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carb balancing
tony_de_whitt - April 6th, 2008 at 10:19 PM

Hello.

Has anyone got any hints or advice on balancing carbs.
Thabks in advance

anthony

Dasdubber - April 7th, 2008 at 08:33 AM

Hi Tony,

Can you give us some more information re. which carbs you have and engine as well?

Cheers
Al

tony_de_whitt - April 7th, 2008 at 10:52 AM

The engine is an 1800, and they are the standard carbs for this engine. Solex. I can find exact model if required.
Thanks

Bizarre - April 7th, 2008 at 12:08 PM

read the following and see what helps

This is the best link
http://www.clubvw.org.au/tuning_tips_for_tips_twin_carb_k.htm 

There is a heap of links here - look under carburettors
http://www.type2.com/library/library.htm 

click here might save some time - under FUEL
http://www.type2.com/library/fuel.htm 

this is more general
http://www.aircooled.net/gnrlsite/resource/articles/dualcarb.htm 

tony_de_whitt - April 8th, 2008 at 09:09 PM

thanks.

aggri1 - April 10th, 2008 at 09:25 AM

Quote:
Originally posted by tony_de_whitt
The engine is an 1800, and they are the standard carbs for this engine. Solex. I can find exact model if required.
Thanks


Oh. Yeah I got those. What a pain in the backside. Wish I had the FI model.

I found that making sure they were opening together was most of the problem most of the time. But of course all the linkages are worn and sloppy, so it's a fiddly thing to do. Make sure the chokes are chocked open, I used screwdrivers, while synchronising the opening action.

I was going to construct a basic differential manometer to hook onto the brake booster elbow ports, for measuring relative vacuum difference, but I am not sure this would work (but the vacuum there IS from below the throttle, so should be OK I think). I haven't done it yet. Would be a basic thing with a few bottles and some clear tubing, nice and simple. Sorry I can't help more. This is one thing I usually let the mechanics do. Sometimes they even get it right.

Cheers, A.

mnsKmobi - April 10th, 2008 at 12:50 PM

Quote:
Originally posted by aggri1
Quote:
Originally posted by tony_de_whitt
The engine is an 1800, and they are the standard carbs for this engine. Solex. I can find exact model if required.
Thanks


Oh. Yeah I got those. What a pain in the backside. Wish I had the FI model.

I found that making sure they were opening together was most of the problem most of the time. But of course all the linkages are worn and sloppy, so it's a fiddly thing to do. Make sure the chokes are chocked open, I used screwdrivers, while synchronising the opening action.

I was going to construct a basic differential manometer to hook onto the brake booster elbow ports, for measuring relative vacuum difference, but I am not sure this would work (but the vacuum there IS from below the throttle, so should be OK I think). I haven't done it yet. Would be a basic thing with a few bottles and some clear tubing, nice and simple. Sorry I can't help more. This is one thing I usually let the mechanics do. Sometimes they even get it right.

Cheers, A.


What about using a flowmeter? Or two if you're cashed up! :)

PurpleT3 - April 10th, 2008 at 01:32 PM

Use a carb synchroniser - the "snail" type. They are not that expensive. I would only use one and move it back and forth between carbs. I say this as they are not the most precise instrument and different ones would probably read differently. It is the difference between the two sides that you want to measure and balance.

General_Failure - April 16th, 2008 at 01:42 PM

Thanks for the links Bizarre!

I had completely forgot about the ClubVW walkthrough for carby balancing. I used to be a member of that club until I moved away.

Anyway I have the same problem with my 1800 dualcarb. Nightmare setup.

Not intending this to be a derail, just a general comment. As some of you may know I've been chasing a vacuum leak that I just can't find. After reading this thread I had a revelation. For the van to idle, the air bypass screw is set so that a nightmarish howl comes from the idle throat when the L pipe is off. It's very loud even sitting in the drivers seat with the hatch closed. Anyway my point is high airflow at low revs = low vacuum. So after I test the brake booster for leaks, which I haven't done yet because I need to get hose to make blanks, I'm going to tackle the idle circuits again.

I mirror the sentiment of wishing my van had EFI.

General_Failure - April 19th, 2008 at 09:49 AM

I know it's a second post, but it seemed to make more sense than editing.

While the first article on tuning the carbs http://www.clubvw.org.au/tuning_tips_for_tips_twin_carb_k.htm is great there is an issue I can see. Plugging the idle throat and disconnecting the solenoid have two very different effects which can influence tuning.
Disconnecting the solenoid will cause the motor to be tuned for the airflow, which I guess is fine because the aim is to get it idling at about 500RPM with that idle circuit disabled.
Plugging the throat however will cause the mix to be off because it is being tuned for a lower airflow than the motor will normally experience.

I had a bit of fun with both methods yesterday messing with the van. I decided to check the initial mixture screws which I previously decided never to touch. Glad I did. I don't remember the setting on the left carb. I know it was really wrong though. And the right one was wound in tight!
After adjusting to the suggested starting point of 2.5 turns, and messing with the air bypass screw to get the revs back down and thankfully stop the horrific banshee howl from the idle throat I tried both idle crippling methods.

Disconnecting the solenoid caused the engine to stop instantly.

Plugging the throat with my finger, which I was no longer scared to do because the airflow is now sane, yielded a drop to what sounded like 500RPM. I couldn't see the tacho at the time. Trouble is after a few seconds it went back up to about 1200RPM. Then I took my finger off and the motor floundered and died.

Anyway, the point of that little story is that depending on what is up with the carbies, the two methods which are almost considered interchangeable in the article have two very different effects.