Timing question

[funky]

Hi all hope yo are well
I have a question with regards to timing.
I have a Pamco fitted with standard ATU and stator 360 degree engine 533 conrods.
The book says that timing is set at 15deg BTDC does the and that when using the timing gun the ignition should fire between the "F" marks . The F Mark is at 15deg BTDC so if you have a timing gun with an advance feature you should set it on 0 deg not on 15 deg, is that correct.
all the best Funky

 

[pamcopete]

Timing guns with an advance feature are not reliable for use with a wasted spark dual output ignition such as we have on the XS650. Set the preset advance to zero ( 0 ) and use the "F" mark.

 

[funky]

Thanks Pamcopete I thought that would be the case as i was in my friends garage yesterday and he said that you have to set the gun to 15 deg then check the timing . my Gun at home has not got the advance feature and i can see the "F" mark is physically around 15 deg Before TDC based on the rotation of the engine anti clockwise.
My friend works in the body shop so he can be forgiven but he was trying to convince me that he was right .
Thanks again Funky

 

[5twins]

The idle timing spec is actually given as about a 5° range, 13°-17° BTDC .....

The long slash mark next to the "F" is the 15° mark, the smaller slashes on either side represent the 13° and 17° range limits. Many of us set our timing slightly retarded, over near that right 13° slash mark. This wards off pinging in hot weather and I actually think the bike runs a little better, stronger at high RPMs. This "range" spec is also a way to compensate for an advance unit that is wearing and possibly over-advancing a little bit. Do be sure to check your timing at full advance to make sure that's not happening.

 

[funky]

Thanks 5T great information many thanks.
The Bikes almost run in so want to make sure all is perfect
All the best Funky

 

[funky]

I set the timing at the 13degree mark well to the right of the "F" mark and the bike runs well took it for a 5 mile run it felt a bit more torquey felt good will run it at these setting need to do about another 100 mile to finish running in the big bore kit .
Many thanks again Funky

 

[5twins]

The only issue I encountered when I retarded the timing like that was that the idle got a little "lumpy" and the idle speed dropped off a little. The solution was simple, just turn the idle speed up a touch, lol, and I rather like the "lumpy" idle sound.

Now, you may think you're running your timing at a more retarded setting but in reality, you're not. The timing spec on these when they first came out was different, 10°-15° BTDC for idle timing. So, at 13°, you're actually right in the middle of that old spec.

 

[pamcopete]

The idle timing spec is actually given as about a 5° range, 13°-17° BTDC .....

The long slash mark next to the "F" is the 15° mark, the smaller slashes on either side represent the 13° and 17° range limits. Many of us set our timing slightly retarded, over near that right 13° slash mark. This wards off pinging in hot weather and I actually think the bike runs a little better, stronger at high RPMs. This "range" spec is also a way to compensate for an advance unit that is wearing and possibly over-advancing a little bit. Do be sure to check your timing at full advance to make sure that's not happening.

5twins,
I think that spec was to accommodate the original two sets of points due to the near impossibility of ever getting both sets right on. The TCI has just one sensor, so both cylinders will be the same. The PAMCO ignition has two sets of two magnets with one magnet in each set acting as the trigger so there is a small possibility that there could be a very small difference which would show up as two flashes from the timing light very close together. You may also see two or more flashes from the timing light if you select the positive spark plug wire instead of the preferred negative wire. The dual output coil produces a positive voltage on one of the spark plug wires and a negative voltage on the other. There is no easy way to determine which is which, so if you get an erratic result or no flash at all, try switching the clamp to the other wire, or simply reverse it.

 

[funky]

Thanks Chaps I had the drop in Idle speed but just increased the idle back to 1200 all seems to be running fine no pinking lots of power right through the gears the only issue is i thinks i need to get a smaller rear sprocket as there is a 33 tooth on at the moment probably try a 31or even a 30 not sure yet as i have not tried full speed but have took the revs up to about 7k today for a few seconds i have done about 450 miles so i thought it would not hurt.
All the best Funky

 

[5twins]

Pete, the idle timing "range" spec may very well have something to do with the dual points but I think advance unit wear was another reason for it. The advance unit is made to advance the timing a specific, set amount, 25° when new. As it's parts wear and loosen up, the amount of advance it delivers can begin to grow (26°, 27°, etc.). To get both idle and advance timing in spec, there needs to be some leeway in the setting at one end of the timing curve or the other. Yamaha put that "range" in the idle spec. With it, you can set the timing so it won't go past the 40° full advance mark and still be "in spec" at idle.

