Help with adjusting carbs

[BrandonBJ8]

I've got my timing set at 15' BTDC and the car is running very well. However, I think there's still some room to improve with the carbs as the car seems to be running a bit rich.

I decided to "start over" with the carbs like I was tuning them from new. I've used 3 different methods (Haynes, other manual, and one from the forums). All 3 methods have you backing off the fast idle screws, which I did. Once I do this however, the car will not idle, it just dies. I've adjusted the slow run screws all the way back until the car is screaming (sucking in air) and it still won't keep running. I followed the Haynes guidelines and lined the jet with the bridge and then turned the idle mix screw down 2.5 turns, then 3.5, and it still won't idle. The only way the car idles is if I screw the fast idle screws down quite a bit, but all the instructions I read say to back them off.

Any ideas? I'm not sure if somethings wrong or if there is another way to adjust it? I don't think anything is seriously wrong as the car was running very well before I started messing with the carbs, however I wanted to adjust them properly now that the timing is right. Any help would be appreciated.

Thanks!
-Brandon

 

[Keoke]

Hi Brandon, Set the Tick over screws as per the book.

Set the Mixture screws back to 2.5 turns down.

Pull the choke out 1" and set the fast idle screws [using equal turns for each] for about 1500 on the tach.

Push choke in and see where Idle sets. It should be ~ 800 RPM on the Tach.---Fwiw--Keoke

 

[Guest]

Brandon -

It sounds to me like you have a vacuum leak in your carb/manifold interface somewhere.

Try checking to see if you have any loose nuts on the carb to manifold junction, or if you have a loose nut on the intake manifold to block area. You should also feel on the back of the intake manifold (facing the firewall) and check to make sure the casting plug has not popped partially out.

None of these nuts need to be very tight (only 25 ft lbs), but if you have more than a couple carb moutn nuts loose you could be getting vacuum leaking. That would cause the problems you are describing.

 

[BrandonBJ8]

Hi Brandon, Set the Tick over screws as per the book.

Set the Mixture screws back to 2.5 turns down.

When you say tick over, are you referring to the slow run screws? And then for the mixture screws, do I get the jet even with the bridge and then down 2.5 turns?

Thanks!

 

[Keoke]

Hi Brandon, Set the Tick over screws as per the book.

Set the Mixture screws back to their " original 2.5 turns down position".

When you say tick over, are you referring to the slow run screws?-----/bcforum/images/%%GRAEMLIN_URL%%/yesnod.gif And then for the mixture screws,"[ Set them per the book]" do I get the jet even with the bridge and then down 2.5 turns?

Thanks!

---------------------------Keoke

 

[BrandonBJ8]

Keoke - With your instructions, I was able to get it idling at about 600rpms. Do you think it should be higher?

Also, the jets weren't equal to each other when I adjusted them. It seems the 2nd carb's (closest to the firewall) mixture screw didn't adjust at the same rate as the 1st. It was a bit lose and subsequently did not move the jet down as much with 2.5 turns down. I've attached two pictures; one of each jet after I leveled them with the bridge and turned down the screws 2.5 times.

 

[Dave Russell]

Brandon,
Due to differences between the carb's parts, 2.5 turns will not always put the jets at the same heights. Don't know that it's that important & don't want to confuse the issue.

I personally set the jets to somewhere close to the same number of turns & then measure from the jet bridge to the jet top with the depth function on a dial caliper. Fine adjust the adjustment screws to make the depths equal. Make all further adjustments from this point making sure to turn both jet adjusters equal amounts. The way you did it is probably close enough though.

Set the idle speed wherever you are comfortable with it. Many folks set it just high enough to cause the no charge indicator light to go out. Provided that the engine continues to idle ok as it warms up.
D

 

[BrandonBJ8]

Judging from the pictures, does it look like the jets are too far off? Should I try and adjust carb 2's jet to be equal to #1? (Or vice versa)

Also, from this point on, should I use the fast idle or slow run screws to increase/decrease the idle?

Thanks!

 

[Keoke]

Judging from the pictures, does it look like the jets are too far off? Should I try and adjust carb 2's jet to be equal to #1? (Or vice versa)

Also, from this point on, should I use the fast idle or slow run screws to increase/decrease the idle?

Thanks!

Yes the 600RPM is good. However if you want it a bit higher use the Tick over screws to raise it slightly. If those screw are not sensitive enough Tweak the fast idle screws just a bit too.--Keoke

 

[Dave Russell]

Judging from the pictures, does it look like the jets are too far off?

Since the two pics are shot at slightly different angles, it's hard to know how much difference there is in jet height. It doesn't look to be very much.Since the needle tapers are very slight near their tops (idle position) a small difference is not likely to have much effect on things. As I said above, precise measurment of jet heights would probably make someone who is really fussy about such things feel better. It would only be slightly detectable in engine running, if at all. Don't worry about it, just set things a Keoke says. Didn't mean to get you side tracked.
D

 

[tahoe healey]

After all that is done, pull one plug serviced by each carb after you have driven 15 to 20 miles. If they match in color you are fine. If one is a lot darker than the other the carb it goes with is too rich and you can raise the jet a little to lean it. Then have a beer and pat yourself on the back.
TH

 

[BrandonBJ8]

Ah, the beer goes after your done...that's been my problem.


Actually, I just double checked the timing. Once I disconnected the vacuum advance from the dizzy, the idle got pretty rough. I had to slightly increase the idle using the slow run screws to get it steady. Could that mean anything?

Also, the carbs are sucking in a lot more air than previously. They are much louder. I'm not sure if this is a good thing or not. They are about equal in noise, just much louder than before. I can easily hear them at a stoplight when before I really couldn't unless I tried.

Thanks!

