1998 johnson 3 cylinder 35 hp

[hidef]

Re: 1998 johnson 3 cylinder 35 hp

Sounds like the temp switch is bad. You can run the engine with the temp sensor unplugged until you get a new one. The a lot of older engines have no warning signals you just need to check and make sure they are pumping water every now and then.

 

[JoshKeller84]

Re: 1998 johnson 3 cylinder 35 hp

Motor ran better, but something is still not right. For comparison my merc 25 ran 27 MPH. Boat ran 20 with cover and Carb silencer on. Ran much better with silencer off. But still only 25 MPH. Hole shot was awesome, but im still missing something on top end. Does the motor running better with the carb silencer off point to a fuel problem?

Also the speed was only a few MPH different, but it felt like a totally different motor with the cover off

 

[hidef]

Re: 1998 johnson 3 cylinder 35 hp

Your carbs might need some sorting out the air silencer and cowl shouldn't impact performance like that. Are the carb and throttle linkages setup correctly so that the throttle plates are opening all the way up.

The standard prop for the 35 was a four blade 16" prop depending on the boat that could be a lot of prop. I run a 3 blade 15" Prop on my 35 which is on a 15' Starcraft aluminum she turns 5800 at full throttle with the boat empty.

 

[JoshKeller84]

Re: 1998 johnson 3 cylinder 35 hp

Yessir they are synced. There was no difference with the cowling on or off, just the air box, which leads me to believe its still running rich. Will the idle adjustment screws have any impact on wot running? Ordered three high speed orifices as well as these carbs were sitting with fuel in them for 18 months unused. I have a 3 blade 15p prop on it now pushing my 1648 jon boat that is approx 600 lbs rigged. Definitely a huge difference with the air box off

 

[Kidney]

Re: 1998 johnson 3 cylinder 35 hp

I have the same motor and I'm having pretty much the same problems.

Josh, your updates are a great help.

 

[hidef]

Re: 1998 johnson 3 cylinder 35 hp

Idle adjustment screw would not affect WOT. However a plugged high speed jet could. Have the carbs been thoroughly cleaned?

 

[JoshKeller84]

Re: 1998 johnson 3 cylinder 35 hp

Yes they have been. One of the high speed orifices looks to have been twisted with a screw driver. Maybe that's the issue?

 

[JoshKeller84]

Re: 1998 johnson 3 cylinder 35 hp

any ideas? cowling on or off has no effect, but the air silencer off makes a dramatic different in hole shot,, mid range, and top end. with air silencer on, boat does around 20 mph then starts to mildly shake and sputter. air box off, and its balls to the wall up to around 26 mph.

 

[boobie]

Re: 1998 johnson 3 cylinder 35 hp

Have you got bugs in the air box or some loose foam in it ??

 

[JoshKeller84]

Re: 1998 johnson 3 cylinder 35 hp

nope, clear and clean. nothing at all in it.

 

[JoshKeller84]

Re: 1998 johnson 3 cylinder 35 hp

using this motor as a remote controlled unit, does it require the system check gauge?

 

[hidef]

Re: 1998 johnson 3 cylinder 35 hp

You need the gauge for the alarm to work if the engine overheats. Since you have ditched the oil tank It is not critical to have as you have the tell tale to check if it is pumping water.

 

[JoshKeller84]

Re: 1998 johnson 3 cylinder 35 hp

but the motor itself should run fine without the gauge and the oil/gas mixer? im fairly sure i have a fuel/air problem - the motor literally runs a ton better just by removing the air box. i was able to test it tonight, and put the air box ovver the top two carbs and there was no change, however, i couldnt reach the bottom carb to verifiy it was that one. need to recruit a helper to drive the boat while i test them out.

 

[hidef]

Re: 1998 johnson 3 cylinder 35 hp

Yes it will run fine without the gauge and the oil/gas mixer. The OMS (oil mixing system) used on the 35 and 25 was a poor design and prone to failure. Getting rid of it and running 50:1 pre-mix is the suggested factory fix for it when it fails. Most of the parts required to rebuild the OMS are unavailable if you wanted to restore it.

 

[JoshKeller84]

Re: 1998 johnson 3 cylinder 35 hp

OK, so I'm thinking there is definitely a Carb problem. If it was electric the motor surely wouldn't come alive with the air box removed. Is the proper float setting level with the bottom of the Carb body?

 

[Daviet]

Re: 1998 johnson 3 cylinder 35 hp

Yes.

 

[JoshKeller84]

Re: 1998 johnson 3 cylinder 35 hp

still no progress. Just out of curiosity, i have a buddy with a blown 25 (mixer filled the oil tank with gas and leaned out) and the carbs have the exact same model number on the body. I know the high and low speed orifices are different sized, but what about the hollow tubes inside the carb? since they are the same number (343157)?

 

[pn]

Re: 1998 johnson 3 cylinder 35 hp

looking at your picture i see two fuel pumps...does a 35 hp really need two fuel pumps???

 

[JoshKeller84]

Re: 1998 johnson 3 cylinder 35 hp

Not sure, but the parts schematic shows two and they are different from each other

 

[hidef]

Re: 1998 johnson 3 cylinder 35 hp

The two fuel pumps were required for the oil mixing system. Are they both required after the OMS is removed? I don't know but it is easier to leave them both hooked up than it is to remove them and it doesn't hurt anything.