RedLeader289

iTrader: (2)

Ok, for anyone whose been following this thread: https://www.thirdgen.org/forums/tech...ing-still.html

I've moved to the carburetor forum because it is now totally a carburetor issue.

Holley 750 DP, mechanical secondaries, front nozzle is a 28 and back is a 31.

I recently replaced my accelerator pump diaphragms (primary and secondary). The secondary one was actually still ok but since I had the carb off and the part was 10 bucks I thought "why not?".

Before replacing the diaphragms I got no fuel to the primary nozzle, causing a momentary hesitation when you did anything more than ease onto the gas. Secondary worked great.

After replacing the diaphragms I get fuel to the primary nozzle (verified by taking it off and watching it come up) but it won't squirt out. Again - secondaries work totally fine still.

I made sure the nozzle was clean, it was. When the primaries engage fuel will dribble out of the nozzle and some will leak around the nozzle base.

I took the nozzle from the secondaries and put it on the primaries...SAME THING. which makes no sense to me. But, it proved my nozzle, etc was ok.

I moved the linkage within it's entire range(the little spring and nut) and played with the cam positions - no difference.

The ONLY way that I can get fuel to squirt out of the primary nozzle is if I take my finger and press really quick onto the pump lever itself, and that produces a weak stream.

Any ideas?? I've been chasing this gremlin for a while now, it hasn't always done this.

Would a bad check valve in the accelerator pump cause this issue? I hate to just throw money at it not knowing what the problem is.

thanks,

RedLeader289

ASE doc

Yes, a bad check valve might cause just that, although you say you get a shot of fuel with the nozzle removed? The Holley uses the rubber one way valve that I've never been crazy about. The earlier models used a retained ball. Do you have the discharge check valve in place? It's a little plug with a pencil shaped tip that fits inside the discharge port, under the nozzle block. It should be brass?

Are you getting no discharge from both pumps or just the primary?

RedLeader289

iTrader: (2)

Ok, yeah, that umbrella shaped deal is a little strange. But it looked just like the one on the secondaries so for all I could tell it was fine(but maybe not?). Yes, the discharge check valve is in place and is brass (I was careful not to tip the carb over...since when you do that small things tend to fall out lol). Yes, I get a shot of fuel with the nozzle removed, and it appears to be just as 'robust' as the one that comes up out of the secondaries.

This is just in the primary, the secondary pump works perfectly. And when I swap the secondary nozzle onto the primary I get the same results, a little dribble (if anything) with leakage around the base.

I just realized that the tiny gasket around the base of the nozzle is the only thing I reused when I checked with the secondary nozzle. . . by visual inspection it seemed to be fine. But if it were bad I suppose that would cause the loss in pressure/leakage around the base...maybe. You think?

I really appreciate the help/brainstorming.

87v6Bird

iTrader: (1)

Are the gaskets between the metering block/carb body and fuel bowl/metering block ok? A leak there would keep fuel from making it to the nozzle.

Edit: Looks like you had the same though while I was typing.

RedLeader289

iTrader: (2)

Checking gaskets is currently top on my list. It just so happens there's a big swap meet coming up the weekend after this one so I should be able to pick up a bunch of carb parts for cheap there.

Damon

There's gaskets top and bottom on the squirter nozzle (different style gaskets- wafer-thin paper gasket under the nozzle, thicker (sometimes metal-core) gasket under the screw head).

Do you have a proper retaining screw holding the nozzle in place? They're not hardware store screws.

Check valve (needle or ball+weight system) under the squirter retaining screw- possibly, as mentioned by others above.

Orange check valve "umbrella" in the bottom of the fuel bowl also a potential suspect. If it looks "potato chipped" (wavy), it's definitely toast. Even if it looks good it could not be installed properly. The little "tail" that holds it in place in the bottom of the fuel bowl should stick straight up through the bottom of the fuel bowl. And it's got a little "notch" or "detent" on that tail so when it's pulled up through the proper amount it sorta "clips in". It must be PULLED into place by this tail to install, not PUSHED in place by the flat umbrella side. This is a little difficult to describe over the internet. Hope that makes sense.

The thing that makes me think it's up by the nozzle itself is that you said it gets fuel up that far without the squirter installed, but with it installed it just kinda oozes out all over. WHICH IT SHOULD NOT DO. The ONLY place fuel should be able to come out, even under diaphragm pressure, is the squirter nozzles. The rest of the accelerator pump circuit should be sealed up tight as a drum.

RedLeader289

iTrader: (2)

Thanks! Yeah, I didn't get a chance to check it out last night, hopefully will get to it tonight. It's all the stock hardware (screws and gaskets) on the carb so yeah(no hardware store stuff), and I'm aware of both gaskets (the one on top makes a nice habit of staying on the screw, so far I've fished the bottom one OUT of the carb about 3 times). If I get to it tonight I'll update. My current plan is to take EVERYTHING (both gaskets, screw, nozzle) off the secondary and put on the primary. If that still doesn't work then at least I know it's not the squirter. and I'll put the primary on the secondary(just to prove to myself that it works).

