5000 or so RPM stumble

[joe1267]

I don't know if I am expecting too much and if I should just be happy that my sled starts,idles,runs EVERYTIME. My 73 JDX8 with about 900 current miles on it runs well, BUT despite the fact that the carb is clean and the plugs are a perfect tan with correct gap, I still get a stumble around 5000rpm where it feels like the engine is tumbling a bit before it pulls thru it to around 6200-6300 rpms where it will pull no more. Spark is strong,timing is good and it will sit and idle well. Any thoughts on what it could be, or should I leave well enough alone and simply enjoy it? I am able to get 55-60mph out of her, but somehow feel there is a little more there I am not getting. Drive belt is correct and new as well.

Any thoughts or suggestions?

Joe

[400brian]

The Walbros used in '73 were a bit rich in the mid-range. Deere later recommended it's replacement with the WRA-31 used in '74, which was set up leaner. I don't know if everyone with a '73 experienced this issue, as many still seem to have the original carbs on them. This may or may not be the source of the problem, just one idea.

[Mailman]

Not to steal the thread but was this with just the X8 or did it also include the X4? I had my X4 out today after putting a new carb. kit in it and noticed the same thing. Once you get past 4000-5000 rpm it goes just fine.

[400brian]

What model carb is on your X4 ? If your X4 is a '73, it has a Kohler engine, and I'm thinking they ran a different carb.

[Mailman]

I've got a kohler 295AX engine with a WDA-37 carb.

[joe1267]

Brian, thanks for the info. My 73 has the original carb on it and the sensation when riding it is definitely feels like a rich condition. I guess I will just enjoy it for now and begin my search for a WRA31. I had a similar condition on my vintage Sportster that drove me nuts until I put an S&S Super E carb on it. Enjoy your riding!

Joe

[400brian]

You can try leaning your idle mixture screw a bit if it is a bit boggy off idle, richer if it stumbles off idle
( assuming your high speed mix is nuts on ).

Walbros flow fuel from the idle circuit all the way to WOT ( unlike most carbs ).

[joe1267]

Brian, I will try leaning out the idle mix as I have not played with that one yet. Maybe that will get me closer to where I want to be. I went thru 1.5 tanks of fuel yesterday and she ran great although the top end was inconsistent. I am off today and still at my camp so I will give it a try. As always, thanks for the info...Joe