Carter weber carbs from Langdon - SUCKING SOUND from one only???

[Powerhouse]

Howdy all,

I have a dual Carter Weber setup on my 218. One carb makes a throaty sucking sound when running, while the other is nice and quiet. When shut off the nice and quiet carb makes a very slight hissing sound. The other does not. Is something wrong with one of them? They both have the same jetting and such, and have the same idle and mix adjustment.

Mix set at 1 1/2 out from closed, speeds set at 3/8 after contact and reset timing to 5 BTDC

ANY ideas?

Edited November 3, 2010 by Powerhouse

[moose]

Sounds like they need to be balanced. Quiet one might not be open at idle.

[Powerhouse]

I adjusted them about 5 times so far...always comes to the same point.

Last night I took the speed screws completely out. Checked the carbs to make sure the links are all moving correctly. I disconnected the linkage and checked some more. I put the speed screws back in and turned them in so they just touched the base. I then adjusted the mix screws, seemed best at 1.5 turns out from closed. I then turned the speed screws the exact same amount...about 3/8's of a turn so it ran at 475 rpm. Set timing at 5 advanced.

Is that how to tune them?

Am I missing something?

[TodFitch]

I adjusted them about 5 times so far...always comes to the same point.

Last night I took the speed screws completely out. Checked the carbs to make sure the links are all moving correctly. I disconnected the linkage and checked some more. I put the speed screws back in and turned them in so they just touched the base. I then adjusted the mix screws, seemed best at 1.5 turns out from closed. I then turned the speed screws the exact same amount...about 3/8's of a turn so it ran at 475 rpm. Set timing at 5 advanced.

Is that how to tune them?

Am I missing something?

I was under the impression that to tune carburetors you needed to use an air flow measuring tool attached to the top of the carb. But I've never had a car with multiple carburetors so what do I know....

[Don Coatney]

Balancing the carburetors has nothing to do with the idle mixture adjustment. It is all about adjusting the linkage to insure both butterflies are in sync. A flow meter is required to make this adjustment. Pictured is the one I use on my B&B carburetors. I believe blueskies used a similar tool and modified a tin can to make it work on his Carter-Webbers.

[martybose]

While I agree that a flow meter is ultimately the right way to balance them, if you have a set of small and pliable feeler gauges, you might try measuring the gap at the side of the throttle plates to see if they are open the same amount. The process you described worked fine for my Carter-Webers; maybe one of your carbs is binding slightly and consequently has a different starting point for the idle adjustment.

Marty

[Powerhouse]

Thanks all.

So balancing the carbs has to do with speed adjustment.

The idle mix doesn't need to be messed with as long as they are set.

The sucking sound while running should be the same on both carbs.

OK.

I bought the same Uni-Syn flow tool and am having a hard time getting it to seal on my carb base. I will try that can trick.

I have heard of using vacuum gauges to sync bike carbs...is that also possible with these engines?

[Don Coatney]

Thanks all.

So balancing the carbs has to do with speed adjustment.

Not speed adjustment. You need to insure that both throttle plates are opening at the same time. Balancing is linkage adjustment.

[Powerhouse]

OH...OK.

So adjust each carb by itself first...then connect linkage and adjust linkage so they open at the same time. I think I did that already. When I connect the linkage to the carbs they shouldn't change the way they run. If it does, the linkage needs adjusting.

[jd52cranbrook]

I got some plumbing reducers to get a good seal on the carbs where you don't have to remove the center post. Worked pretty well.

Edited August 31, 2010 by jd52cranbrook

[Powerhouse]

great idea...

[Merle Coggins]

I have heard of using vacuum gauges to sync bike carbs...is that also possible with these engines?

On a multi-carb motorcycle there are vacuum ports between the carb and the head. It's basically the same thing though. You adjust each carburetor throttle plate so that the vacuum is equal across all cylinders at idle. I've done it a few times and it's not too difficult, except for getting at the screws sometimes.

If you have vaccum ports under your carbs it would probably work. You wouldn't be able to use any ported vaccum connections on the carb unless they pull from the very bottom under the throttle plates.

Merle

[Powerhouse]

I wonder if the lowest port is usable...

[Don Coatney]

I am not sure about the lower port, but I believe your vacuum advance should be plugged into the port where I have the pointer pointing.

[Dodgeb4ya]

Here's the factory way the twin carters on the trucks are adjusted-pretty easy way to do it and it works.

Bob

Edited September 1, 2010 by Dodgeb4ya

[jd52cranbrook]

I could be way off base here. But I believe the above balances them at idle, and in theory linkage to both carbs are equally firm, or loose. The key is to balance them when the throttle is opened by the gas pedal linkage or simular.

