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FJ Dragbike Project

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

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Weather looks like a go for Saturday at Albuquerque!

Main focus will be getting the clutch dialed in better.  Ultimate goal is to knock 1/2 a second off the 60' times...that goes to show how bad they really are! 

First step is to try adding additional "base" pressure to the clutch.  This comes from the coil springs that press the pressure plate against the clutch pack - same way the diaphragm clutch spring works in the stock FJ clutch (or the Barnett coil spring conversions).   The base pressure is what gets the bike moving at the "hit." Too much pressure and you spin the tire (or wheel stand if there's enough traction).   Not enough and you're SLOW off the line waiting for the centrifugal arms to start applying additional force to the pressure plate.  That looks like the issue the last time out.

The baseline clutch tune I was given used 4 (out of a possible 6) "heavy" coil springs.  Note - these "heavy" springs are still quite light compared to more normal motorcycle clutch springs.  Since the springs have to be arranged symmetrically on the pressure plate, I have to add two more springs.  The options are to add  two heavy, medium, or light springs.  Adding two heavy springs will increase the base pressure 50% - seems like too big a jump to me.   The medium springs may work, or be too much, or not enough.  Pretty sure the light springs won't be enough.

Now, I have a quick access clutch cover, but it's not big enough to let me pull the hat off the clutch to get to the pressure plate.  To change springs (or to  inspect the clutch plates ) the entire clutch cover has to come off.  So I come up with a plan to only have to do that one time. I'll put in the heavy springs. Then add two medium springs on top of the clutch hat "slider style".  These springs pull outward on the pressure plate - opposing the base springs.  The adjustor nuts on top of these slider springs adjust how much pressure the slider springs take away from the base springs (the opposite effect of shimming the base springs).  And I can make that adjustment through the quick access cover. 

Stole a little bit of time last night to pull the clutch cover. 

Took a quick look at the clutch plates -- they are in great condition!  No signs of overheating and well oiled. 

The original clutch setup

Pressure plate with 4 base springs

6 heavy base springs

Slider springs and adjustor nuts.  Originally went with two - then thought it was smarter to use three to spread the load more consistently.  Making that change this evening. 

Should be all read to set some new personal bests and put up some 9s! 


Looks like I lost a couple pics. 

Original clutch setup:

Pressure plate with 6 heavy springs:

And the pic of the modified setup with two slider springs on top of the hat.


Quote from: fj1289 on November 06, 2013, 06:09:08 PM

And the pic of the modified setup with two slider springs on top of the hat.

Chris, should you not use 3 slider springs, each one on a peg clockwise (or counter-clockwise - as long as they are all the same) to the weights for harmonic balance?

FJZ1 1200 - It'll do me just fine.
Timing has much to do with the success of a rain dance.


[quote author=Harvy link=topic=1698.msg102434#msg102434 date=1383789748

Chris, should you not use 3 slider springs, each one on a peg clockwise (or counter-clockwise - as long as they are all the same) to the weights for harmonic balance?


Thanks Harvey, that's exactly what I did this evening.  I wanted to make sure the force was balanced on the pressure plate.  I was afraid the pressure plate might "teeter totter" with only the two slider springs.

I appreciate the critical and creative thought people on this list have when dealing with things.



What's the stack height and air gap looking like?

I got to take a couple passes on a friend's ZX11 this weekend, even with a very badly slipping clutch (down 3-10mph!) it managed a 1.79 60' with my heavy tail on it.  SWB on it is pretty long, like 58-59", and it's like trying to ride a rocket-powered barstool because it's so tall, even when lowered ~2" and strapped.  I had taken my car up to the track just to see what it would run, but I couldn't beat a 15.07 no matter how hard I tried.  Cars are really weird to run!  Even with a reasonably good 2.2 60', I think the weight was holding me back, but god it's boring to run a 15 when you're used to mid-10's...


Lol!  I've thought about taking the rental car to the track a couple times on my business trips - think it would be strange to get that much time to look at things during a pass.

What car?  15.0 isn't bad - I've read that the 14 vettes are only running high 14s.

I imagine the ZX-11 feels more like the FJ than the 9 (with more power!)


Some rental cars (certain Buick's at least) have a 2step if you're on the gas and brake at the same time, and are really good to bracket race...

I finally replaced my horrorshow of a XJ Jeep with a 08 GTI.  Unfortunately, there was some kid there with an 06 (same engine, trans, and mods), though his was lowered a bit and on lighter wheels.  I was able to beat his 60's, but I think my car was heavier, because he was going 14.9's and I just flat couldn't manage it.  I'm happy though, he had the cloth seats and they're just as awful as I remember them being, with their horrible plaid and lack of heat.

