Inliners International Forums General Discussion Engines jetting Holley 390

Have a hard time getting Holley 390 setup. 77 Chevy 250 clifford cam, headers, clifford intake, and clifford valves and head specs. Started jetting with clifford recommendation and could not get rid of lean spot each time u shift let off gas and stab throttle u get a hesitation. So I took to get dyne tune and developed and intake gasket leak when I got there and they three it on dyne and said it was way to lean and went up in main jet 9 sizes to 60 main 6.5 power valve and I have 17 to 18 lbs of vacuum. the pump nozzle is a 31 and pink cam. I don't have a hesitation but all my get up and go is gone very lazy power band. Need to know where to start and where are your hoped up 250s running with holley 390?

I would get a wide band O2 reader installed.
That will tell you exactly what the engine is getting.
Quicker to tune, more accurate, better everything.

Best thing to get when tuning.



MBHD

What is the timing specs? Do you have the Intake heated?

12 deg hei hotrod vac adv no water to intake.

What is the max timing?

MBHD

What is the Holley list # on the choke flange? Is it a 8007?

12 deg hei hotrod vac adv no water to intake.The ignition man helped me set it it up.
My vacuum adv is locked to limit its travel.The weights have been changed to the dz gm weights .

So I can't find email of all figures I just did all leg work he figured it all out I think 36 sounds familiar but need to recheck.

its a street avenger truck carb 8007

You need to know what you started with: jets in the primary, and what size are the PVCR holes, and what secondary plate is in there and its hole sizes. And then what was changed during the dyno tune - going up 9 numbers is a LOT, I've gone up to that with open headers but even then it is rare. Sounds too rich now, maybe a crutch for something else not happy?

I ran a R6390 Holley 390cfm on my 250, stock w Clifford 4bbl.
Jets 52 pri and .028 PVCR, 52 sec and .031 PVCR, this is a 4150 carb so it has jets in the secondary not just a plate. It ran so good this way, won many of the shootout runs, so I left it alone.

You'd probably want about 2 numbers richer than mine with your cam and headers but need to know what you have first

The dyne guy put 60 mjet and pv 6.5 and s the secondary is vacuum 31 squirter
3/4 turn out on air screw He didn't use dyne info for selection he called a friend at a carb rebuilt shop and told him my specs and got jetting specs from him lol said the intake was hard to get good jetting. There was no stumble but was lazy on power when I left.
I put 56 main 6.5 power valve and 31 squirt and pink cam 3rd hole in second screw. Runs better but I still think my main is to big. I tried a 54 and it ran better but had a lean stumble every time u let off gas all the way and hit gas pedal hard like shifting . And i tried 35 squirter and that didn't cure it I also tried the 8.5 power valve Im pulling between 17 to 19 lbs a vacuum it changes when I start playing with stuff.

Ok on the primary:
The 6.5 PV just means that's when the PV opens. You could try an 8.5 PV that will make it richer sooner.
But the number you also need is the PVCR, Power Valve Channel Restriction, the size of each of 2 holes drilled in the metering block behind the PV. THey show as .038" for your carb but I'd check for sure.

While in there, the secondary metering plate should have a number stamped on it like "34". From this you can look up the hole sizes near the bottom, these are like the secondary jets but they don't flow the same as jets, but you do need that hole size to get started.

Meanwhile here is another easy thing to try:
Clamp the vac secondary SHUT, and try it again ie as a 2bbl. Does the problem go away? Can you now jet it leaner?
Maybe the secondary is too lean or more likely opening too soon.

I suggest putting the Hot water from the engine thru the intake. The fuel is puddling.

There real small can't measure till tomorrow need tool from work.

If I don't have to id rather not I think its cleaner with out out.

When pulling off 2nd bowl I see this, its a screw from the plate in bowl bottom.

x2 what Tom said about the hot water heat.
I live out here in Cali too, have an unheated Clifford but if I could I would heat it. It doesn't really run right til warmed up and it will act funny with fuel puddling in it.