ASE doc

The nozzle and both gaskets, while critical to a good squirt and no leaks, are above the check valve. Unless you left them out altogether, they shouldn't cause the low volume pump discharge you're getting now. I would pull the front bowl and D&I that pump. Make sure the diaphram went in right and there's no interference.

I remember there is a pretty decent shot of fuel up to the nozzle, you said you got a dribble with the pri nozzle off. I'm thinking you're just not getting enough of a shot. I think it's worth looking at. Nice thing about the Holley is it's comparatively easy to D&A.

If you notice, the secondary pump is larger volume(deeper cavity) than the primary. It will produce a bigger squirt.

RedLeader289

iTrader: (2)

I think we may have had a miscommunication, I get a dribble out of the nozzle itself. With the primary nozzle off I get a decent shot. But, regardless what you're saying is still worth looking at.

Just for my own knowledge - are you sure about the secondary pump being larger? I know the nozzle is but my understanding was that Holley made two sizes of pumps, 30cc and 50cc. By the diaphragms that I replaced both the primary and the secondary appear to be the same size (30cc) as they took the same diaphragm. (and had the same covers, etc.)

again - thanks for all the input guys, this is why I love this forum!

Damon

Yeah, 30 and 50cc are your only acc pump sizes on a Holley.

For clarity, here is the path the fuel takes through the accelerator pump system:

1. Past one-way check valve into acc pump
2. Accelerator pump cavity/diaphragm
3. Through passage in the bottom of the fuel bowl straight back toward the body of the carb
4. Through hole in bowl gasket
5. Into metering block down near the bottom right corner
6. Up and towards the center of the metering block at about a 45* angle
7. Straight back out the back of the metering block near the top of the power valve cavity
8. Through the metering block gasket
9. Into the main body of the carb, still traveling horizontally
10. 90* turn up to the second one-way valve (needle valve or ball & weight design)
11. Into accelerator pump squirter and then sprays out the holes into the venturis

As you can see, there's plenty of places things can go pear-shaped on you and produce a weak pump shot.

RedLeader289

iTrader: (2)

Thanks!

Small update - the nozzle gaskets are fine. I realized that gas is just barely dribbling out of the pri. nozzle and running down it, making it appear that it was coming out at the gasket.

All but confirmed the umbrella valve is bad, didn't get to take it apart this weekend (because taking it apart to get it out means having to buy gaskets to replace the 6 year old paper ones that are on it). With both nozzles off the secondaries will shoot fuel straight up and out of the carb but the primaries just push it up slowly and let it roll over. So I have a pressure loss, only logical place that could happen is the umbrella valve.

Anyhow, I'll update when I get it apart, swap meet is this weekend so that's where I plan to get a deal on some gaskets.

ASE doc

I apologize for poor information. After checking myself, I recognize that the larger accelerator pump(s) are only used on higher demand applications of the 4500.

The issue you're having sounds like it pretty much has to be a sealing issue in the check valve. It makes a decent shot with no pressure on it, nozzles removed. Then, with the nozzles in place, pressure demand on the pump, the shot goes away. That sounds like a pump that can't support pressure because of a poor sealing check valve. I would start by rechecking the assembly. Look for any distortion in the check valve.

I've been concerned about the effect of increasing alcohol content in pump fuel on rubber carb parts, it seems to cause premature failure. We encourage our high performance carbed vehicle owners here to run non-ethanol premium as much as possible. There are still a couple of stations out in the rural areas that sell it.

I think you said you've already verified no restriction in the nozzles or the passage through the nozzle screw. With the unit apart, pay careful attention to the circuit leading from the pump to the nozzle. Be sure you have the right gasket between the metering block and body, that there is no chance of leakage from the pump circuit.

RedLeader289

iTrader: (2)

Will do, thanks.

Yeah, what you're saying about alchohol content is really starting to click. It's getting harder and harder to find good fuel in the city.

RWB____s

Have you ever had the check valve out of the carb before? If so when you put it back in did you make sure it was installed right side up? I ask this because you mentioned that you had to dig the gasket for the squirter out a few times. You may have some left over gasket material wedged down in the squirter passage that was missed. If you are going to get new gaskets for the carb, why not just tear the whole carb down and update all the gaskets. Also blow out all the passages in the carb with compressed air also do the metering blocks, the main body and check to be sure that the holes in the float bowl that supply fuel from the accelerator pumps to the squirters are clear also. Good Luck

RedLeader289

iTrader: (2)

Nope, but yeah that's what I plan to do, since most of the gaskets have to come off anyhow to get the umbrella check valve out, might as well. Won't hurt to have all alchohol resistant ones put in. Thanks

RedLeader289

iTrader: (2)

Update and good news: Took the carb off yesterday to investigate the check valves. The primary one was wavy and upon pulling it out I found some cracks/brittleness (shot), the secondary one was still good but broke when I removed it, so it had to be on it's way out.

