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FJ Dragbike Project

Started by fj1289, March 22, 2010, 12:39:45 AM

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Yup!  So much fun!

Some cars actually have a 2step function built in, though I can't think of what they are.  GM's of the type you'd rent with a slushbox.  Read something about someone bracket racing a rented Buick, so there's that.

The usual operation is that you've got a high limiter that is always on, so you don't overrev the motor on the throttle, for an FJ this would be in the 10k range.  A 2step is activated when you pull the clutch in, so now you have a 4250rpm redline.  Pull the lever in, get into the staging beams, hold the gas WOT and the bike will stutter and misfire while staying right at 4250rpm.  When you throw the clutch away, the redline becomes 10k or whatever again.  Pretty silly for a streetbike, but a slider clutch operates on engine rpm.  When done right, the engine picks up a few revs and the clutch bangs in at 4500, and you go vroom with much scootitude.  Too large of a rpm gap between clutch engagement and the staged rpm gives the engine more inertia than the chassis will hold, and you overpower the tire (spin) or overpower the chassis (wheelstand).  Too small of a gap means that the bike tries to creep forward while on the stutter box, burning the clutch slightly and giving you glazing issues, as well as not reacting properly.

2steps aren't allowed in the street classes that I run.  I've thought of a mechanical way to make it happen if you use the clutch as a lockup and have a cable actuated slave, which would be legal as it's not a throttle stop nor an electronic limit, but I don't have a bike that I could try it out on.


Andy - are you talking about a mechanical throttle stop activated by the clutch lever?  Haven't thought about doing it that way!

Reminds me of a guy on that came up with a mechanical way to release his clutch with his thumb while keeping his grip on the bar. Never did figure out how to do hat one either

Pat Conlon

I always wondered about...on a hydraulic clutch, using a line lock, similar to what the cars use on their front wheels, that prevents them from rolling out of the staging lights. Pull the clutch lever in, put your finger or thumb, on the line lock button while releasing the clutch lever, hold the button in until it's time to launch. 
1) Free Owners Manual download:
2) Don't store your FJ with E10 fuel
3) Replace your old stock rubber brake lines.
4) Important items for the '84-87 FJ's:
Safety wire:
Fuel line:


Pat - that has been done. I also figured if I ever went with a 2-step I'd add that at the same time. Guess I figured wrong because I'm going to try the 2-step with the lever.

I read a pretty in depth discussion on a while back about different ways to control the clutch release for consistency -- I think a couple of racers were index racers (top gas) and the others were "high end" bracket racers (delay boxes, down track throttle stops, etc). Both sets of racers that live and die by consistency tighter than .05 seconds per run. They were discussing alternatives to air clutches -- essentially the clutch lever is controlled by an air cylinder with swappable or adjustable air bleeds. And yes,this is a great big monstrosity that takes up most of the left handlebar!  The discussion turned to using line locks on hydraulic clutches. This also include talk of using flow restrictors to control the release rate of the clutch.

Another part of launching "on the button" some people forget is you have for to be ready to GO from the very moment you push that button and open the throttle. It only take a switch to fail, a wire to vibrate loose or any thing else and the bike will go NOW!  Get caught unprepared for that and you've got a good chance of hurting yourself and others...

I may go to a line lock in the future, especially if I get to run the whole season and it proves to be a good deal more consistent. Until then, I've already got a steep enough learning curve to climb!


Chris, rather than a throttle stop of mechanical form, a clutch release triggered from a (near-)WOT condition.

I thought line locks had been illegal on bikes for years now?  There's not much reason to using them if you can set a slider up properly and keep in spec on the setup (airgap and such will change as they wear the plates), and a multistage gives you that much more control if you want to go that route, though those seem to require more maintenance.

If it's a dedicated dragbike, bars or not, just go full slider and use the clutch handle to control the 2step.  Make the switch adjustable for where in the travel it triggers, and you can dial in your r/t appropriately.

