hunting idle - Attn Filthy John

[Vart]

evening all,

whilst sitting in traffic i've noted my idle goes a little odd after a while. is there a normal cause for a stead idle to start dropping by 200/300 rpm then bounce between normal and (normal minus ~300rpm) until a little gas is given to it? the current idle speed seems linked a fair bit to the ambient temperature if this helps?

would the plugs be at fault as in wrong temperature - there NGKs from the (often incorrect imho) hellfrauds guide?

the engine runs on sometimes and judders to a halt when either hot or after a lengthy idle? mixture fault?

that its hunting behavior is new leads me to think mixture but hellfrauds....

cheers

toby

[Chris_C]

I'd agree with mixture mate, the Halfords reccomended NGK's are a good plug.

Those symptons, plus you saying temp related I reckons it's part of the hot air feed to the air filter. Check the spaceman tube primarily, then the flappy paddle that chooses between cold air and space man hot air. I'm running Fake without that setup atm, and she's doing the same in this cold.

[Vart]

with the bonnet open the pipe with the air thermostat clicks wildly and stops when held. i didn't think it would be that influential but i'll look for a swap

other concerns to do with mixture - it runs on a little now, i've adjusted the mixture a little richer as the plugs were white rather than browny (so sayeth haynes). could the run on be related to this? it previously did this when lean which i attributed to running too hotter a mixture.

also when very cold the engine feels like its knocking and the choke bogs the car right down when on - but keeps the idle right - could cold air cause these issues?

cheers for info

toby

[filthyjohn]

Mine was doing everything you just described, it's like you're talking about mine. I fixed it with new leads, rotor arm, cap, plugs. Got a halfords trade card though so all that only came to like £19.

[Vart]

its had recent - 6 months ago plugs, leads and so on but then had a running problem i think came down to a dirty run-cut off box connection on the carb. at least when in desperation i cleaned the throttle switch it was fine...

the space tube is fine but i think the thermostatic bit might be shot - too much cold air means more fuel being consumed?

i've replaced the thermostat with an older old as the new one opened far too early and then appeared to stay like this. new one is a little better - opens when the needle gets to the middle from cold then crawls slowly back there and stays put.

current fuel economy is a fairly constant 160miles from £25 of petrol (30 litres) - i make this about 25mpg. Granted i do start stop through portsmouth for 15 minutes with a cold engine but then its 65mph for 10 minutes then a gentle 40/50 into work for another 5 minutes, but even when the carb only worked by magic it would give back roughly 30mpg....

causes of shoddy fuel consumption is the next step but i fear its consuming at too greater rate to just be a carb problem. i've not checked the top of the tank but i've no reason to suspect this - the car tends to have the same ish reading between 1 day and another. i've swapped the hoses 6 months ago. Do non sealing valves damage thirst that much?

last port of call is the fuel cut-off box - if it was broken what would the signs be? i've a replacement in suffolk but i can't re-call how it comes off its plug - i've tried with my current one but no luck. is it just erm pull off action?

cheers

toby

[pettaw]

Toby I think your carb needs looking at. I bet there's either an air leak or a blocked jet/needle or summat. These carbs will run extremely rich if you wind the mixture screw out too far, and you'll use loads of fuel. Could well also be causing your run on issue. I would say it needs to be checked over before you do anything else.

[Vart]

i'm going with mixture - i've tried the WD40 trick and nothing happened. a rich mixture would ' conveniently' explain many of the woes at the moment,

bad running on choke - silly rich mixture
excessive fuel consumption - rich mixure during stop start traffic
what sounds like engine thumping i believe is exhaust related.
run-on caused by carbon build up perhaps?
hunting idle - not too sure slowly clogging plugs perhaps?

too dark after work to check plugs put they'll probably tell a story - this weekend i'll go over the mixture again. its run otherwise - running quite well even with taxi style driving to reduce fuel excess.

the carbs been scrubbed and cleaned a fair amount - all the jets soaked in white spirit and similar. i altered the 2nd stage jet to a slightly smaller size (still within spec) just to see what would happen but nothing did. it was a 123 instead of 125 or something like that. from a spare 109...

cheers for ideas

toby

[RobT_75]

bad running on choke - silly rich mixture
excessive fuel consumption - rich mixure during stop start traffic
what sounds like engine thumping i believe is exhaust related.
run-on caused by carbon build up perhaps?
hunting idle - not too sure slowly clogging plugs perhaps?

I've got similar symptoms to you Toby but to a lesser extent, and I'm going to do a plug check this evening and depending on condition a tune if I can get enough light.

