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1979 25hp Johnson, 25R79R, won't run right!

S

skiffscott

New member
My first post here! Greetings to all!

My 79 Johnson 25R79R seems to idle fine, but will not go WOT with out chugging and sometimes will just stop running. I just replaced the carb with a rebuilt unit. The old one had a bad low speed needle and the carb's bottom half was, upon research not correct for this year/model so I just replaced the whole darn thing and it idles much better now than before. I have new plugs installed as well, cleaned out the gas tank, fresh 93 octane gas 50:1 mixture. I cleaned out the fuel filter screen (it was fine). When the motor is running, it really wants to run well and sometimes it does run and rev well then the next time you crank it, it wants to chug, cough (like it needs gas or something). Also, when I pull the new plugs out they are black and wet with gas (same when I had the old carb on her). Checked spark (good and strong), checked all elec. connectors for corrosion (all good). If any one has some good ideas, I will really appreciate it. I read over all of the 25hp threads last night when I joined up and saw none pertaining to these symptoms with my year model. I don't have the points style ignition, and the plugs on this one are the type you can not gap. Thank you for any info. Scott P.S. Compression test shows 115# in both cylinders, all testing done in tank. Thank's!
 
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Re: 25hp Johnson, 25R79R, won't run right!

Please don't take my answer for a firm statement but I don't think you should be using 93 gas for it. I think 87 or 89 tops is what should be used on 2-cycle outboards.

let's hear from someone who knows it for sure.
 
Re: 25hp Johnson, 25R79R, won't run right!

I'm a 2 stroke ex dirt bike racer and the higer the octane (race gas preferred)...the better my bikes would run. This is my first boat and outboard so I'm trying to learn the ways. I thought 93 octane would be better? I appreciate your input and will explore the lower octane suggestion. Thank's sashko1 for the reply! :D
 
Re: 25hp Johnson, 25R79R, won't run right!

Start by changing the plugs to Champion QL77JC4.
Then check your thermostat and impeller at the same time.
Wrong temperature will not make the engine run correct.
Use any fuel above 87 Octane, will normally not make any difference on that engine.
Give it a good treatment of Sea Foam/Engine tuner to get all carbon and soot out of engine and exhaust parts.
 
Re: 25hp Johnson, 25R79R, won't run right!

Ok Haffiman37! Thank's! This makes some sense to me (even though I am outboard "green"). I know that this motor has a reputation for a small exhaust sytem (not the thru-prop type with larger passages). It is an older engine with unknown useage so the exhaust can choke the motor just like my old 2 stroke race bikes when the packing gets clogged. Hmmm. Now you have got me thinking more positively. I will try this out and get the plugs. The plugs I bought were the Champion L78V. I bought these since the plug lead had a sticker calling for this plug. The plugs I took off were UL77V for what ever reason. Thank's again for your time haffiman37!

P.S. Water is shooting strong from the motor in the test tank. Do I still need to check the impeller? Will also check on thermostat. Apparrantly, I need to read my factory service manual more closely. I did not know I had a thermostat.
 
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Re: 25hp Johnson, 25R79R, won't run right!

As above, use the Champion QL77JC4 plugs gapped at either .040 or .030 (try both and compare performance).

Thoroughly clean and rebuild the original carburetor using a complete carburetor kit. Adjust as follows.

(Carburetor Adjustment - Single S/S Adjustable Needle Valve)

(J. Reeves)
Initial setting is: Slow speed = seat gently, then open 1-1/2 turns.

Start engine and set the rpms to where it just stays running. In segments of 1/8 turns, start to turn the S/S needle valve in. Wait a few seconds for the engine to respond. As you turn the valve in, the rpms will increase. Lower the rpms again to where the engine will just stay running.


Eventually you'll hit the point where the engine wants to die out or it will spit back (sounds like a mild backfire). At that point, back out the valve 1/4 turn. Within that 1/4 turn, you'll find the smoothest slow speed setting.


