1998 Crusader 350XLI EFI Hunting/Surging

[Capt Happy]

Good Day All,

Recently finished a top end rebuild of the St'bd engine.

Heads replanned, valves replaced, new pushrods. All the normal things you would do.

Issue.
Engine starts and runs fine, after about a minute or so, it begins to fluctuate in rpm. Not what I could describe as running rough, just seems to be up and down in rpm. Unnoticeable on rpm gauge, but definitely not smooth.

Nice thing about twin engines is this is a spare parts locker a foot away.

Swapped out, throttle body, coil, whole distributor assembly. ECM.
Checked and confirmed anti siphon valve clear. Removed fuel cap, just in case. Changed all the fuel filters.

Confirmed no valve overlap.

Any thoughts??

It has the breather hoses up to spark arrestor. Do these engines have a PCV valve as well?

Has anybody had an issue with the throttle position indicator?

Sort of at a loss on this one.

Thanks in advance for your reply.

Cheers, Capt Happy

[bud37]

Source of the post
Has anybody had an issue with the throttle position indicator?

If the other engine is fine with all that and you swapped it then it will be something else IMO.
Put a vacuum gage on and see if you have a small leak, What with the intake new gaskets and all.

Check your plug wires to make sure they are routed away from grounds etc.

No hoses are routed to the throttle body base heh ?

[Capt Happy]

IMG_20250727_102252.jpg

[Viper]

That's an Oberg fuel filter. I bet that's your problem. I thought of mentioning it but when you said you changed "all" of the fuel filters I thought that included the Oberg. Remove the middle bolt/fitting for the two halves to come apart. There is a flat round steel mesh filter inside that can be cleaned and reused if still in good shape.

[Capt Happy]

Hello Viper,

Thanks so much for your reply. We will check this soonest and let you know if issue has been resolved. Thanks again.

[Capt Happy]

Took a while, but figured it out finally!!

As mentioned, one engine surging/hunting.

Issue was a small pin hole about half way down the dip tube for st'bd fuel tank. When boat rolled underway, this would introduce air into fuel delivery. Fill the tank up, hole submerged, engine run fine. Burn some fuel, pin hole exposed and back to problem. It was a bugger to decifer, but all is well again.

Hope everyone is having a great season. Play safe.
Cheers, Capt Happy