Your metering block shows the idle mix screw with a depression around it, sometimes those are reverse idle, so turning them out will LEAN the mix, turning in makes it RICHER. Sometimes. Just have to try it but that could contribute to your problem.

Now on the holes-
In your pic, yup you found the PVCR holes, need to measure those.
Wire of known thickness can help, if youre off by a mil or two its no big deal.

The metering plate screws should NOT be loose in the bowl of course. You may need a new gasket so the plate has to come off anyway. A good phillips bit will work in those goofy things if you don't have the special tool. The main secondary "jet" holes are on the bottom edge of that plate. Looks like a "66" stamped on it, I don't have the specs on that plate so you'd just have to measure it.

Making progress though!

its a 59 on plate

I read online 59 equates to a 56 jet

I would not worry too much about the intake manifold heating, it sits right over a really hot exhaust manifold or headers.

I never had any problems running my Clifford, other than having a large intake runner. Low port velocity. Offy is a better daily driver intake manifold.

Get the carb straightened out & it should run just fine.

MBHD

OK so you have:
56H Pri jets (51H stock)
.038 PVCR ie stock Holley
#59 secondary plate (stock), my calcs say that's a 58H jet but not a lot of difference there

So OVERALL your carb seems a little rich (way rich with those 60H jets in it) but even with the 56H in there, given you have headers, it should not be rich enough to run "badly". Maybe a little slow but should run good.

To tune it much more will take some timing setup, GTECH or dragstrip or other then you can dial the jets in, and eventually the secondary.

Meanwhile I would still try locking the secondary shut just cuz its easy to try, see if that improves it.

And of course, make sure the floats are set right wet.

Is your carb on the car mounted front-to-rear like a v8 or side-to-side (like mine). Not sure it matters but that's 1 more variable.

It runs better with the 56. Shoud I have the 8.5 powervalve in cus of the hi vacuum at idle. I have the 6.5 in now. Im running pink cam 2 hole an 3rd in cam. And 31 nozzle. And it runs good but I think it should be better.

In beginning I ran 51 main jet dual stage pover valve 5/15
31 nozle orange cam. Ran good but had a lean spot shifting in to 3rd gear always. And if I didnt have the accelerating pump adj perfict it would run terrible. Thats when I took to dyno and they just over jetted it.

Ill l;ook in to locking the secondarys. The missing screw hole was that letting gas into a area?

FWIW, Our 243 ci O/T engine ran best with all stock jetting, etc. except for a #37 pump shooter.

When you flycut the main body of the carb do you see solid metal like the carb on the right or "porous and spongy" metal like the carb on the left?

Didnt flycut

Sam,
You may not want to clutter the engine with water lines. But I truly believe/ know that heating , will make it vaporize the fuel that lays in the intake better. Makes for a more responsive engine.

Looking at your intake pics. That Clifford does not look to have heating provisions.

Hank, Don't knock it till you try it. I am not telling him to spend 300-500 on un needed parts.

I also think the 6.5 PV is best to use. On the highway 12 inches of vacuum will be all you see. any hill and you will be into a 8.5 PV when you don't need to be.

Tlowe,

Heating up an intake I am sure it should speed up the heat cycle on a cold engine.

One time I installed the intake manifold heat cross over block off plates on my 350 S.B.C. It was horrible on a cold mornings. But once warmed up ,not a stumble. Freakin thing (intake manifold) also got too hot to touch after driving for a bit.
I later installed the plates with the small holes, which worked perfect on cold mornings. Cold I mean in the 50's.

Have you ever used a infrared temp reading gun on your intake manifold?
http://www.silkscreeningsupplies.com/product/Tempgun?gclid=CIWxoIuQxMACFchgfgodrDQASg

Just wondering, how cool do you think the intake manifold (sitting just above the headers or exhaust manifold) is after driving around with the hood shut?

I know, I do not want to touch the intake manifold after I have been driving around for a bit.

It does not get that cold here where I am.
Never had carb icing conditions or problems.

