Holley 850 street HP pukes off the line

[JackBEEQuick]

Hey guys I’ve recently put on a new Holley 850 street HP and been having troubles with it puking out and dying from a hard launch. After lots of mixing and matching jets, squirters, accel pumps and pump cams there is still something not quite right and wondering what I’m missing, only thing I haven’t tried is changing the power valve. I’m at my closest combo as of now.


69 coronet , Mild 440 , .528 purple cam
3500 stall

primary and secondary Jets are 83s

40 squirter with hollow nozzle screw on primary and 37 also with hollow screw on secondary

50cc accel pumps with yellow cam

Stock 4.5 PV


With a 40 squirter on the primary
And 37 on the secondary it launches perfect at 1000 rpm….
However it still Pukes out at any higher rpm and but also from a still or rolling idle.. so strange.
Now I could just make sure to always launch for that 1000rpm but I noticed my oil is gassy so it’s just too rich and am I’m tryin to figure out how to combat that and also keep it rich enough to launch hard


Any thoughts on which route to try next?

Less aggressive pump cam? I believe the blue is next one down from the yellow.
Increase Timing ?
Jet it down?
Go back to 35cc accelerator pumps (since we figured it was the pump cam?) maybe the 35cc will work but cut the fuel usage down

Grabbing for straws here I know
TIA

 

[furious70]

IMO it sounds pretty rich.

But what does puke out mean to you? Stumbling, big dead spot, big? Is it puffing black when you hit it?

 

[JackBEEQuick]

Yes a big dead spot when launching would be a great word, it completely dies if I don’t let off
Yes at times there’s been black exhaust

It’s definitely rich, but it’s the only combo I’ve gotten to be remotely close..
Ive went the other way down, in jet sizes and squirters and that’s been worse.
Here’s another kicker , i started with a Holley XP 850 and I was having the same issues with that one. Then one day at the track I slapped on my buddies Holley 850 (much older model) that works mint on his road runner, I didn’t touch a screw on that carb and it ran 12.55 , the fastest this car has ran…
So I sold the xp and went for the much cheaper street HP and matched Everything in this new one to his and it still won’t work lol

 

[BSB67]

0-82852SA?

 

[BSB67]

……..Then one day at the track I slapped on my buddies Holley 850 (much older model) that works mint on his road runner, I didn’t touch a screw on that carb and it ran 12.55 , the fastest this car ….

Was it a 4781?

 

[493 Mike]

Have you been trying different float levels?
Mike

 

[Budnicks]

Just spit-balling here, with very limited input or info from you...

**more carb related
If it's actually the carb;
Float level too high ?
or needles & seat are being overcome or need to be replaced
(it's not uncommon today 'junk parts')
& excessive fuel volume in the float bowls, & puking out/vent tubes on launch
or dribbling constant in a way fat condition,
sort of sounds like it
or fuel pressure too high ?,
no more than '7psi flowing' is ever needed
(a return bypass regulator, is best for consistent fuel flow, especially with electric pumps)
usually with a mild build, 6psi is plenty to keep the bowls full all the way down the track

that's a big front squirter

& sounds like too big of a main jet 83 squared, especially in the primaries

can you read plugs?,
you need to
know what's going on, timing or fuel
if you don't have an AFR gauge, even then you should know how to read plugs
NGK plugs are the easiest to read, because of their color (I prefer them too)

read & study this ^^^^ copy it

& take it to the track with you
it will tell you tuning for ignition & fuel


Another place to look, it effects far more then just idle,
it a part throttle transition area
did you reset the idle set screws to the highest rpm &/or vacuum settings ?
also, is a 4 corner idle set up ?
if so do all 4 corners, set screws in both frt & rear metering blocks
or just idle set screws in the front metering block ?

what ignition timing are you running ?
sort of sounds like it could use a lil' more ignition timing advance,
especially out of the launch/hole

727 trans an automatic
(? 3,500 converter with that cam/converter should be OK)
you need more stall speed for the converter,
what rear gears ? if 3.55:1 you probably need more gear (bog)
or
that converter maybe junk, if it can't stall without falling on it's face,
to it's advertised 'stall speed' of 3,500rpm or will push the car thru the lites,
if it not loose enough
or ignition is failing or not working properly too, need a different ignition curve
maybe a combo of both, with an automatic
sound like need more RPM off the launch, if it bogs off the line
Try raise it by 200-300rpm until it will accelerate off the line properly
without stumbling or blowing off the tires

**more carb related info;
(usually people say add squirter, when it bogs, off the line
but IMHFO, you have more than enough squirter now
& especially with a 50cc acc. pump, & the acc. discharge pump cams
really don't do as much as you may think, get a good starting base
maybe go back to the org. white cam or a brown cam,
(or all of the whole carbs base settings) creep up on it,
make sure you don't have too much gap between the acc. pump the gap at
& set flat headed screw with the spring, both front & back 0.010" gap at most, or zero)

I'd go back to basics org. carb setting, & creep up on it
just because one carb worked with certain jet
it doesn't mean 'your carb now, even if same make or cfm, will run the same"
will work the same with the exact jet or other settings, parts you changed

good luck

 

[Geoff 2]

What is the idle timing? I am guessing it should be 30-40* with that cam.

