Backfires and kickbacks

mschmitz57 · Nov 14, 2014

Is the Power Arc firmware up to date?

I think early ones needed to be reprogrammed by Fred so they don't advance timing immediately after 1 revolution, and instead wait several revolutions. I sent mine to OB and Fred re-flashed it, but it still bites back on occasion.

comnoz · Nov 14, 2014

CanukNortonNut said:
+1 and I will add to this. When I talked to Old brits. Fred instructed me to not start the bike the usual way as per points or Boyer type EI with ignition on first.... e.g. key on, tickle , kick, kick till she starts. Instead.... ignition OFF...tickle carbs...bring to compression with kick starter...turn on ignition when you have reached the top of the compression stroke....and put the boots to her. This insures that the slots are counting without any chance for the engine to bounce back from reverse compression and continue to count slots in reverse. In other words this EI is counting slots regardless of which direction the crank is moving and its brains still thinks its going forward.
Try this routine.
Report back.
Cheers,
Thomas
CNN

I was getting ready to post this very thing.
And if it doesn't start with the first kick then turn the ignition off and get ready again before you turn it back on. You don't want any engine movement unless it is a serious kick. Jim

CanukNortonNut · Nov 14, 2014

comnoz said:
You don't want any engine movement unless it is a serious kick. Jim

Right on.

Fast Eddie · Nov 15, 2014

CanukNortonNut said:
comnoz said:

You don't want any engine movement unless it is a serious kick. Jim

Click to expand...

Right on. Sadly, artificial intelligence will probably never be a match for natural stupidity

The Tri Spark does have a protection against this aspect doesn't it?

olChris · Nov 15, 2014

Well, IMO your problem has everything to do with timing and because i forget critical thingies i have this picture flopping around on a clipboard.. Saves me stressing and can refer to previous headaches.. Regardless of what your electronic systems is, if it dont fire up at 30degres- ish static timing (then adjust when running to 28d@3000rpm. IMO for basic riding) Then something is wrong....

You can see the crude arrow indicators A and R direction that i have drawn on me plate.. Its not hard and i like to make it easy..

PS took me 3-4 days to realize that i was rotating the plate the wrong way............ not anymore..

But then theres plugs leads coils....................

MikeG · Nov 15, 2014

comnoz said:
CanukNortonNut said:

+1 and I will add to this. When I talked to Old brits. Fred instructed me to not start the bike the usual way as per points or Boyer type EI with ignition on first.... e.g. key on, tickle , kick, kick till she starts. Instead.... ignition OFF...tickle carbs...bring to compression with kick starter...turn on ignition when you have reached the top of the compression stroke....and put the boots to her. This insures that the slots are counting without any chance for the engine to bounce back from reverse compression and continue to count slots in reverse. In other words this EI is counting slots regardless of which direction the crank is moving and its brains still thinks its going forward.
Try this routine.
Report back.
Cheers,
Thomas
CNN

Click to expand...

I was getting ready to post this very thing.
And if it doesn't start with the first kick then turn the ignition off and get ready again before you turn it back on. You don't want any engine movement unless it is a serious kick. Jim

Absolutely #1 2 years on my Power Arc and it's stone reliable as long as you do this.

tomspro · Nov 15, 2014

comnoz said:
I have seen this problem many times now.

Here is what is usually the cause.

The power arc uses a fine tooth reluctor. The processor must count each slot in the wheel as it goes by. If it counts one too many slots, then it looses synch and will give a miss-timed spark.

When the timing chains is adjusted according to the manual then there is almost enough slack to enable the reluctor to move one tooth ahead as the cam goes over its peak lift. Any extra play in the chain, gears, or cam bushing will cause a tiny bit of extra rotation -just enough to move to the next slot. Then when the next cam lobe gets there the slack is taken up and the result is the processor counts one tooth twice. The result is a backfire or kickback.

When the engine is warmed up, then the timing chain will be tighter because the case expands and the problem will go away. Jim

This makes so much sense as to why it is fruitless to just keep kicking when it does not start first or second time.
If mine does not start after two tries, I turn off the ignition to reset it, get the kicker in position, turn ON the ignition and have at it.
The marriage of old machinery with modern electronics does not always go smoothly, and requires some grey matter plus muscle technique.
Still ... I saw definite improvements with less backfires when I retarded it from spec just a tad. Maybe I need a firmware update too.

Roadrash · Nov 15, 2014

comnoz said:
I have seen this problem many times now.

Here is what is usually the cause.

The power arc uses a fine tooth reluctor. The processor must count each slot in the wheel as it goes by. If it counts one too many slots, then it looses synch and will give a miss-timed spark.

When the timing chains is adjusted according to the manual then there is almost enough slack to enable the reluctor to move one tooth ahead as the cam goes over its peak lift. Any extra play in the chain, gears, or cam bushing will cause a tiny bit of extra rotation -just enough to move to the next slot. Then when the next cam lobe gets there the slack is taken up and the result is the processor counts one tooth twice. The result is a backfire or kickback.

