Help diagnose 2 problems please

[fatboycowen]

Hey all, i have been researching this forum for years, but this is my first post. I am out of ideas on my boat. 2 seperate problems:

1: Cold motor starts right up on first crank, and runs great (aside from problem #2). If you let it get real warm from use (skiing etc) it wont start at all. Next day (cool motor) starts right up. Also, if you dont run the boat under load for at least 10 minutes, it still will start perfectly. Once you run it, it wont start back up.

2: Boat runs excelent when cold. Rips out of the hole with no studder. Idle is perfect at 6-700. Runs absolutly flawlessly until it warms up. At that point, it runs flawlessly until 3200rpm at which point the boat studders and wont run any faster.

Last spring, we had a guy put in a new carb (not marine) and he put in an electronic ignition. The boat started great last year, but had the same hot 3200 rpm problem. We lived with it by just not going fast. Now problem #1 came up, and its a bigger problem.

What could be wrong?

Thanks

Jon

[dave210]

RE: Help diagnose 2 problems please

check coil to see if its a non resistor type

[fatboycowen]

Re: RE: Help diagnose 2 problems please

check coil to see if its a non resistor type

Uhhhhh..... We bought the coil last year. Its one of those yellow Accel ones (i think) from the auto store. It has the big central pole and a small pole top and bottom. Just like the original had. How do i tell if it is a resistor type?

Thanks,

Jon

[cat1168]

RE: Re: RE: Help diagnose 2 problems please

You said it is a new carb? It sounds like vapor lock. You might want to talk to the person that put in the carb. the high speed jet might be clogged? Have you changed the fuel filter? it all sounds like a fuel problem.

[wake-sk8]

RE: Re: RE: Help diagnose 2 problems please

Problem one could be the neutral shift switch. (don't know which boat you have). I had this problem, the shaft that switches the neutral switch was expanding whilst hot (due to too much oil and a blocked vent). Once expanded it would activate the switch and the boat would not start as it thought it was in gear. Once cold, it would start again no problem. Took us ages to find it.

[fatboycowen]

Re: RE: Re: RE: Help diagnose 2 problems please

Problem one could be the neutral shift switch. (don't know which boat you have). I had this problem, the shaft that switches the neutral switch was expanding whilst hot (due to too much oil and a blocked vent). Once expanded it would activate the switch and the boat would not start as it thought it was in gear. Once cold, it would start again no problem. Took us ages to find it.

Opps, the avatar that shows my boat info doesnt seem to show up.

86 SN 2001 with PCM 351w.

I thought the neutral shift wouldnt let the starter crank? The starter is definetly cranking when hot.

[fatboycowen]

Re: RE: Re: RE: Help diagnose 2 problems please

You said it is a new carb? It sounds like vapor lock. You might want to talk to the person that put in the carb. the high speed jet might be clogged? Have you changed the fuel filter? it all sounds like a fuel problem.

Which problem would this be refering to? Hot start, or hot speed?

About the fuel filter, i dont know where it is. I can see the F/W seperator but dont know anything about it (and cant find any info). I also dont know where the filter is. I know there is one in the carb, which i havnt changed because its so new.

Thanks,

Jon

[wake-sk8]

If its cranking when hot then your right, it ain't the neutral switch...

[TrailInn2]

Not sure if this will help or not but I had a 1980 GMC pickup that did the same exact thing. Ran great cold and would stutter and run like crap when warmed up. This was 24 years ago and I don`t remember exactly what was wrong but it seems like it was a vacumn something or other. It was a carburated 350. Replaced the gizmo and all was good.

[surroundsound64]

You might check your choke, it may not be opening up after it warms up. After the boat is warm you can take your spark arrester (air filter) off and look at the flap, it should be open. This is safest when the engine is turned off.

I doubt it is vapor locking because that is most likely to happen when the engine is at low rpm, using less fuel, meaning the fuel is in the line the longes, meaning it has the most time exposed to a hot compartment.

