Drag Launch??

[Drumagician]

I only put on 2500 miles on my bike since I bought it a couple months ago so I am not completely comfortable with it yet. I would like to take it to a dragstrip and see what she has, but not sure what the best launching technique is. I am just curious to hear how you all are launching these bikes in this senario. I know every bike runs a little different but I would like to hear anyway.

[81xsproject]

Step 1- Before leaving for the track, get online and order some new clutch plates
Step 2- Inflate front tire to around 40psi and lower rear tire pressure (I do like 20psi)
Step 3- On the line, rev to 5-6 grand, and when the time comes, feather out the clutch hard while applying more throttle as you apply more clutch.

It is a tricky thing to do in the matter of less than a second. I have not yet gotten it down consistently. It was a lot easier when I had the MSD iggy w/ the launch rev limiter. All you had to do was bury the throttle and worry about the clutch. Once the clutch switch circuit turned off, the rev limiter did too and all the while it was getting full throttle. This is my only gripe about the MS controller. There is no launch control unless you run different firmware.

[Drumagician]

In the instance where it was not consistent, what is the outcome? Stall, backward flip, wheel or just slower time??

[crazy steve]

Step 1- Before leaving for the track, get online and order some new clutch plates

He's only half-kidding about this; the clutch in these is only 'adequate' given the power and weight of these bikes. Beat the snot out of it at the drags and a new clutch is probably in your future; one of the cycle mags killed the clutch in a new '78 while doing strip testing for their review.

There's an 'extra plate' mod for these; you might want to look into that...

[Drumagician]

I actually install a barnett clutch kit about 1000 miles ago; it hooks very well.

[WMarshy]

You need to practice some before you get to the track so you dont look a fool. By that I mean you want to know how your bike reacts so do some practice launches on your favorite back road. Rev'er up to 5000 rpm and feather the clutch out keeping your RPM's above 4000 rpm and dont shift any lower than 7500 RPM.

[xs11widowmaker]

Race

I just ran my bike sunday at norwlak in ohio. I ran it 4 times and never once did the clutch slip. Its a rush.

[Drumagician]

Did you use the same technique described in this thread? What kind of numbers did you pull off?

[xs11widowmaker]

I revved up to about 5000 and feathered the clutch out and shifted at about 7500. This was the first time i ever was down the track. my first run was 13.6,13.1,13.7 and a 12.6 every time i shut down early just due to lack of experiance. so I probably was closer to 12 or a little better.

[Drumagician]

Your the second person that has mentioned a 7500 shift point. Has anyone seen the stock hp curve? I would think that a 8500 red line shift would be best, no?

[WMarshy]

I've done some drags this year, although it was at a 1/8 mile track and they had no clocks so IDK my times. I recently installed a tether kill switch so I can race at the local 1/4 mile and see what times I can turn... Keeping the rpm's above 4000 on launch is important b/c you main jets are being used and the power really comes on strong at 5000... Not many people will recommend winding these old mills up more than 7500. They will take it but for how long no one knows. I ride mine hard and push it up to 7k on a weakly basis but, with an engine that has 43,000 miles on it I don't care to push the limit that hard...

[Drumagician]

if nobody knows how long these motors will last winding them up to 8500m rpm, then they must not be breaking and I'm sure there is plenty of us out there that like to wind them out often. My bike has 33,000 miles on, thats just broke in!! I take it to 8500 frequently; just can't resist.

[WMarshy]

if nobody knows how long these motors will last winding them up to 8500m rpm, then they must not be breaking and I'm sure there is plenty of us out there that like to wind them out often. My bike has 33,000 miles on, thats just broke in!! I take it to 8500 frequently; just can't resist.

I've done it with no ill effects and will continue to do it ever so often but, its my only mode of transportation right now so I don't want to hurt it. If anything, it seems to run better after winding it out like that. Probably blows out some carbon build up... I also noticed the Jardine 4-1 I had on was a better performer up in that high range range... Shift it at the red I'm sure you'll be fine, its just personal preference...

[MaximPhil]

Your the second person that has mentioned a 7500 shift point. Has anyone seen the stock hp curve? I would think that a 8500 red line shift would be best, no?

Hi Drummagician,
When BDF ran my stock 81H on the Dyno. Peak Horsepower was at 7200 rpm so a shift at 7500 would keep you in the powerband nicely.

Phil

[81xsproject]

I've done some drags this year, although it was at a 1/8 mile track and they had no clocks so IDK my times. I recently installed a tether kill switch so I can race at the local 1/4 mile and see what times I can turn... Keeping the rpm's above 4000 on launch is important b/c you main jets are being used and the power really comes on strong at 5000... Not many people will recommend winding these old mills up more than 7500. They will take it but for how long no one knows. I ride mine hard and push it up to 7k on a weakly basis but, with an engine that has 43,000 miles on it I don't care to push the limit that hard...

I too take mine to 8/8.5k regularly. No ill effects yet.