Re: 83 XT550 not starting!
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Re: 83 XT550 not starting! Albrecht via MotorcycleKB.com 08-03-2007
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Posted by Albrecht via MotorcycleKB.com on August 3, 2007, 9:10 pm
Gerrit wrote:
>and had some trouble figuring out how
>to set the crankshaft sprocket timing mark without removing the
>flywheel, but I find the spot. (same as the |T on the flywheel.) Now
>it just won't start any more.

Recheck your cam timing. The electronic ignition will fire a spark everytime
the crankshaft rotates the alternator rotor past the pickup coil, but you get
twice as many sparks as you need because the camshaft is rotating half as
fast as the crankshaft.

When all four valves are closed and the piston is around 10 degrees Before
Top Dead Center, that's when you need to get your spark. But you get an extra
spark when the exhaust valves are open with this system.

Anytime you remove the head, you want to remove the cam chain tensioner
before you pull out the camshaft, Then, when you reinstall the head, you line
up the piston to Top Dead Center, install the camshaft and camchain on the
sprocket and tighten everything down and the LAST thing you do is reinstall
the cam chain tensioner.

Otherwise, the tensioner will pull on the cam chain and pull the cam out of
timing.

>It some times puffs a few times as if it wants to go, but then dies.
>I thought it must be the compress being to weak to keep going. After
>every 5 or 6 try it will back-fire real loud into the exhaust (why?)

If you are getting a weak mixture out of the carbs, it won't fire the first
time the spark plug fires, but may fire after two or three four stroke cycles.


I tend to think that your camshaft may be out of time with the piston
movement though. But it's hard to say, considering that the ignition system
normally fires a waste spark when the exhaust valve is open.

--
Message posted via http://www.motorcyclekb.com


Posted by Gerrit on August 4, 2007, 1:30 pm
> Gerrit wrote:
> >and had some trouble figuring out how
> >to set the crankshaft sprocket timing mark without removing the
> >flywheel, but I find the spot. (same as the |T on the flywheel.) Now
> >it just won't start any more.
>
> Recheck your cam timing. The electronic ignition will fire a spark everytime
> the crankshaft rotates the alternator rotor past the pickup coil, but you get
> twice as many sparks as you need because the camshaft is rotating half as
> fast as the crankshaft.
>
> When all four valves are closed and the piston is around 10 degrees Before
> Top Dead Center, that's when you need to get your spark. But you get an extra
> spark when the exhaust valves are open with this system.
>
> Anytime you remove the head, you want to remove the cam chain tensioner
> before you pull out the camshaft, Then, when you reinstall the head, you line
> up the piston to Top Dead Center, install the camshaft and camchain on the
> sprocket and tighten everything down and the LAST thing you do is reinstall
> the cam chain tensioner.
>
> Otherwise, the tensioner will pull on the cam chain and pull the cam out of
> timing.
>
> >It some times puffs a few times as if it wants to go, but then dies.
> >I thought it must be the compress being to weak to keep going. After
> >every 5 or 6 try it will back-fire real loud into the exhaust (why?)
>
> If you are getting a weak mixture out of the carbs, it won't fire the first
> time the spark plug fires, but may fire after two or three four stroke cycles.
>
> I tend to think that your camshaft may be out of time with the piston
> movement though. But it's hard to say, considering that the ignition system
> normally fires a waste spark when the exhaust valve is open.
>
> --
> Message posted viahttp://www.motorcyclekb.com

So it actual does not matter if I set the camshaft upside down,
because it fires both sides(I tried both side and the bike sounds the
same, few puffs and die). I will open up AGAIN and put the chain
tensioner in after everything is in.

On the flywheel there are three marks, a 1 with a circle around it,
next a |-| sign and last the |t (dead top center), do you know what
the others are for. I will move the cam chain one chain link
earlier. My reasoning is if it fires little too early it will
ping(but go), but if it fires to late it will not start. Am I correct?


Posted by Albrecht via MotorcycleKB.com on August 4, 2007, 3:13 pm
Gerrit wrote:

>So it actual does not matter if I set the camshaft upside down,
>because it fires both sides(I tried both side and the bike sounds the
>same, few puffs and die). I will open up AGAIN and put the chain
>tensioner in after everything is in.

Did you take the camshaft sprocket off the camshaft at any point?

It looks to me like there is a punch mark on the sprocket that should be
straight up (in relation to the axis of the cylinder) when the piston is at
top dead center.

Then there seems to be a punch mark on the camshaft itself, so the mechanic
knows to align the cam sprocket to the shaft before tightening the bolts.

http://www.bikebandit.com/partsbandit/showschematic.asp?dept_id=653868

#1 camshaft punch mark?

#2 cam sprocket punch mark?

As the engine turns, the timing marks should line up every second turn of the
crankshaft, because the camshaft turns half engine speed.
>
>On the flywheel there are three marks, a 1 with a circle around it,
>next a |-| sign and last the |t (dead top center), do you know what
>the others are for.

