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Tuning motorcycle carburettors 6
- Thread starter Brett43
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It has been a very long time since I played around with either bikes or carbies.
But by far the fastest and easiest way to synchronise four throttles is by eyeballing four mercury columns side by side. Very easy to make a multiple manometer. Once you have tried this, you will never do it any other way.
But by far the fastest and easiest way to synchronise four throttles is by eyeballing four mercury columns side by side. Very easy to make a multiple manometer. Once you have tried this, you will never do it any other way.
Well, I guess proper instrumentation will be necessary for the vast majority of builders/tuners...can't fault that.
I've been at it a while and, yes, I have two water and one mecury manometers. The home made one is easiest to use and the mercury one is for fuel injections, it's not sensitive enough for carbs. Sorry to say, I still stick a piece of tubing in my ear and listen to the 'hiss'. Faster, just as accurate and pretty cheap. It's a learned skill...if you can do it, it's accurate. This method is just one of those tuning aids I learned before we all had to have computers and such. Some of this new hi tech stuff (not a manometer, I built my first one in 1957) that's necessary to keep modern cars on the road are great, don't get me wrong on that. I'm just getting to old to learn all these new methods. Guess I'm still stuck in the '80's.
Rod
I've been at it a while and, yes, I have two water and one mecury manometers. The home made one is easiest to use and the mercury one is for fuel injections, it's not sensitive enough for carbs. Sorry to say, I still stick a piece of tubing in my ear and listen to the 'hiss'. Faster, just as accurate and pretty cheap. It's a learned skill...if you can do it, it's accurate. This method is just one of those tuning aids I learned before we all had to have computers and such. Some of this new hi tech stuff (not a manometer, I built my first one in 1957) that's necessary to keep modern cars on the road are great, don't get me wrong on that. I'm just getting to old to learn all these new methods. Guess I'm still stuck in the '80's.
Rod
On a side note, I glued some plastic dowel rod to the underside of my 1150 Suzuki's CV carb tops to fill up most of the cavity above and in the slides. I theorized that engine vacuum has to empty out the slide cavity each time you wick the throttle..
The dowel rod was small enough to fit inside the return spring(s).
Just as on my non-CV carb applications, low speed throttle response was increased dramatically, and the increased vacuum/flow signal over the needle jet required going one size leaner on the pilot jet.
It's worked on every bike I tried it on. The hole/slot in the bottom of the slide on non-CV bike carbs reduces signal strength over the needle jet.
On non-CV carbs I just put a rubber flap cut from an inner tube over the needle plate and let the return spring hold it in place.
The dowel rod was small enough to fit inside the return spring(s).
Just as on my non-CV carb applications, low speed throttle response was increased dramatically, and the increased vacuum/flow signal over the needle jet required going one size leaner on the pilot jet.
It's worked on every bike I tried it on. The hole/slot in the bottom of the slide on non-CV bike carbs reduces signal strength over the needle jet.
On non-CV carbs I just put a rubber flap cut from an inner tube over the needle plate and let the return spring hold it in place.
Kevin Cameron in his Sport Bike tuning book describes that one of the adjustments available on CV carbs is the size of the port/vent connecting the carb throat to the vac chamber. I think the sequence was if the slide rose slowly an enrichening effect similar to an eccelerator pump was obtained. Whilst riding It's mighty hard for me to know the height of my 3 CV slides at any throttle position/rpm, and thus to know what section of the needle needs attention. With my old Mikuni VMs a series of marks on the twist grip make it clear where the slide is. I think the dyno would allow peeking in the carb throats to see how far it is open at a particular rpm and load.
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