High speed/RPM miss on 350 mag 22zx

[jrockin08]

Took the boat out a couple times after the winter and noticed when I get to around 55-60 mph or around 5 k I'm getting a lugging or a missing like its not getting fuel? But never any problems cruising below that speed or idling along. Put sta-bil in a full tank last October before backing it in the barn. Took distributor cap off and noticed its kind go chalky looking? The gasket is all hard and cracked as well. Could that just need cleaning? If so what to use?

otherwise I thought maybe the plugs, so I took them out and will replace just cuz I'm not sure when the guy I bought it from did it. What plug brand is recommended?

Thanks all

[BUIZILLA]

your probably bumping the rev limiter...

[jrockin08]

Never did it last summer,and at higher speeds than that. It's not going above 5k when it happens.

[GeneD]

I just did a motor for a guy.
Motor was spitting and coughing at 4 bbl operation, but started right up! Idled like a dream!
Ran great right up to half throttle...
Had me a bit confused there for a bit...until I replaced the plugs and it went away.
Go get yourself a new cap, and a set of AC MR43T's and call it good.

[Tidbart]

If you don't think it is the rev limiter, then do what Gene said. Replace the cap, rotor, and plugs. I would even go one step further and replace the wire along with them. You would then know the condition and age of all of these parts as well as where not to look if your problem is still there.

I would also put in either the AC Delco or NGK marine plugs. Verify you get the right plug via your serial number for you engine. Some of the later 350s take different plugs than the standard MR43T's. And make sure you check the gap.

B

[MOP]

+1 on the plugs, over time the gap widens or they carbon up.

[MOP]

If your plug wires are more than 3 years old change them, they live in a very damp atmosphere!

[jrockin08]

Ok..so I changed plugs,cap, rotor,filter and still doing this. Lets talk rev limiter...anyone know what it would be on a 350 mag mpi?

if it is the rev limiter what's that mean ? Prop bad?

[jrockin08]

Should say I have a 4 blade 24p bravo 1 prop ... And a 22p sitting in the barn brand new.

Alpha one drive, but idk gear ratio

[Donzi_Dude]

if you dont have a limter (5K?) it sounds like a plug wire to me. it will miss under load, a coil can do this as well..

[biggiefl]

Could be the cam but that would be more of a POP than a miss. Hell...vaporlock? Would only happen when hot.

[Phil S]

Also, check or replace your fuel filters...if you haven't done so already.

[jrockin08]

I'm still working on this ! Work on it during the week, test on weekend. I ordered a new fuel regulator , as with a fuel pressure gauge on it read 20-30 psi at idle on water, and when it started surging it went to 15-20 psi. Never got to the 38-42 range. So regulator first then pump I guess.

Poseibly the fuel pickup tube but I'm not about to try and get that off...last thing I need is a busted tank. I tried and the square angled valve on top wont budge.

[BUIZILLA]

does it have a fuel cooler?

[jrockin08]

Yes...fuel cooler and pump are in the same assembly with the regulator. The pump and cooler come as a kit...$500 ...so I'm praying its just the regulator.