Motor coughs in shallow water drive

Eric Patterson

Eric Patterson

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Staff member
Maybe someone here has a suggestion. My little Merc 15 2 stroke starts the first pull and runs very smooth EXCEPT when tilted in shallow water drive. It coughs in that position and that position alone. Any ideas as to why or what I can do about it. I'm content with it the way it is but if there is a simple solution I'd give it a try.

Thanks.
 
Eric,

I'd concentrate on the float adjustment. It is probably set so that the fuel level in the carb bowl is just a smidgen too high. Not sure how comfortable you are working on this but it shouldn't take a good service guy more than a half hour to correct it. If you fix it yourself it may be trial and error to get correct setting with out the specs.

My best guess with out specs is this. Usually the float itself, will set level with the housing it is mounted to, when held upside down so that the weight of the float is resting against the closed needle.
 
It's the carb and it's a lean condition because gravity is fighting the vacuum of the crank case. It probably only coughs when at low idle..right? Try turning your primer/fast idle knob fully to the right when running in shallow mode so it is getting more fuel and higher rpms(more vacuum). I don't think you need to mess with the float....Merc carbs have a lot of parts on them. My 96 Mariner had 5 shallow settings that worked automatically when lifting the engine..then when you popped it all the way up it would lower back down to the lowest setting again..wish my 25 had the same setup.
 
Lee

Yes, only at low rpms. The problem with adjusting the idle speed up is I use reverse a lot when picking decoys and such. It does help with the cough but feels hard on the gears with all the shifting I do into reverse. Forward doesn't hurt so much. Idled down she shifts and run fine except when tilted ant then she coughs, more like a sneeze. I might ought to jut take it to the shop and let a pro fix it.
 
Eric,

Therein lies to problem with Lee's solution. Cranking up the idle speed is hard on the gearing. I still stand by the float setting being the culprit. Shouldn't hit the wallet too bad and you will have peace of mind. (providing you have a good mechanic)

On a related note, I just bought a fuel pump for my 9.9hp Evinrude. I purchased it online and when it finally arrived it was a Mercury fuel pump. The box had been re-labled to read that it would also fit my Evinrude. I need to try it out today and see if my motor runs better now with the new fuel pump.

BTW, It is 45 degrees outside today and I'm working in my un-attached garage with out a coat. Yet, guys are sitting on 4inches of ice on the local ponds ice fishing today.
 
I don't think any adjustment to the float will help..nature of the beast..without having the vacuum of slightly higher rpms..more gas being introduced to the venturi will lust leak out the front of the carb.2 strokes "sneeze" when a lean condition exists. Dave, merc fuel pumps for the smaller motors were built into the carb after about 1974. My 1967 has a seperate fuel pump that ataches via brass fitting to the float chamber.
 
The Mecury box didn't say what year or model of Mercs it would fit. Mine attaches to the side of the crankcase with two bolts directly over the vacuum port. Fuel line then runs to the carb. I got down to the river for a test run this afternoon. Let my motor run for 10 minutes at about 2/3 throttle and it was fine. Before replacing the fuel pump I had to keep feeding it fuel by squeezing the inline bulb constantly.
 
Having thought about a tad more maybe the best thing to do is next time I hunt take a screwdriver with me. I'll raise it in shallow water and adjust the low speed screw. If Lee is correct and it's running lean maybe I can richen it up enough to stop the sneezing but not get it to rich. If that doesn't work I'll take it to the shop. Besides, the shifting linkage seems to be getting stiff and could use cleaning and lubrication so it's time to tinker the thing back to peak performance if it doesn't cost me too much in down time.
 
What year is it Eric? If it's running perfect while level, then I wouldn't mess with it. I still say you would be better off turning the knob..find where it just starts to not sneeze anymore..shouldn't be more than a 100 or so more rpm's and that shouldn't hurt your shifting. Of course you can mess around with it like I do and fix it till it's broke. First thing I would do is run a half can of Sea-Foam in a 2-3gallon tank through it and see if that helps.
 
Lee

It's a 93 or thereabouts. I actually put some seafoam in the first tank this season but it didn't seem to make a change in the sneezing. To be honest the stiff shifting is more bothersome than the sneezing. I just need to get in in the garage one night and see if I can clean and lube those parts and then tinker a bit with it the next time I have it out. If that makes it worse I'll take it to the service center :)
 
Does it have the shift in the twist grip or a lever on the side? My 25 shifts with the throttle grip and it gets a bit stiff too. You might have too much grease on the nylon cams (if it's a throttle shift) under the cover on the left side looking at the carb. I hosed mine down with wd-40 to clean the old goose grease off and then sprayed them with some thin lithium grease and worked the throttle up and down.
 
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