Help!! Engine Miss

[dartman]

Originally Posted by Ben Kallies

Dion,

I sent the carb back to Deano and made him aware of the issue. He completely disassembled the carb, and checked all of the passages. Everything looked good.

Dirk,

Thanks for the offer to help. I've got family in LaCrosse - beautiful area. Ground wires are my current focus. I'll be changing some things around even if it doesn't prove to be my problem.

Nitroman,




I plan to eliminate the vehicle wiring from the equation one way or another in the testing process. I think I'll start with what Alan suggested and run all MSD wiring straight to the battery to eliminate the rest of the vehicle wiring from the equation. If that doesn't do it, the next step is an HEI to eliminate the ignition as well. The second MSD box that I tried was brand new, and will be in retested in another vehicle this weekend or next, so that will confirm whether or not that box is good.

-Ben

have you tried a different carb?

[Adger Smith]

Ben,
I built a new engine for a customer and it missed and popped from the very first time we started it. Took it out of the car and put it on the dyno and all was fine. Changed everything in the car we could think of. The last thing we changed was the master cut off switch. We should have changed it first.

[Pvt Parts]

Originally Posted by Adger Smith

Ben,
I built a new engine for a customer and it missed and popped from the very first time we started it. Took it out of the car and put it on the dyno and all was fine. Changed everything in the car we could think of. The last thing we changed was the master cut off switch. We should have changed it first.

Now that you mention it, I've heard of that happening before.

[Ben Kallies]

Thanks to all for your input so far.

I've already got a #10 ground strap to one head, and I'm down to bare metal at both contact points. I'll add a second ground strap to the other head, just to be safe. Please keep the experiences and thoughts coming. It gives me places to look, things to check, and God-willing, the possibility of narrowing down the problem.

-Ben

[67camaroracer]

Did anyone mention a firewall feed thru for the coil wire, ?

[goinbroke2]

Flat lobe on exh would cause popping out carb.

If it's a miss while reving in neutral I would of closed off the choke and check the result.
Also look down the throat while reving and see if it's a smooth pattern of fuel or blobs of fuel from the emulsion tubes on both sides. If it makes no difference, rev it and move the dist around(advance/retard) and listen for a difference.

I'd also close the gap on the plugs to about .030 just to test.

Another dist wired directly to batt and another carb will prove if it's external. Your saying you've switched dist and carb so next is;

Comp check and leak down

Valves are adj right.....you didn't leave the break-in valvesprings on did you???
vacuum leak, p/brake hose cracked or carb gasket etc?


And the "out there ones"
Same oil pan as the dyno? thinking oil pump sucking the pan because of lack of clearance and the resulting vibration/cavitation acting on the dist causing spark scatter.

How did you lift the engine to install it? undo an intake bolt or remove carb and use lift plate? Check those area's for warp/vac leak

[Ben Kallies]

67camaroracer,
-coil is mounted on the firewall. No feed-through. Already replaced the coil and wires.

goinbroke2,
- car starts right up and fuel flow is smooth out of the squirters. Fuel pressure gauge is rock steady.
- oil pan is the same as dyno, and oil pressure is good.
- lifted the engine in the car via a carb-plate
- break-in springs were changed on the dyno
- while I haven't hooked up a vacuum gauge yet, I've checked for leaks visually. The engine is running rich as opposed to lean, so I don't suspect a vacuum leak. The unburned fuel brings tears to my eyes when it's running, and the plugs are all over the map, but mostly dark.

-Ben

[Alan Roehrich]

Ben, can the miss be isolated to one or two cylinders, or is it just a miss that moves from cylinder to cylinder?

With a completely different ignition system and carburetor having been tried, if I read correctly, you're starting to move toward a mechanical problem, as much as that is something you do not want to hear. I'd do a compression test, check the lash, check the lobe lift, hook an undampened vacuum gauge to a manifold vacuum source, and check the valve springs.

You might try a fresh set of slightly (1-2 steps) hotter plugs, with a gap in the 0.026" range.

Have you hooked a volt meter to the various 12 volt positive inputs to the ignition system? You might look for a voltage drop when the miss is happening.

[Ed Wright]

Alan said: "hook an undampened vacuum gauge to a manifold vacuum source, and check the valve springs."

Exactly what I was thinking. Found a lot of miss-fires other shops didn't seem to be able to find on my big old Sun Engine Analyzer bu using it's big, un-dampened vacuum gauge.
Invaluable tool if you learn how to use it. You can even isolate the offending cylinder with it. Just put a short piece of vacuum hose between each plug wire and the cap. Using a long screw driver with a jumper wire grounding it to a good ground, touch the short pieces of vacuum hose to ground the spark for each cylinder. If it's a cam or valve or spring problem the gauge will smooth out a lot when you ground the offending cylinder. It will deflect some for any miss-fire, but much more with a leaky valve.

[Ed Carpenter]

Ben when I tried everything I could think on mine a few years ago I just gave up and had Mike Bush completely rewire my entire car. Hope you solve this. trust me it will be something small when you find it. Ed