Jump to content


Photo
- - - - -

Loss Of Power Over 5500Rpm


  • Please log in to reply
10 replies to this topic

#1 Goacher65

Goacher65

    Mini Mad

  • Just Joined
  • PipPipPipPip
  • 161 posts
  • Location: Maidstone, Kent
  • Local Club: Medway Mini Club

Posted 19 July 2017 - 10:33 PM

Evening All,

 

Thought I would put this out there to see if anyone has any simple solutions, or diagnosis options.

 

I have a 1380 MG Metro engine, Bill Richards Head, Kent 276, 1.5 Roller Rockers, Hif44 Carb. Lucas 59D with Aldon electronic ignitor kit. Facet silver top fuel pump mounted on rear subframe, feeding filterking filter/regulator mounted on engine bay bulkhead. Have had it rolling roaded at 105bhp @ 6250rpm, and really pleased with it.

 

Did the track day at Brands last week, and it went well, to start with!

 

Toward the end of the session, I noticed that it lost power/went flat at high RPM. I struggled to get it to rev over 5500rpm in either 3rd or 4th, but would pull well up to this RPM. It had been revving to 6000/6500rpm earlier on in the evening, and was still pulling!

 

I wasn't sure if this could have been a temp problem, but if anything, it was running a little under "N" on the gauge, I have since taken it out on the road, and it's still doing the same thing, so a prolonged track day wasn't causing it, it's there all the time.

 

Can anyone think what the cause might be?

 

Have done a compression test, results were:

1- 225psi (plug mostly brown/beige) Attached File  UNADJUSTEDNONRAW_thumb_38c2.jpg   42.37K   10 downloads

2- 225psi (plug brown/beige with a little sooting)Attached File  UNADJUSTEDNONRAW_thumb_38ea.jpg   42.79K   6 downloads

3- 235psi (as 2) Attached File  UNADJUSTEDNONRAW_thumb_38eb.jpg   40.95K   5 downloads

4- 230psi (as 1) Attached File  UNADJUSTEDNONRAW_thumb_38c1.jpg   42.8K   3 downloads

 

I have attributed cylinders 2/3 having a little sooting due to running slightly richer than the end two cylinders, a common mini problem, but none appear to be white, making me suggest mixtures are generally OK.

 

Have ordered a new coil, to rule out coil breakdown at high RPM, is there any way to test this apart from fitting the new coil and road testing again?

 

Thanks in advance!

 

Howard

 

 

 



#2 timmy850

timmy850

    Up Into Fourth

  • TMF+ Member
  • PipPipPipPipPipPipPipPipPip
  • 2,976 posts
  • Location: NSW, Australia
  • Local Club: MITG

Posted 19 July 2017 - 11:13 PM

Could it be a blocked/restricted air or fuel filter, or incorrectly adjusted fuel bowl?



#3 Ethel

Ethel

    ..is NOT a girl!

  • TMF Team
  • PipPipPipPipPipPipPipPipPipPipPip
  • 25,376 posts
  • Local Club: none

Posted 20 July 2017 - 12:21 AM

Ignition faults will hit it regardless of load, try a lower gear that will get the rpm without full throttle, a hill descent may help.



#4 minimans

minimans

    Speeding Along Now

  • Members
  • PipPipPipPipPip
  • 411 posts
  • Location: Bay Area San Fransico

Posted 20 July 2017 - 12:29 AM

soft valve springs, tappet gap's?



#5 Mervyn

Mervyn

    Mini Mad

  • Members
  • PipPipPipPip
  • 256 posts
  • Location: Telford

Posted 20 July 2017 - 06:03 AM

Agreed, check valve clearances. Bent a pushrod?

Merv

#6 Goacher65

Goacher65

    Mini Mad

  • Just Joined
  • PipPipPipPip
  • 161 posts
  • Location: Maidstone, Kent
  • Local Club: Medway Mini Club

Posted 20 July 2017 - 07:47 AM

Agreed, check valve clearances. Bent a pushrod?

Merv

Yes, that reminds me this was the next thing I intended to try! And it's free!

Ignition faults will hit it regardless of load, try a lower gear that will get the rpm without full throttle, a hill descent may help.

Hats a good thought, it would be nice to have something to isolate it somewhere instead of looking everywhere!

#7 Northernpower

Northernpower

    Mr. 7-Port

  • Members
  • PipPipPipPipPipPipPipPipPip
  • 2,409 posts
  • Name: Graham
  • Location: North Yorkshire (God's County)
  • Local Club: Its out there somewhere

Posted 20 July 2017 - 09:31 AM

Just trying to cover all the bases, check fuel pressure, possibly a collapsed/blocked rubber fuel pipe and as mentioned, possibly a pressure regulator issue. Is the tank venting correctly, remove the cap immediately after a run with the problem and listen for suction.

#8 Goacher65

Goacher65

    Mini Mad

  • Just Joined
  • PipPipPipPip
  • 161 posts
  • Location: Maidstone, Kent
  • Local Club: Medway Mini Club

Posted 20 July 2017 - 10:52 AM

Just trying to cover all the bases, check fuel pressure, possibly a collapsed/blocked rubber fuel pipe and as mentioned, possibly a pressure regulator issue. Is the tank venting correctly, remove the cap immediately after a run with the problem and listen for suction.

The tank definitely vents OK! I can see fuel leaking out if I push into roundabouts after filling up. I just have a "flip top" style cap and nothing else in the neck of the tank. Another issue I need to resolve, but not the cause of this trouble I suspect.



#9 carbon

carbon

    Up Into Fourth

  • Members
  • PipPipPipPipPipPipPipPipPip
  • 2,590 posts
  • Location: UK

Posted 20 July 2017 - 04:57 PM

Have you checked fuel flow?

 

If it's an electric pump connect a hose to fuel line where it goes into carb and run into a good size jerry can, then see how much you pump in 10 minutes.



#10 Goacher65

Goacher65

    Mini Mad

  • Just Joined
  • PipPipPipPip
  • 161 posts
  • Location: Maidstone, Kent
  • Local Club: Medway Mini Club

Posted 20 July 2017 - 09:05 PM

Bit of an update:

 

Checked all valve clearances this evening. All appear to be much as were, give or take a few thou on a couple, but nothing that would be causing a valve to stay open.

Also ran the fuel pump after the filter and seems to have good flow, didn't have a jerry can empty enough, but probably pumped 3-4 litres in the 2-3 mins it was running. Did make a video, but not sure if it's small enough to embed in here.

 

Unfortunately I don't have a pressure gauge take off on the filterking, but I do have a gauge somewhere, I shall have to put it into the the end of the feed pipe to the carb if this will still give the right reading? Any idea what pressure it should be set to for the engine spec?

 

Have also removed the K&N for cleaning, will refit that. Then, if nothing is solved, it's down to ignition. More road testing and head scratching!



#11 Retroman

Retroman

    One Carb Or Two?

  • Traders
  • PipPipPipPipPipPipPip
  • 967 posts
  • Location: Sunny Sabden
  • Local Club: CDMC

Posted 21 July 2017 - 09:23 PM

I would suspect the pressure regulator, you only need a low pressure 2-4 psi for the Su so the regulator doesn't need to alter itself much and bingo short of juice at the top end. Had it recently on a turbo motor, about a turn and a half on the screw, back to how it should be.

Try by-passing the filter and regulator. 






0 user(s) are reading this topic

0 members, 0 guests, 0 anonymous users