Categories: all aviation bicycle gadgets misc motorcycle theater

Sun, 27 Jul 2008

Dyno day

At the last race, a few folks got together and started plotting for an event they've wanted for a while: a dyno day. Cogs, one of the racers, works at Ducati Seattle, who have a very nice dyno. He proposed the idea to his manager, who readily agreed, and the Vintage 160 dyno day was born.

It occurred yesterday, and Jesse and I both brought our racebikes down. We'd picked up these shiny new carburetors from Bateman early this month, and we were anxious to use the dyno time to tune them up. So this week was spent somewhat feverishly making the intake runners we'd use to hook up the carbs. I ended up standing in front of the lathe and mill for many hours, but it worked out well: we now have six complete runners, with four installed on bikes, and two spare.

Anyway, we showed up at Ducati Seattle around noon, to find a moderate crowd of vintage racers milling around, talking, and working on bikes. I don't think anyone was on the dyno at that point, but it wasn't long before the room was filled with the subdued roar of a bike revving towards redline.

I should say a word about the Ducati Seattle dyno. It's a different brand than the one at Twinline (which I wrote about at the time, and posted a video about), and apparently reads horsepower numbers differently by about 2 HP -- the 11.8 HP we saw at Twinline is equivalent to about 9.8 on the DS dyno. The DS dyno is also beautifully enclosed in a little sound damping room, so that when a run is happening, it's still possible to hold coversations outside.

Saturday morning, I was waiting for intake runners, since the timing had worked out that we only had one set finished by Friday. That set was then installed on Jesse's bike, which was successfully test-run. But it left me with a bunch of machined-but-not-welded runners until Saturday morning after Jesse had time to weld them. So, my new carbs were installed mere hours before they were put to the test on the dyno.

In fact, all we had time for before departing for the Ducati dealership was to get the carbs bolted on, not even attached to the control cables or the fuel lines. Jesse had the foresight to check the length of my fuel lines (not long enough) so we brought along some clear PVC tubing I had in my stores.

We got there, and essentially the first thing I did was set to work, getting my carbs hooked up. No real problems until I turned on the gas the first time. For some reason, the new (clear) fuel line was weeping gas. I thought it must not be sealing properly, so I bummed some zipties off Mark Etheridge, who had graciously opened his shop (rented from Ducati Seattle, and literally a dozen feet from the dyno room) for us. One didn't seem to do it, so I put on a second. I turned on the gas, and instead of a weep, it was shooting a stream of gasoline at my face! I shut off the petcock, as I realized that the stupid tube must have split.

Exercising my excellent "sponge" skills, I asked Etheridge if he had any fuel line. He did, and let me use enough of it to get my carbs hooked up. It was nice Motion Pro line, much higher quality than what had been on the bike before. I owe Mark a cigar. But that solved the problem, and the bike was finally looking ready to try starting. It took forever to get all this done -- I had several people come over and ask me if I was rebuilding the engine or something.

So, I rolled the bike off the table (Mark has both a lift and a table with a ramp in his shop -- very nice!), and up into the alley. I spent the next ten minutes unsuccessfully running the bike up and down the alley behind Ducati Seattle, trying to get it to run. Finally, sweating profusely in the mild Seattle sun, I got it to fire off, although it didn't run that well, cutting out at full throttle.

Even though it had problems, when it was running correctly (ie, when I wasn't too aggressive on the throttle) it was shocking how much more power the bike plainly had. It tugged me back unexpectedly in first gear, with a much sharper pull than I'd ever felt before. I was entirely unprepared for it. Etheridge later said it looked like I was close to lifting the front wheel off the ground.

I rolled the bike back, and sat back in one of the provided chairs, glad of the cool warehouse air and the shade. Tamra and I and several others chatted for a while, and watched dyno runs through the soundproof windows. It was informative to watch the other bikes being put through their paces. I saw peak HP numbers anywhere from 11 to 16 that day.

I watched with particular interest as Jesse's bike was rolled up onto the dyno. His bike and mine are so nearly identical that his results (in particular his air/fuel mixture) would indicate the path I should take with setting up my new carbs. He ended up posting 14.4 HP peak, and no real problems with mixture, which was a relief. He was running size 98 main jets, which are the primary determinant of mixture. I had the size 100s in (we bought an assortment of jets for tuning purposes), which looked to be close enough to be worth a try. It'd be interesting to see what the difference was.

Finally, it was my turn to roll up on the dyno. We had some initial problems with the mixture reading, which may have been the position of the sensor (a long copper tube that's shoved unceremoniously up the bike's exhaust pipe). However, after a few tweaks, we started getting real-looking numbers, and things looked good. We saw a peak of 14.0 HP on one run, after tweaking the timing. However, further tweaks dropped the power back down to 12, so we ended up seeing 12 most of the time. By the end, the engine was radiating heat pretty fiercely despite the copious flow of air over it, so we rolled it off to cool down while someone else ran their bike.

As long as I was waiting, I pestered Bateman to see if he had spare 98 jets -- my sparkplugs were on the dark side after the dyno run, so I figured I might be able to go leaner for a bit more power. He had them, so I swapped the jets out. I have to say, swapping jets on the new carbs is remarkably easy compared to the old stock carbs.

The day was wearing on, and by the time it was my turn, Robert, our valiant dyno operator, had a certain limp-rag nature about him. He'd been up there, running puny-horsepower bikes on the dyno, for a full 8 hours, and asked if I could come back some other time. I still had dyno time coming, but he was wiped out. No problem, of course. A bit disappointing that I didn't get to see what the slightly smaller jets did, but that's alright. With my schedule, I probably won't be able to get back to the dyno for a couple weeks.

I have to say, one of the highlights of the day was near the end, when Bateman was in the dyno room with Tom Deem's bike. I had been casually watching the numbers scroll up, when I saw them approaching, then passing 15 HP, and keep going. A cheer went up from the crowd, and the bike topped out around 15.8, I think. Someone explained what was happening: Bateman was adjusting the timing on the fly, as the bike ran! That's a good way to do it, if you know what you're doing. It was impressive to see the peak power he got that way.

Overall, I can only call the day a success. The dyno was running a lot of the time, and lots of people came away with printouts of their bikes' power curve. I had a USB flash drive with me, so I actually have all the data files with me, although it requires a Windows computer to run, so you'll have to wait to see my charts (I know, you can't wait). I may be able to get those charts figured out today, though.

As usual, it was great fun to hang out with the vintage crowd; they're a group of excellent, kind people. It was also interesting to see the power other people's bikes were making in comparison to my own. Particularly with the new carbs, I don't feel too bad about my bike's ability to hold its own.

If you're keeping track at home, the peak HP we saw at Twinline was 11.81 HP. Subtract two to get the equivalent HP on the Ducati Seattle dyno, so 9.81 HP. The peak I saw on Saturday was 14.0, or more than 4 HP gain (over 40%!). I'd say those carbs were a fine investment! Maybe my lap times will reflect the change. We'll see on August 9th and 10th, the weekend of the next race.

Posted at 11:14 permanent link category: /motorcycle

Categories: all aviation gadgets misc motorcycle theater

Written by Ian Johnston. Software is Blosxom. Questions? Please mail me at reaper at obairlann dot net.