600 cfm holley

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Transtar79
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600 cfm holley

Post #1 by Transtar79 » Thu Apr 12, 2018 11:01 pm

Is there anyone running a 600 cfm 4160 holley on a 300? I recently installed one and i cant get it to run right. Ive tryed different jets from 65 to 45, but its either overfueling or underfueling. I cant get it right. Im starting to lean towards maybe an ignition issue. Im currently running the duraspark 2 so its a stock ignition. What is everyone else running for an ignition?

pmuller9
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Re: 600 cfm holley

Post #2 by pmuller9 » Fri Apr 13, 2018 8:12 am

Need more info.
Describe what you mean by not running right.
Which intake manifold?
Is the engine stock?
What year is the engine?

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THE FRENCHTOWN FLYER
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Re: 600 cfm holley

Post #3 by THE FRENCHTOWN FLYER » Fri Apr 13, 2018 9:58 am

For the life of me I just don't get why folks think that carb main jetting needs to change significantly from engine app-to-engine app. It is more likely the idle circuit, or the power valve circuit, or even the accelerator pump circuit that needs attention, to say nothing of other possible adjustments like float level and accelerator pump cam placement.

Describe tha operating condition(s) that are giving you trouble - engine speed / engine load (vacuum), ambient and coolant temps, etc. and we can get closer to giving you an assessment.
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Transtar79
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Re: 600 cfm holley

Post #4 by Transtar79 » Fri Apr 13, 2018 11:07 pm

Its in an 86 f150 4spd 4wd and its got a offenhauser c series dual plane intake. Its running 18 inhg at idle. I have adjusted the floats to where they are half way in the sight glass and the accelerator pump is adjusted properly. The problem is mainly when u accelerate. The engine wants to "bog" when u give it any sort of throttle. I changed the jets bc it was idling really rich and was loading up the engine when idling. I have added an accel super coil that i had laying around and that took care of the smoking and it idles alot smoother. But its still got that bog when i snap the throttle on the floor and it pops and bogs under load......the engine is bored 0.040 but mostly stock

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Re: 600 cfm holley

Post #5 by pmuller9 » Sat Apr 14, 2018 12:20 am

If the engine still has the stock cam then the carb is on the large side.
Read both pages.
http://forums.vintage-mustang.com/mod-c ... -help.html

Transtar79
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Re: 600 cfm holley

Post #6 by Transtar79 » Sat Apr 14, 2018 8:44 am

The carb has a vacuum secondary, so the secondaries are not even opening in the garage and i still have the bog. So since its only opening the primaries in the garage the carb is only producing half the cfm rating right? 300 cfm? Just an example, when i was youngin lol i had an 83 t-bird with tje 3.8L V-6 which i ran a 500 cfm 2300 series holley 2 barrel with a 50 cc acc pump and that thing ran like a champ. But this 300 i cant even get it to take throttle without it falling on its face. ( Oh and this carb has a 30 cc pump )

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Re: 600 cfm holley

Post #7 by B RON CO » Sat Apr 14, 2018 8:46 am

Hi, after making sure the ignition system and timing are on the money, I would go back to around the original 58 jet. I would check the fuel pump pressure because Holleys will flood over with over 6 PSI. I would lower the float level until the level is at the bottom of the sight glass. I would check the power valve to see if it is blown. I have seen loose power valves, which allow gas to always trickle by. Try that. and post back. Good luck
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pmuller9
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Re: 600 cfm holley

Post #8 by pmuller9 » Sat Apr 14, 2018 10:08 am

Did you read over both pages of the link I posted earlier?
http://forums.vintage-mustang.com/mod-c ... -help.html
Last edited by pmuller9 on Sat Apr 14, 2018 2:28 pm, edited 1 time in total.

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Re: 600 cfm holley

Post #9 by Harte3 » Sat Apr 14, 2018 11:36 am

https://www.holley.com/support/faq/

https://www.holley.com/support/

"...lower the float level until the level is at the bottom of the sight glass." That is the Holley recommended float setting.

Other things to consider: The bog is most likely a dry or lean bog because there is not enough fuel getting into the mix when snapping open the throttle. Three things that have a bearing...The Accelerator pump cam for size and duration of the pump shot, the Power valve opening event, and if you don't have heat running to the intake manifold this may also contribute to the bog.
'83 F150 300, 0.030 over, Offy DP, Holley 4160/1848-1 465 cfm, Comp Cam 260H. P/P head, EFI exhaust manifolds, Walker Y Pipe, Super Cat, Turbo muffler, Recurved DSII, Mallory HyFire 6a, ACCEL Super Stock Coil, Taylor 8mm Wires, EFI plugs.

