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Toyota 'surging' on tickover

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Phillmore
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Toyota 'surging' on tickover

Post by Phillmore »

My wife's daily driver is a 1991 Toyota Carina 2 and it's developed a surging tickover (the revs keep rising and falling rhythmically). It seems fine at all other throttle openings. It is fitted with a twin choke fixed jet carb so I suspect it maybe a pilot jet blockage. Has anyone else experienced this problem on any car? Just to add it seemed to start after filling the tank with Morrison's fuel but this could be a red herring.
Andy

1954 Conquest Mk1, 1956 Conquest Mk2, 1957 Conquest Century Mk2, 1955 Austin A90 Westminster

Fossil
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Re: Toyota 'surging' on tickover

Post by Fossil »

Andy

It sounds as if this may be what used to be called "hunting"? My wife's 2005 fuel injected 1.5 Mitsubishi Colt also does this at a certain stage of warming up if left to idle for too long from cold, and after a moment or 50 it settles back to an even rhythm again, so it must relate to fueling v temperature in some way. I'm no expert on hunting or its causes, but something is telling me that it could be the float chamber level set too high, or perhaps another jet issue, a choke adjustment matter, or the idle rpm too low? So I'd check/clean the float chamber, the pilot jet, and if they're all fine check the fast idle throttle setting, and raise the idle rpm to 500 - 600 or even more if it's not already there and see if any of those work. If not I would just give it a good run, which is always worth a try for minor issues.

Now over to the experts...... . . . . .

Regards

Geoff

Phillmore
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Re: Toyota 'surging' on tickover

Post by Phillmore »

Thanks Geoff. Once warmed up the tick over alternates between 500 rpm and 1500 rpm constantly as if someone was revving the engine up. Reading the manual I think I'll start with the IAC valve and the throttle position valve before stripping the carb.
Andy

1954 Conquest Mk1, 1956 Conquest Mk2, 1957 Conquest Century Mk2, 1955 Austin A90 Westminster

Stan Thomas
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Re: Toyota 'surging' on tickover

Post by Stan Thomas »

Try this tip from when I was an an apprentice earning four shillings an hour ...............................

Warm up the engine and remove the air cleaner.

Now rev the engine to about 3000 rev/min, then plant your hand over the carb inlet to starve the engine of air.

Just before it chokes to a standstill, remove your hand and allow the revs to rise again.

Repeat a couple or three times.

Works wonders - try it!!

Phillmore
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Re: Toyota 'surging' on tickover

Post by Phillmore »

Thanks Stan, is that to clear a blocked jet?
Andy

1954 Conquest Mk1, 1956 Conquest Mk2, 1957 Conquest Century Mk2, 1955 Austin A90 Westminster

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theoldman
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Re: Toyota 'surging' on tickover

Post by theoldman »

Sounds like it could be a blocked compensating jet????
Normal for Norfolk

Phillmore
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Re: Toyota 'surging' on tickover

Post by Phillmore »

Is that the intermediate jet between pilot and Main? Mr Haynes is very vague on the subject unfortunately. He only mentions a 'slow jet' and a main jet. Each choke as one of each.
Andy

1954 Conquest Mk1, 1956 Conquest Mk2, 1957 Conquest Century Mk2, 1955 Austin A90 Westminster

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JohnM
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Re: Toyota 'surging' on tickover

Post by JohnM »

Andy,
have you checked any pipes, tubes etc around the carb/inlet manifold for cracks which could cause a small air leak?
Culprits can be vacuum tubes, advance/retard pipes etc.
This sort of hunting can be typical of an air leak and can be a nuisance to find!
Good luck!
John
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Re: Toyota 'surging' on tickover

Post by johnwager »

Andy
From my experience in the old days of carbs, that kind of hunting is usually a blocked slow running jet, and they are usually accessible from the exterior of the carb. We would pull a wire from a wire brush and run it through the jet and then a blow through would clear it.
Worth a try.
John

Phillmore
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Re: Toyota 'surging' on tickover

Post by Phillmore »

JohnM - Yes I have briefly checked that all vacuum pipes are in place and undamaged but certainly worth another proper check.

JohnW - Yes it certainly seems to be part of the slow running/pilot jet circuit but a couple of other circuits are also operational on tick over so an interesting challenge. Looks like the wife might have to drive a Conquest for a day or two which could be even more interesting! I've raised the tick over speed on the throttle stop so that it doesn't actually stall any more but being an auto this means a bit more creep.
Andy

1954 Conquest Mk1, 1956 Conquest Mk2, 1957 Conquest Century Mk2, 1955 Austin A90 Westminster

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