Adjusting a holley 850 double pumper

440 Views 13 Replies 7 Participants Last post by Sinnyone, 10 d ago

Sinnyone

Discussion Starter · 15 d ago

Hi all.
Well, this is my second post on this website. Having issues with a new car I just received that has been in the family for a while. Its a 57 210 post with a 350 bored and sleeved to Im not sure. I still have to through the paperwork from my dad to see what exactly he did to it, cam, bore, how he has the trans, turbo 400 I believe, tuned to.
Anyway, to the immediate issue. As it sits now, it runs a bit hot, has a heavy smell of fuel, probably unburned fuel, and hesitates when the throttle is floored. Im taking a guess that it is running rich, but I know that he put a pretty racy cam in it and there is no pressure guage on the fuel line so I dont know what the fuel pressure is at. I was thinking that it is running rich and that is causing the hesitation. I first thought that it was an accelerator pump, maybe cracked, but my dad said he had them checked, replaced or whatever he did, but he said that wasnt the problem. So, what do you guys suggest to do first.
I will upload more data about the motor and trans at a later time. Lots to go through.

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ericnova72

· #2 · 15 d ago

Ignition timing set too low will also blacken the plugs and cause hesitation to throttle input along with running hot.... it should be the first thing checked before messing around with carb settings.

We need to know engine compression ratio and camshaft specifications to give an accurate suggestion for initial ignition timing setting.

With that said, an 850 double Pump is a lot of carb for a little 350, not the best choiuce unless you plan to turn it 8500+ rpm.

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Sinnyone

Discussion Starter · #3 · 15 d ago

Well, look at that. The first piece of paperwork I dug up. It used to have a 350 in it with a holley 600. I didnt know that he got rid of that and put a 396 in it. So here are some specs.
GM 396 SBC
491hp/509 ft lbs
comp rat is 10.4:1
aluminum heads
forged pistons
roller cam w roller rockers. (havnt found anything on the cam lobes)
4bolt main

More to come

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eric32

· #4 · 15 d ago

Besides on needing more info on the engine do you know what exact Holley 850 double pumper that is on that engine? Timing is very critical and the camshaft specs sure would be helpful and along with the exact Holley model number carb you have. Big sized cams are very picky and time consuming to tune and adjust a carb with as they like a richer mixture vs something smaller and milder. Spark plug heat range also makes a difference in things as well as too cold of a plug will foul in short order especially with an engine that already needs a richer idle calibration.

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Moosecountry

· #5 · 15 d ago

I used an 850 on my old camaro that had a 350 sbc. Just changing from 750 to 850 I picked up 3 mph in the 1/4. They work just fine. on a 396 sbc its still a good choice.
try to find as much info as possible? Trial and error works just fine but experience is well needed. Get a fuel pressure gage. Static timing probably needs increasing to clean up idle.

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Sinnyone

Discussion Starter · #6 · 14 d ago

I pulled the plugs and they look pretty clean. No fouling. The carb is a model 4781-6. The plugs are acdelco 41-629. Just what my dad had in there. I dont know if they came with the motor when he bought it or what. ****, I haven't timed a car since I was 20, uh quite a while ago.

I think I will put an inline fuel pressure gauge just to have that info available. I do have the info on the engine from where he got it. I may be able to get a hold of them for more cam info. Thanks for all the input.

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RAYFIN

· #7 · 11 d ago

what fuel ?

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BogiesAnnex1

· #8 · 11 d ago

Most likely a real big carb and a lot of cam on a 350. This begets pretty slow mixture velocities in the manifold and heads with lots of reversion caused by a big cam and it’s well into the compression stroke piston movement before closing the intake valve so a lot of mixture is either blown out the air horn or flow stalls in the porting system.

if the plugs aren’t fouled it probably says the mixture is about right.

Unless the car spends all of its time on the track and is trailered in-between this is too much carb and probably too much cam for some combination of how your using it, the stall on the converter probably too low for the cam and far to little overall gearing to keep the engine spun up where it runs cleanly, in that it’s at an RPM that minimizes reversion. Ever wonder why hot rod dyno sessions don’t report torque and power under about 2500, it’s because below that point the engine straight coupled to the dyno can’t overcome the amount of load and the rate at which it’s introduced. This relates back on why there are transmission and rear axle ratios that are used to multiply torque and speed the engine up.

We actually need a much better run down on what cam, valve train, heads, pistons, compression ratio, final gearing, converter stall, tire size, stuff like that.

Generally a 750 is plenty for a hot street 350 expeted to run into the low 6000’s and under. A 620 to 650 is much more streetable but gives up some top end to the 750.

