Secondaries not opening up 7.4l carburetor - Solved

K

keysohana

Member
Sep 12, 2019
58
Boat Info
1995 Sundancer 330 DA
Engines
7.4 Carb V drives
So I took the Sundancer 330DA on a test run, both motors ran great up to 3000 rpm, except past 3000 rpm, port motor would easily go, up to 4000 rpm, starboard engine would not go past 3000 rpm even at full throttle.
Also the starboard motor has a few small back fires when she starts cold..not sure if related, but possible.
Thinking the secondaries are not opening up and it appears they are controlled by a vacuum?
Does anyone know where to start looking for that or other suggestion?
Thanks!
 
Not sure, thinking it is a weber though...
 
Note there is a possibility the last mechanic pulled or broke something when doing the manifolds and risers, I found sloppy work after he left including but not limited to 2 spark plug wires not fully inserted onto the plugs, heat exchanger hose not clamped, etc.
Just not sure where to start looking....
 
Sounds like the the test run was a failure. Carburetor, timing and or internal issues are present so there are probably better options on the market unless the price is unbelievably great?
 
Looks like carb is a weber...I am now leaning towards timing as the issue due to the back fire when started cold...ran great and solid at up to 3000 rpm though, no skips, etc.
Maybe ignition sensor...
 
if you check the timing you have to ground one of the wires for the thunderbolt. also double check your firing order. Did you get a survey done when you bought the boat?
 
Sounds like a carb issue itself. Factory carbs on my 96 330DA were Rochesters. I specifically had them rebuilt (with warranty) and flow tested when I did an overhaul this winter. Oddly enough, port was way too rich even adjusted with the set screws turned all the way in. I warrantied it and now it runs like the day off the show room floor. I did do Electric fuel pump conversions which I recommend and love. Dead cold, I turn ignition switches on, wait 3 seconds (the modules used have 3 second auto-prime) and hold for 2 cycles and it idles flawlessly.
 
Thanks, what electric pump conversion did you have done? That sounds like a good idea...
 
 
 
What fuel pump psi do you recommend for a carb 7.4l?
 
Popping back is generally caused by a lean condition. I’d make sure the choke is working right. I’d also make sure the throttle cable is set up correctly. Maybe it’s not stroking fully.

Mechanical fuel pumps are fine for carburetor engines. If you go electric, use something marine rated and properly wire it off of a relay that’s controlled by an oil pressure switch and cranking by-pass. You don’t ever want a situation where the pump is running continually while the engine is off. If the needle and seat leaked and you left the ignition on by mistake, you’d have gasoline flooding over and laying atop the manifold and possibly fill the crankcase up.

BOOM !
 
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