Need a little help with a stumbling 4.3 merc

[silvert]

Back on the prop topic, it has a 1.84 ratio and the ss prop is 21p x 13. Is that too much for the 20' boat?

 

[achris]

Back on the prop topic, it has a 1.84 ratio and the ss prop is 21p x 13. Is that too much for the 20' boat?

That would be right at the top of the range. If you can get a hold of a 19p x 13, then give that a go... I think you'll like the result.

 

[silvert]

Thanks, that is one if the things I will try

 

[Tail_Gunner]

Prop's will not cause a hesitation in most cases, however if you were over proped it would place a heavy load on the engine and would reveal poor timing or fuel issue's. If it just plain sluggish but steady and smooth out of the hole yes underpropping could be a issue.... a 21 with 1.8 gearing is not over the top on a 20' foot boat at all....again though if the boat is loaded with 4/8 people or the foam or boat has taken on a lot of water increasing the weight either one could be a issue.

Is this prop a ss or alum and how many people are in the boat when you are playing.

 

[achris]

Prop's will not cause a hesitation in most cases, however if you were over proped it would place a heavy load on the engine and would reveal poor timing or fuel issue's. If it just plain sluggish but steady and smooth out of the hole yes underpropping could be a issue.... a 21 with 1.8 gearing is not over the top on a 20' foot boat at all....again though if the boat is loaded with 4/8 people or the foam or boat has taken on a lot of water increasing the weight either one could be a issue.

Let's solve one problem at as time. Overpropping can show up other issues, if they exist. What is can also do is cause a hesitation as the throttle is opened. The accelerator pump delivers a fixed volume of addition fuel on throttle opening. The calibration of that volume assumes that by the time it's delivered, the engine will have achieved a certain speed (revs). If the engine is overloaded (prop too big) then the engine will not rev up as quickly, so by the time the accelerator pump has delivered its load, the engine is still too slow, and hesitates....

Is this prop a ss or alum and how many people are in the boat when you are playing.

Already answered.... And it wouldn't make any difference either way, 21" pitch is 21" pitch, Aluminium or SS....

.... and the ss prop is 21p x 13....

Chris.......

 

[Watermann]

Always going back to the carb tells you something, that it's just not working right. Your idea of popping for a new one is a very good idea. Some carbs are just beyond the help of a rebuild kit.

Stern heavy with your well fed friends on board? Try some smart tabs, the Nauticus smart tabs they sell here at iboats are nothing short of awesome IMHO.

 

[silvert]

How do I determine if the foam is water logged? I know the carb is probably the first thing I'm going to replace/fix. Weight wise, it'll do it with two people in the boat. The boat does have 2 batteries, both in the back left corner. One is a standard car battery, the other is a huge deka deep cycle. My guess is it, has about 100lbs of batteries back there. Unfortunately I really don't where else I'd put them. Could try to relocate the bigger one under the pass side glove box

 

[keith2k455]

Alright, back to the hesitation and backfire in neutral. Get the motor running right then you can work on the performance of the boat.

This really feels like a carb problem. If you can check compression easily, do so to eliminate that. If you can't check, try putting everything back to stock (plugs, timing, jets, etc) and start tuning from there.

 

[silvert]

I have a chance of picking up a 97 4.3 with lower miles for $250. It is a vortec with the 8 intake bolts. Thinking of getting it, checking it over, replace head gaskets, maybe do brass freeze plugs, home clean up of the combustion Chambers and the short turn radius of the intake and exhaust Ports, Port match to an edelbrock aluminum intake with a new holley or edelbrock 1409 carb. Engine is rated at 190 hp, I would imagine this would get me at least 215 or more. What do you all think?

 

[cliffblue]

Hello, may not apply, but my 2001 4.3 with a 2 barrel Mercarb uses a plastic spacer under the carb. It stumbled bad when cold. The spacer had warped causing a vacuume leak. New spacer cured it. Good luck!

 

[thegoat86]

I had the same trouble with the heavy stumble on acceleration. Also had some backfire. Found out the person who changed my motor had two plug wires crossed, and the distributor was out 90 degrees. I was chasing elusive critters like yourself.

Image on top is coil, bottom is electronic distributor. It is very important to find TDC on the compression stroke of #1 cylinder on your motor before you start taking the distributor out.

I did this by using my compression gauge hose without the gauge. I had someone crank the motor and when air surged out I stopped. The I put a pencil in the plug hole and adjusted until it was at highest level. Which then happened to line up perfectly with the TDC notch on my balancer.

On my motor, (separate coil) I pulled the distributor out and lined it up with the cap on to get the #1 pointing at the water pump. (as in first photo) If yours is 2nd photo make sure you have it positioned as in photo. Then I pulled the cap off, (leaving screws loose aids in these steps) as I dropped it in, I pointed the rotor toward the front of the engine. (2nd photo will point towards #1 socket. see crude line) May take a couple tries, but you will get it. If it is wrong the dist will not seat. Only when its lined up will it sit all the way in the motor.

Leave retaining nut clamp loose for timing. Double and triple check your plug wires. Like I said, I had two miswired. Also may not hurt to check the plugs again. I had 4 out of 6 cracked when I bought the boat. It is a very tight spot to get a socket and extension on these guys. I used the plug socket and a large stubby box wrench to tighten them. (this is all said assuming you have plugs gapped correctly, and are using the correct marine grade plugs. AC delco is best I am finding out.)

Start the motor, then time it. This solved all of my issues. I am having an issue fine tuning the timing because my timing marks are rusted off. But, if you can see yours, your are in like Flynn. You should be back to square one on base timing. It only takes a few hours. If you try to time without checking the basics you are wasting your time. This will however not solve your performance issue if you have the wrong propeller. Achris is hitting that point correctly.

 

[keith2k455]

^^^ ditto. Start with the basics. Overall a lot cheaper and easier than throwing a motor at it.