I'll pick some up at the swap meet this weekend.

What really made my day is that when I took the carb apart I was expecting cheap brown paper gaskets, that would tear and require me to buy a complete rebuild kit, but much to my surprise I have the newer blue gaskets which are not only alchohol resistant but are also stronger and didn't tear! (this carb is from like, '07, I'm not sure when they came out with the blue gaskets) I put them in ziplocs to keep them from drying out(just a precaution) but they look to be in really good shape.

So, hopefully by Monday I'll be able to post the long awaited "IT'S FIXED!" message.

Damon

You're on the road to Wellsville, I think.

RedLeader289

iTrader: (2)

Alright, went to the swap meet saturday and scored a good deal on a pair of umbrella valves (as well as about 50 various small gaskets/spacers/etc that came with them). Literally the only two valves I saw in the entire meet, crazy.

Installed them and put the carb back together. Put it on the engine and.....nothing. The little voice inside my head then proceeded to go postal while I took the carb back off.

Upon further inspection I found out that the needle valve under the primary squirter was stuck, no idea how, but it was (hadn't been previously), so I took my trusty can of WD-40 and blew out each passage leading up to it and eventually got the valve to unseat and function properly. Bench tested the carb before putting it on(should have done it the first time) and I finally had a good shot of gas to the primaries!

Put the carb back on and the hesitation was still there...just as bad, almost as if I'd done NOTHING. So, I took a break, took the dog on a walk and thought about it. When I came back I put the secondary nozzle on the primary and vice versa (primary originally was a 28 and the secondary a 31). Better. Alot better. Almost not noticeable better.

So, my plan is to eventually step the primary up to a 34 and put a 35 on the secondary and call it good. I put some cleaner in the tank and filled it up this morning, plan to drive it throughout the week to get good fuel circulated through and clean everything out.

So, apparently my problem was (all at once, mind you):
1. Bad diaphragms
2. Bad umbrella check valves
3. undersized squirter

The squirter is what really baffles me, because once upon a time it was all working just fine. So, thank you all for your help and for tuning in....if anything goes south again I'll update!

RedLeader289

iTrader: (2)

Also, bought this at the swap meet, was told it was for a double pumper with mechanical secondaries...it's not. If anyone has a vacuum secondary carb (I think that's what a 3310 is?) it's a really nice piece. This is me selling it now btw.

http://www.ebay.com/itm/291593197130...9#ht_63wt_1362

RWB____s

you should not have to go that big on the squirter size. I run .028 on both primary and secondary. What pump cams are you using on both, also how is the pump shot on the secondary side after you swapped squirters?

RedLeader289

iTrader: (2)

Oh I totally agree, the 28 should work on the front. Like I said, this car was doing just fine (and by fine I mean running like a bat outta. . . .) until a month or two ago when I took it out of storage, then all kinds of stuff went haywire.

It's got the pink cams on both sides, in position 1. When I swapped to position 2 it made no difference, so I didn't even bother with position 3.

Honestly, the 28 looks like it's working just fine on the secondaries, but that's just eyeballing it. It looks the same as it did when it was on the primary.

RedLeader289

iTrader: (2)

Why do the yankees always win? Because everyone is too busy staring at the pinstripes.

Yesterday my car wouldn't start, just crank and crank and crank. Which I automatically knew as a blown ICM (yeah, that part that I just replaced about a month ago).

New ICM in and that pesky hesitation off idle? gone. gone gone gone.

My voltage meter now stays steady too (every since I put the other ICM in it developed a slight, random, tick which I wrote off as a 32 yr old gauge).

I also retimed it, because even though I had timed it just about a month ago and it was perfect, apparently because the ICM I put on a month ago was screwy to begin with the timing was off when I put the new one in, only a few degrees, but still - so now it's back in the right time.

Lastly, I put the 28 back on the primary and the 31 back on the secondary and everything seems to be just fine. throttle response is crisp, clean, and my car is back to being scary.
Granted, if all this hadn't happened I wouldn't have found my faulty check valve/diaphragms until they totally failed but yeah.

stupid ICM.

thanks for all the help, guys!

Damon

Glad you finally nailed it. Go have fun with the car.

RedLeader289

iTrader: (2)

Me too....so's my wallet, haha.

Daniel L Varner

You can shake gas with say 4 parts gas and 1 part water to take out the alcohol and just decant off the gas. My wifes cousin does this for his airplane that runs on car gas but the gaskets wont take alcohol. He uses those 5 gallon glass water cooler bottles