770cfm Holley Too Rich? - Page 3 - Chevelle Tech
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post #31 of 46 (permalink) Old Sep 16th, 19, 9:22 PM
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Rod
 
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Re: 770cfm Holley Too Rich?

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Rick,
Something you might want to check. I just looked at a Holley Street Avenger for a customer that had hardly no miles on it but had been sitting. He wanted me to just make sure there wasnt any gummed up gas in it etc. When I was putting it back together I did my usual routine of spraying brake clean through all of the holes and darned if the hole that feeds vacuum to the power valve had not been drilled all the way through so the power valve was not getting any vacuum to close it That would definitely make it run rich. I got in touch with Holley and they said they had never heard of that but they did send me a new base plate. I attached two pictures showing the hole in the new plate and the missing hole in the old one. I would definitely pull the carb and at least take a look
Bill,
Bare with me. You showed them the picture of the missing hole, correct? (Got to love the modern age and being able to share pictures via email!) You said they had never "heard" of that before. I wonder if that's the pat answer they are supposed to give when presented with an obvious (courtesy of pictures) mistake on their part or whoever manufactures their carbs these days. They've made millions of carbs in their 60+ years and they've never missed a hole before??? Hard to believe!

Lesson: If your brand new carb has some running issues, GET familiar with where all the passages are supposed to be in that carb and check to make sure they are ALL THERE!
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post #32 of 46 (permalink) Old Sep 16th, 19, 9:38 PM
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Re: 770cfm Holley Too Rich?

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Originally Posted by Rmchevelle View Post
Bill,
You said they had never "heard" of that before.

I agree, should have said that was "tongue in cheek" I will have to say I have been fooling with Holley carbs since 1973 or so and have never seen it myself. Someone definitely screwed up in the manufacturing process. The top part of the hole was drilled and the anti-backfire check ball was there, they just never drilled it all the way through. Considering that this is almost certainly an automated procedure I cant believe that there are not others out there the same way



You just never know now days, that is why you have to check everything, especially if you have a problem.

Bill Koustenis
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post #33 of 46 (permalink) Old Sep 16th, 19, 9:40 PM
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Re: 770cfm Holley Too Rich?

Rick,
Have you pulled the carb yet to see if the power valve vacuum passage is drilled all the way through ? Shame on you if you dont.

Bill Koustenis
Advanced Automotive Machine
Waldorf Md


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post #34 of 46 (permalink) Old Sep 16th, 19, 10:08 PM Thread Starter
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Re: 770cfm Holley Too Rich?

Planning to do that Bill, base gaskets I ordered should be here Friday. I got the open type gasket because the Chevy manifold is a dual-plane with the cutout in the partition. I don't know if it's OK to reuse a base gasket, so figured better to get a new one.

Since I have 15 in. at idle, I guess the 6.5 Power Valve is correct.
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post #35 of 46 (permalink) Old Sep 18th, 19, 6:02 AM
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Re: 770cfm Holley Too Rich?

that is indeed a SA auto choke 770. I'd move down on the Pri main jet. try a 70 or 71.

You have a WBO2 hooked up?

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post #36 of 46 (permalink) Old Sep 18th, 19, 9:35 AM Thread Starter
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Re: 770cfm Holley Too Rich?

No, Tom, I don't have any way to measure the 02, just looking at the plugs (not very reliable) and the black, sooty tailpipes. Wish there was an inexpensive unit you could just temporarily put in the tailpipe. I'm going to check the float level today (Holley suggestion for rich running on their support page FAQ's); although, I suspect they are fine.
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post #37 of 46 (permalink) Old Sep 18th, 19, 10:12 AM
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Re: 770cfm Holley Too Rich?

I would use the Holley factory jetting as well but that will only change your cruise AFR a slight amount if at all. I feel like you're pulling fuel from somewhere else. Definitely verify float level. Has this carb ever been apart?

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post #38 of 46 (permalink) Old Sep 18th, 19, 11:15 AM Thread Starter
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Re: 770cfm Holley Too Rich?

No, hasn't been apart. It's as it came along with the ZZ427/480 crate engine, as far as I know. At first, I thought the jets needed changing, but now I'm thinking, between Chevy and Holley, it should be set up pretty well since it's for this engine (the 19172225 is the Chevy #). They originally came with 870's, but Chevy chenged them to 770's. I think Chevy did plenty of research and testing.
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post #39 of 46 (permalink) Old Sep 18th, 19, 12:16 PM
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Re: 770cfm Holley Too Rich?

