Weber 44 IDF Question Options

[orbit398]

Just looking to see if someone can help pin point an issue I am having – assume it’s a carb issue.

Here is what I have: 2.0 liter with flat top pistons (euro style), has ~160 psi on all cylinders, carb cam, bursch exhaust, dual Weber 44 IDF carb set up, idle jet = 55, main jet = 145, F11 emulsion tube, 200 air correction. Carbs are synced and pull the same at idle as well as about 1500. I live in Houston (sea level).

I have read and followed several write-ups on tuning the Weber carbs. Overall, the car runs great above about 2200 rpm. It idles excellent.

Issue: Still getting the occasional popping. More importantly, while under easy acceleration (throttle slightly opened/just limping along in traffic) ~around 2000/2200 rpm, the engine seems to be missing or it shutters. If I open the throttle just a bit more, it disappears and runs great. I cannot replicate this by just revving the motor up in neutral; does this only under a load??

What could be the issue here? I plan to recheck synchronization/insure carbs pulling equally, spray carb cleaner/starter fluid to check for air leaks, try to ensure butterflies are opening equally. Just puzzled at what it could be.

[Elliot Cannon]

It sounds like clogged idle jets. They are fairly easy to remove. Take them out one at a time. Hold them up to the light and look inside them with a magnifying glass. Be careful not to drop the tiny "O" rings. Blow them out with compressed air. Sometimes blowing with mouth will clear them. Sometimes even compressed air will not work. If so, use a tiny strand of copper wire to clean them out. Then get a set of these. (IMG:style_emoticons/default/biggrin.gif) http://www.cbperformance.com/SearchResults...arch=jet+doctor

[orbit398]

It sounds like clogged idle jets. They are fairly easy to remove. Take them out one at a time. Hold them up to the light and look inside them with a magnifying glass. Be careful not to drop the tiny "O" rings. Blow them out with compressed air. Sometimes blowing with mouth will clear them. Sometimes even compressed air will not work. If so, use a tiny strand of copper wire to clean them out. Then get a set of these. (IMG:style_emoticons/default/biggrin.gif) http://www.cbperformance.com/SearchResults...arch=jet+doctor

Will check those again. thanks

[IronHillRestorations]

Elliot's advice is sound.

If we assume that you are correctly jetted, popping through the carbs is a lean condition usually caused by clogged idle jets. That is as long as you don't have an ignition issue.

Make sure the linkage to the two carbs are dead nuts the same length. If the linkage is off just a little bit you can have problems.

What kind of ignition are you running?

If the jets are clean and you still get have that problem, I'd go up one size on the idle jets.

[ClayPerrine]

Just my $ .02

I have never seen a crossbar linkage that worked correctly. Due to the cylinder offset, it will always be off a little, either at idle or at full throttle. If the carbs are a tiny bit out of sync at idle, it will pop when just off idle.

Best solution is the Tangerine racing throttle linkage kit. It is a much better design and will keep your carbs in sync.

[orbit398]

Elliot's advice is sound.

If we assume that you are correctly jetted, popping through the carbs is a lean condition usually caused by clogged idle jets. That is as long as you don't have an ignition issue.

Make sure the linkage to the two carbs are dead nuts the same length. If the linkage is off just a little bit you can have problems.

What kind of ignition are you running?

If the jets are clean and you still get have that problem, I'd go up one size on the idle jets.

The PO added a distributor out of a 1.9 liter water cooled vanagon. Per the PO, it rev's higher and the advance curve was more aggressive (angle of advance is changing over a broader range of revolution). It also has the VW OME hall sensor or opto electronic sensor and electronics ignition module. The car ran fantastic when I test drove in the Austin hill country as we pushed it hard. I never putted along so I didn't know if the issue I have described was there or not.

[PancakePorsche]

If your idle is good but requires more than 2.5 turns out you need to go up in size. If this is the case It can lead to lean transition under load. Try some 60's and reset.

Also interested at what RPM your timing is "all in" Carbs like earlier advance.

[Elliot Cannon]

Just my $ .02

I have never seen a crossbar linkage that worked correctly. Due to the cylinder offset, it will always be off a little, either at idle or at full throttle. If the carbs are a tiny bit out of sync at idle, it will pop when just off idle.

Best solution is the Tangerine racing throttle linkage kit. It is a much better design and will keep your carbs in sync.

I have a crossbar linkage. There is NO play in the linkage. The geometry is the same on each carb. Both throttle butterflies open (and close) at the same rate. They both reach WOT at the same time. Just because you haven't personally seen one that worked correctly doesn't mean they don't. Set up properly, they work just fine.

[jmill]

Clogged idle jet sounds very plausible. Especially at @2k rpm. If the crossbar is stout it'll work just fine.

