Holley carb question

[Mike_The_Grad]

Hey everyone I know I'm in the right place, just not sure if I'm in the right section. Heres my question. I recently purchased a holley 1850-3 600 cfm vacuum secondary electric choke carb from craigslist. The carb is in superb shape. Guy was smart enough to empty the gas out before storing it. Got it for a steal of a deal. I plan on putting this carb on the 388 stroker motor I just finished building and installing in my 72 c10. I'm currently running a edelbrock 1406 that I've done all the calibrating on. But the edelbrock is tuned for my old 357 small block. I want to swap over to the holley. I hear good things about holleys. Dont know jack about them. The holley came to me with #63 jets, from what I understand they came stock with #66 jets. This carb was sitting on a 283 sbc in a 1961 Corvette. So theres quite a difference in just cubic inches already. I dont know where to start as far as just getting me in the ballpark to install the carb and start tuning it without it being completely wrong and having no reference or baseline to start from. So any input is appreciated. I can answer any and all questions about engine and internals. But heres a little info to get ya started.

388 stroker motor CR 10.6:1
4 bolt main high nickel block GM iron "041" heads with 2.02 valves and stainless exhaust valves. No bowl work or massaging as far as I know.
400 crank, 400 rods, forged trw pistons 0.060+
Hyd. Flat tappet cam from elgin industries grind#1028-p
0.437 lift in/exh.
224°dur.@0.050
84°overlap
107
109 lobe center
Aluminum full roller rockers 1.5 ratio
Edelbrock performer EPS dual plane manifold
D.u.i. HEI distributor
Hedman elite ultra duty headers into 3" true dual super 40 flowmasters.

[Accelo]

Carbs run on air flow and don't care what the displacement is. Maximum flow does differ depending on the CFM of the carb.
If getting the Air Fuel Ratio perfect was my goal I would purchase a Wideband Air Fuel Ratio Meter and install it. That or a pay for a dyno evaluation. Most everything else is a long process or testing trial by and error. I no longer have the patience for such.

[Mike_The_Grad]

Wideband sensor is definitely at the top of the list. This is my daily driver btw. And my only vehicle. Who else wouldnt love driving a hotrod everywhere everyday? Ha ha. Well, some may differ. It runs and drives down the road just fine. I'm trying to get it dialed in reasonably well. I am getting spark knock under heavy acceleration. After reading the last couple hours(its raining here right now.) I think I need to get timing figured out first then go on to carb tuning. But I have no baseline to go off of with the new holley carb. It came with smaller than stock jets to me. And I dont have any to change out for these ones. Any idea of a jet size to get me in the ballpark is good enough for me.

[MikeB]

That's an old skool 383 you have there with the 400 crank and rods! However that is a very strange cam with 224 duration @ .050", but only .437" valve lift. Typically you'd be looking at around .470" lift with that duration. Also, the 108 LSA makes for a lot of overlap! Looks like it's a 1950s-1960s design for a hot 283. Job #1 should be a modern cam with a wider LSA. And depending on your desired RPM range, maybe less duration.

As for carbs, I don't know if either one of them will like that cam, especially the 1406, because it doesn't have a secondary idle adjustment. You would have to crank the idle speed screw way in to get a decent idle, and that would uncover the transfer slots. That in turn would make for poor, even stumbling, off-idle throttle response.

[MikeB]

Originally Posted by Mike_The_Grad

Any idea of a jet size to get me in the ballpark is good enough for me.

Go back to stock jetting, and then make changes as required.

Just FYI, the 1850 came with a manual choke, so someone installed an electric choke kit.

Finally, with 10.6:1 compression and iron heads, I'd be surprised if you can get rid of the knocking without running premium gas or backing way off on total advance (initial + centrifugal).

[firedemon]

https://www.youtube.com/c/ThunderHead289 . this guy has a whole series for holly carbs and explanes it fairly well . fair warning he is a ford guy but a carb dont care what engine its on

[Mike_The_Grad]

I only run 91 octane in my truck. I dont even know the meaning of MPG's. Ha ha.
And yes the carb originally was manual choke. The guy I got it from did the choke conversion. He also had a plastic vacuum secondary cap put on the carb. And it has a green accelerator pump diaphragm.

The stroker motor I got from a guy for $500! It had been sitting in his garage for the past 15-20 years. He said it only had about 1500 miles on it.
And he built it to go fast in a straight line in his 70 nova. It came with a Pete jackson gear drive, a few msd 6a spark boxes, rev control, timing computer, mallory dual point dist., accel super stock points distributor, solid lifter cam was in the block, electric water pump(moroso), solid motor mounts, stud girdles, autometer tach, etc. Glyptol block, nodular iron main caps, all machine work was done proper, all in all cost me less than $1,000 to get it in the truck and running. Estimated at 350-380 Hp. And over 400 ft. Lbs of torque.
My guy at the local speed shop checked out everything and was surprised at the work done and the combination of parts. He said it was old school 80s-90s style that he used to do himself practically everyday at his own business. But it was all done right and no issues with components installed. So I built it and installed it. Runs good, starts right up. But havent been able to give it a good flogging yet. Mostly because taking it easy on the first 500 miles and the timing situation.

