Facts: Marine use, 302 V-8, Juccuzzi drive jet, 2 barrel motorcraft carb.
Engine starts and idles fine.

Problem: Put the boat in the water, naturally the jet pump loads the engine, accelerate to 2100 RPM and then the engine starts popping back through carb. Carb overflows from time to time dumping fuel down onto manifold.

Recent changes: Rough idle, pulled out the old mallory distributor (with points) and installed a new Prestolite electronic distributor. Installed new coil (designed for an external resistor). Didn't check air gap between impulse modual and shaft cam thinking it was preset (suppose to be .008). Installed an electric fuel pump in line between fuel pump on engine and fuel tank (4 PSI).

Thinking on solution: A. Popping, Check air gap, reposition spark plug wiring for firing order to the next electrode for #1 to compensate for spark advance, possible fuel disribution problem. B. Float stuck in carb from debris sucked in from fuel tank (stops after tapping float bowl). Most probably two separate problems?

Comments: Popping back is the major problem, another carb after cleaning out fuel tank is a given solution. Need some sound advice please.

 

Moved to the 302 engine forum. Sounds like fuel system problems and we do have a fuel system forum for that but we need to determine if it is fuel or electrical first.

 

i would check needle and seat and second install a fuel pressure reg

 

From what you are saying would lead one to believe that you think the popping problems stems from carb problems? Or are you directing this comment only to the fuel overflow mentioned?

 

Sounds like 2 seperate problems to me.
Back fires up through the carb are usually timing related. I'd get a timing light on it. See where you stand. It should be around 10 degrees at idle with the vacuum advanced plugged(if it has one). You might have the distributor off 1 tooth. I do it almost evey time I put a dsitributor in. You could also have a loose timing chain but that doesn't happen all that often in boats unless the motor is REAL old. They just don't normally get the hours on the motor to stretch the chain.
Tapping on the carb and having it work is a sign of a sticky float. Time for a rebuild on the carb. Boats tend to get gummmed up carb floats from sitting around. The 2 barrel motorcraft carb is great for bumpy rides. They are one of my favorite off-road carbs! Rebuild it and you should be good.
I'm a jet boater too but it only a small Sugar Sand Mirage.
Good luck and come back with an update for more help.

 

Thank you senior user or Ken. Sounds like you know what you're talking about. I called the company in Canada that sold me the dizzy and got his feed back also. I agree that its a 2 fold problem. Tomorrow i will drain the fuel tank through a strainer and eliminate any possibility of contamination from that end. Put the fuel back in the tank and start from there with a rebuilt motorcraft 2 Bl carb. I'll make sure the vaccume is blocked off. Engine starts and idles fine. I'll put the ol'timing light on it and crank it.
At 800 RPM I'll set the timing to +10 degrees. Dizzy supplier says that if it spits at all above 2100 RPM that he'll sent me a replacement at no cost. I haven't discounted the fact that it could be a tooth off, i'll take that into consideration during my trials. I honestly didn't believe that you could get it a tooth off, thought it was right on or 180 degrees out. I don't do this every day for a living so I don't know everything there is to know about engines. I'm a structural engineer by trade but I've built this boat powered by a 302 ford V-8 backed with a Jucuzzi 12YJ jet and according to my calculations it should turn 45 MPH at 3800 RPM. So, tomorrow is another day and I'll report back to you. Lee Armistead

 

your right, it can't be a tooth off. it's either right or 180 out but i would check the firing order, make sure the wires are where they should be.

 

Hate to disagree but I put mine in a tooth off over the weekend. If you do you can't turn the distributor enough to get the timing right. It hits the thermostat housing.

 

Move the thermostat housing Just kidding. Not to thread hijack BUT you're both right.... Technically you can always turn the distributer enough make the timing correct, whether 1 tooth out or 3 teeth out or even 180* out.....but physically that is extremely unrealistic.....plug wires don't like to move that much and there are obsticals, ie the thermostat housing. I'm a frequent user of the plug wire shift Fords hex drive oil pump shafts are harder to line up IMO....

 

