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Pan missfing under load

4K views 26 replies 19 participants last post by  CheaterPY 
#1 ·
Hello gentlemen,

After several weeks of tuning my Pan, I still got the missfiring problem under load.

The bike ran like a champ for two years without any trouble and then started to lightly missfire on the highway.

I have changed the point (I have tested 2 new ones), condenser and weight springs of my ignition system, which as been just fine for 100 miles. Then it's been worst and worst with more and more missfirings and backfires.

I then have changed the coil (teste three differents units), plugs, plugs wires, I have tested for inteake leaks, I have tested the battery, checked the push rods. But nothing cured the missfiring.

The only trick is when I clean and sand the points, the bike runs perfect for 10 miles and it's back to the mad swinging machine. The bike is also runing good at low rpm and start on first kick even cold or hot.

What am I missing ?

Thanks ind avance for your thought
 
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#3 ·
Sounds like it may be the wrong ohm coil. If you are running points, you need the 5 ohm coil. If you have the 3 ohm one, it will burn up the points, and after you clean the burning/arc off the contacts, it runs until it overheats them again. Eventually, it will melt them, or turn the arms blue from heat. Not to mention, allowing the arm to bend, causing the points to be to wide. That is, if this is the real problem.

To eliminate the motor as the problem, do a leakdown test cold, and then hot. It could be a slightly sticking valve. If it pops out the intake, or exhaust, will tell you which one to inspect, if necessary. But my money is on the wrong coil.
 
#4 ·
Thanks for the input guy.

The new coil is 12v 4.8 ohm dual fire from Andrews and I have also try to ride again with the old coil which worked fine for years ... the missfiring is the same.

I don't really get the trick with a wire from the motor to the ground on the battery ? Isn't the motor grounded by the frame ?
 
#8 ·
I have already bypassed the switch to test it, with no better results.

No charging issue, I have a charging light which is working fine.

Points are in place and the gap is good, I have tested from 0.018 to 0.022 with no results. The screw is solid.

I have tested the new points with some grease provided, worked fine until I twisted the thorttle more seriously. Then I cleaned and sanded, works perfect for 10 miles.

I don't have any tach at all

Thanks guys for your help so far
 
#19 ·
Then I cleaned and sanded, works perfect for 10 miles.
You have bad or wrong condenser [Burning the points is a symptom of this] and also maybe wrong or wired wrong coil. This can be checked with a pencil by pulling a plug wire while running and arcing to the top of the plug and putting the pencils lead into the arc it should make a flare towards the plug if it flares to the wire it is wired backwards.
 
#11 ·
Do you have slop in the shaft on your timer ?
that will cause erratic timing firing and cause the bike to run rough
so will a loose plate under your timer cover

give those a check
I had a knucklehead one time drive me crazy trying to find a rough running problem under load and that turned out to be the problem

also check for a loose wire in the timer as well
 
#13 ·
draining gas has been my first idea ... Shaft of the timer is solid everything un timer work
fine. There are no + or - on the coil and has been wired the same way than my old one only one way to fix it on the bike ... Tonight I have been able to retorque the two manifold clamp and the missfiring was lightly better ... I will change the gaskets and will share the result

Thanks for the help
 
#16 ·
I like simple problem solving.

Let me say this, I am a fabricator with a limited amount of motorcycle engine tuning experience.

The intake leak suggestion is the first thing I would go for after verifying the ignition system. I would also check my valve lash too. If that fails, it's time to consider a compression leak down test to check the condition of your valves and rings.
 
#17 ·
Have you checked your generator???

What kind of voltage regulator setup do you have?

Old style? last time polarized?

Hello gentlemen,

After several weeks of tuning my Pan, I still got the missfiring problem under load.

The bike ran like a champ for two years without any trouble and then started to lightly missfire on the highway.

I have changed the point (I have tested 2 new ones), condenser and weight springs of my ignition system, which as been just fine for 100 miles. Then it's been worst and worst with more and more missfirings and backfires.

I then have changed the coil (teste three differents units), plugs, plugs wires, I have tested for inteake leaks, I have tested the battery, checked the push rods. But nothing cured the missfiring.

The only trick is when I clean and sand the points, the bike runs perfect for 10 miles and it's back to the mad swinging machine. The bike is also runing good at low rpm and start on first kick even cold or hot.

What am I missing ?

Thanks ind avance for your thought
 
#18 ·
For years, I checked intake leaks with starting fluid sprayed on the intake until I joined this form. I cant remember who it was now but, someone on here posted a pic of a plate he built with a air chuck in the middle that he bolted in place of the carb and shot low pressure air in the intake to check of intake leaks, I thought and still think it is genius. I took that idea one step farther and took a rubber freeze plug, removed the bolt and washers and glued a air chuck in it. Now I pull the breather off, wedge the freeze plug into the carb and can check the carb, gasket between carb and intake and intake to heads, this has sure made my life easier.

Something else to check, you said it pops while rolling on the throttle and that you changed out the points and springs but, did you check for loose or worn pivot posts for the weights. The slightest snag on these will drive a man bat shit crazy trying to track down a miss.
 
#20 ·
Thanks a lot for all your inputs. I have a cycle electric generator
and a light for the check. The weights of the ignition systems are working fine and I can't see any play or worn pivot. I have tested two differents condensers and the missfiring is the same. I was focused on the standing and clearing points but this made the bike get cooler and I think that made the intake leak less important when the engine is cold ... I still need to check the pressure but I have to make the tool to check first. Thanks again everybody !
 
#21 ·
I feel your pain been going through this same shit for 6 months on a 6 volt 52.

The only other thing may be worth a check is if you have drag pipes weld a washer in the back of pipes to create back pressure.

May check for an exhaust leak on the spigots. (I cut extra slots and a beer can shim)

I'm going through the above tests today to try to get issues fixed. (Pretty sure it's in the shit 6 volt battery>new one should be here soon)
 
#23 ·
You never know when your gonna learn something .I'll make it quick cause its not my thread .50 fl points ,edelbrock carb cycle electric 12 v gen ,accel coil . In 3rd gear cruizin it would break up " almost like a 3rd cylinder joined in . I've been rackin my brain trying all sorts of tricks . Everybody said get rid of that carb ...But she starts on first kick most times and runs pretty decent except for the plug fouling ......Mickey D all I can say is thank you . I over looked the plug wires ,got a set of copper core . Allthough hard to find on a Friday night ,Tractor Supply had a 7mm buildable set for a Ford tractor ...let me tell you the bike is now a different animal .No more breaking up ...................Mickey D you kick ass
 
#25 ·
That's what I love about this place, sometimes the answer is so simple yet, takes a different set of eyes to see it. Kinda like the can't see the forest because the damn trees are in the way.

Now if we can just get Cheater's bike lined out...
 
#26 ·
+1 on the simple stuff, (I'm cahsing the same shit on my 52FL as we speak) I went back checked all leaks, and cleaned every electrical contact point, replaced points after close inpection they had small imperfections, seemed to help, just waiting on a 6v battery now and I will get some of those solid core plug wires. (Also found a bad diaphram on the AC S&S pump).
 
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