1975, Johnson 25HP, Tiller Short staff Engine shuts off while going full speed ahead

[johnknowsnothing]

Recently, my 1975, Johnson 25HP, Short staff TILLER boat engine is shutting off while going full throttle at 27mph on the lake. The boat's running great, crusin' at top speed, then the engine just stops. I notice a little vapor/smoke coming from the carb/plugs area then. Engine is spitting water fine so I know it's not clogged. Is it overheating and shutting down? Thoughts on what can be causing this? thanks in advance.

 

[tmfeaster]

Re: 1975, Johnson 25HP, Tiller Short staff Engine shuts off while going full speed ah

Does it start right back up after it shuts down or do you have to wait a while before it will turn over again?

 

[Monte1961]

Re: 1975, Johnson 25HP, Tiller Short staff Engine shuts off while going full speed ah

Well this could be nothing or could be something. But without more details on what is exactly is happening besides it just shuts off, really leaves a wide open area. We need to do some tests to determine whats happening at wot?

 

[Monte1961]

Re: 1975, Johnson 25HP, Tiller Short staff Engine shuts off while going full speed ah

Welcome to iboats and post back!

 

[johnknowsnothing]

Re: 1975, Johnson 25HP, Tiller Short staff Engine shuts off while going full speed ah

I have to wait a while before i can pull start it again. Sometimes the pull start seems a bit heavy too? (harder to pull)

 

[johnknowsnothing]

Re: 1975, Johnson 25HP, Tiller Short staff Engine shuts off while going full speed ah

Well this could be nothing or could be something. But without more details on what is exactly is happening besides it just shuts off, really leaves a wide open area. We need to do some tests to determine whats happening at wot?

I am going top speed, cruising along like any normal day. Then, the motor stops. Turns off, silent, and my boat glides to a stop. I have to wait to pull start it again. Sometimes it doesn't want to start at all and I have to sail back to shore. I'm not equipped to test anything as I am not a pro at these motors. Therefore, I came to this forum to see what may be causing this and how much it can cost to have looked at and fixed in your opinion. Guy at dealer says $100 an hour. Sounds kind of high to me?

 

[fireman57]

Re: 1975, Johnson 25HP, Tiller Short staff Engine shuts off while going full speed ah

When it does this see if you can keep your fingers on the head for a long five count. sounds like it's overheating. Just because there is water coming out of the telltale doesn't mean that you don't have an obstruction in a water passage.

 

[jbjennings]

Re: 1975, Johnson 25HP, Tiller Short staff Engine shuts off while going full speed ah

I agree with the fireman's advice. If I have anything to add, it's that you may also have a restriction that is preventing enough fuel from keeping the float bowl full. Check for kinks in fuel lines, closed or stopped up fuel tank vents, or clogged fuel filters. Definitely follow fireman's advice on the overheating.
Good luck,
JBJ

 

[johnknowsnothing]

Re: 1975, Johnson 25HP, Tiller Short staff Engine shuts off while going full speed ah

When it does this see if you can keep your fingers on the head for a long five count. sounds like it's overheating. Just because there is water coming out of the telltale doesn't mean that you don't have an obstruction in a water passage.

I'm thinking there's something clogged in there as you mentioned. When I got the boat in the water, the wind pushed me into some weeds with muck and I luckily got out of there in time but thinking i sucked some crud into the engine which brought it to its current state. Before that launch, it was running super.
How do I flush the system? Or will a pro be able to flush it for me at a reasonable price? What does this consist of? Taking motor apart? How many hours of time am I looking at to flush it out and maybe a tune up too?

 

[fireman57]

Re: 1975, Johnson 25HP, Tiller Short staff Engine shuts off while going full speed ah

You need to drop the lower unit. You can put a hose on the water tube and maybe push whatever is in there out but it might just push it farther. You also might need to take the thermostat out and run a wire through the passages or use the hose on the water tube again. It will take about 1/2 hour to take it off if you've never done it before, and while you are there replace the water pump impeller. The kit is about 20 bucks. You can probably flush it out your self. You might disconnect the hose to your telltale so it have a more open flow when you flush it.

