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[Geraintosaurus]

Hi all,

I have two questions about a 2000 Bullet 500, one regarding ignition timing and one about diagnosing a problem involving backfire.

So, question the first: I've been trying to set the ignition timing using the TDC tool from Hitchcock's. I insert the tool, put the bike in 4th and rotate the wheel through the compression stroke with the ignition on and hear the points separate at what I estimate to be about 1.5 mm before TDC. So I'm trying to get the piston to 0.8 mm before TDC as specified but I just can't get it to that accuracy. The stroke seems to be stiffer in some parts than others, and when I get to within about 1.5 mm from TDC it always seems to jump right to TDC or even through it to at least 1 mm beyond. It just seems impossible to get an accuracy down to a tenth of a millimetre. I've tried doing it with the decompression lever on. The way I'm doing it is holding the spokes and nudging the wheel forward a bit at a time. How is this possible?

Question the second is regarding some recent engine trouble. It seems to have occurred fairly rapidly after changing the oil but I'm not sure if it's at all related - changed it from whatever was in it when I bought it to Halford's 20w50 classic motor oil, and it was in need of a change. What's happening is that there's a lot of backfire in low revs - particularly when coming off the throttle to change down or up a gear. I think I can hear a light metallic tapping noise from the engine which is why I thought it may be an ignition timing problem but I haven't had the bike long enough to know whether that's just a normal engine noise I occasionally, much more rarely, get a misfire too. I inspected the points and they don't seem to worn. How can I tell if there's an incorrect knocking noise from the engine - what sort of volume would it be relative to idle?

Thanks in advance! G

[Geraintosaurus]

Balls - forgot to add in line spacing - apologies for the eyesore!

[stinkwheel]

It's very tricky to get the engine to stop so close to TDC using the back wheel, it's like trying to play crazy golf and stop the ball on top of a hill. The only way I've found of doing it reliably is with a socket on the end of the crank.



I usually set my timing at the fully advanced position using a small washer tool available from our hosts. You rotate the points cam to fully advanced then lock it in position by tightening the dished washer down onto it withthe central bolt. The engine spends most of its time with the ignition fully advanced anyway so this is the point you want to be accurate. Then you are setting it a good few mm before TDC (from memory, about 8mm, but check this). There is an article on setting the timing here: http://www.hitchcocksmotorcycles.com/pi ... -08-17.pdf



Incorrect timing can cause a backfire on the overrun as can an air leak at the exhaust or the inlet manifold (with it idling, spray some WD40 over the inlet manifold, if the revs increase, you have an air leak). I would also check the tappet clearances, a partially open valve can cause an odd clattering noise and backfiring.



Worth being aware that that ignition timing measurement is at best a guess. There is a huge amount of backlash in the system so treat your measurement as a starting point and try nudging it a little more advanced or retarded from there until you feel it's running at its best.

[Geraintosaurus]

Thanks for the response stinkwheel. That's the article I've been using but it says 0.8 mm, not 8 mm - hence the problem trying to get such a high accuracy. }BR

As I understand it, tappet clearance is set to zero when the engine is cold by checking that they can rotate but have no vertical play under finger pressure (as per this video: https://www.youtube.com/watch?v=4bmgJPyCUNU). Seems pretty simple if that's correct, will do it now! }BR

When you say "treat your measurement as a starting point and try nudging it a little more advanced or retarded from there until you feel it's running at its best", do you mean adjusting the timing with the engine running? Or just stopping and starting and loads of trial and error? If the 0.8 mm difference is about ten degrees as the article you linked to says, I guess I'll just change it in about two degree increments and see if anything improves. }BR

[Geraintosaurus]

Balls again, I have clearly misunderstood how to implement line spacings...

[stinkwheel]

I was meaning if the points cam is locked in the fully advanced position using the little washer widget, you would then set the timing point at (I just checked) 8.5mm before TDC. (it's in blue on that article.) Thte engien will tend to stop at this point more easily.



Some people do adjust the timing with the engine at idle (set it for the fastest idle) but I generally try moving it one way slightly then the other and see if it runs any better. In fairness, it seems to make very little difference where I set the timing point. As a general rule if it starts easily and doesn't "pink", you're winning. if it starts too easily, it could be too far retarded, if it's hard to start, it's probably too far advanced.



Yes, the tappets are that simple.



To do a line space, bracket the letters BR inside two chevrons. so this one < followed by BR then this one >. Do that twice for each line space.

[Chris [Stockport]]

Try this:



Where you want the break: Type < immediately followed by br followed again by >

Do it twice to get a bigger break. Good luck,

Chris

You can type an i instead of the br if you want to write initalics, like this is.

[Chris [Stockport]]

Stinkwheel: You beat me to it by 3 minutes!

Anyway, here's another Try b between the two chevrons to make it bold

[Geraintosaurus]

OK, so the tappets appear to be fine - setting the timing might have to wait for a bit so I decided to change the spark plug instead...and lo and behold another problem.



I refer you to this image, where the new spark plug and the old have different 'tops' and my cap doesn't fit over the new one - am I missing something? It looks as though the top might screw off on the new one but I can't see how to get it to do so without potentially breaking it. Or do I just need a new cap?



https://ibb.co/mtUJBc

Help is much appreciated - I'm aware I must be exasperatingly ignorant about all this.

[Geraintosaurus]

woohoo! At least I've learned how to make line spacings today! And italics? Maybe even boldface?