DT 115 acceleration problem

[Jrzyking]

A little help requested,
I have a 1998 DT 115 EFI engine that is slow to accelerate the first time I go WOT each day. After about a 12 minute transit down the canal at 1200 RPM I go wide open and engine will get to 3K then slowly reach 4K then about 10 seconds later it opens up and goes to 5K.

Only seems to happen on the first run of the day

Changed all filters, plugs, removed and rebuilt FVS .
All hoses check good, replaced primer bulb just to rule out.

Any ideas? Don't want to throw any more parts at it without some experienced ideas.

Thanks for your time.....

 

[99yam40]

I would monitor the rail and lift pump pressures to see if that is holding while problem shows up.
that should give you an idea if fuel pressure is the problem or not