Less is more?

[budpat105]

Okay, you guys have led me through a complete rebuild on my Model 95 Combat wombat, fixed all my clutch woo's and this led to my first vintage MX today for the MOVMX (nicely ran, thanks Curtis) . It was run on a modern track that proved to be difficult for this old(56) and novice(first mx since 1975) rider. The bike is completely stock with all fresh top end. I had a little trouble keeping the bike reving where it wanted to be and "loaded it up" several times. I hope you understand what I am saying with that. Open to suggestions. I know I could just learn how to ride it but.... maybe a reed valve and a cylinder with a little milder porting. Please help. Thanks Bud

[Bullfrog]

You have experienced one of the "standard" situations with the completely stock Combat Wombat. If you get a little bit "behind the curve", allow the revs to drop a bit too far - and then grab a handful of throttle - WHAM, you are loaded up. While a reed valve and appropriate porting and re-jetting will cure that - it will also put you in a different AHRMA class.

There is a much simpler, less expensive solution which allow you to stay in the Classic class in AHRMA. Simply having carb throat vanes installed at the half-throttle position - one up-stream of the slide and one down-stream of the slide - will essentially cure the problem. Guys who do such modifications will likely recommend more vanes, such as at 1/4, 1/2 and 3/4 throttle positions - and I've been intending to do that to my carb since about 2006. It is still on my "Round To It" list. In the ensuing years, my engine has loaded up only once or twice on very hot, humid days when I got wayeeeee behind the curve (and hadn't adjusted the jetting for the conditions) - and I still have only the half-throttle vanes. Doing the half throttle vanes is also a good idea if you decide to "up-grade" to reed valve - so you can't lose on that modification!
Ed

[---]

Half throttle vanes should be sufficient with a stock sized carb. If you were going to mount something like a 34, I would say at the quarters and half positions. Thing is you can always add more if one on each side proves less than perfect. There is a point of diminishing returns adding extra vanes to a small carb because the vanes take up space.

[racerclam]

Having done many many carbs and getting a lot of feed back from my customers on the venture dividers it is very obvious that 6 dividers (3 on each side of slide ) is the best way to go since the slide always begins at the closed position and travels through the whole venture diameter the 3 on each side provide a more linear power application regardless of carb size I have done all sizes from 22mm up to 44mm flat and round slides . I have several customers that I have done a lot of repeat business with that have had my 4 divider as well as 6 divider carbs and they all prefere 6 including my self. I have done a 26mm carb for Jay layel's trials bike with 4 and it still made better response than a un modified 20mm the principal does not change with size , although the dividers will make a big carb behave like a small one which is a good thing. Another principal involved is the way a cab breathes , air actually likes to enter from the sides rather from straight from the rear , so with dividers at 1/4 and 1/2 positions that are straight across the back even with the casting grab the air and direct it under the slide and the way I make the 1/2 position scalloped inward allows the air a better path in that a straight across divider does not ( tested on a flow bench ) proven.

Rich