| Author | Message | ||
     General_ulysses |
My '97 S1 came with a V&H exhaust, a Mikuni HSR42 and a low restriction K&N type filter (circular canister with no forcewinder intake or anything). Otherwise it appears stock. I took the carb mostly apart and cleaned everything out with gumout (bike had been sitting for a coupla years). Replaced all the rubber manifold intake seals. Put fresh gas in and now have a few hundred miles on the bike. The bike runs strong, but stumbles and pops up through the carb quite a bit. Burbles and pops some through the exhaust on closed throttle decels. Problem is less severe once it's warmed up (yes I use the choke when it's cold). Exhaust smells a bit rich overall to me. I just swapped out the V&H exhaust with the stock muffler. It actually seems to run stronger now overall, but the popping, burbling and hesitation at lower rpms persists. I don't know if the bike ever ran correctly before, for all I know the guy just installed the carb and never bothered dialing it in. Like I said, it does run very strong other than the intermittent burbling, spitting and popping. Or, maybe I did something to it when I disassembled it and cleaned it? I've been working on bikes for close to 40 years and have cleaned and rebuilt my fair share of carbs successfully in the past. This one is a little different because of the flat slide design. I'm no supertuner or anything, so I doubt myself a little. The bike only has 6500 miles on it, I'm guessing the PO put it on shortly after buying the bike new (so not much wear on the carb). After I put the cleaned out carb on the bike and first put gas to it, it spewed gas through the overflow tube. I tapped on it with a screwdriver thinking the float/needle valve was stuck open. The overflowing stopped and I haven't seen it since. Any hints, clues or other ideas on where to start? I'd like to go into solving this problem smartly instead of repeatedly taking the carb on and off and blindly throwing parts and money at it. I did get a new pilot jet (size 25) for it, but haven't installed it yet. What do you guys think? Thanks in advance for any help. | ||
| Buellistic |
Check the jetting ??? (Message edited by buellistic on April 19, 2014) | ||
| Harleyelf |
Check the needle position? Center groove of the five is stock. Popping through the exhaust indicates that for some reason unburnt fuel is getting into the muffler. Maybe your cam position sensor is bad. If it runs well at high rpm, the issue is more likely in the fuel circuit. Got a good rigid mount for the carburetor or is it resting its weight on the intake seals? | ||
| Dannybuell |
get it dyno tuned. out of the box a mikuni is very rich. | ||
| Lynrd |
+1 on dyno tuning. After I had to change exhausts on Rhonda when the Supertrapp blowed up, the poor thing ran like crap with it's new Race muffler. I dragged it to JT&S, Fireman Jim dyno tuned it, and she nows runs like a scalded dog. Just a muffler change made a huge difference in the tuning. I've done tuning on Mikuni's on HDs and other bikes the hard way for years - ride the bike to a certain big ass empty parking lot on Saturday morning with two sets of tools and a jet kit strapped to the seat, put one set on each end of the parking lot, then dial it in per the manual, making high speed passes back and forth to compare settings. The guy I learned from had this methodology that I adopted: "Lean it out, lean it out, lean it out until you are about to hurt something, then go rich just one step from there". Frankly, yanking the carb on and odd the dozen or more times it takes to get one right just was not going to happen this time - so I fixed it with money, let a pro dial it in on the dyno, and could not be happier with the results. | ||
| Dave_02_1200 |
Mikuni publishes a tuning guide for the HSR 42. It is a good source of information and it is available free on the Mikuni web site. | ||
| Buellsrule |
The tuning guide is a pdf file online. Get a simple a/f digital gauge and start tuning. Mikiuni's are easy to tune and once tuned run as well as any fuel-injected Buell. I converted my X1 and it runs like a dream. Very easy to do. | ||
| General_ulysses |
Thanks guys. I've downloaded the tuning guide on Mikuni's website and have received a new pilot jet from American Sportbikes. Hopefully get the carb backfiring/hesitation/popping thing straightened out soon. |
