67 Coronet - 440 Stumbles when in gear

67 Coronet - 440 Stumbles when in gear - 04/30/12 02:05 AM

Hey guys!

Well I just got my Coronet out to the track for the first time after repainting it and rebuilding the engine, plus all the issues I've had to put up with and it just continues!

Started the car up, warmed it up to 180... When I'm in Park or Neutral, I can hit the throttle and I have perfect response, engine doesn't backfire, or stumble or anything...

Now when I have it in gear and I slam on it, it'll stumble real bad and then die out. If I'm easy on the throttle it'll go, but I just can't hammer it...

Carburetor has been rebuilt and I am at 12 degrees before TDC on initial timing. I got the 6T MSD Box w/ Master Blaster Coil. Its a 440, got a 700cfm Holley Double Pumper on there, Hughes "Whiplash" Cam [.518 Lift], 2500 Stall Converter, and a Cheetah Manual Valve Body installed. I was thinking maybe it was low on trans fluid, because I know that engines do strange things when it's low... But it was right where it needed to be...

All advice is welcome!

Thanks, Craig

Posted By: Coronet-R/T-Rag

Re: 67 Coronet - 440 Stumbles when in gear - 04/30/12 02:13 AM

Does it bog as soon as you hit the gas or does it go and then bog?

Posted By: TheCragarKing

Re: 67 Coronet - 440 Stumbles when in gear - 04/30/12 02:16 AM

It'll stumble out as soon as the pedal hits the floor.

Posted By: Dodgem

Re: 67 Coronet - 440 Stumbles when in gear - 04/30/12 02:19 AM

Probably needs more initial advance.

cam degreed in.

No vacuum advance hooked up??

and if you hook vacuum advance up later ported vacuum only!!

Posted By: Coronet-R/T-Rag

Re: 67 Coronet - 440 Stumbles when in gear - 04/30/12 02:19 AM

Quote:

It'll stumble out as soon as the pedal hits the floor.

Sounds like the carb. Not enough accelerator pump shot. Any vacuum leaks?

Posted By: TheCragarKing

Re: 67 Coronet - 440 Stumbles when in gear - 04/30/12 03:12 AM

No vacuum leaks that I know of... It runs just fine in Neutral and Park, but its just when its in gear that it'll do that

I got the vacuum advance going into the port on the carburetor and I blew it out so I know it isn't plugged or anything...

What do you mean by "ported vacuum only"?

Posted By: Dodgem

Re: 67 Coronet - 440 Stumbles when in gear - 04/30/12 02:44 PM

Quote:

No vacuum leaks that I know of... It runs just fine in Neutral and Park, but its just when its in gear that it'll do that

I got the vacuum advance going into the port on the carburetor and I blew it out so I know it isn't plugged or anything...

What do you mean by "ported vacuum only"?

If your on a manifold vacuum port it pulls vacuum at idle advancing the timing the ported vacuum port does not.

So if you have say 12 advance idling in gear but vacuum is giving you 20 of that when you mash the throttle you have 0 vacuum and timing falls to - 8 degrees. Big ass bog!!!!! at that point you really need 20 deg. (or more) purly mechanical advance.

SOOOOO since vacuum advance is a crude gas mileage enhancer designed to work at light cruise lets plug it for now.

With that cam you probably need to re curve you distributor to give you 20 advance idling in gear and all in 38 by 2000.

You set it up this way with vacuum disconnected and plugged for now or forever and your engine will wake right up!

SINCE
Vacuum advance is designed to work at light cruise 50 to 75 mph to in fact over advance the timing to carry the motor and give a 1/2 mile to the gallon better fuel mileage. the throttle blades being open open the vacuum port to vacuum allowing it to work. heavy throttle again no vacuum so the vacuum advance drops out and you are back on mechanical only advance.

Hope this helps a bit. Hear is a picture of typical Holley ported vacuum port.

Posted By: Mr.Yuck

Re: 67 Coronet - 440 Stumbles when in gear - 04/30/12 03:11 PM

You need more initial timing for starters, 18* or so and 36-38* total early around 2200. As for the carb any idea how it's set up? Probably could use at least a 750 but for the 700 I'd probably use 78-84's for jetting, 31 squirters and go from there. No reason it should fall on it's face like that...and it revs fine in N or P is because you don't have any load on the motor. It'd rev w/ a 2bbl.

Posted By: oldsklharo

Re: 67 Coronet - 440 Stumbles when in gear - 04/30/12 03:43 PM

Quote:

Quote:

No vacuum leaks that I know of... It runs just fine in Neutral and Park, but its just when its in gear that it'll do that

I got the vacuum advance going into the port on the carburetor and I blew it out so I know it isn't plugged or anything...

What do you mean by "ported vacuum only"?

If your on a manifold vacuum port it pulls vacuum at idle advancing the timing the ported vacuum port does not.

So if you have say 12 advance idling in gear but vacuum is giving you 20 of that when you mash the throttle you have 0 vacuum and timing falls to - 8 degrees. Big ass bog!!!!! at that point you really need 20 deg. (or more) purly mechanical advance.

SOOOOO since vacuum advance is a crude gas mileage enhancer designed to work at light cruise lets plug it for now.

With that cam you probably need to re curve you distributor to give you 20 advance idling in gear and all in 38 by 2000.

You set it up this way with vacuum disconnected and plugged for now or forever and your engine will wake right up!

SINCE
Vacuum advance is designed to work at light cruise 50 to 75 mph to in fact over advance the timing to carry the motor and give a 1/2 mile to the gallon better fuel mileage. the throttle blades being open open the vacuum port to vacuum allowing it to work. heavy throttle again no vacuum so the vacuum advance drops out and you are back on mechanical only advance.

Hope this helps a bit. Hear is a picture of typical Holley ported vacuum port.

I'm interested in checking my vacuum and setting the metering screws with a gauge as well but your pics says "Good Wrong" place to check vacuum on the lower port

Is that a misprint? Isn't that the best place to gauge manifold vacuum?

Thanks, MIke

Posted By: Dodgem

Re: 67 Coronet - 440 Stumbles when in gear - 04/30/12 04:01 PM

I'm interested in checking my vacuum and setting the metering screws with a gauge as well but your pics says "Good Wrong" place to check vacuum on the lower port

Is that a misprint? Isn't that the best place to gauge manifold vacuum?

Thanks, MIke

Dam phonics! LOL! should say
This is wrong. A good place to hook a vacuum gauge.

Or
This is wring, a good place to hook a vacuum gauge however!!
Sorry

Posted By: oldsklharo

Re: 67 Coronet - 440 Stumbles when in gear - 04/30/12 04:02 PM

Quote:

I'm interested in checking my vacuum and setting the metering screws with a gauge as well but your pics says "Good Wrong" place to check vacuum on the lower port Is that a misprint? Isn't that the best place to gauge manifold vacuum?

Thanks, MIke

Dam phonics! LOL! should say
This is wrong. A good place to hook a vacuum gauge.

Or
This is wring, a good place to hook a vacuum gauge however!!
Sorry

Ooooh I see

Thanks