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Re: 600 cfm holley

Post #10 by SteveP » Sat Apr 14, 2018 11:54 am

I believe your problem stems from two conditions.
First, the Offy C is not a dual plane manifold. It's a high speed manifold designed for 2500 -7000 rpm range.
Second, you're badly overcarbed for a street application.
Combine the two conditions and you're guaranteed to bog if you snap the throttle to the floor as vacuum drops instantly to zero.

viewtopic.php?f=2&t=77749

From the link:

I'm running a 300 (reman from S&J) with an Offy C intake, Hedmann dual exhaust header - no cats, 2" pipes with Flowmaster mufflers, Elgin 1178P cam, ported and polished head with 3 angle valve grind in front of a C6 trans (soon to be swapped for a AOD) and 3.08 rear axle.
When I was deciding what carb to run I read threads here on carb sizing and I was skeptical of recommendations for 4 bbls in the 500 - 700 cfm range as too big a carb can be as bad as too small for a street engine and a 300 isn't capable of flowing 500 cfm without extensive mods. I assume the big 4 bbls are for racing applications.
I referred to several carb sizing calculators online and they all calculated a flow of 332cfm @ 4500 rpm with 0.85 VE. I bought a MC 2150 with 1.21 venturis (351 cfm) from National Carburetors.com ($179.95 + core charge and shipping) and mounted it with a TransDapt 2065 adapter from Jegs. I wanted to make sure I had enough without overdoing it.
It turns out that this is more carb than I need as I never turn the engine any higher than 2600 rpm (194 cfm) (I cruise at 2450 rpm @ 70mph). The 1.08 venturis (287 cfm) would have been plenty for my application.
Even though I'm slightly over carbed the engine runs great and I'm happy with my choice.


Even with my setup I bog if I snap the throttle to the floor. If I open the throttle (relatively) slowly the performance is very good. I believe this is a direct function of the large internal volume of the Offy C manifold. If I can ever find an Offy DP (Offy's dual plane street manifold) I'm going to give it a try.

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Re: 600 cfm holley

Post #11 by pmuller9 » Sat Apr 14, 2018 2:27 pm

Transtar79 wrote:The carb has a vacuum secondary, so the secondaries are not even opening in the garage and i still have the bog. So since its only opening the primaries in the garage the carb is only producing half the cfm rating right? 300 cfm?

Yes. Just remember that 2 barrel carbs are rated at twice the depression as a 4 barrel carb so the 300 cfm is equivalent to a 425 cfm 2 barrel. That's still OK.
You can make this work.

The bog ussually indicates a lean condition so you have to experiment to see if that is the case here.
You can start by putting the original main jet back in (Holley shows a 66) and adjust the idle screw mixture for best vacuum and see if you get any improvement with the bog.

Secondly the power valve needs to be about 1/2 of what you are pulling for a vacuum at idle.
It come with a 6.5 which is too low if you are pulling around 18 inches of vacuum.

Third: Does they acc pump start to squirt as soon as the throttle begins to open?

What is the initial and total ignition timing with the vacuum advance disconnected?

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Re: 600 cfm holley

Post #12 by jason832 » Sat Apr 14, 2018 10:43 pm

An off C manifold I doubt will cause the issues OP is having. I've ran a Clifford intake without the heat passages hooked up, Clifford cam and a 4 barrel street demon Jr. In the coldest times of Canadian winter and it ran fine and pulled as good as a stock 300 down low.

Is the choke working right?
Accelerator pump squirting immediately?
Timing been checked?
When was the last tuneup plugs/wires/cap/rotor?
Vacuum leaks?

A wideband o2 sensor is the best money you'll ever spend on a carved engine like this. With my AEM guage I can see the difference even one metering rod change or 1/4 turn of an idle screw does and can tune it exactly how I want it. I picked up several MPG just from this alone...

600cfm is quite a bit I think for the six. My 625 street demon required probably a dozen evenings of tuning, a wideband o2 semsor, another dozen evenings to get it to run properly. The primary jets and metering rods are each several sizes smaller, and the secondary jets are about 7 smaller but its finally running right. My engine has a Clifford intake, short headers, dual exhaust, comp 268 cam. I would have gone with something smaller and regret getting this carb big time.

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Re: 600 cfm holley

Post #13 by Transtar79 » Sun Apr 15, 2018 1:53 pm

Ok sorry guys ive been really busy with other stuff. But i have been working on this truck and ive been doing some checks that you guys have recommended, but i have developed a huge ignition problem. Its backfiring out the carb and the engine struggles to turn over on some strokes. Like the timing is off. I tryed another duraspark 2 module but its still the same. Maybe distributor? Before all this happened i set the float so the fuel level is at the bottom of the sight glass. Checked tje power valve and it is not leaking and it does have the 6.5 valve. Changed the jets to 58. The accelerator pump is pumping fuel as soon as the throttle is moved. The choke is open. Fuel pressure is 4 psi. And it has brand new cap rotor and plugs. No vacuum leaks....would i jyst be better off going with a 350 2300 series 2 bbl?