I agree with the advice about the initial timing setup. The engine will crank right over at 20° initial. Only way I knew that was because I set total at 34° while breaking in cam with vac. Adv. Plugged off. My vac. Adv. Can is limited down to provide 8° only. I made a limiting plate for it. My distributor was tuned for my other engine a 357 with 10.2:1 comp ratio. So I put a screw and nut in the distributor to limit the mech. Adv. I ground the side of the screw down to basically where the shaft of the screw was. Put it all back together and it made a difference in the spark knock happening, am able to get more throttle before it happens. I know I need to tune it more and limit it even more so I can bump my initial up some. My distributor was built with 22°mechanical adv. In it at 3000 rpms. I dont know what it's at now with the limit screw in it. It's been rain in pretty good around here for the past week and it's just now clearing up. I dont have a garage to work on it out of the rain so that's why it's not dialed in yet. That will change this weekend. Long holiday weekend hopefully with some clear weather and dry roads.

[Mike_The_Grad]

The truck idles in gear at about 700 rpms and about 12-13" Hg. On the vacuum gauge I have installed knee knocker style in the cab. It does have a slight hesitation just off idle. Accelerator pump arm is in hole closest to carb. Full manifold vacuum to dist adv. Can.

[Mike_The_Grad]

UPDATE: installed holley 1850-3 carb on the 388 stroker motor. It looked clean enough to eat off of so I threw it on there. BAD IDEA. Turned out all of the rubber internal components had withered away to nothing. Carb flooded like crazy couldnt tune it and a bad running engine because of it. Long story short, ended up throwing a rebuild kit at it, running 2 stages richer jets, and blocking off the power valve vacuum signal passage that previous owner failed to do when he installed an aftermarket power valve shield, also found out previous owner fried the electric coil spring by capping off the fresh air intake for the coil spring. Didnt know this at the beginning but quickly realized something wasnt right and why he had the choke housing clocked 180° passed the scale on the choke housing. So I wired the choke wide open to eliminate the tuning issues i was having. Not too bad to start in the morning as long as i hold it at 1500 rpms for about 2 minutes.

Also found the "sweet spot" with my distributor although not too happy about what it took to get there. Basically initial is set to around 8° distributor is bringing in around 22° mechanical and I have an adjustable vacuum advance limited to around 8° and screwed all the way in to let the full amount I limited it to to come in around 5-7" of vacuum. Seems to run fine. No noticeable knocking or pinging but I need to mess with the springs inside the distributor to pull some more torque out of this 388. It pulls nice and strong but slow and steady. I like that torquey hop you get when you blip the throttle from a dead stop. So I know it's in there somewhere.
On a side note, I'm gonna have to pull the freshly built th350 back out because its slipping in third gear. And the 2nd-3rd shifts are long and soft. I can feel it slipping in 3rd as I'm driving down the freeway. If I mash the pedal it shifts somewhat normal from 2nd to 3rd but then I also get this high pitch whine that sounds similar to a turbo spooling up. I have no detent kickdown either. I've tried adjusting the cable but no luck so far. So I think the third gear direct drive clutches are fried. I tried a low vacuum signal modulator it helped but not enough, fluid is full, looks dark, and doesnt smell burnt. I'm idling at about 12-13" Hg. And I adjusted modulator as far as i felt safe to do. But i have a feeling the damage is done. Hopefully the trans is salvageable and only needs the direct drive stuff to be replaced. Gonna have to wait about 2 weeks for the stars to align so i can have a secondary vehicle to drive and have all bills paid with hopefully enough cash to cover the repair. I'll let y'all know how it goes. Until then, i will have to take it easy with the $5 gallon this beautiful state of CA has to offer.

[MikeB]

I'd take a stock carb vs. modified any day, because you can't count on modifications being done correctly by someone you don't know. And that's an odd carb the seller chose to modify. Not that it's bad for a mild street engine, but there are much better choices for performance. It was on eBay for a reason!

[Mike_The_Grad]

The carb was listed on craigslist and only a short drive away from me. He said the carb was on a 283 in a 61 corvette. The guy he bought the car from took the dual quad offy intake off and put an edelbrock with this 1850-3 carb on it. It came to me with 64 jets (stock would have been 66). So I put 68 jets in it. It seems to be doing ok. Although I just recently started experiencing stalling and backfiring from the exhaust or up through intake , I'm not sure. It has happened at least 2 times in the last week. But I think I'm due for a new cap and rotor.

