25hp yamaha wont stay running

[FISHFINK]

guys
i have a 1988 yamaha 25hp, 25SG model, two stroke tiller.
had the carbs rebuilt by the local mechanic 8 weeks ago, and he also suggested i buy a new plastic portable 6 gallon fuel tank and fuel line and primer ball. i bought the best ones from bass pro shops.
right after the rebuilt carbs, i took it out and it ran perfect for probably an hour, off an on, stop and restart, etc.
within these 8 weeks, i have started it here at the house at least once every two weeks. no problems.
yesterday i was out fishing, it started right up, and ran at top speed for probably 10-15 minutes, then it bogged down, and although it was still running, it acted as if it were running on one cylinder, or a fuel problem. i shut it off, pulled the plugs, which looked fine, and within 10-15 minutes of setting, started it up, and it ran perfect for about 5 minutes this time, then did the same thing, bog way down and sputtering.
at that time we started fishing, and within about 45 minutes wanted to move on to another fishing spot.
started right up and ran for 8 minutes, and bogged down again.... this problem never went away.
right after it would bog down, i pulled the cowl and touched the engine and both coils and cdi unit, and all were not hot at all, everything seemed ok.
also, i did have the vent screw fully open on the plastic fuel tank. but right after one mishap i unscrewed the fuel cap and it vented quit a bit. but the primer ball was NOT collapsed.
so, on the next run i kept the fuel cap only half on, making sure it was getting vented enough, and it still bogged down.
i am at wits end..... do any of you have any suggestions ?
could the coils or cdi unit be failing ?
although the female end of the quick disconnect is new, its the original male end thats in the engine, and it does seem to be worn, since when i connect the female to it it will rock back and forth. im thinking maybe that connection could be faulty and sucking air ?
im going to order a new male connector and give that a try, and was just wondering if any of you had any other suggestions ?
thanks guys...

[boats.net]

Sounds like it's starving for gas, may have a fuel restriction in fuel hose, filters or connections or loose hose connections, problem with fuel pump or carbs are dirty.

[FISHFINK]

Sounds like it's starving for gas, may have a fuel restriction in fuel hose, filters or connections or loose hose connections, problem with fuel pump or carbs are dirty.

thanks much for the input... although i have a new gas tank, line, primer ball and female quick disconnect, and carbs rebuilt, i did forget to unhook the tank line and that fitting got pulled a bit. and the original male connector that bolts to the front of the motor has looks shaky since day one when i bought the engine in september... so im waiting for parts, new male and female quick disconnect, fuel filter, and pump diaphragm... will report how that works after i get it installed and go for a test run.

thanks much

[FISHFINK]

ok guys, took it for a test run this morning.
after the new fuel pump diaphragm, male and female quick disconnects for the tank, and fuel filter, it does the same thing.
runs awesome for 5 minutes, comes up on plane quick and runs at 30mph, then bogs right down, instantly, after the 5 minutes, and seems to be running on only 1 cylinder.
im now thinking it might be an electrical problem ?

how can i check my two coils ? i have a multimeter, can someone tell me how to check them ?

if i can check them myself, and one or both check out bad, i will replace them myself. if i cant figure out how to check them, i will bring it back to the mechanic for him to diagnose.

thanks guys

[99yam40]

Check spark with a spark tester and check timing with a timing light to see if it is retarding due to safe mode.
Needs to be checked when problem is occurring.
Service manual will help

[FISHFINK]

Check spark with a spark tester and check timing with a timing light to see if it is retarding due to safe mode.
Needs to be checked when problem is occurring.
Service manual will help

UPDATE UPDATE UPDATE......
PROBLEM SOLVED...

guys, although my oil injection tank mounted to my engine was half full, it was low enough to throw the engine in "safe mode", which retarded the timing and made it run bad, as not to burn the engine up.
i went out for a test run this morning without adding the oil, and sure enough after 4 minutes of full throttle it would die down and was running like on only one cylinder.
shut it off, added oil, had it started within a few minutes, and ran it full throttle, back and forth the canal for an hour, getting it up to 33mph, and it ran flawlessly...

many thanks to everyone who helped me out with this problem...
i am now ready to fish.... thanks