Backfires and kickbacks

I've never been able to get my bike to start reliably. Sometimes it's first kick, sometimes it's 12+ with a rest for my leg along the way. If it doesn't start right away there are always kickbacks and backfires that sound like a 12 gage shotgun. I've got an Old Britts Power Arc ignition that I've checked several times, setup is pretty idiot proof really. The carbs are adjusted to run well after the bike is running and any adjustment doesn't seem to affect how well it starts.
I originally installed the carbs without the chokes and just used the ticklers. I later installed the choke system and It doesn't seem to do anything except foul my plugs instantly.
I've tried many different startup procedures with no consistency. I'll do something like: prime both carbs, kick the bike over twice with the ignition off, prime one carb again and it will start on the first kick. Then the next day I do the same procedure and nothing. I've tried about every other combination I can think of with no real consistency. I've been looking for my magic startup procedure and perfect carb setup all season and haven't found it. The bike idols and runs fine once it warms up. pulls clean and strong.
Everyone I've talked to agrees the kickbacks and backfiring is not normal and if I can figure out what's causing that, the bike might start more reliably. Any input is appreciated.

My setup:
-71 750 with combat heads
-stock cam
-Power arc ignition
- New Amal 32 mm series 300 premiers. 220 main jet. using intake manifolds from an 850.
I was told recently to confirm I have carbs for a combat, not an 850. I don't know what the difference is yet. Anyone know?

Thanks Gents

Paul

First suggestion would be to double check ignition timing for proper advance with a strobe light.

Bob Z. said:

First suggestion would be to double check ignition timing for proper advance with a strobe light.

Click to expand...

strobe light not a good match for Power Arc ignition because of the design.

Paul - i have a similar setup and had starting / backfire problems - still do sometimes. but it is better since I re-checked the timing to be spot on with the LED on the Pawer Arc at TDC, then retard the timing by turning the timing wheel counter clockwise just a tad (couple degrees). Seems to have helped.
Also, my Combat (with new Premiers) is very sensitive to how much throttle I give when starting. No throttle when cold, about 1/8 when starting warm seems to work for me.

tomspro said:

Bob Z. said:

First suggestion would be to double check ignition timing for proper advance with a strobe light.

Click to expand...

strobe light not a good match for Power Arc ignition because of the design.

Paul - i have a similar setup and had starting / backfire problems - still do sometimes. but it is better since I re-checked the timing to be spot on with the LED on the Pawer Arc at TDC, then retard the timing by turning the timing wheel counter clockwise just a tad (couple degrees). Seems to have helped.
Also, my Combat (with new Premiers) is very sensitive to how much throttle I give when starting. No throttle when cold, about 1/8 when starting warm seems to work for me.

Click to expand...

Since the strobe pulls off the secondary (plug wires), I'm curious why the Power Arc can't be timed with a strobe.

I've had points, early Boyer, and Pazon and they all can be checked with a strobe.

Thanks

Roadrash said:

New Amal 32 mm series 300 premiers. 220 main jet. using intake manifolds from an 850.
I was told recently to confirm I have carbs for a combat, not an 850. I don't know what the difference is yet.

Click to expand...

The basic difference is the original 850 carbs would have had number [Edit]'3 1/2' slides, stepped 928/107 spray tubes and 928/104 4-ID ring needles, whereas 32mm 750 carbs had 3.0 slides, flat-topped spray tubes and 2-ID needles.

http://amalcarb.co.uk/rebuilding-mark-1 ... arburetter
"Spray tubes" & "Needles"

Im in your club I see. MkII 850, new premiers 3 slide 19 idle jet stock needle and jet. Altair ignition.
It can start first kick or not start at all. Once running and warm it is fine. Fine out on the road.
Will idle reliably forever.
But starting is just so unreliable. Ive tried every technique. Never had a brit bike that wouldnt start by
the third kick and most start right off.
Engine is fresh overhaul.
Also have Royal Enfield Interceptor with a tired motor new premiums and Altair. It also likes to kickback
but is a good deal less vicious. Ive been riding it more than the 850 because it will start and is stone reliable.
Who would ever think this? The bike that Norton put out of business bests the Commando!
Im at a loss.....