Getting the suspension right actually helps as well, for repeatability and reaction time.  Did a shock swap (moderately heavier valving and 10% more spring rate) on the ZX9.  Went to the track and was getting .045 lights on a pro tree.  Couldn't ride to save my life, but damnit I could get the lights!


Andy - suspension has been my kryptonite so far...really lack of time has been.  I'm itching to get a bit of time to get the bike ready for the strip again -- really gunning for Sept 4 TNT, and the 10th for "race car" test night.   There, I've done it, thrown a date out in public to hold it over my head!

This next week I've got to finish wiring up the 2-step and modifying the clutch lever to make it adjustable.  Next up is clutch inspection and oil and filter change.  Then take a WAG at tweaking suspension settings based on notes and the spring change.  And maybe figure out how to attach the GoPro -- initial thought is on the swingarm to watch rear suspension (and maybe rear tire too).   

In the meantime, I'm sitting in a hangar in Toronto Canada  sweating my balls off waiting for yet one more thing that should have been taken care of already. Seems they are a little reluctant to get the plane out of the hangar and put $4-5,000 more fuel on it until they receive final payment for the plane!   :dash2: 

Finally got all the paperwork in place last night from both US and Canadian authorities to allow us to fly this thing into the US for further work (and it needs a lot! Probably the -8 equivalent of "Rusty Helga"... :shok:


Well, looks like I got everything completed with a couple days to spare!  

Changed the oil and filter - made sure not to overfill.   Right now at the top full line - but haven't cranked the engine yet - so need to make sure it doesn't go down too far.  

Inspected the clutch - all the plates looked good and were wet with oil. Looks like the clutch oiling mods are doing their job.  Rechecked the stack height and air gap.  Stack height is 1.648".  (That's 9 thin Busa frictions, 7 FJ steels, and 1 thin Barnett steel).  The air gap was .082. Minimum for the way the clutch is set up now is .08, but .10 is better. So I pulled the clutch hub and measured the shim stack behind the hub -- .049".  Removed the  thickest shim (.02") and put it all back together.  The air gap is now .102". Good starting point for now.

Pic showing the shims.

In process of measuring air gap.  Air gap is the distance from the top of the clutch pack to the top of the basket.

The clutch still drags a bit when in gear, lever pulled and engine not running -- but doesn't "pull" when the engine is running until the RPMs come up enough to start bringing in he lockup arms.  Increasing the air gap will lighten up the static a bit and delay the the lockup slightly.  This will soften the hit slightly and "should" make it easier to get the rear suspension dialed in better.  Of course once the suspension is hooking up, time to tighten up the clutch and get it out of the hole harder!  

The other set of mods were electrical -- new shift light module and the 2-step.

Looks like a Dyna catalog

Replaced the Raptor dual mode shift light with the Dyna shift minder and shift light.  The Raptor was nice because it included a staging light as well as a shift light.  It has two drawbacks though - the engine is so "twitchy" at launch RPM you spend way too much time focusing in the launch light and not enough on the tree!  The other is a nine step process to reprogram every setting in the light when you just need to adjust one setting (like launch RPM or shift point).  The new light is easily adjusted using dip switches but only functions as a shift light (but losing the launch light function is no big deal with the 2-step installed).  The 2-step installed easily enough - just needs to be tested.  

Made the clutch switch activation point adjustable by drilling and tapping the "paddle" on the lever that pushes the plunger for the clutch switch.  I ground the head down a bit shallower and filled the slots with JB Weld. Then cut a slot on the end of the threads to turn the "adjustor".  Right now turned all the way in seems to be close.  May need to be adjusted out slightly - will have to watch the RPMs on launch to determine which way to adjust - if it bogs on launch, need to adjust in to turn off the 2-step sooner. If the RPMs flash up initially, need to adjust out to turn off the 2-step later.   Sounds simple enough in theory...time to see how it works in the real world!  

While digging out my spare clutch parts, I found a few "offerings to the god of speed".  

Typical burnt plates:

Scarred up steel -- how do you do that?

