Friday, June 20, 2014

XS750 Project Part 24: Brakes Working but Engine...Not So Much

For the second year in a row, I tried to have the XS ready for the Ride for Hope, a charity ride in which I like to participate. The cruiser crowd is usually well represented at the Ride to Hope, with a few large-displacement touring bikes in attendance as well. My Strom is typically an odd duck on this ride, as the Ride to Hope usually conflicts with the Dust to Dawson ride, and the ADV crowd usually opts for the D2D. No surprise, since Hope is only 80 miles from Anchorage -- barely a warm-up for ADV types. However, 80 miles would be a good run on a cafe racer, and I'm anxious to show off the XS, so I've been busy swapping out parts and trying to get the XS finished up in time for Saturday's (June 21) ride.

First, I found a pair of front brake calipers on E-Bay for a reasonable price, and managed to swap the new seals and stainless steel pistons out of the original calipers into the new E-Bay brakes. After a false start (I ended up needing to disassemble the calipers and take a brake hone to the cylinder), I finally got a pair of front brakes that no longer leak -- a major accomplishment, considering how many ways I've tried to repair the old calipers first. I wasn't happy with the stainless steel brake lines that run from the splitter to the calipers themselves, so I also ordered slightly longer Goodridge brake lines, and new bleeder check-valves (supposedly, they only allow fluid out, greatly simplifying the task of bleeding the brakes).

I also reworked the tail/brake lights and turn signals. I ended up cutting a few inches off of the metal seat pan to stiffen up the tail light/plate mount, since the old one seemed a bit flimsy and was too easy to bend.

I also spent some time working on a fiberglass seat and cafe hump to fit over the metal seat pan. After sculpting a gorgeous, work-of-art cafe hump out of florist's foam (if I do say so myself, lol), and laying up a couple of layers of fiberglass over the foam, I test fit the seat on the bike, and noticed that the hump was way too high for the lines of the bike. Over the winter, I found a post over at Bike Exif that describes the lines that make a good-looking cafe racer. The seat hump I had designed violated both the "Height" and "Swoop" guidelines in that post. I'm at least as much a rebel as anyone else, but...there's a reason those guidelines work, lol. I ended up taking my Lowe's dozuki saw knock-off to the hump, cutting it down so that it no longer looks out of place with tank on the bike. Unfortunately, there's still more finish work to be done on the seat before it's even close to being done.

Next, I replaced the stock vacuum-operated fuel petcocks with manual parts from Mike's XS, which solved the problem with fuel leaking from the tank. After several test runs in the driveway, then a quick ride in my neighborhood, I was satisfied that the petcocks were no longer leaking, that the carb floats were set correctly, and that they shut off the flow of fuel to the carbs properly once the float bowls filled.

Despite a persistent problem with idle on the bike -- once it warms up, it idles at 3500 - 4000 RPM and I can't figure out why -- I rode the bike to work one Friday morning. It started acting a little odd while sitting in traffic at lunch time, but ran great on the way home a few hours later, making me think that the engine was just getting a little too hot while idling at 4000RPM with no airflow over the engine. It is an air-cooled engine, after all. I installed new NGK BPR7 spark plugs while troubleshooting the high idle, mucked around with the idle mixture setting and idle adjust screw, but the bike still idled at 3500+ RPM. After reading everything I could find on-line about high idle on a carbureted motorcycle, I decided to add some Sea Foam to the tank, and run the bike on the highway for a while. As you can see in this video, the bike ran like a champ...

...until it abruptly stopped running altogether. After sitting on the side of the road for 10-15 minutes, I managed to get the bike restarted and limped back about two miles towards home before it died again. This time, I couldn't get it to start again, and I haven't been able to start it since (grrr!!!)

So, back out to the garage and more troubleshooting. I connected my ohmmeter to the primary leads of each ignition coil and measured the resistance. According to the fine folks at Yamaha Triples, the primaries on the '77 XS750 should measure 4 ohms +/-20%. I measured 6.5, 5.0 and 6.4 on coils 1, 2 and 3 respectively -- that's 62%, 25% and 60% out of spec, respectively. Then, I measured resistance from the primary to the output of each coil. Per the spec, that should be 11K ohms (+/-20%), and I measured 10.4K, 10.2K, and 10.5K on each coil, which is well within spec. Just to verify my tests, I also tried sparking from a plug to the engine ground while kicking the kickstarter -- it sparked, but didn't seem particularly strong. After testing the coils, I ordered replacements and new spark plug wires from Mike's XS as well as new points and condensers from Bike Bandit. We'll see if the makes any difference, but for now -- for the second year in a row -- the XS isn't quite ready for the Ride to Hope, so I'll be riding the Strom again. But at least *it* has heated grips! :)