BJ8 Carb Idle Adjustment

[shorn]

I have my BJ8 back after an engine overhaul. The idle is set a little high (1200 rpm's). As I recall if I turn the jet adjusting screws counter clockwise an equal amount, the mix will lean out and the slow run screws should be screwed in (clockwise) equally to decrease the idle. Just to many darn screws and I want to make sure I have the right ones and am going in the right direction. Hey, its nice to have good oil pressure for a change.

 

[Dave Russell]

Basically correct. Make sure that the choke fast idle screws are not engaged. I would slow the idle before changing the mixture.

You can refresh your memory here:
https://www.hazelden.ca/austinhealey/index.html

Glad your engine is working well.
D

 

[shorn]

Thanks Dave,
I've got to get about 500 miles on it in the next couple of weeks so that we can change the oil, retorque the head, and readjust the valves. Then its up to Nelson, BC for the Healey meet.

 

[Dave Russell]

[ QUOTE ]
Then its up to Nelson, BC for the Healey meet.

[/ QUOTE ]
That's great. I hope to see you there. Who else plans on going North?
D

 

[shorn]

I think we have about 10 or so from the Cascade A H Club in the Seattle area.

 

[sp8]

I'm just starting in on the tuning of the carbs for my BJ8 and when I took apart the carbs for rebuilding I noted that the slow running valves were "opened" (typically about 4 turns counter clockwise from fully closed). I have read the SU manuals and they state that the slow running valves should be fully closed and that all adjustments should be done with the throttle adjusting screws. Is that right? Right now I can't get the car to right anyway. The rear carb sounds like it is pulling in air (like I would suspect is correct) but the front carb I can't hear the air whistling at all. Any suggestions?

 

[Dave Russell]

I think you will find that the manual says to use the slow running valve on SINGLE carb installations & use the throttle adjusting screws on MULTI carb installations. Clear as mud? Follow the above reference for multi carbs if in doubt. Item #9.
D

 

[Keoke]

No that is not correct sp8.The slow running screws should be turned all the way down and then backed off 2 1/4 turns.Make sure the throttle stop screws are clear of their stops. If the idle speed is too high screw each tickover screw in a little at the time in equal amounts to achieve even idling.Idle speed should be about 1000 RPM on the car's tach---Fwiw---Keoke

 

[AndrewMawson]

[ QUOTE ]

No that is not correct sp8.The slow running screws should be turned all the way down and then backed off 2 1/4 turns.Make sure the throttle stop screws are clear of their stops. If the idle speed is too high screw each tickover screw in a little at the time in equal amounts to achieve even idling.Idle speed should be about 1000 RPM on the car's tach---Fwiw---Keoke

[/ QUOTE ]


1000 rpm sounds rather high to me. Mine ticks over at 550 when warm.

AWEM

 

[sp8]

D. Russell-I looked at the reference that you provided and the way I read it, it still seems to me to be saying that the slow running valve needs to be "closed" and that all of the adjustments will be with the throttle adjusting screws.

I've got to admit I wasn't very clear on my first note. I do have dual HD8 carbs and I have been trying to follow the directions provided in the SU manual but I really don't trust the information in the manual about the slow running valve. The SU manual states in the section for tuning multi carbs (Step 2) "Restart the engine and turn the slow running valve or the throttle adjusting screw, an equal amount on each carb to give the desired idling speed." Unfortunately in the same section, in a note prior to Step 1, it states "Whenever the throttle adjusting screws are fitted they, and not the slow-running valves, must be used to adjust the idling speed. Screw down the slow running valves (shich must remain closed) and set the throttle adjusting screws 1.5 turns open."

Yikes, that is really confusing to me.

Keoke offered to open the slow running valves 2.25 turns open. When should that adjustment be made?

Again, let me ask for your experience here but I did do the steps to make sure that the jet is flush with the bridge of the carb but there is a step to "lower the jet by turning the jet adjusting screw down 2.5 turns". That to me means turn the screw clockwise but thinking of the linkage for the carb itself, that would seem to raise the jet. Is this a hit the "I believe" button or should I be turning the screw counter clockwise to lower the jet?

Thanks for all the help and advice by the way, I really have made some progress with my car and I'm looking forward to getting it on the road.

 

[Keoke]

HD8 Carbs do not have a jet adjusting screw-????--Keoke

 

[shorn]

So what is that screw that is lower left of each air filter that corresponds to the jet adjusting screw on HD6 carbs (#3 and #5 on pg 77 of the Haynes Manual)? And what is the Haynes statement on pg 82 that states the HD8 carb "is basically identical to that of the HD6 and therefore all servicing info will be found under that section". Keoke, you have managed to confuse me.

