1275 black exhaust fumes after rebuild

[rayofleamington]

I used to frequent the Arden Works as it was the local supplier of Weber Carb parts and I always came away drooling over the quality of the 8 port heads which you could see being manufactured/machined behind the counter

I never got to see any of that but will never forget the sheer gas flow efficiency of the Arden head on my friend's hillclimb mini.

Drooling is probably the right term.. being able to see the valve stems when looking through a manifold is "as good as many will ge" but seeing the back of the valve head when looking through the carb was a definate reality check to me back then!

[izzi]

I contacted SU Carburetters this morning and ordered full service kits and needles,they were more than helpful.
I am back down to earth after reading your comments regarding Arden Engineering.
I removed the needles and although they were stamped AN, the tips did look different,also their lengths were not the same.( I am hoping this is part of the excess fuel problem ) photo attached for info, please agree something is wrong and not my eyes.[frame][/frame]

[bmcecosse]

They look fine to me - the needle is more than long enough to stay in the jet even if the piston goes full lift. One handy thing with an 8 porter is that in the event of a 'wet' plug - it was easy to find out which one - by feeling the 4 ex manifold pipes..... Worn jet is more likely to give rich mix - assuming fuel not overflowing - rather than worn needle. Of course - someone may have reduced the needle profile diameters in the past - to richen up the mix. Check with micrometer rather than 'eye'.

[philthehill]

I agree that the best way to check that the needle is correct is to measure the dia of the needle at specific distances along the needle. see http://www.mintylamb.co.uk/suneedle for correct dimensions.
Burlen Ltd, a very good company with a vast knowledge of SU carbs and local to me.
I would also check the fuel level in the float chamber as per the instructions on the Burlen Ltd web site and at the same time check that the needle valve in top of the float chamber is not allowing excess fuel into the float chamber so raising the fuel level at the main jet which may cause an excessively rich mixture and which cannot be rectified by adjusting the main jet.

[izzi]

Burlen Ltd are the people that are sending me the needles,full kits and instructions.

Must admit I thought the variation between the two needles (one has the tip almost worn away) would have indicated some kind of serious problem with fuel flow.
Roy

[bmcecosse]

Nah - the tip doesn't do anything - never comes out of the jet. Inspect the jet...... Sometimes you need to cheat slightly - by setting the needle shoulder v slightly proud of the piston -and sometimes (not your case) it is set just inside the piston....

[izzi]

I am still waiting for SU kits and new needles to arrive (SU awaiting delivery of needles).

[izzi]

I am still waiting for SU kits and new needles to arrive (SU awaiting delivery of needles).

At last, SU kits, needles and one new float have been delivered ( the needles were on back order hence the delay )

The good news for me is the black fumes have now gone and I am happy with the result.

Thanks for all your help.

Roy

[izzi]

That did not last long.
I got it slightly wrong, when I removed the spark plugs they revealed loads of oil, (the set up of the carb must have confused me to see black smoke go away ). now blue smoke.
Removed the head and there was oil on top of the pistons and the inlet valves ports and inlet manifold to carbs. where also wet in oil.
One of the valve seals was split and disconnected (that must be down to my bad mechanics)
I am now thinking it has something to do with the breathing system.
there is a 'Y' connector to both carbs with a pipe connected to the timing chain cover.there is no PCV valve fitted.
Roy,

[MarkyB]

Blue smoke is oil burning, it sounds more serious than crankcase pressure to me.
At least you need to remove some valves and see how sloppy they are in the guides.
Take a critical look at the bores too, is there a ridge at the top your fingernail will catch on?
Are there any scratches going the length of the bores?
Also how loose do the pistons feel at the top of their travel?

[izzi]

Hi Mark.

Valves not sloppy.
Yes there is there a ridge at the top your fingernail will catch on.
No real long scratches.
Pistons do not feel loose.
Photo attached
Prior to refit I filled the pistons with oil, left for a few days and no oil leaked passed the pistons.
I am afraid if I have a re-bore etc; and then problem is still there,also why is all all 4 pistons and inlet valves and ports showing the same problem.(have I or the previous owner missed something out)

Roy.[frame][/frame][frame][/frame]

[JOWETTJAVELIN]

The ridge is visible to the naked eye. I'm afraid to say you need to start again.

[izzi]

The ridge is visible to the naked eye. I'm afraid to say you need to start again.

Do you mean rebore ?

[Matt Tomkins]

The ridge is visible to the naked eye. I'm afraid to say you need to start again.

Do you mean rebore ?

yup, afraid so...

[MarkyB]

The finger nail test is conclusive I'm afraid.
To test the valve guides just lift the valve out about 1/4 of an inch and see if there is sideways movement, there should be none.

"why is all all 4 pistons and inlet valves and ports showing the same problem"
They have all done a lots of miles together.

[izzi]

Thanks, rebore is now my next job to do.
I suppose I new this but was being a little optimistic.
Roy.

[Matt Tomkins]

also, drop in some new valve guides and, on reassembly, use the decent 1275-type stem seals, with the springs - rather than the pathetic little 'o' rings provided with some kits

[bmcecosse]

The bores look 'worn' - but not desperate. Try it with GOOD suction on the crankcase from the inlet manifold - and new valve stems don't cost a fortune. Only put the 'top hat' seals on the inlets - NOT the exhausts......

[izzi]

Thanks everyone, after a long period having a complete re-bore etc; the engine is now back to its proper life. I am over the moon.
Roy.

[bmcecosse]

And a much lighter wallet........ Run it in carefully!