[leejoy]

For you Holley carb tuning experts out there............

I'm having a tuning problem with my Holley carb at "off-idle" meaning when I start to open the throttle (slowly) after sitting at idle. There is a hesitation resulting in a "dead spot" when I begin to open the throttle. After the hesitation she kicks in and takes off. She idles well - so that's fine.

Here's what I got:

it's a 454 chevy street car - NOT a drag car. It has a big cam, ported iron heads, dual plane intake, MSD distributor/ignition, headers, and a TH-350 trans. The carb is Holley 750, model 4160, vacuum secondary, dual feed with center hung floats. I upgraded the center section "main body" to one of those ProForm (see photo) aftermarket performance racing bodies. The carb still has the stock 30cc shooter (single shooter - not double pumper) stock jets and air bleeds and #65 power valve.

I tried adjusting the shooter so that it kicks in earlier. No luck. I adjusted it the other way so it kicks in later. No luck. I thought for sure it's a shooter issue. I did not have this problem on the original Holley main body. I wonder if it's one of the "adjustable screw in bleeds" on the primary side. I havent played with any of those yet. Oh, one more thing. I remember having to open the throttle further to increase idle speed (the mixture screws did nothing with that big cam in there) I wonder the primary throttle plates are already open to the "transfer" slots in the venturi's. I guess this is a common problem on big engines with big cams at idle. Some guys drill holes in the throttle plates. I'll run out to the garage and look to see how far the throttle is open.

Suggestions please:

[leejoy]

Originally Posted by leejoy

For you Holley carb tuning experts out there............

I'm having a tuning problem with my Holley carb at "off-idle" meaning when I start to open the throttle (slowly) after sitting at idle. There is a hesitation resulting in a "dead spot" when I begin to open the throttle. After the hesitation she kicks in and takes off. She idles well - so that's fine.

Here's what I got:

it's a 454 chevy street car - NOT a drag car. It has a big cam, ported iron heads, dual plane intake, MSD distributor/ignition, headers, and a TH-350 trans. The carb is Holley 750, model 4160, vacuum secondary, dual feed with center hung floats. I upgraded the center section "main body" to one of those ProForm (see photo) aftermarket performance racing bodies. The carb still has the stock 30cc shooter (single shooter - not double pumper) stock jets and air bleeds and #65 power valve.

I tried adjusting the shooter so that it kicks in earlier. No luck. I adjusted it the other way so it kicks in later. No luck. I thought for sure it's a shooter issue. I did not have this problem on the original Holley main body. I wonder if it's one of the "adjustable screw in bleeds" on the primary side. I havent played with any of those yet. Oh, one more thing. I remember having to open the throttle further to increase idle speed (the mixture screws did nothing with that big cam in there) I wonder the primary throttle plates are already open to the "transfer" slots in the venturi's. I guess this is a common problem on big engines with big cams at idle. Some guys drill holes in the throttle plates. I'll run out to the garage and look to see how far the throttle is open.

Suggestions please:

the throttle plates seem to be in a normal position at Idle - I think.

[cuda66273]

So 1st you say it's a street car not a drag car.....

Then you say it's got:
A big Cam....How big?
Headers...what tube size
Ported heads....how much porting and what valve sizes
MSD Ignition
MSD Distributor.....Does it have a vacuum cannister?

Sounds like a Drag Motor to me?

So you take a decent carb, designed for a high vacuum stock motor that works OK and try and improve on it with a POS Chinese main body and you expect it to work?

They don't work.

They're a feeble attempt to make a 1957 design carb look and work like a Mighty Demon....ain't gonna happen.

You would probably learn a lot from this book:
***************Demon_Tuning_Guide****************

[Guy Hiltz]

I would have to agree with cuda66273 about the quality of the ProFofm peice.I had bought a ProForm throttle body for my 4150 800 dp Holley and it worked like crap,come to find out there were metering holes in it that didnt match up with the rear metering plate,I got a front one from another carb and got it to work a bit better,but all in all I was very disappointed.Went with a Mighty Demon as recommended by the Tech @ BG guy here and now I have no regrets,but I wont buy any more ProForm parts.IMO Bary Grant make a high quality carb and you cant go wrong so long as you get the proper carb for your application.

