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Hey - did you know if you click on the title of a thread it will take you to the first unread post since you last visited that thread?
but were afraid to ask: 
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Trick question . See what you think.
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Robert560
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I recently rebuilt my HD8s, having never touched an SU carb before. I found rebuilding to be very easy, with setting up being a little challenging (not "seriously" frustrating, just "mildly" frustrating). WAY easier than messing with GM Quadrajet carbs, which I've had the unfortunate experience of trying to rebuild and set up too many times in the past.
I basically just used the HD Tuning Service Sheet AUC 9622B (don't have the Haynes manual), and then had a Carbalancer I used to try to balance them. I also bought that SU DVD that Moss sells, and found it extremely informative. I don't think they're perfect, but it seems to run really good. I'll likely tweak a bit more once I can put some miles on the car and see how the plugs look.
For idle, I really just set it "where it sounds good", with a target of 600 RPM, which I read somewhere was correct for BJ8s. It's between 600 and 700 RPM now, though my tach appears to have a bit of error and shows it idling higher than that.
~Robert
I basically just used the HD Tuning Service Sheet AUC 9622B (don't have the Haynes manual), and then had a Carbalancer I used to try to balance them. I also bought that SU DVD that Moss sells, and found it extremely informative. I don't think they're perfect, but it seems to run really good. I'll likely tweak a bit more once I can put some miles on the car and see how the plugs look.
For idle, I really just set it "where it sounds good", with a target of 600 RPM, which I read somewhere was correct for BJ8s. It's between 600 and 700 RPM now, though my tach appears to have a bit of error and shows it idling higher than that.
~Robert
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Not to sound negative, but they should idle at the rpm that's smooth and slow enough with the clutch pushed in and this would be about 800 to 1000rpms. Don't rely too much on the tach because it may be out of calibration. Idle the car with the tach covered. Adjust the HD8 carbs after the engine has been warmed up. Drive it around the block to "reset" the idle smoothness. This was explained to me by a real SU pro many years ago. If you shut the engine off for any length of time you'll need to drive it around the block to get the idle you had before you shut it off. The BJ8's have a 3/4 race cam and this is supposed to create the idle roughness problems.BOBBYR said:
And...you'll never get a good idle if you have other issues with the carbs such as bearings(throttle shafts worn), jet leakages, etc. Yes, I don't like Grose jets because the vibration can let gas seep past the ball seat. I like needle seats best. Tried both for several years.
Patrick
Bob_Spidell
Yoda
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600 RPM is 'book.' The 'sweet spot' is high enough to not run off the battery at idle--where the ignition light lights--and low enough that the engine doesn't run on too much at shutdown. For my BJ8, that's about 700-800 RPM at sea level, where I happen to live. The idle will drop off a bit at altitude and when hot.
FWIW, I've used Grose Jets for probably 20 years--same set--with no problems.
FWIW, I've used Grose Jets for probably 20 years--same set--with no problems.
OP
BOBBYR
Jedi Trainee
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Hi Guys
The reason I asked the question is because you never get the same answer.
If you set up a set of hd8s by the Haynes manual, one of the last steps is to turn the choke idle screws equally so the engine idles at 1000 rpms.I believe because of the type cam in this engine this is where it idles best. In the past I have had many tell me to idle this motor down to 600rpms.I have tried and tried and their is no way this 2912 will ever run at 600rpms.Oh, and by the way,wait until you see how good your choke works if you set your carbs this way. I hope this is a help for some of you.I can't believe how much better mine starts and runs.
Bobby R
The reason I asked the question is because you never get the same answer.
If you set up a set of hd8s by the Haynes manual, one of the last steps is to turn the choke idle screws equally so the engine idles at 1000 rpms.I believe because of the type cam in this engine this is where it idles best. In the past I have had many tell me to idle this motor down to 600rpms.I have tried and tried and their is no way this 2912 will ever run at 600rpms.Oh, and by the way,wait until you see how good your choke works if you set your carbs this way. I hope this is a help for some of you.I can't believe how much better mine starts and runs.
