Jerky engine..Holley?

Simon · 03-23-04, 11:37 AM

My engine is fitted with a Holley 650cfm double pumper and seems to run slightly jerkilly (is that a word?) on part throttle openings when I'm trying to maintain say 30 or 40 mph. When I put my foot down, it runs fine with plenty of power. Would a Holley 600cfm with vacuum secondaries make it a smoother drive or is the way it runs a characteristic of the engine tune (spec below)

Ford 302, balanced, TRW forged pistons, chrome moly rings, solid roller cam (272 inlet, 282 exhaust),crane pushrods, guide plates, roller rockers, high vol oil pump, offenhauser single plane manifold.

Any advice greatly appreciated.

Simon

Kevin M · 03-23-04, 12:09 PM

Simon,

Sounds like the carburetor needs tuning. The single plane manifold is not as good as a dual plane for low RPM response, but shouldn't cause that kind of problems. You need to take it to someone who is experienced with Holleys, or get a good book on tuning Holley carbs and do it yourself. (You will find several at Amazon.com) A carb has to be tuned to the engine it’s used on; it shouldn't be a big problem to fix.

Kevin

Howard Jones · 03-23-04, 01:28 PM

Simon, Kevin's correct. Time to buy a book on holleys and start learning how to tune them. By the way I have a 750 mech secondary doublepumper on my 302 and it runs fantastic.
If you tune yours up right then a 650 will work very well for you. You might start with adjusting the point where the secondarys begin to open but this is going to be a hard one to fix via the forum. Holleys in general are not a real hard thing to learn, just get a couple of books on them.

Simon · 03-23-04, 02:05 PM

Thanks guy,

I got a book on Holleys when I bought the car, but just haven't read it yet.

Simon

flatchat(Chris) · 03-23-04, 05:55 PM

Sounds like "hunting" to me ,usually due to a wild cam--I have a similar set up and it's a fair pig around the streets
but on the track from 4500 rpm to 7200 rpm it pulls like a school boy and loves it!
Hope i'm on the right track?
Chris [img]/ubbthreads/images/graemlins/cool.gif[/img]

Paul Bearman · 03-23-04, 06:48 PM

Hi Simon,
This probably isn't the answer to your particular problem but could be worth keeping in mind.
I had a similar problem to the one you describe, the fault being part carburation, bad engine timing & poor choice of spark plugs.
The carburation problem was solved by replacing the old Holley 650 sec vac with a new Holley 670 Street Avenger. (Kindly purchased for me & shipped by Fran Hall, cheers Fran).
The main problem I had was several cylinders not firing correctly. This turned out to be poor ignition caused by the plugs fouling. The plugs installed were NGK BP7ES which turned out to be too 'hard', that is, they require a high temperature to function properly. The plugs were fouling at low speed/idle & the engine was difficult to start. We changed the NGK BP7ES to NGK BP6ES which has improved the condition. However, I have been advised not to go too 'warm' without good reason as engine damage is possible. Big Ford engines require quite a warm heat range plug & I have since been advised to use an NGK BPR6EIX or BPR7EIX or even a DENSO IW20 or IW22. These are Iridium plugs & should improve ignition/starting & throttle response. I haven't tried the latter as yet as these are resistorised plugs & I am not sure if these are compatable with the MSD6 ignition system? All Iridium plugs have internal resistors & I have been advised these are not usually a problem though as required voltage is far lower than for copper plugs.
Hope this is of some help.