Vacumm Help with 3x1 Weber

[Anonymous]

Hey everyone, i got a question. The reason i signed up here at ford six performance is so you can help me answer some questions concerning my mustang. For starters, I have a 65 Ford Mustang with 200cid and a 3x1 weber kit as shown in the picture below.

At Normal Idling, I get a normal vacumm 20(in.hg), but when raising the rpm to 2000-3000, vacumm goes down to 15 or lower. Is that normal?

Also when driving this car, it hesitates/stalls, basically it doesn't want to 'go'. What are some solutions to this problem?

 

[66 Fastback]

That does seem odd that the vacuum drops. I assume you are saying that the vac drops while the engine is rved in the driveway and not on the highway. Does the linkage open all 3 carbs at once? or does it open the center carb and then the outboard carbs? Maybe the outboard carbs are openning too soon and causing it to stumble on acceleration.

Also, what is your timing doing when you rev the engine? What kind of distributor do you have?. Is it the vacuum only Load-a-Matic or is it a later distributor with centrifugal advance?
If the timing is off, you may feel a stumble that you mentioned.
Doug

 

[wallaka]

Vacuum always decreases when the throttle opens. The throttle blades make a seal that denies air to the engine, thus causing vacuum.

Anyways, it could be a variety of issues that cause hesitation. Timing is a definite cause, as well as a SCV problem, or carb problems. Even if the carbs are in perfect working order, a jet mismatch or float position can cause stumbling.

Nice motor, by the way.

 

[66 Fastback]

Vacuum always decreases when the throttle opens. The throttle blades make a seal that denies air to the engine, thus causing vacuum.

That is why I asked if it is in the driveway. Under no load, engines will generate more vac at higher rpm's because the throttle plates are barely open. But under load, the vac drops since the engine requires more air and fuel.

I guess I should have asked if you were reading the vacuum from a manifold source as opposed a ported source on the carb?
If it is a ported source, then yes, it would be normal for "ported" vacuum to fall as the plates are openned.
Doug

 

[Anonymous]

That does seem odd that the vacuum drops. I assume you are saying that the vac drops while the engine is rved in the driveway and not on the highway. Does the linkage open all 3 carbs at once? or does it open the center carb and then the outboard carbs? Maybe the outboard carbs are openning too soon and causing it to stumble on acceleration.

Also, what is your timing doing when you rev the engine? What kind of distributor do you have?. Is it the vacuum only Load-a-Matic or is it a later distributor with centrifugal advance?
If the timing is off, you may feel a stumble that you mentioned.
Doug

Yes, I am testing it in my garage. The linkage opens all 3 carbs at the same time.
-I have a stock distributor with vacuum advance, (thinking of getting mallor unilite mechanical advace)
-I have no problems with the timing because it runs perfect at idling.

guess I should have asked if you were reading the vacuum from a manifold source as opposed a ported source on the carb?
If it is a ported source, then yes, it would be normal for "ported" vacuum to fall as the plates are openned.

I was reading the vacuum from a manifold source. Is it normal that when you rev the car, vacuum drops? The reason i ask this question is when i'm driving on the street, i could only drive a slow and steady 30mph. When i try to acclerate, it hesitates(doesn't want to go any more)

 

[Hot 6t Falcon]

Nice motor.

What we've got here is the dreaded "tri-carb bog". The only solution is to yank the complete motor and ship it DIRECTLY to me!

But, short of that there are some cheap and easy fixes - and some fixes that'll cost a little of the green.

Which center carb and dist do you have?

1.) Free or cheap. This is CRITICAL. Convert the throttle linkage to a "progressive" linkage. That is so the center carb opens about 1/2 to 2/3 and then the end carbs start to open. Then all three hit Wide Open Throttle (WOT) at the same time.
In the picture, it looks like you have an Edelbrock or Offenhauser intake. It SHOULD have linkage that will do this by adjusting the slides on the rods. If the linkage is not the original Offy stuff, search for a picture of what it looks like, and duplicate it.

2.) Free or cheap. Test the distributor for vacuum advance. To test the advance, take the cap off, and then disconnect the vacuum hose at the carb. Suck on the carb end of the vacuum hose and watch if the advance plate inside the dist to see if it moves. If it does great!, if it does not - hmm, work to do.
Next take the vacuum hose off of the dist. vacuum can and put the other end back on the carb/manifold/where-ever it was, and start the engine. Does it suck? If not, have you got a mismatch of center carb and dist? Early dists used "ported" vacuum. If there's anything wrong with your distributor, jump to #5.

