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That is all I have to add about the HATTA forks that isn't already out there.
Anyway, there's a big difference between harsh and plush in that old stuff, even if their plush is not very plush by current standards The holes have to be right sizes in right places, and the rebound piston has to seal properly. Hodaka was actually doing a decent job, even with steel slider forks, because Pabatco made sure that what Stateside R & D developed actually made it to production. People put Cerianis or leading links on Hodakas mainly to get torsional rigidity for full-size riders.
What I wondered after seeking out the 2020 rulebook is whether the F4 is even Classic eligible, as only the Greenstreak is listed there in the MX section; the F4 only seems to be eligible for Classic Sportsman Stock, where the swingarm can be lengthened period-style, like Z-plates, but forks must be stock. They probably specify eligible models to speed up tech inspections, and ditto for modifications, when they have hundreds of bikes to inspect at some events.
Front forks again! I have spent a lot of time on these forks! The end result has no rust anywhere! New seals, drain screws, and renewed components. I chamfered all the orifice holes as well. I cut the lower fender brackets off, then realized I needed at least one to attach the brake plate brace to, and opted to just make my own clamp out of aluminum to solve that problem. A lot of sanding, re sanding, cutting, and re-sanding! The end result is nice, though!
Before:
After:
And my custom milled bracket to fit the non-round fork tube:
I ordered a f21m seat cover probably a month and a half ago from a company off ebay and it finally showed up after shipping all across the world. I used the junkman's Method for seat construction and it turned out well!
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A little historical knowledge:
The red tank f21m with the kawasaki aircraft logo and knee pads was only made for one year in 1968, then they went to the same shaped green painted tank after that without the badges or pads. Many people with the 1968 f21m bikes would remove the badging and pads and fill in the recesses with bondo and have the tank painted green and white to match the new f21m bikes. Many people don't know that the green streak shares the same tank with the 120ss. The only difference is in the tank- to frame mounting tabs. I paid $250 for this whole bike, removed the tank, and resold the rest of the bike as parts for $200. A very lucky find. I decided I wanted to have dual tank compatibility with this tank and an original f4 tank (which I also have). I discovered if I flipped the rear tank mount grommet upside down, it allowed my "new" f21m style tank to sit in the right place. I simply had to weld in a mounting tube in the front at the appropriate height. While I was at this, I also welded on mounting brackets for my new seat.
Today I grabbed a picture that I think is Brad Lackey winning his class on a 250 Eagle in 1969:
I just found this post today. Have been considering a similar project for some time. It's great to see yours take shape!
Who did you contact at AHRMA regarding eligibility for your bike? Any update on their response? I'm curious. The way I interpret the rules is that your bike would be Classic 250 legal. The fork may be questionable but there is precedent for technology up to 1971 in that class. I do not see that it specifically states you cannot update a suspension component in Section 11.1.7 a-e of the 21 Handbook. And it appears your bike complies with the engine, frame, exhaust design, and carburetor size restrictions.
I'm in Colorado and the chair of AHRMA's Post Vintage MX rules committee. I'm a Kawasaki guy and have KXs for the Sportsman through Next Gen-1 classes. I have wanted to have a Kawasaki eligible for Classic 250 in order to race at the Jenny Ranch event in Steamboat. A real F21M is out of my budget, but a legal F4-based replica could work.
More info on our Region's events can be found here:
https://www.ahrma.org/ahrma-rocky-mountain-region/
https://www.facebook.com/AHRMARM
Feel free to call or email me. My contact info is on the webpage. I'm the region's FB page admin as well as the coordination.
I look forward to meeting you and seeing your bike in person sometime, hopefully at Monticello!
Long story short, I found another f4 sidewinder to use for parts. Turns out the f5 rear wheel will not work. The brakes couldn't hook up or anything. Happy to save someone else the headache!
Luckily, the kx500 rear brake shoes I found fit the F4 rear wheel, so that is awesome!
I got number plates,
I finally got the wiring harness done and have 2 separate systems, one for the ignition and one for lighting.
The idea is when i want to go MX racing I can pull the lights and wiring and speedo off in 15 minutes.
No more having my feet slip off the pegs!
Now I'm down to adjusting all the cables, putting locktite on the rest of the applicable hardware and hooking up the front brakes!
