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Discussion Starter #1
Hi

Where do I start? I'm hoping that you wise guys and girls out there can shed some light on a misfire problem.

I have a 76 bonnie, good condition having been rebuilt a couple of owners ago.

The bikes been running fine plenty of power and starts first kick (by the way I'm back into biking after a lapse of many years having been into classic triumph cars.so understand mechanics and electrics)

I parked it up in the workshop and two weeks later it started fine but I could straight away feel, hear a misfire. Now the only thing I did in that two weeks was replace the steering lock, which meant removing the headlight assy.??

Its not an intermittent misfire, it seems to be be regular.

Ive renewed the plugs, and leads. it has newish 12v coils, which ive put a meter on and all seems ok.

It has boyer mk3 ignition which ive checked out the wiring connections and using the "OZ Bloke" electrical check run checks on the ignition unit. (great document)

The battery holds its charge and has 12 to 13 v. Ive had it on trickle charge for days.

I can see a "sparx" alluminium finned unit bolted beneath the battery box with green/white, green/black leads coming from it.Not sure what this unit does, replaces rectifier?? possible fault??

It starts first kick, no choke. (The carbs are new) wont idle.

Ive not checked any timing, why would it move??

I havent checked valve clearances (was running fine,)

When Ive started the bike I think the misfire seems to be more left side, bit of unburnt fuel smoke coming out.

Ive run out of ideas

I would appreciate some questions/advice to trigger off the thought process.

regards and thanks in advance.
Mark
 

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Welcome!Lucky you're here,we've got plenty of ideas.
The timing won't have changed.Check it if you like with a timing light at 5000 rpm.Boyer works better with 2 x 6V coils,but will still works with 12V coils.
The Sparx unit will be rectifier/regulator.Sounds like the battery voltage is OK.

Check that the pilot jets in both carbs are clear,and not blocked.It sounds like one is blocked.Pull out the mixture screws,and you should be able to push a wire no bigger than 0.016"diameter at least 1-1/2" into the carb body,if the jets are clear.

Re-set the mixture screws to 1-1/2" from bottomed,as a starting point.Adjust the mixtures when the engine warms up.
 

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What Pete said and...
Remove both plugs and earth them somewhere so that you can see both.
What colour are they?
I use masking tape and stick them onto the rear (chrome) mudguard [fender].
Charge the battery and kick-over a few times, both with fire at the same time.
They should be of equal intensity. [nice blue sparks].
Monitor the battery voltage.
It will drop after few kicks.
The timing can slip, stranger things have happened.
Buy a couple of 6V coils, connected in series.

The static timing is easy to check.
Remove the timing bolt behind the barrels.
With the rear wheel above the ground in gear, look through plug hole until the pistons approach TDC.
With the tool in the timing hole turn forwards until it drops into the TDC flywheel slot.
Inch the rear wheel backwards until it drops into the 38 BTDC slot.
Or go past it and turn forwards slightly, to take up the backlash.
Check the EI rotor is aligned with the hole in the stator.


Check the valve lash, .008" inlet and .006" exhaust.
Check for air leaks around the carbs.
You could try reversing the black/white and black/yellow wires to see if the misfire changes sides.
 

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Discussion Starter #4
thanks for that.
Ive not any experience with these carbs, so are you meaning the horizontal screw on the side or the one going in at an angle.? I think from reading the manual its the horizontal one. Also Ive read to wind these back out 2 1/2 turns from stop as a prelim setting.
Haven checked the static timing yet, but Ive healthy sparks.
Just taken it road the block, seems to misfire more at "lower revs" rather than opening it up a bit.
regards and thanks once again
Mark
 

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Discussion Starter #7
checked the static timing. (I dont have the special tool yet" but used a screw driver, I checked it a coiple of times and seemed to get the same result. The white dot on the rotor wasnt in line with the hole in the EI.
To get it inline I had to rotate it clockwise, which I'm sure is retarding.?? The idle speed dropped off and didnt help the misfire.
So I rotated the EI counter clockwise past where it was originally set, Idle speed better and seems a bit smoother, yet to road test.
However, that dosnt ring true with the static timing.

I broke the cardinal rule of only adjusting one thing at once and altered the pilot screw number of turns!!!!
This may be the real cause but hey its all learnings.
Need to read up on carb adjusting now. Any advice appreciated.
I cannot say enough how good theses forums are. Ive belonged to a Triumph car forum for years and the amount of good practical advice cannot be understated. What did we ever do before the net.?
Mark
 

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Need to read up on carb adjusting now. Any advice appreciated.
If you tune the carbs as instructed by your manual you will not have a problem. Do not rush. Many people get spooked about tuning twin carbs because they rush it. Step by step, take your time and you will tune them right.
 

