VCCA Home Forums TECHNICAL - 1945 AND NEWER 1946-1948 Off Idle Lag...

In my previous thread "Lost Horsepower" I talked of retarding the ignition timing and the torque for horsepower exchange...

What I forgot to mention was that it also developed an off-idle lag or "stutter" similar to what I had with my Rochester Carburetor...

Any Thought's/Theory's...? The BTDC timing isn't less than 5 degrees...Thanks, Guy's...

Sounds like exaccelarator pump. Check that when the throttle is pushed down there is a steady stream of gas.

That would be typical...Problem is it's a fresh re-build, and it didn't behave that way up until I re-timed it.
Thanks for the suggestion, though. That would have been my first thought, too.

I'll take a look when the filter comes off...I need to look down the throat anyway...I'm almost sure the butterfly isn't opening all the way...Don't think it ever has, and I'd like to remedy that...

Advanced the timing a bit more (5 degrees) and now the off-idle lag is gone...Runs very smooth...

Had a chance to look down the carburetor venturi while it was idling...What I see out of the center "tube" is a constant dripping..I'm not sure if that much fuel should be coming out of there at idle...? I thought that's what the idle circuit was for..? Butterfly is slightly cracked, so that appears okay. I'm having issues with the idle circuit screw not doing much to vary the idle so...What next...?

A great big caution about looking down the carburetor with the engine running. If you were to get a backfire you run the chance of some serious damage to your face and eyes. Look down ONLY with the engine OFF.

The "center" tube should not be dripping at idle speed. It should produce a mist if operating properly. I suspect that the low speed jet is not properly seated or the passage is plugged or restricted. At a minimum your carburetor should be cleaned with a good quality cleaner.

You can safely observe the operation of the carburetor using a mirror to keep your face and hands out of the "backfire" zone.

Easiest thing is to just replaced the idle adjustment screw with another one/new one. If you still have the problem then take out the passage screw below the idle adjustment screw and check out this area for debris. Any debris in the area should alert you to it being the time for a rebuild. A rebuild kit has the adjustment screw in it and other important parts. You will also want to change your fuel filter or install one. Good luck, Mike

P.S. Be sure to reread the shop manual for suggestions!!! I am assuming you have a Carter carb. You may want to checkout the following: http://old-carburetors.com/Chevy/pages/002-Chevy.htm

Thanks guy's...Your certainly right about not looking down the carburetor while running...I was sneaking a peek at idle...Still scary...The carburetor is a fresh rebuild ( I bought it that way, though ) The problem is in that idle circuit obviously, the screw is new...The only time I get response from it is all the way in, and it dies...4 to 5 turns out and now it's effects the idle some what...I originally sent the carb back saying it didn't work properly and "they" took another look at it and sent it back saying try it again, "they" replaced the float needle etc. but the problem's the same...

Now, with all this "varnish" talk I'm beginning to suspect or wondering if this might be playing a part in on it...

Should be "misting" at idle...Thanks, that's a big clue...I'd better keep a mirror handy, though...!

The only other thing I was concerned about was if the vacuum line to the distributor was leaking right there at the carburetor, and if it would have any effect on the idle circuit...?

I remember telling the re-builder that the idle circuit wasn't working and he said he couldn't find anything wrong...Perhaps I'll have better luck...! Thank you for your time...!

So kevin how old is your tank and fuel lines??Is there a reason you should be worried about the fuel??

The "center" tube should be dry at low speed idle. You should instantly get a mist from the end when you open the throttle plate. Essentially all the low speed idle mixture goes into the throat at the port at the throttle plate.

W-1 carburetors are relatively complicated and good performance depends on all the internal parts being correctly matched for the application. Just because a part looks like the one removed or pictured in the diagram does not mean it will work. I have a few W-1 carbs that I have not been able to get to work correctly. Far from an expert on them I am learning. Have learned that some parts in the rebuild kits don't always work on all year and model carburetors. Also found that the ports on several of the castings are different sizes depending on the original application. As an example, the "fleet economy" bodies do not work with the passenger parts.

I should also state emphatically that when a W-1 carburetor is right they are very hard to beat on performance and fuel economy.

Oh.my...I did have problems...I "walked away" from this car in the late '90's...I had no interest left...Heck, I almost sold it to pay bills...! So the tank sat...1/2 full of gas for about 12 years...! I mean this car sat outside and wasn't even covered...! It had a great two-tone paint lacquer paint job that is now all but ruined...It's Sad...But, I'm resurrecting the old girl...! She will get restored...! By, golly...!

So, I removed and drained the tank only to find it was full of varnish AND tank Liner from the previous owner...And, I started to piece together WHY he sold it to me...! I used Acetone to get rid of the varnish and liner ( it was yellow) unplug the pick-up tube ( it was clogged, causing it to stall on the freeway and on hills ( lack of fuel to the float bowl ) replaced the fuel pump for good measure...It must have happened before, too. To the the PO...i.e. the reason I have found bent push-rods more stuck valves...So, this guy was obviously sick of trying to figure it all out...Remember ! This is pretty much before the times of eBay and chat sites...Can you imagine that...! Hahaha

Sorry, Ken...Back to Carburetors...Please...!

Thanks, Chipper. I understand now what I should be seeing at idle...I had a Rochester on before so I know what difference a smooth idle is like ( that might be a poor example haha ) I think I am getting the mist off idle...It's just I'm getting this "dribble" while idling from the center tube..Must be why it's running at all at idle...I'll have to remove the carb altogether to check the idle circuit...I just hope the problem is obvious. Perhaps I'll plop the 'o Rochester back on in the mean time...I like to drive every day...Can't beat this California weather...But, don't you'all forget...! We here in the Golden State have to pay ($$$) for the nice weather,

So kevin,how did you clean the fuel lines or did you replace them???You don't what to get crud in that re-built carb...Are you running with a fuel filter and if so what type...At one time I got one of the repro's from COT40s,the gasket deteriorated and clogged the carb badly...I have been running with out as I decide the solution

While I had the tank out ( or just dis-connect the line at the tank...Remove the back passenger wheel first ) and the line disconnected from the fuel pump I poured acetone down the fuel line and blew ( blowed, for those of you from east Ohio or Tennessee haha ) it out a couple 'o times...Put a rag around the tank end from...You know on second thought with that nice paint job maybe you should remove it for this process...Or just not worry about it at all...The little bit of varnish that maybe adhearing to the inside is probably not worth worrying about, in your case.

I got a Carter off eBay for less than 20 bucks, even had a new ceramic filter...I got lucky with the filter I think. And you can get new paper filter with the new rubber gasket...Even if the ceramic filter is a bit yellow or...? don't sweat it I think they claim there supposed to last forever...I wouldn't buy a repo...To many good old ones on eBay...

You're ok so far.........but I'm watching

Just get a good rebuild on a Carter W1 and you will have no problems.