Questions about the spark system

[Eomund]

Now I have my bike running and legal, I noticed it starts having issues when it gets warmed up at high RPM. Basically the spark doesnt feel like it can keep up at full throttle.

The plug cap feels looseish and is in pretty bad shape.

I would like to replace the coil, the wire and the cap. Now this I wouldn't mind changing to a different bikes coil and plug. I honestly am not fond of the metal cap.

Is this a common swap? What do you recommend. If not any alternatives?

[Blurredman]

You likely won't need to change the coil. If you do that 'as a matter of course' that is just a waste.

I would however, change the ht lead (7mm) and the cap. The metal ones can short. Silly really.

I myself like to use the car type spark plug cap fixing, as opposed to the little ones...

This type of top


instead of this..



After a time of taking cap on/off all the time- the smaller type fixing wears more, esspecially so due to the vibration of these engines. I would often find the walk off the spark plug- and it happened not long after putting a new cap on too..! So.. Save the hassle.

[Eomund]

Ya. Mine is pretty loose feeling. I don't like having to take the cap off unless it's a snug fit. 4 strokes it's common, but they fit tighter. I ordered a cap and wire for a more traditional setup.

And I know the coil is working fine
I still ordered a new one. I just like having new parts like that. Coils can go bad from sitting, and boy has this bike sat.

I ordered a pack of plugs too. I cross checked the plugs with what is in there. The original owner has it set for 2 numbers hotter than it should. Probably trying to counter the weak spark from the metal cap.,

[Puffs]

Following a biased and flawed moderator choice (someone posting aggressive personal attacks is rewarded, while my technical posts are removed - behind my back & without any justification!), I have withdrawn from this forum.

[Blurredman]

It's may have nothing to do with your problem, but on caps & plugs: best not combine a resistor cap with a resistor plug. If resistors are prescribed, it's normally either in the cap, or in the plug, but not both.

Resistors in the HT circuit are there to reduce the current (when the spark occurs), and thus reduce the radio waves emitted by that. Have a look what the book says on your bike.

The 'R' in NGK plugs indicates the plug has a resistor.

Agree with Puffs here, and as a person who has messed with this sort of stuff in the past..

My Honda has plug caps that have 5k ohm resistors in them - originally at the time the recommended spark plug was a type that didn't have resistor in it.


However these days, pretty much all spark plugs (unless you specifically choose one otherwise) have resistors inside them, and as far as i'm aware no one makes resistored caps anymore for the every day market (unless you choose specifically I guess to get one).

I have experienced resistor break down on my Honda recently, the resistence was something like 110,00k ohms. The bike ran like crap COLD- but not too bad when warm. I had forgotten whether I had replaced the resistors or put a rod in place of them at the time. Regardless (I actually just replaced the resistor in the cap), this is a problem that isn't really around anymore. You have a dodgy sparking? You normally start off with replacing the plug, and who knows it may have been the resistor in that plug and replacing it just happened to fix your problem.

New spark plug=new resistor.

Anyway.. Although I am actually running resistored caps and plugs, this is just because I have no real problem in doing so in terms of use of the bike. 10K ohms total is not much of a spark difference to 5k. However, 110k IS... haha.



TL;DR

Just get a normal non-resistored spark plug cap, spark plugs come with resistors built into them now.

[Puffs]

Following a biased and flawed moderator choice (someone posting aggressive personal attacks is rewarded, while my technical posts are removed - behind my back & without any justification!), I have withdrawn from this forum.

[Eomund]

It's may have nothing to do with your problem, but on caps & plugs: best not combine a resistor cap with a resistor plug. If resistors are prescribed, it's normally either in the cap, or in the plug, but not both.

Resistors in the HT circuit are there to reduce the current (when the spark occurs), and thus reduce the radio waves emitted by that. Have a look what the book says on your bike.

The 'R' in NGK plugs indicates the plug has a resistor.

Agree with Puffs here, and as a person who has messed with this sort of stuff in the past..

My Honda has plug caps that have 5k ohm resistors in them - originally at the time the recommended spark plug was a type that didn't have resistor in it.


However these days, pretty much all spark plugs (unless you specifically choose one otherwise) have resistors inside them, and as far as i'm aware no one makes resistored caps anymore for the every day market (unless you choose specifically I guess to get one).

I have experienced resistor break down on my Honda recently, the resistence was something like 110,00k ohms. The bike ran like crap COLD- but not too bad when warm. I had forgotten whether I had replaced the resistors or put a rod in place of them at the time. Regardless (I actually just replaced the resistor in the cap), this is a problem that isn't really around anymore. You have a dodgy sparking? You normally start off with replacing the plug, and who knows it may have been the resistor in that plug and replacing it just happened to fix your problem.

New spark plug=new resistor.

Anyway.. Although I am actually running resistored caps and plugs, this is just because I have no real problem in doing so in terms of use of the bike. 10K ohms total is not much of a spark difference to 5k. However, 110k IS... haha.



TL;DR

Just get a normal non-resistored spark plug cap, spark plugs come with resistors built into them now.

Long and short it's not a resister problem. Resister problems show up in more low RPM issues as it's not allowing current through. What I'm dealing with is a weak spark at high RPM. The metal cap doesn't sit as tight as I would like, and the plug wire is really bad shape.

I honestly think the coil is working okay. I'm changing it for 2 reasons. 1 is because I want something new. Coils do go bad over time. And this bike is 46 years old. The other is so I can use more common wires. The screw on cap on the coil semi limits me. So I want more modern equipment.

Cap, coil and plugs are just common maintenance things to when getting an old vehicle going. And if this doesn't cure the issue, I'll have to have a look at the points. I looked at them before and they look, well new. But if they aren't gapped right or whatever, it can cause issues.

[DAVID THOMPSON]

if the spring is old in the points they can float at high rpm

have a bunch of BMW points from mid 1974 they are toast the springs were cocked and went bad
bike will start and run on them but 2500 to 3000 rpm is speed limit on motor then it sputters
put on electronic points bike runs fine

there are about 10 sets in a box marked junk in the bottom of spares box if i have not tossed it

Dave

[Eomund]

I've never seen that. If you have a set I'll buy some off of ya. That's good info thanks again.

[DAVID THOMPSON]

not for sale they dont work right does the same thing in 3 different bikes
after much experimenting there dead in the box
dave

also ran into this on a bike that set 18 years put electronic ing on it and it fired right up

[Puffs]

Following a biased and flawed moderator choice (someone posting aggressive personal attacks is rewarded, while my technical posts are removed - behind my back & without any justification!), I have withdrawn from this forum.

[Eomund]

It's definitely electrical. I have 3 sets of points coming anyway. It's just a good idea on old vehicles. I've never seen the springs float before either. But I've never owned a vehicle that had 40+ year old points so you never know too.