One would probably be the static *ignition* timing and the other would be the
timing at some higher RPM, like 2000 or 2500 RPM when the electronic ignition
advance circuit in the CDI box allows the spark to advance.

Is there a hole in the side cover where you can shine a timing light to see
if the advancer is working?

>I will move the cam chain one chain link earlier.

NO! Don't move the cam chain one link earlier, you might bend one of your
valves when the piston hits it!

The camshaft sprocket has 30 or 36 teeth on it. One turn of the camshaft is
two turns of the crankshaft. So you'd be advancing the cam timing 20 to 24
crankshaft degrees.

>My reasoning is if it fires little too early it will
>ping(but go), but if it fires to late it will not start. Am I correct?

Well, the owner of a motorcycle shouldn't have to worry about tinkering
around with changing the cam timing when he does something as simple as
decarbonizing a cylinder and putting the parts back together.

Pinging shouldn't happen at all, but pinging doesn't occur until the engine
is hot.

If you have the timing marks aligned correctly and the mixture coming from
the carburetor is rich enough and you have the right heat range spark plug,
and you're using the right octane gasoline, the engine shouldn't ping.

Light pinging comes from carbon in the cylinder, overheated spark plugs,
excessively advanced ignition timing and lean fuel air mixture.

You can adjust the fuel air mixture in your carbs to reduce pinging to the
minimum, you can use the right spark plug heat range and you can check the
CDI box to see if the ignition advancer is working correctly.

If the fuel air mixture is slightly lean and the engine is running slightly
too hot,
pinging will cause small specks of carbon to burn on the spark plug noses.

The specks will look like tiny grains of pepper. The engine sounds like it
has a loose valve.

Really bad pre-ignition begins to melt the top of the piston. You see tiny
balls of melted aluminum sticking to the spark plug nose.

Then, if you keep running the engine hard when it's pre-igniting, the engine
will start to make horrible sounding groaning backfires before it melts a
hole in the piston.

http://www.sportbikes.net/forums/showthread.php?p=2848946&posted=1#post2848946


You might contact this guy to see what he knows about the XT550, he restored
one and got it running.

--
Message posted via http://www.motorcyclekb.com


Posted by on August 4, 2007, 6:05 pm
>> Gerrit wrote:
>> >and had some trouble figuring out how
>> >to set the crankshaft sprocket timing mark without removing the
>> >flywheel, but I find the spot. (same as the |T on the flywheel.) Now
>> >it just won't start any more.
>>
>> Recheck your cam timing. The electronic ignition will fire a spark everytime
>> the crankshaft rotates the alternator rotor past the pickup coil, but you get
>> twice as many sparks as you need because the camshaft is rotating half as
>> fast as the crankshaft.
>>
>> When all four valves are closed and the piston is around 10 degrees Before
>> Top Dead Center, that's when you need to get your spark. But you get an extra
>> spark when the exhaust valves are open with this system.
>>
>> Anytime you remove the head, you want to remove the cam chain tensioner
>> before you pull out the camshaft, Then, when you reinstall the head, you line
>> up the piston to Top Dead Center, install the camshaft and camchain on the
>> sprocket and tighten everything down and the LAST thing you do is reinstall
>> the cam chain tensioner.
>>
>> Otherwise, the tensioner will pull on the cam chain and pull the cam out of
>> timing.
>>
>> >It some times puffs a few times as if it wants to go, but then dies.
>> >I thought it must be the compress being to weak to keep going. After
>> >every 5 or 6 try it will back-fire real loud into the exhaust (why?)
>>
>> If you are getting a weak mixture out of the carbs, it won't fire the first
>> time the spark plug fires, but may fire after two or three four stroke
> cycles.
>>
>> I tend to think that your camshaft may be out of time with the piston
>> movement though. But it's hard to say, considering that the ignition system
>> normally fires a waste spark when the exhaust valve is open.
>>
>> --
>> Message posted viahttp://www.motorcyclekb.com
>
>So it actual does not matter if I set the camshaft upside down,
>because it fires both sides(I tried both side and the bike sounds the
>same, few puffs and die). I will open up AGAIN and put the chain
>tensioner in after everything is in.
>
>On the flywheel there are three marks, a 1 with a circle around it,
>next a |-| sign and last the |t (dead top center), do you know what
>the others are for. I will move the cam chain one chain link
>earlier. My reasoning is if it fires little too early it will
>ping(but go), but if it fires to late it will not start. Am I correct?
>
http://www.thumperpage.com/
go there, get the correct info and fix.

Posted by Albrecht via MotorcycleKB.com on August 4, 2007, 8:37 pm
someone@some.domain wrote:

>http://www.thumperpage.com/
>go there, get the correct info and fix.

Well, that was sure easy for *you* to type, but where's the answer?

--
Message posted via MotorcycleKB.com
http://www.motorcyclekb.com/Uwe/Forums.aspx/yamaha/200708/1


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