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427 down on power
I have a 750cfm Holley on my 427, which was built by Southern Automotive and something isn't quite right with the engine. Although everything appears OK and it sounds fine, it just doesn't have the "go" that it should have and it's reluctant to rev.
I've checked the plugs and they are very clean and pale, maybe a little too pale. Fuel pressure is fine. How do I know if the secondaries on my Holley are working OK? I've removed the choke assemby and I'm running a K&N filter. Any ideas ? BTW, it has only run for a couple of very gentle hours. Paul |
Can you clarify your statement about not wanting to rev? Will it not pull past a certain point?
Is your carb mechanical or vacuum secondaries? |
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Also is the Holly a double pumper or not. If it has mechanical secondaries you can check to see if they open with the engine not running. Just pull the throttle back and watch to see if they open when it gets to the point the cam is set at. If it is a double pumper you will see gas squirt in the secondary end as well as the primary. And do you have the specs that tell what RPM the engine should make peak power and torque?
Ron |
I'm sorry, I should have said, the secondaries are vacuum.
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Check the timing. If is retarded or erratic, pull the distributor and check whether you're losing the distributor drive gear.
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Try to take it very scientifically, at first especially
- Verify with someone else on the throttle (not running) that the throttle is opening all the way - Check the initial and total timing to ensure it is where you want it, and that it is advancing - Review the firing order and make sure you have it correct - Readjust the valves if you have solids - Check how close the air cleaner lid is to the top of the carb Dont ever discount bringing a good mechanic in for his ear as a backup plan, even if you only pay him to listen. Often it can go a long way |
Cam shaft is retarded, like strictlypersonal alluded to...
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Another suggestion to check if your secondaries are opening is a trick I learned years ago when racing . Take a piece of vacuum line slightly smaller in diameter than the secondary vacuum shaft ... about 1/8 " long and split it lengthwise and then put it on the shaft up as far up as it will go . Drive the car wide open and then look at the tubing . This will tell you not only if the secondaries are opening , but how far . Think of this as a travel indicator like is on a shock .
I also like all the other suggestions .... something like this can drive you crazy ... or in my case , crazier !! |
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http://img.photobucket.com/albums/v2...ck/Holley2.jpg After (if your secondaries are opening, that is...) http://img.photobucket.com/albums/v2...ck/Holley4.jpg |
Why not call Southern Automotive and ask them ? Did they build the carb ? What compression ratio ? Sounds more like a timing issue to me. What grade of gasoline are you running in it ?
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If you want to try the disconnect the secondaries method, it's only a "c" clip that holds the vacuum linkage to the secondary shaft. Just pop it off.
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FB -- How much throttle pedal travel do you have from when your foot is just touching the pedal to when you have it pushed all the way to the floor (in inches)?
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"Reluctant to rev", that description just doesn't sound like a carb issue to me.
Verbal or typed descriptions/symptoms are particularly difficult to get a handle on, by the way... Of course if the secondaries aren't working that will reduce the horse power, but it should not make it reluctant to rev. THAT description does sound more like: Plugged exhaust (not likely). Retarded mechanical camshaft timing. Retarded ignition timing, base or advance curve incorrect or sticking mechanical advance. Along with plugged exhaust factor in valves sticking in the guides or grossly misadjusted, which could give the same symptoms as plugged/restricted exhaust. Weak spark, can't fire the fuel properly. |
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...and inadequate fuel supply.
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Thanks guys for all your input.
The exhausts are fine i.e. not plugged. The ignition is an MSD 6AL with an MSD billet distributor. It starts up and ticks over just fine after a few seconds of warming up. I'm inclined to think it is fuel starvation. The plugs are very clean (possibly too clean). I'm going to pull the carb today to make sure there isn't any dirt in it. With regard to "reluctant to rev", by that I mean it lacks power and starts to miss above 3,000rpm. Thanks again. Paul |
Starts to miss above 3000, whoa, big clue there, the mystery deepens, what does it all mean...
Any hint of a backfire condition (popping sound in the air cleaner/carb in particular), which is sometimes associated with a lean condition (among other things)? |
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