Popping back through the carbs

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Tin Man

Tin Man

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I can't get my bike started. This is what has been done:
1) It has a Pazon ignition system
2) Two new 6 volt coils
3) TDC was checked with a dial indicator to set the valves and the timing at 28 degrees before top dead center.
4) Wet and dry compression tests were done. There is a cylinder imbalance of 10 PSI. 120 lbs in the left and 110 lbs. on the right with the wet test.
5) New spark plugs (checked to see if they fire when kicked)
6) New Premier carburetors
7) Fresh gas

It pops back through the carburetors when kicked and will not start. Help me! I'm drowning.
 
Line up the mark on the alternator with the 29 degree mark on the timing scale, then check to make sure the dot on the ignition rotor is centered in hole in the plate for ccw rotation. You don't have to worry about which cylinder is on compression as the Pazon is "lost spark" and fires both coils at once. Hopefully it will start and you can strobe it. How is the battery? In my experience you need at least 12.4 volts at the battery to get the Pazon to cooperate.
 
I had similar symptoms when I inadvertently set up my Pazon using the wrong timing mark on the rotor. There are two marks, 180 degrees opposed. When I reset using the correct mark, it fired up first kick!
 
Sometimes a spit-back through the carbs is due to a cold motor which has previously been set to idle perfectly without the choke. The choke on some Amal carbs can be pretty crude. Mk2 Amals have enrichers., rather than something which moves down to decrease the slide cutaway, in effect.
 
dobba99 said:
classic mistake of using the wrong timing mark
Click to expand...
Does it spit back through the carbs a few times when the motor begins to run - or does it actually backfire through the carbs or exhaust, when you try to kickstart it ?
 
SteveC said:
I had similar symptoms when I inadvertently set up my Pazon using the wrong timing mark on the rotor. There are two marks, 180 degrees opposed. When I reset using the correct mark, it fired up first kick!
Click to expand...
I'm having the same issue. All new as above only Tri-Spark EI. Just curious how the wrong timing mark could be the mistake if a dial wheel was used to find TDC and set at 29 degrees? Rotor was then marked so there would be no confusion which mark to use.
 
Two things jump out.
1) I rarely had this sympton with the old Boyer.
2) Since fitting the Pazon Altair 4 years ago, if the starting technique isn't perfect, like beginning with an engine just past TDC, and the most robust kick & follow through I can give it, it will backfire through the carbs. Much to the chagrin of the starter pawl, and even bent the kicker pedal.
Personally, I think Pazon's "idle stabilization" circuit is a failed design. The cure is worse than the ailment.
 
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acotrel said:
Does it spit back through the carbs a few times when the motor begins to run - or does it actually backfire through the carbs or exhaust, when you try to kickstart it ?
Click to expand...
It wont start. It just pops back through the carbs. I futzed with it for about 6 months before giving up and taking it to Butch Harper at TriStar motors. He checked my work on the valves, carbs and timing. He is having the same problem of popping back through the carbs when booting the engine.

Fast Eddy, it's never run well. I bought the bike two years ago from a dude who lived North of Philly. When purchased, it started and idled well, but wouldn't rev past 3500 rpm, It would stutter at speed. I wanted new Premiers anyway, so I put them on. It started and the idle was silky smooth, but that still didn't fix the problem of not reving beyond 3500 rpm.

So, I reset the valves and started fixing other problems with the machine: including replacing loose electrical connectors and the coils.

At this point, I'm thinking that Concours may be right and that the Pazon has to go or it has a weak battery.
 
Which Pazon do you have? Yes, the Pazon Altair will kick back as concours mentioned (if weakly kicked), but the standard Pazon ignition should be fine.
Not revving over 3500 sounds like the chokes are on or partially on or maybe a clogged or oil soaked air cleaner element.
A good battery is a must.
 
Dial indicator to find TDC, then a degree wheel to set timing at 28 degrees BTDC. Ignition rotor runs counter clockwise on a Norton Commando.

Nice thing about TriSpark ignition is the LED lights up when the spark plugs should fire. Kind of hard to do wrong unless not using a degree wheel to verify everything initially.

Another thing not mentioned often that can make the engine hit a wall early is a poorly functioning breather setup. I've experienced it. A flat cam could do it as well. I have no experience with a flat cam though. A restricted 2 into 1 exhaust can have poor top end performance, but 3500 RPM is not that close to top end.

Backfiring in the carburetors can have more than one cause. Weak kick, too lean, retarded ignition, way out of sync. I would verify the timing with a degree wheel and get a new battery before replacing the Pazon. If you want to give TriSpark a go, contact Greg Marsh
 
batrider said:
Which Pazon do you have? Yes, the Pazon Altair will kick back as concours mentioned (if weakly kicked), but the standard Pazon ignition should be fine.
Not revving over 3500 sounds like the chokes are on or partially on or maybe a clogged or oil soaked air cleaner element.
A good battery is a must.
Click to expand...
Good point about the choke
Lots of people mistakenly use the choke wrong
It's tight cable for off
Slack for on
 
baz said:
Good point about the choke
Lots of people mistakenly use the choke wrong
It's tight cable for off
Slack for on
Click to expand...
The cables function properly and the choke opens and closes.
concours said:
You've had the pipes & mufflers off, no mouse nests, correct?
Click to expand...
baz said:
Good point about the choke
Lots of people mistakenly use the choke wrong
It's tight cable for off
Slack for on
Click to expand...
I'm trying to start it without the air cleaners
 
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acotrel said:
Sometimes a spit-back through the carbs is due to a cold motor which has previously been set to idle perfectly without the choke. The choke on some Amal carbs can be pretty crude. Mk2 Amals have enrichers., rather than something which moves down to decrease the slide cutaway, in effect.
Click to expand...

The engine should, however, start using just the ticklers. Many owners remove the choke assemblies because they are found to be unnecessary except perhaps in colder climates. The apparent problem here is that the engine simply won't start.

The chokes are more useful after the engine has started when the high carb fuel level from tickling drops back to normal until the engine has begun to warm up.
 
What Throttle setting are you you using during starting?


Also, what do the spark plugs look like? Dry? Wet?

"It wont start. It just pops back through the carbs. I futzed with it for about 6 months before giving up and taking it to Butch Harper at TriStar motors."
What is your skillset? Is TSM a Britbike specialist?
 
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L.A.B. said:
The engine should, however, start using just the ticklers. Many owners remove the choke assemblies because they are found to be unnecessary except perhaps in colder climates. The apparent problem here is that the engine simply won't start.

The chokes are more useful after the engine has started when the high carb fuel level from tickling drops back to normal until the engine has begun to warm up.
Click to expand...
When it was starting, it was needing full choke, even on warm days.
 
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