SOLVED: Still running poorly, still having vacuum issues

[Lazy JW]

....... I hooked back up the vac advance (to ported - sorry) and backed off the intial since the vacuum was advancing the inital now....

RED FLAG!

You must have the WRONG ported vacuum port The "ported vacuum" source should NOT be delivering vacuum at idle. It should read zero vacuum at idle, and then when you open the throttle slightly it will uncover the vacuum port and then deliver a vacuum signal about identical to manifold vacuum.

If you have inadvertantly connected to VENTURI vacuum it will give more vacuum advance the faster it revs. Not good.

This is very simple to test. Just hook up the gauge to the various vacuum ports and rev up the engine while reading the gauge.
Joe

 

[cfmustang]

Now I am confused, because there is only one vacuum port on the carb that I am aware of. I will take pictures and post them this evening for confirmation.

I was also wondering about the manifold vacuum as well. It was said that intake manifold vacuum would be strong at idle and drop under acceleration. I put a vac tee on the line that goes into the log with a brass plug and it had vacuum at idle and seemed to increase as the rpms went up as well.

Anyway, I took the car for a good long ride yesterday evening. My brother was over and verified the the new noise was a broken exhaust hanger (it looks like the one right behind the muffler), so I decided it would be safe to take the Mustang up to the Solon Cruise.

On the way there, it wasn't running too bad. Acceleration was ok (vac advance still removed) with only slight pinging under acceleration on the freeway. I even got it up to 75 for about 15 minutes and it seemed pretty good. All was right with the world, except for the clanging exhaust at rolling idle (little embarassing).

However, on the way back a hour or so later, acceleration seemed weaker. Then, about half way home I felt a surging under lite acceleration. Almost like a real bad miss or unsteady fuel flow. By the time I got off the freeway, of the line acceleration was almost gone and lite throttle off the line was almost bucking. When I got home, I pulled a couple of plugs and they were not black as I expected but looked ok, I guess. Kind of a rusty color. I will post pictures of those as well tonite.

Any ideas?

 

[cfmustang]

Here is my current setup:

The green is what I am assuming is the the ported line (notice that it is plugged by the snazzy golf tee).

The red is what I think is the manifold vacuum. It currently runs to the C-4 and has the capped vacuum tee (partially hidden and white) in it for the vacuum gauge.

I'm not sure what the Light blue line is, but it is running to the pvc valve.

The yellow is just not a vac port, but I was wondering if anyone who knows Webers knows what it is. It looks like an adjustment screw but is not mentioned in any info I have found anywhere. It looks like it might be some sort of primary throttle plate adjustment...

Here is a picture of my #3 plug. Normally, this is pretty sooty. The camera didn't get it very clearly and it looks more fouled than it is, but it is kind of a rust color. I picked #3 since that is normally one of the richers cylinders, right?

 

[addo]

Your hands are too clean! Go back to Mechanical 101.

The PCV-connected line is also manifold vacuum. It's probably a good place for the PCV as the slight extra turbulence through your adaptor will ensure even dispersion of any oil vapour.

Yes, the one below it is manifold vacuum proper, and a good place to plumb in brake boosters and tranny vacuum lines.

As to what vacuum the line your distributor is hooked to, represents - the easiest way sometimes is to look under the removed carb and see where it comes out. You'll probably note it as a hole approximately 1/32".

The yellow arrowed adjustment is your volume control screw. I believe that the screw below it regulates overall flow of the fuel/air mixture at idle, but the volume screw determines the ratio of that mix. It's a little different to the '70s Weber info I've got here but that's "reading between the lines" for a later carb like yours.

Given the nature of it's vacuum behaviour off-idle, I really do suspect valve timing to be an issue. What do you think, JW?

 

[cfmustang]

Actually, the yellow arrow is pointing to somehting else. The Idle mixture screw is the larger screw with the spring lower and to the left.