Boring is refreshing the existing cylinder walls by removing the worn surface, how far this can go is limited by the thinnest cross-section thickness of the cylinder wall. Before about 1974 most any 302/327/350 block was good to .060 and maybe .080 with some wall thickness testing after that with some truck blocks like the 010 they often will go to .060 without having to think about wall thickness most everything else needs to be inspected.

Sleeving is replacing a damaged or excessively overbore cylinder with a pressed in sleeve. This is a costly process generally saved to rescue rare and expensive blocks.

Bogie

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Sinnyone

Discussion Starter · #9 · 10 d ago

BogiesAnnex1 said:
Most likely a real big carb and a lot of cam on a 350. This begets pretty slow mixture velocities in the manifold and heads with lots of reversion caused by a big cam and it’s well into the compression stroke piston movement before closing the intake valve so a lot of mixture is either blown out the air horn or flow stalls in the porting system.

if the plugs aren’t fouled it probably says the mixture is about right.

Unless the car spends all of its time on the track and is trailered in-between this is too much carb and probably too much cam for some combination of how your using it, the stall on the converter probably too low for the cam and far to little overall gearing to keep the engine spun up where it runs cleanly, in that it’s at an RPM that minimizes reversion. Ever wonder why hot rod dyno sessions don’t report torque and power under about 2500, it’s because below that point the engine straight coupled to the dyno can’t overcome the amount of load and the rate at which it’s introduced. This relates back on why there are transmission and rear axle ratios that are used to multiply torque and speed the engine up.

We actually need a much better run down on what cam, valve train, heads, pistons, compression ratio, final gearing, converter stall, tire size, stuff like that.

Generally a 750 is plenty for a hot street 350 expeted to run into the low 6000’s and under. A 620 to 650 is much more streetable but gives up some top end to the 750.

Boring is refreshing the existing cylinder walls by removing the worn surface, how far this can go is limited by the thinnest cross-section thickness of the cylinder wall. Before about 1974 most any 302/327/350 block was good to .060 and maybe .080 with some wall thickness testing after that with some truck blocks like the 010 they often will go to .060 without having to think about wall thickness most everything else needs to be inspected.

Sleeving is replacing a damaged or excessively overbore cylinder with a pressed in sleeve. This is a costly process generally saved to rescue rare and expensive blocks.

Bogie

Thanks for your reply. I was digging and found, maybe I forgot, he replaced the 350 with a 396. My post above gives more info. Still digging

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BogiesAnnex1

· #10 · 10 d ago

A 396 would be a big block they don’t look the same as a small block. At first glance the big visual cue is the big block alternates the exhaust out lets where tge small block has pairs i the middle of the head.

All of this not withstanding big carbs and big cams can be a quite an adventure to sort out for smooth street operation.

Bogie

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ericnova72

· #11 · 10 d ago

BogiesAnnex1 said:
A 396 would be a big block they don’t look the same as a small block. At first glance the big visual cue is the big block alternates the exhaust out lets where tge small block has pairs i the middle of the head.

All of this not withstanding big carbs and big cams can be a quite an adventure to sort out for smooth street operation.

Bogie

There is also a "396 stroker" made from a 350 block....an .030" overbore and 3.875" stroke crank.
It is becoming more common, especially over the last 6-7 years....same crank stroke used to make a 421 out of the big bore 4.155" 400 SBC block.

At this point, it is just about becoming more common than the now obsolete 396 BBC.

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Sinnyone

Discussion Starter · #12 · 10 d ago

Little bit of an update for anyone having same problems. Messing with the car and found the Holley Universal Throttle Solenoid for the AC was acting weird. I just diconnected it for now. That dropped the idle way down to like 300, so increased it to about 800 rpm. Set metering blocks to 3/4 from bottom, they were all over the place. Was still running weird and hesitating when hitting throttle. Was going to check vacuum and see where it was at. Rear vacuum line on intake manifold seems like a good place. Um it wasn't connected to the transmission, massive vacuum leak. new vacuum line and that fixed a lot of things. Still running hot and dieseling when shut down, but no hesitation. I think it was timed and tuned with the leak. Will time it tomorrow. I think it is too advanced and that would cause it to ping/knock, which its doing, and cause it to overheat, which it is doing. Will let you guys know where it is and what happened.

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RWENUTS

· #13 · 10 d ago

Lean jetting and retarded timing makes it over heat.

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Sinnyone

Discussion Starter · #14 · 10 d ago

RWENUTS said:
Lean jetting and retarded timing makes it over heat.

Thanks for the input. I still have to check the timing. Found a bunch of other things happening. Tried by old timing light and the light is kind of a red? crap. no way to see anything. lol. picking up a light later tonight with the bright white lite. Hoping to check where the timing is at tomorrow.

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