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4cyl reluctant to rev, is this normal?

Discussion in 'Rover P6 Engine 4 cylinder' started by Tom W, May 6, 2017.

  1. Tom W

    Tom W Member

    My 2200tc seems reluctant to reach the upper end of the rev range. When accelerating, it pulls cleanly from low down to about 3000 rpm. Beyond that it will rev more, but feels like it's being thrashed. If I put up with the noise and get to 4000 rpm there's a definite drop off in power. Given that the redline is 6000 rpm, is this normal? The car seems happy to sit around 3000 rpm on the motorway which is just under 70 mph.

    Is this normal for a 2200, do the smaller carbs strangle the top end? Assuming the rev counter is accurate, I wonder if there's something else wrong, perhaps with the distributor. I did rebuild it 6 years ago and fitted an electronic module, but didn't fit new springs. If the springs were weak, the mechanical advance would come in too soon, possibly at tickover. When setting the timing to the book value at tickover if some mechanical advance were already applied, then the total advance wouldn't be enough. Any way of telling if the springs are weak?


  2. harveyp6

    harveyp6 Well-Known Member

    Is it fitted with the rev-limiter rotor arm?
  3. Tom W

    Tom W Member

    No, the rotor arm is one of the standard ones, decent one not the dodgy riveted one.
  4. harveyp6

    harveyp6 Well-Known Member

    Nothing to do with the rivet, 2200TC had a rev-limiting rotor arm fitted as standard.

  5. Tom W

    Tom W Member

    I don't have one of those, the original must have gone missing at some point in the car's life before I bought it. Mine just has the plain type. What limit do the rev limiter ones cut in at? I assume it's centrifugal and breaks the HT circuit at a certain RPM?
  6. harveyp6

    harveyp6 Well-Known Member

    Most got changed because they were cr*p! Your assumption would be correct and although I never tried it I presume they'd cut in (or should that be out?) at around the redline.
  7. Tom W

    Tom W Member

    It doesn't feel like mine would get to the redline at the moment, even with a non limiting rotor arm.
  8. harveyp6

    harveyp6 Well-Known Member

    I did think it was unlikely to still have the rev-limiter, but it's such an easy fix it was worth mentioning. All you can do is run through the basics, including valve clearances compressions and mechanical advance and see what comes to light.
  9. sdibbers

    sdibbers Well-Known Member

    You say it sounds thrashy.

    Easy fixes:

    Check valve clearances
    Check valve timing (there's a sticky on here to guide you)
    Ignition contact gaps, spark plug gaps and timing
    Carb balance and tune. (This is a possible favorite for this in my opinion)

    Not quite as easy fixes:

    Maybe pull the valve cover and see if the timing chain is still tight. I have seen the rubber foot on the tensioner part company with its base and make noise. How's oil pressure? Have you any idea of bearing condition?

    The 2000TC engine normally revs easily and pretty smoothly. But it's sensitive to being out of tune.
  10. Tom W

    Tom W Member

    If it's not normal for a 4cyl to feel reluctant to rev, then I've got some investigation to do. It's certainly not willing to reach the upper end of the rev range.

    The carbs are in good condition and balanced. I rebuilt them a couple of years after buying the car, replacing everything that wears bar getting the spindle bushings replaced. I could check with the engine off that I'm getting wide open throttle with the accelerator all the way down.

    Would dashpot oil make a difference? Too thick causing the piston to rise too slowly perhaps, and strangling the engine.

    The ignition timing is correct at idle, though I don't know what it's getting to at full advance. I don't think there's enough marks on the pulley to check that, and my timing light doesn't have a dial to adjust advance to check it off the TDC mark. I've got electronic ignition, so no
    Problems with points or condensors. Spark plugs are correctly gapped.

    I checked the valve timing with the locking pins, and all was correct.

    I've not done valve clearances yet, though I've just bought a dial gauge so checking them should be easier.

    I checked the compression at the last service, 3 were even, number 4 was a little down, both wet and dry. Maybe a burned valve, or closed clearances?

    Does the fuel pump make a difference. Maybe it's worn and not delivering enough fuel for hard acceleration, but will manage steady state driving.

