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...
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...
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