Spitting through HS4 carb

Technical MGB discussion
Ian Fozzard
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Re: Spitting through HS4 carb

Post by Ian Fozzard » Wed May 27, 2020 11:29 am

I am usually concerned most about running lean at high speed/loads. This is potentially damaging.

I check this by a high speed/ full load run and switching off before idling. Then check the plugs.

The important thing to remember (in my opinion) is that setting the mixture correct at idle (and agonising over whether it is spot on or not) is only relevant if you are 100% certain that the needles you have fitted are exactly correct through all engine speeds and loads. My guess is that the needles will usually not be exactly correct unless your engine is exactly as it left Abingdon 40 years ago 😊😊

Ian F
1972 BGT, Blaze, Navy trim, recessed grill
1961 Midget, 948cc, Clipper Blue, Blue trim and weather gear

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Steven collins
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Re: Spitting through HS4 carb

Post by Steven collins » Wed May 27, 2020 11:36 am

Well, that worked!!
It spat once upon starting and wouldn’t tick over properly however, once thoroughly warmed up I set the airflow and balance on both carbs, set Tick over. All seems to be fairly ok will know more when I can get her out for a proper drive. No bonnet on at the moment so cannot just pop down the road.

Ian Fozzard
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Re: Spitting through HS4 carb

Post by Ian Fozzard » Wed May 27, 2020 11:42 am

Paul, thanks for that measurement - 60 thou. I did run my engine at that setting for a while and found it worked equally well. Does that equate to 12 flats down from the bridge? (At least in theory anyway - didn't seem to tally for me)

Ian F
1972 BGT, Blaze, Navy trim, recessed grill
1961 Midget, 948cc, Clipper Blue, Blue trim and weather gear

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Steven collins
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Re: Spitting through HS4 carb

Post by Steven collins » Wed May 27, 2020 7:58 pm

Thanks guys, perhaps I will play around with the settings for a bit to try and get the optimum settings - lets face it I/we have plenty of spare time at the moment.

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Steven collins
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Re: Spitting through HS4 carb

Post by Steven collins » Tue Jun 23, 2020 12:23 pm

Well, been a while and sadly still not sorted the running out.
Misfiring at low revs and stuttering when running. Have replaced the leads, rotor arm and cap (123 ignition) played around with the carb settings and still getting nowhere!! Might be time to call in for reinforcements.... take it to a garage 🥴😞

Ian Fozzard
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Re: Spitting through HS4 carb

Post by Ian Fozzard » Tue Jun 23, 2020 1:49 pm

My usual stance in this sort of situation is to suggest going back to a standard setup if you can.
I always found that with all the standard components fitted the B series engine would run reasonably well even if the settings were well off the optimum.
I see you have a non standard distributor? That would be my first target for substitution. Do you have a 25d lying around somewhere? Get it refurbished by the Distributor Doctor. You must be getting fuelling, so the spark timing has to be the main line of inquiry?

Ian F
1972 BGT, Blaze, Navy trim, recessed grill
1961 Midget, 948cc, Clipper Blue, Blue trim and weather gear

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Steven collins
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Re: Spitting through HS4 carb

Post by Steven collins » Tue Jun 23, 2020 2:18 pm

I did think that the problem may be the 123 as it’s a mare to initially start (fire) but have never heard of one going wrong, I suppose there is always a first time!!
I still have the dizzy that I removed, there was nothing wrong with it at the time worked perfectly well. It was changed purely for the impression of better reliability when on a long run with the boss lady!!

Ian Fozzard
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Re: Spitting through HS4 carb

Post by Ian Fozzard » Tue Jun 23, 2020 4:40 pm

I am assuming that you got the HS4s sorted out of course!

Does the 123 distributor have multiple advance curves and other adjustments? If your 25d is not currently serviceable you could make some adjustments to the distributor and see if that resolves anything?

Ian F

P.s. rather than go to a garage you could try meeting with someone from the Register/Forum who would be willing to have a look at the setup? If you do go to a garage make sure they are familiar with our era of cars.
1972 BGT, Blaze, Navy trim, recessed grill
1961 Midget, 948cc, Clipper Blue, Blue trim and weather gear

Ian Fozzard
Posts: 391
Joined: Fri Mar 27, 2015 8:18 am
Forename: Ian
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Re: Spitting through HS4 carb

Post by Ian Fozzard » Tue Jun 23, 2020 4:56 pm

Does your 123 distributor have one of these unusual Bosch rotor arms? (see attachment)
BA7C-TechnicalArticle-rotor-arms-Bosch.pdf
123 rotor arms
(579.13 KiB) Downloaded 12 times
Seems (from an internet trawl) that these and several other issues do occur with 123 distributors.

Ian F
1972 BGT, Blaze, Navy trim, recessed grill
1961 Midget, 948cc, Clipper Blue, Blue trim and weather gear

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Steven collins
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Re: Spitting through HS4 carb

Post by Steven collins » Tue Jun 23, 2020 5:19 pm

Just had a look at the 25D looks perfectly serviceable so may swap it back as a last resort.
Good idea for a second set of eyes to look over what I have done if there is anyone in north essex willing I would be very grateful.
S

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