Update on Merc 115 motor

[mwinchel]

Hey everyone on a tread a while back i had some problems with my motor. We were trying to figuer out the best prop for my boat and everyone seemed to need some more info that i did not have at the time. I have a 1971 merc 1150 motor on a 1971 trihaul 14.5 foot boat. The motor has good compression on all cylinders, new plugs, wires, re wired the entire motor, carbs have been gone threw and fuel filters have been cleaned. Last year i would be cruising across the lake and i would go to give in the last inch of throttle and it would bog down. A month ago i found a pinched fuel line thinking that was my problem for it bogging down at wot. I took it out this weekend 4 of us on the boat and a cooler this would be the normal 4 to 5 people and a cooler. I have a 19 pitch 2 blade prop on the motor. These motors should run 5000 to 5500 rpm at wot my boat will hold steady at 4000rpm when i go to give it a little more it bogs down like it gets to much fuel or not enough. Is the prop the right one for me i have a 3 blade 17p in the garage should i try it. With the amount of people and wieght i have on the boat is 4000 fine let me know. I really thought that the pinched line would be the problem but it wasent any help will help thanks.

 

[jimg984]

Re: Update on Merc 115 motor

replace all fuel lines if they are very old its the cheapest and easy thing to do and then go from there i would also supect fuel pump

 

[Chris1956]

Re: Update on Merc 115 motor

oK, Try the 17P prop. You want to get into the 5000+ RPM range at WOT.

The fuel pumps on those motors are marginal. Rebuilding them eliminates the problem, and is pretty cheap. Use 3/8" fuel lines from tank to motor. Does that motor have the "Backdrag" carbs, or the old style carbs. Backdrag carbs have a brass fuel screen under the brass elbows on each carb bowl cover. The older carbs have a banjo filter under the round cover on top of the bowl cover. Clean or replace them.

 

[CharlieB]

Re: Update on Merc 115 motor

Also a weak ignition will limit WOT RPM

You need to check the condition of your ignition by the Spark Gap Test

It should fire a bright blue arc across at least a 7/16 gap on ALL cyl's

 

[trussmonkey]

Re: Update on Merc 115 motor

mwinchel
have you taken your boat out with less weight?
I'm not asking because I think you have too much weight, But, It would be good info for others to have, so they can help.

If you have another prop you can swap out, JUST DO IT! it only takes 30 minutes to change. And you will definitely acquire more information, to help find those extra rpm's

 

[j_martin]

Re: Update on Merc 115 motor

mwinchel
have you taken your boat out with less weight?
I'm not asking because I think you have too much weight, But, It would be good info for others to have, so they can help.

If you have another prop you can swap out, JUST DO IT! it only takes 30 minutes to change. And you will definitely acquire more information, to help find those extra rpm's

That's padded time. It takes less than 5 if you know what you're doing, meaning you've done it at least once before. I swap props for the day, depending on what I'm hauling and where.

hope it helps
John

 

[trussmonkey]

Re: Update on Merc 115 motor

j_martin
That's padded time. It takes less than 5 if you know what you're doing

30 minutes, was, using a puller and torch (I think it was the original prop, and had ever been off ) after 26 years of being on the motor, I guess it really wanted to stay, but I changed it's mind

 

[j_martin]

Re: Update on Merc 115 motor

30 minutes, was, using a puller and torch (I think it was the original prop, and had ever been off ) after 26 years of being on the motor, I guess it really wanted to stay, but I changed it's mind

Just like I said. Now it's greased, gets removed and greased once a year (doesn't it) and it's a 5 minute job.

John

 

[mwinchel]

Re: Update on Merc 115 motor

hey everyone i tried to take the prop off and boy is it on there. I mad a puller of some sort this weekend and it would still not budge. i have hit it pretty hard with a hammer and tried a little heat not much. Do you think that this thing should be on there this good. It is 38 years old what should i do. Should i cut it off let me know thanks. These plugs do not have a electrode. How do i check for spark pull one out and put it up against the block and look? I have never seen a plug without a electrode. Let me know on that to thanks again.

 

[j_martin]

Re: Update on Merc 115 motor

On the prop, hitting it will probably do nothing. It's mounted in rubber.

Take the nut off, put some good (like silikroil) penetrant on it, strike the hub with a punch and hammer, (just to make it vibrate a bit and help the penetrant, not to move it) try it again in a day.

If push comes to shove, heat will destroy the rubber hub, enabling you to pull the prop and the rubber and get at the splined core. By this time you will have destroyed the prop seal and have to replace it. Just don't bend the prop shaft, that gets real expensive. Also be careful not to destroy the threads. The prop can be reassembled with a new hub if it's worth it.

If you look real close at the plugs, you will see that there actually is a cone shaped electrode, just like any other plug. It just ends right at the face, and fires straight across the end to the face. It's called a face firing plug. The design will fire reliably under unbelievably dirty and oil conditions.

The best way to test for spark is to use a spark gap tester. It will have 6 or 8 adjustable gaps so you can look at them all at the same time.

A redneck test is to use a clamp on (inductive) timing light. If it's firing, the light will flash. Tells you nothing about the quality of the spark, though. Don't pull the wires off when running. I can kill you, and if a secondary part is a little weak, it will kill it. (coils and wires).

hope it helps
John

 

[Chris1956]

Re: Update on Merc 115 motor

Mwinchell, Remove the propnut, the spider nut and the splined washer. Tilt the motor up all the way and fill the splined area with penetrating oil. Let it set for a while. I like to start using a 2X4 to pry off the prop, but you may be beyond that. Retry the puller. If that fails, use a saw to remove the prop, and then cut (not burn) and tear off the rubber hub. Now you can crack the bronze prop hub and it should come off. I would try a dremel tool with a abrasive cutter to carefully cut thru the bronze hub. Now widen the cut with a cold chistle, and te hub should come off. Don't forget to grease the new prop before installation.