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76 Ski Nautique/Ford 351 - Weird problem I can't solve

liftfilms

New member
I have a 1976 ski nautique with a ford 351 that I just installed a brand new QuickFuel M-600 Carb on. It had a Holly automotive carb when I bought it so I installed the QF marine carb to correct that. The engine/carb runs great other than one problem I’m having: When I’m running the boat under load (approx. 2000-2500 rpm) I am getting a sputtering. I have to pump the throttle on the boat to keep it from cutting off. The boat accelerates perfectly. I’m only getting the sputtering at that crusing RPM. I’ve checked all the fuel delivery options and it seems to be getting fuel perfectly. I also have two aluminum spacers between the Carb and the manifold. This is how the boat was setup when I bought it so I didn’t change that when I installed the new carb. I’m also having trouble with the idle. It starts off idling fine but when I bump the boat in gear and then return it to idle position, the RPM’s do not come back down. My cable is adjusted correctly. Any ideas? Thank you for your help.







 
both of those are outcomes that I've guess at. I'm pretty new to working on engines so I'm trying to learn some of this as I go. One of the difficulties I'm having in trouble shooting is that I only get the problem with the boat is on the water and under load. I can't replicate it in the driveway hooked to the water hose.

I don't have a vacuum gauge so I'll order one today and try that out. If it was a vacuum leak would it only show these symptoms at that RPM range?

I'm not sure about the carb jets. I told them which engine I had when they sent the new carb so I assumed it was jetted correctly. This seems like a likely explanation for the problem since its only giving me the problem around 2000-2500 rpm.

Since I have the idle problem too, maybe i have a vacuum leak and wrong jets? I'll try new jets and check the vacuum gauge and get back to you.
 
I've seen many issues where you can't duplicate the symptoms on a hose....you need to diagnose the issue(s) and resolve them - just throwing on new parts usually exhausts your wallet much faster than necessary....

One thing you can check "on the hose" is the timing advance....if that isn't correct, it can also cause similar behavior as described...

So, why did you opt to change the carb? Based on the Tech info sheet, you got a generic calibration package...it may be ok but isn't likely to be optimal.
 
I changed the carb because someone had put a Holly automotive carburetor on there previously.

Well I can tell you right now that the timing is off as well. It drags a little when turning the engine over. I was going to tackle that after I got this other issue resolved. I didn't realize they could be connected. Shows my ignorance.

I found a few videos on youtube for setting the timing so I will tackle that first.
 
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