Re-adjust after rebuilding carbs?

[boat_beginner]

I have a 1973 evinrude 85393M that I want to rebuild the carbs on. Will I have to re-adjust the carb settings after tearing it down and cleaning it? I'm a little concerned about the adjusting part if it's needed.

 

[emdsapmgr]

Re: Re-adjust after rebuilding carbs?

When you get the carb apart, you will find there is an idle and high speed jet for each throat. (4 of each type) These are fixed, brass jets, of a specific size so it will run properly. Other than removing them for cleaning, there is no further adjustment required upon reassembly. The idle jet hides behind a screw on the both sides of the upper carb body, the main (high speed) jet hides behind the bowl drain screw at each side of the bowls. (you should remove those jets, requiring a special screwdriver, sold by Bombardier dealers, part number: 317002. That's the good thing about these old crossflow carbs-they are pretty simple. The only real re-adjustment is the choke solenoid. Make sure that it is positioned so that it fully closes the carb choke butterflys when the choke switch is activated.

 

[racerone]

Re: Re-adjust after rebuilding carbs?

Agreed , no adjustment needed after re-assembly.----------What is the motor doing / not doing ?---Or is this a preventative maintenance procedure for you ?

 

[boat_beginner]

Re: Re-adjust after rebuilding carbs?

That's what I thought, but wanted to check with the pros first.

I am rebuilding them as a PM measure, and to try to rule out a another problem I am having also. I got the motor last year, after it was setting for a few years in a garage. I mounted the motor on a pontoon, and I can only get 3100 RPM out of it right now, and should be getting 5000, which I know is prop related, because it has a 17" pitch prop on it right now. And after doing the math on what size prop to get, I come up with a 7" pitch, which sounds way to small. The motor sounds like it runs just fine, just bogged down really bad. After researching to subject, it seems as though a 9" pitch pop is kinda small for an 85hp motor. I have been reading where people with 90hp motors are turning 13" pitch props. But, all that belongs in the prop section lol.
So, I'm wanting to see if it will help me pick up a few RPM's, and I know it also needs it done too.

 

[racerone]

Re: Re-adjust after rebuilding carbs?

If carburetors are clean you need to look at other issues.-----Nothing like doing a compression test now ( off season ) -and checking to make sure there is spark on all 4 cylinders.

 

[boat_beginner]

Re: Re-adjust after rebuilding carbs?

I will also check the compression. Good point.

 

[emdsapmgr]

Re: Re-adjust after rebuilding carbs?

My guess is that an 11 pitch would work. Also possible a 13 will. Depends on the size/length of the pontoons. I run a 13 on my small (16')pontoon with a 92 70hp engine. 25" tubes. Runs right at 5650-just perfect. My engine is prop rated, your older 85 is crank rated. So your engine puts out perhaps 10% less when rated with today's propshaft rating system, or 77 hp. (give or take a couple of hp.)

 

[boat_beginner]

Re: Re-adjust after rebuilding carbs?

I considered just getting an 11" prop n going with it, but I want to try to ensure that everything else is right with the motor first. I doubt the carb re-build and compression check will help any, but I figured its worth a shot, and it sure can't hurt nothing. And I was thinking that I would need a smaller prop because the way the motor is rated, but was unsure if how much power loss there was to the prop. But 7" sounds really really small though.

The boat is a 1986 24' pontoon too.

 

[emdsapmgr]

Re: Re-adjust after rebuilding carbs?

Good call. Best to fix any running issues so that you know the optimal prop and only purchase one (hopefully the correct one.) On your 24', the 11 would be better than the 13. You want that engine to run right at 5500 at WOT. Even up to 5700 is ok. Less that that and you are "lugging" the engine.