35hp Johnson Bogging Down and Foot Oil Black

[SouthCarolina1]

Background: bought a jon boat with a 1986 35 HP Johnson tiller handle. The PO said he went to start it up using gas, gas with ethanol... from last year and couldn't get the motor started. Checked the compression and both cylinders had 125 PSI +/-2.

Now: took the gas line and put it into a can of seafoam. Primed the gas system and let it sit for a few days. Reconnected the fuel line to the gas tank, fresh gas/oil, and the motor started up second pull. I took the boat out for a spin and when I opened the throttle wide open it sounded like it was only half way open. Sounded like it was bogging down but when I pulled the manual choke/primer the motor shot up in RPMs, boat took off in speed, but the RPMs slowly died back to what it was before, like half throttle. One thing I found weird, when I hit a wave and the bow of the boat popped up, the motor increased in RPMs. So I am thinking a possible vapor lock? Float level needs to be adjusted? I ordered a carb kit, fuel pumps, and fuel lines.


So while I am at it, I thought I would replace the water impeller. Before pulling the foot off I drained the gear oil. I have replaced the gear oil in several motors and I have never seen gear oil this black. I found a very small amount of metal shavings. I plan on flushing the gear oil until it comes out clear. The motor shifts in out of gear just fine and stays in gear. I have also marked the prop hub to check for slippage. For the gear oil should I be concerned or just assume the PO never changed the gear oil? If the foot was going bad it would cause the motor to bog down or pop out of gear right? Also, when I was draining the oil I took out the top and bottom plug with a flat head but then I noticed a screw for a Phillips head, what it this screw for?

Thoughts?

 

[oldboat1]

screw is the pivot pin that anchors the lever and shifter assembly (numbers 13 and 42, respectively, in the diagram): http://www.iboats.com/Gearcase/dm/cart_id.513072517--session_id.556758055--view_id.1538728

will guess the operation problem you describe might be water in your tank. I would try another tank and line with known good fuel -- see if that improves performance.

The lube looks pretty normal to me (maybe a little dark or some sediment). It doesn't look like water intrusion.

Do some iBoat searches here on removal and replacement of the pivot pin -- takes a little bit of luck and some prayer, but might be able to hook the lever with a finishing nail, and line up the hole (can see it in shown in the diagram at the bottom of the lever). Done with the the gearcase on its side. Try tilting a little fore and aft, and see if you can spot it with a flashlight.

 

[GA_Boater]

The phillips screws is the oh-oh screw as oldboat described. You don't want to remove that one.

Your gear oil looks OK. Old, but OK.

The motor may be revving up as the goes over the crest of the wave and the prop may be partially lifting out of the water causing the motor to rev.

Using the choke/primer and the motor starting to run better tells me to look at the carb as you plan on doing. The motor could be running lean and the choke/primer richens the mixture. Also look inside the carb when you open the throttle to the stop with the motor off and make sure the throttle plate is completely open.

Good plan replacing the impeller. Seeing the lower unit oil, it may original.

 

[interalian]

I have another name for the "uh-oh" screw, but it's not suitable for posting on here.

That oil looks OK but old. No need to flush, just put new in, pump from bottom up.

 

[SouthCarolina1]

I removed the ?uh-oh? screw with the foot laying on the bench. I was able to put it back in. And then using pliers engaged reverse and forward gear, spinning the prop to make sure the shaft still spins. Should I be concerned?

 

[flyingscott]

I removed the “uh-oh” screw with the foot laying on the bench. I was able to put it back in. And then using pliers engaged reverse and forward gear, spinning the prop to make sure the shaft still spins. Should I be concerned?

You should be fine. The problem comes when people pull the screw and bump the shifter and it won't line up again.

 

[SouthCarolina1]

Update: I rebuilt the carb with sierra 18-7222 kit, replaced the fuel pump sierra 18-7352, new fuel lines in the motor and going to the gas tank, new primer bulb, and new spark plugs. When I rebuilt the carb I stripped it down, cleaned it the best I could, soaked it in seafoam for 3 days, before reassembling I blew compressed air through all the ports, and set the float per the instructions. I also installed an RPM gauge

Test run: I slowly opened the throttle up, increasing speed and RPM's until about 3/4 throttle roughly 4k RPMs. After 3/4 throttle the motor bogs down and drops to 2k RPMs and stays there. BUT if I partially cover the carb air intake the RPM's jumped up to 5k RPM's. So obviously I still have a fuel issue. I took the gas tank lid off to see if it was a vent issue but that did not fix the problem... I plan on bending the float to a lower setting. What do y'all think?

 

[oldboat1]

See http://www.iboats.com/Carburetor/dm/...iew_id.1538920 .

