[Healeys] Carb Adjustment Help Requested - BJ8 MkIII
engl at accesscomm.ca
Sun Aug 13 22:47:45 MDT 2017
See notes in CAPS below ....
From: Healeys [mailto:healeys-bounces at autox.team.net] On Behalf Of Bob
Sent: August 13, 2017 6:31 PM
To: healeys at autox.team.net
Subject: Re: [Healeys] Carb Adjustment Help Requested - BJ8 MkIII
How do you know you're running rich; is the car blowing black smoke, even
when warmed-up with the choke off?
YUP. IF I SET THE IDLE UP AROUND 1200rpm, BLACK SMOKE STOPS.
Where did you set the needles in the vacuum pistons?
BOTTOM GROOVE ON NEEDLE JUST ABOVE BOTTOM OF PISTON (SO YOU CAN'T SEE THE
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
FLOATS COULD BE HIGH. I THOUGHT THEY WERE LOW SO I ADJUSTED THEM HIGHER
(USING 7/16" TEST BAR).
WHERE SHOULD THE FUEL LEVEL BE INSIDE THE JET WITH THE PUMP ON?
Did you inspect the jet diaphragms when you had the carbs apart?
I DID INDEED. THEY LOOKED GOOD.
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
I MAY SWITCH TO THE CHAMPION. I'VE HEARD THAT FOR SOME REASON CHAMPIONS ARE
A SWEET SPOT FOR THE CARS.
ON THE JAGS, I SWITCHED TO A 35 GAP WITH THE SPORTS COIL OVER A 25 GAP AS
THIS SEEMED TO BE THE RECOMMENDED APPROACH. DO YOU THINK A LARGER GAP WOULD
I THINK, LOOKING BACK, WHEN I PICKED UP THE CAR IN MAY THE IDLE WAS LOPEY AS
YOU DESCRIBE. ON A RECENT 500km ROUND TRIP, BY THE TIME I GOT HOME THE CAR
WAS MISSING (HENCE THE START OF MY JOURNEY TO ADJUST THINGS).
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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