1998 3 cylinder johnson 35 hp wont open up

i got this motor for really cheap. however, i havent worked on anything this advanced or new. it is a looper. cant provide the serial or model number because i lost the tag when i had it off painting the mid. however, i know for sure its a 1998 model.


Got the Carbs rebuilt and it idles great. great spark on all 3 cylinders that jumps 3/4". carbs were sync and lynced after rebuild. pulling plug wire from each cylinder each has the same effect. However the motor still won't open up. Verified it not being a fuel problem by spray gas and oil mix into the carbs and no change. Figured I had nothing to lose so I ran it on the water hose - still won't open up there either. Pumped primer bulb while running and made no difference. Here is in the water video and one on hose. Any ideas? possibly a slow mode because the oiling system isnt hooked up?

https://youtu.be/EwIiE4rHyN8

https://youtu.be/8c28Znn-6Wc

Have you checked the timing yet? It might not be advancing. You can also check to see if your losing fire with the timing light. Sounds like electrical to me but I cold be wrong. Good luck.

got to messing around with the ohm meter today, and determined the temp sensor on the motor head was tripping SLOW mode. now the next question is to replace the sensor, or install a water pressure gauge.

You replace the sensor. Only a shade tree mech will leave it disconnected. They are not cheap, being a two wire sensor, but well worth it in protection. The other wire is for Quickstart, which raises the idle RPM until the engine reaches 100F or around 5 sec. once warm.
That engine is a fantastic engine. I have four of them.
A check to make sure that was the issue is to simply disconnect it and run the engine. Shut the engine down first to re set the system.
The first video made the engine sound incredibly rich, as if a High speed jet is missing or the previous owner drilled it out. If it were in slow mode it was hard for me to detect in the video. In the second video you could hear it hitting an RPM limiter.
Disconnect the automatic oiling systems on that engine, no ifs ands or buts about that. That was the only weak link in them. Do not depend on it.
The engine is a beast, nothing in its class will run with it and you can normally pull around 2 additional inches of pitch over a 2-cylinder version.
A word of caution. If indeed the tan lead is grounded I would be checking and replacing the water pump to make sure the sensor didn't overtemp and internally melt. There is no head gasket on them. Those engines are hard to find parts for so treat it right. Feed it a little extra oil on a permanent basis.

It ran better with the sensor unplugged but still not right. Did around 20 MPH. I pulled the air box off and it was like a new motor. 26 MPH and instant hole shot. But still 1 MPH less than my 25. Removing the cowl had no effect, only the air box, so I believe it still fuel related. Possibly running rich? Any suggestions?

Well, we know it is not running in SLOW mode.
In your first video. as I mentioned in my first post, the engine sounded incredibly rich.
Check to see if the primer system is leaking into the intake manifold. The red lever should face rearward, along the body of the primer assembly.
Take a pair of needle nosed pliers and pinch off the center supply line to the primer and see if the engine picks up power. If the engine is equipped with an electric primer check and see if there is power all the time on the purple/white, there should not be. If this is the case then the primer is probably toast internally. The pliers will let you know.
If you have not been inside the carbs go there next.
Check to see that all high speed jets are screwed in properly and not backed out and free flowing fuel.
Check the high speed jets for proper size for your engine and last but not least check the internal size of the jet to make sure some rocket scientist hasn't drilled them out thinking he will get more power.
This should keep you busy for a while..............

This motor only has a manual choke that closes the butterflies. I redid the carbs by soaking, then cleaning all jets etc with a copper wire then hittijg with compressed aair. Do you definitely agree since it runs much bettter without the air box (and the cowling removed having no effect) that its a fuel condition? I am currently waiting on new orifices to come in.

My bad...........forgot they put chokes on these instead of primers. There is one sitting not 15' from me that I run frequently lol.
Check all that linkage then to make sure a blade is not closing. I take it you have new high speed orifices coming in?

yessir, ordered 6 of them since they were cheap and i like having spares. one thing i did find was the choke butterflies were not perfectly horizontal when the choke it off - they hang down about 1/4 of the way. problem?

readjusted the choke and took it out for a spin. same thing.. removing the air box produced a much better hole shot and top end. really debating if i should just get a new carburetor and just swap out one at a time to see which is the culprit. this is really throwing me for a loop. the orifices havent been drilled out - they actually look pretty clean and good. i was able to put the air box on the top two carbs while at wot with no change, but couldnt reach the bottom one. the confusing part to me if just removing a hollow piece of plastic is making this motor perform night and day different.

Just relax until the jets arrive. There are no cracks in the plastic nozzles are there? They are inside the bowl and are attached to the main body.
We have been replacing more high speed jets this year than in any year I can remember and this is for the same reason....rich running engines. I have found jets all over the board when measuring with a number drill set I own. They all look good with the naked eye.

on your personal 3 cyl engines, do you have the oil tank and mixing unit removed? or just the oil tank removed and the line blocked off?

Thanks Pappy for sharing your knowledge. =D>
On a carb off a blower a friend who used to service them battled both options for high speed jet that were available. One peed gas it was so rich, the other wants choke 3/4 closed when at operating temp.
The answer is to use proper orifice drill to increase size of smaller one.(once upon a time i used them for propane applications)I run choke partially closed on the 2 or 3 year interval day of use out back instead of the proper solution.
My point being, Pappy is sharing a possible gremlin worth noting that seems innocent but will make an owner have a non agreeable motor.
Well worth knowing size is proper for your/our application for not only efficiency but in some cases like my sno blower, just to run.

The number stamped on an OMC jet both denotes a flow rate and a flow direction. You will see both "D" and "C" jets in the same numerical line up.
They flow in opposite directions however.
Secondly the number stamped on the jet is that of a flow rate, not a numerical orifice size. They do, however, roughly correspond in thousandths to the number stamped on the jet.
As far as drilling goes, you are on your own.
I will only "preach" good shop practice for the most part.

[url=https://www.tinboats.net/forum/viewtopic.php?p=330322#p330322 said:

JoshKeller » Yesterday, 19:51[/url]"]on your personal 3 cyl engines, do you have the oil tank and mixing unit removed? or just the oil tank removed and the line blocked off?

Click to expand...

Everything except the fuel pumps is gone. Nice and simple.

just outta curiousity since you have several of these - what kind of speed can i expect out of the 35 on a 1648 jon boat that weighs approx 600 lbs with motor and everything. with my 95 merc 25 hp, im getting around 27. with the 35 and the air box off, im getting 26, so surely theres way more to be had correct? i was hoping for around 31 - 32 mph.

Plenty left. I doubt there are any here that have experience with this engine.
I run a 25hp version on my fiberglass 15'6" Gheenoe Classic, Light load I can bump 37mph and heavy loads with my fishing buddy we can run 31. The narrow hull is affected by weight pretty bad. Not a lot of planing surface compared to your boat.
Once the engine is straightened out you will have an ear to ear grin.

I've discovered a high speed orifice in the Carb bowl, however it is broken off at the threads and I can't get the threads out of the hole. Any suggestions?

There is a dedicated jet tool that you may have luck with. Take the bowl by a dealer and see if they can get it out for you. Since the bowls are made of minlon you cannot apply heat. I have had luck with a normal easy-out as well. Not a prob since you are replacing the jets anyway.
By the way. On Sept. 23rd you wrote that you had soaked, cleaned, run a wire through and blown clean, all the jets.............busted !!

no, not busted. i did soak and clean them all. i may have broken the orifice off while reinstalling, but i sure dont remember it. didnt tighten them down, just snug.. not sure how it ended up broken. the jets themselves are in good condition. this is the seperate high speed orifice thats broken off at the threads