Ok guys I'm stumped.

[RPOWELL]

Boat in signature. All new fuel system. Brand new ignition system. No water in the oil. Fresh fuel. New water separator. New carb last year. Boat runs great for about 20 minutes then bogs down and dies. Runs at 150 when up on plane and moving about 35 mph. After it dies it will refire and run great again for another 2-5 minutes before bogging down and dieing again. When this starts to happen voltage at the coil stays perfect at about 13.4 volts. What am I missing? Help!

 

[Bt Doctur]

Re: Ok guys I'm stumped.

Fuel ,check the anti-syphon at the tank and also run a remote tank to check for a collapsed fuel feed hose.

 

[Rocky_Road]

Re: Ok guys I'm stumped.

Fuel ,check the anti-syphon at the tank and also run a remote tank to check for a collapsed fuel feed hose.

Like the Doctor says...and also make sure that your fuel tank vent hose is clear. You can do this by 'cracking' the fuel cap when you have your problem: a clogged vent will create a vaccum and cut off your fuel flow.

 

[RPOWELL]

Re: Ok guys I'm stumped.

Vent is open I've blown low pressure air thru the vent when I drained the old fuel out. The tank is a newer aluminum 27 gallon. I have also taken the cap off when the problem is occurring. Did not change. Also the line from the fuel pump to the carb is new. I have to be over looking a small item it's just driving me nuts.

 

[Rocky_Road]

Re: Ok guys I'm stumped.

A crazy thought...but I have seen this:

Crud in the bottom of a tank finally finds it way onto the pickup screen, and stalls the engine. As soon as the engine stops the crud falls off of the screen, and the engine will fire off just fine. Then the crud gets sucked back onto the screen....

Other than this, I would have to be looking at something in the ignition system?

Happy boating!

 

[vxtech]

Re: Ok guys I'm stumped.

what you describe sounds like a clogging fuel inlet filter on carb, fills carb enough to run then clogs and runs dry then it sits -sediment settles just enough to fill cab again and repeats itself- just a thought

 

[EddiePetty]

Re: Ok guys I'm stumped.

"....When this starts to happen voltage at the coil stays perfect at about 13.4 volts."

Sounds to me you have excessive primary voltage to the coil. Coil heats up (as well as the remainder of the secondary components) and eventually shuts down due to high resitence (heat)..

 

[RPOWELL]

Re: Ok guys I'm stumped.

"....When this starts to happen voltage at the coil stays perfect at about 13.4 volts."

Sounds to me you have excessive primary voltage to the coil. Coil heats up (as well as the remainder of the secondary components) and eventually shuts down due to high resitence (heat)..

That is what I was thinking too. How do I lower the primary voltage. I did have to put a new alternator on at the end of last year.

 

[Stamey]

Re: Ok guys I'm stumped.

How quickly will it restart? I just went through this with bad coils on my Dad's twin engine Wellcraft. When it died, both engines, they wouldn't fire back up until the coils had cooled off. Even stacking ice from the cooler around it took 10 minutes to get the temp down enough so the coil would fire again. That was one engine. The other one the coil was just cooked and it wouldn't run until I put a new coil on.
I'm for the filter screen. I thought I had licked the fuel problem on the same boat by installing new filter/water separators on it, but the crud in the tank made it through them and got caught by the fuel screen in the carb. In my case though, when that sucker got full the engine wouldn't run again until I cleaned it out. Had to clean it out 3 times, on both engines, before all the crud was gone.

Chris

 

[RPOWELL]

Re: Ok guys I'm stumped.

Well I thought I was fighting a bad icm from the old thunderbolt iv system. I replaced the coil and distributor sensor. Problem still there. I couldn't locate a older style box like was on my boat so today I upgraded to the new pertronix system. Which also came with a new coil.

 

[RPOWELL]

Re: Ok guys I'm stumped.

Also the coil and the distributor is hot to the touch when this happens. It will restart after about 5-10 minutes and run great again for about 2 minutes.

 

[greg82255]

Re: Ok guys I'm stumped.

Doesn't putting a resistor in front of the coil lower the voltage? Lots of coils come with external resistors.. did yours?

 

[RPOWELL]

Re: Ok guys I'm stumped.

nope the kit says that it doesnt need a resistor. it also said that is there was previously a ballast resistor that you shouldnt use it. my old setup was the thunderbolt iv so no resistor there either.

 

[Stamey]

Re: Ok guys I'm stumped.

Can you measure the ground side of the coil when this is occurring? This should tell you if the coil is dropping more voltage than it should. I believe it drops about 2 volts across the coil under normal conditions. One of the things that helped diagnose my problem on the twin engine boat was that when the coils were weak from the heat one engine would cut off before the other, and when I tried to restart the engine the other engine, currently running, would cut off because of the voltage drop from stating the other engine. If I started one the other would cut off and it went back and forth like that. It was weird, until I figured out what was going on, and this was with both engines having separate batteries and electrical systems, only tied together through the gauges in the dash.

I'd be looking for less than 10V on the ground side of the coil when the problem is occurring, and if so, try a different coil. In my case, both coils were brand new Accel Superstock coils. I put an old Mercruiser coil in place of one and a borrowed one from another boat for the other.

Chris

 

[RPOWELL]

Re: Ok guys I'm stumped.

I will do that for sure. Im going to take the new carb apart tonight and see if there is debris in it. so it will be a day or two before i get back out on the water. this is the 2nd new coil in two weeks. cant hurt to try a third.

 

[DarrinT]

Re: Ok guys I'm stumped.

Check the fuel lines especially in the tank(s)

Buddy of mine had the exact same symptoms and it turned out to be a crack in the line in the tank that would suck air under high fuel flow conditions stalling the engine. The crack would then close and it would start right up!!!!

Made him bonkers for two seasons before he found the flaw beacuse with a full tank the crack was under the fuel so this problem was only intermittent under the condition of lowish fuel and WOT

 

[Reming870]

Re: Ok guys I'm stumped.

The high voltage may be burning the coils up. I am not sure of this but I thought the coil voltage should be in the range of 8-10 volts. 13 sounds like full power and no resistor on the coils. Maybe someone can help with what resistance and voltage is required.

 

[RPOWELL]

Re: Ok guys I'm stumped.

Just talked to the tech assistance at pertronix. He also said that i need to test the coil, but with the engine off and the and the negitive side of the coil grounded. He said if i had less than 11 volts, im dropping voltage. He did say that the positive side is capable of seeing up to 16 volts.

I will also be checking the fuel screen in the pick up line if i can get to it. i know that the vent is very tough to get too. but it is flowing freely.

 

[RPOWELL]

Re: Ok guys I'm stumped.

I think i have found the culpret. after testing the priamry voltage at the coil with engine off. i only have 8.4 volts. technical assitance with pertronix said i need to remove the resistance wire to the coil and replace it. and supposedly problem solved. i really hope so.

 

[RPOWELL]

Re: Ok guys I'm stumped.

ok well the fuel pick up tube is a solid aluminum tube in the tank that leads to a rubber hose that runs to my water seperator. im only getting 9.2 volts to the positive side of the coil when the negitive side is grounded. i ran a stand alone wire from my ignition to the coil and it only went up to 9.97 volts. im still stumped.