Engine miss

[Taylorman]

Saturday we did a little skiing. When i would hit the gas, motor would miss and sputter just a few times till the rpms got up a little. Its not bad, but its not right.After that all the way to wot, ran like a top. It would only miss under hard initial acceleration. This is the first time ive had this problem. I ran it weekend before last and i did not notice the miss.

[Taylorman]

Bueler, Bueler?
Would moisture under the dist. cap cause this?

[502 JET]

I doubt the moisture would help.
Check your fuel water seperator.
If you are running power valves you may have popped one flooding the engine at lower rpms.

[Taylorman]

Everything i have read regarding new Holley carbs is that powervalves do not blow out anymore. Ive read that only real old Holley carbs blew powervalves.

[502 JET]

The power valve may not have blown out. But they can still go bad.
IE: the diaphram expired
PV's may not blow out if you have the blowout prevention check valve in your carb. Newer carbs may have these. (not positive if all carbs come with it) These pv check valves are also available to retro fit older carbs.

[Beer-30]

How old is the coil? Almost sounds like weak spark under a load.

[Taylorman]

Coil is a year or two old. I had 3 coils go out since ive owned this boat. They were MSD Blaster SS coils. Last time it went out, i replaced it with a Blaster 2 coil.

[centerhill condor]

I'm going with accellerator pump. This can be easily diagnosed by removing the flame arrestor and manually engaging the pump and see/hear fuel shooting into the venturi area. (with engine off)
Ordinarily, I'd go with fuel seperator this early in the season but you do OK at wot after the stall.

[Taylorman]

The more i think about it the more i think it may be electrical. I dont think its accelerator pump. I think it would stumble if it were accel pump. It just misses a few times the when it gets out of the hole, its ok.

[Beer-30]

The more i think about it the more i think it may be electrical. I dont think its accelerator pump. I think it would stumble if it were accel pump. It just misses a few times the when it gets out of the hole, its ok.
Could easily just be a plug wire or two.

[Taylorman]

My plug wires are about 6 years old. I may replace them. Im gonna clean my cap and rotor good, make sure fuel filter is clean and run it this weekend and see how it does. If it still occurs, im gonna change plugs and maybe wires. I looked at my plugs last night, they all look ok except one is black with soot.

[Beer-30]

I looked at my plugs last night, they all look ok except one is black with soot.
I'm not a betting man, but........

[76Tahiti]

I had almost the exact same problem with my boat- If you hit the gas, the boat would stumble and then pick up and go. I'm not a very knowledgeable motor person- I know what all the parts that you can see are and can do simple stuff, but tuning a carb or rebuilding the motor is out of my scope. (I'm learning!)
Last summer I spun a rod bearing and had the motor rebuilt. The carb was fairly fresh, so the mech rebuilding it just bolted it on, but he did note that the power valve was bad and we replaced it. Since then, the boat doesn't stumble when you tromp on the gas- it gets up and moves like it should again.
My power valve wasn't blown out, but it *was* old and tired. (a friend did a partial rebuild and clean up of the carb a couple years ago, but didn't do the PV.) So here's another vote for a bad PV.
My boat has a 455 Olds, Torker intake, and Hardin logs if any of that info helps.

[Taylorman]

I'm not a betting man, but........
So is that a vote for plugs? I just ordered new fuel filter, plugs and new wires.
I had almost the exact same problem with my boat- If you hit the gas, the boat would stumble and then pick up and go. I'm not a very knowledgeable motor person- I know what all the parts that you can see are and can do simple stuff, but tuning a carb or rebuilding the motor is out of my scope. (I'm learning!)
Last summer I spun a rod bearing and had the motor rebuilt. The carb was fairly fresh, so the mech rebuilding it just bolted it on, but he did note that the power valve was bad and we replaced it. Since then, the boat doesn't stumble when you tromp on the gas- it gets up and moves like it should again.
My power valve wasn't blown out, but it *was* old and tired. (a friend did a partial rebuild and clean up of the carb a couple years ago, but didn't do the PV.) So here's another vote for a bad PV.
My boat has a 455 Olds, Torker intake, and Hardin logs if any of that info helps.
This is not a stumble, its a miss. My gut tells me its not the carb. I may be wrong, but usually, my gut feeling is right. Im thinking its electrical. This carb is less than a year old. I'll find out sunday.

[R.A.D.man]

Do you have the hydraulic diverter control. I do and last time out I had an odd stumble like that. Turns out it is happening when I hit the button for the diverter. I have not chased it down yet, but my problem is surely electrical and it took me a while to relate the stumble to the button.

[Taylorman]

Do you have the hydraulic diverter control. I do and last time out I had an odd stumble like that. Turns out it is happening when I hit the button for the diverter. I have not chased it down yet, but my problem is surely electrical and it took me a while to relate the stumble to the button.
Wow, thats a hell of a gremlin. I do have a hyd control but i was not pressing the button when this occured.

[R.A.D.man]

Yea, I was so excited when I figured that one out. It might get interesting.

[TahitiTiger]

if your fouled on one spark plug that could be a wire. Take a DVOM and check the resistance in the wire, and then compare it to the other wires. They should all be of simular resistance. If that one wire is showing higher than all the others theres your problem.
But hust for giggles and a little extra security you might want to do a leak down test on that cylinder with the bad plug.

[Beer-30]

if your fouled on one spark plug that could be a wire. Take a DVOM and check the resistance in the wire, and then compare it to the other wires. They should all be of simular resistance. If that one wire is showing higher than all the others theres your problem.
But hust for giggles and a little extra security you might want to do a leak down test on that cylinder with the bad plug.
That was my point, also. If a plug is different from it's brothers and sisters, there is a reason. More than likely the old wire(s), but as mentioned here, could be a problem with valve springs or valves. That, however, would probably be more constant. An occasional miss, especially under load (starting out of the hole) is usually coil or wires. Those are the least expensive, so start with wires and plugs.

[Taylorman]

Alright, boat is almost ready for sunday. Cleaned cap and rotor, new plugs, plug wires and fuel filter. If that doesn't cure it im gonna be pissed.

[TahitiTiger]

Alright, boat is almost ready for sunday. Cleaned cap and rotor, new plugs, plug wires and fuel filter. If that doesn't cure it im gonna be pissed.
good luck and have a fun weekend :D.

[victorfb]

as mentioned allready, since you had one plug bad, you need to find out why. the new plug wires and such may have cured it but check everything. you may want to check your valve lash aswell. a tight valve can cause your symptoms also.