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Author: Subject: Strange air fuel ratio change
bikecarbfred

posted on 21/6/20 at 01:54 AM Reply With Quote
Strange air fuel ratio change

All I did was leave the car sat 6 months and change the intake runner hoses that sit between the carb and intake manifold.
I changed the hoses because the first lot were abit flimsy and not a tight fit although I did use jubilee clips.

The AFR has now gone seriously lean from idle to partially lean at 1/4 thottle and the air fuel mixture screw is already out 2.5 turns out.
I am hesistant to turn out the mixtures more because I want to know what is exaclty happened.

Ive opened the carbs and they are like new. Not a single stain on the float or bowl. The jets are super clean also.

If the original hoses were lose, shouldnt that mean it shou have been causing lean conditions then.

it seems back to front.

[Edited on 21/6/20 by bikecarbfred]

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snapper

posted on 21/6/20 at 07:10 AM Reply With Quote
First off check for air leaks, spray a bit of WD40 around the rubbers 1 at a time, if revs rise then that’s where the leak is





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gremlin1234

posted on 21/6/20 at 09:12 AM Reply With Quote
how old is the fuel?
is it standard unleaded?

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bikecarbfred

posted on 21/6/20 at 09:28 AM Reply With Quote
99 Ron. I did put another 8 quid of fuel into it. How long does it take for fuel bowls to empty on idle to 2K revving parked up?
Thought it would be richer if dodgy fuel.

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bikecarbfred

posted on 30/6/20 at 10:43 AM Reply With Quote
I believe I have found the problem. I had to turn the mixture screws out abit more to sort the problem but Why did I have the problem in the first place if nothing had changed apart from the colour of the hoses on the runners.

Although they were the same length , there were made out of different material and the carbs angle changed by around 2-3 degrees because the softer rubber hoses made carberutor drop abit. They new hoses are solid and keep the carbs are the proper angle.

I did not realize such small difference can affect AFR so much. Crazy!

[Edited on 30/6/20 by bikecarbfred]

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Mr Whippy

posted on 30/6/20 at 11:47 AM Reply With Quote
so what happens when you drive on a slope...
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bikecarbfred

posted on 30/6/20 at 12:27 PM Reply With Quote
the engine and the carbs change angle at the same time down or up a slope

where as i had the carbs at a different angle to where they are now in relation to the engine

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Mr Whippy

posted on 30/6/20 at 01:47 PM Reply With Quote
Sure it wasn't just a small air leak on the old hoses? Good you got it sorted anyway.
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bikecarbfred

posted on 30/6/20 at 01:58 PM Reply With Quote
There could have been a leak on the old hoses as they were a flimsy thin hose, but why would that cause more fueling.

That should have caused a lean condition. This is what I need to know . any science gurus there

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Schrodinger

posted on 30/6/20 at 02:36 PM Reply With Quote
If the hoses had a slight kink in them the cross sectional area would have been smaller restricting the air flow and in doing so make the mixture ritcher.
Just a guess





Keith

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bikecarbfred

posted on 30/6/20 at 02:48 PM Reply With Quote
That's it , you got it.
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