Forum sponsored by:

failing spark plugs

Search for: in Thread Title in

steve williams 3	19/11/2009 19:43:18
28 forum posts 49 photos	can anyone help, i have recently finished makeing a 23cc 4 stroke engine of which i a realy chuffed BUT i have a problem. the engine starts fine & runs for afew minutes ishut it down make a few adjustments then start it again and it will run again realy good. after doing this a few times i found it wouldn't start invastigations found the spark plug was no longer working new one purchased (MINIMAG FROM REEVES) started fine again for a few times then the same happened, no spark. just purchased a more expensive plug (rimfire from hemingways & blow me after 5 mins of runing same again plug has failed. i am runing 12 v gel battery, mechanical contacts with condensor & a small motorcycle coil. does anyone have any ideas as its getting expensive & frustrating
Pat Bravery	19/11/2009 20:06:43
96 forum posts 24 photos	I would check the coil out as the internal insulation could be breaking down when it warms up,
AndyB	19/11/2009 20:19:50
167 forum posts 7 photos	I would check the condenser, coils tend to misfire when they start to break down before totally failing. Are the points burning from too much arcing? They could be blackened and maybe starting to pit. Please give a bit more detail about what actually happens when it dies as this can give a good clue. Edited By Andy Belcher on 19/11/2009 20:23:08
Les Jones 1	19/11/2009 20:34:32
2292 forum posts 159 photos	Hi Steve, If the problem is caused by the plug and not the previous suggestions then I think oil is getting past the rings into the cylinder or the mixture is very rich. Is the plug black with a carbon build up? If it has a layer of carbon on the insulator this will short out the spark. If the mixture is correct the plug should be brown in colour. Black indicates a rich mixture, grey indicates a weak mixture. Try sandblasting one of the failing plugs to remove any carbon build up and see if it then works. Les.
Martin Cottrell	19/11/2009 21:11:09
297 forum posts 18 photos	Hi Steve, It sounds a bit odd that you should be knackering plugs after a few minutes running and it does point towards a coil break-down as Patrick said when the coil warms up. Have you actually tested the continuity through the plugs to check that they are indeed dead? Have you re-tried any of your "dead" plugs after a cooling down period? Another thing you could try when the fault occurs next, is to remove the spark plug wire from the end of the plug and (using a pair of insulated pliers!) hold the end of the plug wire just off any bare metal surface on your engine and flick over the flywheel and see if you get a spark from the end of the wire. If you get a spark then probably the plug is faulty. If you get no spark then you need to look elsewhere, coil, points, condenser & also check all the associated connections are clean and tight. One thing quite often overlooked is the plug lead itself. Check the continuity through the plug lead. Quite often a broken plug lead will allow a spark to jump the gap in open air when carrying out the test above but will fail to give an adequate spark for ignition in the pressurised confines of the combustion chamber. Hope these few pointers may help but ,as Andy requested above, a few more details of what happens and what you've actually tried would be good! Regards, Martin.
steve williams 3	20/11/2009 18:28:34
28 forum posts 49 photos	thanks everyone that replied, problem now solved. it seams to have been a combination of faulty coil & bad conection on plug both rectified now running well many thanks steve
Ian Abbott	20/11/2009 19:46:48
279 forum posts 21 photos	To check for power at the plug wire, get a bystander, wife, kids, cat's tail, they will tell you if the coil output is satisfactory. Don't ask me if I've done this. Ian

All Topics | Latest Posts

Please login to post a reply.

Magazine Locator

Want the latest issue of Model Engineer or Model Engineers' Workshop? Use our magazine locator links to find your nearest stockist!

Find Model Engineer & Model Engineers' Workshop

You can unsubscribe at anytime. View our privacy policy at www.mortons.co.uk/privacy

Latest Forum Posts

*Oct 2023: FORUM MIGRATION TIMELINE*
05/10/2023 07:57:11
Making ER11 collet chuck
05/10/2023 07:56:24
What did you do today? 2023
05/10/2023 07:25:01
Orrery
05/10/2023 06:00:41
Wera hand-tools
05/10/2023 05:47:07
New member
05/10/2023 04:40:11
Problems with external pot on at1 vfd
05/10/2023 00:06:32
Drain plug
04/10/2023 23:36:17
digi phase converter for 10 machines.....
04/10/2023 23:13:48
Winter Storage Of Locomotives
04/10/2023 21:02:11
More Latest Posts...
View All Topics

Support Our Partners

Shopping Partners

Subscription Offer

Latest "For Sale" Ads

Reeves** - Rebuilt Royal Scot by Martin Evans
by John Broughton
£300.00
BRITANNIA 5" GAUGE James Perrier
by Jon Seabright 1
£2,500.00
Drill Grinder - for restoration
by Nigel Graham 2
£0.00
WARCO WM18 MILLING MACHINE
by Alex Chudley
£1,200.00
MYFORD SUPER 7 LATHE
by Alex Chudley
£2,000.00
More "For Sale" Ads...

Latest "Wanted" Ads

D1-3 backplate
by Michael Horley
Price Not Specified
fixed steady for a Colchester bantam mark1 800
by George Jervis
Price Not Specified
lbsc pansy
by JACK SIDEBOTHAM
Price Not Specified
Pratt Burnerd multifit chuck key.
by Tim Riome
Price Not Specified
BANDSAW BLADE WELDER
by HUGH
Price Not Specified
More "Wanted" Ads...

Get In Touch!

Do you want to contact the Model Engineer and Model Engineers' Workshop team?

You can contact us by phone, mail or email about the magazines including becoming a contributor, submitting reader's letters or making queries about articles. You can also get in touch about this website, advertising or other general issues.

Click THIS LINK for full contact details.

For subscription issues please see THIS LINK.

Digital Back Issues