2+2 Tweaking

[Texasmark]

What is the process for converting a 2000 115 2+2 to 4 cylinder operation at low speeds?
Thanks,
Mark

 

[Faztbullet]

None....

 

[jimmbo]

In theory, since the ignition is always operational on all the cylinders, and it is the carbs that control when the the 2 dead cylinders start working, replacing the two carbs with fully functioning ones would result in 4 cylinders. But that is only theory.

 

[Texasmark]

I looked up the carbs and there are 3 of 1 p/n and 1 of a second. I think it's either the upper or lower that has the different carb. My 90 had the same thing I think...don't know why.

 

[Texasmark]

None....

I just bought a 2002 115, haven't had it on the water. I liked the old classic 4 cyl smooth running at both ends of the RPM band, back when OMC was vibrating itself to death at the low end. Heard you had to get your linkage tweaked just right on the 2+2 to have a seamless transition from 2 to 4.....comments sir? Won't know what it's like till I get it on the water.

 

[flyingscott]

I had a 1996 125 hp Merc,I liked mine very much. The link and sync is pretty important on them and a factory manual is a must. You can help smooth out the transition by being smooth and deliberate with the throttle. The slower you accelerate the more pronounced the transition is. For me the first time off of the dock when it was cold was the worst. After that it was good, I used mine for fishing with a lot of trolling and tubing and skiing. Never really had an issue with it easily the most fuel efficient motor I had for trolling. Your Bottom 2 carbs do not have idle circuits in them. You also want to prop it for the upper end of its range 5250 rpm. Don't try to overrev it because they fall on there face pretty quickly.

 

[Texasmark]

I had a 1996 125 hp Merc,I liked mine very much. The link and sync is pretty important on them and a factory manual is a must. You can help smooth out the transition by being smooth and deliberate with the throttle. The slower you accelerate the more pronounced the transition is. For me the first time off of the dock when it was cold was the worst. After that it was good, I used mine for fishing with a lot of trolling and tubing and skiing. Never really had an issue with it easily the most fuel efficient motor I had for trolling. Your Bottom 2 carbs do not have idle circuits in them. You also want to prop it for the upper end of its range 5250 rpm. Don't try to overrev it because they fall on there face pretty quickly.

Thanks for that over-revving tip besides the rest of your comment. Interesting.

My 115 tower loved 6k. My 90 looper that I had for 10 years and gave to the local fire department since they had no boat for water rescues and I "thought" I was through with boating at 75 years of age at the time. I still have a 13 ¼ x 24 Ballistic SS that I was running on that boat when I snapped the picture in my Avatar.

Did a go-fast.com, Prop Slip Calculator set of numbers on the new rig with the 115 and it looked like that prop would work out nicely.....we'll see........I did notice in a sales brochure that I have that it's upper limited at 5250 rather than 5500 like the other 2 engines I had previously (listed herein) and that the 125 is also listed at 5250.....one would think that the 125 with the same carbs and different jets (seems that's what the Merc online parts list says) would be paced out at 5500????

 

[flyingscott]

All the 2+2 4 cylinders are rated to 5250. The 2+2 4 cylinders share the bore and stroke of your 3 cyl 90 they just added an extra cylinder.

 

[Faztbullet]

If ran over 5500RPM the pistons have a tendency to snap a skirts...…..

 

[jimmbo]

If ran over 5500RPM the pistons have a tendency to snap a skirts...…..

There were several Service Bulletins warning Not to Exceed the WOT rpm range.

I never liked those engines, to me they weren't Mercs. They also had a weird tent shaped deflector in the reed area

 

[Texasmark]

If ran over 5500RPM the pistons have a tendency to snap a skirts...…..

Mr. Bullet sir. While you are following this....and since it's my thread I think I can derail it if I want to.

I am going to lift the engine off the transom to do some work on the hull. I thought about buying an M16 steel bolt and welding a loop onto it. Then I'd just remove the OEM nut, install this adapter to lift the engine and return things when finished. I know Merc has an adapter for lifting engines but I have no access to one.....looked and couldn't find one.

Question is, if you happened to know, is the M16 fine thread a 1,1.5, or 2 pitch?

