Carburetor Issues on Mercruiser 3.0

LawyerMan

LawyerMan

Member
Jul 12, 2012
443
Texas Gulf Coast
Boat Info
270 SLX w/ Sport Arch
Engines
496 Mag DTS, Bravo III, Corsa
I did a terrible thing. We ran the boat all summer long and had a great time with it. At the end of the season I filled up the tank, forgot to add Stabil, then let it sit for a few months. I went to start it up the other day (it's 70* down here :grin: ), and it wouldn't start.

Here at the symptoms: I can get it to start if I give it a hell of a lot of gas. It wouldn't idle without stalling. I could keep it steady on the trailer (hooked up to a hose) at about 3,000 RPMs. I took it out on the water, ran through about half of the gas, filled it up with new gas, and added Stabil.

Yesterday, sitting on the trailer on a hose, I played with the idle speed and fuel/air mixture screws and got it to idle at a steady 900 -1,000 RPMs. That made me really happy. But now, the motor seems to get bogged down when I give it gas. It's almost like a short pause before it accelerates.

Has anyone run into this before? If so, what should I be looking at? Still bad gas? Bad fuel/air mixture? Bad carb? Something else?
 
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Take the carb off and rebuild it. the passageways & jets may have some gunk in them.
 
You could try running a ton of Stabil through it - like 5x the amount you would normally use. Merc also makes a product called Quickleen that you could use - try a triple dose of that stuff and then get it out on the water and run the snot out of it. I've had good luck at doing this type of thing, before having to pull the carb off.

Get your RPM's adjusted back down to around 650. Try to avoid running on the hose above about 1200-1400 rpms, as well. Both can cause problems down the road.

Are you using ethanol-free gas... or at least using the marine stabil or Startron?
 
Great suggestions! You might also want to try soaking it with carb cleaner before running it again. It does a great job of dissolving varnish.
 
Lazy Daze said:
Are you using ethanol-free gas... or at least using the marine stabil or Startron?
Click to expand...

No, we can't get ethanol free gas down here. I run premium (93 octane) fuel, but it has ethanol in it. I do (now) use marine Stabil.
 
Molson said:
Take the carb off and rebuild it. the passageways & jets may have some gunk in them.
Click to expand...

I know that's what I ultimately need to do. After all, my electric choke doesn't work (which hasn't been that big of a problem since we're in a pretty warm climate).

I got the instructions for my little two barrel carb. It looks dawnting (I've never rebuilt a carb before), but I think I can do it. I also talked to Bass Pro Shop's mechanics. They said they will rebuild it for $150 plus the part ($50-$60). I may end up doing that.

Another option is to just change the whole damn carb with one of these: http://www.ebay.com/itm/MARINE-CARB..._Accessories_Gear&hash=item1c2f234b23&vxp=mtr.
 
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Save your money on the 93 octane. Just use 87 with either that marine stabil or Startron.
 
LawyerMan said:
I know that's what I ultimately need to do. After all, my electric choke doesn't work (which hasn't been that big of a problem since we're in a pretty warm climate).

I got the instructions for my little two barrel carb. It looks dawnting (I've never rebuilt a carb before), but I think I can do it. I also talked to Bass Pro Shop's mechanics. They said they will rebuild it for $150 plus the part ($50-$60). I may end up doing that.

Another option is to just change the whole damn carb with one of these: http://www.ebay.com/itm/MARINE-CARB..._Accessories_Gear&hash=item1c2f234b23&vxp=mtr.
Click to expand...

For 30-40 bucks, get a GOOD kit, and do it yourself. I have never taken one apart either, but I ordered a book and a couple good quality kits and am currently rebuilding my quadrajets. (One is complete, other is in pieces) Its really not that difficult. Take a lot of pictures before you start, and along the way, that way you can follow them while rebuilding if needed.
 
I think you messed up the carb adjustment. "I played with the idle speed and fuel/air mixture screws and got it to idle at a steady 900 -1,000 RPMs" tells me the adjustment is off. Go to the adjustment procedure or take it to a shop to do it for you.
 
Burp said:
I think you messed up the carb adjustment. "I played with the idle speed and fuel/air mixture screws and got it to idle at a steady 900 -1,000 RPMs" tells me the adjustment is off. Go to the adjustment procedure or take it to a shop to do it for you.
Click to expand...

You might be right. I'll hook up the hose and follow the adjustment instructions (Starting @ Page 11 of https://dl.dropbox.com/u/22066980/13B5R2.pdf).
 
LawyerMan said:
What would that do?
Click to expand...

If it isn't gunked up too bad, it could clear it up. It doesn't work every time, but I've had personal experience doing this and have had good results. I'd use the Merc stuff, though, as it's a little more potent. It's (relatively) inexpensive and certainly wouldn't involve much labor. Just figured it's worth a shot to try it before diving into the carb.
 
Lazy Daze said:
If it isn't gunked up too bad, it could clear it up. It doesn't work every time, but I've had personal experience doing this and have had good results. I'd use the Merc stuff, though, as it's a little more potent. It's (relatively) inexpensive and certainly wouldn't involve much labor. Just figured it's worth a shot to try it before diving into the carb.
Click to expand...

Are you referring to this stuff that I used to use? I still have some in the garage.

Quicksilver_Quickleen.jpg
 
Yup - that's it. Don't be shy with it.
 
FOLLOW UP...

I tinkered with this thing for a whole year. Eventually I said screw it and had the carb rebuilt and my old gas pumped out. Filled with with 87 octane and it runs like a champ.

Can't believe I screwed around with it for so long before getting it rebuilt.

LESSON OF THE DAY - Just have the damn carb rebuilt. You won't regret it. The whole job cost me under $300.
 
Glad to hear that you got it straightened out! Now go enjoy it!!


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Todd
 
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