Spark plugs & heat range.

[Jonesy]

Mate, until someone comes up with anything better I'll take that line of thought as the truth. Its the  best reason I've heard so far.

[classiXS]

Regarding the BP6ES or BP8ES difference.

I have never had the pleasure of dismantling the engine on either a Midnight Special or a RH, and therefore doesn`t know if they came with the exact same head as the european "Sport", but i suspect that the bike shown on your Haynes-book could be a 5K7 Sport, and also thinks that could be a part of the spark-plug confusion, since that model were fitted with larger inlet/exhaust valves...

Could there be some sence in that assumption?   

[Jonesy]

G,day Cooper
Thanks for the plug info
just going through your list of possible causes of running hot.
Nil brake drag.
Oil ways clear, no sludge
Timing is the next to check. as soon as I can get it running again
just waiting on a valve shim(thanks Grant Aussie XS) and a washer for the carby(thanks Petejw1966)

[Cooper]

Just on spark plugs again I went a little further and installed platinum plugs. Crossed reference from NGK BP6ES or standard plugs Bosch WR7 DPX  apparently a shade hotter than NGK half the price of Iridiium plugs. Plugs not so oily starts are instant whether  engine  cold or hot heat range is similar these plugs generate slightly more power for ignition spark . Have been running now since major service three months ago I think the bike runs better certainly cold starts are easy.
 Had a bike some years back with extra hot engine found rear brake caliper binding didnt really notice much difference in performance  also if timing is advanced a couple of degrees it will have an effect on engine and also restricted oil plug or bolt  into oil filter created by sludge also partially blocked oil galleries`preventing full flow and slowing oil to oil rad.Could be faulty oil pump  Could try an engine flush then install new filters. Brian Cooper

[Jonesy]

Hey Geoff
Yeah they should have the holes , my local bike shop reckons the difference will be very little. and if I were to order replacements for the originals I'd probably be supplied with the ones without holes anyway. The bike had a bit of a flat spot down low before I put it into the workshop for a service/tuneup.
If I dont get any improvement I'll chase onother one with the holes........

[steptoe]

 ay Paul,, dem dere tubes should have holes,  the early ones have 4 holes, mine has 3 holes,,

not engineeringly sure,, but I think the holes are what cause the fuel to atomise, before being light enough to be mixed with the air as it comes thru

[Jonesy]

Emulsion tubes are all good but the pilot jet on No2 was blocked up with that green powdery stuff mentioned earlier, another couple of things I found was
1 & 4 mixture screws were 2 turns out (1&1/4 reccomended)

No 3 pilot jet doesnt look original coz doesnt have those little holes up the side of it like the others do

QuestionFor the trained mechanics
will it make much difference not having the holes up the side?  like restriction of air or fuel or whatever it is that gets sucked through them?

Jionesy.

[petejw1966]

also while u have the main jet out of number 2,
pop the top of the slide off and pull the emulsion tube out,
ull probably find it has muck on it similar to the main jet.

[Jonesy]

PM sent

[petejw1966]

if that washer was missing, that would give u a similar effect
to the float level being lean, as the jet is sitting higher than the other ones,
 which would result in that cylinder
running hotter, and as u said with the affect on the needle would
be on the lean side also.

txt me or pm me ur address if u need a washer,
ive got a spare 1 sitting here.

[Jonesy]

G,day Pete
I'm using a Haynes with mostly orange on the cover and a pic of an RH or midnight special???/ Its not a standard anyway.

Float heights all check out Ok with the method you describe.

I think I might have narrowed it down. (overheating). In the photo you can see the gap between straight edge and main jet on No 2 This is because the washer is missing underneath the jet, and, correct me if I'm wrong this would be the same as lifting the circlip on the needle and leaning off No2

I noticed earlier, before the overheating event. With the temp sensor gun that from cold No2 exhaust was heating up  heaps faster than the other 3. but didnt really register as a problem.

Next Question. does anyone have a spare I can beg borrow or steal......if not know where I could get one?


Only on No2 You might be able to pick out the bowl and the post that main jet screws into have a green powderised deposit on them related or not I dont know? I havent got to the idle mixture screws yet.....I'm hoping to find out of adjustment to further nail down the overheating

[petejw1966]

hey jonesy,

which manual are u using?  my clymers says
bp6es for the spark plugs.

if ur engine is over heating, check ur float heights,
from experience a lean float height is a major cause of
these engines running excessively hot, the early models
are set at 25.7mm with the carbs upside down without the gasket.

[Jonesy]

by the sound of things you blokes are saying and what info is in your books the 6 or 8 thing is really not a big issue and probably not why my bike was smoking. But at least now I have a plug that is one of the reccomended type.
Now I'll have to look for other reasons for overheating.
I found one inlet and one exhaust v/v clearance only one shim size out of tolerance so thats not it.
The carbies are coming off today for a once over
Any suggestions where else to look?

Jonesy.

[steptoe]

the book does say 8, but whether they are all o/s printed or not, I don,t know if that make a difference, but most mechanics and people in the know seem to run 6's,,btw, that's what's in mine, and has been for yrs

[Jonesy]

Like Errol, I've played with the plug ranges and can't find any "measurable" advantages in either direction from the standard BP6ES

BP6ES ay?

My book (haynes) says BP8ES ..........(do do do do do do enter spooky music )

Going through the good book it says incorrect timing can cause motor over heating too so I'll check that too when its all back together with new juices and filters