Everything I read about about Webers mention only two adjustment screws. The Air/Fuel mixture screw (the one lower and to the left of the yellow arrow) and the idle speed screw (not showing in this picture, it is hidden behind the electric choke housing). There is no screw to adjust the actual mixture ratio, that is done internally in the carb by the emulsion tubes. All the mixture screw does is let more or less of the pre-mixted air/fuel into the carb.

I have a Haynes manual for the whole Weber line, but it is not really that helpful. All I can look at is an exploded view of the carb and that it doesn't seem to show this screw.

 

[addo]

I thought the emulsion tubes worked off-idle. I believed the screw I called the volume control works on hot (throttle plates closed) idle only. My picture which shows and labels it, is too gritty to scan.

 

[cfmustang]

Hmmm. I think I may have found something. If you look at the bottom of page 8 here, it looks like it may be an additional ported vacuum source... I will have to see if it is tight. Might be another vac leak.

 

[gtm1086]

Hello Chris.

Have I got a deal for you. I have a Webber/Holley that has never been installed since it was rebuilt. I will send it to you to try out. If it fixes your running issues send me $100.00 for it. If it doesn't just box it up and ship it back to me. At least this way you will be able to rule out your carb as the problem.

Gary

 

[JOHN G]

Hi again from Cleveland-sorry to hear you're still not running proper. I'm still having issues as well, but not keeping from driving. Just out of curiosity, what are your vac readings? Things are starting to slow down around here a bit so if ya need me...

 

[Lazy JW]

....Given the nature of it's vacuum behaviour off-idle, I really do suspect valve timing to be an issue. What do you think, JW?

It does point in that direction, but until he can get some timing cranked in at idle to allow the throttle to be closed and build up some vacuum it is hard to tell for sure.

Have you tried verifying the timing curve at higher rpm's yet? There is really nothing to be gained except frustration until you know for sure where the timing curve limit is.
Joe

 

[wsa111]

Chris,******??????????
After 109 responses to your problem from the best in the world, I think is time to get professional help on a hands on situation.
If you want to bring your vehicle to south carolina or sidney austrailia or orlando florida we can get your problem fixed.
I don't want to come on negitive but now is the time to get a vehicle MRI to fix your problem.
This whole situation sounds like ronnie milsap or ray charles trying to do brain surgery.
The next post should be the final fix. Nuff said. William

 

[Anonymous]

Hi Chris,
I´m in your situation now and I have bin there once before. Unfortunately there was quite a time in between so I’d didn’t put 1 and 1 together fast enough. If I understand you right the cam and related parts has been added quite recently? If so, that’s exact like my situation.
My engine is shaking so bad that it couldn’t possibly be the carb that caused it alone. After revving it up a bit it’s nearly impossibly to let it down to idle. And when it stops the carb delivers a good load of fumes in the air.
After checking the fuel pressure (3.5psi) and timing (6deg) I was convinced that it was something fundamentally wrong. However, my neighbour, who has an Chevy Camaro Z-28, was impressed of the tones in the 2,5â€￾ single pipe system. And then it struck me. The valve springs are too weak. The pumped up lifters made the 260 deg dur cam a 300 deg it felt like. The overlap is increasing rapidly and that causes back pulses and that phenomena makes your vacuum gauge go nuts. When I locked at the label on the box for the valve springs I noticed that the installed pressure was 48 lbs @ 1.600â€￾. Stock springs are rated at 51-57 lbs @ 1.590â€￾. And another thing I did noticed was that the special valve retainers (E6TZ-6A536-A) (4.0 V6) increased the installation height with a couple of mm, well over 1.6â€￾ in my case. At the assembly moment I was adding a “kitâ€￾ so I didn’t gave it much thought. I can easily press down the valve with my thumb 5mm and that’s not good. Nothing less than 75 lbs should be considered says my dealer. Especially when high lift cams are used.

Perhaps that’s something you can check on your engine.

Good luck.

Regards

Jonny

 

[wsa111]

Jonny, Chris has all the right componets, & his quality of workmanship looks great.

I just think he needs help to make sure the distributor has the correct amount of advance, the camshaft is degreed in correctly, the balance has not spun on the crankshaft pulley.

