bpowers135

I have replaced the original Rochester 4bl carb with a dual pumper Holley 800 CFM Quick Fuel Marine carb. The boat will run will up to about 3800

RPM and then appears to ping and tops out when addition throttle is applied at 55 MPH. My new fuel lines have a inline pressure gauge that appears

to fluctuate. My question is this; should I also replace the mechanical fuel pump with Holley Ultra HP series fuel pump or should I be fine with the

existing mercruiser fuel pump? Any comments and suggestions welcome.


Additional info

The boat uses a 23" prop and would run between 66 - 67 at 4850 RPM on the Rochester.


I have had to adjust the lean/rich screws on the Quick Fuel from the 1 1/2 turns out to 3/4 turns out.

AllDodge

So long as the fuel pressure is above 3 psi the pump is supplying fuel, so that shouldn't be the issue
What motor 502 maybe? Have a serial number?
If your getting an actual "ping" sound then your either lean or your timing is off. What is the timing set at?

It it is a lean ping the motor is eating it self

jvthundercat

Start with this. Sounds like your fuel pressure is off. You can flood or starve from it.

Before starting the engine make an initial check of the float level. If fuel is not visible in the sight glass. This carburetor was pre-set at the factory to be in the middle of the sight glass at 6.5 P.S.I. Fuel pressure greater than6.5P.S.I. will cause the float level to be too high. Conversely, if the fuel pressure is significantly below 6.5 P.S.I. the float level will be too low. For the carburetor to operate correctly the float levels must be in the middle of the sight glass. The most accurate way to establish the correct float level is to check it while the engine is running. If the initial float level is not visible in the sight glass then it might be necessary to re-adjust the float level before starting the engine

bpowers135

It's a 454, Timing before Carb swap was right on mark with no ping. I really have only adjusted the lean/rich mixture due to

a lot of black soot on the transom exhaust at idle and rough running , reduce factory setting by 50% (more lean) / Running too Rich.

Fuel bowls are right in the middle during idle.

AllDodge

No ping before carb swap and now have ping, sounds like lean fuel mix. Being a quick fuel carb articfriends could have some input.

Pull the plugs and see if they are white and if electrode is damaged, while doing so check compression