The ZX11 actually doesn't feel like an FJ at all.  The FJ you sit in, the 11 you sit on.  It's much, much bigger from the seat to the bars and pegs, and lacks some of the hotrod feel of the FJ.  That said, it's putting something like 140hp to the tire, and will eat an FJ down the track, and burp afterwards.

There was a 14 Vette there.  Stunning looking thing, other than the ridiculous taillights.  Don't remember what it was running, but I thought it was rather a lot quicker than 14's.  It wasn't going to touch the other car that came out... someone brought a $400,000 Aventadore to the party, and it was running 10.teens @ 130 and change.

Currently shopping for a reflash of the ECU in the VW, with a pretty much otherwise stock car it should end up in the lower half of the 14's someplace in comparable air (the DA was insane, only reason I went).  Shame the vendors are so proud of their work :(


Made the 6 1/2 hour trip to Albuquerque last weekend for their final TNT day of the year. 

Plan for the day is to get my license runs completed. If you run 9.99 or quicker in the 1/4 mile, NHRA sanctioned tracks require you to hold an NHRA license.  There's a total of 6 runs progressively building up to full passes at the appropriate time and speed for the class of license you are applying for.  First run is a half track pass, next three are "moderate" passes where you stay in it a bit longer each time and show progressively quicker/faster runs.  Last two are full passes.  The runs have to be witnessed by the track manager and two NHRA licensed drivers, signed off on the license form, and the time slips sent to the NHRA with your medical and completed paperwork.

Feeling good about the day and have a tuning plan to make sure I get my 9 second runs.  I have four runs to get the clutch tune into the ballpark to make the 9 second runs happen. 

The bike sits at 66" wheelbase and 16/43 gearing.  The starting clutch tune was 6 orange (heavy) springs for static, 3 green (medium) slider springs at 4 turns to adjust static, 6 washers on the arms with 20# holdback springs. 

Weather is nice - sunny and upper 50s and track elevation is 5,600'. This is also where I've run my best time - last year with the back tire spinning through the launch.  This year I've got the suspension set up better, so I can't wait to see what it'll do with some traction.

Have to find the track manager and let him know I'm doing licensing runs. There's an old school KZ1000 small tire/wheelie bar bike doing licensing runs too.  Talk to them a bit - bike used to run pro comp in the 80s.  They took it out of mothballs last year and bent a valve while they were getting it sorted out again.  Also a couple very serious tube chassis cars doing license runs.  They have us lining up in the staging lanes in lane 8 - all the way to the right, next to the tower and a port-a-potty.

First run goes well, except I roll out of the gas before the 1/8 mile.  Also had a little trouble with the 1-2 shift -- not sure if I didn't make a good push on the button, or if there is something causing a problem on the shift.  I miss the early turn off and it seems to take forever to get to the end of the shutdown area for the normal turnoff. 

Pickup my time slip and go to the pits. 
60'        1.798
330'  4.443
1/8       7.296 @ 71.986  really slow since I rolled out before half track
60' is a lot slower then I was hoping to see on the "first guess" for the clutch tune, but I know what to change for the next run.  I realize I forgot to reset the 2-step RPM. It is set about 10,600 and I intended to be 9,000 - the actual engine RPMs are 1/2 the setting!  Don't want to make too big a change for the next run, so I adjust it to 10,000.   Adjust slider springs to 3 1/2 turns out to add more static pressure to launch a little harder and bring the 60' and 330' down more. 

Second run goes well.  Stay in the gas for a bit past the 1/8 mile point this time.  Made sure to make a solid press on the shift button, but still had troubles with the 1-2 shift again. Wouldn't shift until I backed off the throttle slightly.  Thinking now  it's spinning at the top of 1st. 
60'        1.778
330'  4.770
1/8       7.028 @ 111.031
1000'  9.015
1/4      11.135 @ 96.546

60' improved slightly, so take another 1/2 turn off the slider springs to add some more static.  The shifting issue shows in the slower 330'.  I take off 1 washer from the arms to reduce the lock up force to try to fix the shifting issue in case it is spinning at the top of 1st.