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Discussion Starter #9
thanks, the carbs new (PO) but ive noticed that the o ring on the left side doesnt seem so "restrictive" to turn in or out, this may play around with the setting and I wonder if it could have vibrated out/in causing the running misfire problem.
I think I read on the forum (Mr Pete), saying that removing a plug to sync was the carbs was detrimental to the ignition system. If so, is there a preferred method of carb adjustment with EI fitted
Mark
 

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thanks, the carbs new (PO) but ive noticed that the o ring on the left side doesnt seem so "restrictive" to turn in or out, this may play around with the setting and I wonder if it could have vibrated out/in causing the running misfire problem.
I think I read on the forum (Mr Pete), saying that removing a plug to sync was the carbs was detrimental to the ignition system. If so, is there a preferred method of carb adjustment with EI fitted
Mark
The small O-rings on the air screws are important.
1) they prevent unwanted turning, by friction.
2) they prevent air leaking through.
3) tuning will be nigh impossible and liable to alteration.

Bear in mind both slides should be synchronised to lift at the same time by adjusting the cable adjusters.

The spark energy has to go somewhere.
If the plug cap is removed, its likely to reflect back to the EI unit and damage it,
Using the Hughie Hancox method is preferable.
He treats each cylinder as a single, by restricting the others effect.
This is done by unscrewing the the throttle screw [angled] of the one NOT being tuned.
In the video below, I am being very careful because previously it was spitting back through the carbs after the rebuild, and other nasties. [fire prevention :eek:]
I was also being wary of revving to much when strobing.
The mark varies very little after about 4000 rpm.
So blipping was the order of the day.

Tune by turning the [horizontal] air/mixture in, until it begins to stutter.[rich]
Then unscrew similarly.[lean]
In between the engine will run nicely, faster and even for that cylinder.
Then repeat for the other side.

Concentrate on the exhaust for eveness and speed, not the overall noise.

Also I have included a film of setting the static timing.
 

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Discussion Starter #11
The small O-rings on the air screws are important.
1) they prevent unwanted turning, by friction.
2) they prevent air leaking through.
3) tuning will be nigh impossible and liable to alteration.

Bear in mind both slides should be synchronised to lift at the same time by adjusting the cable adjusters.

The spark energy has to go somewhere.
If the plug cap is removed, its likely to reflect back to the EI unit and damage it,
Using the Hughie Hancox method is preferable.
He treats each cylinder as a single, by restricting the others effect.
This is done by unscrewing the the throttle screw [angled] of the one NOT being tuned.
In the video below, I am being very careful because previously it was spitting back through the carbs after the rebuild, and other nasties. [fire prevention :eek:]
I was also being wary of revving to much when strobing.
The mark varies very little after about 4000 rpm.
So blipping was the order of the day.

Tune by turning the [horizontal] air/mixture in, until it begins to stutter.[rich]
Then unscrew similarly.[lean]
In between the engine will run nicely, faster and even for that cylinder.
Then repeat for the other side.

Concentrate on the exhaust for eveness and speed, not the overall noise.
http://www.youtube.com/watch?v=cjUU1eDyesI&feature=autoplay&list=UUZSGgAoIUtPZfo8Y0qTNW0g&playnext=1

Also I have included a film of setting the static timing.
http://www.youtube.com/watch?v=gnR-aObRKwY&list=UUZSGgAoIUtPZfo8Y0qTNW0g&index=5&feature=plcp

Thats gold, really appreciate it. Ive put the bike to bed for the day, give the neighbours a rest!!
I'll get back on it in a few days time.

Mark
 

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Set your timing at 5000 rpm with a timing light.The static setting is only approximate/preliminary;just close enought that it will start.It already started and didn't need static setting;it may have been perfect,but it pays to check with a timing light.

Are then pilot jets clear?
 

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Discussion Starter #13
Set your timing at 5000 rpm with a timing light.The static setting is only approximate/preliminary;just close enought that it will start.It already started and didn't need static setting;it may have been perfect,but it pays to check with a timing light.

Are then pilot jets clear?
Point taken about the timing, although I moved the static setting slightly I marked the original setting and can revert back to that.

Yes the pilot jets seem clear, I used some strands of copper wire twisted together and measured with a vernier, all seems clear.
The o ring on one pilot screw seems a bit undersized, I'll change that.

