Holley Carb - Hesitating and Running Rich

Status
Not open for further replies.
Jun 29, 2017
1
0
1
Hello,

I have an 82 Malibu Wagon, I'm 16 and this is my first car. I've only had for about 6 months. The guy I bought it from did a lot of work to it, but couldn't remember a lot of specs for it, so there are things I'm not sure of.

What I do know is this: it has a 350 bored over to about 355 (.030 over I think). High compression pistons (couldn't remember the brand or model) he said they are 11:1, and if I run less than 91 octane I get a lot of knocking so Im thinking the compression is quite high. Stock heads with port matching done, but didn't know the size of the heads. Edelbrock Performer RPM air gap intake with about a 1 inch spacer on top. He thinks it has a Comp cam, but know it was 505, not sure of duration etc or model, but solid lifters not roller or hydraulic. Holley 4bbl carb, I think he said its a 750, double pump mechanical secondaries, choke not hooked up.

When I first got it, he said it was running a bit rich to combat the knocking a bit. It ran and idled good, and did not hesitate when you stepped on it to open the secondaries.

Lately it seems to be running much richer, leaving spray on the driveway when idling. It has also started hesitating when you hit it hard from a stop, or step on it and open the secondaries. It hesitates to a point that it almost completely stalls, but if you let completely off the gas it will come back. Seems like once it gets really warm the hesitation lessens.

I am not good with carbs, they confuse me. Any suggestions on simple adjustments I can make to this to try and solve it? I was also thinking of replacing the carb with an Edelbrock to match the intake. This Holley, even though he said it was rebuilt, looks a bit rough.

Thanks,
Brad.
 

Longroof79

Rocket Powered Basset Hound
G-Body of the Month
Oct 14, 2008
12,156
9,762
113
Gainesville, Fl
Welcome aboard, Brad,
Looks like a cool first car, and a wagon no doubt. Good for you.
First off, I think a 750 DP is a bit too much carburetor for your engine. I've successfully been running a Holley 600 cfm vacuum secondary carb for almost 30 yrs. Yeah, I know it's a long time. It's been rebuilt a few times over the years and still runs great.
However, my engine is milder than yours with 9.1 compression, milder hydraulic cam.

I would suggest getting a good Holley manual to educate yourself. They're not difficult to work on.
It sounds like your carb is dumping gas. which could be the float level being too high...and/ or your needle and seat could have junk in it.

It also could be that this carb has had a rough life. I've heard good and bad about Edelbrock carbs. Some people love 'em...others, not so much.
Whatever you decide, don't go more than a 625-650 cfm. vacuum secondary, electric choke. I assume it's going to be a street driven car.

I would suggest doing some research online about different brand carbs.

You're going to have to post some pics of your wagon for us wagon lovers to see.
 
  • Agree
  • Like
Reactions: 2 users

vanrah

G-Body Guru
Apr 16, 2013
879
1,189
93
Near Afton, Wisconsin
Welcome aboard Brad; I don't have time tonight, but within the next couple of days I'll get back to ya with a couple of ideas that may help. First BUY a good Holley book, as they are the easiest carburetors to tune. And you will be able to make some improvements, but like Jack said your carb is a bit to big for your set up. Later Ole' Bob
 

Attachments

  • IMG_0382.JPG
    IMG_0382.JPG
    1.8 MB · Views: 437
  • IMG_0385.JPG
    IMG_0385.JPG
    1.8 MB · Views: 767
  • IMG_0378.JPG
    IMG_0378.JPG
    1.7 MB · Views: 434
  • IMG_0365.JPG
    IMG_0365.JPG
    1.6 MB · Views: 538
  • IMG_0163.JPG
    IMG_0163.JPG
    1.7 MB · Views: 607
  • Like
Reactions: 1 user