 

[hunt2elk]

I run 850's on my cars, and your jets are larger compared to mine. Why the same size on primary and secondary? With a power valve your mains should be around 8 sizes
smaller than the secondary's. I would think you are running rich.

 

[BSB67]

I run 850's on my cars, and your jets are larger compared to mine.

The OP has not answered either of my questions. Exactly what 850’s work, and which ones don’t.

One of them comes with 83s on all four corners, I think.

With the important information we’re lacking on this, I’m kinda inclined to think the OP is missing something big, and maybe as part of the installation.

Let me re-cap the way I see it. He tried 3 different 850s. Two cause horrendous operating problems. One works perfect.

Nearly all Carbs need tweaking to get good. But having two new carbs that appear reasonable for the application and to be this f***ed up suggests to me something else is going on.

 

[JackBEEQuick]

Wow , awesome guys. Very humbling.. in my experience, short experience, I’ve never seen holley 850s be this finicky.

Appreciate all the input. I’ll try to answer these questions entirely

The carb I have on now is a 0-82851SA
The carb that worked is an unknown older Holley 850 we don’t have the list number as it was on the choke tower which was cutoff, bummer.

I have not tried Different float levels, only what the suggested Holley setting is , halfway up the sight glass. I could bring that down a smidge.

I certainly am working on putting in AFR gauge in. I’m not great at reading spark plugs that precisely.

Running 6psi and new COAN 3500 stall.

I think I’ll start fresh.
I should add that none of the adjustments regarding the bigger or smaller jets and/or squirters.. seemed to change the outcome , it all reacted the same. It ONLY was able to launch well at that 1000rpm when I did the aggressive yellow accel pump cams….
So I think I’ll keep those cams and start dropping sizes on the jets.

In my head, it seems it only works when it’s tuned rich , but then at the same it’s too rich as I’m getting fuel washed down ..

Looks like it’s backing me into a corner and making put an afr gauge in

Thanks again guys
Oh and running 37 degrees timing all in.

 

[Texas97]

i run an 850 qft , i think your jets are too big and you have too much fuel in the bowl. back your fuel level down to bottom of sight glass.

also, have you tuned your 4 corner mixture screws using a vac gauge? what is your vac reading at idle rpm? this would help you determine what power valve you need, it may be blown. would explain why its so rich and black smoking. pull the bowl and check the PV.

im also running initial mechanical timing at 19. 38 all in at 2500 rpm. no pinging.

 

[69conv]

I was also wondering what vacuum you were pulling.

 

[BSB67]

How does it idle?

How does it cruise at 50 mph?

Is your testing wot on the street, or track only?

Have you visually verified that both the front and rear squirters are functioning fully/properly ?

 

[furious70]

It's starting to sound like something structurally wrong with that specific carb. All pieces accounted for, all screws and fasteners, all plugs? There was another thread about surging and the guy found one of the plugs fell out

 

[BSB67]

The 0-82851 SA comes with 82s on all four corners.

Jetting is not causing the wot issue. But if it is truly running that fat, it could be related to a larger issue.

Large vacuum leak will cause a near undetectable miss that causes the exhaust to stink like it’s fat. And would bog badly at first hit.

 

[BSB67]

It's starting to sound like something structurally wrong with that specific carb. All pieces accounted for, all screws and fasteners, all plugs? There was another thread about surging and the guy found one of the plugs fell out

that’s what I’m thinking too, but he said it was doing the same thing with 2 different carbs.

 

[furious70]

I thought he said it ran great with 2 other 850's and he set his up exactly like one of them and it ran like crap. Hence my comment that there's something structurally wrong with his.

 

[BSB67]

I thought he said it ran great with 2 other 850's and he set his up exactly like one of them and it ran like crap. Hence my comment that there's something structurally wrong with his.

Post #3

 

[Texas97]

The 0-82851 SA comes with 82s on all four corners.

Jetting is not causing the wot issue. But if it is truly running that fat, it could be related to a larger issue.

Large vacuum leak will cause a near undetectable miss that causes the exhaust to stink like it’s fat. And would bog badly at first hit.

the only issue is why did he have a vacuum leak with 2 carbs he owned but didnt have the same vac leak with the borrowed carb? if it was a massive vac leak that was unrelated to the carb, it would still be there with the borrowed carb. unless he has an open port on the carb base that was blocked off on his borrowed carb.

check all holes plugged on the carb base.