Yamaha ProV mistereous issue

[qhn]

1988 Prov150hp with 110psi on all 6cyl, good spark, clean carbs, starts nice, idles great, planes out powerful, runs warm, but vibrates and bogs down to trolling speed, nearly cutting off, put back to neutral in less than 5 sec and it's all good again for a few miles more. What fixes itself in less than 5 seconds? Resistance test all coils found 1 out of spec 15.2M Ohm, 1 at 3.5K Ohm, the rest at 2.56K Ohms. Changed one coil no help, run off portable tank, no help. Rectifier charges good.
I am stumped. Any advice is greatly appreciated!

 

[aliboy]

Fuel pumps been checked? Poor fuel delivery to the carbs (assume it is carb'd?) could catch up at idle then drain the bowls again as you plane off.

 

[racerone]

Test run with a " known to be good " hose and portable tank.

 

[qhn]

Thank you for all the recommendation and advice. Yes, 2 new fuel pumps, yes ran it off of a known working portable tank, hose/primer, change fuel connectors to Mercury's, no oil fouled, all circuits are tested, absolutely not the cdi, will bypass Tstats and reduced relief valve tension next...
it is a mystery at this point! Haven't seen an issue that fixes itself in less than 5 seconds and happens again at the same distant every time!

 

[aliboy]

How clean are the carbs and how are the float settings?

 

[aliboy]

Still thinking fuel delivery. Is there 2 or 3 fuel pumps on that engine?

 

[samaha]

degraded fuel hose lining collapsing. check engine fuel lines, then others.