Cold starts on only a few cylinders

[Burgs]

It's a Pond aluminum KCraft 482, Pro System Carb, msd 6al, blaster 2, and under 500 miles. This thing has been starting without hesitation, all summer. The last few times I started the motor it's been in the mid 50s. It starts and runs on what seams like only a cylinder or two. Rather than let it stall, I slip it into gear and roll away slowly. Every 1/8 mile or so additional cylinders start firing, and as things warm up everything smooths out and it runs smooth as silk. Yesterday, maybe 60-65*, it started on maybe 5 or 6 cylinders, and rather than roll away, I held it at about 12-1500 rpm, and as it warmed up, a minute or two, it smoothed out. I rolled out and had an hour and a half ride, smooth as ever.

Could this be the lack of a choke causing this? Anything else to look for?

Thanks,
Brad

[undy]

The colder it is the more fuel is required on a cold engine to sustain combustion. I'm assuming the Pro-system's carb is a modified Holley HP, no choke. That's about the only way to do it.. Play with the pedal until it starts hittin' on all eight. Don't rev it much until you come up to operating temperature.

Dave

[Burgs]

Thanks Dave, Yes, it is a modified 4150 Holley, with no choke.

[lineslinger]

It's asking for a bigger fuel charge Burg's, in essence there isn't enough fuel to "go around", the charge being too dense to reach all cylinders, so you are probably only getting ignition on those cylinders to which the fuel air mixture flows most readily.
As the motor heats up the mixture atomizes more readily, this expansion is a result of heat build up, which offers a better fuel charge flow to the lean/starved cylinders, thus the gradual improvement in engine performance.
I run twin Holley's but only one of them has a manually operated choke, which is more than enough to supply cold start fuel needs.

[Bryan Wilson]

I used to run a Holley street avenger with choke and would start and idle from cold with a little choke.
Now I run a Holley HP with no choke and it runs like a dog until it gets a bit of heat into it but I can live with a bad cold idle as the bigger carb now gives a noticeably better top end.
Cheers,
Bryan

[Wayne Maybury]

As Undy said, play with the gas pedal until it runs better. Don't allow the revs to come way up with a cold engine but if you don't have a choke, about the only way to keep the mixture rich enough is by tapping on, or playing with, the throttle. Each time you press on it slightly, the accelerator pump gives a little squirt of raw gas thereby making the mixture richer. It usually will only require this for a minute or two before it will begin to run normally. Starting an engine and keeping it running at a temperature well below freezing, requires much more aggressive use of the gas pedal if there is no choke. An automatic transmission also makes it much more difficult to employ this technique as you have to constantly shift it between drive and neutral.

Wayne

[Rick Parker]

With the air temprature and the interior surfaces of the manifold both cold the fuel will fall out of suspension at low throttle openings and will puddle on the floor of the manifold. Not until a small amount of heat is transfered into the manifold causing the fuel to resist puddling will it begin to idle acceptably. Manifolds without an exhaust crossover and single plane type manifolds are the worst. A choke will reduce the amount of air that can be pulled through the carburetor and causes additional fuel to be pulled, temporarily making up for what is puddling. Once some heat is developed and all the fuel is being atomized the air fuel ratio has to be leaned out to keep it running (by relieving the choke). If you have no choke, additional fuel is added by blipping the throttle pedal.

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