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FJ Dragbike Project

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

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Wow, this has been a lot more difficult that just turning the streetbike loose on the track!  Amazing how many gremlins hide in a full up build.   :ireful:

Went to the track Friday night (160 miles each way).  Still no results to post, but progress has at least been made - bike actually moved under it's own power!  I did get one "easy" launch - the rear suspension setup was WAY off - shock bottomed immediately and caused the front to come up pretty quick.  Then, due to my own carelessness (didn't tighten the lock nuts when I modified the shift linkage), the shift rod came loose before the 1-2 shift.  So no shift when I pushed the shift button.  Luckily it was supposed to be an easy pass and I purposefully short shifted - don't think I banged it off the rev limiter (that can be pretty hard on the bearings).  

Bigger issues was the return of oil leaks.  Spent most of today getting rid of those.  A spin on filter conversion from Randy helped with the first one.  Replacing the shift rod seal helped the second.  Hopefully replacing the generator o-ring got rid of the last one.  Each time I got one leak sealed, I found another.  Of course, they are all lined up vertically so it's a bit like trying to stop up a waterfall!

Tomorrow will be spent tracking down an intermittent electrical glitch that sometimes resets the datalogger (and possibly the ignition) when the revs come up.  

Sucked to not get a clean run - there was a custom painted chromed out Busa with a wide tire kit running low 11's!  That would have been ugly for him!  


What intake manifolds did you use for the lectrons?
1985 FJ1100 Finally Home
1984 FJ1100 New purchase
1978 KZ1327
1973 H2


When the head was at Fast by Gast, they welded on aluminum spigots.  The carbs attach with a short section of rubber hose. 

You could do a similar arrangement without having to weld spigots on the head - just add flanges to the spigots and bolt them on the same as the stock rubber manifolds.  I can take some detailed pictures if you want. 



Thank you, I would be very interested.


What stage of headwork did you have done at FBG?
1985 FJ1100 Finally Home
1984 FJ1100 New purchase
1978 KZ1327
1973 H2


Ahh, teething problems... hopefully you're getting them all instead of me ;P  Need some finishing touches to the oiling system on mine and some mild buttoning up and I'll be in the same boat :)

Get a 60 out of it, or did you have to bottle out when the front lifted?


Tim - it was done as an all-out drag race head.   The pistons were machined based on molds taken from the head and cams were spe'c for it.  I'll have to look at my notes, but I think the cams are .425 lift. 

Andy - Yeah, hopefully the gremlins are mostly done for here - hope you don't have to deal with any.  The part that sucks most is how far I have to travel to get to a track!  If I get the electrics sorted today, I may try to take it out on one of the back roads here and make sure it shifts and all the electronics work right.  Then I can focus on chassis and clutch setup next time at the track!


FINALLY!  Got some passes in!  1 partial and 2 full passes.

Track had NO prep and had seen a lot of rain for last couple of weeks.  (This is a track that is usually prepped well for the entire length according to the regulars there)
The rear suspension was also way off - way too soft with the shock bottoming out to begin with, so it was SPIN city, big time!  (Even a jr. dragster out there was having issues with tire spin!)

All that said, I'm OK with the 10.73 - but that is WAY slow for this bike.  It did mph at 142!  So it's got a lot of potential!  Should at least be a mid 9 second bike once it's sorted!  60's were 2.1's all night due to tire spin.  With a decent track and the suspension even remotely in the ballpark, the 60's should at least be 1.5's and start working down from there.

The slip for the last pass was:
60'         2.1120
330'       5.1222
1/8        7.3112   @  114.20
1/4       10.7320  @  142.92

To show how bad that front half was, compare to my best slip from the streetbike with a 1314 from last summer:
60'         1.6670   
330'       4.4890
1/8        6.8910   @  101.94
1/4       10.7950  @  124.67

Big props to Randy for the block off plate for the alternator - finally got the oil leak under control!  Now I've got to remember to bring the charger to the track!

Pushed the RPM's a bit on the last pass and blew some oil out the breather.  Have to see if there's a bigger issue or if I just need to improve on the breather system a bit (probably with the 85mm pistons!)