Utterly destroyed friction...that's how!


Jeez man, are you driving it back in slider mode or something?


Quote from: andyb on September 03, 2013, 02:02:16 AM
Jeez man, are you driving it back in slider mode or something?

I had been doing that - using the "hit & coast" technique. It worked OK, but speeds were a little high through the pits. This however was a much dumber incident...

Just made a run at night at the strip at Hobbs, NM - an old WWII airfield they've turned into a dragstrip. Old pavement, lots of tar snakes, poor lighting. Anyway, about 1000' down I lose the lights on the bike so roll out and start slowing down.  I ended up taking an early turnoff that went nowhere - dead ended in a buch of waist deep weeds. Stopped quickly!  Then turned the bike around and twice tried to get rolling --- in 5th!   :dash1:  one moment of inattention cost an entire clutch pack.   :mad:


Amazing what a 5krpm launch will do to a clutch when you're in top gear. :)



Last night was return of the electrical gremlins.  Total electrical failure...

Test N Tune was much better than last go around.  Last time they were running from 2 lanes while 4 other lanes would be full.  Last night they never had more than 2 lanes half full - great chance to get several runs and do some tuning.

Got thru tech fine.  Rode back to my pit space to test and adjust the two step. Worked well - needed to tweak the RPM setting down slightly. 

Geared up and rode to the staging lanes.  Kill the motor while I wait -- maybe 6 or 7 cars back.  Talk a moment with the guy behind me running a Harley sportster with a slick and bars (and uses an off board starter).  Roll on up until I'm second in line and fire it up. Go through the burnout and staging drill in my mind.  Get waived into the burnout box, start moving and the bike dies.  Completely.  No electrical power to anything.  Cycle the main toggle switch.  Nothing.  Unplug and replug the tether kill switch.  Nothing. Push it back to the pits (up hill of course!) and take off the seat and left side panel.  Get out the volt meter.  Battery is pretty much dead - about 10 volts if I recall.   Hook up the charger and wait.  About 25 minutes later its reading 13.1 volts -- let's go!

Fires right up and back down the staging lanes again.  Pretty much same drill as before.  Get waived into the starter box, roll up (going around the water) and shift into 2nd, line up, and wait to be signaled to burn out.  On the front brake, "set" the front end, bring the revs up, drop the clutch and lean to the right for 2 counts, lean left for 2 counts, on top of the tire for 2 counts and roll it out.  Shift back to 1st!  flip the toggle switch for the 2 step, push forward to the pre-stage beam, roll the throttle to the two step at 4500rpm and continue to WOT.  Push into the stage beam, and throw the clutch away on the third yellow!  Engine RPMs sound good on the launch - RPMs don't "flash" up and doesn't bog - launch feels a little lazy and suddenly falls on its face about 20 feet out.  Total electrical failure again!  Coast to the outside of the lane, flip the main switch off - and start pushing.  It is dark and I have no tail light - luckily the track officials know I'm broken and send the ATV with the coolest pusher attachment I've ever seen.  A lot better than not noticing you haven't cleared and sending two cars down the track instead!  To be honest, not really a danger at this track as well run as it is -- but I've been on a couple smaller tracks where that was a real possibility. 

Get back to the pits and do some more troubleshooting/fix something NOW because they are closing the staging lanes in a few minutes.  Of course back in the pits the power switches on again.  Figure the main switch must be to blame (burned or loose contacts maybe) and swap it out - while throwing a quick charge at the battery to keep it topped off. 

Make it to the staging lanes before they close.  This time it dies just after the burnout.  ATV push again and that's it for the night.

I think about it on the drive home and figure the little 8 cell lithium battery is just not holding a charge anymore.  It is 4 years old now and has had a fairly hard life.  It gets used to start a high compression 1447cc engine, and powers a wideband O2, the Dyna 2000 ignition, tail lights, air shifter, data logger, shift light,  and now 2 step -- with a total loss electrical system.  Then it gets hit every 2 or 3 runs with a 6 amp charger.  And has sat for nearly a year on two occasions.  Wouldn't surprise me if it was done.

