Points gap and timing.

[Oldfartaussie]

After top end rebuild bike runs great for a few day's then it will start backfiring on deceleration. Reset timing then it's good for a few more days?. I fitted the two green monsters and new plug leads and points and it starts easy ,runs great but loses timing after a few day's. I opened up the points gap to .o18 which reads about 35 on the dwell meter? But that has advanced the timing so far that the plate is retarded as far as it will go and it is still firing slightly early on both cylinders even after widening the adjustment slot in the timing plate to get more retardation. Still starts easy and runs well, a bit sluggish mid range. Looking forward to receiving boyer ignition in the post.

 

[RustiePyles]

After top end rebuild bike runs great for a few day's then it will start backfiring on deceleration. Reset timing then it's good for a few more days?. I fitted the two green monsters and new plug leads and points and it starts easy ,runs great but loses timing after a few day's. I opened up the points gap to .o18 which reads about 35 on the dwell meter? But that has advanced the timing so far that the plate is retarded as far as it will go and it is still firing slightly early on both cylinders even after widening the adjustment slot in the timing plate to get more retardation. Still starts easy and runs well, a bit sluggish mid range. Looking forward to receiving boyer ignition in the post.

I've had trouble with cheap Chinese points (thats all thats currently available) in my little Honda CJ360T. I had to take them apart and shim them, burnish the contacts, and properly lube them with some light weight grease. Seemed ok after that. But wandering timing can sometimes be caused by worn cam chain guides or a worn cam chain. Do you have lock washers on you breaker plate retaining screws? Try scribing a line across the breaker plate/head and see if it's moving.

 

[gggGary]

Those green monsters pull a pretty heavy load. Engine running watch the points in a darker room are they arcing "strongly"? I'm no guru but you may need to adjust the size of the condensers to more closely match those coils.

 

[Oldfartaussie]

I Fitted new cam chain and tensioner guide at rebuild so it can't be those and there aren't any lock washers on the points screws but when I check them they are tight. It started misfiring on acceleration and backfiring when decelerating on the way to work this morning so I will checking it all again tonight. I also fitted new Hitachi point's when I fitted the green monsters and they seem pitted already and I can't find my point's file, maybe the boss has been doing her nails. Can't wait for the boyer to arrive.

 

[5twins]

Pitted points indicate the condensers aren't matched well to the system.

 

[kopcicle]

Idle and 3,000 rpm timing are not the same. The Yamaha ATU is famous for curious failures.
Most often you will see just fine idle timing but seriously over advanced run timing. Give it a good look.
Curious , I don't remember having to open points much more than .014-.015"" to get sufficient dwell ...

The following was written for a 4 cylinder but it is essentially the same .

Well the manual doesn't do a very good job of explaining this so ...

Set one set of points to the proper gap and place a dwell meter on that set of points and take down the reading .
(doesn't really matter what the number is or how many cylinders because you are going to make the other set the same . Just pick a setting that gives you a reading around mid scale)

Now get the bike running and set the other set of points to the same reading .
Ok now the almost kinda tricky part . Connect a timing light to the bike and moving the entire breaker plate assembly place the timing mark (usually for 1 & 4 ) within the 1/8" or so that is the full advance mark .
You will notice that one set of points is "usually" solidly connected to the breaker plate assembly (again usually 1&4 but not always ) and the other set (2&3) will move not only in advance and retard but in gap also .
Switch the timing light to 2&3 and again place the mark in the 1/8" that is full advance .
go back and check dwell for both 1&4 and 2&3 . if the dwell and the timing is reasonably the same for each set within a couple of degrees you are done .

Again it's important to not exceed the full advance mark.

Photo credit and hand model Stormie Ray .

(there are unusual cases) . If the timing does not retreat to "T" mark but to a retarded position your ATU needs a serious look.

I'm no guru

Boy I'll say!

but you may need to adjust the size of the condensers to more closely match those coils.

And finally....

Testing Ignition Coil Wiring Reversal.

With the ignition off, engine off, pull a spark plug wire loose from a spark plug. Place it loosely back in place.