 

[healeynut]

Bradon -

When your car is at idle, the manifold vacuum is high, so the vacuum advance will be in operation at this time. That means if you take off the vacuum lead, then the timing will retard and your idle timing will be off. This is normal. With a healey you always adjust your idle timing with the vacuum line on, not off (not like some american cars).

By the way, the carbs are NOT sucking in more air than previously, this is a misconception on your part. The HD type carb operates with the throttle valve completely closed at idle. This means the air bypasses the throttle completely and goes through the slow idle bypass. The slow idle bypass is a very small little tube drilled through the throttle body, and as a result the air speed through this little tube is very very high... causing the impression that you are sucking alot of air, when in reality the high velocities in the little tube are just making alot of noise. You can call it the "great sucking sound" if you wish.

I like the HD carbs because this idle bypass means the slow idle speed is always very constant with this type of carb, and also helps with efficiency at idle because the little tube, causing high velocities, causes the fuel to vaporise much more effectively causing cleaner burning and less fuel requirement at idle.

You are learing a great deal in thiss process. You'll figure it all out eventually, keep at it, and keep asking questions. Before you know it this adjustment will be second nature for you.

/bcforum/images/%%GRAEMLIN_URL%%/cheers.gif

 

[Keoke]

Bradon -

When your car is at idle, the manifold vacuum is high, so the vacuum advance will be in operation at this time. That means if you take off the vacuum lead, then the timing will retard and your idle timing will be off. This is normal. With a healey you always adjust your idle timing with the vacuum line on, not off (not like some american cars). /bcforum/images/%%GRAEMLIN_URL%%/savewave.gif Never in your sweet life.---Keoke

By the way, the carbs are NOT sucking in more air than previously, this is a misconception on your part. The HD type carb operates with the throttle valve completely closed at idle. This means the air bypasses the throttle completely and goes through the slow idle bypass. The slow idle bypass is a very small little tube drilled through the throttle body, and as a result the air speed through this little tube is very very high... causing the impression that you are sucking alot of air, when in reality the high velocities in the little tube are just making alot of noise. You can call it the "great sucking sound" if you wish.

I like the HD carbs because this idle bypass means the slow idle speed is always very constant with this type of carb, and also helps with efficiency at idle because the little tube, causing high velocities, causes the fuel to vaporise much more effectively causing cleaner burning and less fuel requirement at idle.

You are learing a great deal in thiss process. You'll figure it all out eventually, keep at it, and keep asking questions. Before you know it this adjustment will be second nature for you.

/bcforum/images/%%GRAEMLIN_URL%%/cheers.gif

 

[Keoke]

Ah, the beer goes after your done...that's been my problem.


Actually, I just double checked the timing. Once I disconnected the vacuum advance from the dizzy, the idle got pretty rough. I had to slightly increase the idle using the slow run screws to get it steady. Could that mean anything?


Thanks!

"Mean anything" Yep, it means after you disconected the vacuum line you did not plug the end. Or if you disconnected it at the carb you did not plug the carb fitting off. So go back and do it that way.---Keoke

P.S. On the nose of the Vacuum advance unit are three numbers: X-Y-Z Tell me what those numbers are.

 

[BrandonBJ8]

Alan, thanks for the great explanation and advice.

Keoke/Alan - Keoke, You're saying adjust the timing with the vacuum line off and plugged while Alan says to do it with the the vacuum advance on? Which is the proper way? Thanks!

 

[Dave Russell]

Bradon -

When your car is at idle, the manifold vacuum is high, so the vacuum advance will be in operation at this time. That means if you take off the vacuum lead, then the timing will retard and your idle timing will be off. This is normal. With a healey you always adjust your idle timing with the vacuum line on, not off (not like some american cars). /bcforum/images/%%GRAEMLIN_URL%%/savewave.gif

Never in your sweet life.---Keoke

Hi Brandon,
I pretty much agree with Keoke. There are several different schemes to obtain vacuum advance. Alan is describing the manifold vacuum scheme which Big Healeys DO NOT have. This scheme applies full engine idle vacuum to the advance mechanism.

Big Healeys DO have a PORTED vacuum scheme in which the vacuum takeoff point in the carb is outboard of the throttle blade. Vacuum advance does NOT come into play until the throttle blade is somewhat open.

Because on some idle setting combinations the vacuum port "may" be partially in operation, it's recommended that the vacuum line be disconnected & plugged when setting the timing so that "any" unintended vacuum & it's resultant advance at idle does not screw up the setting.

This has been explained in previous posts but seems to require repeating occasionally.
D

 

[Keoke]

Alan, thanks for the great explanation and advice.

Keoke/Alan - Keoke, You're saying adjust the timing with the vacuum line off and plugged while Alan says to do it with the the vacuum advance on? Which is the proper way? Thanks!

:G---Now please send me the Numbers I asked for off the nose of the Vacuum advance unit---Keoke

 

[BrandonBJ8]

Sorry, didn't see that you asked for them.

The numbers are 7-13-3.544. I'm not 100% about the ".544" as it wasn't a good angle, but I know the 7-13-3 is correct.

Also, is the much louder sucking sound okay? I understand where it's coming from, but is having it that loud normal?

Thanks!

 

[Keoke]

Sorry, didn't see that you asked for them.

The numbers are 7-13-3.544. I'm not 100% about the ".544" has it wasn't a could angle, but I could the 7-13-3 is correct.

Also, is the much louder sucking sound okay? I understand where it's coming from, but is having it that loud normal?Yes its ok for now. However, I am now at a loss that is not the proper Vacuum advance for a late BJ8 engine. The numbers should be 5-12-8 Perhaps the PO swapped in a different DIZZY as ther are several versions of the 25D6 Type----Keoke??

Thanks!