[BigBird05]

Lots of times when a Holly carb backfires it runes the power valve diaphragm.

[RustyPile]

Originally Posted by BigBird05

Lots of times when a Holly carb backfires it runes the power valve diaphragm.

That's very true of the earlier models.. Starting around 1992, design changes all but put a stop to that. Taken directly from the Holley INSTALLATION, TUNING, AND ADJUSTMENT MANUAL.

There still seems to be a lot of misconception about Holley carburetors blowing power valves. Nothing could be further from the truth. Holley performance carburetors built since 1992 have utilized a power valve check system that effectively eliminated this infrequent problem. Consisting of a spring, brass seat and check ball. The check ball system is 100% effective protecting the power valve diaphragm from damage due to engine backfires.

[67 cst swb]

This is the best thing you could ever do... buy this book and read it.

[68 P.O.S.]

Check out this thread, it goes pretty far in depth. https://67-72chevytrucks.com/vboard/...d.php?t=713728

[Mike_The_Grad]

Thanks 68, that's the kind of info sharing that makes this forum worth visiting. Appreciate it.

[MikeB]

Be sure to keep us updated.

[Myself]

Originally Posted by Mike_The_Grad

UPDATE: installed holley 1850-3 carb on the 388 stroker motor.......... running 2 stages richer jets.......
Seems to run fine. ........ pull some more torque out of this 388. It pulls nice and strong but slow and steady. I like that torquey hop you get when you blip the throttle from a dead stop. So I know it's in there somewhere.

That carb is too small for your engine. I've been all through the carb rat race, tried everything and learned to tune Holley carbs. I don't care what you do......your torque and power are missing from this small carb. I LOVE the Holley Street Avenger carbs for a street rod. They're just about dialed in perfect right out of the box with only minor tuning to your specific combo required. On a 383 stroker I would go with the 770 Avenger with vac secondaries, NOT a double pumper. That engine will really come alive!

570 Street Avenger on a street 305
670 on a healthy 350
770 for 383 and 400 smallblocks


Oh,.....and after you get all your power that's missing by changing carbs, you're welcome

[MikeB]

Holley's CFM calculator shows 600cfm for a mild 383 with 5500 RPM max.

Bump the RPM max to 6000, and they recommend a variety of 650 carbs.

Anything larger will hurt your low-mid RPM throttle response (due to larger primaries). And will make no difference at high RPM.

Go 1/4 of the way down this page: https://www.holley.com/products/fuel...s/carburetors/

[RustyPile]

Originally Posted by MikeB

Holley's CFM calculator shows 600cfm for a mild 383 with 5500 RPM max.

Bump the RPM max to 6000, and they recommend a variety of 650 carbs.

Anything larger will hurt your low-mid RPM throttle response (due to larger primaries). And will make no difference at high RPM.

Go 1/4 of the way down this page: https://www.holley.com/products/fuel...s/carburetors/

EXACTLY!!!! The question to ask is: What RPM and below will the engine be operating 80 - 90% of the time?? How many people run around on the streets with their engine reving above 5,000 RPM?? Probably closer to 3,000..

[Myself]

Ok, I don't know what I'm talking about......you guys just go ahead and keep pissing in the wind,

[RustyPile]

Originally Posted by Myself

Ok, I don't know what I'm talking about......you guys just go ahead and keep pissing in the wind,

AAwwww, quit lettin' the wind blow your skirt up so high.. It's exposing your arse..

[MikeB]

Originally Posted by Myself

Ok, I don't know what I'm talking about......you guys just go ahead and keep pissing in the wind,

By "you guys" does that include Holley engineers as well?

Seriously, if a 770 works well for you on a 383, that's great! But unless it's a high RPM engine I think you'd be surprised at the performance of a 600-650, especially during part-throttle acceleration.

I'm reminded of a Holley DP shootout several years ago in Chevy High Performance magazine. In that test they found a 600 or 650 (I forget which one) to be the best all around carb for a mid-performance 383. The 750 or 850 made the most horsepower at some very high RPM, but didn't make as much power as the smaller carbs at anything below 5000 RPM. Funny, but the authors were even impressed with the little 390, which was the low-mid RPM torque king as I recall. Wish I could find that article to see how accurate (or poor) my memory is.

[BigBird05]

This is what I hate. If you don't agree with something or you don't like something, lets just get mad and let the insults fly.

[RustyPile]

Originally Posted by BigBird05

This is what I hate. If you don't agree with something or you don't like something, lets just get mad and let the insults fly.

I'm in total agreement.. When that happens, it's totally stinks up the place.. Opinions are like women.. Everybody either has one, wants one, or can't handle the one they have.