Fouled plug - still

[Macbeth]

Guys I had this 1960 SR rebuilt, cost an absolute ridiculous amount as top to bottom build. It was running ok (cheap Chinese carbs were fine prior) yet inside was damaged considerably inside the bore, piston, crank shim etc etc so I decided full rebuild

It popped a head gasket on its first start with the new engine. He replaced that & it appeared to run 5klm perfectly. At about 6klm it started fouling the left plug heavily .. it’s an oily sort of carbon. If I put a clean plug in I get 1-2 klm before it fouls again

Enricher looks ok & operates ok. Never had any issues with the carb, enricher prior

So is it a best guess with a black oily plug (photo)  that it’s popped a head gasket again ?

I only ask so I have a direction to ship the bike back to the engine builder. I have absolutely nowhere other than the side of the road to investigate as I don’t live in a place where I can do anything with it at all

Whilst the plug photo looks like dry carbon - if I wipe my finger on it ..its sort of oily

[BagONails]

Sorry to say but I think I would have to be taking it back again Mac... It shouldn't have blown the gasket the first time and it looks likely that it's happened again. Do you know what CR it's running now, does he?

Time for head off and close inspection of all mating parts, are all the joint faces flat? Are all the threads good? Were the barrels decked? was the cylinder head joint face skimmed?  If solid copper was the gasket fully annealed? (necessary even with a new one). What torque did he do up the head bolts to? (50 Nm) Did he use the correct sequence?  Look at the bolts/ washers/ threads/ spot faced areas the washers sit on are they clean and flat (should be thick, hardened washers, no spring washers etc.)

If possible, stay there with the guy while he inspects everything have a good look yourself and ask questions.
Good luck with it all.

[Macbeth]

Cheers Ian. I was worried when I noticed it was oily soot. I’ve limited mech experience myself. The bloke has extensive experience re- building old brit bikes from the 20’s onwards up to crazy blown turbo Harley’s & owns old brit stuff himself..a very busy shop where he did my bike himself. I’ve full confidence in his skills base as I saw how pedantic he was building it.

I’m just concerned now that if this is the 2nd time on an engine with 6-8 klm on it ..where’s it stop ?  Anyway mate I appreciate it & it’s time to get the bike tpt or stop every 2 blocks to put a new plug it as I attempt to ride it there

From my knowledge it was rebuilt to a stock spec

[muskrat]

G'day Ian.
I have those carbs on my Cafe (twin carb same as yours) and had similar problem. The enricher (choke) plunger has a rubber seal on the bottom of it. One of mine had fallen out when it was in the ultrasonic cleaner and I didn't notice when reassembling. One side was running rich as buggery.
The problem with those carbs is their bot left hand, the right side pilot screw is very hard to get to and a bit of a contortion to get to the enricher button. I converted to cable and lever on the bars.
Cheers

[Macbeth]

G'day Ian.
I have those carbs on my Cafe (twin carb same as yours) and had similar problem. The enricher (choke) plunger has a rubber seal on the bottom of it. One of mine had fallen out when it was in the ultrasonic cleaner and I didn't notice when reassembling. One side was running rich as buggery.
The problem with those carbs is their bot left hand, the right side pilot screw is very hard to get to and a bit of a contortion to get to the enricher button. I converted to cable and lever on the bars.
Cheers

Musky that won’t give me that oily plug in minutes as in my photos though will it

[muskrat]

G'day Ian.
Yes it will and especially on a new motor. Easy enough to check that than lift the head.
Cheers

[Macbeth]

G'day Ian.
Yes it will and especially on a new motor. Easy enough to check that than lift the head.
Cheers

Ok ta mate.  Im useless on mechanical stuff outside oil changes & small adjustments. I just need it sorted & then just keep changing the oil. I’d assumed unburnt petrol couldn’t oil the plug like that

[trevinoz]

Did the builder give the bore a coarse hone or real fine as modern engines require?
Usually the rings supplied with the pistons for our old bikes need a coarse hone.
I have seen it before, nice new bore and smokey, honing cured it.
The bloke that does my work took a bit of convincing as he honed as per the modern ring manufacturers but several people had smokey engines as a result.
He did come around to my way of thinking.
Did you over oil when assembling? Minimal lubrication and start it and give it hell.

[Macbeth]

Did the builder give the bore a coarse hone or real fine as modern engines require?
Usually the rings supplied with the pistons for our old bikes need a coarse hone.
I have seen it before, nice new bore and smokey, honing cured it.
The bloke that does my work took a bit of convincing as he honed as per the modern ring manufacturers but several people had smokey engines as a result.
He did come around to my way of thinking.
Did you over oil when assembling? Minimal lubrication and start it and give it hell.

No mate I wasn’t there for any of it. I tend to try & keep out of their hair. Busy shop & they don’t need me in there. He kept me up to date though & it took a long time getting acceptable barrels etc A lot of new ordered parts were very poorly spec’d like rods, wrist pin bushings, cam parts etc I remember. He is a bit over the top with specs & I was ok waiting knowing that. The shop was his dads from the 60/70’s & he started his apprenticeship in there on old brit bikes. Very pedantic type of bloke

Any way it’s going to go back. It is such a beautiful bike when it’s running though & im a dyed in the wool BM guy. I do like its sound & its handling

[Macbeth]

G'day Ian.
Yes it will and especially on a new motor. Easy enough to check that than lift the head.
Cheers

Maybe time to just buy 2 (or 1 if the manifolds are available) new Amals & start at the front also.. I was always going to ditch the Chinese things anyway

[muskrat]

G'day Ian.
Good luck finding a single carb manifold, they do appear on fleabay from time to time. Don't get caught by the long stroke one.
My carbs are proper Keihins by JRC, but am tossing up to go back to Amals Mk2 this time. Waiting for the Lotto win a pair is $1000AU and I'm unemployed at the moment.
Cheers

[Macbeth]

G'day Ian.
Good luck finding a single carb manifold, they do appear on fleabay from time to time. Don't get caught by the long stroke one.
My carbs are proper Keihins by JRC, but am tossing up to go back to Amals Mk2 this time. Waiting for the Lotto win a pair is $1000AU and I'm unemployed at the moment.
Cheers

Yep I’m still picking myself up off the floor mate.

[Macbeth]

G'day Ian.
Good luck finding a single carb manifold, they do appear on fleabay from time to time. Don't get caught by the long stroke one.
My carbs are proper Keihins by JRC, but am tossing up to go back to Amals Mk2 this time. Waiting for the Lotto win a pair is $1000AU and I'm unemployed at the moment.
Cheers

Ok head gasket it is

Musky what’s the go here ..put another copper one in or find a composite one ?

If this next head gasket doesn’t work you’ll likely see the entire bike on fleabay for the highest bidder. Beautiful bike..love it but I can’t own something I can’t ride or pay to get fixed

[muskrat]

Mate, have you checked the enricher seals?
Cheers

[Macbeth]

Mate, have you checked the enricher seals?
Cheers

Had a bloke look at it just now- he pulled carb apart & said it’s fine & said it’s the gasket. Engine builder said it’s the head gasket (he knew it was) so I’m lost as to just what I have to do to get this thing going.