It's great to be back on the strip again!  KOOKALOO!!!!!


Woohoo!  That'll be right up there when you can actually use the gas in the first few gears...  and the mph will gain too from better track prep and using more gas...


I'm happy with the potential it showed!  Now I just have to get it there!

Dug into the clutch yesterday - looks like the steels and fibers were nearly dry and got pretty hot.  Luckily they are still good to go - didn't glaze over or tear them up.  Going to make a couple mods this week to improve oiling to the clutch.  With the clutch being this dry, I'm sure it only made the spinning issue worse. 

I'll be switching the rear sprocket from 45 to 43 - 144 or so is the max for the gearing on it now (144 @ 10,500).  43 tooth rear should give 150 @ 10,500 and allow for some overrev if needed. 

Weather's looking good for Friday or Saturday - can't wait to try it again! 


May want to try using the trick of tipping the bike over after your burnout and pumping the clutch a bit to get the plates oiled up some, also.

If you have your logger working decently, you should be able to plot rpm over time and get a rough approximation to how much thrust you've got in a given rpm within a single gear.  Using that, it's possible to backtrack and figure approximate torque, and thus power, to find your power peak and work the shiftpoints out properly.  Makes a big difference to have the motor still pulling the last 300' instead of spinning too much rpm!  Sounds like you'll be in the ballpark with a 43 though, but if the motor is grunty enough you may want to pull it down even further.  Remember that changing the gearing will also slightly change the force on the arm at launch, but it's not really a problem because you're not dialed in real finely yet.


I used to do that on the streetbike, but this one has a full basket and slider style top to it.  All the oil has to come from the inside as best as I can tell...

I'm going to drill some more holes in the hub (180 out from the ones already there) and chamfer the backside holes like what was needed on the FZR1000's.   The FJ hub design is very similar - just bigger!

I will try a 41 sprocket later to see how it likes it.  After a 9+ month layoff, and riding much milder bikes previously, the way this thing pulls is nuts!  I'l need a few more passes to get used to it and be able to feel better what it's really doing during a run vice just thinking over and over HOLY CRAP!


Hey, justbecame a member and saw your dragbike pics. Just wondering what windscreen you are running on your fairing? It seems to lay down more then the lockhart one I have. Thanks


Wow!  It's been a while on this thread!  I'm also surprised fj1314 wasn't taken yet   :good:

Quick answer - I think it is a standard lockhart phillips screen.  Longer answer - it may be a bit of an illusion -- one thing I did while building the bike was move the fairing forward about 2 inches to gain clearance above the front fender and gain some clearance for the clip on handle bars. 

This project has been in storage for about two years during my trainups and deployment to Afghanistan.  I've been back for a few weeks, but have been attending to a family medical emergency.  But, the last couple days I've been spinning wrenches on the dragbike again and hope to get back to the strip again next month. 

Also wonder - should this one be moved to the projects section?

Kookaloo!   :drinks:

I make oil

 :good2: I've enjoyed this thread.  I wondered what happened.  Looking forward to seeing how it goes.
Semper Fi


Short version - melted clutch pack followed by a one year deployment to Afghanistan (including several months of training before hand).

Longer version - big learning curve on the rear suspension (was WAY too soft = instantly bottoms and then spins like crazy), big learning curve on tuning the clutch, all the while chasing some electrical gremlins (data aquisition not getting good power, ignition cutting out occaisionally, lights going out in the middle of a run at night!). 

I returned about 6 weeks early from the deployment due to a medical emergency with my wife.  We're on a long road to recovery (physical and occupational rehab) but making good progress.  Now that things have settled a bit, I've got a little time to start working on some projects again. 

Got the dragbike back out and think I've found the bad electrical connection as well as replaced the finicky (but very capable) data aquisition system with something simpler.  Have a new tune for the clutch -- going to a multistage lockup mode vice the previous slider mode.  And a slight tweak on the rear suspension based on the notes from two years ago.  Now I've got to try to find the time to get to the dragstrip before the end of the season...