I cured my bike of the need for complicated starting rituals when I changed the original carbon HT leads for stainless wires. It wasn't the intent but the benefit quickly became apparent. Just a thought

tomspro said:

Bob Z. said:

First suggestion would be to double check ignition timing for proper advance with a strobe light.

Click to expand...

strobe light not a good match for Power Arc ignition because of the design.

Paul - i have a similar setup and had starting / backfire problems - still do sometimes. but it is better since I re-checked the timing to be spot on with the LED on the Pawer Arc at TDC, then retard the timing by turning the timing wheel counter clockwise just a tad (couple degrees). Seems to have helped.
Also, my Combat (with new Premiers) is very sensitive to how much throttle I give when starting. No throttle when cold, about 1/8 when starting warm seems to work for me.

Click to expand...

Is the green light indicator still on after you retard the timing? or are you setting the wheel just outside it's suggested range?

L.A.B. said:

Roadrash said:

New Amal 32 mm series 300 premiers. 220 main jet. using intake manifolds from an 850.
I was told recently to confirm I have carbs for a combat, not an 850. I don't know what the difference is yet.

Click to expand...

The basic difference is the original 850 carbs would have had number [Edit]'3 1/2' slides, stepped 928/107 spray tubes and 928/104 4-ID ring needles, whereas 32mm 750 carbs had 3.0 slides, flat-topped spray tubes and 2-ID needles.

http://amalcarb.co.uk/rebuilding-mark-1 ... arburetter
"Spray tubes" & "Needles"

Click to expand...

Thanks for that. I'll check it out.

Roadrash said:

Is the green light indicator still on after you retard the timing? or are you setting the wheel just outside it's suggested range?

Click to expand...

No - the light will be off. This was not recommended by Fred at OB, but it cannot hurt anything and easy to try. Just do not retard too much.

tomspro said:

i have a similar setup and had starting / backfire problems - still do sometimes. but it is better since I re-checked the timing to be spot on with the LED on the Pawer Arc at TDC, then retard the timing by turning the timing wheel counter clockwise just a tad (couple degrees). Seems to have helped.

Click to expand...

When turning the Power Arc disc counter-clockwise you will advance the timing, not retard.

Holmeslice said:

tomspro said:

i have a similar setup and had starting / backfire problems - still do sometimes. but it is better since I re-checked the timing to be spot on with the LED on the Pawer Arc at TDC, then retard the timing by turning the timing wheel counter clockwise just a tad (couple degrees). Seems to have helped.

Click to expand...

When turning the Power Arc disc counter-clockwise you will advance the timing, not retard.

Click to expand...

OOPS! I believe that is correct. Forgot.
Def do NOT want to advance for startup backfire problems. :mrgreen:

There have been prior reports of Powerarc slot wheel not fitting stable on cam taper so a special cone adapter was made sold that solved the mis fit timing. Don't have source handy but a search might find it before I or someone else can. I gave up on time lights and just dial back til don't backfire but don't know if practical on power arch supplied curve yet.

Holmeslice said:

When turning the Power Arc disc counter-clockwise you will advance the timing, not retard.

Click to expand...

In this view (thanks, Jim), the crank turns clockwise, which means the cam (and ignition) turns counter-clockwise through the timing pinion gear. Turning the backing plate counter-clockwise will retard the timing.

Nater_Potater said:

Holmeslice said:

When turning the Power Arc disc counter-clockwise you will advance the timing, not retard.

Click to expand...

the crank turns clockwise, which means the cam (and ignition) turns counter-clockwise through the timing pinion gear. Turning the backing plate counter-clockwise will retard the timing.

Click to expand...

With the Power Arc system, it's the 'encoder disc' attached to the camshaft that is turned to alter timing, and not the 'backing plate' as would be the usual way with most other types of electronic ignition, so as Holmeslice says, turning the Power Arc disc counter-clockwise advances the timing.

https://www.oldbritts.com/51_150101.html

Since you said any input is appreciated here goes. No poster has mentioned Battery health and tight connections including ground(s). Modern connectors ? Voltage ? :roll:

Ah crap tonto - smacking my forehead - realizing I got into wrong hobby keeping a thinking man's motorcycle.

Torontonian said:

Since you said any input is appreciated here goes. No poster has mentioned Battery health and tight connections including ground(s). Modern connectors ? Voltage ? :roll:

Click to expand...

always a good reminder, thanks, but those should all be ok

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

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

Click to expand...

+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
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