Help! My Holley 4000 doesn't suck!

R

RPS

Junior Member
I have a 55 TBird that I've been trying to get back on the road for a while. I had the carb rebuilt before I put it away in the fall. Took it out on the road once and it was very weak and overheated. After some detective work I discovered that the secondaries weren't opening and the ignition was not advancing.
I was hoping to get some advice on what to do to troubleshoot this to avoid pulling the carb and sending it back to the rebuilder. Maybe it's not even the carb- what do I know? So here are the facts:
-The secondaries are definitely not opening. You can open them manually by hand and the motor roars to life.
-The ignition is not getting vacuum. I removed the end of the vacuum line at the distributor diaphragm and placed my finger over it while revving the engine. No suction.
-I replaced the power valve (1" circular thingy on the passenger side of the carb near the primaries) and the vacuum diaphragm at the back, passenger side of the carb. They were new with the rebuild but I had a spare kit and just wanted to eliminate potential easy solutions. The "old" diaphragm looked brand new, no punctures or tears. With the diaphragm inspection cover off you can manually manipulate the arm and the secondaries will open. Also when you rev the motor you can see the power valve in and out. With the power valve removed you can stick your finger over the hole and feel plenty of suction as the throttle opens.

So that's what I know. Any ideas? My guess is that there's a clogged passage in the carb that's not allowing suction to open the secondaries or advance the ignition. Is that crazy? Obviously if I was a mechanic I would have this solved already. Any help or suggestions with troubleshooting would be appreciated!

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It needs to go to a rebuilder if it didn't perform right to begin with, kinda hard to read your post, but thats what i got out of it.
Those things are difficult to rebuild properly and I'd hate to speculate on what is wrong with yours - I've done a few of them and they are odd ducks and have special challanges to get clean if there is years of fuel dried in them because many critical passages are at the lowest point. I've seen them so bad that the jets look like 2 lumps in the snow.
 
So is it right to assume that since the secondaries do not open and the distributor isn't receiving vacuum to advance, the carb needs to be rebuilt again? I don't see how it could be anything else.
 
I'd check out this video, particularly at 2 minutes in. In fact this is one in a series of four very informative videos on the Holley 4000. What appears to be a power valve is actually the "spark advance valve", maybe remove carb and see if the spark valve restrictor is in place. Also, the video is not exactly high-definition but try to see if your SAV looks like the one he is installing as compared to a power valve.

http://www.youtube.com/watch?v=VeelVBo6J_M
 
Was the carb working correctly when you first got it back from the rebuilder? Just wondering how many "good hours" you have had with the carb running on the engine. If you installed before the winter but never used it, call the rebuilder. If he is reputable and the one you want, he should want to make it right.
 
My guess is that the vacuum pot on the distributor is leaking. The vacuum measured at the carb source is much too low to "finger test" as the maximum available there is around 2"hg, not the regular manifold vacuum of around 18-20"hg. The vacuum provided by these carbs is a mixture of venturi vacuum and manifold vacuum and the "mixing " is controlled by passages within the carb and a valve on the front right side near the vacuum port. All pre-'57 Y blocks used these loadamatic distributors with ONLY manifold-venturi vacuum to provide the spark advance and as well, the carb and distributor must match to function correctly. There is NO provision for centrifugal advance. If the vacuum pot is leaking or ruptured, the engine will get absolutely NO spark advance , run like a dog as well as overheat due to retarded timing. I fixed my 54 Merc 256 with a Holley 390 CFM carb and a modified '57 distributor. Good luck : Bruce
 
'Bruce' has a good point, I have seen the old vacuum pots leak and even NOS ones so I avoid them.
You have to really 'hammer' a carb to get the secondaries to open when it is not under a load, like when you're working on it. I have never been able to actually see fuel dumping from the secondaries. So part of what you originally described as a 'problem' or 'concern' is normal.
I'd get a 'mighty-vac' and test the vacuum pot on the distr before tearing the carb back apart.

Edited thought: we are all wary of backfire thru carb causing the powervalve diaphram to rupture but if you think of it the vacuum pot would suffer the same fate wouldn't it? I bet it is more common than we thought.
 
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I hadn't guessed that a leak at the vacuum pot would cause the secondaries to not open as well. I guess I'll have to get a vacuum gauge and get some numbers for everyone.
also to answer the earlier question, it has never ran right since the carb was rebuilt.
 
RPS said:
I hadn't guessed that a leak at the vacuum pot would cause the secondaries to not open as well. I guess I'll have to get a vacuum gauge and get some numbers for everyone.
also to answer the earlier question, it has never ran right since the carb was rebuilt.
Click to expand...

No, a vacuum leak at the distr will retard the engine so it won't make any power.
The secondaries probably won't open if you are 'whacking' the throttle in your driveway, the engine really needs to be under a load before they'll operate proper. The secondaries might be trying to or are open while driving and with your timing retarded you can't tell.
This is just a good guess giving the rebuilder the benefit of doubt. A test with the mightyvac on thre vacuum pot will resolve it quick enough.
 
Finally got my hands on some tools and did some diagnostics on my situation. Threw a timing light on it and sure enough the timing isn't advancing at all under any throttle load. I put a vacuum gauge on the line going to the carb and it was drawing a maximum of about 2" when I whacked the throttle. I put a mighty-vac pump on the other end of that line to the distributor vacuum advance and it did not hold vacuum. Is it safe to assume that's my problem and I should replace the vacuum advance? If so, is there any place anyone would recommend to get one? I'm seeing a few NOS ones on ebay but I'm leery of a part that's been sitting on a shelf for 60 years.
 
any of the Tbird catalogue guys have rebuilt advances. I have sold roughly ten 55 nos advances with no complaints. Any of the rebuilders are happy to pay a premium for a nos advance, more than they are selling rebuilds.
 
another comment on the teapot carb setup you have. I had one for years on my 55 bird also with 6volt. I have to stress that these cars function better if driven more often as in at least once a week or more. Mainly because the fuel and its additive today will not last sitting in that carb. It is bound to run more poorly from non-use. Fuel stabilizer will help. But driving them more is best.
As said before you do probly have a vacuum canister issue.
You can go thru all the gyrations of upgrading to something else, but I can guarantee you can make it work WELL with more patience and driving it more often. Teapots and that dizzy get a bad rap. (even though I have to confess I no longer run them!)
 
I replaced the vacuum advance diaphragm and it seems to be running worse. Won't idle for more than a few seconds, stumbles hard coming off the idle circuit, etc. What do I need to re-adjust now that I have a working timing advance?
 
Does the engine idle okay with the vacuum advance disconnected? If so, then look at the breaker points first both for gap setting and contact face wear.
 
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