Started looking for batteries last night and more this morning. Came across new charging instructions for the LiPO batteries.  The old instructions said how long to charge it for at a certain number of amps.  I'd normally charge for about half the "amp-minutes" called for assuming the battery was only about half discharged.  Now the new instructions call for charging up to 14.2 - 14.4 volts!   Maybe it wasn't fully charged?  But will it still carry the load it should?  Maybe Batteries Plus can test one of these things.

Either way, I think I've decide to try adding a second battery to the system and splitting the system between the two.  Starting and wideband O2 (and maybe head & tail lights) on one battery.  And ignition, shifter, shift light, 2 step, etc on the second.

I was able to pull the data log off the WEGO III this morning - looks like the clutch lever switch is pretty much where it needs to be for the 2 step release point.  At least one usable piece of info from last night.


Do the rules require a headlight? If so, do they require a full-power light, or could you get away with an 1156, for example? I know most tracks require a tail light when running at night....
Rich Baker - NRA Life, AZCDL, Trail Riders of S. AZ. , AMA Life, BRC, HEAT Dirt Riders, SAMA....
Tennessee Squire
90 FJ1200, 03 WR450F ;8^P



Don't know if they require a headlight here - very well lit. The last time I lined up I didn't have it on...

But have been to some places that you NEEDED one!  I think I have a 35 watt bulb in now. A low watt bulb is a good idea.

I'm running 2 tail light bulbs now - figured if one burned out I'd still be good to go.

Did some more troubleshooting last night. The little battery took a full charge and seems to be holding it -- I may not have had it charged up enough.  Found a charge -vs - capacity chart for LiPO batteries; evidently 13.1 volts is only 40% charged!  Didn't know that before.

I've also found the power at my main switch is not stable -- sometimes reads battery voltage, sometimes none, sometimes jumping all over the place between maybe 3 and 11 volts  :unknown: 

Time to redo some of the electrics...again. Going to simplify a little and set it up to be split between two batteries later on.  Plan to add a larger shorai battery from RPM. Old battery will get starter, lights, and 2 step.  New battery will get everything else. Each battery will operate through its own relay and fuse - should be able to get several runs between recharging. If one fails, simply jumper between the relays to power everything from one battery.  That's my theory anyway.

Hope to have the basics sorted for Tuesday nights "race car" (running slicks) test and tune (street tires quicker than 11.00 allowed too). Then the following Sunday is a bike only event - plan to enter the streetbike class.  Also need to get my physical done so WHEN I break into the nines, I can get my license runs done and not be asked to slow down or leave!


Quote from: fj1289 on September 06, 2013, 02:25:59 PM
I'm running 2 tail light bulbs now - figured if one burned out I'd still be good to go.

You need to get some LED tail light bulbs too since they use even less power; LED tail/brake light bulb

I do not recommend them for a street bike. They do not reflect enough light to illuminate the complete light housing to allow the brake light to function properly.

Randy - RPM
Randy - RPM


Quote from: racerrad8 on September 06, 2013, 02:42:23 PM

I do not recommend them for a street bike. They do not reflect enough light to illuminate the complete light housing to allow the brake light to function properly.

Randy - RPM

Randy, you are right about the poor illumination from the LED globes you mentioned.

However these cree tower globes (yes, they fit ) have outstanding performance in plate, stop and brake light illumination from all angles. I have these very globes in mine. The brilliance of the number plate almost requiring eye protection.
I also have a brake light modulator that flashes a dozen or so times rapidly when the brakes are first applied then settles into a solid bright light.

I am told my rear lights, including brake, are a standout amongst other traffic.

Even conventional LED's with lights on the sides and top do not offer much better performance, but these cree units definitely do.

"Tell a wise man something he doesn't know and he'll thank you, tell a fool something he doesn't know and he'll abuse you"