88 Mercury 115 inline 6 questions

[sodakdave]

I have a "new to me" 88 115 on a 84 16 foot Ebko. I've been going over a bunch of stuff an have the motor running MUCH better than it was when I got it, but I have a couple questions I'm having trouble finding the answer to.

When I'm on muffs, what should my RPM be in idle drive? I've seen 650 tossed around, but I never see if that's on or off the water. What should it be in neutral?

Am I correct that wide open on the water should be around 5000-5500 RPM?

A couple things I'm noticing that I'm not sure what to look at.... The boat starts just fine on muffs, but once I got it in the water the last couple times, I basically have to use the trolling motor to get out of the way, and prime and crank for 20 minutes before I actually get the motor to start. Once it starts once in the water, I can drive around and turn it off and back on with no issue. I'm GUESSING that my idle may be set too low and it's having issues starting with the back pressure.

The other thing that doesn't seem right to me, but being new to boats could be totally normal, is it seems to take some time for the motor to get up to WOT rpm. From idle forward, if I push it wide open, the boat will move, and will start to plane out after a certain point, but it's a very slow increase in rpm to get there. Once it planes then the rpms do come up quicker. What would I look at on that?

Thanks in advance for the help.

Dave

 

[jimmbo]

First thing to do is run a compression test.
You are correct about the WOT range being 5000 - 5500 rpm, of course that will be dependent on prop selection
Idle speed should be, 600 - 650 in gear, shifting to neutral will result in a higher speed, but how much depends on how big the load(varies with different prop size) was when in gear.
My guess is a 17 in pitch prop will be the correct one for you boat.
Poor holeshot is often too much prop, but if the Sync between the timing advance and carbs is misadjusted, it can affect accelleration.
Poor starting is often poor technique. Lower engine fully, or as much as you can. Squeeze primer bulb until firm, disengage gear shift from throttle, advance throttle, push key in to dump fuel into tranfer ports, continuing to hold key in, turn to crank engine. If engine hasn't caught in 10 secs pause a half minute to allow starter to cool a bit, then repeat. Once engine starts, release key, and reduce to about 1100 rpms for about 30 secs, you might have to push key in if engine stumbles while cold.

 

[racerone]

Start with a compression test.----Check for spark on all 6 leads too.-----If you are cranking that much the starter may be done.-----I would take the starter apart for inspection and an ohm test.----Some will argue but slow cranking is a major cause of hard to start condition.-----One of those motors should start right up and run sweet.

 

[sodakdave]

... Idle speed should be, 600 - 650 in gear, ...

That would be in the water... correct?


Ok... since my post deleted itself as I saved, let me re-type this.

I have run a spark test, and all the cylinders behaved as I expected, so I don't have a completely dead one. Full compression test is in the plan for later this week.

I'll probably pull the starter and get it inside to test between rainstorms today if I can get enough time to get it pulled.

 

[jimmbo]

In the water is correct

 

[sodakdave]

So did the whole link and sync, and now she's running like a top.... almost.

I can hit the gas and it'll jump right up on plane and get going across the lake. The one thing that bugs me is that it'll feel like it's topped out as far as rpm and speed go, and then after several seconds it'll feel and sound like it's gaining power. Almost like there's a delay in the carbs coming fully open, but when I have the cover off and check the pickups, the carbs are fully open with the throttle all the way forward. I do pick up more speed so the motor is getting stronger there.

This is without adjusting the trim at all. Any thoughts?

Dave

 

[racerone]

Run with a timing light to see if you can find a cylinder that does NOT have constant good spark.----And you have to make sure that carburetors are CLEAN and adjusted properly.----Fuel restriction means a risk of engine damage as oil goes into the motor with the gasoline.-----Check fuel pump diaphragm too.