Carburetor throats stopped matching Options

[98101]

I pulled the carbs to install a new linkage, and blew out the jets while I was at it. The two carbs are synchronized with each other better than they've ever been, but now there's a discrepancy within one of the carbs (DRLA 45s). I'm wondering if I bent a throttle plate, or if there's something else I did that could cause this?

The lower one is cylinder 3, if that matters. There was a slight discrepancy before, but now they're further apart.

[stugray]

An intake leak would do that.

Spray some WD40 (or even water works) around the base of the carbs and base of the intake manifolds and see if it make the engine run different.
Some people use starting fluid.

Some carbs have vacuum ports at the base. Maybe you knocked a cap off?

You should be able to look down your throttle bodies and see if you can see any gaps on the butterflies (but it is much easier to do with them out and a flashlight behind them).

[98101]

An intake leak would do that.

Spray some WD40 (or even water works) around the base of the carbs and base of the intake manifolds and see if it make the engine run different.
Some people use starting fluid.

Some carbs have vacuum ports at the base. Maybe you knocked a cap off?

You should be able to look down your throttle bodies and see if you can see any gaps on the butterflies (but it is much easier to do with them out and a flashlight behind them).

Thanks -- I'll try those things.

One other detail: there was previously an open vacuum port (nearest #4) that I sealed off. But unsealing it didn't seem to affect this condition.

[98101]

With the carburetor on the engine, I was not able to perceive a difference in the butterfly opening.

Running the engine and squirting water around the carburetor to manifold connection, I was not able to change the way the engine was running. I wasn't able to reach most of the intake manifold to engine connection with the spray bottle.

For lack of another idea, I tried swapping the idle jets between the throats. No change.

[ottox914]

Back to basics but did you check the adjustment screw to see if it was loose or had backed out? Could be just that simple.

[rhodyguy]

Are the air by pass screws in the same adjustment they were when you started the carb work? Did you preset them equally while going thru the preinstall procedure? New linkage...start at the beginning. What is your idle rpm? What are the readings when you measure the l&r front venturi flow at a stable idle? Equal?

[rhodyguy]

I just finished up trying to find the pre-install procedure in the Dellorto Superformance (CB actually) manual. Compared to their Webber book it's like night and day. More about that in a dif thread, later. I would not recommend the Del book to anyone.

I found something you might want to consider if you haven't done it. P.79 #6,"Re-install the air by screws to a closed position".

[nditiz1]

(IMG:style_emoticons/default/agree.gif)
Check the air bypass.

I was having a similar issue. If the values were within 1/2 unit it says don't worry, but yours is more than that. Something you might want to check is the velocity stacks. Before I bought CB ones the set I had on there were not flush with the tops on the carb plate. I put tape around it and sure enough air was escaping between the carb plate and velocity stack. Try taking the stacks off and put the meter right into the carb throat.

[98101]

Thank you everyone. Indeed the air bypass screws weren't seated. ALL FOUR OF THEM. We screwed those back in and checked the stacks, but no change. VW mechanic feels the throttle shaft is bent. This is the carb that doesn't leak as much gasoline on itself as the one on the other side.

[MarkV]

Strange? Mine are off by a little from one throat to another but at least one throat matches from bank to bank. Make sure the air bleed adjusters are closed all of the way on all 4 throats. It was recommended to me from sources here that it is better to run those all closed. You may have a small vacuum leak. I always smear a light coat of grease on the intake gaskets at the carbs and at the heads to make sure they seal and to be able to reuse the gaskets. Check them at like 2500 RPM and see what kind of reading you get. I doubt it would have much effect but have you set the mixture screws? After I rebuilt min it took some tinkering around but then all of a sudden they will fell into place and haven't touched them in ages. If you change the timing you have to pull one linkage and re-sync the idle adjustment.....best to get the timing where you want it before you set them.

[98101]

I just finished up trying to find the pre-install procedure in the Dellorto Superformance (CB actually) manual. Compared to their Webber book it's like night and day. More about that in a dif thread, later. I would not recommend the Del book to anyone.

I have spent too much time in this book and agree it's a mess. This is part of the Dellorto experience I guess.

[MarkV]

Thank you everyone. Indeed the air bypass screws weren't seated. ALL FOUR OF THEM. We screwed those back in and checked the stacks, but no change. VW mechanic feels the throttle shaft is bent. This is the carb that doesn't leak as much gasoline on itself as the one on the other side.

Throttle shaft is pretty stout and would be hard to bend.

[MarkV]

I only have one meter so this may seem obvious .... have you tried using one meter and going from throat to throat with it? (IMG:style_emoticons/default/confused24.gif)

How does the car run ?

[rhodyguy]

3 read just to 3 and 1 to just past 5 with the by passes closed?

[98101]

I only have one meter so this may seem obvious .... have you tried using one meter and going from throat to throat with it? (IMG:style_emoticons/default/confused24.gif)

How does the car run ?

Yes -- the VW mechanic had just one meter and used your technique. It was running awful, backfiring several times per block, unable to hold idle until I advanced the timing to 30º at 1000. I don't think that one throat was the only problem.

3 read just to 3 and 1 to just past 5 with the by passes closed?

That's right.

To make a long story short, I have new old-stock Dellortos now and all the drivability problems are gone. I'll write more details on the other thread.

[MarkV]

I only have one meter so this may seem obvious .... have you tried using one meter and going from throat to throat with it? (IMG:style_emoticons/default/confused24.gif)

How does the car run ?

Yes -- the VW mechanic had just one meter and used your technique. It was running awful, backfiring several times per block, unable to hold idle until I advanced the timing to 30º at 1000. I don't think that one throat was the only problem.

3 read just to 3 and 1 to just past 5 with the by passes closed?

That's right.

To make a long story short, I have new old-stock Dellortos now and all the drivability problems are gone. I'll write more details on the other thread.

Sounds like you are getting close to having it dialed in. New old-stock Dellortos are the carbs that came on the car? I am a little stumped by all of the timing....30 degrees at an idle and 39 degrees total?

(IMG:style_emoticons/default/smilie_pokal.gif)

[98101]

Sounds like you are getting close to having it dialed in. New old-stock Dellortos are the carbs that came on the car? I am a little stumped by all of the timing....30 degrees at an idle and 39 degrees total?

(IMG:style_emoticons/default/smilie_pokal.gif)

Yes... today I'm much happier with the car (even if the clutch is slipping).

Better explanation about the funky timing and then new carbs here:

http://www.914world.com/bbs2/index.php?s=&...t&p=2566292