GotTheFever

What would cause me to loose power as soon as I get under boost? Everything is perfect, until I start to get boost into the manifold. This happens right at 4700 – 4800 RPM. Here are some engine stats.

Engines: 502 carb(x2).
Exhaust: CMI 2-piece
Carbs: Holley 750, re-worked by Nickerson Performance
Ignition: Mercruiser with Accell Supercoil & Mallory Soft Touch Rev Limiter
Fuel Delivery: Mallory 140 GPH performance marine pumps

Any help would be greatly appreciated

Nordicflame

iTrader: (4)

Check your belt tension and also your ducting for leaks.
If the belt slips or the boost blows off, it feels like the power just falls off.
-The boost loads the pulley which will make it slip if it's not tight.
-If you have loose hose it may just blow off the boost when it loads up.

Just words of experience..
Dave

Dixie Doug

Are you using a flame arrestor?

Pure Energy

What is your fuel pressure, at idle and 4700rpm?

fstboater

Check for good voltage at the plugs and proper fuel flow filters ect!

Dave F

Fever,

If you start to loose power as soon as boost kicks in, it sounds like your fuel pressure is incorrect and/or the regulator is not boost referenced to the carb box.

That Mallory pump is only good for 14# fuel pressure. That means you can only run 6-7 # of boost, max. Also that pump has an internal bypass. That lock nut and screw is located at the bottom of the pump. It should be set all the way in and locked, and you should use the 4309 regulator that returns to the tank.

Let us know how you make out
DAVE

Turbojack

You do not start going into boost until 4700? Procharger M4 with twin carb box? I also agree that fuel is the problem, or very loose belt.

If you want to talk, email/PM me you phone number & I will give you a call.

GotTheFever

Thanks all for your input:

I’ve checked the belt tension and they are very tight. The hoses are also tight. The pulleys I’ve got are for 5 lbs of boost. The fuel pressure at idle is 7 lbs, and at 4700 rpm it is 14 lbs. Since it is boost referenced in the box, I know that I’m getting 7 lbs of boost in the box, and that the pumps can keep up with the demand. I was told that the fuel pump was set to 12 lbs of boost from the factory, and that I had to remove the spring, and stretch it out to get the 14 lbs of boost that I need, without having a return line to the tank. I have a boost referenced regulator between the carb and the fuel pump. I don’t have flame arrestors, I use the K&N filters that come with the Prochargers. The loss of power happens weather I nail the throttle, or roll into it. It seems relative to the position of the butterflies being open enough to allow boost into the intake.

Budah, you asked what has changed, it’s a long story.

I got the Prochargers with 3 ½ lb pulleys and a stock marine holley 750 carb (rejetted of course). I put it on and tweaked it, but never felt I was getting the gains out of it that I should. I purchased 5 lb pulleys, and sent the carbs to Nickerson performance. They said that I needed to upgrade my fuel delivery system and sold me the Mallory 140s. The only problem was that they did not modify the pumps to deliver any more than 12 lbs of psi, even though they told me that I should be getting 14 lbs of pressure. I was assuming that this was because I was not putting out enough boost to obtain more than 12 lbs of fuel pressure. It was not till recently that I learned to obtain the fuel pressure levels I needed, that I had to elongate the springs in the pumps. In the mean time, I’ve been trying to correct the problem by adjusting the jet size. I was still having WOT problems. After getting the fuel pressure correct, I went back to the original jet size that Nickersons had put into the carbs. When I told them of the problems I was having, they suggested I tighten up the belts. I really cranked on these things, but nothing changed. Now they are telling me to go down on jet sizes. I only make it out to the boat every other week or so, so each test takes a while. I was hoping that the expertise on this board could help expedite this process.

Thanks again

Gary Anderson

Rev limiter kicking in too early? Try removing it.
BTW, how do your plugs look? Wires & cap OK? What's your ignition timing? Initial & total.
Gary

Turbojack

We can give you guesses all day but need more info. Sounds like you have hit on the ovious.

Does the motor just stop climbing or does it slow down once up to 4700?
I still want to know about starting to go into boost at 4700, motor should be in boost before that rpm.
Type of boat?
Prop, outdrive, Outdrive gear, speed of boat at 4700
We know 502 but heads, cam, compression, timming, exhaust (kind & tail pipes) gas you are using?
Plug gap?
Ignition type/kind?
Procharger model number? M4?? The procharger dual carb box or something else?
Enclosed engine compartment getting enough air?

Just some of the questions.

Last year I could not get mine over 4K, motor would scream to 4K & stop. Changed out MSD box & first pass out motor turned 5600.