Author Topic: instable iddle and low rpm with modified air flow sensor position  (Read 952 times)

Offline ManX84

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Hello all,

First, I made some mods on my bike, remove the big air box and put my air flow meter verticaly with a big cornet.

I have an unstable rpm a idle and low rpm (just after idle, after it's perfect, working like a fighter plane ;-) could not say precisely because for now my rpm counter is out of order but I say between 1000 and 1500-2000 rpm).

Of course I made butterfly synch, and it is a little better. I will have soon new injector and already check pressure regulator who look to work well (but could not measure pressure because I havent manometer for now)

Before exploring more my problem, is there here some peoples who made this mod ? is is a common problem with vertical air flow meter ?
(because I suspect at low rpm the the flow meter flap could oscillate in vertical position)
(and unfortunately I never run the bike before the air flow modification)

Thanks for your return!

oh please no answer like : put your air box back... this is no way ..  :nono2:   (it's a special dedication for a Frenchman  44271)

  • Aix en Provence
  • K100

Offline Laitch

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Re: instable iddle and low rpm with modified air flow sensor position
« Reply #1 on: August 20, 2023, 03:32:42 PM »
I suspect at low rpm the the flow meter flap could oscillate in vertical position)
I suspect that is the problem, but you can always put the air box back.  :laughing4-giggles:
  • Along the Ridley in Vermont.
  • 1995 K75 89,000 miles

Offline ManX84

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Re: instable iddle and low rpm with modified air flow sensor position
« Reply #2 on: August 20, 2023, 04:39:47 PM »
oh no Laitch, not you !!
I have already one in France !
 :laughing1:

I don't doubt what you say but, this is also an hypothesis for me but just would like a return from guies who made same mod.
  • Aix en Provence
  • K100

Offline Laitch

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Re: instable iddle and low rpm with modified air flow sensor position
« Reply #3 on: August 20, 2023, 08:59:35 PM »
I'm happy to be given the opportunity to state the obvious. If you are able to temporarily reorient the air flow meter so its vane axle is vertical rather than horizontal then start the engine, that could possibly reveal a validation or refutation of your hypothesis in a more convincing way than hearsay.  :laughing4-giggles:
  • Along the Ridley in Vermont.
  • 1995 K75 89,000 miles

Offline ManX84

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Re: instable iddle and low rpm with modified air flow sensor position
« Reply #4 on: August 27, 2023, 02:12:59 AM »
Hello, I come back with good news and hope useful information for peoples got same problem.

Yesterday I change my injector by new from bosch (recent 4 holes injector, bougth here : www.caferacerwebshop.com, ref on them are 0280158034).

first look to my old injectors :


* 20230826_122100 (Grand).jpg (39.47 kB . 576x576 - viewed 214 times)

I mounted new (after some adventure with ramp and stuck old injector), I made also an idle adjustment, I wend riding..and all my problem goes away!
No more instability at low rpm, velvet and watt !

Conclusion : For those who went remove big air box and put flow meter in vertical position with cornet or other filter, this work perfectly !



  • Aix en Provence
  • K100

Offline Laitch

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Re: instable iddle and low rpm with modified air flow sensor position
« Reply #5 on: August 27, 2023, 08:56:07 AM »
Thanks for the update, Man! I hope you've recovered from the shame of beautifying your ride but leaving those dilapidated injectors in its gut.  :laughing1: What is the brand and specification of the brake cylinders and levers you are using?
  • Along the Ridley in Vermont.
  • 1995 K75 89,000 miles

Offline ManX84

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Re: instable iddle and low rpm with modified air flow sensor position
« Reply #6 on: August 27, 2023, 12:48:40 PM »
Not exactly recover Laitch.. you're right, it is a shame !
I admit that I did not take the time to do much on the engine..
Brake master cylinder come from china : https://fr.aliexpress.com/item/1005004146097008.html
there are not expensive and good quality. Just one things, levers are a little loose (ok on the axis, but need a plastic washer)
 
  • Aix en Provence
  • K100

Offline ming

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Re: instable iddle and low rpm with modified air flow sensor position
« Reply #7 on: September 24, 2023, 03:45:13 AM »
thats good information m8 as i'm planning to do the same mod to my k100 and i had reservations about mounting the Maf sensor vertically. my injectors also look like yours and the T/B are minging so they are away for ultrasonic cleaning and i will try the injector refurb kit from bmw parts holland first as its only £25 , if that does'nt work i will replace with EV14 injectors
cheers
ming
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Offline jbt

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Re: instable iddle and low rpm with modified air flow sensor position
« Reply #8 on: September 25, 2023, 04:39:07 AM »
How do you know that it works perfectly as you did not ride the bike before you made the mods?  :wink:
  • France
  • K100, K1100LT, K1, K100RS, K75GS, K100+Sidecar, K1+sidecar

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