1970 Merc 400 40 HP weak tell tale stream?

[reelfishin]

I looked at a mint clean looking Merc 400 today, it looks nearly new old stock and has 155 psi compression. My only concern was that when we hooked it up to a pair of muffs to test run, the tell tale stream was weak, it was always present but not really a stream. It was more or less coming out there in spurts.
It's been sitting for years, maybe since 1970? It ran fine, no carb issues and sounded 100%. I plan to replace the impeller before putting this to use either way. It didn't overheat in about 20 minutes of running, I could comfortably touch any part of the motor while it was running. The water that was coming from the tell tale was warm but not hot.

Also, might anyone have any opinions of these motors? I plan to put this to use on a 15' aluminum boat I have here for use in the river.

 

[jebeebe]

Re: 1970 Merc 400 40 HP weak tell tale stream?

Could be an obstruction in the teletale tube like a mud dobber's nest or a piece of impeller. New pump impeller should fix the problem. I would run some weedeater string up the tube. I don't know much about the motor it's self................Jerry

 

[reelfishin]

Re: 1970 Merc 400 40 HP weak tell tale stream?

The motor came out of a defunct dealer, it had been stored for all these years. I'm not sure whether it's new old stock or just super clean. I did check for anything being in the tell tale, but it all looks clear. I was surprised when it fired right up, it started right up, all I had to do is add fuel and a battery and it fired on the 4th or 5th revolution. The part I find odd is that the stream is weak, if the impeller had rotted over the years, I'd expect it to not work at all, unless it's missing half of it's wipers. In that case I suppose there may also be some impeller debris in the system, but I guess I'll find if that's the case soon enough.

 

[Willyclay]

Re: 1970 Merc 400 40 HP weak tell tale stream?

Telltales can be very misleading. All it takes is a couple of grains of sand to restrict/block a telltale. Your observations that you could touch the heads without getting burned and the telltale water was warm, not hot, are important bits of information. You could backflush the engine with a water hose through the telltale hose and see if that makes a difference in the flow. Another thought is that the water pump impeller may not be disintergrated or damaged, the wiper arms may have taken a "set" after being stored all these years and do not completely seal to the pump housing. Sounds like a great old engine that may only need a new impeller to be certain. The compression reading of 155PSI sounds awfully high. Good luck!

 

[burroak]

Re: 1970 Merc 400 40 HP weak tell tale stream?

Follow the tell tale tubing back to the powerhead, disconnect it and put it on the muffs and start it. If it's a weak stream there, an impeller is in order. Probably should be done anyway just to know what you have.

 

[reelfishin]

Re: 1970 Merc 400 40 HP weak tell tale stream?

I sort of figured on a new impeller either way, I just wanted to make sure that these didn't have any concerns. I am more familiar with the OMC brands.
I don't doubt that the impeller has taken some set over the years either.
It's sat for at least 30 years. What surprised me the most was how easily it started after all these years. It cranked a few times and started and idled like new. If it's not new old stock it could sure pass for it.
Was there anything to watch out for on these?

 

[danford1]

Re: 1970 Merc 400 40 HP weak tell tale stream?

I have a 79 40 hp. My tell tale stream was like yours.
I pulled the tell tale tube as the other guy said and water came out strong. I poked a wire backwards through my teletale tube and pushed out a dead bee. I figure he crawled in and couldn't back out and died. He was doing a good job of plugging the pee hole.
Once the bee was out and I replaced the tube, it shoots a nice stream like it used too

 

[reelfishin]

Re: 1970 Merc 400 40 HP weak tell tale stream?

This one sort of shoots it out in spurts, it never stops but its strong then weak, and always the same regardless of rpm. I ordered a new impeller either way, the tube seams clear.
I'd be more apt to think there's a clog if it were a motor that was stored outdoors or uncovered. When I found this it was wrapped in brown wax paper standing in a wood crate. I suppose it's the crate it came in. Someone had stretch wrapped it somewhere along the lines too.
I found another minor problem, the recoil doesn't always return and when it does it's slow to go back. There's very little spring tension. It was fine the first few times but lost tension after the engine ran a few times. (I had the recoil rope extended for a while with the cover sitting on the bench while I ran it, I didn't have the controls at first and needed to be able to get to the switch box to shut it down.
It don't feel like a broken spring, there's some tension, but it feels sticky or gummed up. It will recoil if you help it slightly.
I'll pull the recoil off and clean and re-lube it first.