Making Progress!

Well, today felt a bit better. I was still suspicious that the pilot, needle and main jets were all related, so I did some fishing around in the ol' interweb. I bumped into a web page published by Factory Pro, a very reputable shop in San Raphael. They are one of (I believe) two motorcycle tuning shops in the entire Bay Area that tunes by Dyno! I am familiar with them, because I have bought parts from them before for my SV650S. Excellent quality and well thought out and tested stuff.

All the tuning tips pages I have read so far start with tuning from the bottom up- get your idle going, then mid-range and lastly WOT. Their method has you start with the main jets and then you work your way down, since the main jet has an affect on the way all the other ranges operate. This made total sense to me and it is what I had suspected. With their methodology, you do not go to the next step until you complete the current step, since the fatter jets play major parts on tuning the smaller jets. Also this tutorial had a blurb in there about adjusting the float heights, where no one else even breathed a word about that. I changed my floats from 23mm to 24mm, effectively lowering the fuel in the bowls by a smidge.

By the end of the day, I had my bike running well into the red line and pulling pretty substantially! Best of all, not a single plug fouled all day!!

The last range I worked on today was the idle range. I had been running the 30 pilot jets all day, so just for yucks, I swapped out and put in 27.5 pilots. Amazingly, the low range suddenly had a crisp snap and got off the line without dogging! How could this be?? I fiddled with the A/F screw and took my final test ride at 0.75 turns out, basically trying to richen the pilot close to as much as possible. The bike ran well with no real flat spots, and the rpm's would climb steadily. I took her on the freeway for a couple of miles. The bike ran easily at 65-70 mph @5500 rpm. But the engine just wasn't as powerful as I thought it should be. I'll have to work on that- maybe raising the needle one more position or going back to the 30 pilots- we'll have to see.

Anyway, it was a very encouraging day indeed. Tomorrow, I'll be taking Angie into Alan & Sons to have them take a look at my electrical, signals and brake light specifically. Once those are sorted out, I'll feel okay about taking the bike out at night. 

Trying to Keep Sane....

I'm just taking a few minutes to reflect. Building the bike was [somewhat] easy. Sure there were lots of little one-off problems to solve, as is with any "custom" situation. But having to tune carburetors goes to a whole new level!

2-stroke bikes are a completely different animal already, so we're already starting off at a disadvantage- everything has to be just perfect. Then there's the fact that these bikes have been around for so many decades and everyone has them set up differently! Ported cylinders, modified heads and higher compression rates, different air intake systems, expansion chambers, crossover tubes and bottles, reed cages, spacers, etc., not to mention differences in altitude, climate and fuel. So one bike's setup isn't going to be the same as another. And since these bikes are so old, if you've got a more rare pipe, it'll be harder to find someone with another to help you. Yes, there are plenty of forums and QA websites to help, and there are general formulas and methodologies to help get them dialed in, but in the end it's still your headache.

Plus when starting with a freshly built bike and something's not working right, it's not always easy to figure out what is the issue that's hold you back. Since the entire bike is a "system", one area/component can cause another to not function properly. i.e. if your electrical isn't functioning properly you may not get a spark, so the motor won't fire. Or more recently in my case, the head bolts weren't tightened enough, so I was loosing compression hence making it harder to start. So in order to work on one problem, you have to know that the other factors are working.

Last week, I did the famous Dave Feist carb mod (which is a refinement of the Dale Alexander carb mod), which basically reverts the "modern" RD carburetors back to the older R5 carburetors. As I understand it, the R5 carbs were using the primary-type needle jets and had amazing fuel flow. When the RD series came along, the bleed-type needle jets were employed, introducing better gas mileage and emissions. I bought the various Mikuni parts from EconomyCycle.com, as I already had some of the included items in their packaged kit. The conversion simply opens the air jet to 2mm by drilling out the brass ball, then swapping the bleed jet to primary, then swapping out the needle for a more compatible needle. So much fuel is free to flow that smaller main jets are needed that if using bleed-type jets.

I'm still in the process of tuning the carburetors. I just want to be able to pop wheelies like the bike's supposed to, and to know that if I take it out to the track or on a hard ride, the engine will be fine (not seize or foul out). And I know that if I can't figure, I can always bail and hand it over to BRG Racing to stick a sniffer up her ass and Dyno tune her.

Since the Dave F. carb mod, I'm feeling more confident about not hurting the engine (although now I hear ticking noises coming from the top end). I keep a long running Excel spreadsheet with all the different combinations of carb variables i have tried. For a while, the engine would keep dying on me when I take her out for test runs. After the first time, I just bring extra spark plugs with me, since the issue seems to be plug fouling. I'm still learning lots as I go and I'm not always sure what's happening to my engine. But as far as I can logically reason, if the bike dies and new plugs bring her back to life, then the plugs are fouling, which is most likely caused by a fuel mixture that is too rich. As long as the oil injector is working (and is hooked up), then the fuel is getting lubrication and the engine [in theory] shouldn't seize. I'm finally getting out on some longer test rides that demonstrate that the plugs are darker than they should be. I do believe that I have the pilot jets and needle positions figured out, so it's just the main jets now.

I'm constantly feeling that I may just have to resign the bike to a professional tune. But if I have to get the bike up to 500 miles on the new motor first, chances are good that I have effectively figured out the jetting anyway. I'm about half way there now on miles. We'll just have to see...