Dragstrip plugchops

[pdxjim]

In the fall, Broken Bone Patch Patrick bought a $1600 '85 GS1150 dragbike.

He worked on it all winter, and has been taking it out to the strip at PIR Friday and Saturday nights for their "Late Night Drags".  These are test n' tune sessions to prep for Wednesday night bracket racing.

He's getting the kinks worked out and improving hit ET and top speed, and is now running 10.4's @ 133mph.



He was the oly bike, but there were a few modern supercars out last Friday, and the fastest was a newish $200k Lamborghini Huracan running almost the exact same times as Patrick's '85 beater at over 100x the expense.  There was a VERY fast '55 Chevy pulling similar times as well.

Anyway, I've been having a bit of a challenge finding the time and space to do main jet plug chops on my LC.  Seems the Friday night test n' tune sessions might be a good opportunity.

It feels pretty fat with 165 mains, so thinking a pair each of 160, 155, 150, 145's and a box of fresh BR9ES' should get me there.  I can fine tune the steps inbetween later.

Hopefully I can swap the plugs down near the finish line so the slow putt back to the pits doesn't affect the coloring.


Is this a good idea, or am I crazy and gonna blow up my brand-new high-zoot motor?

[EE]

My first year racing I'd carry a set of plugs and a wrench in my leathers, Kill the motor as I'd cross the line wot and swap the plugs before heading back and look at them in the pits. I had a .5 mile street in an industrial area too on the weekends those areas are pretty empty so with straight stingers at least you get in, unload, make your passes quickly, and get out before the federalies show up..

[pdxjim]

Thanks for your input Ed!

Don't wanna mess up your hard work!

[teazer]

10.4 is good, 133 is a nice number.  What do his 60 foot times look like? 

I tried that an it's really hard to read the plugs after a 1/4 mile run. Are you running leaded or unleaded race gas?  The colors are very different.

I need to buy /build a spare rear wheel so I can strap it to a dyno and get the jetting right.  To do that I also need to take accurate notes and record EGT as well as power/torque and A:F.  Then I can adjust jetting at the track based on changes in RAD compared to the dyno runs and use EGT as a check.

I once tried to use an A:F meter and other instrumentation at the drag strip which is a waste of time unless you can make sense of that data as you watch for the tacho to bounce or the shift light to come on.  Above my pay grade.  It works with a data logger, but I have come to believe that dyno time is the most important investment.

Not that the bike is in any way similar to yours but I'm running #310 in VM34s on a TZ700 (40900) top end with Blaster reeds and open stingers (no mufflers).

[pdxjim]

I agree about dyno time 100%.

The smart experienced dyno guys in town have forgotten everything they knew about twostrokes, and "don't wanna gunk up their A:F probe".

I do have another dyno option with the local scooter tuners.  They are def 2T nuts and aren't scared to clean their A:F probe.  I need to scoot on down and get serious with them.  I had my TDR on their dyno a couple years ago and everything went well.

I really wish I were in the UK where I could drop the bike off with KrazyKatt, or Mutt's Nuts, or ... any of the other dyno guys who specialize in 2t's and can jet, adjust the ig curve, etc and return the bike optimally tuned.

I'd be running pump premium at the strip, as that's what I'll be running on the street.

I'm running PWK28's at #55/N68A@3/#165 currently.  As I said the main feels fat (and the plugs are way dark).  Pilot and needles feel good tho (and are a lot easier to tune in the city).

[elliottles1]

hi all,

years (and years) ago a certain Terry Beckett in the uk helped me jet an rd400 that i was working on. he told me to jet big enough to get it to splutter and cough at WOT and then back down on the jets just until it cleans up. much like you would do when adjusting the high jet on your chainsaw.

it worked for me every time and marked the point in my motorcycle career when i stopped blowing up engines!!.

hope this may help.
cheers
les.

[rodneya]

Somebody described a method to check your main by backing off the throttle a bit at WOT, but I cant find it now. Anybody know what it was?

[Greaser Greg]

The way I remember that post, it was to watch/feel for a slight pickup with a slight letting off on throttle.

[elliottles1]

greaser greg,

yup, that would suggest that it is slightly too rich on WOT, so, as above.

les.

[Yamaha 179]

Somebody described a method to check your main by backing off the throttle a bit at WOT, but I cant find it now. Anybody know what it was?

I mentioned that several years ago as a tool we used to check our main jet size.  It works because the Jet Needle reduces the flow of fuel through the Needle Jet more than the air is reduced by slide closing the carb venturi.  Now, there are a couple of things to consider: We did this at the race track and it was after the engine had been run a few laps so that it was good and warm and all residual fuel/oil was cleaned out of the crankcase.  The throttle was closed only slightly, just a touch.  I can't quantify how much, just ease off a bit and check for a reaction.

After that and during our tuning progression a group of five of us bought a used Patrako water brake dyno.  Kept it at a friends plant and used it for a number of years.  It was quite old fashioned, no exhaust diagnostic sensors, just torque and HP meters. (The HP meter was suspect.)  We used the bike Tach and the dyno torque meter to calculate the horsepower, which was farcical, but we could produce a curve and we could always compare one curve to another.  A great tuning tool and we had great luck using it.  The group finally reduced to just two of us and we sold the dyno off.  Best tuning device ever made.
Lyn Garland