compression question

[bstream97]

any help please 1988 v-4 yamaha ( I KNOW) top cyl both 140 psi bottoms are at 128 and 132. motor looses alot of power after it runs for 10- 15 minutes, wont even get on plane , runs great when cold, all plugs burn evenly. thanks bryan also has new gas line -vent - bulb and has no anti siphon valve. thanks bryan

[flabum1017]

Your compression doesn't look way too bad, you might try some engine tuner to bring the compression back up.

As for your problem, you need to do some testing. The first thing I would do is put the antisiphon back in and put a vacuum gauge betweet the tank and the motor and see if there is a restriction or leak somewhere in the fuel system. Too much vacuum means a restriction too little means a leak. You said it looses power after 10- 15 minutes. that sounds like classic vapor lock which cabe be caused by several things such as a clogged vent or vent hose, clogged filters or a collapsed fuel hose or bulb.

[bstream97]

thanks for the help flabum1017, i havnt put a vac gauge yet, but all other stuff is new. thanks b