Hey,
You seem to be the resident Holley doctor.

After returning my brothers 289 to it's original shelby form, WE CAN'T GET IT TO RUN FOR CRAP!
Here's the build info.
Shelby 289 long block.
Shelby optional LeMans mechanical cam.
Specs are .525"/.526" lift, 246/256* @.050 with a 107 lsa
10-10.5:1 comp
Roush 200 heads.
Full MSD ignition system.
10* initial
29-30* full out @ 3000rpm
Running 5" of vacuum at idle.
Currently running a 1850 holley 650 w/vacuum secondaries.
Changing to a 4777 650 DP.

Our problem is, every time we start it, when it's cold, we can't keep it running. If we even touch the throttle at all, BANG it backfires. It does that until the car has ran for 10 minutes.
Also, when we're driving it, it doesn't have any balls when you punch it. In fact, if you punch it too hard it'll back fire.
I had thought that it was running to lean, so I richened the mixture. But it still does not run right.
Also, the secondaries were not opening at all when I tried it in the driveway. I opened them manually and then they stuck open.
It's only getting about 1 gallon a mile, yes that's right, 1 GALLON PER MILE.
So I know something is not right with this carb.
That's why we went with the 4777. Starting all over with this new carb.

What I need to ask you is, what do you think is causing our low vacuum? And why is it backfireing so much?

Im no ford expert but 10* intial seems too low for that engine. Ever drive a car with retarded or very low advanced timing? If you have youll now that they run like crap, have no power and get shitty fuel mileage. With that cam and those heads locking out the dist. mechanical advance might be the only way to get this engine to perform. Try giving her another 6 degrees and see how she does, I beleave fords like about 36* of total timing like chevys but if you hear any detonation back her down rightaway.

More initial timing just like Joe said. Also your accelerator pump arm should have no play, the only clearence should be at wot, then the arm should go another .015 before it bottoms out. Your vacuum secondary should not open up in the driveway, the engine needs to have a load on it to open up, like going down the road. If the timing and the pump don't help you might need to change the squirters and or pump cam. Low vacuum = 246/256 on 107 lsa, more timing might help. Mark

I think Damon is more f a Qjet guru, but he could probably fix you up.

BTW, that's a LOT of cam for a 289!!

This might sound silly and stupid, but hear me out. If the raising the total timing doesn't help or makes it worst....Check your firing order and make certain all the wires are on the dizzy in the correct order(follow each wire from dizzy all the way to the plug). SB Fords will run with a couple plug wires mixed up, but it will run like you describe, with the popping when bliping the throttle.

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John Wright
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Ok, now go change all your passwords :)

I agree.... timing issue. If adding timing does not work...make sure your balancer has not slipped on the rubber ring.

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Ray in Bama
78z,355 roller on the sauce!!

I never really had a use for a Holley. More of a QJet man, myself. But it doesn't mean I don't know how to tune one!

Here's what I do when faced with a head-scratcher of a carb problem:

Step 1. Confirm it IS a carb problem. Yank one off a friend's engine that is known to run well and install it on yours temporarily. No, it won't be perfect, but it should run reasonably well once you get the idle speed and mixture screws set close. If 90% of your problems suddenly go away you know there's something wrong with your carb. If not, you know the problem is elsewhere. In this case I think it's safe to say there IS a carb problem- secondaries hanging open is bad bad bad. That reason alone leads you right to step 2....

Step 2. Assuming the carb is at fault you do a complete rebuild on it- including a thorough cleaning of all passages. Holleys can definitely get "weird" from old gaskets and gummed up passages. When it's time to do the vacuum secondary chamber on the side of the carb shoot me an email- they're easy to screw up if you've never done one before.

Step 2-and-a-half: Put it back to stock calibration while you're in there. Confirm that the jets, metering plate, power valve and such are what the carb came with originally. You can get original calibration specs for every Holley 4bbl ever made off their website. If you're finding yourself 6 or more jet or squirter sizes from stock you probably did something wrong. Their calibrations are not perfect, there's no way they could be for every engine, but they are almost certainly "in the realm of sanity" and the carb should run reasonably well with stock calibration.

BTW- you won't see the vacuum secondaries opening by just zinging the throttle in the driveway. Takes quite a bit of WOT airflow through the primary venturis to start opening the secondaries.



[This message has been edited by Damon (edited October 18, 2005).]

Elminator,

With all the backfiring, I would assume that the power valve is blown.

With the LeMan cam, you should be running a 4.5" powervalve and probably some larger center squirters.

The 1850 is such a generic Holley that you literally have to have a full tool box of tuning parts to dial it into a performance engine. The secondaries should not open just revving in the driveway. It will need to be under a load and sense a vaccum drop. Often they will stick due to linkage interference, bad seal on the vaccum can to main body, weak spring, and sometimes the secondary opening adjustment screw allows the butterflies to go "over-center" and lock open. If you opened it at idel, the engine willmore than likely quit since there is more airflow but not enough fuel.

The 4777 is more performance oriented and will still a little work but it is more suited for that engine build. Be sure to check the accelerator pump lever adjustment. Like

As with everyone else, I would suggest dialing in the timing first. After you can get a decent idle, then start adjusting the carb. I imagine you will need another 4-6 degrees advance.

Early small block fords are notorius for damper marks not lining up properly due to changes in the placement of marks on the waterpump / timing covers and shifting of the balancer rings.

I know the set-up you are running very well. I used to hang around a Ford Performance shop restoring Shelbys, Cobras, and Panteras. The LeMans cam is vicious but with the Roush 200 heads it should work really well. The car should have a manual tranny with some steep gears or an automatic with a serious stall!

Well part of the problem is we can't seem to keep one of the vacuum plugs on the carb. For some reason it keeps blowing that plug appart. Almost like when it backfires, but I'd think that is one of the reasons it is backfiring. Anyway it was off again, and I'm tired of buying new ones so we're just leaving it off for now.
Other than that I know for a fact that the current power valve in that carb is a 8.5.
I reset the timing to about 14-15* initial. And it runs a whole lot better, but it still backfires all of the time.
Another problem is, the timing curve is at full advance of 30* at about 3000rpm.
We also have a problem with the idle, it keeps revving up and down ever so slightly. Makes me think that with the idle set at around 1000rpm, the distributor is already advancing.
We need new springs and weights for sure.
The 4777 is going to help allot as well.

Get you a 3.5 to 4.0 powervalve and put in the carb before you install it, that way you won't be dumping gas in it while your idling. If you pick up more vacuum as you are tuning it, you may need to go up on the powervalve. Take care of the vacuum leaks. Check the plugs and change the oil. At a gallon of gas per mile, I bet the oil has seen some gas as well