Subject: Re: [Healeys] HS4 carb jet head and spitting

From: Austin Healey <[email-masked]>
Date: Fri, 7 Jun 2013 08:15:35 +0200

They should be more or les the same height. Have You checked the needles?
Are they the same for sure? Are they not worn? Float level has instant
effect on the jet heigth. Compare the floats.The slightest air leak at a
carb can cause different jet settings. Although completely lever setting is
also not realistic with theese engines.

Backfiring is an issue this case caused by overly lean mixture. The choke
is there to adjust the mixture while cold. When hot it should not happen at
any circumstance.

Gergo

2013/6/7 john spaur <[email-masked]>

> I have questions concerning a BT7 tricarb.
>
> While tuning the car, it was noticed the two rear jet heads were at about
> the same level but the front jet head was considerably higher (all were
> below the bottom of the Venturi). It is my understanding the height of the
> seat is related to float height setting and lean/rich jet adjustment.
>
> Should I recheck the float levels to see if something is amiss and adjust
> so the jet bearing seats are more uniform before I tune the carbs?
>
> The carbs sometimes spit petrol, while cold (common issue I believe) and
> upon acceleration when the engine is hot. Is this an issue related to valve
> timing and/or rocker clearance? I think spitting back fuel can be caused by
> a too lean condition.
>
> Could the valves be staying open too long? I have a Denis Welch road cam
> which is similar to a BJ8. Per DW, the rocker clearance is set to .015 cold.
>
> Needing clues to fine tune the healey.
>
> TIA
> John Spaur
> San Jose
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From: Oudesluys <[email-masked]>
Date: Fri, 07 Jun 2013 11:13:32 +0200

Before setting the mixture, set your float level, valve clearances, ign. 
timing, spark plugs (renew?) and balance the carbs first. Failing to do 
so makes setting the mixture a waste of time.
Kees Oudesluijs
NL

Op 7-6-2013 8:15, Austin Healey schreef:
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-- 
Kees Oudesluijs
Dorpsstraat 183
2995XG Heerjansdam
T: 078-677 1233
E: [email-masked]

Technische commissie Jensen Healey en GT
Het Jensen Genootschap Holland
www.jensenholland.nl
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From: Alan Seigrist <[email-masked]>
Date: Sat, 8 Jun 2013 07:15:42 +0800

John -

You have to do all the presets for the floats, jet levels and Idle screws
first before tuning (also all the spark plugs etc.).  Failing to do so
means you'll get tuning over-compensation from one carb to others through
the balance tube, and the carbs will falsely appear balanced when tuning,
when in fact one carb will be running too far rich to compensate for others
running too lean at idle.

Once all the presets are done per manual, especially the jet presets level,
then you set idle speed as slow as possible then adjust richness for all
three carbs in unison until roughly correct, lower idle speed a bit more,
then adjust further, in unison as much as possible, then adjust each carb
individually once the general setting is approximated.  If you do this
right, the individual final richness setting for each carb will then
be only within about a turn and a half of the setting nut from each other.

Of course as you are adjusting, make sure your linkages are delinked during
the process.

Best,

Alan

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From: john spaur <[email-masked]> mail.com>
Date: Fri, 07 Jun 2013 21:00:58 -0700

All the presets; static timing, rocker clearance, points and plugs 
were spot on.

My HS4 tricarbs have plastic floats which are non-adjustable. 
However, there was a very thin fiber washer (stock) under the float 
needle seat. The washer changed the float level so it was out of 
spec. Removing the washer put the float level back to normal. 
Incidentally, the SU tuning manual states that float level is not critical.

Bottom line is I was able to setup the carbs and a little more micro 
advance (the knob on the distributor) resolved the spitting through 
the carbs. All is good.

John Spaur
'62 BT7  

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