What causes an engine to 'buck' at low speeds?

[Marc #561]

Here is my very simple nsolution, as every high performance US Po

[Cobrajames]

Originally Posted by Marc #561

Here is my very simple nsolution, as every high performance US Po

I think that I will try that first thing tomorrow.

[Dwight]

Marc
you need to explain what you mean by "Here is my very simple nsolution, as every high performance US Po"

I don't understand your comment.

Dwight

[SNClocks]

GOOD DAY TO Club Cobra!

Kelly and I bought our Superformance Daytona Coupe (0065) nearly 2 months ago and have put 1,500 miles on her so far. Our Focus, for now, is to wipe out niggling little issues – we have gotten both doors to open and close smoothly, added Freon, quieted her down a bit, started tuning on the carb so she will start and even idle when cold or hot, hooked up the reverse light switch, adjusted the emergency brake (suspect I will need to modify a bit to get more leverage/less travel), and generally are getting used to driving her. We’ve had her in a couple of shows and ‘cars and coffees’ and gotten very kind comments from all and sundry. Heck, a few even knew of these cars.

I am in hopes that, since you folks have had your cars for a while, that you can provide some well-needed technical guidance on the remaining techie issues.

First question that I could use help on: When the engine (427R with 770 Holley) is running at below 2,000 rpm, at minimal to slight throttle opening, the car bucks. From reading on this forum, it sounds like the transition from the idle circuit to the high-speed fuel circuits can be tricky and result in a lean mixture – specifically at slight throttle openings. In our car, opening the throttle more than just a little eliminates the bucking, but with a slight opening, as in cruising down the road at less than 2,000 rpm, it bucks pretty hard.

This forum indicated that changing the “idle feed restrictor jets” on the secondary side from 0.035 to 0.037” eliminated 95% of the problem. So, finally the question: Have any of you with a 427R and a 770 Holley addressed this issue? Somehow I suspect the 750 Holley's are pretty similar.

Looks like it is easy to buy jets on-line. My gut feeling is I need to get an air/fuel ratio meter and use it to troubleshoot – likely we need it anyway to set the triple carbs on our XKE (of course, we have put 130,000 miles on her just setting the carbs by ear – but surely a meter would make her run better). I will admit it is tempting to put fuel injection on the Daytona – it really does make a big difference, and we love the MSD system we put on our Pantera. But, heck, if just some jet work would resolve this issue – it would be a lot easier.

Your comments please!

[blykins]

Originally Posted by SNClocks

GOOD DAY TO Club Cobra!

Kelly and I bought our Superformance Daytona Coupe (0065) nearly 2 months ago and have put 1,500 miles on her so far. Our Focus, for now, is to wipe out niggling little issues – we have gotten both doors to open and close smoothly, added Freon, quieted her down a bit, started tuning on the carb so she will start and even idle when cold or hot, hooked up the reverse light switch, adjusted the emergency brake (suspect I will need to modify a bit to get more leverage/less travel), and generally are getting used to driving her. We’ve had her in a couple of shows and ‘cars and coffees’ and gotten very kind comments from all and sundry. Heck, a few even knew of these cars.

I am in hopes that, since you folks have had your cars for a while, that you can provide some well-needed technical guidance on the remaining techie issues.

First question that I could use help on: When the engine (427R with 770 Holley) is running at below 2,000 rpm, at minimal to slight throttle opening, the car bucks. From reading on this forum, it sounds like the transition from the idle circuit to the high-speed fuel circuits can be tricky and result in a lean mixture – specifically at slight throttle openings. In our car, opening the throttle more than just a little eliminates the bucking, but with a slight opening, as in cruising down the road at less than 2,000 rpm, it bucks pretty hard.

This forum indicated that changing the “idle feed restrictor jets” on the secondary side from 0.035 to 0.037” eliminated 95% of the problem. So, finally the question: Have any of you with a 427R and a 770 Holley addressed this issue? Somehow I suspect the 750 Holley's are pretty similar.

Looks like it is easy to buy jets on-line. My gut feeling is I need to get an air/fuel ratio meter and use it to troubleshoot – likely we need it anyway to set the triple carbs on our XKE (of course, we have put 130,000 miles on her just setting the carbs by ear – but surely a meter would make her run better). I will admit it is tempting to put fuel injection on the Daytona – it really does make a big difference, and we love the MSD system we put on our Pantera. But, heck, if just some jet work would resolve this issue – it would be a lot easier.

Your comments please!

Could just be the camshaft. It's sometimes difficult to balance a "lopey cam" with pleasing low-rpm characteristics.

That Holley Street Avenger is not doing you any favors though....

[Gaz64]

Originally Posted by blykins

Could just be the camshaft. It's sometimes difficult to balance a "lopey cam" with pleasing low-rpm characteristics.

That Holley Street Avenger is not doing you any favors though....

Agree.

Some part throttle roughness just might be the way it is.

There are many carbs available now that would be better than an "out of the box" avenger.

Some of mine have been rough at low speed, I just live with it as a trade off for the explosive mid to top end.