I'm getting to the end of my rope with this 300 and I'm not sure what else I can do to get it run better. I've got a small laundry list of things I've done to make it run better so help me if I'm missing something.

Duraspark II conversion with new dizzy, new plugs, and new wires.
New single barrel carb from Rally. (Manual choke)
New manifold gasket, including the gasket between the intake and exhaust. Also wired the flapper in the open position.
New gasket between the intake and EGR plate
New gasket between carb and EGR.
All new vacuum lines and plugs for everything else.
New PCV and hose.
The compression is 110 to 130 front to back.
I'm pulling about 21 lbs of vacuum at idle.

When I crank it in the morning, it cranks right up and idles great! After a few minutes you can begin to detect a slight miss and after about 10 minutes is a very distinct miss. Under throttle it runs great but as soon as you level off to just cruise down the road, it begins to sputter and miss. Pull up to a stop light and it runs really rough. I

I'm beginning to think it is the carb, but I don't know what to look at next. Thanks for any insight...

 

With all the ignition components being new, I'd wonder about the carb myself except for the fact that it is also new. Granted, new doesn't always mean good when it comes to parts so we're back at square one there.

Have you ever changed the coil? They do fade out over time and they give temperature problems, like it developing the miss only after its been running for a period of time. It does make me wonder if that could be your issue. The next time it goes to missing, pop the hood and touch the side of the coil and see how hot it is. If it is so hot you can't touch it, then you need a new one. If its just warm, then I doubt it is the problem but it couldn't hurt to swap it with another one if you have it.

 

We'll do. The coil was new with the dizzy, but you are right, it could be, especially when it comes from the generic parts store.

 

Yep check the coil.

You stated...

"Also wired the flapper in the open position."

Do you mean the heat riser? Maybe the carb is getting to hot.

You also stated...

"I'm pulling about 21 lbs of vacuum at idle."

With that much maybe you are sucking the hood down to the carb and choking it off. Sorry I could not resist.

I assume you mean 21"? Is this after it is at operating temp, is it steady? Try torquing everything to see if maybe their is a leak.

Jim

 

The heat riser is wired in the open position meaning it is wired so exhaust is aimed toward the exhaust, not the intake. It was broken when I pulled everything apart to replace it and was broken so the exhaust was always going into the intake.

I have noticed the hood flexing inward... I'm sorry, I did mean inches. It is after it is warm and it seems to be very steady. After I replaced the manifold gasket, I ran it till it got hot, then after it cooled down, I re-torqued everything to make sure it was tight and right.

I'm really starting to question the carb more and more. I wish I had another to test with, but I may just purchase another one other than the Rally to check. One of the things the Rally carb doesn't have is a venturi vacuum port and I need one for the vacuum advance.

Any recommendations on a one barrel replacement?

 

Any chance you'd post up or pm the source for the carb?

Thanks.

 

IIRC, I think I posted either in this forum, or the 80-86 Forum about a replacement reman holley carb. Search under my name and it should pop up. I can vouch for the carb working about flawlessly out of the box, only needing the typical idle/fuel mix adjustments to get it 100%.

I'll see if I still have the receipt with the PN to post up, let me dig around.