Bucking in first... is it normal

[Usudno]

My 99 Saleen s351 used to buck in first when near idle. I get some pretty rough bucking in the same situation in the cobra. It's a bit worse than I remember. I could manage it by letting of and easing into the throttle on the mustang.. I almost have to gas it to smooth out in the cobra!! Do any of you guys have this issue?

[NAZ]

I see this on cars with a low inertia light flywheel / clutch combo. It will buck a few times if you don't give it enough gas and slip the clutch more than a conventional flywheel. The lower inertia combo also makes it easier to stall the engine if you don't gas it enough when starting from a stop.

[AC Bill]

My roadster does that. Even with the 3.55 rear, which I would have thought may prevented that. I just depress the clutch and coast a bit, or as you say, give it a bit more throttle. Only happens in slow moving traffic, or say when moving up to take a turn at a 4 way stop.
That's one of the issues I run into on some of these organized car cruise nights, that they hold here on the Island every summer. We have 300+ cars all moving along sometimes at just a snails pace.

[CraigS]

Yes, below maybe 1200 trying to maintain a steady speed it will buck. I don't get into that situation much but my cure is push in the clutch and coast a bit.

[Mark Dougherty]

Naz is correct
I have replaced more than 1 alum flywheel with a steel 1 just to help eliminate that issue.
sooo many guys think ah its a race part so it is better when in reality it is not, on the street.
If you are using a your car for cruising and street driving then stick with a steel flywheel.
if you are racing on a regular basis then a aluminum flywheel might be better.
at the cost of the before mentioned low speed bucking.

[GoDadGo]

It Depends On A Lot Of Factors!

What is the operation range of your engine?
My daily driver has a basically stock LT-1 350 CID SBC that makes 300 HP and 330 lbs of torque, but idles like a dream and does not buck because the car is NOT all cammed up.
No bucking occurs even with a very light dual mass 13 lbs fly wheel, McLeod Clutch and 3.55's out back.

The GoDadGo Go-Kart will buck a bit at low RPM's simply because everything in that engine is designed to run well between 2,300-6,500 RPM's.
That engine is a 383 CID SBC, which should make between 430-450 HP and have torque figures between 440-460 lbs.
Some bucking can occur at lower RPM's, even with a 28 lbs billet steel fly wheel, same McLeod Clutch and slightly deeper 3.73's gears out back.

Both cars have the same transmission, same clutch, same size tire, and the daily driver weighs considerably more than the GoDadGo Go-Kart, but the Corvette's combo is set up to run between IDLE and 5,500 RPM's.
My point is that if your car is set up to run at a higher RPM range because of your combination, then some bucking will be likely at lower RPM's simply because your engine may not be designed to run at lower RPM's

Daily Driver: https://youtu.be/svZX2BMSDEs
GoDadGo Go-Kart: https://youtu.be/BcsVu80VG5k

Good Luck & You Likely Just Need To Slip That Clutch Since I Bet Your Engine Is Likely A Tad More Radical Than A Stock Mil!

Steve

PS: I plan to put about 100-150 miles on the MK-4 prior to starting the body work so that I can properly shake it down while things are easy to get to.

[ThickCobra]

Thanks for the thread. I have been taking more neighborhood test runs and find the same thing happening. I found by feathering the clutch at low speeds, and coasting helps.

[JJ in Cbus]

I have a 5.0 with an 'E' cam and 3.55 rear gears and below 1500 rpm my car bucks like crazy. 25mph streets are a challenge to drive without down shifting to raise the rpm or feather the clutch to smooth out the ride.

[phileas_fogg]

My roadster does that. Even with the 3.55 rear, which I would have thought may prevented that. I just depress the clutch and coast a bit, or as you say, give it a bit more throttle. Only happens in slow moving traffic, or say when moving up to take a turn at a 4 way stop.
That's one of the issues I run into on some of these organized car cruise nights, that they hold here on the Island every summer. We have 300+ cars all moving along sometimes at just a snails pace.

That's a good looking parade.


John

[Usudno]

Thanks for the info. I have an aluminum flywheel... I didn't have many options going 351 to tko. I can learn to manage

[Usudno]

Thanks for the info. I have an aluminum flywheel... I didn't have many options going 351 to tko. I can learn to manage

[CraigS]

Two thoughts; 1- There are no details of your car in you signature lines so I have no idea what type of intake you have. Pls add info. 2- If you have a carb, try moving the idle mix screws some. Assuming you are at lean best idle or max vacuum setting now, turn all of them the same 1/2 turn richer (counter clockwise) and go for a drive. Also try 1 turn richer. This is a temporary test to see if the idle system (which affects the engine up to about 22-2400 rpm) is good. If the 1/2 turn helps, I'd leave it there. If the full turn helps, you will need to make some jetting changes as leaving the idle that much extra rich wouldn't be good long term.

[Usudno]

Sorry Craig.. 351w, tko500, 3.55 rear, performer rpm manifold. I'll get around to adding a sig with details.

[CDXXVII]

I imagine your aluminum flywheel is not helping much. Ford Racing offers a billet steel unit that should work for your application.

I had similar issues with my setup but my root cause was my McLeod Twin disc clutch and also throttle control.

Measure you pedal travel. A lot of guys end up with a throttle that is more of an on off switch than a smooth throttle. I did not have adequate pedal travel and any bump would translate into bucking.

Where are you connecting to on you carburetor? I moved my connecting point all the way out. I needed to get some brass throttle adapters to allow using the 1/2" hole. My bucking is mostly gone and the throttle is much more predictable.