351-W carb?

nautique74 wrote: ...it turns over but takes several minutes to even start hitting. It just turns over and over for several minutes then Pup...pup-up...pup....pup-pup-pup..pup-up...pup-pup-pup..boom-boom-boom-varoom with a gasy smell and smoke out the exhaust.

Ok, now that is a PERFECT description of what I experienced last week on the Rochester carb on my pontoon's Mercruiser 140. I mean, exactly that pup...pup-pup... and so forth. However, oddly, in my case it was one morning with the engine cold. After messing with it for a long time (more than an hour), I came to believe that I had a combination of problems. I think I had some dirt in the carb, so I blasted it with more carb cleaner than I care to admit. Then I held the choke plate (which was closed too tightly) wide open with a screwdriver while I cranked it to pull the cleaner through. It started pup...pupping more and more then finally sort of pupped into running and then ran, with that gassy smell and the exhaust smoke, just as you describe. I ran it in neutral a little high on the rpm's, like around 2000 to 2200, for about 20 minutes; don't usually like to do that with no load. Anyway, it smoothed right out and never had the exact problem again... but... later in the trip the engine wasn't happy starting when warm. I've worked on this engine a lot over the years, and it generally starts as soon as I turn the key. But I had to grind for maybe 4 or 5 seconds when warm. I am convinced now that my problem is twofold -- the battery in that boat is 7 years old and isn't throwing her over as fast as it should, so I'll be picking up a new one. And I'm convinced the choke is misbehaving. I converted the Merc 140 over to electric choke about two years ago, so I am going to run through the choke calibration procedure when I find the time. For one thing, I noticed the choke plate is sitting fully closed when it should be cracked open a bit. Anyway, I know this isn't the same carb or engine, but the principles are pretty much universal and your pup...pup description matched exactly, so maybe this will be of some help to you. I hope you find it sooner rather than later!

So I have had the same problem. I just had mine rebuilt the problem with mine was the secondary butterflies were not opening when the engine was at operating temperature to compensate for the choke being open. I also found the rear floats were set high causing gas to drip out of the front jets. The other issue found was a bit of dirt in one of the jets. The boat has NEVER started so AWESOME. Sounds like a new boat starting. Hope this helps.

yep

start with the choke

see if it gets power.

Then see if its grounded

Then see if it has continuity

If cant be corrected, loosten and rotate the choke so its open til you get a replacement.

Meh, my nicest starting boats (warm and cold) have the choke bypassed entirely.

1984 SN2001
351W

Ok, still having trouble with this. Last September the threads that connect the fuel line to the front bowl were leaking and found to be stripped. Found a used bowl with floats and installed it. The float adjustment looked the same as the old bowl but that was just a visual check.

After that, the engine won't fire when cold unless we hold the choke plate open. Starts great when warm. Tried disabling the choke but experienced a hesitation on hole shot acceleration, never had that before. Doesn't sound like a choke issue.

Now have set choke to 1/16" gap when cold. Still have to hold choke plate open and sometimes use starting fluid when cold. Electric choke opens normally. Not sure if we still have the hesitation; finally getting ready for summer.

Thoughts?

No more fuel leak. The fuel line wasn't in the best of shape after trying to get the leak to stop last Labor Day weekend. I replaced it with USCG approved soft line with an inline fuel filter, no more filter at the carb inlet.

No, I didn't know about that. I watched the video tonight from another post. That was new to me. I think I have all the manuals, is that covered in the manual? Not home to look thru it right now.

Adjusting the accelerator pump linkage is super easy. There's a nut and bolt with a spring, and you just unscrew it a little, and that opens it up a little and takes out any slack. The linkage is kind of line a see saw, with one side riding the acc pump cam, any the other side actuating the lever. The lever side has the adjustment. Holley has some great videos on YouTube.

The cold starting... not sure on that though, the acc pump lonkage would have to be waaay loose, but anything is possible.

Good video from Holley on accelerator pump adjustment:

Video Link

JQ

Looks like you found the problem

Might be time for an accelerator pump rebuild. You may also try a different size squirter / nozzle. Try going larger by 3 or 4 sizes. If you have a 31, try the 35. That can also solve the bog or hesitation.

JQ

Bri892001 wrote: ...if you have the screw opened up so much, that the actual pump lever is never able to fully return to the full start position, you're not going to get a proper pump shot either.

I think that was it, Brian. Yesterday I had the boy tighten down the nut (shorten the bolt) until the pump lever arm lost contact under the fuel bowl. Then I had him use his fingers to actuate the pump arm, to feel where the resistance of the pump just started--and then to set the bolt head to exactly that amount of stroke, as a starting point. All of this was with the engine warmed to operating temp. Then he took it out on the water and tested it. After each poor result, I had him loosen the nut (lengthen the bolt) a thread at a time. He's got it dialed in pretty darn good now--the hesitation is gone. I was going to have him do the final adjustment a quarter turn at a time, but he thinks he's right on the sweet spot now. I'm not sure how "wide" the sweet spot is in terms of turns of the nut.

Thanks to all you guys! You saved a lot of frustration on our vacation. :)

Steve