 

[johnknowsnothing]

Re: 1975, Johnson 25HP, Tiller Short staff Engine shuts off while going full speed ah

You need to drop the lower unit. You can put a hose on the water tube and maybe push whatever is in there out but it might just push it farther. You also might need to take the thermostat out and run a wire through the passages or use the hose on the water tube again. It will take about 1/2 hour to take it off if you've never done it before, and while you are there replace the water pump impeller. The kit is about 20 bucks. You can probably flush it out your self. You might disconnect the hose to your telltale so it have a more open flow when you flush it.

OK, thanks for all of the suggestions. I'm thinking I'm gonna buy a manual and actually sit down and teach myself about my motor. I think it's time to understand it a bit clearly.

But before I end, what lower unit lube do you suggest using for this motor? I've talked to many people and everyone suggests different brands... which ones is best or better for this older engine? thanks again

 

[Tim Frank]

Re: 1975, Johnson 25HP, Tiller Short staff Engine shuts off while going full speed ah

Has this happened more than once?

 

[johnknowsnothing]

Re: 1975, Johnson 25HP, Tiller Short staff Engine shuts off while going full speed ah

Has this happened more than once?

Is using Yamalube M2 Gear Lube in the lower unit safe to use in this motor or does anyone recommend a different lube?

Yes, this has happened a few times while running. Runs great but then shuts down.

 

[Tim Frank]

Re: 1975, Johnson 25HP, Tiller Short staff Engine shuts off while going full speed ah

Is using Yamalube M2 Gear Lube in the lower unit safe to use in this motor or does anyone recommend a different lube?

Yes, this has happened a few times while running. Runs great but then shuts down.

Try with a known-good tank and fuel line.

 

[fireman57]

Re: 1975, Johnson 25HP, Tiller Short staff Engine shuts off while going full speed ah

You have to make SURE that your tank is vented. If you have to, loosen the cap on the tank. Did you ever do the fingers on the head yet? We need to determine that is not overheating before we jump somewhere else. good idea about getting the manual. There is really not to much to the smaller horsepowers. Make sure that you get an OEM manual and not some cheap Seloc or Haynes. They are junk.

 

[johnknowsnothing]

Re: 1975, Johnson 25HP, Tiller Short staff Engine shuts off while going full speed ah

You have to make SURE that your tank is vented. If you have to, loosen the cap on the tank. Did you ever do the fingers on the head yet? We need to determine that is not overheating before we jump somewhere else. good idea about getting the manual. There is really not to much to the smaller horsepowers. Make sure that you get an OEM manual and not some cheap Seloc or Haynes. They are junk.

I wasn't able to do the touch test cuz the motor doesn't start. I noticed that it's leaking gas from the carberator? The part that has an air intake and is situated below the pull string handle, on the front of the motor. When I do try to pull start, it sometimes backfires a "pop" and air and spray of water shoots out of the tell tale hole. nothing more.

 

[CatfishMN]

Re: 1975, Johnson 25HP, Tiller Short staff Engine shuts off while going full speed ah

Sounds like maybe a stuck needle or improperly alligned float in the carb. Is the fuel spilling out when you squeeze the bulb hard?

 

[johnknowsnothing]

Re: 1975, Johnson 25HP, Tiller Short staff Engine shuts off while going full speed ah

Sounds like maybe a stuck needle or improperly alligned float in the carb. Is the fuel spilling out when you squeeze the bulb hard?

It's dripping, not spurting out but it's there. I squeezed gas bulb and this is when it's noticeable most. Would this cause the motor to die when it was at full throttle? Also, would this cause it not to start?

Thoughts?

 

[CatfishMN]

Re: 1975, Johnson 25HP, Tiller Short staff Engine shuts off while going full speed ah

If it is overflowing before start, I would say you might be flooding a cylinder, which would make it very hard to start. Pull the plugs after the carb overflows and see if they are wet.

 

[kfa4303]

Re: 1975, Johnson 25HP, Tiller Short staff Engine shuts off while going full speed ah

If flooding, you my have a stuck float valve needle.