What has prompted me to do this now though is I went to fill up yesterday and the car hadn't warmed up properly. I went to start it again and it took ages to get going, loads of cranking over and "dear god please start, otherwise I'm stuck at Esso". Or words to that effect...

I put redex in my tank last week to sort the carbon build up and it seems to have helped a bit, but I obviously need to look at the carb properly otherwise it'll build up again.

[Vart]

backed the mixture down half a turn with a smidge more throttle opening and it idles as before but by accident or design shut-off fine after a minute or so idling. this adjustment down engine cold as a best guess. can't report on fuel usage due to my current sub 2500rpm driving style. i'd estimate 2 and a bit gallons usage in about 65 miles. so i think its getting better. if i can do more than 160 miles i'll know its better. heres hoping for at least 30mpg...

re: the bogging down on choke under gentle throttle - this seems unlikely to be mixture related as this part should be controlled by the main circuit of the carb which i understand is self governing. would an adjustment to the choke throttle opening help? add a little more air into the mix? i've set it to the factory spec of 0.9mm opening on full choke.

mine used to give up when a little warm, a complete carb clean up sorted that but that was some time ago.

[RobT_75]

Here's hoping you get more than 30mpg now you have a tinker with it.

I tuned mine earlier, meter was saying around 3.5% CO to start with. As I suspected it's been running rich, although only plugs 1 and 4 were black the other two were fine, wonder why that is? Getting it right was a bugger and is now just idling below the 1000rpm (B14.4 engine) with CO around the 2.5% mark. Any weaker and I figured it'll pink.

Spent ages tuning it this evening so will take it for a run tomorrow and hopefully it'll be performing better under choke and starting up better too as cleaned up and re-gapped the plugs.

BTW what gap should plugs be on the B14.4? Haynes gives two measures, 29mm or 32mm so I went around the middle of the two.

[pettaw]

Rob, you might be getting air leaks from your manifold gasket next to the head, that would show up as uneven coloured plugs. Also check the tappet adjustments, they need to be done once a year or so to keep them right. You should be able to get it to idle very nicely at 2.0% CO or so, with no ill effects when driving.

Toby you shouldn't be guessing your adjustments, see the 1.4 running shakey read me first FFS thread, and I've detailed how you can adjust your carb properly without a meter. The choke issue is a bit of a tricky one because its quite difficult to set up right because of the pneumatic pull off that it has and the way it works. Its too difficult to go into here on the forum, but the full procedure is detailed in the green book. I really wouldn't tinker with it unless you have very good reason to. Full choke and cold engine you should have enough fast idle throttle to give 2000rpm on the engine. That one is quite easy to adjust, but checking is a bit diffcult and fiddly, because as soon as you started the car, it then puts enough heat into the combustion chambers that its over rich on full choke again.

Hope that helps.

[RobT_75]

Rob, you might be getting air leaks from your manifold gasket next to the head, that would show up as uneven coloured plugs. Also check the tappet adjustments, they need to be done once a year or so to keep them right. You should be able to get it to idle very nicely at 2.0% CO or so, with no ill effects when driving.

.

Thanks for the info, that's the weekend sorted!

[Vart]

followed the haynes 'fixing rough running' procedure and checked the ignition out - everything ok 'cept for a but of fur in the dizzy cap and wrong plug gap settings (right plug tho).

John - you said you replaced the plugs - offhand you don't recall make and model of old and new do you?

i checked the plug gap on my helfrauds NGKs and i'd set it to 0.65mm but NGK claim a gap of 0.8mm, the car seems much happier on choke now - could an incorrect gap on rich mixture be the cause?

excess fuel usage through me needing to be more go pedal happy and generally bad combustion?

soot not from a rich mixture but poor combustion?

i'll report back when i've driven it a bit more.

as an aside i've replaced the 'solex' fuel cut-off box as the old one makes me suspicious - does anyone know if theres an approved test procedure for these? also why its a solex box on a weber carb?

cheers

[filthyjohn]

Yo Vart,
They were halfords NGKs *edit, whichever ones were specced in the little parts guide thing*, want to buy some cheap that have only done 200 miles prior to a crash?

[cheshire190e]

im surprised no one has mentioned the idle solenoid. This being faulty caused all the same problems on mine. If you unscrew it from the side of the carb and hold it against the carb body the plastic pin should retract when you turn the ignition on. If this doesnt happen then it is faulty. On mine it was so i just snipped the pin off the end so it acts like its always retracted. solved all my problems.

Matt