470 intermittent fuel issue

000utback

Cadet
Joined
May 15, 2010
Messages
9
Hey, first post on the forum. There's a lot of great info around here! Please help! eBay purchase "totally reconditioned" (ha ha ha) 1980 Regal Imperial 19 ft, 170 mercruiser 5642254, Rochester two-jet 1376-5990A1 carb.

I suspect that this boat set for a couple years, then the previous owner says he ran it 4 times last summer pulling a small boy on a tube. I bought it this spring and put it in the lake Memorial Day. It takes a while to get it started, but then it sounds really nice. The first day we puttered around, never going over half speed (I'm a good mechanic, but new to boats, and it's 30 years old). Ran great! Second day we gradually tried more speed, to give my big boy a good tube ride. Running at close to wot, the engine would stumble occasionally. Then it would stumble more. Then it would stumble at lower speeds as well. Then it started cutting off entirely. We got to the point where we could ride for 5 minutes at slow speed, then it would cut off, we'd restart and try again, etc. The duration of run time got less and less.

My first thought was gummy fuel or moisture (I have added an entire bottle of Dry Gas) from lack of prior use, leading to a blocked fuel filter. Midway through the adventure I replaced the in-line fuel filter. No improvement. Great hopes when it started up, but within 10 minutes we were sputtering again. The duration of run time continued to decline. Finally I couldn't get it started again, and took the ride of shame behind a loaded pontoon boat to the ramp.

Today it's setting in the yard with the garden hose attached (2 hours to nearest lake), and try to do some trouble-shooting, but it started up and ran great. Low throttle, half throttle for 30 minutes, a little high throttle (can I hurt anything running wot in the yard?) - it never stumbled.

The only thing I was able to check this morning is that the accelerator jets give their little squirt when the throttle moves. I didn't take the line off to test the fuel flow, cuz it looks like it's getting flow. My original plan for the day was to 1) confirm that the boat doesn't run 2) test for fuel flow 3) remove/clean bowl on fuel pump 4) research if there's a built in filter on the carb inlet and after each step try to run the boat to confirm my efforts. But now, since it's running so good, I have no confidence that any of my proposed efforts will fix the root cause.

Second-hand advice told me immediately "it's the carb. don't waste your time on anything else. get a new carb." Well, I'm cool with that, if it's expert advice. This carb has the bypass fuel line from the fuel pump, so I doubt I can find a cheap alternative. But if 3 of you write in a say "new carb", I'll do it immediately and rest easy.

What would you guys do before you take the next trip to the lake? Is there a filter in the pump? In the carb? Any help is appreciated.

PS tachometer doesn't work, so I don't know real running speeds. It also used a lot more fuel than I expected, but maybe cuz of not getting up to plane speed.
 

000utback

Cadet
Joined
May 15, 2010
Messages
9
Re: 470 intermittent fuel issue

or, like, am I off-base in chasng the fuel system? What in the ignition would act like this?
 
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