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#293270 - 01/09/10 11:07 pm Dominator 88 misfires when hot  
Joined: Aug 2007
Posts: 11
lngbdr Offline
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lngbdr  Offline
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Joined: Aug 2007
Posts: 11
New Zealand - North Auckland
Hi,
Wondering if someone could help us here/point us in the right direction.
Have recently purchased a 1962 500cc SS model 88 (complete with the prev owners issues..)

The bike only misfires as soon as it gets hot-it normally takes 5-10 mins.
Its happening in every gear and not necessarily under load either.
It has has the original Magneto ignition, has a Monobloc AMAL carb and it seems to foul plugs easy as well.

What we have done:
Replaced plugs.

What we havent done:
Havent replaced HT leads.
Havent cleaned the Carburetter.

Does this sound like Ignition/Wiring or Carburetter?

Thanks - any suggestions welcome!


Thou shalt ride Nortons, Flyfish and enjoy the odd beer or two...
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#293302 - 01/10/10 12:29 pm Re: Dominator 88 misfires when hot [Re: lngbdr]  
Joined: Oct 2007
Posts: 722
norton bob Offline
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norton bob  Offline
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Joined: Oct 2007
Posts: 722
bromley uk
I have had the same problem on 2 bikes,and spent a lot of effort chasing thro electrics carbs etc,when the problem was oiling up,Is the plug deposit shiney or matt black,The mag can also oil up if the engine breather is not clear,does the breather exit near the drive sprocket?they can be flattened by the chain.Plug oiliing gets worse as the engine heats up and the oil burns instead of being blown out the exhaust.You could try a softer plug to get more running time to aid diagnosis, go carefully soft plugs can cause overheating/siezes.You have drained off the sump before starting I hope, is the oil returning to the tank?these bikes wet sump unless ridden regularly.A wet sumpped motor will oil up.

Last edited by norton bob; 01/10/10 12:41 pm.
#293613 - 01/12/10 10:18 am Re: Dominator 88 misfires when hot [Re: norton bob]  
Joined: Aug 2001
Posts: 1,921
Rohan Offline
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Rohan  Offline
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Joined: Aug 2001
Posts: 1,921
Oztralia
Does it sound like one cylinder, or both cylinders ?
Does it idle OK once hot ?
Have you set the idle once hot ?

Checked your valve clearances ?
Classic problem if the clearances are too tight somewhere, especially the inlet.

Is the petrol (gas) clean ?
No great floods of rust particles swilling around in the tank - and into the carb ?

Try a grade hotter new plugs.
They may be masking a carby or ignition problem

Does this bike have a choke system - what happens if you pull the choke on when it starts misfiring ? Or tickle the carb ?

Ultimately, the only way a magneto ignition bike will be reliable is if the maggie has been rebuilt - hint hint...
If the ignition is weak, it will easily foul plugs.

If the problem is unsolvable, and bike has been raced or had a hard life, its not unknown for a cracked head to cause this.
Crack can sometimes be very hard to see cold.
Could be a lightly burnt valve too.
But eliminate all other possibilities first....

Remember, 90% of carb problems are electrical, and vice versa.
Opethiselps, Good luck.

#293614 - 01/12/10 10:22 am Re: Dominator 88 misfires when hot [Re: Rohan]  
Joined: Aug 2001
Posts: 1,921
Rohan Offline
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Rohan  Offline
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Oztralia
P.S. Dirty points on the maggie would be worth a look first too...

#293664 - 01/12/10 7:28 pm Re: Dominator 88 misfires when hot [Re: Rohan]  
Joined: Mar 2006
Posts: 226
injunmort Offline
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injunmort  Offline
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Posts: 226
sugarloaf ny
in all liklihood, you mag has packed up. the condesor is probably perished as they made of paper the unit is 40 plus years old. i would also say the the armatture windings have broken, when the mag is cold there is continuity in the armature, as it gets hot it expands and continuity breaks down as the wire in the armature separates. i always have my mags rebuilt when i get a new bike as the first order of business. it should run about $300.00 and there are a few people on this site that offer the service. unless you have specialized tools and experience with these units it is best left to a specialist. it is real easy to break something like the slipring when taking it apart and then it gets real expensive to fix.