Now start the engine. Hold a no.2 lead pencil carefully in one hand. With the other hand, pull the loosened spark plug wire slowly away from the plug. You shoud see a good size spark jumping from the wire to the plug. Now... CAREFULLY place the sharpened lead point of the pencil into the path of the spark... you should see a "flare" of particles flying from the pencil lead TOWARDS the spark plug. If you see a "flare" of particles flying from the pencil lead TOWARDS the wire... you have the coil hooked up backwards. Remove the pencil lead from the spark path. Replace the wire. Shut the engine off, and re-reverse the coil low-tension wires and re-test. Get it right!

Why does this matter? If you got this wrong, you will be losing about 50% of your voltage at the spark plugs! Weak spark! Essentially, if the ignition low tension coil wiring is reversed, the coil will... "pull" spark, rather than... "push" the spark. Electrons prefer to leave a high-temperature (high energy) surface (like the center electrode of the spark plug) rather than a low-temperature (low energy) surface (like the arm of the spark plug). More voltage (more spark) is available if the electrons move in the correct direction, in the direction they prefer, from the high-temperature center electrode of the spark plug to the (relatively) low-temperature arm of the spark plug.

Oh yeah , I know I do this all the time but ,
Adjust the valves. If not gawd almighty will create another politician or kill a kitten.

 

[gggGary]

Testing Ignition Coil Wiring Reversal.

With the ignition off, engine off, pull a spark plug wire loose from a spark plug. Place it loosely back in place.

Now start the engine. Hold a no.2 lead pencil carefully in one hand. With the other hand, pull the loosened spark plug wire slowly away from the plug. You shoud see a good size spark jumping from the wire to the plug. Now... CAREFULLY place the sharpened lead point of the pencil into the path of the spark... you should see a "flare" of particles flying from the pencil lead TOWARDS the spark plug. If you see a "flare" of particles flying from the pencil lead TOWARDS the wire... you have the coil hooked up backwards. Remove the pencil lead from the spark path. Replace the wire. Shut the engine off, and re-reverse the coil low-tension wires and re-test. Get it right!

Why does this matter? If you got this wrong, you will be losing about 50% of your voltage at the spark plugs! Weak spark! Essentially, if the ignition low tension coil wiring is reversed, the coil will... "pull" spark, rather than... "push" the spark. Electrons prefer to leave a high-temperature (high energy) surface (like the center electrode of the spark plug) rather than a low-temperature (low energy) surface (like the arm of the spark plug). More voltage (more spark) is available if the electrons move in the correct direction, in the direction they prefer, from the high-temperature center electrode of the spark plug to the (relatively) low-temperature arm of the spark plug.

Yeah but all dual tower coils fire one plug "backwards"

 

[kopcicle]

^^^^^^^!!!!!!!!!

 

[gggGary]

He states recent new chain.

 

[Oldfartaussie]

Pitted points indicate the condensers aren't matched well to the system.

Thanks for the tip 5twins, the condensers are only a couple of months old. Stock one's that i fitted after the alternator rotor self destructed but the twin green monster coil supplier said were ok to use. I have never had this bike lose the timing every couple of days before installing the coils but the points would eventually get pitted after six months or so and I would just clean them up. So do I need to find condensers with a higher voltage?.

 

[5twins]

I read an article years ago that explained how to tell if your condensers were above or below the correct spec by observing which point face the pitting occurred on. Unfortunately I don't remember it, lol. But something else in that article was that if you have a good, well matched condenser, don't change it. It's very possible the new ones will be a worse match. They are manufactured with a tolerance range and some match up better than others.

I'm really not sure why your timing is changing on you so quickly, unless the points are pitting up badly enough to cause it. The spark jumps between the pits so the points gap grows as the points pit up. You can't accurately measure the gap on pitted points because of this. The gap will actually be larger than what your feeler gauge is measuring and telling you. That's why the only accurate way to gap used points is with a dwell meter. The dwell value for these bikes is given in the back of the factory shop manual. It's 93° ± 5°, or 88° to 98°. But that's on a 2 cylinder dwell meter, which I've never seen. Most of us are stuck using an automotive dwell meter set on the 4 cylinder scale, so we have to do some math. You have to divide the 2 cyl. value by 4, so on the 4 cyl. scale you'll read 22° - 24.5°. The reading you get on a dwell meter is inversely related to the point gap size. That means a smaller number represents a bigger gap. So, when I use it, I try to get the points as close to 22° as I can. This will give me the largest in spec gap.

