Vire 7HP spark plug - which one?!

T

Trevelyan

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Hi all,

My Vire 7HP (new to me last season) has been cooking NGK spark plugs (although I think that might've been through fuel starvation - carb now overhauled).

So which plug do I fit? Manual says Champion L86C, the web says...
AC M44F
AC 46FF
AC M47
Autolite A11 X
Autolite AE6
Beru 95/14
Bosch W95 T1
Bosch W175 ZIM
Champion 592
Champion LB8
Champion L86
Champion RJ 12C
Champion UJ 12
KLG F20
KLG FS30
NGK B4H
NGK B7H


Any advice from Vire owners please?

Best wishes,

Trev
 
If the manual says Champion L86C that should be your first choice.

L defines the physical size, ie thread size, reach and hexagon size

86 is the heat rating. It is a little hotter than most 2stroke outboard engine plugs.

C indicates a "copper plus" design.

NGK plugs are perhaps more common in the UK. The nearest equivalent is B6HS possibly B5HS if you need to go a grade hotter.


If you need a suppressed plug then use RL86C or BR6HS (or BR5HS)

I cannot comment on the other brands
 
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Thanks VicS that's really helpful - as the NGK plugs don't seem to have been reliable for me I'll try a Champion - however to ask the perhaps silly question - how will I know if I need to go hotter/colder on the plug? Thanks, Trev
 
Trevelyan said:
Thanks VicS that's really helpful - as the NGK plugs don't seem to have been reliable for me I'll try a Champion - however to ask the perhaps silly question - how will I know if I need to go hotter/colder on the plug? Thanks, Trev
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If you have been cooking plugs, go for a slightly colder one ... they conduct heat away better. However, Vire probably knew what they were doing when they recommended the grade they did, so it might be worth trying to find out why the last one suffered. Weak mixtures burn hotter, so that may well have been your problem.

NGK plugs are generally reckoned to be far and away the best, and I'd recommend sticking to them.
 
Trevelyan said:
Thanks VicS that's really helpful - as the NGK plugs don't seem to have been reliable for me I'll try a Champion - however to ask the perhaps silly question - how will I know if I need to go hotter/colder on the plug? Thanks, Trev
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Hotter if if tending to foul. Cooler as JD says if its burning plugs.

NGK do seem to be the most popular except for OMC Johnson and Evinrude outboards where by and large only Champions are recommended... but there were good technical (and maybe undisclosed business) reasons for that.

Which NGK plug(s) have you found unsarifactory
 
VicS said:
NGK do seem to be the most popular ...
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When I had an LPG conversion done on my Citroën DS, the warranty explicitly required that I use NGK spark plugs. Propane is harder to ignite than petrol, and generally only NGKs are seen as up to it. Fitted a set to my Herald today.
 
The NGK plugs listed in the original post -- B4H and B7H -- are miles apart in heat range. Difficult to believe they're both viable plugs for any one engine, although the heat range of modern plugs is far broader than it was when postmen smoked about on BSA Bantams.
As said, you use a hot plug in a low-tuned engine. NGK nomenclature is that a higher number describes a colder plug.
So if 4 is correct, 7 would certainly be prone to fouling. If 7 is correct, 4 could be at risk of pre-ignition. Most two-stroke outboards seem to use 5s, which seems to be a 'heavy load' alternative for the Vire.
NGK plugs have an excellent reputation.

PS. Trevelyan: it's worth stressing that you will not harm an engine by running a plug which is too cold, although you may be at risk of plug fouling/erratic ignition. You can most definitely cause harm by running a plug which is too hot, at worst melting pistons. That should tell you which way to go if experimenting to find the best one. Incidentally, do you know how to do a plug chop?
 
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There a guy in Hampshire who is the guru on all things Vire. On ebay his id is nicktheengineer. I think if you google vire, his website comes up to. Some years ago I had a boat with a failing Vire 6 and he was a useful contact.
 
macd said:
The NGK plugs listed in the original post -- B4H and B7H -- are miles apart in heat range.
Click to expand...

Most equivalence guides - I've looked at a few - say that an L86C is equivalent to a B5H or a B6H, suggesting to me that its heat rating is about a 5.5 in NGK terms.
 
