77 merc 115 shift problems

I have a 1977 Merc 115 Thunderbolt outboard on a 17ft 77 Silverline Tri-hull. Engine runs very well at full throttle forward. My problem is at idle speeds it sometimes sputters/stumbles and dies and anytime I shift it bogs down. Forward it still does ok, but in reverse it almost always kills the engine...and if it does go into reverse there is a lot of clicking (like sound when prop engages). In addition, there is alot of "dead space" in throttle/shifter when going from neutral to forward (or reverse)...it will engage the prop but then long push to get it to throttle up and when it does...it goes to very high rpm (not sure how much...rpm guage inoperable). I just bought this boat about a month ago, so still learning its nuances...but will try to fill in any details required to help. Thank you for your help!! Katmandu72

Re: 77 merc 115 shift problems

Bogging at idle is indicative of dirty carbs, misadjusted idle mixture or heavy oil mixture. You can try to adjust them a bit, but use fresh 50::1 gas-oil mix. Remove th wrap cowl. Put control into neutral and remove shift cable from barrel clamp. Wiggle shift slider a bit to make sure you are centered in neutral. Now adjust barrel nut to fit clamp. Shifter is now adjusted correctly. If you still have slopping in reverse gears may be bad.

The rest of your observations sound about right for that motor.

Re: 77 merc 115 shift problems

Thanks Chris1956!!! I will give that a try and let you know...I did have it out again today and no reverse!! It just throttled really high, no prop engaging that I could tell, but it got me around and back on the trailer with forward!!

Thanks again!...also, it seems to need a shot of starting fluid in each carb the first time you turn it over, then it is fine rest of day?? Someone said needle valves may be sticking??

Re: 77 merc 115 shift problems

You should skip the starting fluid. Heavy choke should be all that is needed. Pump up the primer bulb until firm. Hold choke button down and crank it (cold start lever all the way up) until it fires. Hit the choke button a couple of times during warm up, if you need to.

Re: 77 merc 115 shift problems

Thanks again! I will be working with it tomorrow hopefully, will let you know how it goes, I really appreciate all your help!