Idle variation SOLVED

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Mike Robinson
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Idle variation SOLVED

Post by Mike Robinson » Sat Mar 09, 2019 3:41 pm

Hello Collective

Just wondering if anyone has been down this road before , not a biggie, but something.

When coming to a stop the revs drops on idle to nearly stalling then builds back up.

Any clues! Worn needles?

The usual suspects are fine, balance, timing, jets

Thanks

Mike
Last edited by Mike Robinson on Sat May 25, 2019 6:18 pm, edited 1 time in total.
2010 Patrol T
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2016 Triumph Scrambler

rivers
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Re: Idle variation

Post by rivers » Sat Mar 09, 2019 4:59 pm

A new issue or since last tune/servicing? If the later, first suspect would be you set up/tuned the carbs on a cold motor? Throttle cable splitter getting worn/wonky? Dirty plugs?
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Mike Robinson
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Re: Idle variation

Post by Mike Robinson » Sat Mar 09, 2019 6:37 pm

A new issue after reducing the idle as it was a bit high and sometimes has a hint of dieseling when turned off.

Just rechecked the balance.

Just to make this more annoying it is intermittent.

M
2010 Patrol T
1987 BMW R65 Mono
2016 Triumph Scrambler

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Eric N
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Re: Idle variation

Post by Eric N » Sat Mar 09, 2019 8:39 pm

Dieseling is usually a lean condition on the fuel screw. Might put idle back up where it was and just crack open the fuel screw 1/4 turn on each side. If it makes it worse, you could have the less common rich dieseling and tightening the fuel screw could solve it. Lean also causes high idle, they could be related.

Vacuum petcock sometimes does the fuel starvation trick but that's more a come to a stop, things are cool for 30 seconds, then engine stalls. Fuel filter same thing.

It wouldn't be a needle thing, the needle's not really doing much at this point. I suspect you're either on the lean or rich side, and a slight tweak to the fuel screw should solve it.

Your breather may be puking oil and it's taking the bike a moment to adjust. Oil level on the high side? The slightly higher idle adjustment would be a way to compensate for it.
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Mike Robinson
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Re: Idle variation SOLVED

Post by Mike Robinson » Sat May 25, 2019 6:23 pm

Solved this by accident!

I changed the idle jet from 40 to 42 and it ran better, but still with an idle that could be nearly stalling sometimes and quite high others.

I bought a new carb sync tool - DigiSync - Highly recommended. Checked that the carbs were balanced, and they were, and adjusted the idle slightly up (my Harmoniser is somewhat broken so no RPM indication). Then put the 2new vacuum caps that come with the DigiSync on the carbs and all was well!

I guess one of the caps was leaking. Who knew.

Thanks for the input everyone. Runs very well again.

Mike
2010 Patrol T
1987 BMW R65 Mono
2016 Triumph Scrambler

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