It doesn't pop when you press the throttle more because you give it a shot of fuel from the accelerator pumps.

[stugray]

My latest 2 "carb problems":

1 - Using pump gas with ethanol will clog your idle jets & passages quickly with a white chalky substance. Use ethanol free gas or add Stabil.

2 - My accel pumps were not pumping the same amount on each side.
I used the lid from a hypodermic needle attached to the end of a wire to stick down in the barrel of the carb when I actuated through a full open cycle.
I used this method to measure how much fuel came out with a full pump.

My two sides were different by a factor of ~5:1.

I replaced the pump diaphragms and they then pumped the same amount.

Car ran much better and no longer had the same "flat spot" when stepping on the throttle.

EGTs and AFR gauges really help a lot.

[HansJan]

My car with new dual 44mm EMPI carbs linked with a Crossbar (103mm cylinders) is popping like crazy as well. The mechanic wants to open up the valve gaps.

Is that making sense to the brain-trust, as a solution to this problem? or is it solely an issue with the adjustments of the carbs?

[IronHillRestorations]

My car with new dual 44mm EMPI carbs linked with a Crossbar (103mm cylinders) is popping like crazy as well. The mechanic wants to open up the valve gaps.

Is that making sense to the brain-trust, as a solution to this problem? or is it solely an issue with the adjustments of the carbs?

I'd want to make sure the carbs were tuned dead on the nuts before anything else.

I've had a few cars in with different types cross bar linkage set ups that ran fine and sync'd up good enough to run without trouble.

Foley's cable system is well engineered and works nice. The one (hot rod) engine I've had in my shop had it, and the pulleys made plug changes really difficult.

[stugray]

Foley's cable system is well engineered and works nice. The one (hot rod) engine I've had in my shop had it, and the pulleys made plug changes really difficult.

Not if you put the pulleys on the back of the carbs

[jmill]

My car with new dual 44mm EMPI carbs linked with a Crossbar (103mm cylinders) is popping like crazy as well. The mechanic wants to open up the valve gaps.

Is that making sense to the brain-trust, as a solution to this problem? or is it solely an issue with the adjustments of the carbs?

Lean pops through the carb is usually a fuel problem or ignition is way advanced. Increasing valve gap IMHO is silly. You won't get full lift out of your cam and leave power on the table. Back off the advance or richen up your mixture.

At what RPM or situation does it pop? What size idle, main and AC jets do you have along with what ET and vent size?

[HansJan]

My car with new dual 44mm EMPI carbs linked with a Crossbar (103mm cylinders) is popping like crazy as well. The mechanic wants to open up the valve gaps.

Is that making sense to the brain-trust, as a solution to this problem? or is it solely an issue with the adjustments of the carbs?

Lean pops through the carb is usually a fuel problem or ignition is way advanced. Increasing valve gap IMHO is silly. You won't get full lift out of your cam and leave power on the table. Back off the advance or richen up your mixture.

At what RPM or situation does it pop? What size idle, main and AC jets do you have along with what ET and vent size?

Sorry, must be misunderstanding.
These pops Im talking about is more like gun-fire coming from the exhaust pipe.
Seems to happen most when slowing down or steady speed. Under accelaration it is a lot less.

But am I highjacking some one elses post?

[jmill]

Yeah, it's a highjack but we're waiting for him to check his idle jets. I'd check for exhaust leaks.

[HansJan]

Yeah, it's a highjack but we're waiting for him to check his idle jets. I'd check for exhaust leaks.

Just realized that its called "back-fire" not popping.

What causes back-fire? Is it because exhaust valve opens too early, or bad adjustment of the carbs?

Thanks in advance.

[jmill]

Fuel, heat and air cause a backfire. I once blew a muffler clean off of a 1979 Ford Fairmont.

Check for exhaust leak sucking in air, check for an over rich mixture and make sure valves are adjusted correctly. IMHO it's one or a combination of those 3.

[orbit398]

Fuel, heat and air cause a backfire. I once blew a muffler clean off of a 1979 Ford Fairmont.

Check for exhaust leak sucking in air, check for an over rich mixture and make sure valves are adjusted correctly. IMHO it's one or a combination of those 3.

_________________________
Here is what I have in the carbs - been on travel and have not had a chance to mess with the car yet.

idle jet = 55, main jet = 145, F11 emulsion tube, 200 air correction

[Elliot Cannon]

Fuel, heat and air cause a backfire. I once blew a muffler clean off of a 1979 Ford Fairmont.

Check for exhaust leak sucking in air, check for an over rich mixture and make sure valves are adjusted correctly. IMHO it's one or a combination of those 3.

_________________________
Here is what I have in the carbs - been on travel and have not had a chance to mess with the car yet.

idle jet = 55, main jet = 145, F11 emulsion tube, 200 air correction

Venturi size?