Starting to develop a routine now for adjustments between runs.  Park the bike in the front wheel stand, unzip the leathers and take off the helmet.  Get the book out and look at the time slip.  Compare what changed to what I was expecting, and try to figure what change to make for the next run.  Write down any notes or observations from the run (before you forget!).  After a couple of runs, wrenches, sockets, allen wrenches, handles and rag needed for adjusting the clutch are now in a plastic bin wrapped in a larger towel.  Spread out the towel, unbolt the mount for the megaphone, pull it off quickly because it is a little warm, put the nut and bolt back through the mount so you don't lose it!   Loosen all the quick access cover nuts, then go around again to take them all off and put them in the plastic bin so they don't get lost.  Make the clutch adjustment -- slider spring adjustments are easy, just a quick turn with a wrench.  Arm weight adjustments are not so easy -- one, because the metal parts are HOT!  And dropping one inside the clutch cover means some time consuming work to retrieve it before it finds its way into the bottom of the oil pan...  Then, button it all back up.  Then double check everything you've touched.  Quickly check the catch bottle and empty if needed.  Then the most important part - write down the will get it all confused by the end of the day if you don't!   Grab a quick drink of water, decide you can wait to hit the port-a-potty after he next run.  Gear up, go to the staging lanes, and wait to do it again.

Talking with the KZ1000 rider and (I think) his Dad that used to run the bike in the 80s.  Seems they are having ignition issues and working on the clutch tune too.  Glad I'm not the only one that faces these gremlins at the track -- hope they get passed them like I seem to finally have managed to do.  If I remember right, they finished up last year running 10's.   Its a 1428 motor and has a one piece fiberglass body -- painted like an old warbird to match his helmet - pretty cool. 

Third run - another "moderate" pass.  Launch feels good - feel it pulling through the bars harder than the previous runs.  Roll out of it around the 1000' mark.  Coast thru the shut down and need a little tap on the brakes to make the turn - first time for today (has felt strange just cruising through the shutdown area).

Roll up to the timing shack and get my time slip and have to take a quick peek (I usually wait until I get back to my pit area).  Think I saw a 1.5 something for the 60'!   

Get the bike parked and look at the time slip again.  Yes!  My quickest 60' yet -- 1.571.  Not really stellar for this combo, but good progress for today and will be quick enough for my licensing runs.
60'        1.571
330'  4.298
1/8       6.531 @ 108.017
1000'  8.583
1/4      10.531 @ 108.274

Make the decision to leave the clutch tune as it is and focus on riding for the last three runs.  Download the datalogs out of the WEGO since it only holds enough data for about three runs.  Take a quick look and don't see anything that really stands out.  Wish I could log rear wheel speed.

My in-laws show up at this point.  They live in Albuquerque and came out to watch.  My mother-in-law likes racing events, especially where you can wander thru the pits and look at the cars and talk with people.   She makes regular trips out to Bonneville  with some cousins?  aunt and uncle? that run a mustang and a corvette on the salt.  We have a family trip penciled on the calendar for next year for Speed Week - that may include the street bike....  But for now, more important is the fact they've shown up with lunch from a taco truck they found when they got lost on the way to the track.  The other half of my little trip to Albuquerque is to take home a load of furniture and stuff for our upcoming Thanksgiving home invasion -- 20 or 30 cousins, uncles, aunts, grandmothers, nieces, and nephews coming for Thanksgiving at our house.

After a good lunch break its back to the staging lanes.  This will be the last "moderate" run.  I plan to run it hard until 150' or so remaining and roll out of the gas.  I know from the last run the bike won't try to do anything stupid so I focus on cutting a good light and throwing away the clutch lever.   Didn't notice anything notable on the  launch, but I am more aware of the lock upcoming in than before.  Definitely feel more speed at the top of the run than before. 

Looking at the time slip in the pit I'm taken back - the 60' slowed down over a tenth -- 1.70x.   But the 330' is quicker and the ET is 10.03 even though I rolled out before the 1/4 mile! 
60'        1.772
330'  4.391
1/8       6.508 @ 116.326
1000'  8.340
1/4      10.037 @ 122.391
Sure wish I ran that one out the back door!
Either way, that'll get the job done when I run it out the back door for the next two runs.  Decide to tweak the tune slightly.  I take a flat (1/6 of a turn) off the slider springs, bump the 2-stage to setting 10,500, and increase my shift point to 9,500 RPM (I've been short shifting at 9,000 RPM up to now).

Fifth run now - first full pass, looking for 9s.  Run goes well, but runs out of gear a little before the lights (shift light on prior to the traps), but let it over rev a little (not too worried with the balanced, nitrided crank, Carillo rods, lightweight pistons and shim under bucket head).

Look at the times lip and I can't believe it -- a 10.4?!   A 1.963 60'?!  WTF?!  Slowest run of the day ... 
60'        1.963
330'  4.787
1/8       6.962 @ 113.684
1000'  8.838
1/4      10.447 @ 139.430
Seriously, what's going on here?  And more importantly, what changes should I make for the next run?  I've only got time for one more run and hope if its a 9 the NHRA will accept the licensing package.  Go back to 3 turns on the slider springs and try bumping the 2-stet to 11,000 RPM.  In the staging lanes I bump the shift RPM another 250 to 9,750. 