 

[Keoke]

Shorn:
Like my old proff use to say ; Keoke! you can fail this couse any way you want too.--Keoke- /ubbthreads/images/graemlins/grin.gif

 

[Dave Russell]

[ QUOTE ]

HD8 Carbs do not have a jet adjusting screw-????--Keoke

[/ QUOTE ]
Of course they have a jet adjusting screw. See item 3 on the attached pic. It raises & lowers the main jet.
D

 

[Dave Russell]

Hi SP,
A direct quote from the above reference & also from my SU carb manual:
-----------------------------
Tuning single carburetters:
1-
A. Run the engine up to normal running temperature.
B. Switch off the engine.
C. Unscrew the fast idle adjusting screw (2) to clear the throttle stop with the throttle closed.
D. Screw down the slow running valve (1) onto it's seating, then un-screw it 3 1/2 turns.

Note: Paragraph 2 covers setting the jet levels even with the bridge.

3-
C. lower the jet by turning the jet adjusting screw (3) down 2 1/2 turns.

4-
A. Restart the engine and adjust the slow running valve (1) to give the desired idling as indicated by the glow of the ignition warning light.
B. Turn the jet adjusting screw (3) up up to weaken or down to enrich, until the fastest idling speed consistent with even running is obtained.
C. Re-adjust the slow running valve, if necessary, to give correct idling.
----------------------------
---------------------------
Tuning Multi carburetters:
9
Note -
Whenever the throttle adjusting screws (6) are fitted, they, & not the slow running valves, must be used to adjust the idling speed. Screw down the slow running valves (which must remain closed) and set the throttle adjusting screws (6) 1 1/2 turns open. In items 10 & 11, adjust the idling speed with the throttle adjusting screws.

A. Slacken the clamping bolt (8) on one of the throttle spindle interconnection couplings between the carburetters.
B. Disconnect the jet control interconnecting rod at the forked end (9).

10
A. restart the engine and turn the slow running (1), or throttle adjusting screws, an equal amount on each carburetter to give the desired idling speed as indicated by the glow of the ignition warning light.
B. Compare the intensity of the intake hiss on all carburetters and alter the the slow running valves (1) or throttle adjusting screws, until the hiss is the same.

11
A. turn the jet adjusting screws (3) an equal amount on all carburetters, up to weaken or down to enrich, until the fastest idling speed consistent with even running, is obtained.
B. Readjust the slow running valves or the throttle stops, if necessary.

12
A. check the mixture etc.

13
A. Tighten the clamp bolt (8) of the throttle spindle interconnections with the pin of the link pin lever resting against the edge of the pick-up lever hole. This provides the correct delay in opening the front carburetter throttle.
B. Reconnect the jet control linkage (9) so that the jet operating arms move simultaneously. If necessary, turn the forked ends.
---------------------------
Forgive my if I have repeated what is obvious. The point is, that single carbs are adjusted with the slow running valve & multi carbs with the throttle stops. The note at the top of 9 takes precedence over following notes to adjust the slow running valve. Note that later, it always says slow running valve OR throttle adjusting screw.

I think that turning the jet adjusting screw in - down - clockwise, lowers the jet. You can easily tell by watching the jet in relation to the bridge & see which way it moves when turning the screw. Turning the screw in raises the end of the lever which pivots & lowers the jet end.

In reality I've not found much difference between the two procedures. Opening the throttle stops a bit prevents any possibility of the butterflies binding in the bores, as they might if they were completely closed. I believe it is also easier to synchronize the carbs by using the throttle stops rather than the slow running valves. Or, maybe a combination of the two (throttle stops & slow running valves) will work best for you.

Note in 13A, there is an intentional delay in opening the front carb. I think this is to assure that both throttles get fully seated against there stops. With them linked solidly together there would always be a tendebcy for on or the other to seat first & prevent the second one from completely closing.

Happy tuning,
D

 

[Keoke]

Oh my goodness yes Dave,But I wonder what happened to the mixture adsjusting screws?. Your "D" pretty much agrees with my ealier "NO that is not correct" response which seems to have fallen on deaf ears.--Keoke

 

[Dave Russell]

The "D" only applies to the single carb applications. A very subtle difference. See the note under Multi carbs # 9. So now where are we?
D

 

[Keoke]

Better check with the factory Manual and let them other things alone.--Keoke-- /ubbthreads/images/graemlins/grin.gif

 

[Dave Russell]

To quote from my earlier post "In reality I've not found much difference between the two procedures." "Or, maybe a combination of the two (throttle stops & slow running valves) will work best for you."
D

 

[Keoke]

Yeah Dave, thats OK. tunin worn rebuilt 40 year old carbs by the book which has not aged a day since it was printed requires a bit of compromise.However, if the tick over screws are closed and the throttles are also closed I think they gonna have a hard time breathing.---Keoke- /ubbthreads/images/graemlins/grin.gif