AFR testing

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Dormouse
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Re: AFR testing

Post by Dormouse »

Float is adjustable at the tab for holding the float needle.
jgra1
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Re: AFR testing

Post by jgra1 »

i think it's a plastic tang though DM ? i am used to metal ones you can bend.. I will look into it all a bit more soon, and report back ;)
Dormouse
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Re: AFR testing

Post by Dormouse »

Sportax tune these engines. Might be worth looking up.
Typical. They make the needle carrier fixed so you have to change the lot when it wears slightly.
A less restrictive/ better designed exhaust will help too.
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moizeau
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Re: AFR testing

Post by moizeau »

It would still be very worthwhile checking the fuel height even if the float isn't adjustable. If nothing else it will tell you if the needle jet seals in it's seat. I can't remember whether amals have a small sprung pin on the top of the needle jet that gets pushed by the float tang but if they do and the fuel height is too high or flooding it's quite likely that this spring has relaxed with age. If you need to replace it only ever buy genuine for the brass parts. They are expensive but worth it, after market kits (even Keyster) are good for the seals but not reliable for the brass bits. I've just had to replace 2 needle jets out of the 4 carbs, probably the most expensive part of the bike £/gm.
Dormouse
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Re: AFR testing

Post by Dormouse »

moizeau wrote:
18 Jun 2021, 15:20
It would still be very worthwhile checking the fuel height even if the float isn't adjustable. If nothing else it will tell you if the needle jet seals in it's seat. I can't remember whether amals have a small sprung pin on the top of the needle jet that gets pushed by the float tang but if they do and the fuel height is too high or flooding it's quite likely that this spring has relaxed with age. If you need to replace it only ever buy genuine for the brass parts. They are expensive but worth it, after market kits (even Keyster) are good for the seals but not reliable for the brass bits. I've just had to replace 2 needle jets out of the 4 carbs, probably the most expensive part of the bike £/gm.
found this which also describes your fuel height tube
https://www.classicbritishspares.com/bl ... oat-height
jgra1
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Re: AFR testing

Post by jgra1 »

thanks all.

the good news is:
The machine just fitted into the X7 Saloon! and once home, the scope and the exhaust analyser appear to work!

I did a quick test on the exhaust anyway, and the AFR was anywhere between 12 and 10! (I may hook it up to a newer vehicle to prove it's reading sensibly)

Is it possible to see the high voltage trace? These machines always appear to have a grey clamp (for the centre lead into the distributor cap, and a red clamp for cly#1) also, I think I need battery + / - and a wire from the coil (terminal CB?) - obviously this is a single coil bike with one HT lead. Coil wires are orange and black (so I am guessing orange is the signal wire, and the one I need)

edit. CB of course refers to contact breaker! so, the wire from the coil to the CDi unit on the bike.. this is the signal wire I need to attach the crypton to... makes sense ;)
jgra1
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Re: AFR testing

Post by jgra1 »

I used the analyser on my new(er) bike, and the needle stayed at about 13 and slightly drifted up (leaned) with revs, showing good emissions on the gauge. I may repeat this on the MG as well as it's all good info :)

I also noticed for the first time, the idle speed screw was doing nothing in the bike carb! I think a previous owner has cross-threaded it, and this was masked somewhat by an o-ring making things feel tight! so, using the spare carb body, and reverting back to a main jet of 190 (from 230) and the 2A7 needle, the bike felt better to be honest, however, it is still running rich according to the exhaust analyser (especially with rising throttle), is still a bit boggy and has the slight backfire through from the exhaust and also in the air box (also, for this test I have removed the Airfilter)

assuming the bike is in good condition otherwise, the float height is acceptable, and the none-adjustable ignition (I will check this) is ok - I am not sure how to progress now.. I did move the needle one step down but to no avail really..

IT sounds like I am throwing the towel in ,but not yet! :) I am still just messing around and enjoying it...
next I will experiment with the 2 slides, one is marked 3 1/2 and one marked 3 - what do these numbers mean? (edit, height cutaway)

also, I managed to get some sort of trace on the scope part! nothing that useable, but it was alive!

other things, I will check the fuel height, and may buy a new main jet / needle and will do another carb dismantle, clean and blow through as I cant remember if I did that on this carb body before !
I will also read up a lot more now on carb principles, as I have avoided anything to do with them until now... :twisted:


edit - there is plenty of reading, and new jets are cheap