I would pull off the carb again, and go back through it. I soak mine with lacquer thinner, tops and bottoms after anything non-metal removed. Leave linkages attached. Concentrate on the high speed jet (19), and be sure the nozzle gasket is in place (7). I would soak the high and low speed jets without removing them -- finish with a piece of soft wire and carb spray to make sure the orifices are clear. I would also remove the domed fitting (5) before soaking to make sure the idle passages are clear. Remove the float seat and needle before soaking, and attach the wire clip if using a new needle meant for use with the clip.

 

[SouthCarolina1]

No Title

The motor is a 1986 MARS (Military Amphibious Reconnaissance System) MFG. NO. AML35D, NSN 3H2805-01-267-5047. From what I found the equivalent of a Johnson/Evinrude 35hp. The PO (told me he was the original owner also) said a few years ago he took the motor to a shop for carb issues and they had to replace the carburetor (what an idiot). Anyways the carburetor is stamped 339169. From what I found is for a 40 or 50 hp motors that have dual carbs. Could this carburetor be starving me of power?

 

[trailking82]

My question to this and the other similar thread you created is what does the original carb look like, or supposed to?

I am assuming with this motor a factory service manual wouldnt be bery helpful. Maybe looking for the -20 or -30 TM manual may prove more useful. You have the NSN info, finding the related TMs should not be too difficult.

 

[trailking82]

A service manual is what you need, should get you close enough. Rarely there is changes to equipment over the years.

 

[SouthCarolina1]

Ok I took the carburetor apart again. Soaked it in carb cleaner for three days. Using compressed air I blew through all the ports. Used my carb cleaning tool and put the small brushes in all the ports. Then I used carb cleaner in a can and sprayed everything. I gave extra attention to the high speed jet. Then using compressed air I blew through all the ports again. Reassembled the carburetor and nothing changed. Still bogging down at 1/2 to 3/4 throttle. When I partially cover the intake to the carburetor the RPM's jump up and the boat increases in speed. I came up with a temporary fix and made a small aluminum plate, 1/2" wide, going over the carburetor and it allows me to give it full throttle without bogging down but I am only getting up to 4900 RPMs.

What's next???? Ideas?

 

[F_R]

If it had an adjustable high speed jet, it would be a simple matter to just richen it up a tad. But since it is a fixed jet, you are going to have to experiment with some different orifices (high speed jets), I'd pull the existing one out and read the number on it, then order one a couple of thousandths larger. If that isn't enough, use a number-size drill to go the next size up. Don't drill the existing one, you might have to go back to it.

All this assumes you cleaned the existing one as you said you did.

 

[racerone]

Many folks can not find the high speed jet.-----It is screwed into the carburetor bowl.----It is about 5/8" long

 

[heypawpaw]

My 66 Johnson 20 hp was doing same thing as yours and turned out to be one of the small holes in carb throat was plugged.

 

[SouthCarolina1]

My Johnson has the manual primer pump system. A new primer pump is $100, does anyone know of a rebuild kit? Looks like its just four O-rings. I know this probably is not my issue but I want to replace everything I can in the fuel delivery system.

 

[racerone]

Does the primer not work ?-----Is the primer leaking ?----Have you done any testing on this unit ?

 

[SouthCarolina1]

Well as far is priming the system, yes it works, the motor starts up first pull after 3 pumps. But sometimes it gets slightly stuck and requires extra force to push back in. I am also having an issue of the motor getting flooded. Yesterday I was coming back to the ramp and when I backed off the throttle the motor died. I tried starting, nothing. Then I tried priming the system and still nothing. I looked into the carb. and say gas pouring out, motor was flooded. Had to paddle back. In attempt to fix the bogging down issue I adjusted the carb. floater to sit open at a lower level, which would allow the floater needle to sit lower. So this might have caused the flooding issue. But I know if the primer pump is leaking by this could also cause flooding issues.

 

[racerone]

With the carburetor upside down the float should be level.----No need for any fancy adjusting.=====Pinch the primer discharge line closed when motor is running as a test.---What does a compression test show on this motor.

 

[SouthCarolina1]

As a temporary fix I made a small 1/2 inch wide aluminum plate and zip-tied over the carb intake. The plate causes additional suction, pulling more gas in, and prevents the bogging down issue. But I can only get up to 4,000 rpms....

I removed the fuel disconnect fittings on the motor and gas tank, and installed barbed fittings in their place. No change.

When this all started I replaced the fuel pump, well I thought maybe I got a faulty fuel pump. Replaced the fuel pump. No change.

So I am going back to the carb. I got a new carb. rebuild kit coming in. I just want to start over with the carb float because I have adjusted the metal tab so many times.

I found three youtube videos for what the correct throttle linkage setting / how to adjust, how to verify the timing / adjust, and how to rebuild the carb. and correct float setting. I am going to do all three. Check them out:

https://www.youtube.com/watch?v=LeIwKyei9pM

https://www.youtube.com/watch?v=za6NJfclfkI&t=42s

https://www.youtube.com/watch?v=WIF0d_L2riA