Texas Two Step Taco

[John Murray]

It would be so much easier just to have you at the track. That sounds about how each run ended up going.

So it starts fine idles fine. It did a nose dive on the first two runs in the same place. It wasn’t the flywheel because as soon as it got fuel it was back on the pipe. When I rolled on hard on the throttle up to the rev limiter it did the same thing last the shift light. When I pulled up to get the time ticket it died. Pushed it all the way back.

Now on the third run I camped out on the line had a cappuccino and then launched. Kept it at the shift light which was 7500 and kept it lit down the track. Pulled up to get my time ticket this time the one that actually had a time and it died.

Did I read the plugs like I should have? Nope.

I will pull the jets out to the track and do some more testing and tuning this time instead of doing testing and wtf’kng.


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Fatten the jetting by a fairly big amount. Don't pull plugs, it's just a waste of time. Limit the idle and warmup time as much as possible though you're at the mercy of the starter. You'll have a rich spot off the line but if you can have the engine at just the right temperature it won't matter. You want to be cold enough to use the momentary richness but warm enough to run cleanly.

 

[John Murray]

I love Bill's reaction.

Those runs were almost as bad as my last time at the strip where first off the kill microswitch stuck "closed" for almost a second and finally stuck closed so I also had that walk of shame. Followed by a series of equally horrible runs where components did not do as they were supposed to. That's why we do shakedown runs and we go when there's no one that knows us....

Your bike dies off the line as soon as the clutch is fully out and the load is too high. Looks like the clutch is engaging too fast and I suspect that the throttle isn't wide open at that point. Set up a simple TPS. all you need is a microswitch that is linked to the throttle or a second cable on the throttle (twin pull or splitter) so that at full throttle it makes a connection. That can be connected to a small battery and LED rear lamp so your team captain can watch and he gets to hit you with a long stick fr every time he sees it go out. It's analog and very basic, so feel to upgrade any part of that to actually log results.

The thing bogs pretty soon, and the revs should not drop like that. It could be loading up with unburned fuel or it could be that the clutch is out too far too soon.

John's observations about large reed cages make sense, but your motor should come off the line at 7000 or more and not drop until it goes into second gear so we should be at peak load off the line. My guess is too rich combined with too much clutch release too soon. I went back and watched the "clean out" video and it has a similar stutter but came off the line much cleaner in that earlier run. I don't like holding a motor at the red line for seconds at a time on the line and a launch rev limiter tends to cause excess fuel to build up in the cases which John mentioned.

Get the launch right first and then look at the other symptoms one at a time. MPS sells a pneumatic clucth lever that is easy to adjust and consistent. It's not cheap but may resolve one issue.

I agree about the poor start technique. But I think there is more to it, the engine shouldn't cut out altogether even with a poor start.

 

[Texasstar]

Fatten the jetting by a fairly big amount. Don't pull plugs, it's just a waste of time. Limit the idle and warmup time as much as possible though you're at the mercy of the starter. You'll have a rich spot off the line but if you can have the engine at just the right temperature it won't matter. You want to be cold enough to use the momentary richness but warm enough to run cleanly.

We fire the bike up on the before the starting line, go around the water, back all the way in the water till the front tire is just Outside the water box. Do a burn out. Stage.


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[teazer]

It's interesting, John thinks it's lean and I think it's rich. And it could be either. He's right about checking the plugs. Mine show no color at all after a 1/4 mile run. EGT would tell you something, but only compared to what the EGT was on the dyno when jetted for maximum power as the baseline.

I didn't like the dead spots down the track. Do you know how long the kill time is set for? Allowing for the old heavy shift, the kill time will probably be closer to 60-70 milliseconds where a modern bike can get away with 50 or less. Yours sounds much longer. If you are using electric over air Pingel air solenoid with microswitch on top, you may have to shim it up a bit.

Somewhere on the web it said that a sound has to last at least 65 milliseconds at a fairly high frequency to be heard and we can clearly hear the break in sound, so it's probably 100 or even longer.

 

[John Murray]

It's interesting, John thinks it's lean and I think it's rich. And it could be either. He's right about checking the plugs. Mine show no color at all after a 1/4 mile run. EGT would tell you something, but only compared to what the EGT was on the dyno when jetted for maximum power as the baseline.

