Author Topic: starts, idles, won't rev  (Read 420 times)

Offline schrocketeer

  • ^ Motobrick Curious
  • Posts: 105
starts, idles, won't rev
« on: February 06, 2023, 02:58:33 PM »
My RT will start and idle fine, but as soon as I give it gas, it 'stalls' and dies.

Response is the same whether I open the throttle from twist grip, or the "bar" on the throttle bodies.

On the attached 'wav' all I do is try and twist the throttle a bit.

Work recently done: throttle cable slack adjusted, fast idle A / B positions adjusted to Clymer manual.

Starts very well from Cold on Fast Idle full open (A position, according to Clymer). After a few minutes, moving the Fast Idle to the middle position (B in Clymer), it still runs clean. Multiple minutes later, it will run nicely with no Fast Idle.

Removed the Fuel Return line off of the fuel rail, and hit the Starter, to purge the fuel line (a pint on the driveway and my pant legs). Reconnected the Fuel Return line, and it started right off.

A couple of weeks ago, it was running, but the throttle tube gears were slipping, after I wrongly routed the throttle cable and it was binding. Then I resolved the binding and it worked fine, rode it 80 miles last week.

3k miles on new fuel filter.

1985 K100RT, 70k miles* bmw_start_not_rev_shorter.wav (3524.08 kB - downloaded 12 times)
  • North Alabama
  • 1985 K100RT
Ken   Current: 85 K100RT, 70 CT70, 91 XR250, 97 XR100, 06 YFM400. Past Bikes: 95 VLX600, 86 TRX250, 02 GZ250, 83 Z50R, 78 ATC90, 86 XR250, 79 XR500, 72 AT1, 75 YZ360, 78 DT400, 75 DT125, 73 Trail 70, Dad's bikes I rode: 69 CL175K3, 71 R5-B

Offline The Mighty Gryphon

  • Administrator
  • ^ Quintessential Motobricker
  • Posts: 6319
Re: starts, idles, won't rev
« Reply #1 on: February 06, 2023, 03:04:29 PM »
Check the crankcase breather "Z" tube for cracks and get back to us. 

Air leaks in that tube will cause a lean mixture at idle and just off idle.  A lean mix that starves the engine for fuel as the throttle is opened. 
  • In my garage in Marilla, NY
  • '94 K75RT Mystic Red, '91K100RS White/Blue
Current:
'94 K75RT "Ilsa, She Wolf of the SS"
'91 K100RS16V "Moby Brick Too"

Past:
'92 K100RS16V "Moby Brick" (RIP, deceased in a vehicular assault)
'94 K75S Special Edition Dakar Yellow "Cheetos"
'89 K100RS Special Edition "Special Ed"
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Offline schrocketeer

  • ^ Motobrick Curious
  • Posts: 105
Re: starts, idles, won't rev
« Reply #2 on: February 07, 2023, 09:06:33 AM »
Thank you Sir Gryphon!

"but I just replaced that Z tube. . ." Um, 4 years and 25k miles ago

Took the Z tube off, double wrapped it with electrical tape. Bike started just fine. Started, rev'ed, Stopped, 5x at home. Took it on a 10mile test ride. Squawk signed off as closed.
  • North Alabama
  • 1985 K100RT
Ken   Current: 85 K100RT, 70 CT70, 91 XR250, 97 XR100, 06 YFM400. Past Bikes: 95 VLX600, 86 TRX250, 02 GZ250, 83 Z50R, 78 ATC90, 86 XR250, 79 XR500, 72 AT1, 75 YZ360, 78 DT400, 75 DT125, 73 Trail 70, Dad's bikes I rode: 69 CL175K3, 71 R5-B

Offline frankenduck

  • Adrninistrator
  • ^ Quintessential Motobricker
  • Posts: 4626
Re: starts, idles, won't rev
« Reply #3 on: February 07, 2023, 10:11:59 AM »

3k miles on new fuel filter.

1985 K100RT, 70k miles* bmw_start_not_rev_shorter.wav (3524.08 kB - downloaded 12 times)

How many months/years?
Once I had a Collie pup. Dug a hole and covered him up. Now I sit there by the hour. Waiting for a Collie-flower.
New to K bikes? Click here.
K Bike Maintenance & Mods: Click here.
Buy parts here.

Offline The Mighty Gryphon

  • Administrator
  • ^ Quintessential Motobricker
  • Posts: 6319
Re: starts, idles, won't rev
« Reply #4 on: February 07, 2023, 11:03:40 AM »
Thank you Sir Gryphon!

"but I just replaced that Z tube. . ." Um, 4 years and 25k miles ago

Took the Z tube off, double wrapped it with electrical tape. Bike started just fine. Started, rev'ed, Stopped, 5x at home. Took it on a 10mile test ride. Squawk signed off as closed.

Does that mean it's working now?
  • In my garage in Marilla, NY
  • '94 K75RT Mystic Red, '91K100RS White/Blue
Current:
'94 K75RT "Ilsa, She Wolf of the SS"
'91 K100RS16V "Moby Brick Too"

Past:
'92 K100RS16V "Moby Brick" (RIP, deceased in a vehicular assault)
'94 K75S Special Edition Dakar Yellow "Cheetos"
'89 K100RS Special Edition "Special Ed"