Texas Two Step Taco

It's strange that the TMs seem so much more susceptible than the VMs - maybe it's just because they are lighter. The lack of fuel may not be causing the present problem but it'll almost certainly be an issue once the engine can run at full rpms continuously.
 
teazer said:
? That doesn't sound right. Please PM/email me details.
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Here is the Keihin carb you sent us for Victoria our cb175 build. See the weight that was epoxied on the bowl? You also removed the choke and did some fancy epoxy work inside
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I must be losing the plot. I have epoxied a few carbs over the years to clean up the inlet tract but I have no recollection or record of any with stuck on weights. So I checked my photos of the carbs I sent and they had no weights on. We know that UPS or the USPS didn't stick them on. Are you sure you didn't have another pair of carbs that they could have come from?

Is this the same bike? That carb doesn't appear to have weights on it, so now I'm stumped. motorleft.jpg

Was this a BB idea to drive me mad?
 
The bowls with the weights were on these extra bodies you sent me. These are the bowls from your picture.
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teazer said:
I must be losing the plot. I have epoxied a few carbs over the years to clean up the inlet tract but I have no recollection or record of any with stuck on weights. So I checked my photos of the carbs I sent and they had no weights on. We know that UPS or the USPS didn't stick them on. Are you sure you didn't have another pair of carbs that they could have come from?

Is this the same bike? That carb doesn't appear to have weights on it, so now I'm stumped. View attachment 226447

Was this a BB idea to drive me mad?
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Maybe I stuck them on??? Lol! I may have to go back through that string to see.


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I think I remember why we put the weights on the carb bowls. We were chasing something similar to what is happening with the taco and we thought it may be fuel frothing but it was caused by harmonic resonance and made the rotor mounted on the timing advance to move at a specific resonance and we shimmed the advance and then the magnet stayed lined up with the trigger on the Dyna S electronic ignition.


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teazer said:
That would explain why I don't remember it. LOL
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I picked up U4.4 yesterday. We have a Mikuni VM38 to test with. Got the basics screen filter instead of the rock filter and picked up 1/4” fittings to plump with. The plan is to get this dialed in with the stock head and see what kind of power we make. The first 3 dyno pulls at 19 degrees advance were all around 20 whp and EGT’s were around 1050 degree F and as soon as we changed timing to 21 degrees then bam we were making 10 more HP. Just for reference, last time we dyno’d and stuck the piston we were at 23 degrees advance. Another interesting thing is at 21 degrees advance the EGT temp dropped dramatically. This is the same thing that the H2 did on the dyno and the more you retarded the timing the more the EGT’s temp went UP! So the spent fuel is igniting in the chamber and raising EGT.

It is a miracle I haven’t stuck this piston yet. Have so much respect for y’all who did this without EGT’s, CHT, O2’s. We did have a failure on an O2 sensor for two of the runs and we kept jetting down until we said wait a minute and checked the O2 sensor. If you remove the sensor from the chamber it should read around 18:1.


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Rev limiter 8k, timing set at 19 degrees, 350 main jet. FAT. Half cocked.



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Texasstar said:
...Have so much respect for y’all who did this without EGT’s, CHT, O2’s. We did have a failure on an O2 sensor for two of the runs and we kept jetting down until we said wait a minute and checked the O2 sensor. If you remove the sensor from the chamber it should read around 18:1.


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I have to disagree - I think the EGT, CHT and O2 stuff are slowing you down. O2 can very often be misleading, CHT is too slow to be useful and EGT is a reference point, not so much a tuning tool. Listen to the engine and watch the torque gauge, they'll tell you all you need to know and they won't lie to you like the other gauges will.

I'll track down my notes for the air cooled Pursang engine; the jetting and timing figures for it might be a good starting point. It's normal for EGT to go up with retarded spark, and it's also normal for the big 85 odd mm bore to want around 20 degrees or so. Wanting a lot of advance is a sign that the jetting is off and the timing requirement will go down as the jetting is dialed in. I doubt that the piston stuck because of 23deg advance, more likely a lack of fuel. Make sure you have a cold plug - these things are prone to preignition with prolonged WOT.
 
Thank you! About to do the fuel flow test on one petcock then the other.


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Vibration Mitch better back to being fat. Going down to 300 jet.


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Still rich making more power torque is moving up 32.4 whp and torque was 23.80
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So all the runs had a dip between 7 and 8 k like this and we were only making around 32whp . Still running rich but torque was starting to go up.
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Then an accident happened. There was a 230 jet mixed up with the 280 jets and the 230 got put in...and we made 36
Whp. We made a couple more pulls with the 230 jet and we are still running rich on the top end. The last run we raised the clip one notch on the needle and it flattened out the curve. All runs we 21 degrees advance. We ran out of smaller jets. We ran a 250 jet and it only made 32 whp. Progress...we are heading in the right direction. We know 14:1 air fuel makes 30 whp at 6k. Going to pull this head since we are in a safe spots and put Ralfs head on and see what we get. Also we haven’t started tuning on the chamber yet. Thanks for all your help. You can call me two petcock Tex.
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Nice progress. The power curve is starting to shape up nicely. Still only 36rwhp but with Ralph's head and some more work, you will get there soon.

I just hope that BB has really tolerant neighbors..
 
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