Triumph Rat Motorcycle Forums banner
  • Hey everyone! Enter your ride HERE to be a part of September's Bike of the Month Challenge!
1 - 20 of 23 Posts

·
Registered
Joined
·
18 Posts
Discussion Starter · #1 ·
ignition problem on my T140D Special 1979 mod. Spark is weak on the right cylinder and fails to spark from time to time, resulting in loss of power. At idle engine run fine, but there is a 50 degre C difference on the exhaust pipe telling me that the spark is partly missing. Have checked the timing ok. Compression ok. Coils ok measured to equal ohm. Wireing to spark plug ok. Spark plug cap ok. Where to look next? Is it just to get the whole electronic ignition system changed? Please advise!
 

·
Registered
Joined
·
8,380 Posts
There might be a crack in a coil,or maybe the seat is touching the coil top.Worth a look.Best to check for a crack with bike in the dark so that it is easily seen.Change the plugs.
 

·
Super Moderator
Joined
·
8,836 Posts
Hi Per,

Checking coils after warm up? What should the Reading be then? Measured 4.3 ohm on both when Cold!
The problem is either the bike has the wrong coils or they have been connected wrongly.

"4.3 ohm" indicates '12-Volt' coils, and pattern ones, so someone has made a mistake, or you haven't posted much relevant information.

As standard, your bike should have a Lucas Rita electronic ignition. As this has only one coil switching circuit, multiple coils are usually connected 'in series'. If two coils are connected in series, they must be '6V' - you should measure in the range 1.5 Ohm to 2 Ohm between the 2BA threaded terminals.

This would also be the same for any replacement electronic ignition - I am guessing no-one is crazy enough to replace a Lucas Rita with points and mechanical auto-advance?

Just with a Lucas Rita, it's possible to connect multiple coils 'in parallel'. However, each '12V' coil draws between 3 Amps and 4 Amps, so the bike's electrical system has to supply between 6A and 8A just to the ignition system all the time the engine is running. :( You would also need a diode between the Rita and each coil, or each coil's back-emf affects the charging of the other one at particular rpm. :(

If your bike has any electronic ignition, including the original Lucas Rita, I advise replacing the coils with '6V' ones. Please post which ignition the bike has and I will advise correct coils connection.

Hope this helps.

Regards,
 

·
Registered
Joined
·
18 Posts
Discussion Starter · #9 ·
Hi again Stuart! Thanks for Your response. Had my T 140 D Special 1979 model for the past 10 years and it has been running fine at all time with the BOYER BRANDSEN ignition system fitted. (I belive from New, and the bike is a US import). As for coils fitted wrongly nothing is changed as from running fine last season. Over the Winter somthing has happend to the bike and I can't find out what. Compression checked ok, timing cheked ok, carburator adjusted to and aligned ok, plugs changed ok and as stated the bike runs fine on idle, but has no Power when on the road. Measuring temp on the exhaust pipe there is a difference of approx 50 degrees from left to right With the rigth on beeing the Cold one. Take that as an indication of missing sparks.
Hi Per,


The problem is either the bike has the wrong coils or they have been connected wrongly.

"4.3 ohm" indicates '12-Volt' coils, and pattern ones, so someone has made a mistake, or you haven't posted much relevant information.

As standard, your bike should have a Lucas Rita electronic ignition. As this has only one coil switching circuit, multiple coils are usually connected 'in series'. If two coils are connected in series, they must be '6V' - you should measure in the range 1.5 Ohm to 2 Ohm between the 2BA threaded terminals.

This would also be the same for any replacement electronic ignition - I am guessing no-one is crazy enough to replace a Lucas Rita with points and mechanical auto-advance?

Just with a Lucas Rita, it's possible to connect multiple coils 'in parallel'. However, each '12V' coil draws between 3 Amps and 4 Amps, so the bike's electrical system has to supply between 6A and 8A just to the ignition system all the time the engine is running. :( You would also need a diode between the Rita and each coil, or each coil's back-emf affects the charging of the other one at particular rpm. :(

If your bike has any electronic ignition, including the original Lucas Rita, I advise replacing the coils with '6V' ones. Please post which ignition the bike has and I will advise correct coils connection.

Hope this helps.

