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Paul, Good to hear you are making progress,so many times threads just leave us hanging.

It is pretty easy to bump the points when installing flywheel, I don't think any manual really

points out to turn the crank to prevent contact between cam & rub block.

Hope you have luck.

The Iridium plug has served us well, & the condenser is a no brainer to not have. (leave the original,wont hurt)

PS OEMs don't seem to be good quality of late; if the mag isn't vented sealing up not good.

Hope it starts. We will be here.


Edited by lbhbul
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Paul -
Where were you going wrong ? The answer is now glaringly obvious !
Using that printout was your first BIG mistake........
Reading it through several times made my head spin ! (and I'm familiar enough with servicing CB-pointed ignition systems that I don't have to think about it) - I can sympathise with the confusion you were experiencing.

To be honest, the last time I did points and timing actually on a Bultaco was some while ago, but the general principles and m.o. apply whatever the set-up - I'm relying on my imperfect memory for the Bultaco specifics here.
I can also appreciate that we all have to start somewhere.

Edited by lorenzo
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Sadlotus -

Your original post asks "Where am I going wrong?" - well, taking each point in turn, here's a few thoughts of mine :-

1/ "the bike had been sitting for years and the stator and accociated bits were dusty, rusty and neglected. I cleaned everything, new points, condenser, replaced the lighting coil, all seemed to go together easily."

Referring to the photo......+1 johnsy's post re the cleaning. Has someone been using the joint face to lever against? Do you have a paper joint to keep the crud out ? Why did you replace the lighting coil ?

2/ "Set the points gap and bought myself a dial guage to set the timing." .......How did you set the timing when fitting EI on the Sherpa ?

3/ "Anyway, decided to check points and timing again.

Points gap was a bit wide - reset that." .......How come ? What happened the first time ?

In the pic. I don't see any evidence of lube on the moving contact heel, in which case the heel will wear rapidly and REDUCE the gap, not widen it. The felt pad that should lube the cam and control any excess looks rather black, by the way.

4/ "I had marked the timing on the back plate and that hadn't slipped as I thought it might have done" .......If 'slipped' means you expected the stator plate had moved, that's not very likely with three screws securing it...and marking the timing on the backplate is meaningless anyway, as you've altered the timing since - by resetting the points gap...

5/ "timing test light .........workshop manual)........ I can't make it go on/off with the opening of the points" .....Nope , when setting timing I've never been able to myself, or detect any dimming/brightening either, as the test light circuit completes itself by finding another earth. The answer for me is to use a timing/continuity buzzer, which detects the change in resistance when the points open - this allows you to concentrate on looking at the DTI only - far easier than trying to watch both DTI needle and bulb at the same time. Which workshop manual ?

6/ "Everything else works fine - stoplight, headlight, tailight, horn (haha)" ......Assuming you have AC electrics (i.e. direct) how have you wired the stoplight ? Is the stoplamp operated by one or both brakes ?

The backfire/banging in the exhaust sounds like an intermittent ignition breakdown is causing unburnt fuel to collect in the system, which is then ignited when normal firing returns. There are many and varied possible causes....

Hope this helps -


Hi all

really pleased with the response to my question. Thank you for all you replies.

Here's an update - more to follow tomorrow - not actually started it yet because it's quarter to midnight and a Frontera - even with it's bazooka exhaust - is a loud old thing. Don't want to give children (or the dogs) next door a fright!

From the beginning I've been following instructions from the InMotion Bultaco workshop manual and a printed out post from on here:


I found myself going back and forth between the two so (unwisely) used the printout - No. I don't know why I followed that primarily. I do (now) know that I should have read the post properly and to the end!


After a bit of logic circuitry in my head I found that if the green and black wires were disconnected at the junction under the tank I can attach my battery, light and crocodile clips between the green wire and earth and make the light go on and off as the points open.



After setting the points I can turn the magneto CLOCKWISE to set the timing BTDC (as the workshop manual says) and find the points opening moment. NOT COUNTERCLOCKWISE AS THE ARTICLE ABOVE SAYS!

This is proven by pushing on the kickstarter (easier to rotate the crank than by hand) which will rotate anticlockwise. ie the way the engine runs. So BTDC is clockwise.

After that epiphany, it was all plain sailing.

To answer questions above:

Larry, thanks, green wire was the clue. Condenser stays where it is at the mo to avoid another possible fault (mine).

Greychapel and Feetupfun, I did notice that the light dimmed but didn't realise the significance then - also don't have a strobe where I am at the moment.

Larry, Steve and Zerorev3rev4, the plug is new NGK B8ES (non resistor type)

JLpar, checked thru the magneto holes to check for touching - all good.

Sherpa325, checked cleanliness and tighness - all good.


1. I have a paper gasket. the exterior joint looks good and the allen bolts all do up snug. Lighting coil was replaced because it was unwinding and someone had made a temporary repair with tape.

