closing the idle mixture screw for that barrel, I get no change in RPM (basically the same original issue). Checked spark plug, swapped spark plugs, checked lead from dizzy and everything seems to be flowers and spring from an electrical standpoint.

Had the weber off again to check out the cold start circuit. Someone apparently had caused trauma to one of the cold start pistons and it was stuck partially up. Remedied that and ended up just blanking off the whole system with a kit to try to stay sane.

No real change. I've made sure fuel can successfully feed in through both the progression holes and the idle mixture hole, and after running, both areas do have fuel in them. Idle jets are cleaned out and have been swapped before to no effect. Butterflies at idle are just uncovering part of the first progression hole. I can't find anything that could be keeping fuel out of the cylinder or leaking it in from elsewhere, nor can i find any reason for ignition not to occur.

Odd symptoms:
1. When covering other carb barrels to starve that cylinder of air, the engine loses RPMs precipitously as expected. When covering barrel #4, it starts gaining RPM very quickly.
2. Spark plugs for other cylinders were someone white-ish after idling for several minutes. The plug for that cylinder was light brown and uneventful.
3. Barrel #4 still pulls at about 80% vacuum compared to the other 3 (slightly low). Checked mounts, checked brake booster attachment, but everything seem to be in order.

I feel like symptom #1 is the key somehow. Do I potentially have a cam problem? What other things can I be checking here? Thanks.
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post #22 of 76 (permalink) Old 12-08-2018, 03:58 PM
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It might be drawing air through the brake booster. You have changed the hose but maybe there is a problem with the booster itself, or the plastic hose connector or the check valve at the manifold.

Ed Prytherch
79 Spider
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76 Suzuki GT500
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A little government and a little luck are necessary in life, but only a fool trusts either of them. - P.J. O'Rourke
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post #23 of 76 (permalink) Old 12-09-2018, 10:17 AM
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+1 for a brake servo (booster) problem.
I had a similar issue about 18 months ago with number 4 cylinder. I'd discounted the booster as there was no burning of brake fluid through the exhaust.
Found out that the leak in the booster wasn't very big, and there was no noticeable smoke at cold start-up, or any at all when the engine was warm
However, after everything else was checked, there WAS enough leakage to affect the performance of number 4 sparkplug, in that I could never get a good colour on that plug, and adjustment of the airscrew made almost zero difference.
When I disconnected the servo hose, there was just a hint of dampness on the inside, where vacuum from the inlet manifold had sucked it through.
Changed booster, issue disappeared, air mixture screw worked perfectly again.

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post #24 of 76 (permalink) Old 12-09-2018, 02:26 PM
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Thanks for the replies, y'all. I checked the booster hose and there is some slight residue inside it, nothing dripping or anything, but it's there. Technically if I temporarily block the check valve at the intake, I should be able to isolate the issue to brake booster system overall, right?

Does the engine RPMs rising at idle when partially blocking barrel #4 just mean that that cylinder is running extremely lean due to air entering from elsewhere?

Also, any tips on checking out the brake booster itself? I've never removed it or messed with the braking system. Is it possible to service it without replacing it?
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post #25 of 76 (permalink) Old 12-09-2018, 04:00 PM
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Use one of these to clamp the hose closed and repeat the test: https://www.harborfreight.com/4-piec...set-65116.html

Ed Prytherch
79 Spider
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76 Suzuki GT500
2011 Jaguar XKR

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post #26 of 76 (permalink) Old 12-11-2018, 10:05 AM
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Re-tested with the booster hose blocked - engine running quite a bit better and the mixture screw on #4 is now responsive. Closing mixture completely on #4 only brings the RPMs to 800-900 though so I'm wondering if I in fact do have a little air leaking in elsewhere on the manifold, so I'll check for that tonight.

Any recommendations on the booster? I see new ones on classicalfa for about $250, and rebuild parts for about $100 but they appear to be for Benditalias. Or should I just pull the unit and inspect and go from there?
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post #27 of 76 (permalink) Old 12-11-2018, 11:55 AM
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There is a thread about some new aftermarket boosters from Vick Auto giving problems. I would take my chance on a likely good used one. are you sure that the leak is not between the booster and the plastic connector for the hose?

Ed Prytherch
79 Spider
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76 Suzuki GT500
2011 Jaguar XKR

A little government and a little luck are necessary in life, but only a fool trusts either of them. - P.J. O'Rourke
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post #28 of 76 (permalink) Old 12-11-2018, 12:11 PM
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I just finished reading the Vick Auto booster saga. I will avoid that if I can!

I am not sure where the leak originates - the plastic connector on the booster seems finicky to begin with although it doesn't have any cracks. I saw in some other brake servo threads a statement to the effect of brake fluid leaking into the booster, and it makes me wonder if that could be involved given the fluid residue inside the hose. I'll try to isolate further.
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post #29 of 76 (permalink) Old 12-11-2018, 02:16 PM
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It's likely the inner seals. You have an issue that is a copy of mine.
I got a new booster from Classic Alfa and the problem went away. Their p/no BR100R, (now 205)
I sold the old Benditalia booster on Ebay for 75 , as needing a rebuild. That compensated a little for the expense. It has now done 3000 miles + and has been perfect.
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post #30 of 76 (permalink) Old 12-11-2018, 03:01 PM
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GOOD information here!


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