Skip to main content

Hi everyone,

I Finally got my car running. Having issues, when I'm driving the car makes a weird sound from the engine at 2000-2500 rpm underload. I'm getting decel pop and little backfiring. My fuel pressures at 3 psi, timing is at 28 degrees. I am running Weber 40 IDF dual carburetors with 50 idles, 200 air, 145 main jets. So I did some tests. I found when I cover #1 cylinder on the top of the carb it doesn't stall or slow down. I did a compression test and it is good. I did a leak down test and it was not leaking anywhere. I sprayed a little brake clean around the base of the intake near the cylinder head while it was running and I didn't notice any change. I sprayed the throttle shafts on the outside and didn't notice any change.I pulled the intake thinking it might be the gasket. It tore a little on the stud ends coming off so I couldn't tell if there was a problem there. I checked the base of the intake where it attaches to the head it is flat. My carbs are new but they were sitting for a long time. I did go through the carbs and check for dirt and corrosion and cleaned them. I noticed the top gasket is thin. When I disassembled the top of the carb it appeared the gasket had good compression marks like it was sealing.

Do I have a bad carb?

Last edited by JB356SR
Original Post

Replies sorted oldest to newest

I hope you have a snail for checking the airflow. If the dead cylinder has the same airflow then it's DEFINITELY a clogged idle jet. You need to remove the jet AND the mixture volume screw and blow out the whole circuit. Just removing the jet and cleaning it isn't enough to clean the whole circuit.Snail

If the airflow is not the same, did you do an ICE-COLD valve adjustment first?

Attachments

Images (1)
  • Snail
@DannyP posted:

I hope you have a snail for checking the airflow. If the dead cylinder has the same airflow then it's DEFINITELY a clogged idle jet. You need to remove the jet AND the mixture volume screw and blow out the whole circuit. Just removing the jet and cleaning it isn't enough to clean the whole circuit.Snail

If the airflow is not the same, did you do an ICE-COLD valve adjustment first?

Yes I did a snail check when I was setting up the carbs. I was getting 5 on all four cylinders. The valve lash was set when the engine was cold.

No snail needed. Snail takes care of AIR, not fuel.

Turn the screw in gently until it stops and count the turns. After I get carbs set I screw them all in and write it down, then turn them back out to where they need to be.

That's what I recommend. Also make sure the screw(and spring, washer, and O-ring: don't lose anything!) and jet go back in the same cylinder/throat. It matters.

@DannyP posted:

No snail needed. Snail takes care of AIR, not fuel.

Turn the screw in gently until it stops and count the turns. After I get carbs set I screw them all in and write it down, then turn them back out to where they need to be.

That's what I recommend. Also make sure the screw(and spring, washer, and O-ring: don't lose anything!) and jet go back in the same cylinder/throat. It matters.

Thank you. I've been cleaning just the idle jets at the start of each season but I can see why it'd make more sense to clean the whole circuit.

And just confirm we're talking about the Idle Mixture Screw:

idf_tunning

Attachments

Images (1)
  • idf_tunning
Last edited by Robert M

Yeah, watch out for those teeny-tiny washers and the even teenier o-ring at the end of the screw.   That o-ring has a habit of (a.) hanging up inside of the screw port to mess  things up when you re-assemble the screw or (b.) falling off somewhere not to be found (the original “rubber thingie”) and then you forget to put the new o-ring on.

It’s always something......

On Webers, which is what we're talking about here(not Dells), the idle volume(mixture?) screw O-ring likes to stick to the carb. The O-ring doesn't go into the threaded area like Dells do, it just sticks to the flat that it tightens on. Remember, get the screw, spring, curved washer and O-ring.

On the idle jets, those JayCee jet holders can really change the way your day goes on a Speedster. You can use an allen key to spin them out, without getting interference from the carb top/fuel inlet, like you do when using a flat-blade screwdriver.

When you take the idle jet holder out along with the idle jet, make sure you get the O-ring too, that likes to stick in the holder well. VERY IMPORTANT not to lose this. This O-ring is best kept track of by rolling it down towards the head of the jet holder over all the threads.

Robert, that is the correct screw to remove along with the idle jet to clean the entire idle circuit.

I never had a problem like others seem to with plugging jets. I drove my car often and used Stabil to mitigate the white goo that forms in float bowls. Once the air is synched and linkage is set there is no reason to remove the air cleaners. IMHO this is where a lot of problems occur as there are openings on the carb top for the idle air intake and float well venting: great places for dirt to fall into. Every time you pull an air cleaner top you are asking for a clogged jet.

Good fuel filtration, clean carbs, and leaving the air filters alone are all you need for problem-free Webers.

Turning the carbs around by using CB Performance Space Saver manifolds is a GREAT idea, but only if you're running a 911 shroud or possibly a DTM. The regular VW shroud is so close to the number 1 cylinder idle jet and mixture screw it is VERY difficult to remove either.

Last edited by DannyP
@DannyP posted:


On the idle jets, those JayCee jet holders can really change the way your day goes on a Speedster. You can use an allen key to spin them out, without getting interference from the carb top/fuel inlet, like you do when using a flat-blade screwdriver.



@Bobby D posted:

The jet holders are a must for speedster as it hard to see the idle jet.  The allen key makes it so much easier.

When Pat built my engine the Jet Doctors were an automatic. I cut off an allen head key and use it in the appropriate size socket and remove them with a small driver. I reinstall them by hand and just a small amount of twist with the drive to snug them up. I think my idle jet cleaning has just because a common ritual during pre-season prep for the greater amount of driving during spring/summer. I drive it all year since the cold white stuff never lands on the ground where I live and mid-day temps in the winter can still be in the 60's. But I figure if I'm cleaning them they won't get dirty.

Add Reply

Post Content
×
×
×
×
Link copied to your clipboard.
×
×