The sixth run feels better run, but still doesn't feel as strong as the third run.  It does feel fast at the top end though.  Time slip is better than the last, but not enough. 
60'        1.807
330'  4.469
1/8       6.606 @ 115.101
1000'  8.465
1/4      10.054 @ 141.220

Load up the bike and all the gear trying to figure out what's causing the erratic times   This clutch is known for its consistency.  Only thing I can come up with is I got more confident in the whole setup and got more aggressive with my clutch release - the difference between letting the clutch out quickly, but it still touching your fingers on the way out compared to releasing the clutch so fast it can't keep up with your fingers.  Only thing I can come up with, but doesn't totally explain it for me.   

Over the next week I try to find more info about setting up these clutches specifically and find a case where someone had problems with the clutch acting erratic because of a notched clutch basket.  That gets me to thinking - the first set of steels I used in the clutch had been ground to the same diameter as Busa clutch plates.  Tim bought the stock FJ steels would work, but wasn't completely sure.  Long story short - FJ steels are slightly too large to be used in the Busa clutch basket.  I pulled the basket and found notching on the inside of the basket from the steels.   That will cause problems with the plates hanging up and not releasing smoothly or consistently. 

So now I'm coming up with a fixture to turn down the clutch steels on my little harbor freight lathe.   

This was the best day I've had at the track in a year (really three!).  Good to have most of the gremlins worked out and be running laps when I get to the track.  Now, just take care of a couple details this winter and be ready to go quicker in the spring!


Great track report, thanks for sharing. It's all about consistency and it sounds like you found the culprit with the FJ steels in the Busa basket. What sucks is we have to wait til spring to hear how your next round goes.
It will be great when you get to the point where your not second guessing your tune and all your concentration can be focused on the ride. Sounds like you are close. :good2:



I read all of these, by the way. Super interesting.

Not everyone understands what a completely rational process this maintenance of a motorcycle is. They think it's some kind of a knack or some kind of affinity for machines in operation. They are right, but the knack is almost purely a process of reason.



I figured this would be a fairly straight forward build thread.  Had I kept the build more basic - a 1314 engine and hand clutch - it would have been a lot easier and been quicker up to this point.  

The project got its first big push when a friend I met when I stared drag racing forwarded an ad on - someone parting out a big block FJ motor.  I ended up buying an aftermarket cast cylinder block and 1380 pistons, stock crank with Carillo H beam rods, ported big valve head, cams, and the modified cases (a strengthening rib welded to the front of the block and what looks like a one-off set of heavy duty studs with larger than standard threads in the block).  I foolishly tried to bolt it all back together and run it - didn't make the power it should.  The rings weren't sealing well.  I replace the 1380 block with a used 1314 block - ran much better and ran the best times for the streetbike ... just before spinning a rod bearing.  

That's when I decided to turn my old parts bike into a dedicated drag bike and began collecting parts.  


Well, took a closer look at the data logs today (again!).  I noticed the big WTF on the log of the 5th run I hadn't noticed yet.  I kept focusing on the launch portion of the run and trying to figure out what was different to cause it to be so slow.  This time I noticed there were only four acceleration "peaks" for the whole run.... Yep, looks like I didn't get it into 1st after the 2nd gear burnout.   :dash2:  Can you say launched in second gear?!   :ireful:

I guess it did pretty well for a second gear launch.

Pat Conlon

Oh man, that would explain a lot... :dash2:

I really enjoy reading your posts Chris. Too bad I am going to have to wait 'till late spring to read more..

Why don't you move to SoCal?  We race all year long out here...

Think of all the snow you won't have to shovel.  :good:

Thanks again Chris, I learn from every one of your posts.

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 - I'm sure year round in CA is nice, but I think I'm actually starting to enjoy having a "season".   When you get to ride in Colorado in the winter, it's like you're getting away with something!  Also helps to have an enforced break -- time to clean up all the hastily made repairs made during the season. 

Many people here also on  I haven't been on there in a while, but I enjoy reading some of the build threads and ride reports - especially the ones that find a way to become more than just the build or ride.  I like the ride reports section here too. 

I need to make more time at the track and get some pics of the cool stuff there. Tried the GoPro mounted to the tank on a cou


"Many people here also on"

Yes, I enjoy the builds and mods. Also keep up with the Cafe group as I enjoy the engineering and artistry involved. If the FJ ever gets done it would be easy for me to get involved with a custom build, the problem is to build what.... So many ideas, so little time.... And of course money....  :good2:
Life isn't about having the best, but about making the best of what you have...

1990 FJ 1200