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Dead cylinder method
- Thread starter DaveO
- Start date
I haven't done the dead cylinder method yet on the 74 TXA but will at some point in the future. I have done it on a BMW airhead as the carbs are definitely non-linked since they are on opposite sides of the bike. One handy thing I learned on the Airhead List from member Snowbum was that BMW spoke nipples, and likely others, have the same thread as spark plug tops. You pull the boots off the plugs, install the nipple with a short length of spoke on the plug and put the boots on the end of the spokes. To kill the cylinder just take a suitably long insulated tool (I use a long plastic handled screwdriver) and short between the spoke and the cylinder head. Both wheels on the BMW needed new spokes as the originals were so rusty so I have many lifetimes supply of plug shorting tools on hand.
If someone has some Yamaha spoke nipples laying around they could verify that they thread onto the sparkplug.
If someone has some Yamaha spoke nipples laying around they could verify that they thread onto the sparkplug.
You'll get all sorts of suggestions for tuning carbs, the funniest ones are the ones who say they can tune carbs better by ear than any vacuum gauge or manometer. Whilst it is is true you can tune by ear, why the hell would you when vacuum gauges are so cheap or DIY manometers cost very little to make.
I made my own manometer which uses a fairly large volume of water so the readings are steadier than a looped tube. Watch the video, syncing is about 10 times quicker than in the video, this old fart got confused and turned the screw the wrong way a number of times.
I have VMs on my bike, but the process is the same with BS carbs.
Large volume of water, .08 jets in the vacuum tube, water level below half way ensure stable movement and the water doesn't get sucked into the engine.
I made my own manometer which uses a fairly large volume of water so the readings are steadier than a looped tube. Watch the video, syncing is about 10 times quicker than in the video, this old fart got confused and turned the screw the wrong way a number of times.
I have VMs on my bike, but the process is the same with BS carbs.
Large volume of water, .08 jets in the vacuum tube, water level below half way ensure stable movement and the water doesn't get sucked into the engine.
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I also recall clipping a jumper wire from the spoke to the head when I needed two hands for an adjustment, but you have to careful with that one as it's easy to get a finger too close to the clip and get zapped!
I've never tried it , but can you short a plug on a dual output coil? Seems to me shorting one side might kill the other side too.
Anyone ever try it?
Anyone ever try it?
I've done it with my Boyer, worked ok.
I tried the dead cylinder method as per the carb guide.
"Warm the engine to operating temperature, then raise the idle to around 1500 rpm. On bikes with breaker point ignitions, pull off a sparkplug cap. Electronic ignitions can be damaged by operation with an ungrounded ignition wire. To prevent that, shut down the engine, attach a spare sparkplug to a cap, ground the plug solidly on the engine, and restart. Adjust the throttle stop to hold lowest steady idle, then move the fuel screw 1/4
turn each way, seeking highest idle. When you find the direction of improvement, set the screw 1/8 turn in that direction from your starting point and again move it 1/4 turn each way. As idle rises, lower it with the throttle stop, as changes are easiest to detect at low engine speeds. Set the screw at the inmost (leanest) position that yields highest idle speed. (And yes, I know; some owners advocate finding the point where idle drops due to leanness, then the point where it drops due to richness, and setting the screw at the center point. I do not concur.) Repeat for the other cylinder."
But neither direction made any difference.
Broke out my ancient tachometer and discovered that although the timing had been manually set (Boyer Bransden - white dot visible at the full advance mark) adjusting the back plate so that at tick over the ignition was firing exactly at the 5 degree mark made the tickover speed increase considerably.
Back to the carbs, and despite getting to the point where it wouldn't start at all, it is now is a lazy one kick start, warm, and two kicks on the enrichener from cold. Comes off the enrichener much more quickly too.
But still it will not respond to the mixture screw.
So, is this a sign that the pilot jet too large, or too small? EX500 carb conversion.
