GEneral Engine Problem

[Jim K.]

I'm still not done checking it out but I am having a problem with my 61 that just started.
Here's what it's doing:
Starting fine; runnung low to mid range RPM fine; Breaking up mid to high RPM range with loss of power and backfiring, don't know color of exhaust.
Here is what I have checked:
Vacuum advance working, no other apparent vacuum leaks; centrifical advance weights and springs working; replaced in line fuel filter; replaced cap and rotar (has petronix breakerless 2 wire); no apparent carb backfiring.
I'm thinking more a spark thing than a fuel thing, but may be a valve thing??? Could be a plug wire thing or fouled plug. I'm going to pull a few plugs next. Maybe it's the petronix breaking down... Anythoughts out there?
Thanks!
Jim

[Mike B.]

Re: GEneral Engine Problem

Jim,

I don't know what tools you have at your disposal but if you have a vacuum gauge check if the needle is steady eliminating the possibility of valve issues such as incomplete closure or valve bounce at higher speeds. It could also help to diagnose the ignition timing through the rev range.

My guess is the ignition system. Could be the advance curve although you believe the advance unit is working. If you have access to a modern timing light where you could dial in the timing at different rpms that could help the diagnosis.

But short of that pull the plugs and see what they tell you. Also check for "dumb" things such as the plug wires crossed (particularly #5 & #7).

I am sure others will have more suggestions.

[Dennis H.]

Re: GEneral Engine Problem

I agree with the previous post. Check those plug wires. Check and double check.

[Jim K.]

Re: GEneral Engine Problem

Thanks Mike!
Part two:
Checked a couple of plugs on each side - grey no fouling
Checked all the wires for crossed and melted areas and connections on both ends all 9 wires - good
Pulled the valve covers, saw no apparent broken springs or rocer arms.
NEXT Tomorrow: vacuum guage and timing light tricks (thanks Mike) also thinking a new air filter may help as high revs while under the hood 9no air cleaner) seem fine, maybe a flooding thing? It all started about a week ago after a 1/2 hour ride home from work intraffic and highway, suddenly started breaking up at the high end... I'll keep playing tilll I figure it out...

[Duke W.]

Re: GEneral Engine Problem

Get a couple of test leads and rig up a dwell meter inside the car and go for a drive. You can also use a voltmeter if you don't have a dwell meter. If the dwell/voltage drops way off when the engine breaks up it's a distributor problem - bouncing points, wobbly breaker plate, excess end play, etc.

If the dwell holds steady it could be something else in the ignition system like the coil or wiring or it could be a fuel starvation problem. A new filter can plug quickly if there is debris in the fuel system, or debris can block the needle seats.

OE type RFI wires should have about 5K ohms per foot resistance, and it should hold steady as you wiggle the wire.

Duke

[Ray G.]

Re: Old gas ? Plugs can look good, but b fouled. *NM*

[Terry R.]

Re: GEneral Engine Problem

Had a very similar problem a few years ago,ground wire from breaker plate to housing, broke but insulation intact. Started good idled good above 3000 RPM did all kinds of wild things. Have fun.

[Jim K.]

Re: GEneral Engine Problem

Thanks again to all (Mike Dennis Duke Ray & Terry) I like the dwell meter idea, I'll try that today. I was also thinking fuel starvation and plugged jets. I sealed the tank 5 years ago and the filter is aftermarket in line type didn't have a ton of crap in it, but who knows. The carb is an aftermarket Edelbrok 600 and I was thinking of a jet change, but want it running right first... wish me luck!!!

[John O.]

Re: GEneral Engine Problem

Hi Jim

You say it,s an Edelbrock Carb with an in line filter? I just wanted to ask, does it still by any chance have the small filter in the Carb at the inlet that you may have forgotten about? Cause that would get dirty and with 2 filters, you would restrict the proper fuel at higher RPM,s. Also how is your timing and are you getting enough Vacuum for the Vacuum advance? Lastly, you may want to take the top of the carb off and and check for debri and check float level. Just my 2 cents.

Good luck....John

[GL Anderson]

Re: GEneral Engine Problem

Had a problem very much like yours and chased it till I found the coil was bad. Good enough for low rpms and starting but it would start breaking up past about 3K. Worth a try. GL

[Mark S. Lovejoy]

Re: GEneral Engine Problem

Hi Jim,

Have you checked the distributor cap/rotor? Look inside the cap for carbon tracks, look at the rotor for pitting. A previous post mentioned the coil, have you tried a different one?

Best Regards,

Mark

[Jim K.]

Re: GEneral Engine Problem

Yes edelbrok but I didn't know it had an in carb filter, I'll look at that next. The funny thing is that when I take the big vacuum cap off the idle picks up to about 1200 andruns smooth with steady vacuum... I'll keep checking, thanks John, GB and Doc Lov. I checked the dwell and it was steady but there are no points anymore (Petronix) it feels like fuel starving, pot pops and farts like a spark timing thing. I can go back to my old coil too... stand by...

[Rob Dame]

Re: GEneral Engine Problem

Perhaps the tank sealer you used is coming loose and collecting on the filter in the tank

[Chuck R.]

Re: GEneral Engine Problem

If you have no indication of bogging down before it starts it's antics, it might be a plugged filter at the carb, but usually a clogged filter affects the engine at most all ranges.

I would be suspect of the coil as well.

If you DO change out the coil, verify that the filters are clear and the problem still exists, then the Petronix system would be next on the suspect list.

[Duke W.]

Re: GEneral Engine Problem

The intermittent breaker plate ground wire has bitten a number of people. The wire fatigues over many miles due to action of the vacuum advance. If it goes open the dwell will effectively go to zero.

GM's spec for dwell variation is 2 degrees and more indicates that the distributor needs work.

Since no new breaker plates are available (The wire is part of the breaker plate assembly), you will have to repair the wire. The NAPA part number for the repair wire is LW42.

Duke