When the engine is warmed up, then the timing chain will be tighter because the case expands and the problem will go away. Jim

I like the logic here. During my build I was advised and did adjust my timing chain looser than what the manual called for, to take stress off the system. Following this theory, that would make my bike more susceptible to skipping a slot on the reluctor.

Torontonian · Nov 15, 2014

Looks like you're going to be pulling off the Timing cover. This could be an opportunity to fit one of those hydraulic TC tensioners and be sure to use an idler support tool when tightening things up a little tighter ? :|

Roadrash · Nov 15, 2014

Torontonian said:
Looks like you're going to be pulling off the Timing cover. This could be an opportunity to fit one of those hydraulic TC tensioners and be sure to use an idler support tool when tightening things up a little tighter ? :|

Whats an idler support tool? is it a timing cover that's been cut away enough to measure chain tension?
May as well add taking the timing cover off for inspection to my winter list. 5 months till good riding weather again.

CanukNortonNut · Nov 15, 2014

Roadrash said:
Torontonian said:

Looks like you're going to be pulling off the Timing cover. This could be an opportunity to fit one of those hydraulic TC tensioners and be sure to use an idler support tool when tightening things up a little tighter ? :|

Click to expand...

Whats an idler support tool? is it a timing cover that's been cut away enough to measure chain tension?
May as well add taking the timing cover off for inspection to my winter list. 5 months till good riding weather again.

http://www.andover-norton.co.uk/News.htm
06-7325 Scroll down about one third of the items listed to see. If you do not have the money for the hydraulic tensioner then get an 850 tension slipper with the rubber pad and apply more pressure. The rubber will give a bit of cushion. I have got the hydraulic tensioner and like it. Set and forget. :wink:
Regards
Thomas
CNN

Roadrash · Nov 15, 2014

Thanks for that Thomas. I hadn't seen that tool before.

gripper · Nov 15, 2014

You can make something similar with a piece of steel or alloy plate, Drill and ream the hole for the idler gear spindle. locate the hole over the hole in the inside of the timing cover with a piece of similar diameter steel. ( I think I used a endmill shank) and spot the nearest holes through from the edge of the cover. Rocket science it ain't and timing covers are becoming scarce.

Onder · Nov 15, 2014

Andover offers a tool to hold the spindle. No longer a reason to trash a primary cover to make a tool.

CanukNortonNut · Nov 15, 2014

Onder said:
Andover offers a tool to hold the spindle. No longer a reason to trash a primary cover to make a tool.

Yes Onder :cry:
I paid more to trash a primary timing chain cover and modify to hold the spindle. I found out that the primary doesn't fit earlier bikes e.g. P11 or Atlas twins. Works only for commandos

Live and learn.
Cheers,
Thomas
CNN

Roadrash · Nov 15, 2014

gripper said:
You can make something similar with a piece of steel or alloy plate, Drill and ream the hole for the idler gear spindle. locate the hole over the hole in the inside of the timing cover with a piece of similar diameter steel. ( I think I used a endmill shank) and spot the nearest holes through from the edge of the cover. Rocket science it ain't and timing covers are becoming scarce.

I'm going to hijack my own thread since it's looking like it's about played out; something that I always thought was missing from any timing chain stabilization tool, be it a cutaway cover or that Andover tool, is that they only stabilize one gear out of two that deflect when under tension from the chain. It seems to me that both the idle gear AND the cam shaft gear would need to be stabilized to completely compensate for deflection. Maybe I'll make the first brace that stabilizes both gears and still gives access to the adjustment nuts. Some sort of big "u" shaped plate :idea:

Fast Eddie · Nov 16, 2014

Roadrash said:
gripper said:

You can make something similar with a piece of steel or alloy plate, Drill and ream the hole for the idler gear spindle. locate the hole over the hole in the inside of the timing cover with a piece of similar diameter steel. ( I think I used a endmill shank) and spot the nearest holes through from the edge of the cover. Rocket science it ain't and timing covers are becoming scarce.

Click to expand...

I'm going to hijack my own thread since it's looking like it's about played out; something that I always thought was missing from any timing chain stabilization tool, be it a cutaway cover or that Andover tool, is that they only stabilize one gear out of two that deflect when under tension from the chain. It seems to me that both the idle gear AND the cam shaft gear would need to be stabilized to completely compensate for deflection. Maybe I'll make the first brace that stabilizes both gears and still gives access to the adjustment nuts. Some sort of big "u" shaped plate :idea:

The cam is a different situation though, its a thick / heavy duty item compared to the spindle, its also much longer and supported at both ends. So you are unlikely to 'bend' the end much.
Basically, the cam is supported fully, as in normal use, with the cover off.

The spindle is thinner, and one end is totally free with the cover off.
Basically, the cover is an integral part of the spindles support during normal function. So, with it removed, and under torque from tightening, it may flex.

I'm unsure how much it matters though to be honest, anyone more knowledgable care to comment?

Roadrash · Nov 16, 2014

Thank you Fast Eddie. I didn't really want to make that thing anyway

Backfires and kickbacks

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