Webers - Acelerator jet

[Tim Kay]

302 SB, 48 IDF (4)
What size accelerator jet is right?

Idle jets and main jets seem ok but I get a terrible bobble under early acceleration in each gear. Feels just like too much fuel being dumped when accelerating. Evens out fine at 3500 rpm & up and when slowly rolling on the throttle.

Thanks
Tim

 

[Mike Christian]

I don't have quad 48IDFs, but I do have a car with dual 44IDFs. The accelrator pump circuit is a function of the pump jet, the bypass/return and the pump squirt setting. The 44 and 48 IDF carbs are set up similarly.

The small lock nut is adjusted to administer the correct volume of squirt generally (the other two items being left alone - I have zero return/bypasses and .50 pump jets in mine). Mine started out at 30 mm from the end of the locknut to the end of the threaded rod. Running the locknuts out/in 1/2 turn at a time until the issue went away worked for me. Just a few 1/2 turns were required. Obviously, all carbs need to be adjusted in unison. You might check to see that all accel pumps are working properly, squirting with the same enthusiasm and that no followon dribbles are taking place (engine off and looking down the throat of the beast) before doing any adjustments.

Personally, your issues sounds like it could be a jetting one. From my experience, the accel pump works equally well when in rolling accel and full accel due to the spring pressure being constant on the pump lever.

The idle jet circuit are mainly used in normal driving and influence driving up to about 2500 rpms, mains between 2500 and about 4500 and air correction circuit above then. Have you positively ruled this out?

Mike

 

[Tim Kay]

Mike,

Thanks for the info and direction /ubbthreads/images/graemlins/cool.gif

I assumed all else was correct in that the idle circuit seems to be working correct and clean, carbs are synced for airflow at idle, bowls are clean, accelerator jets don’t dribble.

Although, you bring up a good point, one that I wasn’t considering, about jetting. I do have a bit of concern about running lean because my plugs, although not white, are very light colored and the exhaust is light tan. (Someone told me because I mix super with a VP C16 112 octane fuel my plugs and exhaust will run lighter).

I thought that if my main jets were too small then I would only notice poor performance at the top end. So, maybe I should increase my main jets? Is it possible that the flat spot, ie hesitation under acceleration, isn’t lack of accelerator pump fuel but a main jet issue /ubbthreads/images/graemlins/blush.gif

My main jets are 35 and my accelerator jets are 50.

Thanks,
Tim

 

[Tim Kay]

[ QUOTE ]
The accelrator pump circuit is a function of the pump jet, the bypass/return and the pump squirt setting.

[/ QUOTE ]
[ QUOTE ]
The small lock nut is adjusted to administer the correct volume of squirt generally (the other two items being left alone

[/ QUOTE ]

Mike,

Excuse my inexperience but, what you eluded to above, are you refereeing to the air bypass screw just next to the idle mixture down at the base of the carb /ubbthreads/images/graemlins/confused.gif

Tim

 

[Mike Christian]

Tim, I am by no means an expert on this, I just went through months trying to get my car to run right. After chasing the carbs and not getting anywhere, I went back to basics. The shop thatI paid to go through the engine from top to bottom, didn't. Among other things, they did not set the valves correctly, they didn't set the timing correctly, and they didn't notice that the dizzy wasn't tracking with the RPMs smoothly. This is a centrifugal advance distributor and the weights were hanging up at 2500 rpm and then jumping. I had to open it up and clean it out and lube it. Anyway, it was only after ruling out what I had previously assumed that I could get to the problem and solve it. Over the months I read tech manuals and talked to engine builders and redline weber. There is a lot of confusing info to be sure.

Performance VW guys use a lot of webers 44 IDF, 48 IDF and 48 IDA mostly. I used some of the tech notes at www.aircooled.net regarding setting up and troubleshooting webers to best understand the sequence. I know, I know - aircooled? VW?, hey ... webers don't know what engine they are on. HA!

To check my idle circuit I drive steady state at 2000 rpnm or run the engine steady state there and then check plugs. I also have an exhaust gas analyzer that I used. The lean engine pops, sputters and backfires. The rich engine smells it. At steady state main circuit (between 2500 and 4500 - I pick 3500 rpm), how does it sound?

The accelerator pumps work at any crack of throttle, so you have to be careful about not allowing their influence. If the engine bogs and then clears what accelerating, then the pumps could be squirting too much. Surging is usually asssociated with a lean condition.

Did you buy the carbs and bolt them on or did someone dial them in for you? My carbs were problematic out of the box - I couldn't get all barrels to similar setting on the mixture screws. I pulled them and they were all different shapes - I had to get replacements. Of course I also had to reject the carbs for my application idle, main and air correction. I have my jet kit, gauges and reamers if you need to borrow any of that.

What I do know is, when properly dialed in they are sweet.

regards,
Mike

 

[Mike Christian]

No Tim, on the IDF that is a threaded rod that actuates the pump lever arm. It has a small lock nut on it.