I also doubt that heating my intake manifold would have gained me any better ET.
Heck, I would have still held a record for the quickest ET, for what class my Camaro would have been in. According to the last info I got from Harry Blecha.

14.3 ET, (slow to me mind you).
My daily driver combo:
10:1 250 CI, Clifford, 500CFM AFB carb, headers, 4speed 4:10 gears, large chamber head w/1.94" intake 1.60" exhaust valves.
Camshaft specs "solid" was around 520" lift 236 degrees duration @ .050 on a 110 lobe separation. From ED @ Camonics
This was an uncorrected ET @ a 3000 Ft altitude track (on average the norm is .5 second slower, so corrected it would have been a 13.8 in the 1/4.

Not bragging by any means, I kept getting beat from most V-8's

I think once he (the OP, original poster) gets a wide band reader, he can actually see what the A/F ratio is when he stomps on it, cruising around, that will be the best tool to get for him.

He could try & use a heated intake manifold, but I doubt that will cure his problem.
He would get better results if he switched to a Offenhauser intake manifold over a heated intake manifold, But that is still a debate I guess.

I will take a guess here & say, that the average person trying to tune a carb will not know if the A/F ratio is rich, lean or somewhere in-between.

Not saying this is the case w/the OP here, but just saying.

A wide band reader will tell you how your acceleration squirt is, too rich, lean.
It will also tell you if the duration on you cam pump squirted is too short, a shot.
Best tool for tuning, especially if you are not too familiar with any one particular carb.

MBHD

Thanks for all the great input I know everyone just trying to help. I took it for a spin tonight and everything smooth no lean spot that back screw that was in secondary bowl was screwing with my float. I reset float which was set low and put 56 main
6.5 power valve 31 squirt nozzle pink cam and ran good I just don't have a lot rev up high i think I can go leaner on main jet.

When I had the 51 main jet in it ran like a raped ape but always had a lean dead spot down below. Im only going by seat of the paints and how the motor reacts to changes. I do have a bung welded for ob2 sensor maybe should look in to getting reader.

If it runs like a raped ape w/a 51 main jet, I am sure you could make other adjustments to get rid of the mentioned dead spot.

http://www.ebay.com/itm/Innovate-LM-2-LM...21b&vxp=mtr

http://www.ebay.com/itm/INNOVATE-MOTORSP...46c&vxp=mtr

MBHD

Don't overlook the benefit of water heating the manifold. That addition has cured more off idle stalling and hesitation than all the jet changes ever. Take a look at the article in "Tech Tip" by Langdon....he knows of what he speaks!! He is a retired engineer from the engine division of GM.

i drive ramblers. i live on a desert island and reinvent everything.

carbs are carbs. they are subtle devices. y'all talk about "carburetor water heating" but more correctly, it's "carburetor constant temperature". it's not just the "heat" that's important, it's the *CONSTANT* temp that matters.

you want most of the intake above the temp that gasoline becomes a vapor. i actually instrumented my intake and found that air+fuel intake physics drops the mixture temperature 95 degrees F below the coolant temperature -- the physics of carbs is very complex. http://worldpowersystems.com/AMC/195.6OHV/Intake/index.html (scroll down) (my current head has three separate temp sensors, the new computer will read them all, so bug me later if you want info)

when fuel falls to the plenum/runner/intake floor, mixture osclliates instantaneously between rich and lean, even if the AVERAGE is correct. the engine will run like crap even with the plugs (averaging) looking good.

in short, you want carb+runners to be at or above coolant temp, and more or less constant, or nothing will make sense. at WOT the evaporative cooling effect is quite substantial; the mixture moves rapidly, spends little time (millseconds) in the runners, while that doesn't allow for much heat energy transfer from iron to gas, fuel that *does* fall out (droplets) really needs to re-evaporate get inducted and burned ASAP.

all of these variables are negated with power FI. relationships of fuel density and all that are not linear just above and just below gasoline's boiling point, so seat-of-the-pants understanding of what's going on in there is not necessarily correct.

OK i got crawl back under my rock now...