No idle without choke
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From: Tony Jones on 1 Jul 2010 17:33 I have a 1987 Mazda 626 with 1.6 carburettor engine and a manual choke. I've been having some trouble with it idling - it'll only idle when the choke is pulled out all the way. Otherwise it runs OK, though fuel consumption is a bit poor (25-30mpg, probably due to the choke). As soon as the choke is pushed back in, the revs fall too fast and it stalls. The trouble is, when it's warm with the choke out it idles at about 3000rpm which is a bit annoying. It'll quite happily drive without the choke, but as soon as it comes back to idle it stalls. I was also having some problems where it would run fine, but that all of a sudden the revs would fall. A push on the accelerator sometimes kept it going for a bit, but it would usually stall - even at 70mph. I've taken it for a few 20/30-mile runs on the motorway without much change to the idle behaviour (and it's been driven on some hundred-mile runs since the problem first started to arise, so I don't think it's cobwebs in the engine). I first tried replacing the fuel filter and cleaning the points and rotor arm, with no luck. Then I removed and cleaned the carb (with spray carb cleaner) and replaced it with new gasket. That didn't seem to help much. I've also replaced the fuel pump and the spark leads. That may have helped the random stall problem, though as it's random I can't be sure. I did manage to keep it usable for a while by tweaking up the idle screw to 2000rpm, which it will idle at OK when it's hot. Below that it starts misfiring. I've played around with the mixture screw and a dicky Gunson CO meter (reckons a range of about 1.3-1.5% CO but I'm not sure I trust it) but I can't seem to prevent it misfiring below 2000rpm. The mixture setting doesn't seem to make a lot of difference to the revs or the CO output. After putting the carb back together it's behaving slightly differently... now it will only start from cold (and we're talking summer cold here - 15-20degC) when the choke is held out (that's about 2.5 stops), while before it would start OK in the winter (-10degC) on just 2 stops. There's not much I can adjust on the choke cable other than a millimetre or so, which I can't see making a difference. I've listened for vacuum leaks around the carb and head gaskets but haven't heard any. It's possible there's clag in the fuel tank, but it happens even with a new fuel filter. Sadly I can't seem to source a replacement carb or one to compare mine against, which might be the simplest option. It probably needs a decent tune up, but I need to fix the idle problem first. Any ideas? Cheers, Tony
From: Mrcheerful on 1 Jul 2010 17:44 Tony Jones wrote: > I have a 1987 Mazda 626 with 1.6 carburettor engine and a manual > choke. > I've been having some trouble with it idling - it'll only idle when > the choke is pulled out all the way. Otherwise it runs OK, though > fuel consumption is a bit poor (25-30mpg, probably due to the choke). > As soon as the choke is pushed back in and there's no pressure on the > accelerator, the revs fall too fast and it stalls. The trouble is, > when it's warm with the choke out it idles at about 3000rpm which is > a bit annoying (and eats lots of fuel). It'll quite happily drive > without the choke, but as soon as it comes back to idle it stalls. > > I was also having some problems where it would run fine, but that all > of a sudden the revs would fall. A push on the accelerator sometimes > kept it going for a bit, but it would usually stall - even at 70mph. > I've taken it for a few 20/30-mile runs on the motorway without much > change to the idle behaviour (and it's been driven on some > hundred-mile runs since the problem first started to arise, so I > don't think it's cobwebs in the engine). > > I first tried replacing the fuel filter and cleaning the points and > rotor arm, with no luck. Then I removed and cleaned the carb (with > spray carb cleaner) and replaced it with new gasket. That didn't > seem to help much. I've also replaced the fuel pump and the spark > leads. That may have helped the random stall problem, though as it's > random I can't be sure. > > I did manage to keep it usable for a while by tweaking up the idle > screw to 2000rpm, which it will idle at OK when it's hot. Below that > it starts misfiring. I've played around with the mixture screw and a > dicky Gunson CO meter (reckons a range of about 1.3-1.5% CO but I'm > not sure I trust it) but I can't seem to prevent it misfiring below > 2000rpm. The mixture setting doesn't seem to make a lot of > difference to the revs or the CO output. > > After putting the carb back together it's behaving slightly > differently... now it will only start from cold (and we're talking > summer cold here - 15-20degC) when the choke is held out (that's > about 2.5 stops), while before it would start OK in the winter > (-10degC) on just 2 stops. There's not much I can adjust on the > choke cable other than a millimetre or so, which I can't see making a > difference. I've listened for vacuum leaks around the carb and head > gaskets, but can't hear any. It's possible there's some clag in the > fuel tank, but it happens even with a brand new fuel filter and > drives quite happily apart from at idle. > > Sadly I can't seem to source a replacement carb or one to compare mine > against, which might be the simplest option. > > It probably needs a decent tune up, but I need to fix the idle problem > first. Any ideas? > > Cheers, > Tony clean the idle jet and check that the idle jet solenoid is actually working. there is no provision to alter the mixture at above idle speed. also the dwell and timing will need to be reset after the points have been replaced.
From: Tony Jones on 1 Jul 2010 18:29 Mrcheerful <nbkm57(a)hotmail.co.uk> wrote: > clean the idle jet and check that the idle jet solenoid is actually > working. there is no provision to alter the mixture at above idle speed. Thanks. According to Mr Haynes: http://i50.tinypic.com/2lik9pv.jpg I have two solenoids: 10. the idle cut solenoid valve and 11. the coasting leaner solenoid valve and idle switch. Am I right in assuming it's number 10? The idle cut solenoid has a spring and plunger, but which one is the idle jet? Cheers, Tony
From: Mrcheerful on 1 Jul 2010 18:47 Tony Jones wrote: > Mrcheerful <nbkm57(a)hotmail.co.uk> wrote: >> clean the idle jet and check that the idle jet solenoid is actually >> working. there is no provision to alter the mixture at above idle >> speed. > > Thanks. According to Mr Haynes: > http://i50.tinypic.com/2lik9pv.jpg > > I have two solenoids: 10. the idle cut solenoid valve and 11. the > coasting leaner solenoid valve and idle switch. Am I right in > assuming it's number 10? The idle cut solenoid has a spring and > plunger, but which one is the idle jet? > > Cheers, > Tony Does the solenoid click nicely when the ignition goes on? No.14 is the idle jet.
From: Conor on 1 Jul 2010 19:13
On 01/07/2010 22:27, Tony Jones wrote: > It probably needs a decent tune up, but I need to fix the idle problem > first. Any ideas? > Vacuum advance diaphragm on the dizzy split? Remove the vacuum pipe going to it and block with a bolt and see if that cures it. -- Conor www.notebooks-r-us.co.uk |