Help with adjusting carbs

[healeynut]

Brandon -

Ok, sounds like you have them adjusted properly for mixture.

Let me ask you this... when was the last time you changed the bushings in the throttle shafts on your carbs (this is not the same as putting the rebuild kit on the carbs)?

It sounds to me like your throttle shaft bushings on your carbs are shot. This will cause a great deal of variability in the idle running of your car, because depending on the engine temperature - different amounts of air will leak in through the throttle shafts where they go through the throttle body.

Aftermarket teflon bushings can be bought from the Nocks at https://www.britishcarspecialists.com for your HD8 carbs.

Trust me, when you put these in your carbs (you can do it on your shop bench, it's an easy job), your idle will become rock solid regardless of how lousy your carbs are adjusted.

I also forgot to mention that having good o rings in the slow idle screw are important as well. Have you rebuilt your carbs? It's an easy job you can do yourself.

The teflon bush was the single most important fix I ever made to get a steady idle on my BJ8 - second was going with the Pertronix. Third... having good O rings on the slow idle screw are very very important.

Lastly, what sort of air filters do you have on your car? If the two little holes on the sides of the main throttle throat are blocked by your air filter (some after market air filters do this), then your idle will be all over the place as well. Please confirm.

 

[Keoke]

These carbs are becoming a mystery to me now. Just went for a drive and came back...car at 190-200'F. Idled okay at around 500-700, but noticed it earlier at a stop wanting to die. So I screwed down the mixture screws one turn each (turned to the right). I started the car, and it just died. It wouldn't idle at all, even though it just did before I adjusted the screws. Any ideas?

Thats OK Brandon, back off the mixture screws 1 turn and just a tad more, then set fast idle screws down until the Tach shows 1000 RPM when idling hot.

 

[healeynut]

Keoke / Brandon -

That's cheap way to set up HD8 carbs... and will lead to very heavy fuel consumption (much more costly over time than a carb rebuild!). Obviously this is the easy way to get it running without dieing, but will waste a huge amount of fuel in regular running.

When the car is hot, you definitely should be able to get a decent idle using the slow idle screw only. If you want to check the o-ring seals on the slow idle screw, pull out the slow idle screw (make a mental note of the turns to bottom before pulling it out) and then lubricate the o rings using dashpot oil. If the idle all of a sudden changes after you screw in the slow idle screws... this means the o rings on your slow idle screws are shot and need to be replaced. This is a very easy a cheap fix.

 

[Keoke]

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Healeynut! I am noted for approaching potentially expensive repairs using the Cheap!---My Regards Keoke- /bcforum/images/%%GRAEMLIN_URL%%/cowboy.gif

 

[healeynut]

I spent two years working in the Philippines. I bet I learned more about how to do a cheap repair than you could ever know. Amazing what the Filipinos can fix with some bailing wire, duct tape and a match book.

/bcforum/images/%%GRAEMLIN_URL%%/hammer.gif

 

[Keoke]

I spent two years working in the Philippines. I bet I learned more about how to do a cheap repair than you could ever know. Amazing what the Filipinos can fix with some bailing wire, duct tape and a match book.

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Ah shucks, I thought you was gonna tell me how to make a fire using a flint but you had matches.--Keoke-- /bcforum/images/%%GRAEMLIN_URL%%/laugh.gif

 

[GregW]

I have to disagree with you here Keoke. I think its rubbing two sticks, not flint. Lots of friction.

 

[Keoke]

---- /bcforum/images/%%GRAEMLIN_URL%%/iagree.gif Greg, Good call. I momentarily forgot about that method. /bcforum/images/%%GRAEMLIN_URL%%/thankyousign.gif---Keoke- /bcforum/images/%%GRAEMLIN_URL%%/thumbsup.gif

 

[BrandonBJ8]

Alan,

Thanks for the great advice. I'm pretty sure the carbs were rebuilt just before I took possession of the car 2 years ago (checking into this to confirm), however I don't think the throttle shaft bushings were replaced. I know for sure that they were rebuilt in 1993 by an SU expert. However, the bushings are cheap, so I'll go ahead and order them to see if that helps.

As far as the O-rings for the slow idle screw... Are they #50 or #51 on Moss's catalog (BJ8 Carburetor)?

I think my air filters are original. Can you tell from the attached picture if they are original? (I can take a better one later...ignore the damper, its an old picture.)

Thanks!
-Brandon

 

[tahoe healey]

If that is, infact, the damper rod protruding from the black cap on the front carb, that is the problem.
TH

 

[Ed_K]

Brandon,
Your air filters look like mine fron that angle. Mine are the original ones. The paint has flaked off of them some, just like mine.
Ed

 

[GregW]

Hi Brandon,
I think TH is hot on the trail. I looked at the photos when you first got the car and the damper rod didn’t look like it projected up as far as it does now (coming out of the black cap on top). I’d replace that before you pull the carbs and re-bush the throttle shafts.
I don’t use SUs, so my knowledge here is very limited. To test bushing wear, could you spray carb cleaner on the outside of the bush/ shaft junction (we’re talking carbs here) to see if the idle changes?

 

[BrandonBJ8]

That is an old picture from about a year ago, I just didn't want to get out and take another picture last night. The picture was just to see if you could tell if my air filters were original. I replaced the dampers a after I took that picture.

 

[BrandonBJ8]

Here are two updated pictures. One of the air filter and one of the carbs.

 

[Keoke]

Hi Brandon, from these pictures of your carbs it seems:

1. you have a persistent fuel leak from the rear carb

possibly both from the fuel bowl and the inlet banjo fitting.

2, the throttle shaft actuators seem to be too far out of alignment but that may be the picture angle.-?

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

 

[BrandonBJ8]

I'll check the fuel leak tonight, that could make sense. (What exhaust pipe does the rear carb correspond to when looking at the rear of the car?)

Here's another picture of the throttle shaft. How does it look from this angle?

 

[tahoe healey]

It appears there may be a little difference in the angle of the throttle forks. Is the space (gap) the same on the two forks? When you pull the throttle do both engage at the same time?

 

[BrandonBJ8]

Nice observation TH. I've taken another picture and made a few marks on it.

In red, I circled the gaps. The gap of the front (right) carb is greater than the rear carb.

In blue, the angle between the two are different. The front carb's is at less of an angle (more vertical).

The same is true with the yellow circles, however the difference in angles are a bit more dramatic.

However, when I pull on the throttle, everything seems to engage at the same time.

 

[Keoke]

-Brandon: new picture confirms suspicion.
Pulling on he throttle and everything seems to engage at the same time, does not assert that the butterflies in both carbs are at the same position which they must be at for the carbs to operate correctly. However, it is possible that if the carbs were rebuilt the shafts were drilled incorrectly. Consequently, it is necessary to determine that the butterflies are at the same position and move in synchronism.---Keoke

 

[tahoe healey]

Keoke's got it. Pull the air cleaner off and look inside to see if the butterflies are both closed completely. Then pull on the throttle and see if they open at the same time.