1995 Johnson 175's Idling Issue

[ajv00303]

Have twins.....Just bought the boat ~1 month ago.

Rebuilt all 12 carbs, replaced filters, etc. Did the link and sync.

Not too easy to adjust the idle mixture on an engine w/ 6 carbs.....is there a trick to this?

Run the mixture screws in until the engine runs rough then back out slowly?

I set them at ~4.5 turns out when I rebuilt the carbs.

Engines start great and have a lot of power...

After running for a while at 4K RPM, then through a no wake zone @ ~1200 RPM's...they stall while docking.

Doesn't make for a good end to a nice ride!

They are idling at ~600 RPM when this happens....stumbling then stall.

Is it my idle mixture?

I understand there isn't any real way to adjust the idle except for the timing tabs.

Gotta be something I'm missing!

[316jughead]

Here is what you are missing. Get a OMC service manual for this motor, that's needed to answer all of your questions. Of course there is a real way to adjust the idle, what do you think the adjustable idle orifices are for.

[ajv00303]

I have the manual.
I know I can adjust the idle mixture.....but what about the RPM's?

[316jughead]

I have the manual.
I know I can adjust the idle mixture.....but what about the RPM's?

Well, read the manual on adjusting the idle.

[ajv00303]

I did read the manual.
To my knowledge there isn't an adjustment for the RPM idle other than the timing tabs which I do not want to change yet.

[ChampioNman]

You'll need an ignition analyzer for the timing to make sure it is in sync. then adjust your idle jets, sounds like you're running twins.

[ajv00303]

I am runnig twins. The boat is a 268 Grady White.
I actually have the analyzer, haven't tried it yet though.

I looked at the timing w/ a light and verified the "Fast Start", saw the timing change after the initial start and the timing looked like it was 6*ATDC. Guess I should check it with the analyzer also?

So there isn't a seperate adjustment for the idle speed?

[316jughead]

OK, follow the manual on the idle adjustment sequence. To richen the idle turn the idle screw counter clockwise, to lean turn clockwise. Richen the idle will up the rpm's. No separate idle screw. You will have better luck with the idle at 800 rpm. I would start 5 turns out.

[ajv00303]

Was looking at the paper work from my Ignition Analyzer..........I bought it from you jughead!

[ChampioNman]

Check this while you're at it. http://www.bbcboards.net/showthread.php?t=11790

[316jughead]

Was looking at the paper work from my Ignition Analyzer..........I bought it from you jughead!

I've sold over 600 of them, all over the world, even to Russia. It's a good tool, follow the timer instructions, not the OMC way.

[ajv00303]

So went down to the boat last night.
Started the stb engine and let warm up......the warmer it got the worse it ran at idle.

I started adjusting the mixture screws.....turning them in until I felt/heard a stumble then backed of 1/2 turn at a time until it seemed optimized.
By the time I got to the 3rd carb it stalled and would not idle at all now. Got it started and increased the throttle at ~1000RPM and continued the carb adjustment - not sure if this was a good idea.
Still would not idle. Then tried to adjust the throttle cable to see if I could pick-up some RPM's - no help here.
Then tried adjusting the linkage - spark lever/throttle cam......

At this point I had to walk away from it. Will need to start from scratch by the manual.
I did use the timing analyzer and verified the idle timing was 6*ATDC....I adjusted to 4*ATDC w/ no real effect.
Seems like after the engine warms up it only idles at ~600RPM.....would like to see 800.

Any/all suggestions are welcome!

[316jughead]

Me thinks your getting info from some where besides your service manual. Your idle screw adjustment procedure cannot be found in your service manual. Your idea about starting over is a good one. You should test the recirculation system as per the manual. Make sure that the plastic sleeve is on the smaller black roller that opens the carbs.. You need to sync the carbs so all will be closed at idle as per the manual. Then I would start at installing the throttle cable, and how to set the timing and carbs to open at the same time, this is the sure way to get it right. The idle timing should be at the 6 degrees ATDC, 4 degrees is OK but I wouldn't go any less, these motors like to idle rich. Set the idle screws at 5 turns out to start with. You must adjust the idle with the boat in the water, unrestrained and in forward gear. I think you could get by with adjusting them 1/4 turn at a time, I believe the book states 1/8. To fine tune adjust only the 1/8 turn. After the motor is warmed up if you need to adjust, do all carbs the same, then get up on plane and run the motor at least 4000 rpm for a few minutes, and then drop down to idle and check the rpm, this procedure balances out the carbs and gives you the true idle. The motor should be level or slightly higher at idle. Repeat if needed to get that 800 rpm or close to it. Do one motor at a time, I have no experience with twin motors, should they idle at the same RPM? If this doesn't work look for another problem. Remember, on the idle screws. counter clockwise to richen, this should raise the rpm. you can get to rich then the idle will be rough. This take time and is a pain in the ass, but it works. I might have missed something, ChampioNman will be along to straighten me out.

[ajv00303]

Thanks for the reply......
Yes, my plan is to start from the beginning including the throttle cable install.
Is there an additional plastic sleeve over the black roller that opens the carbs?? That could be missing, I only saw the black roller! I don't see an additional plastic sleeve on the parts diagram.
I already did sync the carbs closed when I did the carb rebuild. Will re-adjust the linkage per the manual for the timing and carb opening at the same time.....then install the throttle cable per the manual.
I will adjust the mixture screws to 5T out as mentioned to start.
How can you adjust the mixture in forward unrestrained?.....Boat will be moving??

Not sure about the recirculation system......will need to read the manual. Dos this affect the idle?

Thanks for the help........not used to these OB's!

[316jughead]

There should be a clear or yellowing plastic sleeve over a smaller black carb roller, it should be on the parts diagram or maybe now you have to buy the roller assembly. This sleeve cracks and falls off. A piece of clear 3/8 hose from the hardware store will work, I gave up on the OEM sleeve after my spare cracked in my tool box, I've run the hose for years with no problem with cracking. On idle adjustment, after checking at 5 turns out, you don't have to balance the carbs on this first setting, then stop motor adjust and then start motor and check idle, repeat if needed. When you think it's close, then you could do the on plane thing. The recirculation system can certainly affect the idle, I would check it first as I mentioned, follow the manual. Spark plugs Champion QL78YC gap at .030. When you get done working on these motors, ChampioNman and I can ask you for advice.

[ajv00303]

Here is the diagram of the throttle linkage.......are you saying to add a pc of clear tubing over item #54?

Carb.png

[ajv00303]

Found a pic including sleeve:

Roller.jpg

[Bassmeister]

Yes sir....there used to be one on there....

[316jughead]

Here is the diagram of the throttle linkage.......are you saying to add a pc of clear tubing over item #54?

Carb.png

Item #54 is both the small black roller with the sleeve on it, as your other picture shows. You used to be able to buy just the sleeve, some dealers would have them in stock because they only came 5 in a package.

[ajv00303]

I added the plastic tubing and re-adjusted the linkage (see pics) and adjusted the carbs to 5T out.
Started right up, after it warmed up it was idling at barely 700RPM.....improved, but would like more.
Going to see how it runs after running hard this w/e.

Thanks for the tip about the sleeve!

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