JumbleDuck said:
Most equivalence guides - I've looked at a few - say that an L86C is equivalent to a B5H or a B6H, suggesting to me that its heat rating is about a 5.5 in NGK terms.
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That may very well be the case, Jumble. And a '5' in NGK parlance is probably the commonest heat rating for small marine two-strokes. Certainly an equivalence guide which recommends both a '4' and a '7' looks a bit wonky, to say the least.
 
Tried to reply, seems to have lost it, try again...
Thanks all for your responses, much better than the info on the web - which is indeed wonky to say the least! I have some L86C on the way, as the original manufacturer's spec, so will try them first. The engine is 30yr old (and inboard), so I wouldn't exactly imagine is a highly tuned beast. If I try NGK afterwards, I will start off with the cooler heat rating plugs first to play safe. Due to carb diaphragm problems (Tillotson) the engine was running weak at the end of last year, but I think I have sorted that now.

What's a plug chop macd?

Trev
 
Trevelyan said:
What's a plug chop macd?
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Something that harks back to my higher-revving years, and probably over the top for your needs.
Rather than describe it, here's a link: http://www.thequadconnection.com/walkthroughs/how-to-plug-chop!/
(WOT is wide open throttle.)
And another showing (extremes of) plug colours: http://www.apriliaforum.com/forums/attachment.php?attachmentid=52509&stc=1&d=1162587212

Although plug grade and ignition timing will have some bearing on the resulting plug colour, it principally shows fuel/air mixture ratios.

If you want to be utterly thorough you'd strip the top end and examine the colour of the underside of the piston after putting the engine through its paces, but you probably wouldn't want me to recommend that ;) Besides, it would be anal overkill on a little marine plodder.
 
Trevelyan said:
The engine is 30yr old (and inboard), so I wouldn't exactly imagine is a highly tuned beast. If I try NGK afterwards, I will start off with the cooler heat rating plugs first to play safe.
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Sounds sensible - start with a B6H and go to a B5H if the B6H isn't that nice light brown colour shown in old Haynes manuals. They're dirt cheap on eBay - couple of quid each - so you could buy one of each and experiment afloat.

Good luck!
 
Trevelyan said:
T Due to carb diaphragm problems (Tillotson) the engine was running weak at the end of last year, but I think I have sorted that now.

Trev
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Yes, apparently the carb comes from a chain saw! (you can still get the parts). Guess they had loads of those in Finland, where Vire;s come from.
 
Plug chop looks interesting macd, although chopping off the end of the thread to see the insulator seems a bit extreme - can you see enough just by looking at the end of the plug that is visible? I have also seen there are those 'colourtune' plugs available, not sure if they are any good/appropriate for a water cooled 2 stroke!

It was a B6 which it cooked last time. Then ran it on a B7 which survived... (but in the meantime I discovered that the carb diaphragms were knackered, hence running lean/low on top end power).

I managed to get the carb diaphragms straight from Tillotson which was great, however the jet settings are now completely finger in the wind... i.e. manufacturer's base settings only. Was going to go for that, then turn them out a bit more for luck....

Trev
 
Trevelyan said:
Plug chop looks interesting macd, although chopping off the end of the thread to see the insulator seems a bit extreme - can you see enough just by looking at the end of the plug that is visible?
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For your purposes, yes, you definitely can. You can also rest assured that when Valentino Rossi was winning 500cc world titles, his mechanics were not physically dismantling spark plugs: they just examined the deposits on the insulator nose.

You obviously have some determination to get the Vire running. It won't be too fussy about settings but surely you can find some better jetting information? Anyone out there have any suggestions?

Good luck (not meant in the least ironically).
 
I had managed to track down the original manual, what was causing the confusion was multifarious sites recommending a massive range of plugs which appeared to have no correlation with each other! The discussion here has been really useful to work out the appropriate heat range in modern plugs. Fingers crossed!
 
Trevelyan said:
I had managed to track down the original manual, what was causing the confusion was multifarious sites recommending a massive range of plugs which appeared to have no correlation with each other! The discussion here has been really useful to work out the appropriate heat range in modern plugs. Fingers crossed!
Click to expand...

I rebuilt one of these things the year before last and actually managed to sell it. The Tillotson carb is interesting in that it works at any angle (being ex chainsaw). The whole thing is quite cleverly designed but a bit of a nightmare. Parts are hard to find and the Vire expert is seriously expensive... Fun none the less!
 
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