1948 indian chief
1937, 1939, 1962 norton es2
1950 triumph trw
1970 triumph bonneville
1975 norton commando
1972 bmw r75/5
various projects
#293756 - 01/13/10 12:45 pm Re: Dominator 88 misfires when hot [Re: injunmort]  
Joined: Oct 2007
Posts: 722
norton bob Offline
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norton bob  Offline
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Joined: Oct 2007
Posts: 722
bromley uk
Diagnose the problem BEFORE you start repairs! otherwise unless you are experienced you will build in lots of other issues and another E-Bay basket case is forming!Yes it could be lots of things including mag old age,although my 75 year old mag is still giving out Killer sparks and my 1960 alternator works just fine,Look at the simple things first that cost nothing to check.Clean the Mag points,earthing brush and pick ups,if oily check the engine breather,softer plugs should allow the engine to keep running and may eliminate mag problems. If the plug deposit is shiney then oil is the problem ,we can go from there,block the rocker feed for 10miles,if the oiling stops look at valve guides,still oily? look at rings,could be worn or new and not run in.Do check the oil is returning to the tank,the pump may be siezed or loose etc.Try to avoid a stripdown untill you find out more.Check the tail pipes for temperature, is one side colder? thats the side to look at,faulty mag windings/condenser dont create this effect.Don't rush into a stripdown or it could be years before it runs again!

Last edited by norton bob; 01/13/10 1:10 pm.
#293802 - 01/13/10 5:47 pm Re: Dominator 88 misfires when hot [Re: norton bob]  
Joined: Mar 2006
Posts: 226
injunmort Offline
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injunmort  Offline
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Joined: Mar 2006
Posts: 226
sugarloaf ny
i dont disagree with other problems as well, but yes a faulty mag does exhibit these exact symptoms. there was no mention of low compression or oil in original post. this condition will also occur with a faulty coil as stated previously. when the spark breaks down, the incoming charge just goes undetonated on the plug hence fouling.this is due to the heat build up in the armature winding. taking a mag off to have it rebuilt does not constitute the end of the motorcyle. all my mags have been rebuilt and my bikes are on the road. i dont know who you use to rebuild your mags but the service i use is generally around three weeks turnaround. i also rebuild the mags in my gravely tractors too because i work my machines.


1948 indian chief
1937, 1939, 1962 norton es2
1950 triumph trw
1970 triumph bonneville
1975 norton commando
1972 bmw r75/5
various projects
#293817 - 01/13/10 6:34 pm Re: Dominator 88 misfires when hot [Re: injunmort]  
Joined: Oct 2007
Posts: 722
norton bob Offline
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norton bob  Offline
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Joined: Oct 2007
Posts: 722
bromley uk
A mag with bad windings or condensor will bring a missfire to both sides,and needs an expert rebuild, one side out is just maintenance.

#293821 - 01/13/10 7:18 pm Re: Dominator 88 misfires when hot [Re: norton bob]  
Joined: Mar 2006
Posts: 226
injunmort Offline
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injunmort  Offline
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Posts: 226
sugarloaf ny
a motorcycle that breaks down when hot generally is ignition. starts cold runs fine til hot is almost always coil/mag. on brit twins w/2 coils if one fails the breakdown only occurs on that cylinder. he doesnt state that it is one cylinder, he says when it gets hot it starts to misfire = bet its the mag. could have a bad condensor or suffering from shellactitis or bad amature but it is almost assuredly in the mag.


1948 indian chief
1937, 1939, 1962 norton es2
1950 triumph trw
1970 triumph bonneville
1975 norton commando
1972 bmw r75/5
various projects
#293828 - 01/13/10 9:27 pm Re: Dominator 88 misfires when hot [Re: injunmort]  
Joined: Oct 2007
Posts: 722
norton bob Offline
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norton bob  Offline
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Joined: Oct 2007
Posts: 722
bromley uk
It wont be shellactitus as these mags didn't use the product.

#293929 - 01/14/10 3:30 pm Re: Dominator 88 misfires when hot [Re: norton bob]  
Joined: Mar 2006
Posts: 226
injunmort Offline
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injunmort  Offline
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Posts: 226
sugarloaf ny
i beg to differ all of my original armature were covered in shellac. from the 30's to the 50's.


1948 indian chief
1937, 1939, 1962 norton es2
1950 triumph trw
1970 triumph bonneville
1975 norton commando
1972 bmw r75/5
various projects
#294067 - 01/15/10 8:40 am Re: Dominator 88 misfires when hot [Re: injunmort]  
Joined: Oct 2007
Posts: 722
norton bob Offline
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norton bob  Offline
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Joined: Oct 2007
Posts: 722
bromley uk
d! Shellac was discontinued in the late 30S early 40S, its for sure it wasent used in the 60s on the machine we are discussing,all I'm really saying is its best to not rush into exspensive work but to look at the simple cheap to solve issues and keep the bike a runner till you are really sure of the diagnosis.Those that really know Nortons will confirm that the 88ss was a cracking bike ,fast,reliable good in all areas,perfectly capable with no modern upgrades needed if properly set up.It doesent need new valve seats for unleaded,or a belt drive and the chaincase can be leakproof.Mine is.Valve timing is crucial to making an 88 fly and the std set up often can be tweaked to wake the bike up.Ignition timing needs to be checked on both sides and errors corrected.Some O/e valve guides are too loose and Triumph ones are sometimes used.Its a better bike than my 99 or Atlas.

