Weber Carburetor, Ignition Advance Question

[keitho64]

I have a few questions about my Weber equipped 2.2.

The carburetors have 60 idle jets, 130 mains, 180 air correctors, F1 tubes and 32mm venturies. I think I have them adjusted correctly. What will happen is the car will sit and idle at 1,000 and be perfectly smooth. Then for no apparent reason the rpm will jump to 1,500-1,700 and start popping out the exhaust and the top of the carburetors. After a while the idle will drop to the 500-rpm range. If I blip the throttle it will stabilize back to 1,000 and then in time the whole cycle will take over. The performance seems very smooth, throttle response off idle is great and through the entire rpm range.

So my questions are:

Could this be caused by a sticky float and/or needle valve?

Could this be caused by an advance curve that is hanging up? (The car still has a Marelli distributor)

Is this normal until an engine is broken in? I have put about 200 miles on this engine and the more I drive it the smoother it runs. I know the engine had been sitting for at least 5 years prior to being run.

I am looking for ideas before I tear into this. I should note that I rebuilt the carburetors but never changed the floats. I tested them and they appeared good. The valves have been adjusted, the timing is correct and the plugs, coil and wires are new. I really believe it lies within the float assembly or mechanical advance system. There is no vacuum advance on the distributor.

Thanks for the help.

[rs911t]

Keith,

Welcome to the Weber club! I'm out driving/adjusting today and have many of the issues you mention. I'll let you know if I figure it out!

Good luck.

[RoninLB]

I have Tomlinson's trouble shooting 4 pages on PFD/big bits..if you want a copy e-mail me and put Webers in the subject.. ignition sounds like a long shot from the info you gave

[dhoward]

I've been fighting the EXACT same thing for a few weeks! Took the dizzy apart, cleaned and lubed the weights. Nothing looks wrong. I was thinking fuel pressure? Ron sent me the troubleshooting guide. It's excellent, but still having the same problem. I'm heading out to tweek some more today. I've never had anything like this happen before. It's almost like a vacuum leak, but everything is tight as a drum. If you figure it out, let me know, I'll fix mine the same way, and meet you in Springfield for beer!!!

[cstreit]

SOunds like dodgey fuel pressure... It maybe be going rich if the floats are overfilling. What fuel pressure are you running Keith?

[cstreit]

You should be running around 3-4 lbs. You can check for intake leaks easily by spryaing brake cleaner or the like around the intake seal areas (BE CAREFUL!). If the revs go up, it's sucking in air... Sounds more like fuel to me.

[rs911t]

Just got back from a 45-minute drive and tweak. A couple obvious things:

(1) The popping will lessen if you roll up the driver-side window. It will increase if you roll the window down.

(2) Don't expect immediate reaction to small adjustments. Patience seems to be a big part of the process.

(3) My problems are mid-range and partial throttle. Full-on throttle and it hauls a$$! Small adjustments on the idle mixture are the rule-of-the-day. After some tweaking, the popping was reduced (even with the window down).

It's a Zen thing, isn't it?

[dhoward]

More than zen.
Ooooohmmmm.
I think Keith is having the same problem I am though. Runs ok, but idle hunts. Sits at 1K for a few minutes then up to 17 -18 hunnert. back down to 600 then stabilizes at 1K again. Sound right Keith? I'm going to pick up a pressure gauge this week and see what's what. Looks like an aftermarket fuel pump on mine....

[yelcab1]

I fought the same 2 idle-speed problems for a long time before I solved it.

1. Make sure your fuel pressure is 4-5 psi. NEVER install a Napa cheap fuel pressure, the damn thing almost burned my car down. THank God I always travel with my own fire extinguisher. I never buy anything from Napa anymore.

2. Change all of your needle valves/seats and the problem disappear.

[dhoward]

Thanks yel. That's what I've been thinking, but still pulled the carbs to go through them any way. I think Holley makes a couple of different regs. Off to Jegs I go....

[keitho64]

rs911t – I agree it is a Zen thing. I think Weber tuning is more art than science. Of course, the window idea is one I never thought of. I do not have much for drivability issues. It will stutter on initial some times but pulls very smooth throughout the rpm range. The throttle response out of the corners is perfect.

