MOP

When you run into a situation like this the very first thing to do is to read the plugs, screwing around with other stuff first can make the difference of mechanical damage or not! Once you know your cylinders are doing Ok then start checking the other related items.

SB

iTrader: (1)

Read that fuel psi at time it breaks up. Fuel psi needs to be correct at WOT and full load.

Check for voltage drop at coil and fuel pump. Proper voltage at these components is imparitive. The more the better. Also, make sure no other components are hooked up to / draw power from either of these components. Furthermore, a battery or alternator on it's way out will not provide enough amperage and same symtom will happen. Been bit by this a bunch of times. An easy check I do is to bump the tabs and or trim and see if problem get's worse - these draw a bunch of amps that a good battery/alternator won't flinch at, but bad ones will.

Is you carb's Power Valve(s) boost referenced ? What kind of carburetor ?

Do we have a TBIV or V ? Or something else ? Remember, the V's have rev limiter.

If all checks fine and components are rigged correctly, then I agree with a new set of plugs gapped on the small side (.025-.030) and then go from there.

Hot Boat

The carb is a boos referenced Holley 850 . The ignition is a TBIV. coil is a MSD high vibration. There is nothing tapped off the purple ignition wire other than a pump relay. Fuel pump & trim tabs draw right from the batteries. Amps stay steady when I trim the tabs all the way up. The alternator is 1 year old. Plugs are NGK BR6FS gaped at 35.

I just ordered a Mallory fuel pump and a new coil and MSD 6 marine box.
I will try this along with new plugs and cap and rotor.

Hot Boat

I feel that its running out of fuel. but the gages say 8 psi and never move much at all. Last season they would drop 1.5 psi at WOT. I did install new senders this season , I wonder if something is up with them.

SB

iTrader: (1)

Senders? You mean electrical. Never use a electrical fuel psi guage for exact psi reading. Use it as a reference only.

Say mechanical guage shows 7psi and electrical in cockpit says 12psi (very common btw) , set the regulator to the mechanical guage. Note the electrical guage.

If while running the electrical guage shows that 12 psi and then falls to 7 psi at WOT and load, there is a big chance your mechanical guage on engine also dropped near 5 psi to 2psi.

So, again, use mechanical as absolute and only use electrical as reference for drop in psi.

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If you are throwing some parts at this in hopes of a fix I would also highly suggest new needle and seats (cheap $$$) even if they appear to work fine. A fuel psi guage will not show if these don't flow enough fuel to keep bowls full since the guages/senders are before the needle and seat.

Strip Poker 388

iTrader: (6)

I ve allways ran about 32 on the Blower motor and my NOS motors.35 should not be the prob unless the inigition is weak.he #6 is kinda hot. I have run the 7 and 8th ,being the 8's might load up at idle. I ran the R5674-8 in my Scarab motor.

I am running the ac 42TS now and at 11.5 psi it started to roll down the base of the eletrode sowing some heat ,But its fine at 7-9 psi

Dont they run the merc IV's on the merc 800's and 1000hp motors??????

Wobble

If you switch to MSD be sure and install their surge suppressor PN 8830 and use di-electic grease in all connectors.

I lost an MSD box due to a voltage spike, didn't know about the 8830 until I saw it on another thread.

MSD recommends .033 gap.

zt260

There is a very good change you are suffering from iginiton failure. At boost you need more power. I had to step up to the Hyfire system from Malory to supply enough juice.

Strip Poker 388

iTrader: (6)

Wobble I thought that was just for RF??? Would it help in a spike? It goes between the bat source /starter and the MSD.I put it in the race car for RF trying to help with the interference with the electric shifter,etc.

tech sheet on it
http://www.msdignition.com/pdf/tech%...adio_noise.pdf

CIG3

What size pick-up is in the tank. I would suggest 1/2" with a 1/2" feed line to the fuel pump. Then 3/8" to the regulator and carb. Your pressurecould show good but you may not be getting enough fuel to the motor. Also check your electric gauges reading by using a mechanical after the regulator.