Another member of the forum even offered another carb to try, that would be an easy way to see if conditions change.

Good luck Chris.

Please make the next post as problem solved. William

 

[cfmustang]

Sorry.

Been out of town for a few days.

I have one or two quick things I want to try today (re-test compression - correctly, verify that that screw is a additional vac port, check the float adjustment)...

Gary, I will pm you later today or tomorrow about taking you up on your suggestion. That may be just the ticket.

John, you will probably be hearing from me in the next few days as well. We'll see if we can both find a day where we can meet up and see if we can sort this out.

Jonny - Actually, most if the components are from the original rebuild a decade ago (cam, carb, exhaust, rocker assembly). The rebuild last year was hot-tanking the block, an over-bore, new pistons & rings, and a lot of head work. New oversized valves and associated parts including new double springs. My concern is that the garage did something fundimentally wrong in the reassembly. I have already found a bunch of little details that they ignored or did incorrectly that leave me to believe that they had no attention to detail. (i.e. How did they not notice the TDC mark on the damper was 10 degrees off?)

From there...if it is not worked out, I may have to go on hiatus for a few months to build up some funds and find a trustworthy garage. If it goes that far, I may cam down, replace the damper and timing set and have them re-verify everything.

 

[cfmustang]

Bah!

Tried re-testing compression and either I was doing it wrong, the gauge is broke or something is really wrong with the engine.

I pulled the plugs, disconnected the power to the coil and hooked up the gauge. I had my wife step on the gas (made sure the trottle was WOT) and crank the engine. I saw the compression step up to around 150 and then it would drop around 70. Up and down, up and down. Like the gauge's one way valve wasn't holding the pressure. Does that sound like the gauge or the head gasket? If the head gasket were that gone, could the car even run? Could I have screwed up the valve lash so they aren't closing all the way?

Still don't know what that screw is...

Pulled the top of the carb to try and adjust the float. Had no clue how to measure or adjust it. While I had the carb off, I replaced a stud to the adapter that had some bad threads. Buttoned it all back up and it runs the same. Actually, vacuum seemed a little lower than before. It was at 11 with a minor drop here and there. Now it was around 9 with a minor drop here and there.

Also noticed that if I put the timing light on the engine while at 900 RPM, it would sit at about 13 deg and then every few seconds it would drop to around 10 and then jump back to 13. What could possibly cause that?

 

[cfmustang]

One more thing:

I was going to try and map out the advance curve, but ran out of time. I will try and do that tomorrow after work.

Any suggestions on how to do it. I don't have a dial back light.

 

[Anonymous]

Any suggestions on how to do it. I don't have a dial back light.

You need a tach/dwell meter, and some tape.

Measure the circumference of the balancer and divide that by 360. Now you know how far apart the degrees are. Example: 6-1/2" balancer times 3.1416 = 20.42" circumference. divided by 360 = .0567" apart for each degree, or .56" per each 10 degrees.

Mark out 40 degrees worth on a piece of tape, with zero on TDC and just look at the degrees on the tape at each RPM.

 

[Anonymous]

"GENERAL INSTRUCTIONS:
Float level, in mm, typically refers to the distsance from the face of the carburetot top cover to the float. With the top cover held vertically (float pivot at the top) and the float tab resting against, but not depressing the spring loaded ball in the needle valve, measure between the face of the carburetor top cover to the bottom of the float"
Distanse = 41mm with brass floats (check for leaks). Distanse with plastic float = 35mm.

Good Luck

Regards

Jonny

 

[cfmustang]

Sorry about the lack of update... Been real busy.


Linc, that 6 1/2 inch damper you mentioned. Was that jut a example or what the damper should be? It is hard to get a measurement around the radiator and fan, but mine was measuring at about 6".

Does that sound right?

 

[Anonymous]

YOU WILL HAVE TO MEASURE THE CIRCUMFERENCE TO BE 100% CERTAIN, AND DIVIDE THAT BY 360.

(Dang Caps lock...)