RoninLB - thanks for the offer on the trouble-shooting guide. I will send you a pm.

dhoward – I will keep you up to date on what I find out. By the way, I am in St Louis Thursday – Saturday of this week for work. I am thinking it may be a fuel pressure issue especially after seeing the responses here. I still have the t fuel pump for the Zeniths.

yelcab1 – chris – I think you two are on the money with the fuel pressure.

I do not have a gauge on my car so I do not know what pressure I am running. This week I will buy a gauge and regulator to install and see what happens. The needle and seat assemblies are new but there could be a problem with dirt. I have two very fine fuel filters but that may not stop everything. Today in Chitown it is VERY cold so I did not attempt to try anything but I will later this week.

Thanks for all the ideas, I will keep you posted.

[TimT]

It's a Zen thing, isn't it?

yes the weber tuning mantra will continue.. I have my carbs so dialed in, yet once in awhile Ill get a nice POP out if the intake......

[Chuck Moreland]

I too spent a lot time chasing erratic weber performance. Suspecting everything from ignition to worn throttle bodies. After replacing lots of stuff and tuning, and retuning, and retuning I finally got a new fuel pump, pressure regulator and gauge.

Chased my tail for another week since my pressure was erratic. Until I exchanged that new gauge that wasn't working properly.

Another new guage and I got the pressure dialed in properly. Life has been good since.

[rs911t]

Ok. Someone will need to explain to me how fuel pump pressure (or lack thereof) could be responsible for Keith's idle problem. Fuel in the float bowl isn't pressurized and the needle valve is toggled on/off by the float when the fuel level drops/rises within the bowl. Idle isn't consuming gas as quickly as full throttle, but he reports there's not a problem on throttle. If the pump wasn't delivering enough fuel for idle then the car is going nowhere at full bore.

The sticky needle valve theory sounds good, in that it would manifest itself during the transition from closed to open, or cause one barrel to lean out (and drop throttle) until the bowl with the ill-behaved valve refilled.

I have the exact same problem, as well as some backfiring during deceleration and partial throttle. The backfiring goes away at full throttle and responds to mixture changes. But, I'm wondering ...

Keith, when did you rebuild the carbs? I rebuilt mine in December with the Pelican kit. What did you use?

[red-beard]

Tuned the Webers today, after rebuilding ysterday. It is not an easy thing to get them dialed in. But I do have to admit that having the exhaust gas CO anlayzer really helps in setting the idle mixter.

Also, for a really smooth engine, getting the carbs synched is essential. You have to get the match the airflow perfectly in each barrel.

Even with all of this, I still get a pop out the intake once in a while.

James

[lateapex911]

I agree it's probably a pesky tuning thing. I had it with my car before it settled in for it's long snooze. (A 2.7 w/Webers).

But- this is a longshot, but so easy to check it's worth it. Check the dizzy shaft run-out. Doubtful that's it, bit worth the 30 seconds to eliminate it!

Good luck! Post your results so when it's spring we all know what to look for!

[cstreit]

Greg,

Too much fuel pressure can cause overfilling of the float bowls... The pressure forces the gasoline past the needle valves. Noodle on it at bit. The only thing closing those valves is the pressure of the float "floating". Too high a pressure will not allow the needle valves to seat and thus allow too much fuel in the bowls, then, raw fuel actually overflows and dumps into the intake. This especially happens at idle when not much fuel is being used.

Keith, I assume you have the nice syncrometer? If not, come borrow mine. If so, come borrow mine and have an easier time balancing... ('cause then I can borrow yours later )

Chris

[dhoward]

Well....
I certainly dont have the issue with the accelerator pump linkage anymore. Trying to loosen the nuts snapped both of the little buggers in two. I'm not talking about cranking on them either. Think Wayne would have these or should I fax PMO? I really shouldn't get irritated it is a 33 year old car and all, but man! I really think we're fighting a pressure issue here. It's the only thing left for me. I've got some kind of weird aftermarket fuel pump with no label on it, so heaven knows what its putting out. Keith, let me know where you're going to be. Oh yeah, can anyone tell me what the rectangular box with the yellow Bosch label is?

[Chuck Moreland]

Chris is right on. My car always ran great at full throttle and erratic at idle.

[dhoward]

Oops, picture....