Oh and today I got back into the online Merc parts list and I must have been smoking dope or something as what I said about the carbs being 3 alike was hog-wash......as you well knew I'm sure. Wink!
Thanks,
Mark

 

[Faztbullet]

It should be 1-1/2 by 16 TPI...Amazon has plenty of combo flywheel lift/removal tools. Mount it back in same holes as 90 as lower unit casting is the same.

 

[Texasmark]

They also had a weird tent shaped deflector in the reed area

They flaunted that in their 1997 (to name one) sales brochure quoting: (Our "Rose Petal" reed block assembly atomizes fuel more completely for smoother performance.)

 

[Texasmark]

It should be 1-1/2 by 16 TPI...Amazon has plenty of combo flywheel lift/removal tools. Mount it back in same holes as 90 as lower unit casting is the same.

Thank you sir.

Oh on the 2+2 operation. Compression was 129, 129, 129, 131 (per mechanic testing at the dealership where purchased and he wrote the numbers adjacent to the plugs on the water jacket when he tested it). I didn't really test it when purchased for my own reasons. When I got home and had time I went through it determining just what needed what. LU fluid replaced, nice and blue-black, sampled PTT fluid and crystal clear....ATF in this pump, and plugs were the alternate plugs for the engine and were in need of replacement. I put new NGK BUZHW-2 Surface Gaps back in, hooked it to a known, standby, fresh tank of 87 gasoline and lit it off yesterday on muffs.

I was really impressed with the smoothness of the operation. For some reason I expected a step function in performance at the crossover point but in looking at the linkage setup, by them using the fuel flow (analog) valve to feed 3 and 4, operated by the throttle linkage, and as the linkage moves to higher rpm settings, slowly depresses the fuel flow valve for more fuel to 3 and 4, they just smoothly start contributing to engine power increasing. Having never seen one I just thought they had a solenoid valve that would open at 2000 rpms.

Idle was much smoother than I expected and it "lit off" in a heartbeat with a little throttle and a few seconds of fuel enrichment. I think I will really like this engine. Thanks for the comments.

 

[flyingscott]

That is an accelerator pump like the old carbed cars had.

 

[Texasmark]

That is an accelerator pump like the old carbed cars had.

Hummmmm. Interesting. Refresh my memory.... diaphragm in the carb? Or was it on the side of the carb, about the size of a silver dollar, operated by the throttle linkage, GM Quadrajet for a number........seems to be coming back.

 

[flyingscott]

Qudra-jets had an arm attached to a plunger. All it does on your motor is smooth out the transition to 4 cylinders. Since there is no real idle circuit in the bottom to carbs. The bottom 2 carbs only supply enough mix to lube things no more. If you tried to accelerate without adding more fuel it would just stumble through the transition to 4 cylinders..

 

[Texasmark]

It should be 1-1/2 by 16 TPI...Amazon has plenty of combo flywheel lift/removal tools. Mount it back in same holes as 90 as lower unit casting is the same.

Thanks, it is as you say, ebay has it for $35 including shipping.

 

[Texasmark]

Qudra-jets had an arm attached to a plunger. All it does on your motor is smooth out the transition to 4 cylinders. Since there is no real idle circuit in the bottom to carbs. The bottom 2 carbs only supply enough mix to lube things no more. If you tried to accelerate without adding more fuel it would just stumble through the transition to 4 cylinders..

Makes sense. Thanks

 

[Texasmark]

If ran over 5500RPM the pistons have a tendency to snap a skirts...…..

On 5250 or 5500 rated engines? Asking the question being the 115 is 5250 and I'm working on getting the tach running....haven't had the boat out yet......butttt since all we did is to add a 4th cylinder (basically) and the triple 90 is rated 5500?

But in thinking about it, the crank in the 90 is on 120 degrees whereby the top 2 on the 115 are alternate firing as are the bottom 2 but the relationship of the tops to the bottoms is 90 degrees. That may have something to do with it.
No doubt the the way the crank is built, makes sense for running on 2 cylinders at low rpms where you want alternate firing, like was/is had on 2 cylinder engines.