Exhaust analyzer

Started to make adjustments to the SU needle last week, but its hard to see what’s happening, so I borrowed Wayne’s exhaust analyzer to check the mixture.

I Noticed that at lower rev’s it was running very rich and at high speed it was still lean I think. It’s a bit hard to say as the readings are very erratic, but I think that’s what it was.

So I adjusted the low speed mixture with a screw on the carb, and adjusted the needle a bit more to give me more fuel at higher speeds.

After installing the needle back in the SU carb, I was thinking “I don’t really know how far the piston goes up at full throttle, I need to find out somehow“.  This is so I know where to make the needle thinner, to get more fuel.

And that’s when Brian, showed up, he’s in our club. He loves photography, so with his massive tele-lens he made some great photos. Thanks Brian!!

SU piston 60{7d16e8204fe0e6723feb9d00795e42e38ac880e6f88f519e81a8ab927d02eaa1} up

As you can see the piston is up, about 60{7d16e8204fe0e6723feb9d00795e42e38ac880e6f88f519e81a8ab927d02eaa1} or so. This is at full speed !  🙂

Now if you do the calculations, the carb has an 2″ opening, the engine has an 1.5″ opening, that means that the carb needs to open 56{7d16e8204fe0e6723feb9d00795e42e38ac880e6f88f519e81a8ab927d02eaa1} to get all the mixture into the engine, so that’s looking good.

Just not sure yet if that’s a good thing or bad. Doesn’t matter I suppose for the fuel / air mixture ratio.

I think its still running a bit rich at low speed now and about 14{7d16e8204fe0e6723feb9d00795e42e38ac880e6f88f519e81a8ab927d02eaa1} at high speed which is what is required, so maybe that’s it.


Here is me looking at the rev counter and the exhaust analyzer:

Checking exhaust analyzer

So at the moment, the engine is running really nice, and people say it runs a lot nicer, so that must be good, just not sure if I have more power….

1 thought on “Exhaust analyzer

  1. Hi Gert,

    Looking good.
    Just an observation from your photo’s etc.
    To get maximum airflow through your intake system, there needs to be a smooth transition between each component.
    The inlet to the carb requires a a bellmouth. (flared trumpet).
    If there is a sharp reduction fom the carb 2 inch diam to the manifold 1.5 inch, then this step will not allow the full airflow possible. Requires a smooth matched diameter tapered connection.

    Cheers, Neil.

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