carbed engine: missing or rebuild?

getting the ballast system i installed over the winter dialed in. (man, i'm enjoying the hell out of that thing.) So, the engine has got a bigger load on it. Comes out of the hole ok. Will prob reprop in the near future. Yesterday when I it, I noticed it was "missed" a couple of times. maybe 3 or 4 times and it happens when its throttled pretty and still getting on plane. is it missing and where should i start? new plugs a carb cleaning would prob do a lot

i should add that it doesn't do this when idling or on plane

New prop is the best.

You could give the carb a bigger power valve. A larger number power valve decreases the vacuum needed to open it allowing more fuel in the manifold sooner.

Some people swear by it. This is all assuming you have a really low powervalve like 2.5-3.5. If so you could drop in a 6.5.

Also...are you sure the miss is not a slip of the tranny? It sounds like you got a lot of weight in an old boat.

675 hours on her - tranny seems to be in good shape. i notice the miss in the sound of the engine...

got a holley carb on a 351W. Not sure of the make. Did a quick search and it seems that most holleys have the 6.5 power valve.

(Message edited by denverd1 on July 25, 2006)

Did you convert to electric ignition yet?

its a Holley 4160.

You might want to start with the timing. See if that takes care of it then the plugs then have the carb looked at.

yes, electric ignition. this isn't my engine, but I think it has the same carb. When I pull of the air cleaner I can see 4 circles. (are those the barrels?) when I move the throttle cable, only two of them will fill. Could I run a line to the other two? any reason to do that?
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Coach - wouldn't I have a list of other probs if the timing was off?

(Message edited by denverd1 on July 25, 2006)

or are those secondaries?

If the timing is off you can find that it will cough and fart out of the hole but be fine after that. With the extra weight in the boat you might have too much gas when you come out of the hole and it is burning it off when you first get on it. You can always take the carb off and have someone check it out for you. I go with the easiest fix first and see if work then go to the next step. I just went through this for 7 months with my jet and just got it fixed.

Timing
Plugs
Check the Alternator to make sure it is putting out the proper amps- low current = poor spark and it will sputter out of the hole
carb

With 600+ hours have you replaced the plugs and wires on the boat before?

the problem is really minor. from dead stop to on plane it may do it 3 or 4 time if i'm careful with the throttle. if I hammer it down, the problem gets worse.

electric ignition system at @ 600 hours so plugs/wires are from then. How often should they be changed? and how do you check the timing?

nacho wrote:
"when I move the throttle cable, only two of them will fill"

I am trying to tranlate this: If you look down the carburetor (don't do this with the engine running!) and operate the throttle you will see a spray of gas down two of the barrels (holes). Is that correct?

This would be the accelerator pumps working. It is common that only the primaries have the accelerator pumps, and if I recall this carb is that way.

It is common for a four barrel carburetor to be divided into a "primary" and "secondary" side. At low throttle settings the secondaries are closed and you are only operating on the primary. As you open the throttle more the secondaries will start to open. In this case I believe that the secondaries are operated by a mechanical linkage. Other systems use venturi vacuum to open the secondaries.

The carburetor shown in the picture, while it is a common marine unit it is a bit unique in that it has two separate float bowls, one for the primaries and one for the secondaries. This can give you some interesting symtoms when just one side starts to get fouled up!

I would recommend starting with the easy stuff. You said it was electronic ignitions, which to me means that it doesn't have points and condenser, which would have been my first guess as the cause of a miss.

Change the plugs for sure. Check the timing, if it is off all sorts of things can happen.

Perhaps it would help if you explained what you call a "miss". To me a miss is something that you can hear but not really feel. At 3000 RPM there are 8 cylinders firing 1500 times a minute, which is 200 firings a second. Missing just one firing can be heard. Ignition problems can have just one cylinder occasionally miss.

A fuel related problem will generally cause a much bigger problem, like a momentary failure of all cylinders. Not one miss out of 1500, but all 8 cylinders failing for half a second. You can feel this.

To chase fuel problems I would start by changing the fuel filter and inspect the fuel line for any air leaks. If you have a water separator I would inspect it to see if there was any sign of water getting into the carb.

Once all the easy stuff was done then I would pull the carburetor off and have it rebuilt. (I have stopped rebuilding carbs myself, for some reason I never get them right).

Nacho, Thats not a 351W (ford) its a 350 (chevy)
My experiance with hollys on older motors is they are very touchy you might try a carter style (Eldenbrock) they are alot easier to tune and stay tuned for alot longer.
al

al - thats not my engine, just my carb

rod - not a fuel problem. put in a new filter a few weeks ago. How do you check the timing?

and what i call "missing" is when one of the 8 cylinders doesn't fire. something you can hear and barely feel. it does this maybe 3 or 4 times when trying to get on plane.

Nacho, you're gonna need a timing light. You can buy one for 30-50 bucks at the auto store.

That's what missing is. When the spark doesnt occurr at the right time in the cylinder stroke.

tks derby. Went out last night, loaded her up, i didn't notice it at all. I remember hammering it a few times a little harder than normal to see if it would miss, but nothing. new plugs tonite. probably be good... tks everyone.

Make sure you "read" the plugs as they will have a story to tell. Any plug that looks different than the rest needs to be remembered where it came from. Assuming your engine has never had the plug wires changed, I would also inspect both sides of the terminals. You can also ohm them to make sure they are roughly the same. Replacing the cap and rotor can never hurt, again check it for corrosion on the terminals. Might want to put some die-electric grease on the plug wire terminal ends.

DO NOT CHANGE YOUR CARB OR ANY OF ITS PARTS TO FLOW MORE GAS. The engine was dynod to function perfectly at sea level. Swapping carbs or changing the power valves size etc will not do anything but make the engine run worse. If it was a carb problem it would most likely be consistant and the problem would be noticable for a longer period of time. Although you would have to know what you are listening and feeling for.

had the points and condenser swapped for electric (at 600 hrs; today 675) so cap, rotor, and wires are 75 hours old. i remember them saying the carb would need to be rebuilt pretty soon... Can I even take this thing apart and clean it?