[bigbadbowtie]

ditto... I have tried to piece together 2 proform units. One for myself and one for a friend. Its just NOT worth the hassle. In the end you spent more time/money than you would have buying a GOOD carb.

As stated above.. ports don't line up, gaskets are JUNK. I won't make that mistake again.

I have seen their complete units run well.



Have you tried a bigger squirter?? Sounds like a lean bog to me.

[cuda66273]

Guy Hiltz:
Your right on there Buddy!

For the price you just can't buy a better carb, period, end of conversation, no argueing.

*******************

*******************
I can't believe that BG has been able to hold the pricing down on these carbs for over 3 years while the competition keeps jacking up the price and turning the jack handle to left on quality.

******************

[leejoy]

holy crap - you guys are killing me.

I thought I made a significant upgrade here by going to a "high flow" low restriction contoured "choke towerless" main body with adjustable everything and now you're telling me it's a piece of crap.............

I think Holley makes one of these. am I right? Is that unit any better?

I'm happy with the unit so far except for that off-idle issue. I used all Holley Blue gaskets and all other parts are Holley so those are not an issue.

I may endup in the end going for a better carb though like a Demon. I had sticker shock though looking at the prices. they were like $500 and up easy. the equivalent size in Holley were like $300-400. I wish I had 10 different carbs from 10 different manufacturers and had all day to install and test each one but I don't. I thought I was being smart by swapping the main body for a Proform racing style unit............

Lee

[cuda66273]

Where are you getting these prices?

A Speed Demon 750 Vac is **********
Mighty Demon is ************
For a few more days anyhow

A comparable Holley to a Mighty Demon is ***********
It always amazes me at the power of these marketing depts., how they able convince people to send them Millions of dollars buying Chinese low quality copycat parts and the consumer will actually believe that it's better than the original.

I've worked on Carburetors and Ignition for nearly 40 years, started helping my Dad in late 60's as a punk kid cleaning parts. Of all the stuff (And I'm being nice) I've seen there's nothing that can measure up $$$ for $$$ to a Mighty Demon on just about any combination. The 650 and 750 Mighty's are in my opinion the best bang for the buck available in this industry, Bar None!

All this experience condensd into a 40 page book:
*************Demon_Tuning_Guide***************

Excuse me I just checked Smummit and the HLY-0-80528-1 is ***********



Compared to **********Mighty Demon (Soon ***********)

**********************************

So look at then closely...
Demon has Bigger Float Bowls
Better air entry
Billet Base plate compared to Cast....ever seen a Holley with a broken base plate ear?
Better finish
Better sight glass
Better fuel bowl connections
Better pump linkage (Doesn't look like it came off a 57 Ford Y Block)

[leejoy]

Originally Posted by cuda66273

Where are you getting these prices?

A Speed Demon 750 Vac is **********Mighty Demon is **********
*******************
A comparable Holley to a Mighty Demon is ************

It always amazes me at the power of these marketing depts., how they able convince people to send them Millions of dollars buying Chinese low quality copycat parts and the consumer will actually believe that it's better than the original.

I've worked on Carburetors and Ignition for nearly 40 years, started helping my Dad in late 60's as a punk kid cleaning parts. Of all the stuff (And I'm being nice) I've seen there's nothing that can measure up $$$ for $$$ to a Mighty Demon on just about any combination. The 650 and 750 Mighty's are in my opinion the best bang for the buck available in this industry, Bar None!

All this experience condensd into a 40 page book:
*************************
Excuse me I just checked Smummit and the HLY-0-80528-1 is *************


Compared to ***********Mighty Demon (Soon **********)

***************************
So look at then closely...
Demon has Bigger Float Bowls
Better air entry
Billet Base plate compared to Cast....ever seen a Holley with a broken base plate ear?
Better finish
Better sight glass
Better fuel bowl connections
Better pump linkage (Doesn't look like it came off a 57 Ford Y Block)

ok, ok, ok.............

you've convinced me........ I know about Demon carbs a little bit. I know they are among the best carbs available for racing.............

