UNEVEN SMOKE TRAILS

[terrylangley]

My mates Arrow SS smokes more from the left silencer than the right and my Arrow smokes more from the right than the left especially working the engine up hill. I am not planning to try and fix it but would love to know why the exhaust smoke trails are different. I have noticed a difference on other Arrow and Leaders too. Any theories would be interesting.
Terry Langley

[bob.keevil]

hi Terry
Because they can its independent thinking (character)!

Cheers, Bob K

[bh.sprint]

Hello Terry,

My Arrow has a slight bias between the cylinders, so on start up when the choke is pushed in one cylinder does not work as well until the engine is warm.
The off-side cylinder crankcase has a slightly different shape or may be capacity due to the hollow shaft and sealing arrangement + there are some castings with porous sections.
I think there will be other things which cause variations in the smoke given off eg. compression,ring sealing , variation in passages shape and finish etc.

Brian H.

[adrie.degraaff]

The oilseals are onesided so the leftside barrel is drinking the primary oil, if you turn it round it's not drinking the oil but loosing some crankcase pressure.
To proof this you can drain the primary oil, than the smoking will stop.

If the rightside is smoking it could be a weaker spark or the plug is to cold for that side so the oil is not burned, some 2 stroke twins benefit from differend timing or pluggs.

[Eero.Korhonen]

Basically the twins left cylinder is weaker and hotter, because of direction of rotation and mixture flow.
Br, Eero

[Ivor Collins]

Hi Eero

You are right, the left does run hotter when checked with a lazer thermometer, both on the plug and around the cylinder head when the engine is stood.However, the (external) temperature difference dissapears when riding and only increases again when parked.

I still don't really understand why the left runs hotter though, can you explain?

Regards
Ivor

[keith.hodgenia]

Single carb setups usually result in one side getting more of the flow than the other. One side slightly weaker and hotter the other slightly richer and cooler.

[Ivor Collins]

Hi Keith

Thank you for your reply.

I get the idea that small variations in volumetric efficiency and thermal mass affects temperature rise but I was intrigued by the suggestion from Eero that "rotation" was a contributing factor.
It also begs the question that, having established the 'disadvantaged' cylinder, should the inlet be changed to give it more bias.

Regards
Ivor

[keith.hodgenia]

Hi Ivor, I have heard of people doing work on inlet manifolds to try to solve the problem. I think it was single carb triumphs I read about.
If the volume of each half of the crankcase is different that will have an effect, any nooks and cranies could passibly collect oil. I'm not familiar with arrows and leaders so my remarks are only general points.

[iansoady]

BSA A10s used to bias the mixture to one side. I don't think anybody actually knew why but ISTR that a slightly skewed manifold gasket / spacer was available to "correct" it.

https://www.a7a10.net/forum/index.php?topic=2570.0