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Weber Carb Install: Still a little Rough Idle
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Author:  Wesola78 [ Sat Jun 21, 2008 12:14 pm ]
Post subject:  Weber Carb Install: Still a little Rough Idle
This is on my Volare with the DCNV36 Weber carb on an Offy intake. It's running better now, but the idle still doesn't feel quite right. It runs smoothly while cruising, but just sitting and idling, it feels a little rough. Two things:

1) I don't think that I have a vacuum leak, but I'm not positive.

2) I must confess, I'm not very experienced at tuning carbs.

Any suggestions?

Thanks!

Wes
Author:  LUCKY13 [ Sat Jun 21, 2008 5:52 pm ]
Post subject: 
Where are the idle mixture screws at , 1 1/2 turns out, 2 turns out , 1 /2 turn out ?

When you ajust these idle mixture screws what does it do when you turn them in, or out?

Can you turn them in and make the engine die ?


I expect it will be idle jets that need changed but knowing where and how the engine responds to the idle mixture screw will help tell which way they did to changed ( richer or leaner).


Where does the idle base speed screw end up at ? Did you turn the screw until the throttle shaft was all the way closed, then turn it two complete turns for a base idle starting piont ?


While your at it, what are all the jet & air bleed sizes that you are running in the carb right now?


Jess
Author:  Wesola78 [ Sun Jun 22, 2008 10:52 am ]
Post subject: 
I've adjusted them back and forth a few times, and I'm not sure where the idle screws are now. Should I turn them in and see how it idles?
I think when adjusting idle mixture screws, your'e supposed to go from rich to lean, is that right?
Thanks for your response!
Wes
Author:  Wizard [ Sun Jun 22, 2008 3:33 pm ]
Post subject: 
Amount of idle jet size is curcial.

If too big or too small the idle mixture screw is in wrong range which forces you to fiddle with throttle which is causing your problem.

Weber starting point:
The starting point is: small idle jet in primary, 5 to 10 size larger in secondary (ie: 50/60). THis was from someone who told me the all the documents for putting bigger idle jet first in primary is causing my tuning confusions/hassles.

One turn on the throttle stop screw from intial contact. 2 turns out from lightly seated idle mixture screw.

Fire up and keep engine alive till choke is completed and engine warmed up sufficiently, may need to bring throttle up SLIGHTLY to keep alive but slow enough.

Turn idle mixture screw out till engine go soft or sound odd (vacuum drop, idle quality drops off etc), Note it's position (I mark the screw to make it easier for counting turns), then turn slowly till engine starts to run raggedly. THen put screw in between for best idle and speed.

Kill engine, turn the screw in till seated (counting the turns). Should be less than 2 (too lean idle jet) and 1/2 turns but not less than 1 turn in (too rich idle jet.).

Cheers, Wizard
Author:  Wesola78 [ Sun Jun 22, 2008 8:44 pm ]
Post subject: 
Well, I don't know what the jet sizes are now. This carb was part of a setup; Offy dual carb manifold with two of these carbs. Now I'm running just one of these carbs on an Offy 4bbl intake with an adapter.
This carb is a Weber DCNV36 2bbl synchronous, not staged.
So, I'm guessing that the idle jet, (or jets?) needs to be bigger.
It feels okay when I'm cruising, but the idle still feels a bit rough.
How can I find out what jets are in this carb now? I have another carb just like it to "play with", by the way.
I also consider myself to be a novice where carburetors are concerned.
Thanks for the responses fellas! :D
Author:  Wizard [ Mon Jun 23, 2008 6:33 am ]
Post subject: 
Ahh!

Okay part of my comments about weber applies to progressive type. Yours the sync dual throttle, kinda agressive carb for daily driver use and not a MPG carb.

About the idle jets still applies. I think you need to open it up and get numbers off the jets and two idle jets are on the outside by a 2 screw plugs on one of each side and post here.

