Tecumseh timing procedure for 7.5hp Eska

[Tommy Two Stroke]

After refreshing all the seals on my 7.5hp Gamefisher and rebuilding the ignition system, all that was left was to set the timing. Here's a case where the timing procedure spelled out in Tecumseh's 2-cycle engine manual doesn't seem to work nearly as well as leaving the engine's timing set where it originally was. As shown in the attached pics, I used the special Tecumseh timing tool, and a clamped-down dial caliper since I don't have the depth gauge spark plug hole adapter. Per Tecumseh's manual, the engine was set to 0.115 BTDC and the timing was set exactly the way the manual describes. It turned out that the opening of the carb butterfly was happening too late in the full ignition advance travel, when set according to Tecumseh's procedure. This made the engine extremely difficult to start, and when it ran, it would shut down periodically due to lack of fuel in the early part of the ignition advance curve. The wide open throttle position did, however, turn out to be dead-on when set per the Tecumseh procedure.

The point to all this is that Tecumseh's timing procedure may result in an engine that does not run as smoothly or start as easily as before being set this way.

 

[Tommy Two Stroke]

Re: Tecumseh timing procedure for 7.5hp Eska

I should also say that I wonder why the timing procedure and what makes my engine run seem so far off. I can't speak for all Eskas, but in this case, the Tecumseh procedure resulted in butterfly that would not open until more than halfway through the throttle range, making the engine really hard to start.

 

[mrcrabs]

Re: Tecumseh timing procedure for 7.5hp Eska

Tommy you seem to be one step ahead of me, I have been waiting for a month for my timing tool to get here. I ordered it from these guys. http://www.lawnmowerpros.com/detail.asp?id=670238A

I expect to backward engineer the timing setup since my Eska runs excellent, I was hoping to gain a little by sneeking the advance up a bit???.
When I got my engine she had about 40hrs on it according to the old man who had it since new (1977), I noticed that I wasn't gettin full butterfly opening so with out taking the flywheel off I just bent the butterfly rod back enough to touch the cam and open the butterfly at full advance...presto!

quoting from a conversation I had with Dale Colvert:

It turns out that my good friend from Tecumseh was correct that the timing is about 17 degrees BTDC full advance and 17 degrees ATDC full retard. It turns out to be at top dead center when the lever is bumped up against the stop that keeps you from going further until shifted into gear.

You sure have put a lot of $$ in that lawn mower on a stick...


http://www.youtube.com/watch?v=DLuzKsh1vy8

I weigh 240 and have a deep cycle battery and ankor up front, when I lean forward she planes and picks up another (guessing) 300 rpm, hard to believe this engine is rated at 7.5 hp @ 5650 rpm

 

[mrcrabs]

Re: Tecumseh timing procedure for 7.5hp Eska

Tommy 2 stroke, look at this photo I took of Ed's test engine before I tore it down to ship, I set the throttle at full and the SSI bottomed out against the stop, I'm having a hard time believing any timing setup is needed if full advance is hitting the stop, I guess it could be retarded but I would guess you can never advance beyond the stop in the lower part of the pic. I can however see how the throttle cam could be manipulated but thats it...any thoughts?

 

[Tom @ Buzzard Bluff]

Re: Tecumseh timing procedure for 7.5hp Eska

Tommy 2 stroke, look at this photo I took of Ed's test engine before I tore it down to ship, I set the throttle at full and the SSI bottomed out against the stop, I'm having a hard time believing any timing setup is needed if full advance is hitting the stop, I guess it could be retarded but I would guess you can never advance beyond the stop in the lower part of the pic. I can however see how the throttle cam could be manipulated but thats it...any thoughts?

And the kill switch limits travel in the other direction. About all the 'timing' necessary AFAIK is 'link & sync'. Having that out of adjustment will certainly affect starting and running however.

 

[Tommy Two Stroke]

Re: Tecumseh timing procedure for 7.5hp Eska

mrcrabs, the shop I ordered it from online (I think it was H&H Lawnmower Pros) took a while to get it - they said they were temporarily out of stock. Not sure if they are still making these tools, given that Tecumseh is essentially out of business other than the Tecumseh inventory CPC bought.

I was just very surprised at how the second step of the timing procedure calls for setting the throttle actuating cam to the carb-butterfly-full-closed position with the timing tool position #2 at the RUN trigger on the ignition module. This position seems to be fairly far into the throttle actuating range, and the original setting on my engine, which made more sense, was to have the carb butterfly open somewhat at this point. As I mentioned, setting the engine to the exact Tecumseh specs made it nearly impossible to start, and when I finally got it started, it would cut out periodically and just outright die.

Glad you were able to get better performance by bending the butterfly rod. I'm not sure I have the guts to do that, though - I fear that the swage at the bottom of the rod on mine would come loose and I'd have to either re-swage it in place or, more likely, solder it.

Sadly, yes, I have put some cash into this 2-stroker, but it's been a fun project.

Regarding that pic you posted, looking down on top - the original setup on mine activated the throttle butterfly very early in the travel of the cam. There are wear marks on the cam from this, it looks like it's been set this way for a long time. My right slotted hole had the screw more in the middle of the slot than yours, until I changed it after following the Tecumseh procedure - then setting it back to where it originally was.

That's a nice video you put up on YouTube, thanks for sharing it. Great engine, and seeing one run the way yours does gives me hope that I can do the same thing. I've got a Riverhawk B60 that I'm about ready to shove off the dock with next week, can't wait to try it. The scenery in your area looks fantastic - very nice place to check out in your boat.

 

[mrcrabs]

Re: Tecumseh timing procedure for 7.5hp Eska

Per Tecumseh's manual, the engine was set to 0.115 BTDC and the timing was set exactly the way the manual describes.

My Sears Tecumseh manual specifies .118 BTDC, for a pre 640-07 engine.