Hitchcocks Forum

So I've been having trouble with my spark plugs recently resulting in them sooting up and failing almost after every journey and for the life of me I couldn't find the reason why.

A friend offered to have a look at the bike for me and almost immediately he noticed that there was only one cable attached to the throttle body. The bottom cable housing was in place but there was no cable and no nipple.

I tried to trace the cable back through the bike and it looks like it only goes back to the throttle handle grip to complete a loop (so to speak) so my question is this:

Does the cable run through any other sensor that I can't see and would it affect the running of the bike and spark plugs?

Thanks in advance for any thoughts...

Suds

It must be the closing cable which has broken or you would have noticed.
Perhaps the butterfly isn't closing properly and confusing the TPS and ECU?
There doesn't seem to be any sensors on the cables.
Frank

Thanks Frank.

Further research leads me to believe that it is basically an opening cable and a closing cable, even though it seems to close without the cable because of the strong throttle spring.

I wonder if it is worth repairing it or not as the throttle seems to work ok at the moment, however, like you said could it be affecting the fuel mixture and therefore the plug?

Suds

The butterfly shaft is held closed down and onto its stop screw purely by return spring pressure.



The return cable needs enough running slack to prevent any binding inside the cable loop that it's rendered useless for pulling the butterfly closed until such times as the main pull cable breaks thus allowing it to do so.

However if that were to occur and the broken inner cable jammed inside its outer preventing the return spring from doing its job, then in that particular instance one might wish for a working return cable...

The parts book lists it as a twin cable so unless you just fit an inner cable, it looks like you'll have to buy both.
I'm only guessing that this might be the problem, but you must have part of the closing cable in there and it could probably
have a frayed end which could jam inside the outer cable and hold the throttle open - something you don't really want to happen!
I would at least remove the broken inner cable, even if you don't replace it.
Frank

With regards to plug sooting, assuming the correct grade is being used; is the idle too low or the TPS set a bit high?

This makes me wonder why modern bikes have two cables plus a return spring. Is it just H&S belt and braces?

I think its to comply with American laws, like having the gear lever on the wrong side and having a kill button on the handlebars.
Frank

Soon these bikes will come fitted with handlebar holsters and the old tax disc holders will be used to display the relevant gun permit

Thanks for all the replies...

Definitely the correct spark plug as I've checked it against the service manual, I've even tried a lower number plug to see if it dealt better with shorter journeys but no luck.

One other thing I've noticed is a very small hole in the rubber tubing (connecting the throttle body and something behind it. Would that affect the plug?