[james49ply]

I have had to set multiple carbs on motorcycles, they have one carb per cylinder, no balance tubes between them. Book tells you to set the plates by vacuum reading then set the mixture. After experimenting with the set-up, I decided to add one more step, I checked the balance the carbs at 2500 rpm and they were not equal, rebalaced at 2500rpm and made a big difference in performance and fuel ecomomy. You could do that with the flow meters also, but you would need one for each carb. The reason I did it my way was that normal operation of the engine is at an rpm above idle, say 55mph and I belive that to have them balanced there would be much more benificial than at an idle. My dimes worth. (inflation).

[jd52cranbrook]

You can do it with one flow meter. As long as you find a way to keep the throttle steady, you could swap back n forth on the carbs. And your right, so much more important to be balanced above idle.

Let's not talk about inflation,

[blueskies]

Here's how I did mine. The secret to getting them dialed in was revealed with the secret decoder ring that came in the Ovaltine....

Pete

[Powerhouse]

Thanks all.

I took the rear carb off because I noticed it not closing all the way. Fault was a catchy spring. Fixed the prob...and checked out all points on the carb. It was clean and worked smoothly(off the engine). Re installed it...checked linkage it was off by a tiny bit. Fixed that by eye. It ran much more evenly.

But, since my car definitely hates me, it has started a lovely occasional stumble. After nearly taking the sledge to it...very nearly. I thought maybe something in the fuel line is clogged. So I removed and checked every point back to the electric pump...and then all the way to the tank. I took of the filter before the pump...a little bit of junk in there, came out when I tapped it on the table a few times. Put it all back. Still stumbling. I decided to go to bed. Got up early to check it out. Started up nice and strong...ran for about 2 minutes and started it's new stumbling act again. I revved it up to about 1500...seemed to have lost the stumble. I am thinking maybe too much fuel pressure? I have a carter electric pump...straight to the carbs...with a filter in between. Filter was replaced 2 days ago just as a precaution.

Fuel Pump - (Univ. In-Line Rotary Vane Type)

Part Number: NFP P4259

Attributes Fuel Pump Fitting Size : 1/4" NPSF

Fuel Pump Fitting Type : Rotary vane

Fuel Pump Gallons Per Hour : 72 gph

Fuel Pump Line Size : 3/8"

Fuel Pump Pressure Rating : 4 - 5.75

Edited September 1, 2010 by Powerhouse

[martybose]

My recollection was that they suggested 3 pounds of fuel pressure for these, and that's what my gauge at the fuel block shows I'm getting.

Marty

[Powerhouse]

maybe too much pressure? Fuel might be pouring over into the mixture. SO if I should be getting 3 psi..would it have to double for 2 carbs making it 6 psi?

I just read on another forum..."he recommends using an inexpensive adjustable pseudo-regulator (such as the Mr. Gasket--NOT SPECTRE) from your local auto parts store to drop the stock mechanical pump pressure to 3-1/2 psi. "

Edited September 1, 2010 by Powerhouse

[jd52cranbrook]

I would look elsewhere then pressure. It's not that much higher. My stock pumps puts out about the same, and even higher on my two carbs with no issue.

I would go back to basics, you've got a plethora of ideas on here that have you chasing your tail I believe. But it never hurts to put a regulator with gauge inline if you suspect the pressure. But I think you have other issues.

Stick to the basics, you will figure it out.

[littleman]

Just a thought,Langdon supplies these carbs with a bonnet type aircleaner. If that is what you're using you may be experiencing air restriction. I had to modify mine to allow more air flow, and I have noticed others with some interesting variations.

AL

[Powerhouse]

I put a fuel pressure gauge in between the carbs and filter. I noticed NO pressure. I followed it back to the electric pump. I then took of the large metal fuel filter in between the tank and elec pump and replaced it with a see thru plastic one of the same size. Still no pressure...it didn't even suck fuel into the filter. I followed the line back a bit more. Just in between the tank and filter the line is rubber joined to pipe. The connection was loose..I found that out by blowing in the tank...I then heard gas spray out at the connection. It must have loosened up. I tightened it...and got a whopping 2 psi. ??? That electric pump is rated at 4 -5.75psi. So I figured it must be a blocked line...nope. Tank clogged at fuel line? Nope. I turned on the electric pump again..and had my wife look at the gauge to tell me what it registerd when I blew in the filler neck. She said it went up to 4. So, i am guessing the pump is not working fully. I connected the mechanical pump in line....still the same reading...with or without the electric one on.

Any ideas?