I didn't like the dead spots down the track. Do you know how long the kill time is set for? Allowing for the old heavy shift, the kill time will probably be closer to 60-70 milliseconds where a modern bike can get away with 50 or less. Yours sounds much longer. If you are using electric over air Pingel air solenoid with microswitch on top, you may have to shim it up a bit.

Somewhere on the web it said that a sound has to last at least 65 milliseconds at a fairly high frequency to be heard and we can clearly hear the break in sound, so it's probably 100 or even longer.

I'd put money on it being lean, rich sounds completely different.

 

[John Murray]

We fire the bike up on the before the starting line, go around the water, back all the way in the water till the front tire is just Outside the water box. Do a burn out. Stage.


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Sounds good, a good burnout would purge any fuel from the crankcase and get enough warmth into the engine to provide clean running.

 

[Texasstar]

It's interesting, John thinks it's lean and I think it's rich. And it could be either. He's right about checking the plugs. Mine show no color at all after a 1/4 mile run. EGT would tell you something, but only compared to what the EGT was on the dyno when jetted for maximum power as the baseline.

I didn't like the dead spots down the track. Do you know how long the kill time is set for? Allowing for the old heavy shift, the kill time will probably be closer to 60-70 milliseconds where a modern bike can get away with 50 or less. Yours sounds much longer. If you are using electric over air Pingel air solenoid with microswitch on top, you may have to shim it up a bit.

Somewhere on the web it said that a sound has to last at least 65 milliseconds at a fairly high frequency to be heard and we can clearly hear the break in sound, so it's probably 100 or even longer.

This is why we know Bandera is female. She is completely ruled by her temperament or temperature. One minute she is fat and one minute she is lean. When we were on the dyno it was a hot humid week. I was surprised and shocked at the jettting being 220. However this night we had a slight head wind and we dropped into the 50’s and just had a glorious dry cool front blow in.

I asked BB on several occasions how in the heck did he ever tune his bike without being able to see how his bike was capturing the air coming into the carburetor. His bike has cute little scoops going into an air box.

Since this was our first date and I had already had premature evacuation twice on the line I was a little bit more contemplative in line the third time. I was reflecting how fast she revved to the shift light and how she no longer had that horrible vibration. No vibration like the other times I had road her before her overhaul. So much vibration it was damn difficult to hold on to her. Now she was more sophisticated and refined. (a side note Dave Sposito is 5 foot and 100 lbs and he was on the line helping start Bandera. Well the first time he tried she about threw him to the ground. I smiled.). Bill was spotting me on the track. So supposedly you can get anywhere from 3 to five seconds on a pro tree between the last staging light and the 3 lights coming on. I left on the last staging light twice and one ticket is -.5 and the other -.4. Interesting. On a sportsman’s tree I use to leave on the second light and never red lighted. How can those guys get an .003 light without anticipating on a pro tree? You have to be able to anticipate it is like what Teazer says on the sound.

Yes the cut off is air over electric and the time is dictated by how long the air hose is. In this case this is the only hose that is long in my life. If you listen in the video where BB is laughing you can hear me shift into second. That was the first run on the other video that has both runs.


My third run has no video. But I think I am shifting into second gear within the 60’ and that is killing my 60’ time along with the shift kill killing it. Interesting side note. I was told by an old timer who raced Bultaco’s not to launch in first but to launch in second. I am trying to find a tire that is 100/90-18 that is around 9 lbs that will give us 25” inch diameter and take 3 lbs off the rotational mass. The slick has a 26.6” diameter. The Mitas MC-50 is available. I am waiting for him to email me the weight. I have the specs on the Mc 50- 120/90-18 and it weighs the same as the slick. So no gain there. Also we are still shifting into 4th at the 1/8 mile line.

If we can launch in second we eliminate having to shift in the 60’ zone we eliminate a shift kill.

We need to have 1.7 in our 60’ to get into the 7’s in the 1/8. Oh how glorious is our world at the race track. Red and yellow black and white they are precious on the line!


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[Texasstar]

The first run I shifted into 2 at the 60’ the second run I didn’t it just bogged.


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[teazer]

I watched the videos again several times and there are different things going on. The initial bog is clutch/rev control, but as you pointed out, there's something else going on. It absolutely dies and it isn't subtle. It's like you lost sparks for a moment or two. Sounds like my last runs where the kill switch was having problems.

I would start by testing the air over electric switch with a meter and blank off the tube to the shifter to save the forks. It may be sticky or it may be the push button that's sticking and not releasing fast enough.