Cheers, Wizard
Author:  Wesola78 [ Sun Jul 13, 2008 10:27 am ]
Post subject: 
Okay, the engine is running better, I've been playing with the idle mixture screws. She starts right up, but the idle still doesn't feel like it should be. I'm going to open up the carb, which makes me a little nervous. Actually, I have a spare Weber just like this one, so I may practice on it first.
So, I don't know what idle jet (jets?) is in it now, but how will I know if it needs a bigger jet, or a smaller jet? Again, this carb is a Weber DCNVH36 2bbl. I originally had an Offy dual intake with two of these carbs on it, now I have just one on an Offy 4bbl intake with an adapter.
Also, just in case I jave a vacuum leak, is WD-40 good for spraying around the carb while its idling?
Thanks!
Wes
Author:  Wizard [ Sun Jul 13, 2008 6:20 pm ]
Post subject: 
Also ingition advance is bit different with using weber also.

Reason I wanted you to close the throttle AS POSSIBLE AS you can that means advancing the timing a bit to raise the idle rpm so you are NOT exposing the progression hole/slot.

Also adjusting the mixture raises and lowers the rpm also. I find weber likes to be between lean and strichio mixture.

As others have said about idle jet so important, if you get it right iwth certain number of turns on the idle mixture and NOT getting bogs, then you are spot on.

Very important everything else in good shape (no other leaks, working ingition, no slop in distirbutor, etc. What was LAST time the weber had rebuild and documented all the jets? So you know where you stand on at this moment.

Cheers, Wizard
Author:  Wesola78 [ Tue Jul 15, 2008 9:06 am ]
Post subject: 
Thanks for your response Wizard!
Something else I forgot to mention, I have a Dutra Dual exhaust manifold on the front (its been there for a few years), and a modified stock manifold on the rear. However, when I changed intakes, I also changed the rear exhaust manifold to another modified one, but this one has been "cut down"; meaning that the section that would be in contact with the intake manifold for carb heat is no longer there. I've also noticed that the intake still feels cool after the car has been running for a few minutes.
I thought that I would be okay without carb heat, I live in south Texas, but maybe I should rig up something.
Thanks again for your response Wizard!
Author:  Wesola78 [ Tue Jul 15, 2008 2:39 pm ]
Post subject: 
Quote:
Where are the idle mixture screws at , 1 1/2 turns out, 2 turns out , 1 /2 turn out ?

When you ajust these idle mixture screws what does it do when you turn them in, or out?

Can you turn them in and make the engine die ?
Okay, after the slant warmed up, I removed my "jerry-rigged fast idle screw". I can turn in the idle mixture screws and make the engine die, but right now, the engine is idling okay with the screws about 2 & 1/2 to 3 &1/2 turns out. It still acts like the engine is about to die when I put it into gear.
Author:  Wizard [ Tue Jul 15, 2008 6:21 pm ]
Post subject: 
Sounds like youre either too lean on the idle jets. We need jets documented here. The idle jets are external, so start with these and pull them out and record the numbers on them.

Cheers, Wizard
Author:  Wesola78 [ Thu Jul 24, 2008 9:38 am ]
Post subject: 
Update: Okay, I pulled out one of the idle jets, but I'll be danged if I can see any numbers on it. Is there a way to measure an idle jet, i.e. micrometer?
The idle jets are real easy to get to, but I do not see any numbers on it.
Thanks,
Author:  Wizard [ Thu Jul 24, 2008 9:54 am ]
Post subject: 
Need magenifying glass to see numbers on the jet. Need to pull both.

And get more idle jets from weber resellers.

Cheers, Wizard
Author:  Wesola78 [ Thu Jul 24, 2008 11:42 am ]
Post subject: 
Okay, ny son Daniel read them for me :) He said there was a "50" on each one.
So, I guess I need to go up one or two sizes?
Thanks!
Author:  Rust collector [ Thu Jul 24, 2008 1:44 pm ]
Post subject: 
I think you might end up with a set of 60 idle jets...
But it is just a feeling I have


Maaaaaybe 65 or 55
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