Weber acrurators spitting at under 3000 rpm

[yellow car]

I have a 1973 rs clone with a 2.4 and webers.
Under 3000 rpm I am getting intermittent
spitting up through the carbs and sometimes at idle
the same problem occurs. Could be warm or cold.
Carbs were adjusted twice.
Could valve adjustment be problem? Timing is good, Distributor is new, plugs are new.
Any Ideas.
Thanks, Eric

[jpnovak]

Sounds like a clogged idle circuit causing a lean pop through the intakes. I assume you have a low rpm hesitation too.

remove the idle jets, clean with compressed air. blow compressed air through idle circuit. reinstall jets and drive. this should solve your problems.

[yellow car]

Thank you.

The idle jets are on the sides of the carbs and when removed
split in two and have small rubber O ring- correct?

Once removed should I blow compressed air into
the openings where jets came from as well
as clean the jets.

Could jets be to small a size?

Thanks, Eric

[ttweed]

Originally posted by yellow car
Could jets be to small a size?

This is a very good possibility, as the changes in fuel formulations in CA over the years have resulted in much higher RVP numbers which allow fuel to percolate much easier. I would try swapping them out for the next higher size or reaming them if cleaning does not solve your problem. Also check for any false air entering the carbs from intake leaks (manifold gaskets, throttle shafts, etc.) and leaning your mixture.

TT

[yellow car]

Thanks Tom

I have checked for leaks and throttle shafts are tight
with no wobble. Idle jets are clean.

I think that since I am getting intermittent spitting
from carbs on various cylinders I will try the next bigger idle
jets.

If not that the only thing I can think of is valve adjustment.

Thanks, for the information

Eric

[73911guy]

You mentioned that you have a new distributor, but has it been re-curved for the carbs?

I spent much money and much time trying to get my '73 2.4T to stop spitting and missing, just as you describe. A new distributor and a re-curve job fixed it all. No problems in 3 years.

Let me know if you need a contact.

Jim

[yellow car]

Thank for the Info Jim.

At this point in time it seems that the symptoms are
very similar to clogged idle jets but they are not clogged.

The transition from Idle circuit is not smooth.

I have size 57 and 60 idle jets coming tomorrow.

I have 55mm now. If the 57mm improves the situation I am on the right track.

Distributor is a new RS unit that has really improved
throttle response so I think it may be ok with the curve.

Thanks for the info.

If this does not work I need to go back to fuel injected cars.

Thanks, Eric

[jwetering]

You say the carbs have been adjusted....it sounds like one or two of the cylinders may be leaned out too much. Just for laughs maybe try turning each screw out a full turn (richer) and see if that helps.

??

[yellow car]

Thank You Jasper,

I will try this also but after three tries including myself
in addition to two very famous Porsche shops in Orange County adjusting them I suspect idle jet size issues.

I will try your suggestion later.

If adjustments are required after installation of larger
idle jets should mixture adjust screws go out
or go in slightly?

Thanks, Eric

[73911guy]

I believe I've got 60 idle jets in the Webers in my '73.5 2.4T.

You'll probably need to re-set the idle mixture in each throat after replacing the jets. Do a search on how to adjust the Webers - there has to be something on this BBS covering it.

Check your timing and dwell also - dwell per factory spec, total advance at 6,000 RPM should be 35 - 36 degrees. It takes nerve and knowledge to wind one up to 6,000 and make adjustments!

Check with Barry at IAE (International Auto Electric) in Detroit about the curve in your distributor - 313-532-5350 - to see if he thinks it will work with your engine setup.

Jim

[yellow car]

Thank You Jim

I installed a pertronix recently so I think dwell should not be an issue.

I will check on how to adjust the mixture.

Timing is good.

Eric

[john walker's workshop]

NEVER blow air into the idle jet bores! the floats will implode. chances are the jets are too small. originally they had 0.45 and 0.50 sizes. a mild 2.4 would normally need 0.55 to run properly without spitting and popping. a lot depends on how well someone has balanced the airflow through each stack and precisely adjusted the idle mixture. it takes experience and a very good ear.

[yellow car]

Thanks for everyone's advise!

The 60 idle jets are in and the spitting, popping and flat spots are gone.

Now the idle is slow approx 500rpm and lumpy.

Should mixture screws go out or in a little?

I also have a set of 57 mm idle jets that I have not tried.

Original jets were 55mm.

Thanks, Eric

[jwetering]

The short answer is neither just yet. To get the idle speed up you want to adjust the idle speed screws, these are the screws at the throttle shafts. You can see that by turning these in (clockwise) you are effectively opening the throttles. Shoot for 1200 rpm to start. Then turn each of the idle mixture screws out 3 or 4 turns from the bottom. One by one then turn in the idle mixture screws slowly (slowly) until you hear the idle start to falter just a wee bit, then back the idle mixture screw out a half turn, maybe a full turn depending on how quickly you stopped turning the screws after you noticed the falterring idle. Once the idle mixtures are dialled you can back off the throttle speed to 900 or 1000 rpm or whatever keeps the plugs from foulling. This is quick and dirty....

The long answer is that you need a synchronising tool to make sure the air flow through any one throat on each of the two carbs is the same after you adjust the idle speed. Then adjust the air correction screws to even out the air flow through each of the six throats so they match the air flow through the original two (which matched remember). Once you're happy that you're making 1200 rpm with even air flow through each of the six throats, then go through the idle mixture adjustment procedure described above. Turning the screw in will eventually falter the idle, and cause spitting through the throat you're working on. If you're spitting, then you'll probably need a full turn out. If you've noticed a slight falter and you haven't started spitting yet then you may only need a half turn out.

Once the mixtures are dialled in you can back of fthe throttle speed - you have to use the synchronising tool to make sure the air flow through the two carbs are the same though.

There's an even longer answer, which involves setting up the linkage, but the long procedure described above is what I do every month or two throughout the driving season to keep the idle smooth.

It gets easier after you've done it a hundred times, and even easier after 1000.

[yellow car]

Thanks Jasper,

Just got back from a 700 mile ride from Orange county to Sacramento and back in the car. Did some skiing at Tahoe also.

Runs better than ever. No spitting, popping, flat spots or anything
abnormal.

Some short stints at 120mph + on the 5 freeway really
shows how stable these cars are at speed. I am sure that the Koni's,
elephant bushings, and corner balance also help.

Thanks, Eric