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Comet Timing on 4 star

youngjohn

Well Known and Active Forum Website User
Non-VOC Member
I'm lucky to live 50 yards away from a garage that sells ethanol free Bayford 4 star leaded petrol, so I run all my old stuff on it. I'll be fitting a BT-h mag over Xmas, and I'm just pondering on whether or not to retard the timing to 35 degrees (which you would do if you were using normal unleaded). Any comments welcome.
 

davidd

Well Known and Active Forum Website User
VOC Member
35 sounds as good as any. If your jetting is good the timing will not be a big issue. The new BT-H can vary as much as 9 derees ( at least mine does) with the rod in place when setting the timing. If the rod is slipped in the center of the armature (and threaded hole), you with be able to move the crank 4.5 degrees on either side of TDC as everything takes up the clearances. Because I was trying to do repeatable runs I needed to know more exactly where the spark was firing. I checked the timing with a strobe and found that after you slip the rod through the armature you need to move the wheel in the direction of travel to take up all the slack on the rod. On mine, this is where the spark was firing, i.e. not the 4.5 degrees earlier when the rod can slip in or out with ease. I do not think these numbers matter to you, but I mention them to urge you to pick a way of setting the timing that will be repeatable by you with ease. Then you will at least be consistent.

David
 

davidd

Well Known and Active Forum Website User
VOC Member
I have a Newby clutch so I just marked the engine sprocket. You can strobe a stock bike with the usual timing set up. If the bike is warmed up it will run without additional oil to the crank for the short time of the timing check. If you can buy or borrow the setup that will allow oil to the crank while timing, that is the safest. I have seen them mentioned elsewhere in the forum. It screws into the timing cover like the quill, but it is drilled to pass oil and has an "O" ring seal.

David
 

vincenttwin

Well Known and Active Forum Website User
VOC Member
I made up an bolt that fits into the drive side crank nut(lots of spare thread to do this) and this bolt has an smaller bolt in the end that holds the timing disc with an couple of large washers . you can run the bike, the only thing you have to do is take off the chain case cover. thats on a A comet .
 

davidd

Well Known and Active Forum Website User
VOC Member
Roy,

My point was that if the BT-H instructions are followed you will not know where the spark is occurring. I think if the ignition is non stock it is worth checking with a strobe to see where it is timed. If it is important to optimize the timing (and it is usually not important) it should be done on a dyno. This would also allow the bike to be tuned with the desired fuel.

I thought BT-H sold recently. Does "Geezer" still apply?

David
 
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