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Re: 600 cfm holley

Post #14 by Shorty » Sun Apr 15, 2018 3:21 pm

Could it be a plugged/ restricted exhaust? I had a truck a while back that did the same to me, would turn over hard and shoot flame out the carb. I changed the carb then the duraspark II module and then the distributor all off a truck that was running great. Still the same issue. I ended up by disconnecting the exhaust from the manifold and it fired right up and ran great (a little loud). I re installed all the original parts and it ran fine. Turns out some water got into the tailpipe and got trapped in a bend and froze to form the cork (it is my yard and snowplow truck with a vertical stack for a tailpipe, I made a much larger drain hole for it now)

img/picture.php?/2140/category/76

My $0.02. hope you get to the bottom of your problem soon
85 F150 on 78 bronco frame C6 np205 welded dana44 front, trussed posi nine inch rear. EFI exhaust manifolds into one 2 1/2" rolls on 35x12.5x15 Maxxis Trepador.

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Re: 600 cfm holley

Post #15 by pmuller9 » Sun Apr 15, 2018 4:12 pm

Did you check the timing with a timing light?
Is the initial timing at 10 degrees BTDC with the vacuum advance disconnected?
Does the timing advance smoothly when you rev the engine?

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Re: 600 cfm holley

Post #16 by Transtar79 » Sun Apr 15, 2018 5:56 pm

I cant even get it to run long enough to put the light on it. And it doesn't change either way i move the distributor. I did have an accel super coil on it, im just wondering if maybe it may have did something to the distributor.

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Re: 600 cfm holley

Post #17 by pmuller9 » Sun Apr 15, 2018 6:47 pm

Transtar79 wrote:I cant even get it to run long enough to put the light on it. And it doesn't change either way i move the distributor. I did have an accel super coil on it, im just wondering if maybe it may have did something to the distributor.

The coil won't hurt the distributor. The Duraspark module runs the coil.

You will have to set the distributor timing since it has been moved.

Take out sparkplug #1 so you can bring #1 piston up during the compression stroke.
It will try to push your finger out of the spark plug hole during the compression stroke.

While turning the crankshaft clockwise during #1 compression, bring piston #1 up till the mark on the harmonic balancer is at 10 degrees BTDC.
Remove the distributor cap and check if the rotor is pointing at #1 plug wire on the cap.

Next remove the rotor so you can see the magnetic pickup coil.
The tooth on the armature should be dead center with the pickup coil stator.
If not then turn the distributor until it is lined up.
Your armature will only have 6 teeth instead of the 8 teeth shown.
Image
After turning the distributor make sure the rotor still pointing to #1 plug wire on the cap.
Your ignition timing is now very close to correct.
You should be able to check the timing with a timing light during starter cranking.

Is the carburetor new?

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Re: 600 cfm holley

Post #18 by Transtar79 » Mon Apr 16, 2018 9:57 pm

Ive set the timing exactly as you have posted and i can get it to run but very poorly and its backfiring out the exhaust. Yes the carb is brand new. Ive never ever had an engine do this. I have the timing set exactly as it should be. And it wont run. At this point its not a carb issue. I have put the original one barrel back on it with the same results. If i pull the coil wire off, the engine cranks over nice. As soon as i put the wire back on it cranks over hard. And thats at 10 degrees btdc.

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Re: 600 cfm holley

Post #19 by pmuller9 » Mon Apr 16, 2018 11:46 pm

There have been rare cases where the outer ring on the harmonic balancer has slipped on the elastomer under it so the timing mark will no longer represent TDC.
Take #1 plug out and do your best to locate the piston at TDC by feel.
Then check to see if the timing mark on the balancer is close to TDC.

But first double check the spark plug wire firing order on the distributor cap.

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Re: 600 cfm holley

Post #20 by Transtar79 » Wed Apr 18, 2018 11:11 pm

Well after doing everything i could think of, i purchased a summit HEI distributor for it and now it runs. So im gunna set the timing tomorrow and then back to tuning this carb.

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Re: 600 cfm holley

Post #21 by dftuttleF250 » Fri May 04, 2018 9:23 pm

I run the same carb & intake combination on my 300 along with a Comp cam and it runs good. It will take a some patience to get the squirt just right.
My experience was that the squirt was enough volume with the standard accelerator pump cam but delivered too quickly. Going smaller on the discharge nozzle increases the duration and eliminated the flat spot when opening the primary. It currently has a .037" discharge nozzle. I think it was a .039" when I built it.
One thing I did not see was is this a new or used carb? I made the mistake once of using the wrong gasket for the metering block. The engine vacuum will draw fuel right out of the float bowl.

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