[Healeys] Carb Adjustment Help Requested - BJ8 MkIII

Bob Spidell bspidell at comcast.net
Sun Aug 13 18:31:26 MDT 2017

How do you know you're running rich; is the car blowing black smoke, 
even when warmed-up with the choke off?  Where did you set the needles 
in the vacuum pistons?  Sounds to me like your floats are set too high; 
take the dashpots off and see where the top of the jets are relative to 
the jet bridge, and where the fuel level is inside the jet with the pump 
on (don't leave the key in the 'on' position for long when the engine 
isn't running lest you fry your Pertronix).  Did you inspect the jet 
diaphragms when you had the carbs apart?  If the car sat for a long time 
they could have cracked; if so you'll never get the mixture set right.

FWIW, I have a BJ8 with DWR-1 cam and Pertronix and the idle--at 750 
give-or-take--is a bit lopey but solid (I gap my plugs at 0.028").   
There were some bad Sports Coils going around, and I'd stick to Champion 
or NGK plugs.

Timing for a BJ8 is set at 15deg BTDC at 600RPM with vacuum advance pipe 
disconnected and port on carb plugged (doesn't make much difference).


On 8/13/2017 4:20 PM, David Porter wrote:
> what are the compression numbers? Timing is set at 750RPM and 6 
> degrees BTDC. Is it better or worse with chokes engaged? DP
> On 8/13/2017 3:23 PM, Bob England wrote:
>> I've had a rough idle in the car since we picked it up in May and it 
>> seems
>> to have gotten worse ever so slightly since then.
>> I've putzed around trying the easy stuff and finally got the bullet and
>> pulled the carbs yesterday (that was fun!) as one of the carb pistons 
>> was
>> sticking ever so slightly.  Stripped the carbs except for the 
>> throttle shaft
>> and found the floats were set a bit low.  Put it all back together 
>> and still
>> having an issue as she is running quite rich, hence the call for help.
>> Car: late '64 build BJ8 MkIII
>> Carbs : HD8 (I think they were new about 15 years ago - not original to
>> car).
>> Cam : Dennis Welch DWR-1 (installed about 15 years ago).
>> Distributor : stock with Petronix Ignitor (Petronix installed last 
>> weekend
>> in the hopes it would help).  New rotor.
>> Coil : Lucas Sportcoil
>> Plugs : new Autolite gapped at 25 (installed a couple of weekends ago)
>> Timing : 15 degrees with strobe (my attempt at static timing was a 
>> dismal
>> failure!).
>> I set the carbs as per the manual - 3.5 turns open on the idle trim 
>> screws
>> and 2.5 turn rich on the jet adjusting screw.  Fast idle adjusting screw
>> completely off of the cam lobe.
>> The best I can get it is with the jets totally lean (i.e. not sitting 
>> on the
>> cam lobe) and the fast idle screws setting the idle speed.  Idle trim 
>> screws
>> backed way out with little impact on idle.  Carbs are still running 
>> rich.
>> I think I have memorized the adjustment procedure from the manuals I 
>> read
>> them so many time - (Bentley, BMC, and Haynes), and Norman Nock's 
>> wonderful
>> collection of papers.
>> Should I be going to a leaner needle in the carbs?  Or am I just 
>> screwing up
>> somewhere?  This is my first attempt at adjusting SU's and I'm not 
>> too happy
>> with what I have done so far.
>> Any and all suggestions appreciated (except maybe if I have to yank the
>> carbs again).
>> Thanks in advance.
>> Bob England

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