Note 1: As a final double check setting of the slow speed valve(s), if the engine has more than one carburetor, do not attempt to gradually adjust all of the valves/carburetors at the same time. Do one at a time until you hit the above response (die out or spit back), then go on to the next valve/carburetor. It may be necessary to back out "all" of the slow speed adjustable needle valves 1/8 turn before doing this final adjustment due to the fact that one of the valves might be initially set ever so slightly lean.


Note 2: If the engine should be a three (3) cylinder engine with three (3) carburetors, start the adjustment sequence with the center carburetor.
When you have finished the above adjustment, you will have no reason to move them again unless the carburetor fouls/gums up from sitting, in which case you would be required to remove, clean, and rebuild the carburetor anyway.


Thousands of parts in my remaining stock. Not able to list them all. Let me know what you need and I'll look it up for you. Visit my eBay store at:
http://stores.ebay.com/Evinrude-Johnson-Outboard-Parts-etc?refid=store

Black spark plugs........... Check compression, what are the readings? Check spark (with s/plugs removed).... spark should jump a 7/16" gap with a strong blue lightning like flame... a real SNAP! Does it?
 
Re: 25hp Johnson, 25R79R, won't run right!

Joe. Thank you once more for the reply. I'll set the idle as you specified. I'm getting a lightning bolt out of the plug. The spark is hot blue and strong. Compression is exactly 115# on both cylinders. I changed the carb because the low speed tube in the carb (small brass tube inside the large tube) was damaged (smashed with an idiot's pliers), so I figured I'd pull it out and replace it. Did not know that this part is not serviceable and it broke when I pulled it out (pressed the remnant out from the plug). Also the lower half did not have the choke solenoid bracket and the low speed jet was a little funky (looked altered, bent) and the high spped jet was worn. Though it would be easier to buy a rebuilt unit alltogether.

Come to find out...I called the previous owner. He said he had his guy replace the carb. Upon disassembly of it, I found no little spring on the float. I thought that to be strange, too.

Question for the pros: The old carb has a round plastic insert, kept in place by the low and high speed tubes in the venturi. My new bolt-on rebuilt unit does not have this restrictive plastic piece in the carb. What does this mean?

Joe, I appreciate your time! And all of you here helping us less knowlegeable ones!
 
Re: 25hp Johnson, 25R79R, won't run right!

Ok. Today I got the Sea Foam and I had to order the plugs. I'll get them Monday. I'm gonna give it a shot!:cool: If any of you guys read this post and know what the carb plastic insert vs. no insert, please advise. Thank's to all!
 
Re: 25hp Johnson, 25R79R, won't run right!

Piper ...I have no vent on the fuel tank, but I did notice that the filler threads are distorted and bent such that is you shake the gas around in it the gas will seep through the filler cap ( if the tank is tilted suck that the gas is in contact with the filler cap). Thank you for the reply, but what are you saying?:confused:
 
Re: 25hp Johnson, 25R79R, won't run right!

Just saying that some motors - not sure on yours, need to pressurize the fuel tank to work -- do you have a pressure bulb? Those system need tanks to hold pressure - if tank bleeds down - no pressure - therefore - will not get fuel to run motor.

I am guessing your motor is a 1979?
 
Re: 25hp Johnson, 25R79R, won't run right!

Before I did anything, I would try a new 6 gal can of fresh fuel, with a new fuel line bulb assembly. You would be amazed at how many engines this "fixes."
 
Re: 25hp Johnson, 25R79R, won't run right!

Yes, It is a 1979 Johnson motor and it does have the bulb you pump to prime the fuel pump on the motor.

I appreciate your input Piperjak.
 
Re: 25hp Johnson, 25R79R, won't run right!

Martino1...thank's for the reply. I did try cleaning out the gas tank. It was a mix of last year's gas mixed with this year's and it had a little crud and maybe a drop or two of water. I got fresh gas, but I think I will follow up with a new 6 gallon can and assembly as you mentioned.

Thank's again!
 
Re: 25hp Johnson, 25R79R, won't run right!