You suspected fuel supply. I'm not convinced that's the issue, but check it. Hang on a minute. Where is the fuel tank mounted now? Is it possible that fuel is sloshing rearwards under acceleration and starving the carb? On mine, I extended the (aluminum tank) at the back so that fuel is pushed back into that and it can't starve the carbs. Same idea as a TZ tank but the sump is tiny. You thought about moving the tank forward at one point. That sounds like a good idea. As long as it's ahead of the carb, it should be OK.

You can also test the fuels supply to make sure it's adequate.

At this stage I wouldn't worry about where you shift into top gear because when you get a clean run, that will all change and with a relatively wide ratio transmission you could think about leaving in second, but it will put more strain on the clutch. Keep the faith. The solution is close.

 

[Texasstar]

I watched the videos again several times and there are different things going on. The initial bog is clutch/rev control, but as you pointed out, there's something else going on. It absolutely dies and it isn't subtle. It's like you lost sparks for a moment or two. Sounds like my last runs where the kill switch was having problems.

I would start by testing the air over electric switch with a meter and blank off the tube to the shifter to save the forks. It may be sticky or it may be the push button that's sticking and not releasing fast enough.

You suspected fuel supply. I'm not convinced that's the issue, but check it. Hang on a minute. Where is the fuel tank mounted now? Is it possible that fuel is sloshing rearwards under acceleration and starving the carb? On mine, I extended the (aluminum tank) at the back so that fuel is pushed back into that and it can't starve the carbs. Same idea as a TZ tank but the sump is tiny. You thought about moving the tank forward at one point. That sounds like a good idea. As long as it's ahead of the carb, it should be OK.

You can also test the fuels supply to make sure it's adequate.

At this stage I wouldn't worry about where you shift into top gear because when you get a clean run, that will all change and with a relatively wide ratio transmission you could think about leaving in second, but it will put more strain on the clutch. Keep the faith. The solution is close.

This is off the meth quad. Joseph told me that we needed at least a 1/4” breather hole. He modified this tank for methanol

This is where are tank is mounted

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[teazer]

1/4" is way larger than you need, but you do need the air to get in to replace the fuel. No harm in drilling a larger breather hole in the cap, but before you do that, fill the tank and see how fast it drains out of the carb float bowl drain.

Let's say you have a BSFC of 1.2 ( way higher than it should be but makes the calculation simpler, and say 50 crank HP, so the motor would consume 60 pounds of fuel over an hour or 1 pound per minute. How much does yours flow? Measure flow over say 1 minute?

A less scientific but more empirical measure is, did that fuel tank supply sufficient furl at peak revs on the dyno for say 8 seconds. If so, it flows enough.

 

[Texasstar]

Interesting. Last time I did this I just used the tank and measured it at 650ml per minute. But I will do it through the carb tonight.


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[teazer]

That's just over 1 pound per minute out of the tank - with the lid on?- should be sufficient. Now let's see how much the float valve restricts flow.

 

[Texasstar]

That's just over 1 pound per minute out of the tank - with the lid on?- should be sufficient. Now let's see how much the float valve restricts flow.

500ml per minute with cap on and vent tube attached through the float bawl. 1/8 vent hole.


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[Texasstar]

With a 3/16 vent hole 500 ml per minute
With a 7/16 vent hole 500 ml per minute
With no cap 570 ml per minute.


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[Texasstar]

900 ml per minute through the petcock


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[teazer]

So fuel flow is adequate. Try a run down the street with that main jet, 2 sizes smaller and 2 sizes larger just for comparison. A short blast through to second gear should be enough.

 

[Texasstar]

The filter flowers 500 ml per minute and I removed the filter and we are now flowing 800ml per minute through the float bowl. (I only timed it for 30 seconds)

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[Texasstar]

Cap made a huge difference only flows 600 ml per minute with the cap on


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[teazer]

Data is good. Now to put that back into context, a high performance two stroke should have a BSFC around say .65 or half the number I used earlier for that simple illustration, so it should burn through 32.5 pounds per hour or around .5 pounds per minute. That's more or less 225cc per minute, so it looks like you have more than enough flow under any of those conditions - cap on or off, but get rid of the filter.

Race fuel is much cleaner than street gas and I'm sure you use a clean ratio rite or Accu-Mix jug and a clean filler funnel.

That leaves us electrics and or jetting. I think I covered both of those, but I am more inclined to think that it's a sticky switch or maybe a thumb stuck on a switch perhaps.