251-Convincor

Hello,

I have a 1987 (original Date) 454. In roughly 1990 - 1995 it was upgraded to an HP-500 by High-Tek Marine.

To the end of last season, the thing ran like a sewing machine.

This season, I have done all the usual PM items... Plugs, wires, cap, rotor, etc...

in addition, I replaced the fuel pump, and eliminated the circulating water pump with a cross over.

Fired the Boat this past week on the hose, and for the first 20 minutes all the thing would do is turn over, pop, and it hick-up'd (popped) once pretty hard through the carb (Holley 850).

Once I realized that I had the cap on wrong one half turn clockwise off, I adjusted it, re-traced my wires, and gave it another try...

************** The Problem***************

The Engine fires up, and some may say that its fine...

Like most of you though, I know this thing like I know my own Ass...

-It has a small vibration, like something is out of balance...?

-It idles very poorly. If I drop into neutral, it stalls out most of the time. If it does stay running, it is very sluggish...?

-If you NUT it, it either POP's or HESITATES then all seems ok..?

-There is a loud sucking sound from the carb. When you close the hatch, there is an audible whistle / vaccum sound with or without the flame arrestor in place...?

??? What did I screw up, and or break ???


Please Help... Like to run this weekend


Thank You In Advance,

Anarchy Powerboats

sounds like the timing is still out a lil bit.

pantera232

set it around 8*-12* initial and get a total timing between 30-34*

Unlimited jd

iTrader: (5)

double check the firing order 18436572, if all is ok timing wise maybe some varnish built up in the carb, take it off soak it and put new gaskets, needles and seats, mine got gummed up and did the same thing

fbc25el

I would guess fireing order also.

soldier4402

Carb cleaner, new plugs

tommymonza

Blew the power valve out of the carb when it backfired.

soldier4402

Also have you been putting ethanol treatment in the tank

Cold Sweat

Just a thought, maybe the engine builder changed cams and used a #4-#7 swap cam. I used them in my rebuilds??? What gph fuel pump did you use? Pretty sure if you used a 130gph pump, you'll need a regulator.

Budman II

iTrader: (1)

X2 - very common on Holley carbs with a bad backfire thru the carb - relatively easy to change out - pop the primary float bowl and metering block off the carb and replace with another 6.5 PV.