Regards,
 

·
Registered
Joined
·
18 Posts
Discussion Starter · #10 ·
For Stuart Mac.
Ignition system is type Boyer Brandsen MIKRO MK III. part no. BOX 00023 (Transistor Box)
Stator plate Pnr; STA 00152. Magnetic Rotor Pnr. ROT 00118
 

·
Registered
Joined
·
8,380 Posts
Just to confuse a little,my Boyer MK 111 has always run on 12 volt coils so they can run OK.As it does run very well,i have never thought about replacing them.
 

·
Registered
Joined
·
18 Posts
Discussion Starter · #13 ·
No need to debate on what was fitted on day one!I have the MIKRO Mk III With two coils and the set is named KIT 00052. The bike has been running fine for all my time and I just want some of you to help me solving the weak/missing spark on the rigth cylinder.
 

·
Registered
Joined
·
236 Posts
You are assuming this is an ignition system issue but have you checked and cleaned the carbs? Several things could have happened over the winter to cause what you are describing. The overflow tube from the carb body could have become plugged / pinched which will limit the flow of gas into the float bowls. A rodent or other animal could have crawled up into the airbox and deposited all kinds of stuff in there. A float could have started leaking and filled with gas. An air filter could have become oil fouled (the engine breather runs up into the right airbox from 79 on). I would look at the carbs first.

Pull the sidecovers and inspect the air filters and carb throats. Drop the bowls and ensure they are clean. Clean all the jets. Check that both slides are rising at the same time. Check the enricheners and the linkage. I bet your ignition problem is a carb problem. Once the carbs are clean run the bike in your driveway without the air filters and see if you get the same discrepancy in temps between the 2 cylinders.

Scott
 

·
Registered
Joined
·
18 Posts
Discussion Starter · #15 ·
To all of you helpers out there! I have considered all option and don the following: The air filter is checked ok, carburators off and cleaned and adjusted to best standards, coils checked and swapped around, spark plug cables and plugs changed, checking for cracks in coils not done in darkness as 24 hrs of daylight is present nort of the Arctic circle, seat does not touch the top of coils and the compression on both cylinders are ok. Called Mr Hawkshaw today and ordered 2 new German made 12 V coils aschanging them would be the cheapest option when starting to replace parts! Thanks to all for advise to date. Will report back when New coils ar in Place. Still open to suggestion that has not been aired to date!
 

·
Registered
Joined
·
1,123 Posts
Hey Per,

Changing parts without need is a long road to chasing a long tail.

Get it running with what's currently installed might be a better option .

Good Luck

Triumph's Rock!
 

·
Registered
Joined
·
66 Posts
Checking coils after warm up? What should the Reading be then? Measured 4.3 ohm on both when Cold!
Not sure what they should be without looking it up, but I do know coils can work fine when cold, but fail when they have been working for a while. I would expect both to be a similar value, hot or cold.
Have you tried swapping the coils over to see if the problem moves with the coils?
 

·
Registered
Joined
·
18 Posts
Discussion Starter · #19 ·
Hi guys! A while since my last report,. Now I have got the suggested coils of 6 V to work with the Boyer B ign system and the bike still misfire on the RH cylinder and that temp difference is the same. To sum up what has ben done I go with: Carburators out/ in and cleaned and adjusted to spec. Plugs changed, plug caps new, HT cables new, the 2 new (6V)/ and old(12V) coils tested and swapper to both LHand and RHand cylinder and the misfire is still the same. Air filter checked ok, compression tested to read 150lbs both sides. Have no more ideas as to what is wrong but have ordered new ignition type PAZOZ. If any of you out here have more ideas as to were I should go next I would appreciate a reply. Summer is short in the Arctic, and I'm in a hurry!
 

·
Registered
Joined
·
178 Posts
Hello Per.
It seems you have a very tricky problem.
I had an intermittent misfire on the left side of my '69 / 71 Tiger. I did all the usual checks but couldn't find the problem.
I know you are running electronic ignition and I'm running points, but I found the fault almost by accident. I decided to pull off the points back plate to look at the auto-advance. As soon as I removed the plate, I spotted that the insulation on the feed wire from the left hand points set, had worn through at the point where it passed through the case. It was intermittently shorting out against the case. Once I repaired the insulation, the problem was cured.



I know you're system is totally different, but my point is, check all the ignition wires for broken insulation. even the tiniest break could cause a short.

John
 
1 - 20 of 23 Posts
Top