tuning issue (help)

[mike stover]

Gen3 sport hydro w/zen 26, 6719/3 554 ppw prop, carb settings at 2 & 1 turn.

Had motor checked and all seems good including timing numbers.

Why would it fall off pipe when warmed up after a couple laps, and cant get back on. Launches great and as long as you stay in throttle its fine. The minute you let off its off pipe and just struggles. Have tried different pipes at all different lengths and doesn't seem to help. Will come back up with a pipe at over 14", but have no speed.

What are some possible causes of this boat requiring a really long pipe.

Thanks, mike

 

[mike stover]

Sorry, this was meant for gas forum.

 

[Brian Sorgente]

Hey Mike,

Obviously I saw your boat at the race, I didn't realize it was falling off only when you let off the throttle. A few years back when I was running my gas rigger I had the same issue and it ended up being that the low end needle was set too lean. Like you, I tried setting the pipe ridiculously long thinking I didn't have enough torque to pull the prop I was running. I also ran the boat at full bore in the mill to keep it on the pipe which was also rather exciting to watch LOL...

Anyway, I was told that the fuel goes through the low end needle first before it gets to the high end, so if the low end needle is set too lean whatever you do to the high end needle wont make a difference because its already being choked by the low end... Im not sure if that's a 100% true but in my case it worked and after that I could throttle the boat from a crawl to full speed. I want to say the typical starting spot its like 1 turn out on the high and 3 on the low? Im sure someone else can comment on that to confirm.

Hope this helps,

Brian

 

[moparbarn]

Mike, if you're running a walbro 257 start at 1 high & 2 low. I've ended up at 7/8 high & 2 1/8 low.

 

[mike stover]

Thanks guys, will try some carb adjustments

Mike

 

[Brian Sorgente]

I didn't see your carb settings in your original post until now. Regardless I just checked my notes and in my rigger I was running the low end needle at 2-1/8 and the high end at 9/16 turns out. I was also running my pipe at 14" to the center of the cylinder.

Brian

 

[Rene Danner]

Also Mike check the carb iso block for air leak, and prop it down a bit.

Rene