454’s no throttle response issues
 

Wondering if anybody had or is having the same issue. Have a 88 Nova Spyder with twin 454’s – fresh heads and exhaust. Ran excellent last year. Pulled boat out of storage last week. Added E.Gas treatment prior to winterizing. Anyhow boat runs great at idle, as soon as you attempt to get on plane engines serge and has lack of power, also herd a backfire or 2 – thinking could be bad fuel or possible clogged carbs – changed fuel separators, same issue. Marina claims gas was fresh and delivered 2 weeks prior to purchasing. Any thoughts? Thanks!

Does it stumble then come back to life and run ok once you are on plane? Sounds like your accelerator pumps in the carbs might be shot.

Thanks for the replay – after its planes, its somewhat ok but if you hit the throttle it acts up. Would these typically go bad together?

Sounds like you are not getting fuel. Could be the accel pumps or the main fuel pump(s) or the anti-siphon valve(s). The best way to tell is to buy a low pressure fuel pressure gage from the auto parts store and hook it up to one engine. You should see at 3 psi though 5 is better from idle to WOT. It should not be more than 9 psi.

As both engines are doing it, I am more inclined to think that the anti siphon valve(s) are stuck.

In short ,yes they can . These older carbs need updated parts to deal with the Ethanol fuel as it is very hard on the acc pump seals , float and needle tip . Anyone else notice the increase in Quadrajet problems as of late .

It wouldn’t hurt to replace any rubber sections of your fuel lines if they are original with the latest marine fuel line that is rated for ethanol. I have a friend with an 1988 Fountain that did that because the inside of the fuel line was starting to deteriorate, you will notice tiny black specs in the filters/and or float bowls.

Problem resolved! Had water in fuel. Added dry fuel treatment and fresh gas – ran it – changed fuel separators – ran great at 1st then started again – removed and emptied fuel separators again – running great now. Thanks for all help!

Thats exactly what I was fixing to ask you is if you checked for water in your fuel. I have experienced this many times here at our shop. The engines will run perfectly at idle, but have no power under load, stumble and backfire.
Glad to hear you are up and running again!

correct me if i'm wrong but I thought the ethanol fuels don't allow water to lie at the bottom of the tank. Doesn't the ethanol absorb the water till it becomes too saturated then phase seperation occurs?