Yamaha won't rev up

I have a (1 year old) 70 Yamaha that cuts back to 1/2 throttle when I try to go. Changed plugs, gas , gas line , fuel filter. Still same problem, but started fine and ran fine till you raise throtle.
They first said probably water in gas. Took it in and they changed plugs, pulled the carbs, compression test, and finally said air leak in the gas line. They redid my gas line conectors and charged me over 200 bucks!:eek: Took it home and it was hard to start and still won't take the throttle!:mad: I think it's fuel pump or electronics. Before I take it back to the shop, any suggestions?:confused:

Could be a bad intake gasket. It don't take much of a leak to cause problems.

Nim, does it just go to a certain RPM and not any higher, or does it get to a certain RPM and stumble?

Have you checked the pick up in your fuel take for debris?

It is a carberator problem or that's what the shop is saying this time. Sure hope this is the fix or I will be letting everyone know where not to take their Yamaha motors for service. :(

Nim, I sure hope they get that thing running. If this weather cooperates, I'm gonna get a line verrrrrrrrrrrrry wet.

If it is a four stroke, check the oil. If it is over full or smells like gas, there is a rubber stopper in the main carb body that when missing, causes the carb to flood the engine at anything over an idle. I had this problem with my Yamaha. Got a piece of trash in the carb, paid to have it fixed, they cleaned the carb and forgot this stopper. Three trips to the shop later I got the schematic of the carb and figured it out.

Have they checked the power pack, My 70 Yamaha is doing the same thing. We just checked it today 26 May, and middle cyclinder was not firing we could change the wires and it would fire just fine, it would crank real easy and idle but when you started to take off it would only run half throttle also, may be it or the coil but I assum they check the fire??

Nim what did you finally find out?

nimrod did you every find out what was wrong with It?