Idle off idle miss - stock 914-6
 

I'm trying to tune a 1970 2.0 with webers and have an idle miss that I've not been able to tune out. The car runs strong under acceleration but has a miss at idle and under light throttle (maintaining speed). I've changed points set dwell replace plugs wires cap rotor, sync'd carbs several times. The car was at a well known local shop and they were unable to fix and after 5 months I took the car back. They didn't get much done so I have no idea how much time they put on it. Idle jets are 50s. Carbs are clean fresh rebuild. Any ideas or troubleshooting techniques would be greatly appreciated. Thanks. I can shoot some video tomorrow.

Additional info - at idle sounds like I'm missing one or two cylinders. With slight throttle there is a little hesitation then all 6 hit like a switch goes off. Running through the gears the car performs well accelerates hard.

Where are you located?

1. webers run on the idle circuit up to about 3000 rpm

2. under acceleration - you are on a different circuit - so you will never know if the idle circuit is the problem

3. if you search Weber idle issues on various forums you will get 100 ideas most of which boil down to:

dirt in the idle passages

4. remove the idle screws

5. blow with about 15psi air pressure thru the screw holes - most of the time that will clear up the problems - if not you will have to remove the carbs andf clean the passages with fine wires (like welding-tip cleaners or tiny jet drills (see Holley))

NEVER blow with high air pressure - you will destroy the floats (btdt)

6. good luck

Thanks Larry! That gives me some hope. Up to 3k sounds right based on my test runs today. Will try the idle jets/passages tomorrow. Are 50s pretty standard? I have another set of carbs which I think have larger sizes.

I'm in Gilbert Arizona.

Cleaned out the idle jet passages with 15 psi. Was able to get the car idling with about half the idle jet mixture I was using. 1.5 turns rather than 3. No matter how rough it gets it sounds like all 6 are firing. Need to go back from the start and resync but it's almost there. Appreciate the help! Took some video but they aren't too exciting looking at they ceiling - dansk sounds awesome though!

2 more things to consider:

1. if the carbs EVER got water in them - there will be a lot of white oxide-like "growth" everywhere - including in all the tiny passages - the only solution to that is to completely refurbish - which means - you have to drill out all the lead plugs at the passage ends and physically clean the passages - (fine wires)

2. if the carbs sat for a long long time & possibly had any fuel in them when put away in storage - there will be "varnish" in those passages - same resolution as above is required

a. you can replace the lead plugs with fisherman's shot sinkers after you have it all cleaned up

b. Mike Pierce ("Mr. Weber") at Pierce Manifolds - or Paul Abbott, below - will do the full refurbish for you at a price




also check these if you have not already

Weber stuff on Pelican

http://forums.pelicanparts.com/porsche-911-technical-forum/687453-tuning-webers.html

Porsche 40IDA 3C Weber

http://forums.pelicanparts.com/porsche-911-technical-forum/768023-weber-carb-upgrade.html

http://forums.pelicanparts.com/porsche-911-technical-forum/9098-has-anyone-just-bolted-webers-onto-2-7-cis-engine.html

Weber jetting search - www.google.com weber+jetting

Weber IDA jetting - www.google.com weber+ida+jetting

.

Two suggestions:

1. Pull idle jets and blow carb cleaner through them and check them by looking through them
2. the idle air bleed jets can be easily blocked with dirt from various sources and need checking

To check idle air bleeds you will need to remove the tops of the carb bodies (ten hex nuts) and see if crud is accumulating around them. These are located just inboard from where the idle jets are installed and pressed into the top of the carb bodies. They are brass and about 3/16" in diameter with a little hole in them. Blowing air through the idle circuit passageway will probably clear the air bleed if there is some crud there so see if cleaning the idle jets fixes your issue first.

Check out my comments regarding sources of crud in the fuel bowl from my site: Weber Carbs Technical

Great info guys. Thank you! Will put these to use hopefully before the weekend. Appreciate the help. Todd

Anyone know where I can buy the idles mixture screws individually? Some of mine are pretty worn. Thx.

Looks like they come in the rebuild kits. My gaskets are new. Carbs were rebuilt and in a box hen I got the car.

Are the tips tapered or are the stepped? Scroll down to see the different types after going to this site: Weber Carbs Technical

The ones with the long taper are for IDA type Webers and the ones with the stepped tips are from IDTPs and are not so easy to acquire.

I can help you with either.

Paul,
I will pull all six and shoot a picture. They look like the tapered ones on the left in the article. Some have a smooth step I am guessing is wear. I have another set of webers I will pull those and compare. Need those for another project so would rather not steal those yet. That article is great as I've noticed some subtle differences between the two sets. Will read up on those this weekend. Thanks, Todd