2. The InMotion Electronic ignition on my 92 just bolts up - there is no adjustment! Three bolts - done.

3. Don't know why points were wide, wasn't much, I assumed I'd done them 'slack' the first time , What should I lube the little felt pad with? I've been using plain old engine oil. The heel doesn't look any more worn than the others in my box of points (admittedly, we're talking thou here).

4. Good point about the three screws and the stator plate. Not sure I understand how the timing changes when I reset the points, only if I open or close them up or down a bit. Explain please.

5. Yes, I need to get a buzzer. Inmotion Bultaco workshop manual. I also have a Haynes and the WWW (but..."Don’t believe everything you read on the Internet just because there’s a picture with a quote next to it.” – Abraham Lincoln)

6. Stoplight is direct - only on rear brake as per original wiring diagram.

7. The backfiring was happening before it wouldn't start, I'm hoping that by resetting the ignition I can at least eliminate that as a cause. What is strange is that it ran really well for a while then gradually deteriated to a no start. As for an intermittent ignition breakdown, how can I test that?, it ticks over fine and revs high fine, it's the loading on acceleration where it backfires, as tho there's no spark or no fuel. mmm... Ok.... maybe the ignition under load might be breaking down. i have a spare stator to test that - my money's on a carb setting..... I'll let you know.

Setting the points and timing these last couple of days has meant taking the magneto off and on lots of times. It has occured to me that the woodruff key is quite shallow in it's 'trench'. The magneto would only have to slip the tiniest bit to stop the bike and give the backfiring and stop scenario. Next time (hopefully not) I'll check the key before I take off the mag.

Thanks for all your help and enquiring questions.

Update v soon.



Gapping the points on a Bultaco is not easy due to the awkward access through the slot in the flywheel and the magnetic field grabbing the feeler gauge making it hard to assess the friction in the gap. A pal got hold of the cam from a disintegrated flywheel (don't ask) and used that to set things up but the chances of that and his own cam being in the same relation to the system must have been slim.

If you think about it opening the points advances the timing, and vice versa, so when you fit new points the timing will change uness you get the gap exactly the same.

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Evening/morning all.
Busy day - must do some Christmas shopping soon!

New plug in, tank on, petrol in.
Fourth kick and it started. YAY!
Choke off and for a few minutes it was responsive and smokey. I don't like to rev too high when engines are cold.
As it warmed it began to misfire as I revved up. Standing next to it, it sounded like a backfire/afterfire in the beginning/middle of the exhaust.
Ticked over fine.

Couldn't get past the bogging and backfire to higher revs. (with or without the air filter)
Changed plug - the same.
Changed premix from 50:1 to 25:1 as in manual.
Predictably worse.
Changed plug
Back to 50:1 - same as before.

Then stopped and no start.

Changed coil and cap, rubbed away paint for good earth.
Good spark. (bizzarrely one of the spark plugs refused to spark when the other three would)
Checked last nights work:
Woodruff key good.
Points clean, correct and opening
Timing spot on.

Getting late again, so can’t start it up, so checked the carb out.

All clean inside except a bit of greenish verdigris on the main jet and needle jet but not enough to block things, very thin and difficult to remove with a toothbrush.

This is what I found compared to what it says in the manual:

Needle: Marked 2F1 - 5 grooves - on the top groove. Manual says clip position 4 (which is 4 from top!)

Slide: marked 4 - Manual says 2.5

Main jet: 330 - Manual says 360

Needle jet: 107 - Manual says 108

Just researching as to whether it’s been set up lean or rich for altitude - It’s an import from Colorado -which has a quite a few high places doesn’t it?

Might just order the standard jets etc
Just found this: ....raising the needle richens the "middle" a little bit. At full throttle, the carb should be all main jet... At near-closed throttle, the carb is on the pilot or slow jet...

All of which is inferring that it's running rich.

If I get a chance tomorrow - I’ll reassemble the carb and see how it runs on the middle groove (down two) and new (different) coil

Also going to check the exhaust manifold joint - as I believe airleaks there can possibly cause backfiring.

What's baffling is that it ran fine first time out and for about ten miles after that, then started to play up.

Annoyingly, a fella two doors down has been showing off by starting his Honda CR500 at will all day!

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Paul, Please add an automotive condenser, 302 Ford from your local parts store.(works for me)

Mount it to coil bolt under the tank,lead wire goes to little wire (black) on coil.

You should have a good coil from the Sherpa you can try next.

Doubtful if you have a fuel problem (carb) don't just go bad all of a sudden.

OEM condensers seem to be junk over here.

Good fire & your troubles will lessen.


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This is what I found compared to what it says in the manual:

Needle: Marked 2F1 - 5 grooves - on the top groove. Manual says clip position 4 (which is 4 from top!)

Slide: marked 4 - Manual says 2.5

Main jet: 330 - Manual says 360

Needle jet: 107 - Manual says 108

Just researching as to whether it’s been set up lean or rich for altitude - It’s an import from Colorado -which has a quite a few high places doesn’t it?