After fooling around with different combinations for 6 or so hours yesterday and using the specs and guidelines in the service manual, I properly set the float height, and settled on a #160 main jet, #30 pilot, f4 spec O-2 190 needle jet and SDP7 needle with the clip in position 3. The idle air screw is 1- 3/8 turns out. The bike runs awesome. I put a brand new plug in and about a 30 minute ride though in 100° weather, the bike cut out and died and would not restart. It seemed flooded. I put a new plug in and it barley started. The ignition system checked satisfactory. Previously on this engine with the only difference being using a 180 main jet, the original F4 upper carb body and everything else the same, this carb on my other f4 sidewinder always ran awesome for me up in Washington, but since being here in Utah it seems to randomly just kill spark plugs after a while. If anyone has any input or ideas on what could be happening, please chime in!
F4 upper carb body
F21m upper carb body.
The bowl had holes eaten through it, and the idle air screw had to be extracted and the body had to be sonic cleaned and vapor blasted.
The manual notes that adjusting pilot air screw and jet needle clip is sufficient for most tuning purposes which I agree with since I spent so much time and effort dialing everything else in just as the manual outlines....
Pit Row
BR9HS on the left, plug that I put in after installing dialed-in carb, rode for about 30 minutes with it at a play area then while cruising on a dirt road for a bit the bike cut out and died and would not restart. The tip:
The B9HS on the right is the plug my wife brought me when the bike would not restart. It was brand new and I rode maybe 10 minutes on it home. The tip:
Jetting differences are less forgiving at higher elevations and at lower relative humidity. That might explain why it is more sensitive/finicky in UT than in WA. The manual's base jetting spec is for sea level to about 1200 ft and probably around 80 degrees.
The Mikuni jetting slide calculator indicates approximately 1 main jet size per 1000 ft of elevation change or 10 degrees of temperature. Jet leaner as you go up in elevation and higher in temp and jet richer as you go lower and cooler.
Another thing I have come across is resistor type vs non resistor type plugs. It seems that in theory, a resistor type plug would "suffer" and display more issues with a hot ignition system than a non resistor type plug that is going to offer no resistance to whatever amount of electrical charge that is being generated. The manual initially called for a non-resistor type plug, but I have gone back and forth between the two with this engine for a while.
I am seeking some assistance on a Kawasaki F21M engine. Mine is in an American Eagle Geronimo frame. The engine is consistently difficult to start. I have been unsuccessful in finding the factory specs for the basic tune up. Can anyone provide the proper spark gap and breaker point gap. I am confident I have the correct ignition timing. The engine has the stock point/condenser/magneto, no mods, no electronics. Also, I need the stock carb float level. The engine runs fine, smooth, responsive once started. The only mods are a Webco head and a custom, high expansion chamber. Any help will be appreciated. Thanks
Update: The bike won the 2023 AHRMA Rocky Mountain Region Classic 250 Expert Championship! I bought the bike in September of 2021. After completing some finishing touches and the addition of an HPI C2 ignition in 2022 the "F41M" was finally ready to race in 2023. I had originally thought I would just do the Steamboat race this year, but with the the bike working well and feeling fast in testing, when that race got cancelled, I decided to race the series. Glad I did!
Float level from the manual is 24-26 mm
Plug gap is 0.7mm
Breaker gap is 0.3-0.4 mm
Thanks.
For some more information about the F21M and other Kawasaki rotary valve engines click here.
Kawasaki F4,F21M, F8 & F81M 250cc - The Junk Man's Adventures (thejunkmanadv.com)
Hey Junkman, I enjoyed watching your your Bighorn videos! You are in Evergreen, CO? Come race some of our vintage events, you are in the neighborhood!
https://www.ahrma.org/ahrma-rocky-mountain-region/
Feel free to reach out any time. Hope to meet you sometime.
Thanks.
I would have to get into shape to even try to ride a decent lap on my "hot" Big Horn. lol. I should get out to a vintage race sometime just to watch as it has been a really long time since I have been to one.
I most recently had both of my Kawasaki Big Horn's invited to be shown at the Morgan Adams Concours D'elegance.
Which is a charity event that is invite only for show participants.
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