Not Today

I just ran a newly rebuilt 502 and can't get it to turn any faster than 4000 rpms. The base timing is set a little advanced at 10-12 degrees. Is this why it won't turn over 4000 RPMS? The engine shop that did the work told me there was not really a break in procedure to follow. I ran it for about an hour and on the way back to the launch tried to give it more throttle and when I got to around 4000 it throttled back on its own to about 3500. Did the knock sensor sense detonation and retard it back? What do you think. This is MEFI 1. I'm running the same prop as I was before the engine was rebuilt. 4 blade bravo prop 24 pitch.

Mseuro

Dont know if this applies but mine also ran a bit rough and would not go over 4k rpm, no codes where thrown and no alarms went off. The cure was to replace a bad plug wire we also changed all the plugs too.

Crude Intentions

iTrader: (1)

What was done to the engine? The mechanic who did it didn't test it?

Trash

Make sure the base timing mechanically set matches what is in the Spark Reference Angle table.

getrdunn

iTrader: (7)

Many threads like this. I like my carbs... Be sure and check all your sensors. Crank tigger and distributor. Confirm all connections good first. These seem to be the culprit in many cases so I've read anyway.

So earlier in the day before backing down was everything ok? Might wanna see if you can get your hands on a scanner and see what code it's giving you. Wished I was more help. When it comes to computers I unplug them and plug them back in. I hate them almost as much as Hilary.

Blueabyss

Timing should be 8 Degrees. 10 is iffy and 12 is probably bad unless you have race gas. If timing is high like that the knock sensors may be shutting it down.

Chris

tunertech

did you send the injectors out for evaluation and cleaning?

BUP

iTrader: (9)

^^^^^^ Often a missed piece of the puzzle and I know first hand from many boaters with their sent in fuel injectors way after the fact.

I would check fuel pressures thru out all rpms first to see what psi readings are collectively

Not Today

Thanks for the comments. Yes I did send out the injectors as part of the rebuild process for flow testing and cleaning. They all passed the flow testing after being cleaned up. It is possible something in the VST tank is restricting the fuel flow and not providing full pressure to the rail. I will check that, and better yet, I plan to run an in line fuel pump and trash the VST system and mechanical lift pump all together. I winterized the boat yesterday so this is all stuff I will need to look at in the spring. Could I have potentially detonated the engine and melted a hole in the piston? I'm nervous about this. The timing can't be retarded back to 8 degrees the way it is now. There is no more movement in the distributor. I will need to pull the distributor out and move it a tooth and then re-adjust. I think this will be my first step before running this engine again. Please let me know your thoughts on if you think detonation occurred. Do I need to do a compression check, or do you think the knock sensor caught it in time?

Appreciate all the responses.

Blueabyss

Im not saying or thinking you burned a piston. I would simply get the timing set to 8 degrees and then re test and go from there.

Chris