Funky, I feel a 33T sprocket is ideal on an 18" wheel but not so much on a 16" one. A 32T works better on the 16". Keep in mind that you're only dealing with about a 50HP bike here. Gear it too high and you'll lose most of the take-off performance, and it won't pull redline in top gear either. And I feel anything smaller than a 32T is too high, unless maybe you weigh something like 130 lbs soaking wet, lol.

 

[funky]

Well i wiegh 145lb dry lol like i said i will try a speed test once i have done the oil change and oil filter at 500 miles i will red line in all the gears and see what top speed i get . Any prediction would be fun i supose lol

 

[5twins]

Well, doing the math gives 113.6 with a 33T on a 16" wheel. As you can see, a 32T on the 16" wheel is very close to what a 33T gives you on an 18" wheel, and like I said, I consider the 18"/33T combo just about ideal for this engine's power output .....

 

[5twins]

Keep in mind, the above chart is just showing math calculations. I wouldn't expect this 50HP engine to pull an 18T/29T sprocket combo on a 16" wheel to redline in 5th or to that 136.9 MPH, it's just not powerful enough.

 

[funky]

Thanks for the chart that was intresting.
Remember i have fitted the big bore kit so this obviously increases my horse power. Probably more to 60HP but can't be sure.
My limited knowledge on this, is one tooth on the front equals 3 on the back.
I have a mt90 rear tyre obviously on a 16" wheel.
my goal is the 100 MPH " the Ton" as they say over here ...
Many Thanks Funky

 

[5twins]

I think it's closer to 1 tooth on the front equaling 2 teeth on the back (34 ÷ 17 = 2). Any of the combos in the chart should give you "the ton" if the motor will pull them. Mine does it with an 18"/33T rear and 17T front no problem.

If you gear these bikes too tall, you kill their "fun factor". They have wonderful midrange power and give a very satisfying "lunge" forward when you whack the throttle open in the lower gears. Gear them too high and you lose a lot of that. Your 650 will feel like a 350, lol.

I do think these bikes benefit from a gearing change, but only a very small one, 1 or 2 teeth on the rear. I'm not a fan of changing the front. Space is very limited up there under that front cover and the larger 18T sprocket can create clearance issues. I don't feel it's necessary because you can achieve pretty much the same ratios just by changing the rear.

 

[funky]

Thanks 5Twins
I will probably go to a 32 if i need to , but i will see what i get with whats on at the moment which is 17/33.
All the best
Funky

 

[pamcopete]

Here is a Excell spreadsheet that will yield MPH for RPM for any combination of gears, sprockets and wheels. It uses the rolling distance for these calculations. Rolling distance is the distance that you bike will roll forward for one revolution of the rear wheel. This is necessary as it is impossible to calculate the RPM vs MPH using either the circumference or diameter of of the tire as a motorcycle tire has an infinite number of circumferences due to its circular cross section.
www.amckayltd.com/xs650revs3.xls

 

[funky]

I looked at this i think i will go 31rear for two reasons 1 I want good top speed and with the big bore kit i am in fifth gear at 40mph if i want..... loads of torque ... 55mph 4000rpm
2 I have an MT90 rear Tyre and they ride really close to the swing arm with a 33t rear so its an extra link on the chain or smaller rear sprocket will ease that issue.
If the 31 is not right I will get a 32
All the best
Funky

 

[gggGary]

running a 750 on 17-33 and might go to 32 next (aluminum) sprocket don't think I would go 31. Put 2K on this set up so far with mostly state roads but a few hundred miles of freeway.

 

[funky]

Hi chaps got a problem ran the engine in 500 miles took it easy then did some speed runs the bike went well top speed 105mph first run did a few more around the same speed ,,,,, then this happend l need a new cam shaft as the ATU stripped the threads, i was doing about 90mph and ATU exploded looks like a catastific failure of the part. I will also fitting a new ECB clutch and springs as they are worn. The Gods of speed needed a sacrafice again
I think one of the weights came off and jammed in the cup the engine over reved and then it sounded like a coffee grinder i stopped and the engine was running fine so i was about a mile from home and i road thye bike back in first gear lol .
Pain is i have to pull the engine to change the Cam shaft .
All the best Funky