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Late last summer my car ('79, 427 small block, TKO 600) started pinging at part throttle around 2000-2200 rpm. My differential diagnosis includes ignition timing, stuck power valve, and bad gas. Alcohol free premium is getting hard to get in Canada and I suspect the station where I have been buying my gas may have started adding ethanol.
I checked my timing today. Here is what I got. It is unchanged from what I charted last year so I'm thinking it's not timing. I'd appreciate any input.
You don't need Ethanol free. In fact, Ethanol increases octane. So thats not your issue.
Ethanol Free is a "storage" fuel for long term parking of carbureted engines.
You have something else going on.
Check the plug wire routing of # 5 and # 7. Make sure that from the cap, all the way to the plugs, those two are well separated.
Use your wire looms to keep them on opposite sides of the loom.
Your pinging may be Cross-Fire-Induction. Number 7 may be firing before 5.
You don't need Ethanol free. In fact, Ethanol increases octane. So thats not your issue.
Ethanol Free is a "storage" fuel for long term parking of carbureted engines.
You have something else going on.
Check the plug wire routing of # 5 and # 7. Make sure that from the cap, all the way to the plugs, those two are well separated.
Use your wire looms to keep them on opposite sides of the loom.
Your pinging may be Cross-Fire-Induction. Number 7 may be firing before 5.
Excellent suggestion. Thank you. That's exactly the kind of ideas I am looking for. I doubt if that's the problem as I can't imagine how that would start suddenly, but I will definitely check it out.
If you suspect alcohol in the fuel you can test it. Just put a little water in a see through tube/jar and mark the water level. Add gasoline. If the water rises above the mark then there is ethanol in the fuel since ethanol will readily mix with water. If it doesn't rise then it's pure gasoline.
If it is pinging at part throttle.....it is most likely the vac cannister.....unplug the cannister and go for a ride.....does it stop?
Ethanol has zero to do with it......
If you have a std vacuum gauge it likely came with about two feet of hose.
You can go to a parts store and purchase about six feet of that hose. Find a Vac port you can tap into.
Run that extra long hose into the cockpit thru an open window. You can leave the hood unlatched, won't hurt a thing.
Go for a ride. Notebook and pen.
Note different RPM ranges and jot down your vacuum reading.
What you don't know yet is where your Power Valve is opening (or should open). You might be running lean until the P.V. kicks in.
What number is stamped the P.V?
If it is pinging at part throttle.....it is most likely the vac cannister.....unplug the cannister and go for a ride.....does it stop?
Ethanol has zero to do with it......
Jebby
Thanks for the suggestion. I did try that last Fall just before I put the car away. It did not solve the problem, and on the same ride I developed another problem that took priority so I didn't get a chance to chase it further. I may repeat the experiment in the Spring. This time, if disconnecting the vacuum canister doesn't help, I'll start backing off the timing until the pinging stops. I have to admit though, I was getting the distinct impression that it was not related to ignition timing. I would have expected some change in response to disabling the vacuum advance, and there was exactly zero.
If you have a std vacuum gauge it likely came with about two feet of hose.
You can go to a parts store and purchase about six feet of that hose. Find a Vac port you can tap into.
Run that extra long hose into the cockpit thru an open window. You can leave the hood unlatched, won't hurt a thing.
Go for a ride. Notebook and pen.
Note different RPM ranges and jot down your vacuum reading.
What you don't know yet is where your Power Valve is opening (or should open). You might be running lean until the P.V. kicks in.
What number is stamped the P.V?
That's an excellent suggestion. I was toying with the idea of installing a vacuum gauge in the cockpit, but it's getting crowded in there. I'm really not even thrilled with the AFR gauge I have mounted in there but that's just too useful to give up. But I digress.
The PV is the 6.5 that came with the carb. What is your philosophy when it comes to PV selection? I've heard more than a couple over the years, none of which impressed me as very logical.
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Check for burned plug wires....look lnto methanol injection.....try using seafoam to steam clean your pistons and valves, maybe it will scorch off the deposits...or just use water in a spray mist bottle hold your rpm up to 2500 rpm and mist above the carb...it will also steam clean the pistons if its a deposit issue.
The other school of thought seems to be to go closer to idle vacuum. I have about 12” at idle. I’m thinking of trying an 8.5. Any thoughts?
No thoughts. Power Valve tuning is an art.
I tried one size up. One size down. Little effect.
At $25 a piece, you don't want to keep doing that all day.
I did notice on Ebay years ago, that you can get a bag assortment P.Vs all within a few inches of each other a lot cheaper than individually.
Some tech forums said to stay away from "two-stage" and avoid those power valves with huge windows. Racing valves, not street.
Stick with original Holley or QuickFuel parts.
03-25-2024, 05:15 PM
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