5.7 Cobra runs great on muffs, Not on the water.

[paston11]

I wanted to freshen the motor up. Heres what I have done. New camshaft, new Edelbrock carb, new edelbrock intake, new Mallory distributor, new Mallory coil, Made the Mercrusier style shift assist. The only thing not marine is the camshaft and it is a very mild street cam. This thing runs like a champ in the driveway as soon as you back it in the water it wont start and if it does it wont stay running. Thought it might have been the extreme angle of the ramp so we floated the boat off and it started, but wouldnt stay running. I am out of ideas and patience. HELP

 

[Gettinther]

Re: 5.7 Cobra runs great on muffs, Not on the water.

I wanted to freshen the motor up. Heres what I have done. New camshaft, new Edelbrock carb, new edelbrock intake, new Mallory distributor, new Mallory coil, Made the Mercrusier style shift assist. The only thing not marine is the camshaft and it is a very mild street cam. This thing runs like a champ in the driveway as soon as you back it in the water it wont start and if it does it wont stay running. Thought it might have been the extreme angle of the ramp so we floated the boat off and it started, but wouldnt stay running. I am out of ideas and patience. HELP

Was the drive down when you put it in the water?:facepalm:I have experienced hydrolock with the drive up. Don't know if your unit would be affected by this or not.
Your cam may be causing reversion as well

Just a couple ideas

 

[paston11]

Re: 5.7 Cobra runs great on muffs, Not on the water.

I was thinking of reversion. Is there a way to tell if it is reversion? Wouldnt it revert on the muffs also? Would the plugs show like they do when a head gasket is blown?

 

[Gettinther]

Re: 5.7 Cobra runs great on muffs, Not on the water.

I was thinking of reversion. Is there a way to tell if it is reversion? Wouldnt it revert on the muffs also? Would the plugs show like they do when a head gasket is blown?

depends on the cam and water quantity in the exhaust but not as likely, When in the lake you have the whole lake looking for a place to go, on the muffs the exhaust has little to no restriction.

And if the drive was up when ya dropped it in the lake it goes up the exhaust , in the open exhaust valves , and no start, or runs very poorly as it trys to get the water back out.Carefull not to force it thru hydrolock, tends to do a lot of damage

"Is there a way to tell if it is reversion?" pull the plugs and look for signs of water

"This thing runs like a champ in the driveway as soon as you back it in the water it wont start and if it does it wont stay running. sure sounds to me like water is coming up the exhaust, just what it sounds like to me.
Is it hard to turn over when this happens
Untie the back of the boat from trailer when you head to the lake

 

[paston11]

Re: 5.7 Cobra runs great on muffs, Not on the water.

Went to the ramp last night, back it down the ramp but not in the water, wouldnt start. Pulled back up the ramp checked float heights in carb, adjusted float heights and tried again. Backed it in and fired it up. Still a bit on the rich side, little more tuning I think I might get her fixed. Plugs show no sign of water, and it cranks at a decent RPM.

 

[Gettinther]

Re: 5.7 Cobra runs great on muffs, Not on the water.

sounds like you are goin the right direction

good luck

 

[Don S]

Re: 5.7 Cobra runs great on muffs, Not on the water.

Have you set the timing with a timing light, or just by ear?

 

[paston11]

Re: 5.7 Cobra runs great on muffs, Not on the water.

Timing has been set by light. Going to check again tonight and see how the advance is working.