Accelerator pump?

[TheMoGr]

Hey everyone. I just bought a Sea Ray 175 with a 115 Merc 2 stroke on the back. The motor runs very well, but I'm having a problem with acceleration. From what I understand, the motor runs on 2 carburetors at idle, and when you increase the throttle, an accelerator pump squirts fuel into the other two carburetors and they kick in. The problem is, I have to bring it all the way up to about half throttle before the other two carbs kick in, and there's a sudden burst of acceleration. If I want any kind of midrange power I have to pretty much nail the throttle, then back off to where I want it. It's really annoying when I'm trying to pull skiiers, because if i hit the throttle too slowly, I'll just drag them through the water, but if I hit it too quickly, it'll almost yank the rope out of their hands. Is the accelerator pump bad? Is there some kind of adjustment I can make to get the pump to actuate at a lower RPM? Or is this just the way the motor is supposed to run? Any advice would be greatly appreciated!

 

[CharlieB]

Re: Accelerator pump?

The link and sync of the carb linkages together on the throttle vertical bar is critical, as is the accelerator pump setting, the throttle cam contact point and ignition timing advance.

ALL MUST OCCUR in perfect harmony, as will happen by following the procedure spelled out in the FACTORY service manual.

The ONLY thing different on my 115 is spark plug selection, because I change plugs annually I run NGK BPR8HS-20 instead of the more expensive precious metal plugs specified by Merc.

 

[fasassvalk]

Re: Accelerator pump?

I have a 125 with the same carb system and there seems to be no gentle transition from two carbs to four (which is most peoples complaint that owns them) The transition should happen @ 1800-2000 rpm and you will get a whip lash effect.
If you go through the stickeys there is plenty of discussion on the 2+2 carb system.
You get used to it after awhile, if you do a lot of idleing around it is a bit of a bonus for fuel saving and helps not to load up at idle.
I have been told by a merc mechanic (But dont know it to be fact) that you can replace two of the carbs with the uppercarbs that come on them and do away with this feature, But my question would be if it would idle ok or if it would load up idleing.

 

[MercGuy]

Re: Accelerator pump?

I have the same engine, and I think I've got the exact same boat (1998 SeaRay 175 sport). Therefore we should both get the same performance.

When I first bought my 2+2 115 it ran fine, and I didn't even really understand that it was a 2+2. Then over the years it started to run worse, but it snuck up on me so slowly that I didn't really notice until it was pretty bad.

I started doing everything that others suggested, link-n-sync, carb rebuild, new accelerator pump, all without help.

Then one day I did 4 things at once:

1) I put on new fuel line from the tank to the engine, including inside the tank. I found a screen strainer on the hose in the tank and removed it completely.

2) I rebuild the fuel pump (didn't notice anything wrong with the old components)

3) Replaced the vacume hose to the fuel pump (didn't notice anything wrong with the old one)

4) On a lark I re-torqued the bolts on the exhaust plate covers, which were pretty loose.

Since I changed 4 variables at once I can't say exactly which one did the trick but my personal theory is that tightening up the exhaust plate cover did the trick.

In any event my 2+2 will stumble at the transition point which is right when my boat is climbing on plane. Other than that the transition is pretty seemless. I can move the throttle back and forth and the engine will go from 2 to 4 cylinders and it's only barely noticeable.

Hopefully you can get yours straightened out so that it runs well, it should be possible.

Good luck.