classic motorcycle forum

Motorcycle Discussions => Japanese Bikes => Topic started by: petrolderek on June 23, 2018, 07:45:43 PM

Title: spark plugs
Post by: petrolderek on June 23, 2018, 07:45:43 PM
Has anyone else had any problems with new spark plugs. I have worked with engines all my life and am now retired so I have had quite a bit of experience but in the past few years I have had loads of problems with new plugs breaking down. I have a 305 dream and its on its third set of new plugs and its not done 100 miles. Today I started my Yamaha yds5 and it was misfiring on the right cylinder checked the plug and there was no spark changed the plug for one that was in the bike when I got it that must be 30 years old and its fine. These plugs in the Yamaha were new a month ago. Checked the plugs resistance and its showing 30k but the old ones show OL. So what's happening any ides the only thing I can think of is I have had them in and out quite a few times when I had a piston ring problem could it be taking them out when hot or just handling them is causing the problem.
Title: Re: spark plugs
Post by: murdo on June 24, 2018, 12:29:40 AM
I've had similar problems with new plugs. Remember when you had to save up your pocket money to buy a new plug for your paddock basher? These days the plugs are made cheap and cost about the same as 1/2 cup of coffee.
Suggest you look for some old stock plugs. I found two Champions in USA for my YDS5 that ran better than the NGKs I could by at local shop.
Still have some Belgium and German made Champions for my Maico. They would last for a couple of years of hard riding where as the NGKs might last a day.
Title: Re: spark plugs
Post by: TGR90B on June 24, 2018, 07:46:42 AM
A couple of years ago there were a lot of fake NGK plugs on the market. Perhaps some are still about, but not a problem I've heard of recently. Have you tried Bosch plugs?
Title: Re: spark plugs
Post by: iansoady on June 24, 2018, 10:09:23 AM
As I understand it, older plugs had a "gloss" finish to the insulator nose inside the body of the plug, which allowed for cleaning. Modern ones have a matt finish and once fouled are almost impossible to clean so are effectively scrap.
Title: Re: spark plugs
Post by: Rex on June 24, 2018, 10:34:42 AM
I'd go along with that. If new plugs get "wetted" under the nose insulator it seems they can't be cleaned effectively any more. The so-called Green Spark Plug Co refused to replace two 18mm plugs which failed from the first start-up as they said I'd put the plugs in a cold engine and "wetted" them. They couldn't explain what I should have done  with an engine which hadn't run in decades and this was the first start.....
It seems amazing to me that old bikes and cars carried the owners to work without any problems but cossetted classics seem to have failing plugs on a regular basis.
Title: Re: spark plugs
Post by: petrolderek on June 24, 2018, 06:06:49 PM
This is interesting. These plugs were NGK and have been "wetted" a few times, I had a contact breaker fault then found that at some time it had been fitted with some under size rings so the engine has been flooded a few times. I have never herd of this wetting issue before. So just drying them out doesn't  work. I am going to have to take the carbs off again and fit some new float valves to stop it flooding or I am going to be knee deep in spark plugs.
Title: Re: spark plugs
Post by: murdo on June 24, 2018, 10:58:39 PM
This may be of some interest to you.
Title: Re: spark plugs
Post by: iansoady on June 25, 2018, 10:21:43 AM
Interesting article.
Title: Re: spark plugs
Post by: petrolderek on June 25, 2018, 12:30:01 PM
I have just read the article I think it should say more leakage occurs not less leakage.

And when the green spark plug company said you fitted the plug in a cold engine they must have been referring to the mixture being too rich and not the actual temperature of the engine because it make no sense otherwise.

Its occurred to me that the plugs have never failed while the engine was running its always when the engine has been left for a few days and the engine is cold and it doesn't start, could it be putting the choke on wets the plug. The Yamaha was running fine when I stopped it but two days later it wouldn't start due to the plug. I don't remember having these problems back in the day.