Eating Plugs

[b40rt]

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.

Hi Pat

Having this problem with an Amal carb, bike starts easily, runs well, plenty of power - but I can feel the plug going off, then a slight misfire, then stops. New plug, good as new.

Ross

[motomike]

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

Ross

Why dont you give bigwig`s sugestion a chance ?

I dont know if you know who he is , but believe me ,he has a wealth of knowledge on all kinds of competition motorcycles,

and is worth listening to !

[charlie prescott]

Hi Guy's.

I think a lot of the problem is the fuel we have to use now-a-days. The only way to cure a plug problem is to keep trying different ones until you find one that works. Try Big wigs idea. Any way surely you carry a couple of plugs in your pocket, and a plug spanner taped to the bike ? So what is the problem, some bikes eat plugs some don't, you has to live with it.

Regards Charlie.

[old trials fanatic]

Was thinking about this very thread earlier today. What prompted me revisiting the issue was this.

I was sawing some logs for the wood burner with my petrol powered chainsaw. Now this chainsaw has been in use for at least two years by me and it was second hand when i bought it. Whats the significance you may ask? Well i have never even had the spark plug out never mind replaced it. I run the chainsaw on whatever fuel is left over from the trials bikes, remember the ones that seem to eat a plug every 3rd or 4th trial, and some of it may be standing for months. So why does the trials bikes get through plugs like they have shares in NGK and the chain saw has never seen a new plug? Well back to my original premise. The chainsaw runs at full throttle ALL the time and the trials bike very rarely ever does. They both run on exactly the same fuel other than the bikes get new and the chainsaw the dregs.

So my conclusion is we dont thrash the bikes enough. Thats why they keep fouling the plugs.

Well it's logical. Whadda you think?

[charlie prescott]

Hi Guy's

Hi OTF.

Yes you could be right, but don't forget the chain saw has oil in the mix? or it is not going to last very long.

Could it be if you use the dregs, the evil ethanol has evaporated from the can? Perhaps we should add a drop of oil to the fuel mix and see if that makes a difference?

Regards Charlie.

[pat slinn]

Yes, the Old Trials Fanatic may have something here. Remember in the good old days before the advent of closed circuit trials, and acrobatic sections there used to be some good long flat out in 2nd muddy climbs ? I am thinking of some of the Cotswold sections, Camp, Warren, Dovedale etc. AND, not to mention some of the fairly long road sections, between sections where you had to get a move on or you suffered a time penalty. You really did have to "work" the motors then.

[ausy300pro]

My thoughts, is ignition system ok ? don't know who it was but only one person suggested testing ignition system, when an engine eats plugs it is usually a weak ignition unless it's throwing oil up the bore, can you get an iridum plug for it ? any iridium plug requires far less voltage to create a good strong spark, the denso one's are the best in this respect (have a look at the sparkplugs.co.uk site for the full explanation). I know it's not rectifying the problem but if it keeps bike running it must be worth a try for nine quid, I always run iridium plugs in my bikes and they last forever. (not literally before anyone get's smart)

[jon v8]

I think you need to treat each problem individually,back in 1988 I ran a TY250r that ate plugs.I went through allsorts trying to sort it out,in the end it was just going down on mainjet size that fixed it.The plugs didnt matter as they were only old V8 Rover ones - but once the mainjet was sorted a secondhand plug lasted for ages.As a kid I had a D3 Bantam that would only start from cold after the plug had been scratched around with a pencil lead - yet the spark looked fine.Later I had a Beamish RL250 that had such a weak spark you could not see it in daylight - yet it always started first kick and ran fine.

There is a bloke locally having problems with a Whitehawk fouling plugs,he has had it for years,rides it the same way still - does nothing different.Yet a plug wont last 2 trials,so something has changed.In his case I think its a weak spark that is just strong enough to work when the plug is new,but as soon as the electrodes get slightly coated in carbon there is not enough voltage to make it jump the gap.

I guess its what is called experience.......

[bigwig]

Final -final say. Go to ngk usa website and it will explain a lot better what me and jon v8 are telling you. Look at bultaco for instance ,trials bikes list 5s and motocrossers 9s. The correct heat range for all trials bikes is 4 or 5. If your bike runs a bit rich and has any guide or bore wear use a 4, it will be no problem. manufacturers always cover themselves by quoting to colder plug no as standard so if you totaly abuse an engine they are in the clear. I am totaly fed up with this subject,now. So order up some 4S of the correct configuration and if you are not happy I will buy the rest from you. I reiterate you are riding a trials bike not going for a land speed record on an air cooled Indian.

[jordi]

I reiterate you are riding a trials bike not going for a land speed record on an air cooled Indian.

Now that was a good film!

However do take bigwigs advice on the plugs.

[b40rt]

Thanks all

Ordered, as no one keeps them on the shelf.

Ross

[big john]

Final -final say. Go to ngk usa website and it will explain a lot better what me and jon v8 are telling you. Look at bultaco for instance ,trials bikes list 5s and motocrossers 9s. The correct heat range for all trials bikes is 4 or 5. If your bike runs a bit rich and has any guide or bore wear use a 4, it will be no problem. manufacturers always cover themselves by quoting to colder plug no as standard so if you totaly abuse an engine they are in the clear. I am totaly fed up with this subject,now. So order up some 4S of the correct configuration and if you are not happy I will buy the rest from you. I reiterate you are riding a trials bike not going for a land speed record on an air cooled Indian.

Ross, believe me 'Bigwig' is a very knowledgeable fellow, sincerely if he told me to do something, I wouldn't hesitate in taking his advice!

I had a similar problem with the Matchless in 2004 during the Pre65, I went through heaps of spark plugs (I reckon I kept NGK going that year!) Turned out the carb had completely worn itself out (Amal 624) but having said that, the NGK 4 grade plug lasted longer than any of the other ones I had in my tool belt that weekend.

A new carb was fitted up another Amal 24mm job and I doubt if I have changed a plug since! (except as a treat for the bike anyway!)

Cheers,

Big John

[Andy]

believe me 'Bigwig' is a very knowledgeable fellow, sincerely if he told me to do something, I wouldn't hesitate in taking his advice!

Wiggy, tell Big John to buy a round

[matchlessman]

My AJS (Magento ignition) tends to eat NGKs, but seems fine on Champions. It's obviously concerned about the Japanese invasion, if a little late. I do have to give it a good blat every so often between sections to 'clean the plug'. I'll be giving NGK - 4's a go to see if that works.

From another angle, a road going B40 of mine used to get through plugs every 500 miles until I replaced the coil.

Edited April 22, 2010 by Matchlessman

[b40rt]

My AJS (Magento ignition) tends to eat NGKs, but seems fine on Champions. It's obviously concerned about the Japanese invasion, if a little late. I do have to give it a good blat every so often between sections to 'clean the plug'. I'll be giving NGK - 4's a go to see if that works.

From another angle, a road going B40 of mine used to get through plugs every 500 miles until I replaced the coil.

Thanks Matchlessman, also just replaced the coil & HT lead. Couldnt get NGK 4's anywhere so have ended up with Champions equivalent.

29th & 30th should be a reasonable test !