Idle adjustment while on muffs/hose?

[spoilsofwar]

Hey all,

While I was dewinterizing the boat yesterday and running the engine I noticed it was idling around 1000-1100 RPM even when up to temp. I diagnosed it as some slack having developed in the throttle cable which is keeping the throttle from returning fully and bumping up against the idle stop screw. Anyway, I am familiar with procedure to adjust idle via disconnecting the cable, setting the idle stop screw, and readjusting/reattaching the cable. What I'm unclear on is whether this procedure can be accurately done while the boat is on the trailer running on a hose? Does the lack of exhaust backpressure affect idle rate? Am I better off dropping it in the water first?

Engine is VP 4.3 GL-P, 2bbl Demon carb

Thanks!

 

[Scott Danforth]

Drop it in the water, yes the back pressure changes engine loading and idle speed

 

[Augoose]

I'm not saying it is correct, but I set my 5.0 GL idle based when on muffs and didn't notice a change when actually in the water. Of course tweaking it later when you are on the water isn't hard either.

 

[skydiveD30571]

My 5.0GL has 75-100RPM difference in forward idle while on muffs vs. in the water. I factored that in when I set the idle in the driveway, then tested again in the water to verify and it was right on.