How clean are your spark plugs? And are they gapped correctly? Also, do you have any exhaust leaks? I doubt that's the problem since you say it idles fine, but have you noticed any black suit under the hood?

[jthooker]

I agree with cat1168 that you may have a vapor lock problem.
If a vapor lock isn’t too severe it can usually be overcome by a good fuel pump.
If your fuel pressure is low it would also explain your 3200 RPM problem.
If it was low last year then the new carb may have compensated enough for it that at least it would start.
Now the pump or actuator lobe may be worn further to the point of not starting.
A few other points:
1. Your non-marine carburetor could be a serious safety hazard depending on its set-up.
2. Check your engine operating temperature.
3. Check your fuel tank vent.
Hope this helps.
Let us know what you find.

[fatboycowen]

You might check your choke, it may not be opening up after it warms up. After the boat is warm you can take your spark arrester (air filter) off and look at the flap, it should be open. This is safest when the engine is turned off.

I doubt it is vapor locking because that is most likely to happen when the engine is at low rpm, using less fuel, meaning the fuel is in the line the longes, meaning it has the most time exposed to a hot compartment.

How clean are your spark plugs? And are they gapped correctly? Also, do you have any exhaust leaks? I doubt that's the problem since you say it idles fine, but have you noticed any black suit under the hood?

How far should the choke open? It gets to around 45 degrees when the engine is warm (i believe). I know it moves freely. It was closed when i started it, and open (at least partially) when it was warm.

The spark plugs look prety good. When i checked them, i had been cranking it for a while. They were somewhat black (charcoal color), but it was just a very thin layer of soot. The gap was correct and the electrode was not worn (replaced plugs and wires last year).

Thanks for the help so far

Jon

[fatboycowen]

I agree with cat1168 that you may have a vapor lock problem.
If a vapor lock isn’t too severe it can usually be overcome by a good fuel pump.
If your fuel pressure is low it would also explain your 3200 RPM problem.
If it was low last year then the new carb may have compensated enough for it that at least it would start.
Now the pump or actuator lobe may be worn further to the point of not starting.
A few other points:
1. Your non-marine carburetor could be a serious safety hazard depending on its set-up.
2. Check your engine operating temperature.
3. Check your fuel tank vent.
Hope this helps.
Let us know what you find.

How easy is the fuel pump install? If someone has a guide of some kind, im sure i can do it. How much are they, and where do i get one? I heard they werent too expensive.

My new carb looks very much like the old one, but slightly larger and lots shinier. I believe it has 2 fuel inlets instead of one (primary and secondary bowl). My mechanic spliced the fuel lines so fuel runs to both.

How do i check the fuel tank vent? If i unscrew the gas cap, and the no start problem goes away, i will know, right?

Operating temp: Just remembered last year i replaced the thermostat with one from the auto store. Couldnt find a cool enough one, so i drilled a small hole in the top to let some water through (on the advice of another boat owner). Runs a little warmer than stock. Runs about 160 or so opposed to 150.

Thanks so much thus far..

Jon

[surroundsound64]

It should be nearly at a 90 degree from where it is fully closed, in other words, fully open. You might try setting the choke, just unscrew the 3 or so screws (losten them, don't take them out or you'll have a fun time putting the spring back in) and then rotate the black cap looking thing until the flap just closes. Do this with the engine cold. Then tighten the screws back.

Interesting problem your having though.

[DavidF]

Seems to me it is electrical related since it only happens with warm engine AND misses badly at speed. This tells me to start looking for electrical components that fail with heat and thus cause a weak spark condition. My first thought is the ballast resistor, if so equiped. Trying connecting all wires to one side of the resistor (does not matter which side) and see if the problem is resolved. If so, then replace the resistor (do not simply bypass permanently).

If problem presists, then suspect the coil next (even though it is relatively new). Then start looking for bad grounds and electrical connections on engine and key switch. Poor electrical connections can get hot, once hot, resistance builds, once resistance builds, electrical current is compromised, blah, blah, blah....