Burning out stick coils

[Biker9090]

Having a nightmare with the old CBF500 at the moment.

A year or so ago I fitted a pair of CBR stick coils (somewhat popular as an "upgrade" over the old stubby style oem coil and plug cap combinations). A little bit better pickup and a HUGE amount of space saved undeneath the tank.

This worked - for a while - until one started to misfire BADLY. Albeit, this was due to it cracking on prior removal and getting corroded (my own fault).

I've now had the same symptoms again. Horrendous misfire under load, running on only cylinder etc. The idle was particuarly bad. This seemed to happen after a month or so of non use.

I then found another stick coil in the shed and it sorted it - for about 50 miles where I got a slight hesitation on acceleration intermittently again which got progressively worse by the time I got home.

Carbs have been thoroughly cleaned, no air leaks, cables are all checked and good, earths good, no corrosion, charging system is 100%, compression seems great and lots of power up top. Clearances are good. No issues starting hot or cold (until they get worse when it can slighlty hesitate).

OEM coils have a primary resistance rating of 2.6 to 3.2 Ohms iirc - the stick coils have a primary rating of around 1.6. Secondary ratings are similarish at around 11-13 iirc. Oddly, the most recent one to "fail" had a primary of 1.6 and a secondary of 12.7 I think which was in the middle of the other two.

Can someone please try and explain why they would be burning out/overheating on my bike? Should everyone who's done this mod be expecting the same? It's difficult to compare against others due to people either not doing the mileage or and just using them when racing as this generally only seems to start after the engine has been on for an hour or two.

I'd just like to understand it before either trying to source another stick coil of unknown quantity or getting an oem set back on. Annoyingly I gave my old set to a friend so can't just swap them over at the moment.

The one person who lead me to an explanation said that "CB does not use a CDI, it is an inductive ignitor. Compare the resistance of your stick coils to the stock coils, if the stick coils have a lower resistance, they will flow more current which can overload the IGBT's in ignitor".

TLDR - Why would a stick coil conversion cause intermittent misfires?

Edited by Biker9090 on Monday 18th August 16:04

[Rubin215]

My first step in fault finding any ignition issue is to change the plugs for a new set, you would be amazed how many times it does the trick.

[Steve Bass]

If the stick coils are overheating it can be due to either the primary winding resistance being lower than the original items and pulling more current or the heat they are being subjected to in the head is excessive.
Regarding wiring, are the stick coils 2 wire or 3?? If three and not fully connected this might be an issue too
As a sanity check, refit the original parts snd see if the issue is resolved.

[Krikkit]

Could you rewire it to fire both stick coils in series on every event? Effectively wasted spark

[Biker9090]

Thanks. Got some plugs on order and a secondhand set of oem coils coming tomorrow (shall test them prior). There are two wires to each coil (same as original).

I'll likely end up puting the oem style back on (trying to find a good pattern set) but it's part curiosity and part hating how much dam space they take up.

[Biker9090]

Little update to this.....

The OEM style coils arrived along with new wires and caps (I tested them prior to use and all in spec). All seemed well until yesterday when I was riding for just over an hour (longest time on this bike since swapping them over).

Dropped to one cylinder again and then full on died. Refused to fire until I waited about 5 minutes then ran fine. (this was on a country road so the temp gauge wasn't particuary hot and even with the fan on in traffic it was running fine earlier).

Same thing happened again about 15 minutes later.

Then again.

Then again.

I give up at this point and pull the bike apart at the side of the road and swap back to the stick coils to see if that makes a difference. It doesn't run well (intermittent misfire and a bit boggy) but it got me home without dying completely.

I'm now thinking ignition pickup/pulse generator? I've read a few excerts and this somewhat seems to correlate with the issues? I must have gone through about 7 different coils now so surely it can't be them???

Charging system is fine (voltmeter on dash), fuses and wiring all good. Driving me absolutely insane.

[Rubin215]

I take it you did change the plugs?

Have you also tried with a different battery and checked your earth strap?

[Biker9090]

Rubin215 said:

I take it you did change the plugs?

Have you also tried with a different battery and checked your earth strap?

Have changed the plugs and no difference. Not tried with a different battery but earth points I'm going to check and clean again when the rain stops

[Steve Bass]

If it's failing with both coil types fitted, it's likely upstream of the coils.
Check the ignition system, might be overheating and breaking down. Might be worth changing the cdi/ignition box as appropriate

[trumptriple]

Symptoms sound quite similar to the problems I had on an old Hinckley Triumph, took me a while to find the cause but it was the ignition pickup. Scariest moment was the engine dying in the outside lane of the M1.

Quite easy to change and totally fixed it.

[Biker9090]

Yeah definitely don't see how it is the coils now.

Ahaha this was bad enough on a 60mph country road, can't imagine it on a motorway!

Glad I chose the V Strom to go into london with last week - via the M4 at rush hour.....

[camb10]

i had something similar years ago in damp or wet and occasionaly when dry - turned out ti be the crank pickup sensor wiring had degraded near a hot exhaust and would intermittantly short. Was an easy fix, albeit it cost me new undies when it did it on a wet M40 droppng to about 20mph!

[s p a c e m a n]

If this was a car I'd be changing the crank sensor, all symptoms point to old sensor failing when heat soaked.

[Biker9090]

Tested the old one "cold" and it was within range. Will have to strip the cases off today to get to it. Got a spare turned up with what looks to be considerably less than 82k miles on it.....

Am I right in thinking then that a crank sensor is the same as the "pulse ignition sensor" Honda seem to call it?

[fred bloggs]

Was it running ok with the standard coils ?

[Biker9090]

fred bloggs said:

Was it running ok with the standard coils ?

Now or when it had them a few years ago?