[B40RT]

My B40 has a bit of an appetite for plugs, tried different makes with little discernable difference.
Also use different carbs, Amal for those where you have to, and Kehin the rest of the time.
Burns a bit of oil so plug gets black anyway and difficult to get a proper picture.
Runs a ticks over fine (particularly with Kehin) then develops a slight misfire before plug gives up completely.
New plug and away she goes. Have heard this isn't unique to my bike.
Any ideas ?
Thanks
Ross

[Old trials fanatic]

B40RT, on Mar 28 2010, 09:28 PM, said:

My B40 has a bit of an appetite for plugs, tried different makes with little discernable difference.
Also use different carbs, Amal for those where you have to, and Kehin the rest of the time.
Burns a bit of oil so plug gets black anyway and difficult to get a proper picture.
Runs a ticks over fine (particularly with Kehin) then develops a slight misfire before plug gives up completely.
New plug and away she goes. Have heard this isn't unique to my bike.
Any ideas ?
Thanks
Ross

My old one was the same in fact so is my James and the Ossa. Noe fit a new plug before every 3rd trial just to be safe. Well it's not as if they are that expensive.

Still would be nice to know a reason they dont seem to last all that long nowadays.

[houseape1000]

I know its not quite the same, but....I bought about 10 plugs off ebay for about 3 quid when I was trying to set the carb up properly on my old 96 scorpa, I thought for the price of the plugs, once Ive fouled them I will throw them away......The electrode was bigger than standard, wider.....kind of. When I put the correct plug in it seemed to run crap, and I ended up using the plugs with the fatter electrode, just ran better somehow.

[Stork955]

Gday - what colour is the plug? If "wet" looking and black, it is oil fouling. Fix that and your plug problems will go away. Modern plugs are better than old plugs and are commonly blamed for other engine issues. If the plug is "dry" and black, it is fuel fouling and menas your carburettion needs adjustment. Of couse it may be perfect at idle and too rich on the needle, or vice versa, or it also could be caused by a blocked or over-restrictive air cleaner. Also, are you using the correct heat range plug for your engine? Always go with the plug recommended by the manufacturer, they really do know what they are talking about (in most cases anyway...)

Let us know.

Cheers,

Stork

[bigwig]

What plug no are you using? Try a ngk 4 heat range , end of problem. One blip and plug will burn off clean. Always used them on Ariels, Triumph twins and Villiers Dots. ie Ngk bp4es 3-4 reach and bp4hs 1-2 inch reach. no problem with melt down, summer or winter and road trials. Bet you are using 5, 6, or 7s.

[jon v8]

If the motor is burning oil then you are not going to get the best out of it anyway,do you think its ring,bore or valve guides or all three causing the oil use?
I think I'd concentrate more on getting the motor up to scratch before worrying about carburation or plug heat ranges.

[B40RT]

Thanks OTF,houseape1000, Stork955 & bigwig.

OTF - its about a plug a trial so would like to find a solution.

houseape1000 - tried all sorts of plugs, crossreferenced, not much difference.

Stork955 - plug is dry and blackish, carb (Amal) is new and has all the jets, slide cut away, needle etc as recommended by Surrey Cycles. Plug is NGK BPR5ES or Bosch W8DC which is recommended. Bike runs well and foam air filter is oiled with Partner air filter oil, I have tried less oil in the air filter but it makes the running worse. What do you think of bigwigs recommendation of a BP4ES ?

bigwig - have tried a 5 & 6 and as you say has made no difference. Thought you risked you piston by using to cold a plug, so never went that way. Is this a long term solution?

Thanks

Ross

[B40RT]

jon v8, on Mar 29 2010, 01:03 PM, said:

If the motor is burning oil then you are not going to get the best out of it anyway,do you think its ring,bore or valve guides or all three causing the oil use?
I think I'd concentrate more on getting the motor up to scratch before worrying about carburation or plug heat ranges.

Hi jon v8. Plenty of power, and its only a slight blueness to the exhaust gas, so never bothered to do anything about it.
Would agree if there were clouds of smoke following me about.

[jon v8]

A blue tinge shouldnt be a problem then,I'm wondering if its that fussy about its plug then it could be down to the strength of the spark.I run a Land Rover garage specialising in diagnostics and emission problems - esp Range Rover v8's running on LPG.This has taught me lots about engine tuning/running problems.Now,the first thing I do with them is to scope all the HT leads,this tells me a great deal about whats going on.I've found that coils and leads etc,(which all seem OK with a multimeter) can give a weak spark and cause partial misfires etc.
Might sound a bit much but its worth a thought ?

[Old trials fanatic]

Dont know about running a BPR plug. Why run a resistor plug ?

I know the PVL system doesnt like resistor plugs. FWIW i never use em but then again mine still eats plugs every 3 or 4 trials. Perhaps i need to open the throttle more? Perhaps i'm just pottering around too much ?

Did try gettings some 4's but everybody local is sold out and have been told by their suppliers that they dont have any either.

Dont know if NGK are phasing them out ?

[Stork955]

Gday Ross, a dry looking black plug plug is too rich. I assume the bike runs OK? The next step would be drop the needle a notch (raise the circlip one spot) and see how it goes. Id leave the plug as is for now, Im always worried by going to hotter plugs to correct other issues. In fact Ive made quite a bit of money out of it over the years. Let us know what you find.

Cheers,

Stork

[B40RT]

Thanks again for your input all -

jon v8 - I've literally just put on a new coil and havn't been out since, I will see what happens.

OTF - only plugs I could get were resistor, will keep using them with the new coil to try and rule the coil / ht out.

Stork955 - you may well be right as it runs fine at the the bottom of the rev range.

I'le keep you posted, may be some time as winter has returned !

Ross

[bigwig]

if you seek advise why dont you take it. I told you I have used 4 s on road trials even in summer. These will cure your problem. You will probably have to order a box from your local ngk dealer. Fed Hardy of Hardy Triumph fame also found the same and always used them. You are not road racing you are riding a lawn mower. These plugs are what you need. Only need to worry about over heating is if the head thread has been badly helicoiled exposing the plug thread to combustion.ngk plugs go down even to a 2 heat range though very hard to get. Loads of road cars run on 5s. Finished

[B40RT]

bigwig, on Apr 2 2010, 10:17 PM, said:

if you seek advise why dont you take it. I told you I have used 4 s on road trials even in summer. These will cure your problem. You will probably have to order a box from your local ngk dealer. Fed Hardy of Hardy Triumph fame also found the same and always used them. You are not road racing you are riding a lawn mower. These plugs are what you need. Only need to worry about over heating is if the head thread has been badly helicoiled exposing the plug thread to combustion.ngk plugs go down even to a 2 heat range though very hard to get. Loads of road cars run on 5s. Finished

'bigwig' I thank you for taking the time to answer, but your answer does confict with others above, hence my hesitation.

This post has been edited by B40RT: 03 April 2010 - 11:47 AM

[pat slinn]

I find it hard to understand what people are getting at here. I admit I have no experience of running B40's with electronic ignition or funny carbs. Just for the record I ran a C15 and a B40 thru most of the 60's and into the early 70's. I used Ordinary bog standard Lucas energy transfer, or std coil ignition on the B40. ( the C15 had a Lucas experimental system on it from 1965) I used a Champion N5 in both machines. If you checked the contact points before each event the systems were virtually trouble free. I s'pose I looked at and checked the spark plug every so often, and probably put a new one in before the Scottish !. O'h and by the way both bikes usually started 1st or 2nd kick.