PlatinumGrit
23-03-2010, 12:05 PM
OK, I just recently picked up a used 1988 Honda Bros 650 a week ago, and having thrashed it a bit on the weekend, it needs a tune. I'm no stranger to the old tweaking the mixture on a carby on the old car, but, I'm having a hell of a lot of difficulty getting hold of the details for the carbies on this thing.
Back in the day, adjusting the mixture on the old LTD was simply a matter of revving the bastard, turning the mixture screw in increments until the black puffs out the exhaust went away. You then proceeded to drive it, and back off the mix a bit until you got a hint of ping, at which point you richened it up a tiny bit. Admittedly, it was a solitary single barrel stromberg with one fuel circuit, so hardly an art, but the theory remained the same when I put the 2 barrel w secondary circuit on some time later. (do we call primaries & secondaries 'fuel circuits' here in Aus? I think it's a yank thing?)
Anyway, it's been 14 years since I tuned a carby, and, it's been never since I had to synchronise 2 of 'em. I'll work it out, but, if there are veterans of the game on this forum, a few pointers would be welcome.
Specifically:
1. Carbs on the bike - what are they? How the hell can I find what's on there? (I've had a look for a service manual, but '1987/88 Honda Bros 650 is turning up very little)
2. How many fuel circuits? I can see the primary mixture adjustment screw, but the problem I'm having is when I get up in the rev range under full throttle where it would start drawing on the secondary (if it has a secondary) it's running so rich it's fouling the plugs and miss-firing like a bastard. If anything, I need to back the secondary off... then sort the primary.
Given the nature of old carbies like these, and the vibration inherent in a V twin, it's going to rattle out of tune after a day of riding, so tuning will be a fairly regular thing in my life. Getting it tuned every weekend is not feasible when I know I can tune the bastards once I get my head around 'em.
3. Synchronising the mixtures between the two. I'm a little stumped here; I could get one of those exhaust probes you stick in the tailpipe but that's not going to help as it measures the mix coming from both cylinders. It doesn't help me find the mix one particular cyl is getting. I could do the whole 'tune by ear' thing, but that takes time n patience and I'm an impatient man.
Does anyone know of resources online which can help me with the theory of synchronising fuel mixtures between carbies? I know, I could google myself but I'm getting smashed at work, and time's a bit of a precious commodity atm.
4. Synchronising the two carbs. I believe there's vacuum guage tools for this, and the service manual (which I am yet to find grrrrrr) should have info on adjusting the linkage. I think I'll also need an auxillary fuel tank to hook up while the guauges are doing their thing. Google has heaps of info on this, so I'm pretty sure I got this covered but any hints from those more knowledgeable than I are always appreciated.
Cheers,
-J
BTW, would anyone be interested if I were to post my findings once I work it all out? Is this a common item of interest? Or is everyone out of the stone age and riding fuel injected bikes?
Back in the day, adjusting the mixture on the old LTD was simply a matter of revving the bastard, turning the mixture screw in increments until the black puffs out the exhaust went away. You then proceeded to drive it, and back off the mix a bit until you got a hint of ping, at which point you richened it up a tiny bit. Admittedly, it was a solitary single barrel stromberg with one fuel circuit, so hardly an art, but the theory remained the same when I put the 2 barrel w secondary circuit on some time later. (do we call primaries & secondaries 'fuel circuits' here in Aus? I think it's a yank thing?)
Anyway, it's been 14 years since I tuned a carby, and, it's been never since I had to synchronise 2 of 'em. I'll work it out, but, if there are veterans of the game on this forum, a few pointers would be welcome.
Specifically:
1. Carbs on the bike - what are they? How the hell can I find what's on there? (I've had a look for a service manual, but '1987/88 Honda Bros 650 is turning up very little)
2. How many fuel circuits? I can see the primary mixture adjustment screw, but the problem I'm having is when I get up in the rev range under full throttle where it would start drawing on the secondary (if it has a secondary) it's running so rich it's fouling the plugs and miss-firing like a bastard. If anything, I need to back the secondary off... then sort the primary.
Given the nature of old carbies like these, and the vibration inherent in a V twin, it's going to rattle out of tune after a day of riding, so tuning will be a fairly regular thing in my life. Getting it tuned every weekend is not feasible when I know I can tune the bastards once I get my head around 'em.
3. Synchronising the mixtures between the two. I'm a little stumped here; I could get one of those exhaust probes you stick in the tailpipe but that's not going to help as it measures the mix coming from both cylinders. It doesn't help me find the mix one particular cyl is getting. I could do the whole 'tune by ear' thing, but that takes time n patience and I'm an impatient man.
Does anyone know of resources online which can help me with the theory of synchronising fuel mixtures between carbies? I know, I could google myself but I'm getting smashed at work, and time's a bit of a precious commodity atm.
4. Synchronising the two carbs. I believe there's vacuum guage tools for this, and the service manual (which I am yet to find grrrrrr) should have info on adjusting the linkage. I think I'll also need an auxillary fuel tank to hook up while the guauges are doing their thing. Google has heaps of info on this, so I'm pretty sure I got this covered but any hints from those more knowledgeable than I are always appreciated.
Cheers,
-J
BTW, would anyone be interested if I were to post my findings once I work it all out? Is this a common item of interest? Or is everyone out of the stone age and riding fuel injected bikes?