The Triumph Dolomite Club - Discussion Forum

The Number One Club for owners of Triumph's range of small saloons from the 1960s and 1970s.
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 Post subject: Eratic idling
PostPosted: Sun Feb 03, 2019 2:32 pm 
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Joined: Wed Jul 11, 2018 1:07 pm
Posts: 14
Thanks very much for previous advice.I replaced the twin carbs on my 1977 1500 HL using studs instead of bolts,and found it easy to do that.I replaced all the gaskets,sealing them heatshield to manifold and carbs to heatshield.I got the carbs balanced,jets adjusted etc by a trusted mechanic while I watched,and he got it idling smoothly at 800 rpm.I then took the car fro a run of about 6 miles,and a couple of shorter runs.Everthing went well.However when I went on a longer runs of 15 miles,every time I had to stop at lights etc,the revs crept up to around 1500,with my foot off the pedal.I had previously fitted a new return spring and had made sure the throttle cable was not sticking and the choke was off the cam.Spraying carb cleaner on the throttle shaft ,engine running,did not effect the RPMs at all.Wondering what the problem could be,as it seems to only happen when the engine has been running for a while and the temperature is midway on the guage. Any advice much appreciated.Joe.


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 Post subject: Re: Eratic idling
PostPosted: Sun Feb 03, 2019 2:57 pm 
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Joined: Thu Oct 06, 2011 12:13 am
Posts: 2700
Location: The continent
When you are very sure it isn't an airleak and you have a stroboscope by hand you can check the ignition timing. Sometimes an advancesystem is very worn and has within 50 engine rpm a totally different timing at idle.

Sometimes it happens that you cannot adjust the idle of an engine properly because of very variable advancing around idle revs. Some engines do idle correct at 800rpm and when slightly under they die and stall immediately. That's because the weights inside the dizzy have a lot of play because of wear. For example at 800rpm they are swing out and advance and at 780rpm they just don't and cause a 8-10 degrees retard at once and making the engine stall.

Maybe at 800 revs your engine is just not advancing and when hot the idle becomes 830rpm and the ignition advances and makes the engine idle instantly high.

These other way around cases are very rare but do occur. Most of the time it's idle ok and the stall at slightly lower revs but when your's is adjusted in the revs that the weights just not swing out and a little higher revs they do that can cause your symptoms. You should be abdle to see with your stroboscope when there's a lot of timing variations around idle and an instand advance at slightly revving from idle.

Jeroen

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 Post subject: Re: Eratic idling
PostPosted: Wed Feb 06, 2019 3:13 pm 
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Joined: Wed Jul 11, 2018 1:07 pm
Posts: 14
Thanks very much Jeroen ,for your advice.I will be away for about a week,and when I get back I will check the timing and also have a look at the dizzy/weights etc.Much appreciate you taking the time to answer.Joe.


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