The airbypass screws do just that - allow air to bypass the butterflies - generally used to set equal flow through all barrels at idle. Some say do not change these from factory presets, others say to adjust whese with your synchronizer to match the other barrel in the carb. I matched mine on all carbs and the engine ran smoother.

Mike

 

[Mike Christian]

What I have been told (by several people)on the IDFs, the idles jets handles most driving steady state and up to 2500 rpm. main jets transtition in around 2500 through 4500 rpm and then the air correction jet influences above 4500 rpm.
Here is reline webers tuning instructions:
http://www.redlineweber.com/html/Tech/idf_adjustment_controls.htm

here is the VW process for tuning - for theory only - the jet sizes will probably be different:
http://www.aircooled.net/gnrlsite/resource/articles.htm

Mike

 

[Tim Kay]

[ QUOTE ]
What I do know is, when properly dialed in they are sweet.

[/ QUOTE ]

Can't wait to get there /ubbthreads/images/graemlins/grin.gif

Air cooled? VW? My humble beginnings. I'm a sandrail nut and many years ago played with these darn webers and loved them. Thought I'd never see 'em again until I picked up this GT40 about 2 months ago. I just doubled my enthusiasm for them, instead of two now it's four /ubbthreads/images/graemlins/laugh.gif

Sounds like I'm going down the road in your tracks. When I purchased the car, carbs were pretty rough. The guy told me they have been dialed in real sweet before but needed to be redone.

Thanks for you offer, I would at least like to keep in touch and maybe pick you brain through this process.

I will take your suggestions and check out 'aircooled.net

Tim

My father taught me to work; he did not teach
me to love it. --Abraham Lincoln

 

[Tim Kay]

[ QUOTE ]
the IDF that is a threaded rod that actuates the pump lever arm. It has a small lock nut on it.


[/ QUOTE ]

Mike,

Ok, now I'm with you. Currently my lock nuts are only showing one thread. I'll follow your suggestion. Do you want the credit either way /ubbthreads/images/graemlins/grin.gif /ubbthreads/images/graemlins/shocked.gif

Tim

 

[Tim Kay]

Mike,

What a difference /ubbthreads/images/graemlins/shocked.gif /ubbthreads/images/graemlins/smirk.gif

I adjusted the lock nut on the accelerator pump lever and so far I got about 2/3rds of the hesitation out. I'll continue tightening it a bit at a time to see if I can get it all out.

Thanks a bunch.

Tim

 

[Mike Christian]

From what I have been told - once you dial webers in the hold pretty well. Should be much need for rejetting or fussing with them. Sounds like you are going in the right direction.

Let me know the final outcoome please.

Thanks,
Mike

 

[Tim Kay]

Mike,

Im back at it, trying to get the Webers to run smoothly. Long story short, I've gone to basics, fuel system good, carbs rebuilt, linkage in good shape, ect. I've tried to eliminate any problems other than carbs and at this point I believe I truly have the carbs isolated and my ignorance is the only thing between fine tuned Webers and my sanity /ubbthreads/images/graemlins/tongue.gif

So, I want to ask you a couple questions.

First: In your experience, does it matter whether you synchronize carbs before or after you get your air/fuel mixture dialed in. By 'synchronizing", I'm assuming that is with linkage hooked up. Or do you adjust your air/mixture with each carb idling on it's own - no linkage attached then go back and hook up the linkage and work on the synchronizing.

Second: What size idle jets are you using, main jets as well.

Third: Was it necessary to make any turns on your 'air bypass' screw to assist in air/fuel adjustment or are they seated (closed).

That's all for now. It's late and I can't think to clear right now cuz I've been inhaling exhaust fumes for the past four hours. Finally, after waking up face down on the garage floor I said "screw it, ask Mike what to do" /ubbthreads/images/graemlins/blush.gif

Tim

 

[Mike Christian]

I sent you a PM - did you get it?

 

[Mike Christian]

Subject: Re: Webers

here are the contents of my PM-

I know where you are - I've down this road. I feel for you.

I use the two resources (web linkes I posted earlier) and the Weber Tech manual:

Initially, I would pull all mixture screws and compare them they shoudl look identical = fine pointed. If they aren't all the same and fine pointed, then the carbs will not all have the same settings.

Disconnect the carbs from the linkages.

I started with mixture screws out 1 turn. So screw them into lightly bottom them and then out one turn.

Check to make sure all carbs butterflys move freely and that each carb snaps back to closed. Any that bind or have friction will cause you headaches.

Now back out the idle speed screw until it doesn't touch the thrttle shaft lever. Slowly screw it back in until it just contacts. Now screw it in a further 1/2 turn.

Loosen the locknut and close all air bypass screws and then tight those locknuts.

Start the car and warm it up - it might not idle great, but it should idle.

