Newly Rebuilt 1968 55HP - Fouls Out Plugs in 30 Min

[atengnr]

So, I took out my newly rebuilt 55hp (3 cyl) for the first time yesterday. At first it seemed to run OK, though somewhat rough at low speeds. At WOT it run quite nice (only ran it there for a bit due to beinga new rebuild). Then after 30 min, it essentially lost a cylinder and began missing.

I called the shop and they suggested putting another set of plugs in as they could have fouled due to running 25:1 for the break-in period (Im running XD 50). I put in a new set of plugs, and it ran OK again, for about 20 minutes; and then the plugs fouled again.

The shop says something is wrong and to bring it in. Any ideas on what might be wrong?

I checked the choke linkage, and it seems to be fine, with the butterflies open with the choke set to auto or off. The shop had set the low speed needles in the test tank. Is there any chance these could be off enough to cause this condition?

Thanks alot.

 

[tashasdaddy]

Re: Newly Rebuilt 1968 55HP - Fouls Out Plugs in 30 Min

let the shop handle it, or you void any warranty.

 

[Silvertip]

Re: Newly Rebuilt 1968 55HP - Fouls Out Plugs in 30 Min

Were the carbs rebuilt along with the engine or did they just slap the originals back on? The next question was what killed the engine in the first place that required it's rebuild. Very often lean carbs are the issue when an engine dies. Rebuilt engines will also die quickly unless the original problem was corrected.

 

[atengnr]

Re: Newly Rebuilt 1968 55HP - Fouls Out Plugs in 30 Min

Were the carbs rebuilt along with the engine or did they just slap the originals back on? The next question was what killed the engine in the first place that required it's rebuild. Very often lean carbs are the issue when an engine dies. Rebuilt engines will also die quickly unless the original problem was corrected.

Yes, they rebuilt the carbs during the rebuild.

I owned this engine from 1998 - present (though I shelved it in 05 when I briefly owned an 88 60hp thru 2008). There was no catastrophic issue with this motor - it was simply worn out. Pistons, rings and cylinders were worn from useage (I have the originals). Prior to the rebuild, it did not have this issue. It was simply finicky to start and idle, lacked power.

Engine has new wiring, power pack, distributor, rebuilt carbs, pistons/rings, among others.

 

[jonesg]

Re: Newly Rebuilt 1968 55HP - Fouls Out Plugs in 30 Min

..many of the experts here will tell you its near impossible to wear them out, something always causes excessive wear.
A 1968 is just broken in.

maybe you had an overheat or lean run somewhere along the line.

 

[R.Johnson]

Re: Newly Rebuilt 1968 55HP - Fouls Out Plugs in 30 Min

Check the spark, and point setting's.

 

[atengnr]

Re: Newly Rebuilt 1968 55HP - Fouls Out Plugs in 30 Min

..many of the experts here will tell you its near impossible to wear them out, something always causes excessive wear.
A 1968 is just broken in.

maybe you had an overheat or lean run somewhere along the line.

In my tenure owning this motor, it has been well maintained (water pump impellers, points, carb adjustments, etc), but it came to me in the worn condition that it was when I last used it prior to the rebuild. All 3 cylinders, pistons, rings had pretty uniform wear, no heavy scoring, just plain old wear. I cant speak to how it was treated prior to 1998. I can post pics of the original pistons, ring if that helps.

 

[atengnr]

Re: Newly Rebuilt 1968 55HP - Fouls Out Plugs in 30 Min

Check the spark, and point setting's.

What is the plug gap supposed to be on this motor?

Whats odd is for the 30 min before it fouls the plugs, it runs very good above 1/2 throttle, though somewhat poorly below that.

 

[atengnr]

Re: Newly Rebuilt 1968 55HP - Fouls Out Plugs in 30 Min

BUMP.

Can anyone suggest possible causes here? If there was something wrong in the ignition system, could the engine run well at > 2/3 throttle, as it did?

Also, what is the spark plug gap supposed to be?

Could low speed needles being off cause this condition?

Thanks.