Tired Combat Wombat

[hodakamax]

If I had any words of wisdom on this project (which I'm not really qualified--I'm from the past you know), I would mention something we learned (from the past, of course) is to not forget reliability. Our racers sometimes were built to such extremes that races were lost because of weak links that we had created in our quest for more power. Battery ignition was an example, it added more power but at a cost of more systems and more places for failure. The short tracker ran faster down the straight but got worse starts because of lack of a flywheel. We did better with flywheels at days end and got rid of a weak link. Things like compression were backed off to friendlier standards, and jetting was always borderline rich. Of course racing is about power, If more was needed it could be added at a cost of reliability if a competitor was beginning to threaten. At the end of the season we dominated because we finished every race.

OK, that's my advice (for what it's worth) for today!

Maxie

PS--Danny, Great job on the project! Keep up the good work.

[dcooke007]

Engine is now assembled and some preliminary testing has been completed. Below is a picture of the 97 model reed valve fit and assembled to the combat wombat engine. Since this is a spigot mount carb arrangement a different carb had to be selected. The combat wombat was originally equipped with a 28mm flange mount carb. The 30mm Hodaka 250sl carb is the same diameter as the combat wombat where the air filter boot connected and that is the carb I used. The jetting on this carb proved to be a close match to the needs of this engine. Tuning resulted in the following changes.... pilot jet from a 40 to a 30, raised the jet needle clip to the 4th richest position and 220 main jet. Tuning for the main jet and needle jet / needle are not finalized yet but are very close. The carb is equipped with a o-6 needle jet and I will probably go up one step richer. The taper on the 5dp7 needle works well at all throttle positions it affects. Also as you recall I modified the reed cage and installed a pair of one piece carbon fiber reed petals I got from Rich Gagnon.

The rear sprocket was changed from a 62 to a 58 tooth to better match conditions anticipated for cross country racing. If you viewed the prior video you know Will was running out of gear on the long straight away.

I performed testing / tuning with the 03 wombat head with torque grooves installed and the stock .020 Hodaka head gasket. Cranking compression with this combo is 160 psi with the new production Wiseco piston and ring. At this point cranking compression is reduced 35 psi. As for performance, the goal was to make the engine live and maintain performance. At this point the bike runs cleaner in the mid range, was easier to tune and just as strong as before with less cranking compression and a lower ratio gear so I am happy.

I may install a UFO if time allows and I still have a Torque Engineering pipe to test.

Danny

[dcooke007]

Completed some additional work on Will's bike today. A minor adjustment needed to be made to the shift cover and thought I would check the ignition timing. Checked timing with my timing light and found it was retarded. We are using the standard point ignition and the plug was firing about half the distance between the two timing marks......maybe .045 btdc approximate. Using my dial indicator I scribed a line on the engine case for .094 inch btdc. The factory timing mark was a little off to the advanced side of things. So with accurate timing marks I adjusted the points until the timing marks aligned using the timing light. Ended up with a loose .013 inch point gap to get the timing marks to align. Made the required adjustments to shifter cover, installed and test drove.

I spent a good deal of time jetting the carb a couple days ago and should have verified ignition timing prior to any carb jetting. After adjusting timing to desired setting the engine was running leaner and hotter. The insulator on the 8 heat range spark plug was too light and the very tip edge of the center electrode was eroding. Ended up going to a 9 heat range plug and working up to a 310 main jet instead of the 220. The 310 is two steps richer than I think ideal for the conditions today. Will picked the bike up this afternoon along with an assortment of main jets and a quick lesson on reading plugs.

These spark plug pictures are with the 310 main jet, correct ignition timing and with very little run time. On the center electrode you can see the fuel residue developing and the clean part at the very tip which is about 1/32 inch long. In the second picture you can see the nice chocolate brown color developing on the tip of the insulator. But just as important is the dark carbon ring developing at the base of the insulator. More run time is needed to fully develop the fuel coating / residue to get a better reading but looks like we are heading in the right direction. Before setting timing correctly unburned fuel due to retarded ignition timing caused the spark plug ceramic to appear dark and uniform in color with a smaller main jet. There was no gradation in insulator color with retarded ignition timing. Bottom line is check ignition timing before attempting carb jetting.

Will is back racing the tired combat wombat the 20th of this month. I am hoping he will have his GoPro camera for a video review.

Danny

[hodakamax]

Hey Danny, I'm starting to look forward to the weekly reports. They bring me up to date on what's been happening the last 45 years! Keep up the good work and reports.

Maxie

PS--the fire thing was funny at the time after I got things under control. Picture me sitting on it--Lessons learned!

[dcooke007]

Hey Max,

Seeing how you were sitting on the bike are you sure your eye brows were the only part that got a little warm? Do you walk with a limp?

Sorry cant help myself.

Danny

[hodakamax]

Fortunately most of the fuel went on the front wheel sacrificing the eyebrows for the "Good" parts. ( It's a family joke-My last name is Good!)

Again,

Maxie