Hi, Tim here. The proper fuel tank for your motor is steel and 6 gallon. This is vented automatically when you plug the fitting to the tank, it pushes a couple pins.....one opens the output line and the other cleverly vents the tank through a shielded hole. Aftermarket tanks are manual vented and work fine too. The older (1959 and back) use air output from the outboard to pressurize the tank. It is a completely closed system which works great when everything is right. The newer motors as Piperjak mentioned do use a pressure tank as well, however it is plastic so it can expand in the hot sun. I try to keep fuel tanks shaded in my boats.
 
Re: 25hp Johnson, 25R79R, won't run right!

I recommend plug gap @ .030 and an L77JC4 or QL...... as mentioned. That is not your problem however. If its not fuel starvation......and probably not, as you mentioned the plugs were wet..........I would look at loss of spark at full operating temp and under load. Early breakerless or electronic spark can be problematic. Trigger unit or module are the culprits......thats just my guess from what I've seen. If you have an inductive timing light or can borrow one, simply monitor each cylinders spark when it acts up. This won't cost you a thing and then we know where to go from there.
 
Re: 25hp Johnson, 25R79R, won't run right!

Skiff.... You state "Question for the pros: The old carb has a round plastic insert, kept in place by the low and high speed tubes in the venturi. My new bolt-on rebuilt unit does not have this restrictive plastic piece in the carb. What does this mean?"

The 1979 carburetor would have an adjustable slow speed needle valve with a RED nylon retainer which keeps it from moving and also acts as a restrictor to any possible air that might try to get by the needle valve. There is no adjustable high speed needle valve but rather a fixed high speed jet located in the bottom center of the float chamber.

The spring on the float needle valve thing...... the older needle valves didn't have the groove for that update. Nothing to be concerned about.

Your mention of slow and high speed tubes..... I have no idea what you mean by that.

Are you still having problems?

Thousands of parts in my remaining stock. Not able to list them all. Let me know what you need and I'll look it up for you. Visit my eBay store at:

http://stores.ebay.com/Evinrude-Johnson-Outboard-Parts-etc?refid=store
 
Re: 25hp Johnson, 25R79R, won't run right!

Thank you for the input Guido2, I'm going to get a new tank and bulb...I'll hook up the timing light and see what she says.:)

Thank's Joereeves. I know I don't know the proper terminology for this stuff. I'm sure you got a laugh! :D

What I was referring to is inside the carb and as you are looking through the carb from either side and open the butterflies, you can see the stump of the larger brass tube with the thin brass tube that goes up to the top of the carb. My old carb has a plastic ring that is held in place by the brass tubes. The plastic ring fits snugly to the inside of the carb and essentially narrows the inside diameter of the carb where the brass tubes are located. My rebuilt unit does not have this element. I'm just wondering what this means.:confused:

Thank you to all again for all of the help here! I'll break out the wrenches and we'll see what happens! Scott
 
Re: 25hp Johnson, 25R79R, won't run right!

guido...I switched the motor out for a Force 35 hp remote. I'm not done with the Johnson. I think you guys gave me some good input....Its fishin time and not wrenching time so now I have a good running Force and I can wet my hook!

I really like the Johnson and will undoubtedly hold on to it for a long time. I hear that when you have a Force and it breaks you throw it away. I'm keeping my fingers crossed!

PS guido...I'm going to learn how to test the power packs. I think that may be the culprit.
 
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i am having problems with this motor having no spark it ran fine when i took it off my jon boat now i put it on my pontoon and i cant get spark. i have checked the statorand everything else with a ohms meter and everything seems to be fine. I am confused can someone pls help me out.
 
Start by disconnecting the Black/yellow wire from power pack.
hook the power-pack end to an AC Volt meter (set at 250 Volt), pull/crank and check.
If 'nothing', check both OHM and power output from both charge coil to power-pack and trigger to power pack.
 
Check your lower seal on the powerhead. It's a cheap fix but it means pulling the powerhead. Motor won't run consistent if seal is bad.
 
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