vanrah

G-Body Guru
Apr 16, 2013
879
1,189
93
Near Afton, Wisconsin
Greetings Brad & all; So lets see if I can help ya. First off with your compression & iron heads you will be near denotation often. So double check your timing & as you know 93 octane if you can get it. I would keep it around 37 total max & No vacuum advance. Now to the carb, it's not so much that you have too much CFM for the engine it's that your car is too heavy for a double pump style carb. And I'll bet that your rear gear is too tall also? Your engine has some similarities to the 1970 Lt1 350 inch 350-360-370 HP engines found in Vete's & Camaro's & they came with Holley 780 Vacuum secondary carbs. So did the 1967-69 Z-28 302 engines. So first I would replace the primary power valve as they are easily blown out with a back fire. And if they are blown your engine will be way rich under idle & part throttle. And since you're not sure of cam specs consider moving down to a 7.5 or 6.5 power valve. As for the secondary PV, put a plug in that hole as they tend to run inconsistent as fuel sloshes away from the opening under hard acceleration. Depending on witch book you read when blocking the rear PV you will have to step up the secondary jet sizes 6 to 10 sizes larger than the primary jets. I have found that 8 to 10 sizes work best. So consider size 71 primary jets & 79 or 80 secondary jets for starters. And if you decide to buy another carb, don't get a double pump unit as they dump WAY TOO much air into the engine way too fast & cause a BIG BOG. Exceptions, BIG engine, Light car & or a Tight gear. I'll try to attach a spec link to a stock Lt-1 Holley. Good luck Ole' Bob.
Ps: if you let it detonate too often you will blow away the top ring land, loose compression, start burning oil & you can say good by to HP!

http://www.c3vr.com/vrforums/original-lt1-holley-specs_message143346.html
 
  • Agree
Reactions: 1 users

MrSony

Geezer
Nov 15, 2014
6,793
6,678
113
Des Moines, Iowa
Id rebuild that holley 750, get it running good, sell it, then get a qjet for practically free and rebuild that. :D
Do a compression test. The PSI can tell you a lot about the engine and how it was built. As ypure 16, this is probably your only car so I won't suggest tearing into the engine to see what you have. Just run the highest octane you can afford, buy a gppd dial back timing light (usually the 100 dollar one at the parts store) and as said above see what the timing is at idle (as low as ypu can get it to idle with the adjustment screw) and what the timing advance maxes out at. Vacuum advance hose disconnected and plugged for testing of course.
 

pontiacgp

blank
Mar 31, 2006
29,270
20,391
113
Kitchener, Ontario
Welcome to the forum, if you are going to be using that car for a daily driver I'd sell that engine and get another engine that will do the job, it'll save you on gas money and gas mileage. The 750 carb is too big for that engine, even properly tuned, and does the engine have the egr working?
 
  • Agree
Reactions: 1 user

fleming442

Captain Tenneal
Dec 26, 2013
13,046
24,216
113
I've also run into a couple of situations where the cam is too much for the combination, and the only way to get it to idle is for it to be pig rich.
All of the above is good advice. I do think it will be fine for daily use if the combination is optimized. Might not get the best mileage, but would be a light to light killer!
 

TURNA

Rocket Powered Basset Hound
Jul 24, 2009
10,941
19,990
113
Socialist NY
Take the air cleaner off and see if there is any fuel dripping into the main body.

If there is you have a clogged or dirty needle and seat.

Very cheap and easy fix.

If no fuel is dripping then I would check/change your power valve.

Once it is running the way it was before re jet the carb.

All these things can be done cheap and easy.

Also when was the last time the spark plugs were changed?

Have you checked to see what your plugs look like or smell like?

One other thing to check is how is the choke disabled? Not wired? stuck open stuck closed?

Hook up the choke or safety wire it completely open for the time being until you get it straightened out.

I have run 750 double pumpers on street driven small blocks without issue.

One thing you should do before anything else is figure out what you have!!!

Post some pics!!!

holley9.jpg
 
  • Agree
  • Like
Reactions: 3 users

online170

G-Body Guru
Oct 28, 2010
726
319
63
I have run 750 double pumpers on street driven small blocks without issue.

Thank you!!!!

750cfm is just fine for that engine. I've run a 750 DP on very mild 350s, and they work great. Street driven.
 
  • Like
Reactions: 1 user

MrSony

Geezer
Nov 15, 2014
6,793
6,678
113
Des Moines, Iowa
Thank you!!!!

750cfm is just fine for that engine. I've run a 750 DP on very mild 350s, and they work great. Street driven.
No one was really saying that one couldn't, it's that for a 400ish hp sbc that will probably never (on purpose) see over 6000 rpm, 650 is plenty.
 
Status
Not open for further replies.

GBodyForum is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to amazon.com. Amazon, the Amazon logo, AmazonSupply, and the AmazonSupply logo are trademarks of Amazon.com, Inc. or its affiliates.

Please support GBodyForum Sponsors

Classic Truck Consoles Dixie Restoration Depot UMI Performance

Contact [email protected] for info on becoming a sponsor