    Cheers, Tom
  11. Tom W

    Tom W Member

    Mine's a 2.2, not a 2l. If that makes any difference to the characteristics.
  12. sdibbers

    sdibbers Well-Known Member

    No, should feel the same. I have rebuilt my 2000TC as a 2200TC with HIF6 carbs in my car.
  13. Tom W

    Tom W Member

    This weekend I had another go at balancing the carbs to see if that improved things and to try and cure the sticky throttle linkage which was giving me a slightly high idle. The sticking throttle was due to no end float on the throttle link rod. Adding in a little end float cured that, I think things were binding as the engine heated up.

    I then went back to first principles on balancing the carbs carefully by ear. I thought I'd done a good job of balancing it before, but this has made a big improvement. It starts more easily and the idle is smoother.

    I have one of those Gunson carb balancer things, but I never had much success with it. The reading seemed to more sensitive to how the cup was placed in the carb throat than what the flow was. Plus as it relays on drawing air through the device to lift the indicator, it strangles the engine and makes it run worse.

    So, I decided to apply a bit of school boy science to it and make myself a device for properly measuring flow through each carburettor. See how accurate my "by ear" measurement was.

    A few odds and ends from the motor factors and hardware store later, I came up with a manometer. It works on a venturi, so doesn't restrict the engine. It's remarkably sensitive. Turns out my tuning by ear was within a few mm. 1/2 a turn on the throttle stop seemes to make a change of much more than this.

    IMG_0001.JPG IMG_0003.JPG

    I simply measured the vacuum on each carb and noted the level. I later added a bulldog clip to the side to mark the level so I don't need to keep drawing on the back board. Then adjust the high carb down to match the low one. Then if necessary, bring both up to get the correct idle speed.
    Quagmire and Demetris like this.
  14. sdibbers

    sdibbers Well-Known Member

    Love the manometer. Very sensitive way of calibrating things. The HIFs seem more sensitive to balance the the HS8's my car had previously, it may just that they have a higher air velocity at idle than the HSs.

    The car is revving properly now? Did you check the valve clearances before balancing the carbs?
  15. Tom W

    Tom W Member

    The car definitely seems keener to rev beyond 4K, so happy with that result. I've not tried taking it right up to the red line yet. I'm surprised carb balance made that much difference at wide throttle openings, I would expect errors to be more noticeable low down where the percentage error is larger.

    I've not had a chance to check the valve clearances yet, it was only a quick play this weekend. I have a dial gauge, so once I've bought a stand I can set that up and take some measurements. I've not managed to get consistent results with feeler gauges. Then I'll have to see if I can get my head around valve shim measurements.
  16. sdibbers

    sdibbers Well-Known Member

    Yes, I've found the dial gauge a more reliable measure too.

    On the carbs, you don't think that maybe only one carb was operating at higher revs? ( Maybe the spindle clamps was loose?) I agree the imbalance normally makes for more of an effect at low revs.
  17. Tom W

    Tom W Member

    Resurecting an old thread, I know, but I’ve been playing around with my distributor today to try and improve the top end performance. It seems weak distributor springs are part of the problem. Checking the distributor revealed the rotor arm didn’t snap back as cleanly as I’d like, so I investigated a little further. With the primary spring removed, it was possible to advance the timing to the stop without any pull back from the secondary spring. Clearly the secondary spring wasn’t doing anything! Swapping the springs over and changing the position of the cam relative to the rotor base resulted in a combination where both springs do something. There’s now always some tension on the rotor arm, whereas before there was a bit of free play at rest. I have had to move all the leads round 180deg on the cap though, so maybe this isn’t where things are supposed to be. When I checked the timing compared to where it was before fiddling with the distributor it was now retarded a couple of degrees, so clearly there was some mechanical advance coming into play at idle speed. I will replace the springs for new next, and see what difference that makes.
  18. pat180269

    pat180269 Active Member

    Are the throttles opening fully ? They weren’t on my 2200tc
  19. Tom W

    Tom W Member

    I think so. I’ll have to get an assistant to help me check where things get to when the pedal is pressed to the floor
  20. Tom W

    Tom W Member

    Checked the throttle link and cable. Everything’s opening fully as it should. I’ve been experimenting with trying to sort the distributor properly. I’ve tried substituting some different springs out of one of the spare dizzys I have. I don’t think there’s enough tension on the primary spring, so the centrifugal advance comes in too early, possibly whilst it’s being set. I need to buy an advance timing light to see where it’s getting to at the top, and work from the top down. Also, the secondary spring seems too long. The mechanism can be advanced almost to the stop before it cuts in. It also seems the inductor ring for the electronic ignition isn’t a tight fit on the cam any more, so the timing is able to wander slightly.

    More experimenting to be done.

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