 

[Oldfartaussie]

The lowest reading i have managed to get on the dwell meter is about 35 and that is after setting to .018 with the feeler gauges, and as you say the gap will actually be more because of the pitting. Also when I open the gap the timing light is intermittent. Think I will close the gap on the points today and reset the timing. The boyer ignition i have coming is a kit with double coil, leads, condensers and auto advance . So it's just a matter of perseverance etc.

 

[5twins]

Points gapped at .018" shouldn't read 35 on the dwell meter, they should read less than 22. Your meter may be screwed up. The points gap spec is .012" - .016". The dwell meter degree range (88° to 98°) should equate to that. A 22° readings should give about a .016" points gap, a 24.5° reading a .012" points gap.

As points wear, they usually close up. That's why I try and aim for the largest in spec gap. I figure that will give the longest interval between needed adjustments.

 

[Jim]

Point gap... the factory spec that is, is just a starting point... close enough if you're not using a dwell meter. Dwell is actually the better measure. Here's the routine I follow for a dual point twin.
Set both points to factory gap spec. That gets you close enough to run. Disregard if it already runs and hook up the dwell meter.
Now set the dwell on both sides . Ignore the gap... adjust to whatever it takes to get the correct dwell.
Setting timing is last... right side first, then the left (on an XS).
Something to remember...
If dwell increases over time (gap is shrinking), it means the the rub block is wearing down.
If dwell decreases over time (gap is increasing) it means the point contacts are eroding/pitting.

 

[Oldfartaussie]

The dwell meter is only a few weeks old which i bought after reading your post about gaping the point's and it sounded like a great idea and more accurate than the feeler gauges. Probably just operator error. I will regap today and see what reading i get on the dwell meter. I've gone about it backwards, buying coils and points then boyer ignition but if I pick up another xs I have plentiful of parts.

 

[Oldfartaussie]

Point gap... the factory spec that is, is just a starting point... close enough if you're not using a dwell meter. Dwell is actually the better measure. Here's the routine I follow for a dual point twin.
Set both points to factory gap spec. That gets you close enough to run. Disregard if it already runs and hook up the dwell meter.
Now set the dwell on both sides . Ignore the gap... adjust to whatever it takes to get the correct dwell.
Setting timing is last... right side first, then the left (on an XS).
Something to remember...
If dwell increases over time (gap is shrinking), it means the the rub block is wearing down.
If dwell decreases over time (gap is increasing) it means the point contacts are eroding/pitting.

I haven't been able to adjust the dwell with the engine running, as it will stall when I try to move the points. Faulty operator. I am about to have another go at it. Thanks for the help.

 

[Jim]

I haven't been able to adjust the dwell with the engine running, as it will stall when I try to move the points. Faulty operator. I am about to have another go at it. Thanks for the help.

The old GM distributors (and others) used a sliding door and a hex screw on the distributor. Was a piece of cake to adjust dwell while running. Our bikes ain't that easy. I shut it down, tweak the points, fire it up and see where I'm at. Rinse and repeat until I'm happy.

 

[5twins]

Yes, setting this dual points system can be a trying experience, lol. Not only are you setting two little separate ignition systems but then you're trying to match those settings to one another. Perfect setting is both points gaps matched as well as the timing on each cylinder. While I still had them, there were times I just threw the towel in and came back for another go in a day or two, lol.

 

[Oldfartaussie]

Just reset the points gaps to 013 after filing them lightly. Then set the timing with a test light, both were early so I set them both slightly late. I then started it up and the dwell was 22.6 on the right set and 21.9 on the left, tried the timing light and both are firing just past the F range. I am working 6am to 6pm for the next 6 days so hopefully it stays in tune and I won't have to do it all again after work. Thanks again for all the help.

 

[Oldfartaussie]

Ran great for a few day's then it started backfiring and the point's had closed up. Looks like I did not fit spring washers when I fitted the new point's, so I installed them and also noticed a 1-2mm side play in the advance rod and slight chamfering of on the outer edge of the point's lobe in two areas but not the entire circumference where the left set of point's pad rubs on the lobe. I installed a spare advance rod and lobe which removed the side play and the lobe has no chamfering on the outer face. Reset the point gaps to 016 with the feeler gauges, dwell meter showed both at 32/ 33. Gave up and started it, runs fair but when I went to turn the choke off I got shocked when my finger touched a bare section of throttle cable where it has been rubbing on the fuel tap??. Looks like i will be taking the fuel tank off tomorrow after work to find where the throttle cable is arcing?.