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IanM
United Kingdom
2238 Posts |
 Posted - 26 Jun 2012 : 17:35:13
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As the subject says. Our BMC 1.5 was sitting ticking over in neutral, just to run the engine for a while, and the revs suddenly went noticeably higher and have stayed there. It wasn't a dramatic increase but was enough to notice and enough to make the new idle speed sound a bit "rushed", if you see what I mean. I checked that the throttle cable was not sticking and this weekend I turned down the adjustment screw until the engine speed was more "normal". I have nothing as complicated as a rev counter so it's all done by ear (and by vibrations!).
The adjustment screw is fairly stiff to turn so I don't think it moved on its own. Any suggestions for the cause? Anything to worry about? |
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df
United Kingdom
5994 Posts |
Posted - 26 Jun 2012 : 18:47:26
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Did you adjust the right screw Ian, often on a lucas/cav pump the screw the throttle rests on at idle is an anti-stall device and not the idle screw, theres often another screw on the stop lever that the idle should be set on.
Fuel starvation will cause revs to increase on a diesel, what happens under way with a bit of load on?
Modern diesels are more prone to the bug.
NBAS--The communal colostomy bag of the boating community.
Visit leomagill.co.uk |
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IanM
United Kingdom
2238 Posts |
Posted - 26 Jun 2012 : 19:00:59
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No idea if it's the right screw. Couldn't see much in the way of adjustment on the throttle or stop cables or where they attach. I've got a couple of workshop manuals for the engine but neither tell you where the screw is (despite mentioning adjusting it!). There are two obvious candidates. One is vertical and the other is shorter and angled towards the block. An experimental quarter turn on each revealed that the angled one changes the idle revs. The other had no apparent effect so I set it back to the starting position.
The fast tickover remains fast when under load. Before I made the adjustment the engine performance seemed fine. I have not really had chance to test the performance since the adjustment, apart from engaging gear on the mooring to make sure it didn't stall. We'll be out again in three or four weeks so I can test it better then.
(For the purposes of your reply, are you classing the engine as modern?) |
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df
United Kingdom
5994 Posts |
Posted - 26 Jun 2012 : 19:41:41
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quote:
(For the purposes of your reply, are you classing the engine as modern?)
No, I don't class mine as modern either, is it a rotary pump or inline, piccies would help, I'm guessing it's a lucas dpa or similar (mine have roto-diesel(ie.lucas/cav/delphi) dpc's).
NBAS--The communal colostomy bag of the boating community.
Visit leomagill.co.uk |
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IanM
United Kingdom
2238 Posts |
Posted - 26 Jun 2012 : 22:56:17
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Yep, as I was typing I was thinking "should have got some piccies".
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cliveshep
Thailand
1324 Posts |
Posted - 28 Jun 2012 : 19:03:42
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The usual reason for a revs increase is air in the system somewhere.
This can be simple - slight leak in the pipework or filters allowing the air to get trapped in the main injector pump - and old BMC's were notorious for this having a rotary pump which was and is a total pig to bleed out.
Another thing I learnt recently is that this Government's mania for adding ever increasing quantities of bio fuel to diesel is producing ever more breakdowns on older engines as the pump seals degrade with it.
Replacements seals are now of a different material not affected.
The cost of boating is insignificant compared to costs of a young wife and two teenage kids! |
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BMC idle speed suddenly increased