Bobby R
John_Progess
Jedi Warrior
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Bobbyr,
I just tried to set my HD8's with the Haynes manual as an aid with mixed results. I borrowed my manual so I don't have it with me but I believe that the last step does say to adjust the choke "half way out" and adjust the choke idle screw to get an idle of 1000 rpm's. I rebuilt my carbs and my car seems to have a roving idle so I must still have something out of sync. My low speed idle screw is about 5 turns out and this sounds a bit much. Often when I blip the throttle the rpm will not stop at 600 but will cotinue down all the way to engine stop. Still got some fiddling to do. Have a good day!
John
I just tried to set my HD8's with the Haynes manual as an aid with mixed results. I borrowed my manual so I don't have it with me but I believe that the last step does say to adjust the choke "half way out" and adjust the choke idle screw to get an idle of 1000 rpm's. I rebuilt my carbs and my car seems to have a roving idle so I must still have something out of sync. My low speed idle screw is about 5 turns out and this sounds a bit much. Often when I blip the throttle the rpm will not stop at 600 but will cotinue down all the way to engine stop. Still got some fiddling to do. Have a good day!
John
SideShifter Tri-Carb
Senior Member
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On a BT7 with BJ8 cams, I can get my idle down to 650-700 easy with the pertronix and rebuilt dizzy from Advance Distributers.
Robert560
Senior Member
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I've had no problems with my BJ8 idling at 600-700 RPM. It sounds great there, and seems very consistent (albeit a bit of a rough idle, which is to be expected). I checked this using a multimeter though, off the coil, as the tach in the dash says 200 RPM higher. If I tried to idle at 600 using the tach in the dash, I doubt it would run very good - way too low. Currently, with the choke pulled it idles near 1500 RPM, which I still haven't set properly since the rebuild. I'll move it down a bit, as it seems too high. But fast idle is independent of the off-choke idle as set by the slow running valve... so I haven't been in a hurry to mess with it (don't need much choke here in Texas this time of year).
FYI, I'm using a stock coil with a Pertronix module inside the original distributor.
~Robert
FYI, I'm using a stock coil with a Pertronix module inside the original distributor.
~Robert
Bob_Spidell
Yoda
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When I put a Pertronix in my BJ8 I got it to idle down to just over 300 RPM, just to see if it would (pretty rough, of course).
The electronic tachs can be calibrated. Theres a potentiometer ('pot') inside that can be adjusted, but you have to drill a hole in the back of the case. My tach now agrees exactly with my Craftsman dwell-tach-volt meter (FWIW). With an accurate tach, you can calibrate the speedometer (and use the tach for a backup if the speedo goes south). Then, with a GPS you can cross-check the speedo, and hence the tach, closing the 'loop.'
The electronic tachs can be calibrated. Theres a potentiometer ('pot') inside that can be adjusted, but you have to drill a hole in the back of the case. My tach now agrees exactly with my Craftsman dwell-tach-volt meter (FWIW). With an accurate tach, you can calibrate the speedometer (and use the tach for a backup if the speedo goes south). Then, with a GPS you can cross-check the speedo, and hence the tach, closing the 'loop.'
OP
BOBBYR
Jedi Trainee
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Hi Guys,
There is no doubt that these engines aren't easy to get to the perfect setup.Lately, I have adjusted the valves to .012 and I think that is a little too tight. I guess trying different setups is what it's all about.I usually put some time into it and it gives me a good reason to go out for a long ride.Anyway, I hope you guys are enjoying your Healey,as much as I am.
Bobby R
There is no doubt that these engines aren't easy to get to the perfect setup.Lately, I have adjusted the valves to .012 and I think that is a little too tight. I guess trying different setups is what it's all about.I usually put some time into it and it gives me a good reason to go out for a long ride.Anyway, I hope you guys are enjoying your Healey,as much as I am.
Bobby R