Holley 4150 issues

[Mark H.]

Hi all,

I have some issues on my Holley 4150 on my 327. I recently rebuilt it since it would only run (well) when on the gas hard. Even idling was very bad. So it seemed the secondaries were fine and the primaries and idle circuit had issues. (One note here: sometimes, after a long drive, the primaries seemed to come alive. But other times it didn't matter what the motor temp was.)

I rebuilt it with a Holley kit with new everything. It now idles perfect and revs fine while in the garage. All is fine I thought. Once on the road a new problem arose: unless the car is essentially idling down the road it runs as if were on 4 cylinders - very rough. A little throttle or a lot, same problem (as long as there is any load on the motor, the problem is there). So now it seems only the idle circuit is good. I checked all the stuff: float level is fine, throttle plates were OK as is, idle mixture screws backed out 1 1/4 gives 15" of Hg manifold vacuum, everything cleaned out, new gaskets/seals everywhere, etc

I checked the secondaries by putting a tie strap on the vacuum rod (going into the diaphragm) up close to the housing. After a short drive and giving it full throttle, back home I saw that the strap had not moved which suggest the vacuum advance is not working (during the rebuild I got lazy (on this one thing!) and didn't open the housing up to check the diaphragm, which I guess is at least one of the problems, but not all). Note: Motor was not fully up to temp, but I don't think this would prevent the secondaries from opening. At WOT, the secondaries open, regardless, I think.

I'll be taking it apart again to get the vacuum advance fixed but wanted to bounce it off everyone to get some thoughts. I'm afraid there's something other than just the advance's diaphragm (if in fact it is bad).

One final note: after my last rebuild years ago, I must have put the jets in wrong. I had the #73 jets in my primary metering block, and the #65 jets in the secondary block. I reversed them back (having said that, the car was running fine even in this wrong-jetting mode. Just an FYI).

Any thoughts are much appreciated.

Thanks,
Mark

[Mark H.]

Re: Holly 4150 issues

should have mentioned the Holley is off my 65 vette

[Duke W.]

Re: Holly 4150 issues

So I guess it's a 350 or 365 HP engine. Is it the correct number for that application?

What you refer to as "vacuum advance" is more likely the vacuum diaphragm that opens the secondary throttle plates. You should check it against specs with a vacuum pump before you take it apart, and make sure it has the correct spring.

The vacuum advance is mounted to the distributor and adds additional spark advance at low load.

Duke

[Timothy B.]

Re: Holly 4150 issues

Mark,

Are you sure the metering block gasket holes matched the old gaskets exactly. Plus, when you had it apart did you clean the small air bleed holes in the carburetor air horn. When you throttle up does the engine act rich or lean.

The Holley vacuum secondary will not open until higher Rpm's when air flow through the primary venturi creates a signal at the small diaphragm feed hole. This feed hole is located inside the passenger side primary venturi and also inside the secondary passenger side venturi.

I was just thinking you did install the metering blocks on the correct side of the carburetor.

[Mark H.]

Re: Holly 4150 issues

Mark,

Are you sure the metering block gasket holes matched the old gaskets exactly. Plus, when you had it apart did you clean the small air bleed holes in the carburetor air horn. When you throttle up does the engine act rich or lean.

The Holley vacuum secondary will not open until higher Rpm's when air flow through the primary venturi creates a signal at the small diaphragm feed hole. This feed hole is located inside the passenger side primary venturi and also inside the secondary passenger side venturi.

I was just thinking you did install the metering blocks on the correct side of the carburetor.

Hi Tim,

I did double check that the holes in the new gaskets lined up with the holes on the metering blocks (and on the old gaskets). They were identical. So far as those small holes near the top of the primary's (just below the choke plate), I did read about cleaning them out and I looked 10X with light and mag glass, and my carb does not have any holes up near the choke plate (or lower). Ditto in the secondaries. Go figure. When parked, at idle and when throttled up, its runs perfect. I believe unless the car is under load the secondary throttle plates will never open. Can't check in garage. That's why I used the zip tie on the rod going up to the secondary's vacuum diaphragm. It should have slid down when I went WOT on the road. It did not. Certainly a problem I'll fix since the secondaries aren't working. I was just wondering if them not working would effect the primaries. I thought not. Again, the car is very rough even at 1000 rpm with even a little throttle (on the road). I do have the right metering blocks in their locations. Seems to point to the diaphragm as at least one of the problems.

Thx much,
-Mark

[Timothy B.]

Re: Holly 4150 issues

Mark,

You will not see secondary operation until high engine RPM, even if the diaphragm leaked I don't think it would effect the primary operation. You should still see normal engine operation until higher RPM's and it will just lay down.

I would like to see a picture around the air horn where the air bleeds are supposed to be, is this a Holley 2818 carburetor.

Are all the primary and secondary ignition componits (points, wires, plugs and COIL) in good condition.

[Mark H.]

Re: Holly 4150 issues

Tim,

Your first paragraph aligns with what I was thinking (diaphragm shouldn't affect primaries). It is a 4150 carb (list # 2818-1). All electrical is fairly new other than the coil which is years old - good point, I'll check that.

Here's some photos that might help: Thanks

[Timothy B.]