3.) Free or cheap. Get a 3 foot or so length of rubber tubing. Put one end in your ear and the other end to possible leak areas. With the engine idling listen around the carb bases and where the o-rings hold the aluminum carb to the cast iron manifold. Where-ever you hear a hissing you have a vacuum leak.
Also stick the tube down all three carb and compare the "hiss". The center carb should be much louder. The two ends should be mostly silent.
Even from this great distance, I am suspicious of the o-ring seals between the adapter and the cast log.

4.) Free or cheap. Check the timing. If you don't have a timing light, I'd strongly suggest buying yourself one for Christmas. I'd reccommend the type with the knob on the back to "Zero" out the timing.

You need at least 12 degrees initial advance (BTDC) set with the vacuum hose disconnected from the distributor and plugged with a golf tee. Don't forget to reconnect the vacuum hose when it is all set. Your engine will idle nicely wilth the advance so far off that the only thing it'll do when you step on the gas pedal, is die.

What Doug was telling you about the timing, was that you need to leave the timing light hooked up when you hook up the vacuum hose to see if the spark jumps WAY up. (You can use the knob to zero it, and read the total advance.) Then disconnect the hose again, and with the light still hooked up, rev the engine to see if the mechanical advance is working correctly. The advance should again increase as you increase the revs. (Again, you can use the knob to zero it, and read the total advance.)

I once had a v/8 Pontiac with 3 twos. It ran like crap with the stock distributor. Yup, the dreaded "tri-carb bog". An old fart showed me the solution. It was to leave the vacuum advance disconnected and recurve the inside the distributor's mechanical advance. Do a search on the forum and read the articles on recurving the DS II. (hmmm... now I'm the old fart)

5.) Some money. GET RID OF THE STOCK DISTRIBUTOR! If you like new high tech, get FSPP DUI electronic distributor. I'm told it works much better than the Ford DuraSpark II (DSII) electronic distributor. The DSII will be head, shoulders and stepladder better than your stock distributor, so the DUI is stellar.
The DSII can be got at virtually any junk yard - do get ALL of the wiring and associated parts with it. (Cap, plug wires, ign module, coil, wiring harness between the coil and the module and the dist.) You can also get a new/rebuilt at virtually any parts store. The DS II uses manifold vacuum. The DUI can be had at FSSP (ad at the bottom of each thread) You mention a Mallory Unilite w/o vacuum. That is a good solution too, but IIRC it still has points. IMHO, go electronic.

6. ) Go back to the first paragraph and just ship the whole works to me - actually it would be best if you just dropped off the whole car in my driveway and left the title on the dash and the keys in the switch.

PS welcome to the Ford SIX Forum.

 

[66 Fastback]

Stomping on the gas while driving will drop the engine vacuum. You have opened the intake manifold to the atmosphere, and the only restriction now is the carb venturis.

In the driveway, a quick blip of the gas will open the throttle and momentarily drop engine vacuum. The thing is that no one runs their engine at anything near wide open throttle while the car is in the driveway exceeding the redline rpm's of the engine. However, if you open the throttle slowly and slightly, the engine rpms will increase and since it is under no load, the throttle is still nearly closed and choking air flow into the manifold. Engine vac will increase in this scenario. Sorry for any confusion I caused.

I don't have experience with the Offy tri-power setup, but the multiple carb setups that I have had used a progressive linkage setup, meaning that one carb provides the control until say half throttle when the other carbs start openining. If all 3 carbs open together synchronously througout the full range of throttle, it seems to me it could easily cause a big bog in power off idle. You'll have to get some feedback from some of the other folks that have run the tri-power setup.

Lastly, if the ignition timing at idle is good, that does not mean that the timing at any other point along the engine rpm / load map is optimum.
If your vacuum cannister is not working, you could be setting the static timing to give a good idle, but as the rpm's increase, the timing may not be advancing and it will result in a driveability problem. Try hooking a hose to the vacuum can and either use a vacuum pump or suck on it and see if it is holding vacuum. Then do it with the engine running and use your timing light to see if the ignition timing advances.
Doug

 

[66 Fastback]

I guess I was typing when Dennis answered. Basically, do what Dennis said.
Doug

 

[Mercury Mike]

When you use a DUI system, do you have to change carbs from the 1100 w/ SCV? Or can you still use it? And at that point, where does all the vacuum hook up?