I then put my synchronizer on and measure the flow in each barrel - write then down. For each carb I used the air bypass screw to bring the lower reading barrel of a carb to the higher reading barrel of the carb. You shouldn't have to open it much. Only work one carb at a time. Do not try to match all carbs to the same setting...only the two barrels of the same carb. Move from carb to carb.

Now you can match all carbs to eachother by using the idle speed screw - try to bring the higher reading carbs down to the lowest reading carb by slowly backing out the idle speed screw one at a time. If the engine dies, put the screws back to the initial setting of 1/2 turn and try again. If you can't get them all down to the lowest, then try to get them all to the same lowest setting that runs. You do not want your idle speed screws in more than 1/2 turn. Using my synchronizer, my engine reads somewhere around 6 on the scale - yours might be different - at idle.

Now, I usually tweak the mixtures next. Starting on one carb I slowly screw in one mixture screw in 1/16 increments and pause. Ddoes the engine speed up or slow down? If it speeds up, you are leaning into teh correct region. If it slows down and popping, then you have passed the corect spot and are too lean. Back it back out slightly and try to home in on the sweet spot. You are trying to find the lean best setting which causes the engine to run best - highest rpmm and smoothest - without being too lean. This might be hard as there are 8 barrels and one might not change the overall engine that much, but you have to tune your ear to the sound. You should not have to make any more that a 1/2 turn in either direction (from your 1 turn out initial setting) if your idle jet is correct. If you are more than 1-1/2 turn out then you idle jet can be larger. If you are less than 1/2 turn then your idle jet can be smaller.

You will be working back and forth between carbs - work through all four one at a time and then go back over them again. It is an iterative ting - the engine should sound smoother and smoother each time.

Now when this is done, I hook up the linkage and try to not disturb the settings of the throttle shaft. Try to match the linkage perfectly to the carbs now. I then start the engine and make sure it is warm. Put the syncronizer meter and all carbs will tell you which linkage arms are opening the throttle shafts - adjust the linkage so that your readings from first setting the carbs are reached (try to remove any affects of the linkage).

Now run up the engine to 2500 rpm or thereabouts and hold it. Dial in the linkage to tweak each throttle shaft setting to match all airlows of all carbs. You should be only adjusting the linkage - nothing previously touch should be touched again.

You should be done after this. I sacrifice and un-even-ous at idle for a smooth running engine at 2500 rpm - because I will mostly be cruising around 2500 rpm.

PM me your number if you want to talk.

My idle jets are 50, my mains are 135 and air correction 200. Yours might be completely different based on twhere you are and your motor. My weber tech manual has all kinds of jetting for various cars (but not the GT40). What jets do you have in your carbs now?

Mike


PS - I hope I haven't made any serious mistakes here - my typing sux.

 

[Steve Toner]

I'd be careful about trusting the "one turn" rule for the mixture screws. I think it depends on which kind of idle mixture screws you have. From the book by Aird & Elston: [ QUOTE ]
Some have a point with a comparatively long taper; these should be initially set at about 2 1/2 turns out. Others have a blunter taper that gives a much faster action; these should be screwed out just 3/4 turn from fully closed.

[/ QUOTE ]

Now, they're talking about DCOEs here, but you say you've noticed two differnet kinds of screws for the IDFs as well? I'm still sorting through the jetting on my own car, but I can tell you that the "one turn" rule led me the wrong way on my carbs (44IDFs). I was about 1 1/2 turns out and so tried a bigger idle jet. This definitely did not improve things. Checking it with a Gunson Gastester showed it to be running really rich off idle with both sets of jets - I need to go smaller. I think the jets I have (started with) are about right for sea level operation (I'll check this with the Gastester when I get to Michigan), where they are indeed about 2 1/2 turns out, so my carbs appear to have the "2 1/2 turn" mixture screws.

I *think* IDAs only have one type of mixture screw, so the "one turn" rule should apply there. Would certainly like to hear if anybody knows for certain.

 

[Mike Christian]

Steve,

My 1 turn rule comes from Redline Weber based on what they are shipping with IDF 44s now. The last set of IDF 44s I bought (within the last year) I could not dial in due to poor quality control on the mixture screws - they were not all tapered at the same angle. The were all matched and ended up near 1 turn. That is why I suggested pulling the mixtres first and looking at them.

The pair of IDF 44s I just sold were 15 years old and had blunt mixture screws - not even 1/4 turn open to get the correct condition.

I use the Gunson as well and found it helped me understand my mixture screw problem and led me to look there.

Tim asked me my method and that is it. I am by no means an expert as I stated before. Tim, be aware theat the quality of parts and your engine could result in settings different than what I describe. Check the mixture screws and even check the jets to insure they are labels correctly. Some people will ream them out and they won't be what is described on the jet. CB Performance is one place that sells jet gauges and reamers if you want to go that route. I will loan you mine if you want.

The process, however, seems to be the same from several reputable sources (not necessarily me!).

Regards, and keep us posted on your efforts please.

Anyone else out there that dialed in their IDF44s want to chime in and help Tim out?

Mike