Rick, that's good logic and I wish it were the case. Truth is Chevy has given very poor ignition and carb specs on crate engines since they started selling them. There is speculation that they're recommendations are for their safety during the warranty period. If you use their specs you'll be leaving a lot of power and driveability on the table.
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post #40 of 46 (permalink) Old Sep 18th, 19, 12:30 PM Thread Starter
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Re: 770cfm Holley Too Rich?

Thanks, Tom, I've heard that too, and it makes sense that they want a richer mixture, etc. to prevent issues. My base timing at 16*-18* is above their recommended 10*-12* with no problems and really quick starting.


Also, when I pull the carb. to verify that PV vacuum hole that BillK pictured, do you guys suggest the 5/16" Felpro #17847 gasket (for a little heat insulation) or the regular thin Felpro #1900? Both are open style; thought open would be better for my Chevy dual-plane with the center cutout. I ordered both along with the regular four-hole #1901 just to be safe.
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post #41 of 46 (permalink) Old Sep 18th, 19, 1:02 PM
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Re: 770cfm Holley Too Rich?

Rick, I had the exact same problem with my '67 427 holley 770 about 3 years ago. My eyes would burn in the garage just pulling it in and out. I believe the carb needed rebuilding but I had a 600 edlrebock laying around so I rebuilt that and 50% of the issues went away. Don't really notice any power difference. I then checked my fuel pressure and it was 11-12 lbs. Don't remember where I got that mechanical pump from but I changed out to one that puts out the standard 6 -7lbs and that got rid of almost all the remaining rich condition.

A side note for myself, I've tried to increase my initial timing like has been suggested in this thread, and many others, to solve issues here and there, but if I go more than 2 deg. higher than the 10 i'm usually set at it starts pinging something fierce, I must have something else off.
I'll have to do a little research on that.
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post #42 of 46 (permalink) Old Sep 18th, 19, 1:21 PM Thread Starter
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Re: 770cfm Holley Too Rich?

Thanks, Jim. Fuel pressure is a pretty steady 6psi. I did raise it from 5 when I first got the car; guage is at the carb. I've never had pinging or dieseling, just the occasional brief run-on at shut off that went away when I dropped the idle. Engine seems like 16*-18* just fine.
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post #43 of 46 (permalink) Old Sep 18th, 19, 4:32 PM
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Re: 770cfm Holley Too Rich?

If the car is running good overall, the carb can't be THAT screwed up. Some engines just stink more. I have to change my clothes after driving my car, and I have EFI and the thing tuned lean.

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post #44 of 46 (permalink) Old Sep 18th, 19, 7:20 PM Thread Starter
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Re: 770cfm Holley Too Rich?

Update: When I checked the primary fuel level, couldn't see the gas at all. Long story short, when I eventually took the bowl off, it seemed the needle might have been stuck (although, I would think the gas would have been pouring out). Can't say for sure. Took the carb. off and it does have the PV vacuum bleed hole.

While I had everything apart, I added secondary jet extensions and notched float. I left the same jets in there. Ended up using the thin Fel-pro gasket; I decided since it had a thin one on there, ran fine, and never had any boiling issues, I wouldn't mess with it. Buttoned everything up and set both fuel levels and road tested. Seems fine. I didn't notice the over-rich smell, but it could be I was just too tired after working on it all day. Needs a little more testing to be sure.
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post #45 of 46 (permalink) Old Sep 20th, 19, 12:37 AM
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I had a 770 SA on my old 383. Never got it to idle clean. It would gas you out of the garage. Spent forever getting my timing perfect. Didn’t work. Changed my power valve because my cam didn’t pull much vacuum. Didn’t work. Dialed in my idle mixture screws for highest vacuum and RPM. Didn’t work. Never got that carb to idle without making your eyes water. Ended up doing a rebuild on the engine for other reasons. Sold the street avenger and bought an AED Holley hp 750. Much much better. Great carb out of the box. When I talked to AED on the phone I was concerned with the old wives tale that street cars and automatics need a vacuum secondary. Guy on the phone told me that “unless you have a 300hp slug, mechanical secondaries are fine”. And he was right. Have never had this “bog” you hear of. Anyways, sorry I can’t tell you how to clean up your carb because I could not solve that puzzle either. I recommend a carb from AED or one from quick fuel. I also run no choke and have no starting issues in winter. I live in wa state so it’s not terribly cold either. One pump to the floor and it fires right up every time. Good luck!

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