I've just never had *********to get one that's all. I built my Holley 4160 750 with the Proform Main body for a total of about $200 including new gaskets, shooter diaphrams, needle seats assemblies, etc. I think I did a good job for my budget, but it may be time to upgrade to a "real" racing style carb. which Demon is recommended for a street application for my chevy 500HP 454 setup. By the way, I am ready for "double pumper" mechanical secondaries at this point also. I'm kind of tired of playing with vacuum springs and waiting for those secondaries to open when I nail it.

[T-bucket23]

I think yu can fix it with 2 cans of Motor Medic and some transmission stop leak.

[chevmal]

Hey leejoy, try going with a larger shooter size. What size jets are you running. Al

[leejoy]

Originally Posted by chevmal

Hey leejoy, try going with a larger shooter size. What size jets are you running. Al

I forget. I'll go check. I wrote it down somewhere. I remember them being pretty much stock size for Holley 750 though.

I don't know if it's a shooter problem though. the problem also appears when I "slowly" open the throttle. that's typically not a shooter problem but rather a "idle transfer port" problem. My understanding is there are "idle" ports, "idle transfer ports" for part throttle, then the main metering system. I believe the shooters are for quick opening of the throttle only.

[leejoy]

for what it's worth. I just browsed through 2 of the most popular racing magazine publications in the country. In them were 2 of the most recognized leaders in racing class aftermarket carburetors. I won't mention any names. I even spent 25 minutes on the phone with one of them. Both of them, - yes that's right BOTH of them use the ProForm aftermarket racing style main bodies in the 750 CFM range. Why would they charge well over $600 for these specialized racing carbs using the ProForm body if they "suck and don't work". Maybe its just because you guys lack the expertise to get them to work for your application so you blame the manufacturer?............

I'm having trouble with the "off idle" circuit. that doesnt mean that they suck and "don't work" It's probably just a tuning or tweeking to correct it. this type of situation is very common and expected with aftermarket carbs. standard protocol. that doesnt mean you just give up and quit and buy something new and say "they all suck".

sorry if I am sounding so mean but some of you guys were pretty much calling me stupid for going with the ProForm main body. I guess those guys at the custom racing carb shops are just as stupid as I am right?

[dt196]

Leejoy,
Been there done that , got the t shirt. There's nothing wrong with your Proform body. I've had mine for more than 2 years now and it performs great. This is a 750 vac. sec originally a 3310-1.
Take your carb off and carefully turn it upside down to drain the gas out of the bowls. Next take a look at the transfer slots. You will no doubt find that you have them uncovered too much. To test this out, close the primary throttle by backing the idle screw out until the transfer slot is almost all covered by the throttle plate. Now open the secondary plate by screwing in the secondary throttle screw about 1/2 turn.(this is only accessible with the carb upside down). This will allow you to get the engine to idle without uncovering the primary transfer slot. You may have to play with how much you open the secondary to get this to work.
If this works for you, the primary throttle plates can always be drilled and the secondaries closed back to the stock location. It would be a good idea to write down how much of a turn that you open the sec., so you can return it later if you want.
Dan
On mine, I just left the sec. opened. No more bog.

[bigbadbowtie]

I never said you were stupid. I ended up taking mine to a local engine/carb gooroo (Dennis Mitchell) after spending countless hours screwing with it.

Some of the ports on the main body did NOT line up correctly with the baseplate. He is the one who pointed that out.

I ended up replacing the the main body with another holley main body and it worked FLAWLESS!!!

As I stated up above. I won't make the mistake of trying to piece together a carb again. I will buy a complete unit.

As far as having the knowlegge to tune a car. You can't have a 10 sec pump gas camaro and NOT know how to tune.

I hope you get it squared away....


FYI.. Quickfuel assembles Proform . I spent hours on the phone with them as well........