Re: Holly 4150 issues

Mark,

The air bleeds are the brass restrictions left and right of the acellerator pump shooter, the outboard larger ones are the idle air bleeds. Make sure those little holes are not closed, IAB approx. .070 and MAB approx .028.

So you are saying the engine will free rev but not go under load. The problem could be somewhere else, if you have a spare ignition coil it may be a good idea to swap it and give it a try. Stay away from the reproduction coils..

[Mark H.]

Re: Holly 4150 issues

Thanks Tim. Now I know what those brass plugs are! I had read lots of Holley blogs where guys showed a tiny hole just above the venturi in the body of the carb throat adjacent to the shooter (mine has no such holes), that's the holes I thought you were referring to earlier.

All I did on the bleeds you mentioned was shoot carb cleaner down them, I didn't take any kind of needle to clean any junk out. I'm sure I have to be careful sticking anything down there so as to not mess the diameter up and get them out of shape. Maybe I need "round feeler gauges", or whatever they're called.

Yes the car runs beautiful in the garage at any rpm. Weird because under any, even very small, load everything goes south. Before I buy a $$$ coil, I may try a "decent" one from NAPA. If it solves the problem I'd then go buy a good/$$$ one.

Thanks for the advise, and I'll let you know.

Mark

[Stephen L.]

Re: Holly 4150 issues

A good tool to clean the small holes is a "welding/cutting torch" tip cleaner. It costs about $3 and probably available at Northern Tool or Harbor freight. It has multiple wire probes of various diameters.....

[Mike Z.]

Re: Holly 4150 issues

Had a similar application 65 365hp come into the shop, with similar issues. The carb had just been rebuilt by some Holley guru, so I hesitated to tear the carb completely down. After external adjustments made no affect, I decided to tear it completely down. first thing to check is that the surfaces are all flat.
These Holleys are bad about the main body wrapping-also check flatness of the jet plate and metering plate. Leakage between the main body and jet/metering plate can cause all kinds of issues.
Holley recommends on the power valve divide the vacuum by 2 and round up, so with your vac, you should probably run a 6.5 (factory) or 7.5 PV. The 65 jets are probably right for a baseline.
I found on this recently rebuilt carb that the builder had put a super light spring in the secondary diaphram and eliminated the little check ball. I installed the factory "natural" color spring and installed the check ball.
Then the last thing I did was make sure the accelerator cam was in #1 position and made immediate contact with the pump lever-Holley says .010", but I find immediate works smoother. Along with that adjustment was installing a #31-35 nozzle.
These changes solved both the off idle flatness and the terrible secondary engagement, or lack of. Hope some of these tips help-most of them are right out of Holley's book and the rest from experience.
I should note that total timing with vac connected, all in at say 3500, should be 44-46 degrees at sea level, + 1 degree/1k above. If you don't have the timing where it should be, the adjustments on the carb will not be optimal.

[Mark H.]

Re: Holly 4150 issues

Thanks Mike.

I think I'm OK on most of the stuff you mentioned:
-I've got the 6.5 PV in and 15" of vacuum, the same I had before all my issues, so it should be good. But per you "divide by 2" rule, I'd need a 7.5 PV. Will remember this but hold off for now since I've had a 6.5 in for years with no problem.
- Jets are in good shape and are the same ones that have been in for years (65 in primaries, 76 in secondaries)
-My secondary's diaphragm does have the same/stock spring that's been in for years. When operating the rod by hand, it moves up and down nicely with a slow/"dampened" motion. The check ball is in place with the right clearance between it and the "tang" that holds the ball in place
-Accelerator cam is in the #1 position. I'll check to see if there's any gap to the pump lever - I may have a little
-Quite sure my nozzle was a #31

If I tear it down again (99% chance) I'll check the flatness you mention. Never thought of that. It's been quite a while since I checked my advance. I know I had only a few degrees (non-vacuum) advance dialed in due to today's swill we call gas (in CA anyway). I'll check it at 3500 rpm.

My first plan is to try a new coil that Tim mentioned since that would be easy. If not that I may tearing into again pretty quick.

Thanks much,
Mark
-

[Mark H.]

Re: Holly 4150 issues

Will do. Need to be careful I'm sure about not reeming the holes open

[Mark H.]

Re: Holly 4150 issues

Hi everyone,

Just getting back to looking at my Holley 4150 issue again (haven't been in the garage for a week). Thanks for all the feedback. I am starting to think my off-idle, "out-of-the-garage" stumble is an electrical issue (recall the motor runs - idle and rev - fine in the garage but once on the road, even under the slightest load, it runs very rough as though it's running out of gas, hence the focus on the carb all this time.

Having said that before I tore into the electrical side of things I did look at the carb once again and noticed something that's obviously not right and wanted some feedback. I'm not sure it would be causing my problem, but it sure isn't right.

See the photo: there is a small torsion spring behind the accelerator-pump cam, that is just dangling around doing nothing. Obviously it's come loose from my handling. What's the purpose of this spring and how should it be attached (anyone have a pic or exploded view as to how it should be attached?).

Thanks, Mark

[Timothy B.]

Re: Holly 4150 issues

Mark,

The spring is supposed to be there and it's purpose is to return the throttle blades to a closed position against the idle speed screw. I can see one end but the other end has something like a half square end that clips over the throttle arm, I don't have a picture to show you but you will figure it out.