ET: Engine (Twin) Leak down test

Cyborg

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Bill,

You don't need the lockring. You can bore out the threads and make the guide to fit. As long as the interference fit on the whole guide is fine, they work fine. They were like this on the big port head also. The prewar aluminum heads had lots of problems holding their shape.

David

Was it a photo of one of Alp’s heads I saw recently where he just used the interference fit? Can’t recall where I saw it though.
 

Bill Cannon

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Well the bike is back together. Thanks for everyone's advice.
I got my mini grinder out and put some grooves around the inlet guides to stop oil pooling. I found nothing wrong within the engine.
I did find that the decompression lever was binding slightly on it's pivot and had minimal cable clearance so I fixed these.
Refilled the tank and added BMW/Shell fuel additive as it's easily and cheaply available for me!

Started up and the problem was exactly the same, erratic running on the rear cylinder.
Counter-intuitively I richened the rear carb by screwing the needle out and things improved, after two turns the rear seemed to be pulling cleanly and was sucking the palm of my hand nicely. So pretty sure it's a fuel problem of some description.

I'm now wondering if it's wear in the throttle slides letting too much air through.
With carbs that are now at least 50 years old do I try to recondition as I like them when they are working or change to Mikunis or something else?

Cheers Bill
 

Bill Thomas

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For performance the Gardners were good, Proved that I had a fuel problem with the Mk1 Concentrics.
Was always fiddling with the Gardners , !, Didn't shut down the same twice !.
So went 36mm Dellortos Lots of money, tricky to jet, but once set right, Super, And best performance too,
Good chokes etc.
But needs the float valve out of the 40mm carb'.
Or in your Bike maybe 40mm Carb's ??, Mine was only a 998cc on 12 to 1 pistons, 100 octane petrol, 1970s.
But now 9 to 1 on the road since 1980.
 
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BigEd

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.........


Counter-intuitively I richened the rear carb by screwing the needle out and things improved, after two turns the rear seemed to be pulling cleanly and was sucking the palm of my hand nicely. So pretty sure it's a fuel problem of some description.

I'm now wondering if it's wear in the throttle slides letting too much air through.
With carbs that are now at least 50 years old do I try to recondition as I like them when they are working or change to Mikunis or something else?

Cheers Bill
Is this still using Gardner carbs as mentioned somewhere earlier in this thread? Adjusting the mixture seems to have improved things so you are on the right track. I have no experience with Gardner carbs. I use Mikuni carbs on my Rapide and perform well. They are well made, available in many sizes and spares are easily available. (P.S. Bill must have sent his post above while I was writing this.)
 

greg brillus

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Very difficult to tune race carb's on a street bike unless they are set up the same as a road type carb......That is, the float levels are fine the idle stops are set up (which most race carby's don't have) this issue alone will cause quite a bit of grief. If a slide for example is closed too far, it will draw anything it can, including oil through valve guides.......If set up rich it may still fire on that cylinder but the cylinders will never be even in their running........This may explain why the roof of the combustion chamber was quite carboned up with oil burnt deposits.........Something to think about. I just went through this same process with a pair of racing Amal TT 's on a road going Shadow, and tuning them was not easy.........
 

Bill Cannon

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I just finished stripping and rebuilding the Gardners..
I noticed that the jets are not sealed to the throttle slides so I fitted O rings under the flange. Cleaned up everywhere and because of the modular construction with all screw together parts of the body, decided to put sealant on the joint faces.

This seems to have solved the problem. The misfiring has all gone and both cylinders are pulling properly. It needs synchronising again but already sounds much crisper than it has for a long time.

Maybe the Gardners still have a life left in them after all!

Cheers Bill
 
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