My 402 is cutting out at 4000. I've come to the conclusion it is the coil. I have to buy one to see. Anyone agree or have a better idea. I am sure it is ignition problems somewhere. thanks
Josh

Check for a clogged fuel filter. Might as well do that before spending money.

Tim.

My uncle had a 454 in his jet boat and it did the same thing. He changed everything just to find out it was a tiny diode on the distributor. He changed it and presto boat ran like a raped ape.

what diode on the distributor? And if it was a clogged fuel filter would it do it exactly at 4000 everytime?
thanks
Josh

A points dist. has a diode in it, youll have to look in the wiring diagram for the distributor. When they start to go they are succeptable to heat. My Uncles boat ran great below 4000, Like I said we checked EVERTHING to no avial. We were told by a local rep to bring the Dist. in. He put it on this machine and spun it up, as soon as he hit around 4000 the power dropped to almost nothing. He pulled out a diode and changed it and everything worked great. Now his boat runs 6500 and goes 105mph.

105 MPH IN A JET BOAT!!! Holy cr%p, that is about the fastest jet boat on the planet. All the stuff we build only runs 75-80.

Thats nothin, Theres a guy up here that works in a 4x4 shop that has one that has a blown 454, thats putting out over 1000 hp. Of corse he can only afford to run it to the beach once and then back to the trailer because he has to run race gas. When he cranks that thing up you can hear it up at the resort over 1\2 mile away. Itll fly off the water if he doesnt watch his speed. His boat is capable of going a lot faster if he could figure out how to keep it from lifting off.

My Uncles boat would only run about 75-80 when he bought it. He put a set of Brodix heads on it changed the cam and added a 950cfm carb on top. the first time I rode in it after he fixed, he scared the crap out of me. He can almost pop it completely out of the water when he guns it, with the jetavator in the correct postion of course.

my boat will go 10 mph...if i row fast enough, down river of course smile.gif

the dist. is a HEI. i've decided to just replace the whole distributor because it wasnt advancing correctly and i think the coil is bad because of the cutting out. i had my friend have a look at it and he thought the same. i'll let ya guys know if that fixes the problems.

The problem we have always run into with jets isn't the horsepower, all our engines are well over the 500HP mark. With jet pumps you can only spin the pump so fast before it cavitates. Most of the real high speed stuff we build are V-drives or I/O(big boats). The neighbors v-drive has gone over 2X, Gets up to to 125+ real quick. Just can't imagine even getting a 12JG to spin that fast.

My uncle spent a lot of time filing and polishing inside the pump. Its almost like porting and polishing a head, when he pulled his pump apart after he first bought it there was quite abit of damage inside from cavitation. I'm not sure what impeller he uses.

Has this condition existed always or is it something that just started? If you have had it always, check the power wire to the HEI. If it is the original resistor wire, you will get high speed misfire. You mady need to replace or bypass the resistor wire with copper to get full voltage to the HEI.

Originally posted by jghoppes:
My 402 is cutting out at 4000. I've come to the conclusion it is the coil. I have to buy one to see. Anyone agree or have a better idea. I am sure it is ignition problems somewhere. thanks
Josh i have ran into this a few times......come to find out the hei module was breaking down inside............the engine would cut out and die if you stayed in it, at the same rpm everytime.......the sad thing about it was that the first time this happen i had the module checked with a tester and it passed.........so we moved on to other parts of the ignition system to find nothing else wrong........so we changed the module....lol it was it.....the next few times it happen in other cars changed the module out first thing and it was fixed...........

If you are going to install a new HEI system,
you might try a pertronics flamethrower. Put that in my 68 ss 2 years ago still problem free and
have went 6500rpm a couple of times with no missfires.