Dave O
"Warm the engine to operating temperature, then raise the idle to around 1500 rpm. On bikes with breaker point ignitions, pull off a sparkplug cap. Electronic ignitions can be damaged by operation with an ungrounded ignition wire. To prevent that, shut down the engine, attach a spare sparkplug to a cap, ground the plug solidly on the engine, and restart. Adjust the throttle stop to hold lowest steady idle, then move the fuel screw 1/4
turn each way, seeking highest idle. When you find the direction of improvement, set the screw 1/8 turn in that direction from your starting point and again move it 1/4 turn each way. As idle rises, lower it with the throttle stop, as changes are easiest to detect at low engine speeds. Set the screw at the inmost (leanest) position that yields highest idle speed. (And yes, I know; some owners advocate finding the point where idle drops due to leanness, then the point where it drops due to richness, and setting the screw at the center point. I do not concur.) Repeat for the other cylinder."
But neither direction made any difference.
Broke out my ancient tachometer and discovered that although the timing had been manually set (Boyer Bransden - white dot visible at the full advance mark) adjusting the back plate so that at tick over the ignition was firing exactly at the 5 degree mark made the tickover speed increase considerably.
Back to the carbs, and despite getting to the point where it wouldn't start at all, it is now is a lazy one kick start, warm, and two kicks on the enrichener from cold. Comes off the enrichener much more quickly too.
But still it will not respond to the mixture screw.
So, is this a sign that the pilot jet too large, or too small? EX500 carb conversion.
Dave O
Sorry, I missed all those new posts.
@toglhot I've seen your video and love your manometer. Smart neat work too. I've two white wine bottles which might suit but I might splash out on some Perspex tube.
@5twins great tip on the uses for spokes. My Gunson tacho is so old it does not have the inductive sensor (it clamps around the HT lead) and instead has a spring type thing which is probably designed to work with a distributor cap but is useless with an XS650 plug and cap. It also provides a large area ideal for zapping you when you are trying to move the back plate. Ask me how I know.
The threaded part of the plug is 3mm so I'm on the lookout for some 3mm threaded bar or 3mm nuts and screws. Whatever I rig up is going to have some insulation (or at least something to keep fingers out of the way).
Thanks chaps. Hope it isn't as wet there as it is here.
Dave
@toglhot I've seen your video and love your manometer. Smart neat work too. I've two white wine bottles which might suit but I might splash out on some Perspex tube.
@5twins great tip on the uses for spokes. My Gunson tacho is so old it does not have the inductive sensor (it clamps around the HT lead) and instead has a spring type thing which is probably designed to work with a distributor cap but is useless with an XS650 plug and cap. It also provides a large area ideal for zapping you when you are trying to move the back plate. Ask me how I know.
The threaded part of the plug is 3mm so I'm on the lookout for some 3mm threaded bar or 3mm nuts and screws. Whatever I rig up is going to have some insulation (or at least something to keep fingers out of the way).
Thanks chaps. Hope it isn't as wet there as it is here.
Dave
But, you also must keep in mind that later E.P.A. mandated carbs like these don't show much change when adjusting their mix screws, not like older less pollution controlled carbs. On those older carbs, you go a little past the best running "sweet spot" in either direction and the idle speed drops off and the cylinder starts stumbling or running rough. That usually doesn't happen on later pollution controlled carbs. You may not see any change until the mix screw is nearly closed or way far open (like 4 or 5 turns). So, for tuning these later carbs by ear, I mostly go by plug color and use small throttle blips to test my setting. Get the setting too lean and the throttle blips will produce a hanging idle or lots of popping. Too rich will blacken the plugs.
@5twins That does make sense. I had problems with float levels and to cut a long story short gave up on the Kawasaki forum instructions (EX500 conversion) and set them both the same, using the clear tube method, and to, I thought, the gasket level. There was lots of trial and error involved.
Dave
Yes, that's what I had. I did try setting both to 1.5 and then both to 2 turns out. I've left them both at two turns as this seemed to give a slightly better throttle response. It now starts first kick warm or second kick cold. Blipping the throttle gives a good response. It ticks over rock steady.
I might call it a day and ride it around a bit more.
Dave
dlum515
XS650 Member
Alligator clips will make this real easy. I keep a sapre plug and a wire with alligator clips on each end to tune them with the dead cylinder method.
I always got twin SUs spot-on by ear, and checking with gauges didn't do any better. However, triple SUs on Jags, nope. Four carbs on bikes, nope. Gauges every time for them.
I've not bothered doing the XS carbs by ear, since the gauges are just sitting waiting to be used.
It will be interesting to try it though, to see if my hearing is still as sensitive as it was (probably not).
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