"Manual" means the Inmotion manual referrred to earlier ? (and which I don't have).

Only manual I can find at the moment containing info. relating specifically to Frontera 250 with Concentric Mk. II - a "Haynes Manual #219 "..........definitely NOT to be trusted, in my opinion........not without reason are these frequently referred to as "Heinous Book of Lies" ............ gives the same figures.

However, among my Amal carb. notes for Mk. II Concentric I turned up basic (general, non-manufacturer) specs. for 2- and 4-stroke use, based on the choke/bore dia. and for use at sea-level locations ( and up to 3000ft.) and with recommendations for jetting adjustments (overall reductions/weakening) at higher altitudes.

For a 2036 carb. 2-stroke application these basic specs. are : Bore 36mm

Needle 2F1 clip pos. 3

Slide cutaway 3

Main jet 360

Needle jet 108

This suggests to me that the "Manual" specs. you have are probably correct, and that the carb. has been re-jetted at some time to suit the p.o.'s location ; I suppose you could do worse than return the carb. to original spec.

Whether NOW is a suitable time to do this, you must decide - you could find yourself in the position of having changed so many parts (and the problem persists), that you lose the plot entirely ...........

Edited by lorenzo
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Nope - but will tomorrow

Also, the plug I'm using is an NGK B8ES which isn't the equivalent for WHAT THE MANUAL SAYS...

Should be Champion N57R which equates to NGK B10EG

Admittedly the N57R is an old plug.

I wouldn't rely too much on "equivalents" - they frequently turn out to be no such thing (with costly consequences, unfortunately)

Should be Champion N57R - well, again it depends on where you look.....

N57R is a hard/cold RACING plug, racing denoted by the 'R' suffix - I wouldn't personally see a need for a racing plug if you're not actually racing, just trying to get the bike into some usable state of tune.

An old (1987) Champion plugs application list gives : N3C std. or N3G (Gold Palladium type), for Frontera 250 & 370, without year ref. and a recommended gap of .020".

(A Clymer manual I have lists Champion N12Y for just about every model Bultaco from 125-370cc, flywheel mag. or electronic, and the same gap recommended for all - .013-.017" - clearly WRONG..........)

Edited by lorenzo
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Good fire & your troubles will lessen.


NO ! Surely he can't mean.......................?? !!

.....(Torching my bikes has been suggested more then once by sneering Bultophobes - they just don't appreciate quality !!.)

Edited by lorenzo
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OK. Hope no one out there is bored with this yet. ...not you Larry - I can tell.

Funny how you sleep on things and they come to you in your dreams.
In all my years of playing with old cars and bikes - all those Minis, Anglias, Corvairs and Lotus’ I’ve never come across a sparkplug that suddenly gave up living - outside the cylinder head.
Yesterday was the first time I’d ever experienced it.

Then B40Rt mentioned the condenser - and others said to put it under the tank with the coil, Sherpa325 mentioned ‘a faulty one can give a nice healthy looking spark when cranking the engine over yet cause problems when the engine actually runs’
I remember problems in the past with dodgey condensers/capacitors and points, and how they can give a healthy spark out in the open but give up under the pressure of having to fire an engine.
And... the fact that it ran well for a while then deteriated.
And... as Larry and Lorenzo said - unlikely to be the carb so now is probably not a good time to change things.


Changed the whole stator for the one off the Sherpa that now has Electronic Ignition. Nice new points and condenser, and nice new felt wad oiler - only three wires instead of four but the red was never used/wired in anyway.

Redid points and timing.
Bit of a problem getting enough retardation. So turned stator fully anticlockwise and redid the points (after thinking about 2stroke4stroke’s comments) and this (I found) gave me just enough to get the timing right.

First kick - MASSIVE BACKFIRE - dammit!
Third kick, started and ticked over - once again - a bit late for the children next door, so let it run just for two minutes, sounded so much better.
That backfire was probably/hopefully all the petrol I’d been pumping into the exhaust during the ‘no starts’ the last few days - it certainly woke all the dogs up!

Over the last couple of days I’ve fettled the tools I use - I now have a nice homemade magneto holder and the dial guage sits nicely in the plughole...
Also a picture from sunnier times ...October.

Thanks for all your help - if everything is as good as I hope (Idon’t count chickens until.. etc etc)
I’ll try and put a vid up.

thanks all, lots of good info out there and I'm upping my knowledge... continually.... until it leaks out with age.


PS Larry, you mentioned that you can leave the condenser behind the stator and wire in another one up by the coil - so - there'll be two wired into the points... is that what you meant?




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Paul, what I said about condenser: I prefer Ford 302 (68mod) mounted to the coil bracket, I never worry about the original being in place

(been doing this since 1973)& contrary to popular belief run resistor plugs (Iridium best) no problems on our 3 Sherpas, this is only me.

The automotive condenser is the only one I trust.

Have a good day


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