 

[jahearne]

DUI works fine with a 1100 SCV carb. I hooked mine up to manifold vacuum port just below the carb.

 

[Mercury Mike]

I have an automatic tranny. Can I tee off the vacuum with a fitting to the same intake port as my modulator valve is currently hooked up to? And at that point, do I just block off the vacuum port in the carburetor? I was thinking about putting a permanent vacuum gauge there, with a hard steel line out to the gauge. I think it would look cool coming off of the carb.

 

[Anonymous]

Nice motor.

Which center carb and dist do you have?

I have a Weber 34 ICH-Manual Choke and stock dizzy.
I'll try out your suggestions, i'll post back for good or bad news.
Thanks Again!

 

[Anonymous]

okay.. i installed a mallory unilite 4563001 dist, mechanical advance.. now i feel the power...

What's the difference between progressive and just make all three carbs opening at the same time.. i tried both, no difference once so ever..

Before the car could go on the street, i added a high stall torque converter because my car dies every time i put it in gear, then now when it doesn't die, it dies when applied sudden accleration, then i took out my 264 camshaft and added stock again, now it works but to a limit... At this time, everytime i put the gear to drive and acclerate, i hear like a 'clicking' sound some where at the end of the engine, or transmission area. This doesn't happen when in reverse.. any suggestions?

 

[HighVolkage]

okay.. i installed a mallory unilite 4563001 dist, mechanical advance.. now i feel the power...

What's the difference between progressive and just make all three carbs opening at the same time.. i tried both, no difference once so ever..

progressive runs only off the middle until you push the throttle to a certain point, kicking in the outer 2 carbs. basically the advantage is in gas mileage because at cruise speed your are using 1/3 of the gas

i'm running progressive on my 200 right now

 

[ludwig]

At this time, everytime i put the gear to drive and acclerate, i hear like a 'clicking' sound some where at the end of the engine, or transmission area. This doesn't happen when in reverse.. any suggestions?

You may be running the center carb too lean or your timing is too far advanced. Both of these will cause ping. Back off the timing a touch meaning, move the vaccum can away from the block a slight amount, then accelerate. This will reduce or eliminate the ping. If it only reduces it, back it off a little more until the ping goes away.

As for running all three carbs at once, the problem is that you don't have enough intake velocity yet to suck the air through all three throats efficiently at low speed. That is why a four barrel, especially a quadrajet, comes on gradually from two to all four barrels and why you need a progressive linkage for your 3-1. Furthermore, if you have an operable choke, you only need to choke the center carb, which is all you need at idle anyway.

 

[Anonymous]

I agree with what everyone is saying. I have basially the same set up as you, even the Mallory Dist. You definitely want to run a progressive linkage, and only run off the center one for lower RPM's.

Bill

 

[63Falcon200]

I've got pics of a progressive on my web site.. they might help you...

I run of the center carb until 1/2 throttle and the other two open...

I've also got the front and rear carbs idle screws almost all the way in...
This allows the motor to see the center carb only.. the front and rear carbs seep to compensate for the air getting by the plates of the two...

I run alot timing... as well...

 

[66 Fastback]

In order to get the drivability issues resolved, you might want to disconnect the outer carbs and run on the center carb only. Screw in the idle fuel mixture to shut off the fuel on the outer carbs and also make sure that the throttle plates are fully closed on those carbs. Once the car is running correctly on the center carb, then you can reconnect the outer carbs and start tuning for more power. Simplify the problem and tackle one problem at a time.
Doug

 

[63Falcon200]

Good point Doug..

I made plates and did as you mentioned, to break in the motor and make sure the all was working...

I'll get a bog with mine if I'm at the track and the motor is not warm enough.. But thats the only time....

Also make sure the plates(front and rear) are not being held open by the linkage or a throttle stop screw..
Air will get by the front and rear carbs.. thats the way stock ones are set-up..

If you want to run all three at once, your always gonna have a tip-in bog.. Too much air at once and the carbs are not putting enough fuel (do to the lower vacuum. low RPM) When you have the motor reved up (full throttle) the motor is pulling in the air and fuel ... In theearly 90's FORD tried to use a big oval shaped Throttle Body, the problem was the tip-in, it was hard to match the throttle position to fuel.. (good for wide open throttle and thats it)

If you want to know how carbs work
Take a look at this web site: I just found it.. read the WIKIPEDIA part..

http://www.answers.com/topic/carburetor