Gold Anniv 6hp.. starving for air

[perkdp]

Well folks, I ran across a strange one while working on a motor my brother-in-law just bought... it's a 1972, 6hp, 50th anniv series. Like new.

BIL couldn't get it started after he bought it. So, I checked it out, cleaned the carb (stuck float wouldn't allow gas to bowl) got it running, took to lake to test at WOT. Wouldn't get to RPM at WOT. I assumed clogged high speed jet. Cleaned carb and installed a kit. Will run like a champ in the barrel until I put the cover on. With the cover on it won't get to RPM.
With the cover off it will.

I held the throttle at WO but the motor was running about half WO-RPM.
I reached around and unlatched the cover, raised up a bit and the motor sped up to what seemed right (hard to tell exactly in the barrel test).
Latch the cover back down and it slows down after a few seconds.

Have anyone out there head of / dealt with a problem with these motors where the cover fits so tight that it can't draw enough air through what few other holes are there from manufacturing ????
Have I overlooked something while rebuilding the carb?
Ideas to correct this ?

 

[Chinewalker]

Re: Gold Anniv 6hp.. starving for air

I am guessing it is NOT the carb, rather it is the cowling shorting out the bottom spark plug. It is pretty tight in there and isn't hard to get things tangled up. Either the latch or the cowling itself is probably touching the bottom plug boot or wire enough to short...

If that isn't it, I would suspect an exhaust leak, perhaps at the base of the powerhead...

- Scott

 

[wbeaton]

Re: Gold Anniv 6hp.. starving for air

My first thought was an exhaust leak, but the shorted plug sounds reasonable too.

 

[perkdp]

Re: Gold Anniv 6hp.. starving for air

I thought about a plug short but the wires, the best I can see in there, seem to be clearing the latch enough to not short. The rest is fiberglass so it shouldn't conduct / short.

How would an exhaust leak cause this ? And how does one diagnose that ?

Thanks....

 

[Chinewalker]

Re: Gold Anniv 6hp.. starving for air

Exhaust leaking at the powerhead base gasket or exhuast cover gasket would cause the motor to starve for air as exhaust gas doesn't contain enough oxygen for combustion. Look for seepage of oily residue running down the motor leg or into the lower cowling...
- Scott

 

[perkdp]

Re: Gold Anniv 6hp.. starving for air

I'll look again but the whole motor is as clean as a whistle.

What's the likelyhood of the exhaust from my test barrel funneling straight back into the air ways, since most airflow into the motor is from the bottom, and choking it ?

 

[Chinewalker]

Re: Gold Anniv 6hp.. starving for air

That could be a possibility, too. Try running a fan near the barrel to blow in fresh air...
- Scott

 

[F_R]

Re: Gold Anniv 6hp.. starving for air

An exercise in futility!!! Don't even try to run it in a barrel at WOT with the hood on. Even with a fan, it won't work. It breaths it's own exhaust. Only takes a wisp of that stuff to kill it. It was made to run on a boat.

 

[perkdp]

Re: Gold Anniv 6hp.. starving for air

Did the same thing on the boat.... two exceptions... hadn't installed the carb kit and didn't try WOT without the cover.

Maybe the HS Jet was clogged when it was on the boat.
Now, maybe it is breathing too much of its own CO.

 

[perkdp]

Re: Gold Anniv 6hp.. starving for air

Well, the saying goes, learn somehting new every day .......
The wind was blowing yesterday evening, so I hung the motor in the barrel, started it up and it ran close to WOT while the wind was blowing. When the breeze stopped,, motor would slow down. I took it to the lake and it runs like a champ.

I've been tinkering with old outboards for quite a while and never have I had one so picky about its air.

Thanks for all replies.