I want to thank Ken75Ranger, Scottie2hottie and dmc919 for their input. Here is where the reality is guys. I've read your comments and have HEARD what you have said. I have also consulted with the dizzy supplier in Canada. Action taken: First off I put the crankshaft (timing marks to TDC), pulled the dizzy cap and checked the location of the rotor, it was pointing opposite the #1 stamped on the dizzy cap, I turned the crank 180 degrees and realigned the timing marks to TDC, the location of the rotor (turning counter clock wise) was pointing what looked to be one contact to the right of the #1 position. I then unbolted the dizzy and lifted it out of position, rotated it one tooth counter clock wise and dropped it back in place. So, I know that you can move it one tooth! Keep in mind that this is being done in the shop. Rolled the boat and trailer into the drive, hooked up the water to the cooling system on the engine, fired up the engine, set the timing to 10 degrees past TDC (advanced) @ 800 RPM with the vaccume line sealed off. Let the engine warm up and gradually increased the throttle to 3000, to 3500, to 4000, to 4500, to 5000, ran smooth as silk, idled right down and purrrred like a kitten. At this point I still have not changed the carb.
Float is still sticking but give it a tap or two and it clears up so I know that I've still got a minor carb problem. Put the boat in the water (launch ramp is about a mile away). Nice clean fuel in aux. tank, fire the engine, Jet drive is now pumping water and is loading the engine, throttle up to 2200 RPM and it starts popping back through the carb!!! Damn!!! With engine cover off, I grab a cold corona beer and stare at the engine with thoughts of burning the boat! Time to rethink the problem. After much deliberation I have come to the conclusion that burning the boat is not such a bad idea, not really guys. Here is where my thoughts are taking me. Without a load on the engine it runs great. So, there has got to be a problem with the delivery of spark to the plugs. Its got to be a problem with the coil. I have a electronic dizzy and it requires a high voltage delivery to the plugs. I have a coil that calls for a remote resistor therefore the coil voltage is reduced (right)? If I change the coil to a unit that is hotter (say a UC16T) that does not require a remote resistor, the coil should deliver a super charge volt of elect to the plugs? Under the present condition fuel is getting to the cylinders and at a higher RPM the carb is delivering more fuel that can be burned because of the lack of ignition, becomes overloaded in the cylinders and when it does fire causes the excessive explosion in the cylinder to result in a pop back through the carb. Mind you that the popping has been drastically reduced from what it was before I changed the dizzy, its gotten better. Today is Sunday, I picked up the UC16T coil yesterday and will install it today. I know I still have a carb problem but if the float is clear and delivering fuel it should run at a higher RPM with a Load. If this dosen't work I'll no doubt rethink the burning solution! I'll let you know. Lee

 

ok try to set your timing at a little less advance. 10 is the standard for cars and trucks, but im not sure on boats. It's popping back through the carb because either a) the ignition system is firing too early(aka too far advanced) or b) you're engine has some nasty detonating or preigniting....i would bank on the first. do you have any more specs on the engine, like compression ratio? what kind of fuel are you running? what cam is in it? 302s and 302 HOs have different firing orders...also, water is heavy to move through a jet drive, that is a big load. try to retard your timing a little (like 6), just to see if it makes a difference. the firing order and timing are sticking out to me because you changed out the dist.... also, engines act much different under loads than in the barn, unfortunately in a boat that can get to be a pain....unless you have a pond take the boat to the lake and leave the dist nut to where you can make a simple adjustment there. and leave the light at home, put the timing where the boat likes it. with timing you can't always go with manuals because every engine is different. but, for sure this problem isn't in the carb....im about 99% sure of that.

 

Also, with a really hot and efficient ignition system (like what you've got ) you can afford to set your timing back a little and not lose much performance...i really think you have it too far advanced.....

 

Scottie2hottie,Thank you for your interest in solving my problem. All of your suggestions were performed my last trip into the water. Had the dizzy loose and moved it where the engine liked it. The dizzy was moved to the right until the engine started losing it's smoothness and turned back just enough to regain it's smooth idle speed. Test run until the popping began and then adjusted to the left (same procedure). After both left and right ajustments the engine (in the water) idled and started over and over, ran just just fine. Still no better after 2200 RPM. Having done this tells me that the timing is where it should be and if it is what's left? That is why I have arrived at the conclusion I discribed in my last posting, its got to be a low spark delivery condition at the plugs! I believe that we are on the same page, it has little or nothing to do with the carb at this point, its in the timing and amount of spark being delivered! I was pooped yesterday and didn't get the coil changed out. Its on my agenda for today. This forum helps get rid of the fustration envolved though and your feed back is very valuable. Again I thank you for allowing me the opportunity to openly discuss it because there is always the chance of picking up something that I have missed. I'll check my email later today after the coil change and post an update.

 

Scottie2Hottie, I forgot to mention that I don't know anything about this 302 engine. I was told it was stock so if I refer to my manuals it reflects factory spec's. Fuel is standard unleaded. If it were an HO I wouldn't get the smoothness that is present now, would I? I'm not ruling that thought out but it seems to me that a change in the firing order would show up prior to loading the engine???

 

I'm still thinking it's timing related. You can easily try 351w firing order. Anyone could have swapped cams for a 351w or HO style at some point. How about using the timing light while you increase the throttle in the driveway? If you can do that you can check the timing advance and loose timing chain possibly. The distributor mrg should be able to tell you what the advance curve should be for a given rpm. I think you can take the base timing off the list of suspects. Did you change the plugs with the distributor? They should have reccomended a different plug from the original points distributor or at least a larger plug gap. You wouldn't have access to a vacuum gauge would you?