1975 Johnson 25HP won't start

[CatfishMN]

Hi, thanks in advance for any help. I went through the Top Secret File, and couldn't find an answer to this particular problem there.

So last weekend I bought this motor and had the guy start it for me before purchase. It started on the second pull and he ran it until I was satisfied and I took it home.

This week I took it to the lake and just wanted to start it, put it under load and see how it performed. One the first pull (choke out and throttle in start), it turned over and ran briefly then died. After that, I could pull and pull and it wouldn't even turn over. So today I had it in the garage in a tank and was trying it again and again, it started briefly, then died. After that, no amount of pulling would get it to turn over. So I replaced the plugs with brand new ones. At first I suspected a fuel delivery problem as I was not using the same hose and tank that he did, but I just bought a new one of each. I followed the fuel line and it seems to be getting gas all the way to the carb.

Is there something I am missing here? Oh yeah, the cap is gone from the kill switch, so the two little copper things are exposed, but it was that way when he started it last weekend.

Also, the manual said to use plugs Champion J4J, but at the store, their book said J8C, which is what I bought and installed since they did not have J4J.

Like I said, any advice would be appreciated!

 

[JB]

Re: 1975 Johnson 25HP won't start

The correct plug is a Champion J4C. The J8C is far too hot for that engine. J6C is an acceptable substitute.

I think the problem is likely to be your technique. You may be flooding the engine.

 

[CatfishMN]

Re: 1975 Johnson 25HP won't start

The correct plug is a Champion J4C. The J8C is far too hot for that engine. J6C is an acceptable substitute.

I think the problem is likely to be your technique. You may be flooding the engine.

Thanks for the heads up on the plug, I'll get the correct ones.

Can you elaborate on the flooding statement? I am squeezing the ball until it is hard and putting the engine in start and pulling. How will I know if it is flooded?

Thanks again for the response.

 

[hardwatergrampa]

Re: 1975 Johnson 25HP won't start

pull the plugs out and see if they are wet 2nd are you sure you are getting spark at the plugs iam no pro but thats a good place to start

 

[CatfishMN]

Re: 1975 Johnson 25HP won't start

Once a motor floods, how long does it typically take to un-flood?

 

[bktheking]

Re: 1975 Johnson 25HP won't start

Dry the plugs if they are soaked, put them back it and try it. If they are REALLY bad, take a propane torch and burn off the excess oil/fuel then put them in.P Pump the bulb till hard, pull the choke, set the throttle to start and pull it over. It may take a couple of tries to get it to start or you simple have bad ignition components. I worked on my 6 hp 68 today, the gent who owned it complained it had no power. I check spark with my tester, one plug fired with great gap, the other wouldn't fire unless the tester was almost touching, so that told me something was weak in the ignition. I pulled the flywheel and the one points was black. Swapped out the points for a clean set, presto.

 

[CatfishMN]

Re: 1975 Johnson 25HP won't start

Thanks. I'll give it a shot in the morning. Like I said he pulled it and it started right away last weekend, so I don't know what could have changed. Already swapped for other plugs tonight and will try to start it in the tank tomorrow.

How hard is it to test the ignition system on this motor? What would I need?

Thanks again!

 

[bktheking]

Re: 1975 Johnson 25HP won't start

Failing components is what more than likely changed. Do you have a spark gap tester, worth $5 and it's weight in gold for troubleshooting. Pick one up tomorrow , this is the one I use, it should produce a nice bright blue spark at a wider than normal gap. Pull both plugs and plug the tester into one wire and connect to ground and test by pulling it over, do the same to the other side.

Here is an article published by fluke for testing magneto ignitions.

http://assets.fluke.com/appnotes/electricalpower/B0271b_u.pdf

 

[CatfishMN]

Re: 1975 Johnson 25HP won't start

Thanks! I printed out that guide and will use it tomorrow.

 

[ooldschooll]

Re: 1975 Johnson 25HP won't start

In a pinch you can use an old spark plug with the gap sread way out

 

[CatfishMN]

Re: 1975 Johnson 25HP won't start

OK, so I tried it again this morning, and on the first pull it tried to start but would not. Subsequent pulls it wouldn't go. So I pulled the plugs and connected them to the wires and held each to the block while pulling. Strong blue spark on each one. So while I had the cowling off, I noticed a drop of fuel, then another come off the carb. Is this normal? The bulb is hard, and if I depress the little valve at the end, fuel comes out so I know it that the external fuel line is not blocked.

What would you suggest my next step would be?

Thanks!

 

[Camo Joe]

Re: 1975 Johnson 25HP won't start

Sounds like to me its the float valve in the carb stuck closed.......drain the carb.....sqeeze the bulb.............if fuel don't come out the drain ..tap the carb lightly with the handle end of a good size scewdriver..........

 

[Camo Joe]

Re: 1975 Johnson 25HP won't start

Its also possible the float valve in the carb is not seating .........this would cause it to flood out after it starts....................The best thing might be to pull the carb.........clean , adjust, or repair anything wrong..............


Make sure the fuel pump is working...............

 

[CatfishMN]

Re: 1975 Johnson 25HP won't start

Hi Camo Joe. Where will fuel drain on the carb? Do you suggest getting a carb kit with a new float and giving the whole thing a good cleaning and overhaul? Is there any way to narrow down the carb as the problem?

Also, how would I know if the fuel pump is not working?

Thanks for replying!

 

[CatfishMN]

Re: 1975 Johnson 25HP won't start

Hi. Sorry to bump this before a response, but I have a quick question. If I buy a carb kit, does it come with instructions on installation? If not, is it fairly simple to follow the 'exploded view' diagram of the carb?

Also, I just remembered that the guy I bought it from said it had not run in 2+ years. Could the carb float have dried out and then gotten saturated with fuel and not be working properly?

Thanks!

 

[bktheking]

Re: 1975 Johnson 25HP won't start

The plastic floats never "dry" up and not float, the cork floats lose their varnish over time and take on fuel. The carb kits may come with instructions , the kit I bought for my 52 Merc did- that was a sierra kit, if I remember the OMC kit for my 9.9 didn't.

 

[CatfishMN]

Re: 1975 Johnson 25HP won't start

Thanks. So do you think this rules out the carb as the problem? I am really frustrated at this point as I don't know what step to take next to see why it isn't starting.

 

[bktheking]

Re: 1975 Johnson 25HP won't start

Not at all, i'd clean and kit it, that would rule out a carb problem.

 

[boobie]

Re: 1975 Johnson 25HP won't start

Bktheking, where did you get that dandy looking spark tester? I've got testers that go back to the 70's but haven't see this one yet. Handy to keep in tool box for service calls. Thanks
Boobie

 

[bktheking]

Re: 1975 Johnson 25HP won't start

Got it from a parts supplier here in town, I imagine they can be bought at most auto parts stores.