Puzzled........Carbs are choking on exhaust

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Stoughty Rods

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Aug 4, 2005
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I really need some help now guys! I've got no idea on what to change or what to work on next to solve my issue.<br /><br />I have a 1993 Force 120hp (model # H120422PD). My problem is that the motor stalls out when I'm in idle or a slow troll. Even stalls when I put it into gear. After doing a bunch of searches on the site, I found that this seems to be a pretty common problem but most of the time it seems to be the same fix. In the search, one post said I should try to take the cover of the outboard off and see if it runs ok. I did that and it ran perfect! In one of the topics I read it says to replace the boot that goes from the engine to the 2 "pee holes" and that should fix the problem. I replaced that and it still stalls. When the engine cover is off, I can see the smoke coming up from inside the motor so I know that the lack of oxygen is killing the motor. I can see that the smoke is clearly coming from below that boot. I can't find another topic that can help me out now.<br /><br />The funny thing is, is that I think that the smoke is coming from the water that is inside the outboard and bubbling up inside the motor. I know that is where it is coming from, I CAN SEE IT! Let me see if I can explain this better. Where the body for the motor comes around where the shaft body overlap water is able to come in through there and kind of sits inside the motor compartment. This is where I know the smoke is coming from. It is almost like the smoke is not being forced away from the motor. Instead it is coming straight up to the outboard and the bubbles release the smoke inside of the outboard which kills the motor!<br /><br />Does any of this make sense to you guys. Please help me out.........I'm going crazy with trying to figure this out! THANKS IN ADVANCE!!! - Mike
 
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Oldsaltydog

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Re: Puzzled........Carbs are choking on exhaust

Is the air/fuel mixture of your carbs properly adjusted? Is there a resriction somewhere for the exhaust?
 
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spartanpele

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Re: Puzzled........Carbs are choking on exhaust

I had the same problem with my 1987 85hp. My problem was the exhaust tube seal. For the most part, the exhaust was not going completely out of the engine area, and was being resucked up inside the carbs. It was alwasy the worst during an idle and eventually it would simple kill from lack of fresh air. Your problem sounds similiar and if it runs great without the top on, then it sure sounds like the exhaust system isn't running right....or...your carbs our out of sync and not getting enough air. Could it possibly be that its a flooding situation? Both of scenarios worth checking out.
 
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Stoughty Rods

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Re: Puzzled........Carbs are choking on exhaust

EBG - "Is the air/fuel mixture of your carbs properly adjusted?" <br /><br />I believe so. When I rebuilt them, I turned the screws at 1 turn out like the book says. <br /><br />"Is there a resriction somewhere for the exhaust?" <br /><br />Not even sure!?!? Don't even know where to look for a exhaust restrictor.<br /><br /><br />Roscoe - "I believe you are in need of a spacer plate gasket." <br /><br />How do you replace that? My book doesn't cover that. Would you have to take off the engine block in order to replace? Seems difficult, is it?<br /><br /><br />spartanpele - "My problem was the exhaust tube seal." <br /><br />Would that be part number 17 on this link? Also should I replace #16 while I have it apart?<br /><br /> http://www.mercruiserparts.com/Show...g&inbr=1470&bnbr=220&bdesc=DRIVESHAFT+HOUSING <br /><br />"Your problem sounds similiar and if it runs great without the top on, then it sure sounds like the exhaust system isn't running right....or...your carbs our out of sync and not getting enough air." <br /><br />Well when I rebuilt them I went to what the book said. They are insync with the proper 1 turn out on each carb.<br /><br />"Could it possibly be that its a flooding situation? " <br /><br />I don't think it's flooding because it runs fine when the motor cover is off. It never dies when the cover is off.<br /><br />I called a local boat shop yesterday and asked him a few questions about it. It seems like they don't like to give out answers and help people too much. They would rather just get the boat into there shop (which is understandable) and fix it. But since this guys knows I'll be buying the parts he gave me a little tip (and maybe oyu guys can elabirate on it):<br /><br />He said to take off the cowling (I think that it what he said) and put it in the water (on the trailor) and try to sight see the leak when I fire it up. Is this piece that he is talking about taking off the covers (body) that are shown on the link that I left above? Will I be able to see a leak when I take this "body" off?
 
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speedwrench

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May 17, 2003
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Re: Puzzled........Carbs are choking on exhaust

Not uncommon. There are three gaskets that can cause this, exhaust tube seal at bottom, adaptor plate to lower unit, and power head adaptor gaskets.<br /> Power head has to be pulled to replace any one, so go ahead and replace all three and get it over with. <br />Not as bad of a job as it seems. You don't need to remove near as much as manual calls for. And don't forget the two 7/16" bolts under the throttle cable bracket. <br />Before you set power head back on, cut heads off two 3/8"X4" bolts, thread them into back holes to guide it into place. A lot of this will make more sense when you get into the job.<br /><br />Dave
 
roscoe

roscoe

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Re: Puzzled........Carbs are choking on exhaust

Nice tip on the bolt/positioners there speedwrench.
 
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Stoughty Rods

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Re: Puzzled........Carbs are choking on exhaust

****I FOUND THE PROBLEM!!****<br /><br /> http://www.mercruiserparts.com/Show...g&inbr=1470&bnbr=220&bdesc=DRIVESHAFT+HOUSING <br /><br />Part # 30. Before I took off part #22 (the body with the pee-holes) I had noticed a rubber seal that was inside the motor area didn't look right. It wasn't seated in it's place properly (at least it didn't look that way). Well when I took off part #22 I noticed that the seal (#30) was ripped, torn, worn out you name it this thing was in really bad shape. I ran up the the local boat shop and he didn't ahve one. Looked it up on the net and the part is no longer available. <br /><br />I went to Lowes and found some stuff to make my own seal. Now it's not the same material but we were able to get it in and it is working a lot better now than before. Since we couldn't figure out how to get part #31 off, we greased up the rubber and the driveshaft best we could and slid the rubber back into it on each side. Seemed to work ok, but we couldn't get the rubber to meet in the very back (towards the bow of the boat). Some exhaust can get into the engine area but not enough to stall it every 15 seconds like before. It only stalled 3 times all day yesterday and I slow trolled and idle all day.<br /><br />Now how do I get part #31 off so I can get the gasket all the way in properly? It seems like I have to take the motor completely off the boat in order to take it off. Is this true? Also, how can I get a hold of this part #30 if it is no longer available......anybody? Mike
 
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Stoughty Rods

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Re: Puzzled........Carbs are choking on exhaust

Also, thanks guys for all the tips and leads on where to look. This site rocks. I appreciate it very much!! - Mike
 
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speedwrench

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May 17, 2003
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130
Re: Puzzled........Carbs are choking on exhaust

#17 is usually the one that causes most of the exhaust leak problems, and have to pull head to get to it. And replace the gasket. <br /><br />Yep, have to have motor off boat and supported to get #31 off.<br />Don't remember what # 30 material is, but not really any load on it so match it with what you can find that looks close.<br /><br />Roscoe: That's what tearing up a new $25 gasket will get you to think about!<br />Dave
 
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