Last edited by norton bob; 01/16/10 5:15 am.
#295196 - 01/22/10 7:33 am Re: Dominator 88 misfires when hot [Re: norton bob]  
Joined: Aug 2007
Posts: 11
lngbdr Offline
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lngbdr  Offline
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Joined: Aug 2007
Posts: 11
New Zealand - North Auckland
yes its certainly looking like mag issues - will let you know within the week.
I cant actually tell if its only happening on one cylinder - kinda hard to tell...?

ta
Paul
Whangaparaoa
New Zealand


Thou shalt ride Nortons, Flyfish and enjoy the odd beer or two...
#295286 - 01/22/10 8:23 pm Re: Dominator 88 misfires when hot [Re: lngbdr]  
Joined: Mar 2006
Posts: 226
injunmort Offline
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injunmort  Offline
BritBike Forum member

Joined: Mar 2006
Posts: 226
sugarloaf ny
if you are inclined to bench test the mag go to bolsover.com where you can view a service manual for your mag and it has the bench test procedures to determine where the failure in your unit lies. or you can send it to a specialist have him bench test tell you it is failed and have it rebuilt with modern components so that you will be able to enjoy your norton without the fear of ignition failure on road far from home.


1948 indian chief
1937, 1939, 1962 norton es2
1950 triumph trw
1970 triumph bonneville
1975 norton commando
1972 bmw r75/5
various projects
#295456 - 01/24/10 2:39 am Re: Dominator 88 misfires when hot [Re: norton bob]  
Joined: Aug 2001
Posts: 1,253
Dave Comeau Offline
Crew Chief
Dave Comeau  Offline

Crew Chief

Joined: Aug 2001
Posts: 1,253
Hamilton, Mass. USA
I hate popularist "me too" votes for the right answer, but norton bob has it right... and I feel a need to speak up... I agree 100%.
Though I don't know about the triumph valve guide issue, I do know that the original valve seats are fine for no lead fuel. They are quite hard from OEM, the factory...


dynodave
BSA 3 1961-1963
Ducati 3 1992-2002
Norton many 1951-1975
87 Serv-Equip 100HP MC brake dynamometer,
#295541 - 01/24/10 4:04 pm Re: Dominator 88 misfires when hot [Re: Dave Comeau]  
Joined: Oct 2007
Posts: 722
norton bob Offline
BritBike Forum member
norton bob  Offline
BritBike Forum member

Joined: Oct 2007
Posts: 722
bromley uk
I bought an Atlas for my son to ride,a clunker, the PO could not get it to run for more than a few seconds.We made a snap decision that it must be the old mag that someone had fitted in place of the twin points coil system.We refitted the coil system and uprated it with a Boyer,Easy to start but no mid range guts and always issues if the battery was low.Got fed up with it and refitted the unrestored mag.It starts fine,pulls like it should and starts with a flat battery,The mag doesent oil up now either as I unblocked the engine breather,A proper diagnosis at the start would have saved a lot of time and cash!!

Last edited by norton bob; 01/24/10 4:11 pm.
#295676 - 01/25/10 1:21 pm Re: Dominator 88 misfires when hot [Re: norton bob]  
Joined: Mar 2006
Posts: 226
injunmort Offline
BritBike Forum member
injunmort  Offline
BritBike Forum member

Joined: Mar 2006
Posts: 226
sugarloaf ny
you continue to miss the point. the bike runs fine until hot then misfires. not runs for a few seconds and dies. your faulty diagnosis of your sons atlas was completely wrong for the symtom. like did you check to see if you had spark, fuel, compression. my hunch is if the mag is bench tested it has a faulty armature and bad condensor. in process of diagnosing a misfire, one does not put air in the tire to eliminate low tire pressure from being one of the possible causes.


1948 indian chief
1937, 1939, 1962 norton es2
1950 triumph trw
1970 triumph bonneville
1975 norton commando
1972 bmw r75/5
various projects
#295689 - 01/25/10 3:10 pm Re: Dominator 88 misfires when hot [Re: injunmort]  
Joined: Oct 2007
Posts: 722
norton bob Offline
BritBike Forum member
norton bob  Offline
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Joined: Oct 2007
Posts: 722
bromley uk
I had exactly the same symptons on my Ducati,Start and run fine till warmed up,then chronic miss followed by total cut out,replaced ignition coil,condensor,but fault persisted untill i fitted new valve guides, see where I,m going with this??.Don't make assumptions untill know whether the plug fouling is unburnt fuel or oil.

Last edited by norton bob; 01/25/10 3:14 pm.

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