Falls flat on face

K

Kelly Forest

New Member
Aug 3, 2009
7
GREENVILLE SC
Boat Info
2008 sport 185
Engines
4.3L Alpha 1
Has been a couple of months since I have had the boat in the water.Now after I cut off motor,and restart after a few minutes when opening the throttle falls on its face.After a few seconds will take off and run like the wind.I did perform the 100 services using quicksilver parts and installed new fuel with sta-bil added.Does this sound like a common problem?This is a carburated motor with tks:smt100
 
The throttle pump in the carburetor is no longer giving its shot of extra fuel when the throttle opens. You may have a leaking pump seal, or perhaps the check valve has a small piece of trash in it.

Try exercising the pump and see if you can get it working. Otherwise a carburetor rebuild is in order to get the pump working again. Which carburetor?
 
Does the situation described only occur when it's cold and not fully warmed up? If so, it may be a carburator choke adjustment needed. This is as simple as loostening a couple of screws on the choke housing, rotating the housing slightly and then re-tighteng the screws again. Alternatively is the choke closing fully when closed and free to move? All this would only apply if it only occurs when cold.

If the accelerator pump were bad as in the above post, the problem should be much better if you slowly advance the throttle. The problem would be worst wen rapidly advancing the throttle. The accelerator pump rod is adjustable for more or less spray also.
 
Just a thought, but would that TKS system have anything to do with the this? If the automatic choke doesn't release, could that cause those symptoms?
 
Kelly Forest said:
Does tks even have a choke?The problem occurs after a hot soak only.starts and runs fine cold.Thanks
Click to expand...

I've never had a TKS system apart to see exactly how it operates, so I'll just use the term "choke" generically. But the way I understand it is that there is a pin (maybe spring loaded?) that pushes the choke. As a special wax-like substance warms up or cools down, it allows the choke to be on or off.

What happens if you open the throttle all the way to start it? Of course, be ready to pull the throttle back as soon as it starts.

Again, I'm just throwing out an idea as maybe the fact that you have a TKS system is getting overlooked. I've heard of others having problems with the TKS, but I don't know enough about them to say exactly. Hoping some others with more more knowledge can comment on whether or not the TKS could possibly be your problem
 
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If the problem only occurs after heat soak, it sounds like it is starving for fuel or the fuel is vapor locking causing the fuel starvation. After cooler fuel is pushed through the lines the problem would go away which is what you are experiencing. It would be interesting to see what it runs like with fresh fuel. Possibly there is some issue with the fuel that is allowing it to heat soak and vapor lock more easily.

Fuel starvation could be caused by fuel filter (which I am assuming was changed during your service) or fuel pump problem. Fuel pump would be unlikely because you are running fine after the initial problem. Fuel pump problem should show up during full throttle operation.
 
Wouldn't that be kind of hard being in New York?
 
The younger one is his 16 year old niece standing beside his wife out in the middle of stinky old Utah Lake.
 
This sounds like a classic case of a bad accelerator pump.I had the same problem on my '79 srv195. It has a four barrel carb on it. I don't know what your set up is but the theory of operation is the same. It would start fine , no problems. If I gradually (and I mean gradually) accelerated I would have no problem, but if I gave er some gas, either normal acceleration or gunned it, it would either die or fall on its face. My machine is an older unit and I kinda figured it needed the carb rebuilt. After I determined my choke was working properly I went ahead and got a carb kit and rebuilt it myself. This solved my problem. Don't know if you're familiar with carbs but the accelerator pump is (at least on a four barrel) visible as a 3/16" rod coming out of the top of the carb normally on the same side that the throttle cable attaches to the carb. When you move the throttle it will push down, by way of levers, this rod. This "pushing" action gives the engine an extra shot of fuel so as not to starve during acceleration. If this little pump goes bad it won't give the required "shot" and the engine will stall. You can buy just the accelerator pump if you want, but it comes with the kit to do the whole carb, and chances are if this is bad the rest of the carb could probably use a good cleaning and new gaskets too. Hope this made sense and helped you some.
 
Have your merc dealer check the hot and cold measurement on the tks module since it's purpose is to supply additional fuel when the engine is cold and takes power to expand the wax which pushes the arm to close the additional fuel passage to return normal idle conditions which should be 650 in gear. Those carbs require the module to be working correctly for the proper fuel to air ratio of 14.7 to 1.
But I am just an idiot speaking out of turn.
 
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