Ive ordered 2 x 6v coils to replace the 12v ones, although the 12v look?? good and come up to spec on a meter I cannot help thinking the misfire is HT/LT related. The misfire is there slightly on idle and coasting but really pronounced under load.
Correct me if Im wrong, but even if the carbs were out of tune it would either run rich,weak, underpowered lumpy but still run.
I also dont think its ign switch cct related, its not an intermittent misfire as in a partially broken wire.

Apologies for this ramble, but it helps to clear the mind.

Meter wise the EI checks out and I think they either work or not, and having had them in various cars since the 70's not had one fail.

Thanks for you time once again, Ive learnt a lot already reading through the forum and talking to you guys.
Mark
 

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A simple check.
Measure the battery voltage and then compare it with the white wire at the EI unit using a digital meter.
Should be roughly the same.
Is there a kill switch fitted?

Had similar problems a whie back.
The ignition switch was normally OK, but moving the ign key slightly when switched ON revealed intermittant, variable voltage differences.
Vibration also had a similar effect.

Although it wont start, does it fire, cough, splutter, anything?

I think you should give a report after fitting the new 6V coils.
Using 12V coils, the one with the lowest resistance is likely to spark stronger than the other.

Generally, weak mixture and advanced timing should be avoided.
 

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Discussion Starter #15
no kill switch.
starts first kick.
When I was checking the spark, I did notice that although one was a blue colour the other was a bit yellow. Thought it may have been just a poor earth onto the head but it could be a coil, hence the reason I'm changing them.
 

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A simple check.
Measure the battery voltage and then compare it with the white wire at the EI unit using a digital meter.
Should be roughly the same.
The voltage will be exactly the same,because the circuit is not loaded,even if there is massive resistance somewhere in the circuit.This is not a valid test,because the E.I box supplies no current to the coils at standstill.

You must remove the wire that feeds the Boyer white wire,and connect it directly to the coil that is fed by the black Boyer wire to load the circuit and do any valid test.
Turn on the ignition and measure the total voltage across both coils (from -VE of one coil to +VE of the other coil).That voltage should be within 1/2 V of battery voltage.

If you're making 75 bhp and running 13:1 pistons,you need 6V coils.If you make 40 bhp or less,12V coils work fine.
 

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Discussion Starter #17
Hi All

Thanks for the help to date. I'm back on the fault after a while. The bike was running like a dog, spitting back misfiring, couldnt tune the carbs, left it to go and sulk! Went back next day, would'nt start at all.
Whilst it was running, I checked the timing, static and dynamic. All ok
Ive renewed the coils (2 X 6v) New leads, plugs.
Ive got a colleague who said "check the last place you was" Well I had the headlight off, so I thought better do as he said. I was so chuffed when I checked out the ignition switch as I could hold the switch turn/twist the barrel and get all kinds of resistances. So I got a new switch and fitted that. Still wont start!!

Ive checked through the wiring according the "OZ bloke" fault finding document.
Checking the 12v power side..............as per after kicking the bike over I get 10.38v, its suggests I should be getting 12v.
Checking the pickup sensor I get 135 ohnms It suggests I shouldnt get lower than 132 or significantly more than 135 or there is a fault between the control box and the sensor.
lastly I checked the wiring of the coils, checking the resistance from the neg 12v on the first coil to the pos 12v on the other coil. It suggests no more than 5 ohnms, I have 4.5.

I have wet plugs and sparks. (plugs are new)

So I'm not sure want to do now. My gut feeling is to replace the EI and rectifiier/power unit perhaps with a Pazon??
Mark
 

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Discussion Starter #18
The voltage will be exactly the same,because the circuit is not loaded,even if there is massive resistance somewhere in the circuit.This is not a valid test,because the E.I box supplies no current to the coils at standstill.

You must remove the wire that feeds the Boyer white wire,and connect it directly to the coil that is fed by the black Boyer wire to load the circuit and do any valid test.
Turn on the ignition and measure the total voltage across both coils (from -VE of one coil to +VE of the other coil).That voltage should be within 1/2 V of battery voltage.

If you're making 75 bhp and running 13:1 pistons,you need 6V coils.If you make 40 bhp or less,12V coils work fine.
Hi Mr Pete

Just doing that last check. Remove the white wire and connect to terminal where black wire is. After removing black wire??
Ive done this and get 0V!!
mark
 

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Looking at your last two posts, your battery seems to be knackered or very discharged.
Charge it up. [12.6V or more]
Immediately after a charge the voltage should be 13 V at least. (surface charge).
Turn on the headlight and measure the battery voltage for five minutes.
What is the result?
It will be obvious if the battery is no good. Dim light.
Recharge the battery, if it passes the test.
If not get a new one.
Your EI wont function correctly at less than about 12.3 volts.
 
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