1975 70h poor idle and stumbling @ takeoff

[no.1bradbeer]

Hi all,
I just got a new power head? nice and fresh. It ran well for the first few minutes, the started to surge, then completely died.

I had an older fuel line from the housing to the pump, it looked collapsed, and so I changed it. Now it runs hard at ? to WOT, but doesn?t idle well. It also won?t take off like it should; I can pump the lever a few times, some times it takes off, and some times it stalls.

So after a while, I find this trick? if I blip the choke, with the stick down, off she goes. Any way, I am wondering if I may have sucked the heart out of the pump with the collapsed hose, or maybe the hose from the crank case to the pump is leaking, or maybe it?s something else all together?

Any help is appreciated.
Thanks,
Brad

 

[no.1bradbeer]

Re: 1975 70h poor idle and stumbling @ takeoff

Help? Anyone?
Thanks.

 

[Silvertip]

Re: 1975 70h poor idle and stumbling @ takeoff

If choking the engine makes it take off its definitely a fuel starvation problem. I'd start by rebuilding the fuel pump. If you have a new power head, were the carbs rebuilt before installing them on the engine? If not, you are advised to do that as well. Gummed up carbs are responsible for many if not most engine failures. You can also try running the engine on a different tank to eliminate the tank and pickup as the source of the fuel delivery problem. Do the easy stuff first. If you suspect fuel lines and pulse lines as possible causes, replace them. At least they will be new.

 

[no.1bradbeer]

Re: 1975 70h poor idle and stumbling @ takeoff

Thanks Silvertip. I will try the lines and the fuel pump. I will also take my carbs off and check them. They were beautifully clean when I put them on the new power head. I will also sync the carbs again... I hear this will affect acceleration too?

Thanks,
Brad