Dirty plugs

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fett

Well-Known Member
Posts
8,637
Location
South Hampshire
Well as some of you may have seen in my other post

http://www.landyzone.co.uk/lz/f10/more-problems-my-classic-hell-81761.html

I had seome idling problems and missing on the over-run and most annoyingly only 7 cylinders for a mile in the morning.

I took out the stepper cleaned it and the idling problem is much better and the overun problem was only noticable when revved hard-ish in neutral.

I have done all the service items, as I said before but the new plugs are as coked up as the old ones, (which also had done 1000 miles) which have only done a thousand miles max.

some are only coked up on one side, and one plug looked ok for 6000 miles but not 1000. They are all black with coke, two were a little petroly. I have cleaned the old ones and put them back and it runs well at the mo.

Took it to the garage when I first got it and they said emmisions were spot on and petrol smell was a fuel leak(sorted) so not running rich.

In my old post, I asked if there should be a vacume hose on both sided of the advance and retard and told only one side, which side? as thers a nipple on both.

I was also told if I can suck through pipe then unit is shot, I can suck through with engine off so , do I need to replace vacume unit? can you buy it seperate from dizzy? and will this cause coke-ing of plugs?

If not what else is causing it? It does seem to use too much fuel but then its the 3.9 v8 pulling 21/2 tonnes of classic rangie so I thought it might lol

Sorry about the war and peace length post , just wanted you experts to have all the facts.

Many thanks

John.
 
Back in the day a coked plug, when all else was OK, used to mean wrong grade of plug, I'd try a different grade.
 
Thanks , to some of you lol.

I have tried the champions and the ngks , both the same and the correct plugs acording to LR and Haynes.

Why is the coke only on the 1 side of some plugs, is any part of it to do with the advance/retard on the dizzy?
 
That's what i was getting at Gemsdad .. and fett, it could easily be the advance/retard mechanism .. it's obviously either not sparking at the right time, or the plug is just wrong! Following the line of logic that the plugs are right, suggests that the advance unit or vacuum advance might be shot.

Personally I'd take the whole dissy off and re-build it or replace it. If the plate isn't moving or can't move then that's the issue.

Mind, it could also be the coils, HT leads, LT leads, condensor, could be many things and all need checking and fettling/cleaning up/replacing!! I dunno specifics about the RR V8 but it sounds to me like it needs a damn good 'proper' service ... ;)
 
That's what i was getting at Gemsdad .. and fett, it could easily be the advance/retard mechanism .. it's obviously either not sparking at the right time, or the plug is just wrong! Following the line of logic that the plugs are right, suggests that the advance unit or vacuum advance might be shot.

Personally I'd take the whole dissy off and re-build it or replace it. If the plate isn't moving or can't move then that's the issue.

Mind, it could also be the coils, HT leads, LT leads, condensor, could be many things and all need checking and fettling/cleaning up/replacing!! I dunno specifics about the RR V8 but it sounds to me like it needs a damn good 'proper' service ... ;)

You maybe right about the service. But there are two stages of advance the first one being the bob weights that deploy after start up and the second the vacuum advance which is progressive at higher RPM. If the engine is running retarded at higher RPM because of failed vac it should run hotter not cooler. Maybe something as simple as a new air filter could solve his problem. Putting a strobe on the timing marks and making sure he is getting full advance would answer his question about distributor.
 
Again, that was what I was getting at .. I should have said the centrifugal advance unit or vacuum .. as I say I dunno the specifics of RR dissy, but most have a two-stage advance and it could easily be either stage that's fecked.
 
Ok its had brand new genuine plugs, leads , rotor,cap , air , oil , and filter and fuel filter , and a new fuel tank , not that is relevent though.

It sounds sweet till the plugs dirty up. As far as I am aware there is no condenser on electronic ignition.

I have not the kit or the skill to time it up with a strobe and I am not even sure that the electronic ignition disributers can be timed up ????

So am I now right in thinking that the advance and retard will not affect the dirty plugs issue? if not and some of the plugs are only dirty on one side of the electrode is it that the fuel injectors are not giving the proper spray pattern?

It cant be right to change the grade of plugs from what the factory intended surely?

Is it possible to get seperate parts for the dizzy such as the advance, reatard unit , if so can I fit it in sutu?
 
i think you need to change the fuel filter, get back on ebay and buy a forte petrol treatment for a tenner. change the air filter as well. think you may see a drastic improvement.
 
So, like we said ... from the plug diagnosis .. "Can be caused by many different conditions. Carbon deposits build up when the plug fails to fire correctly and burn them off. Air/fuel mixture too rich, choke stuck on, electrical problem, extended periods of low speed driving, plug heat range too cold. All should be investigated"

You might need different grade plugs 'cos the engine is worn and beyond the original parameters for the grade of plug originally specified!
 
Fair point about the wear , I also do-do alot of town driving , however I have another 4.0 v8 in my bmw and it does not bother it, plugs clean after 12k miles.

I cant imagine I am back to the 1930's having to clean the plugs every 1000 miles to keep it running properly lol
 
I cant imagine I am back to the 1930's having to clean the plugs every 1000 miles to keep it running properly lol

You're not ... try a hotter grade of plug.

The difference could surprise you ..

I know it's not the same engine but on my old Fantic Trials bike if I put a hot plug in it would run cleanly all through a Trial, 'cos it was just pottering about. If I then tried to run it on the road, green-laning, I would have to swap plugs as it'd coke up! Engines can sometimes be extremely sensitive ...
 
Ok its had brand new genuine plugs, leads , rotor,cap , air , oil , and filter and fuel filter , and a new fuel tank , not that is relevent though.

It sounds sweet till the plugs dirty up. As far as I am aware there is no condenser on electronic ignition.

I have not the kit or the skill to time it up with a strobe and I am not even sure that the electronic ignition disributers can be timed up ????

So am I now right in thinking that the advance and retard will not affect the dirty plugs issue? if not and some of the plugs are only dirty on one side of the electrode is it that the fuel injectors are not giving the proper spray pattern?

It cant be right to change the grade of plugs from what the factory intended surely?

Is it possible to get seperate parts for the dizzy such as the advance, reatard unit , if so can I fit it in sutu?

No need to time anything. If you are not sure if the auto advance is working all you need to do is get someone to check it with a strobe. A chalk mark or a little white paint on timing pointer and one on crank pulley timing mark, point strobe at it and as you rev engine the mark on the crank pulley should move as the auto advance acts. If it does not you know your dissy is suspect.
 
someone said that if you suck on the vacume hose and you can keep sucking its knackerd, that seems easier than strobeing with a strobe I dont have. I have sucked and can keep sucking lol. thats with the engine off.

would explain slight miss on overun too.

so if its knackerd, can i get parts or is it a new dizzy?
 
someone said that if you suck on the vacume hose and you can keep sucking its knackerd, that seems easier than strobeing with a strobe I dont have. I have sucked and can keep sucking lol. thats with the engine off.

would explain slight miss on overun too.

so if its knackerd, can i get parts or is it a new dizzy?

You should be able to suck it then put your tongue over the end and it will hold vacuum, if you can't do that there is a leak in the diaphragm. You certainly used to be able to get parts like that but these days it will most likely be a new dissy. Nobody seems to stock bits to repair things these days just replacement units.
 
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