I haven’t read through the complete list but has the car got the aux starting carb?
If this is operating that would cause overfueling.

 

Okay thanks... I’m not sure what I’d be taking a picture of for that. Isn’t everything enclosed until I disassemble? When I unscrew that black cap, doesn’t that pull out the needle? I may be able to get pics for you guys today... just need to know what I’m shooting at, and best angle.

 

Hi Robman... don’t believe my model does. See my carb pic I just posted.

 

The black cap on the top is the damper, nothing to do with the needle, that’s where you need to place an amount of oil (light weight something like 3 in 1 rob the missus’s sewing machine oil) some also use ATF.
Looking at the carbs I will surmise that you have a manual choke rather than the hisser
https://www.google.co.nz/search?q=ja...M_A35k6sPbw3M:

 

Manual choke just to the right of the large speedo gauge in the photo. The link you included brought up a blank page for me, but the heading in the web bar did say a Jaguar Hisser... but I don’t think I have that.

 

They are manual choke HS6 carbs.


I have to say I ddn't clock that before, before you do anything else, make sure there is a little slack on the choke cable at the carb end when the choke is off, I would bet that the choke is slightly on.

 

Undue the three screws in each carb circled in green and carefully lift the piston chamber straight up.
The piston will just be sitting there after you remove the piston chamber.
Now remove the piston on each carb being carful not to damage the tapered needle as you remove the piston.
Take a photo of each carb of the main jet pointed out in red.
Note in that photo your jet should be about in the same position with the choke fully OFF.
Don't get the front and rear carb parts mixed up.


In the other photo, the ridge on the bottom of the needle should be even with the piston bridge as pointed out with the purple arrow.
Take a photo of each piston as you see it where the purple arrow is.
When you turn the piston up side down to take the picture be prepared to catch the oil that will run out of the damper tube.

 

That's a very elegant and helpful post Jeff perfect.


Gbourck, just check the choke connection first, if the cable is tight and pulling the choke on a small amount then you may well have your answer, as you will have a rich situation due to the choke pulling the main jet down, if the choke has some slack, then follow Jeff's instructions above and come back.

 

I have some questions for you Jon...
When this type of SU is choked, the manual choke linkage simply pulls the main jet down to enrichen the mixture, is this correct ?

To adjust the mixture, one turns the large nut on the main jet underneath the carb ?
My Bentley is this way and it's a little awkward to adjust.

The nut is screwed in to lean the mixture (move the main jet closer to the jet bridge)... ?

The nut is screwed out to enrichen the mixture ?

 

All spot on Jeff.

 

Thanks gents... great things to try next. Photos very handy indeed Jeff. And I’ll verify / adjust for choke slack in the “hot” position as well Jon.

Flying to Toronto on business for a week, so unless I can sneak out today, there will be a silent week unfortunately.
Jerry.

 

It doesn't really matter when the choke is adjusted _ engine hot or cold, as long you can fully shut it off when the engine reaches operating temperature.

Have a friend move the choke in the car while you watch the jet move (refer to the picture with the red arrow)
The red arrow points to the jet.
The choke moves the jet down to enrichen the mixture when the engine is cold.
If the linkage is not slack enough to allow the jet to return to the run position (hot engine), the choke will be on partially all the time and you will get the black and sooty plugs as you see in your photo.

With the proper amount of slack in the choke linkage, the underside of the jet (on the bottom side of the carburetor) will come to rest on the big mixture adjusting nut on the bottom of the carb, when the choke is fully off.

 

Well gents... we’ve made progress it seems. The wire that actuates the choke is stiff so it was hard for me to tell if there was “slack”, so I loosened the lock but and placed the thing as open as I could and slid the actuator to HOT. It may not have been much, but it seems there was a slight difference in wire beyond the nut when I did this, indicating “some adjustment was there. I then pulled out all the plugs, cleaned them, and checked gaps (one was slightly too tight a gap). I then did as Jeff suggested and checked the carbs per his photos. They looked as per his, and the jet did move (very little) with the chokes range - I’d say it moved maybe an eighth of an inch.., Is that right?

Photos are below.

Oh and I put thin sewing machine oil in the damper, which seemed very low - almost empty actually. I’m questioning what I put in there to begin with.



Then I fired her up and and it started and idled as always, but a bit smoother even. Took it for a ride and the stuttering in acceleration was gone!!! Basically it was back to where she was when I got her last June. BUT she burned gas heavy and exhausts slightly black then too, so I still have a rich mixture issue I feel.

I’m just elated she runs smoothly again, and owe all of that to your generous support, time, and patience.

Any thoughts to add before I consider a carb adjustent to lean it out next?






Rear carb piston



Rear carb piston



Rear carb



Rear carb



Choke linkage



Front carb



Front carb



Front carb Piston



Front carb Piston

 

1/8th of an inch is fine for the jet travel to choke it.

Jon will probably know better how the choke linkage is adjusted in this specific case, but it does sound like the choke was not totally off when put in the "HOT" position.

On my Bentley, the choke mechanism is the same, but there is no cable, it's done with rods and levers.

If I want to adjust the mixture, I have to warm up the engine operating temp, slacken off the choke rod so there is free play to allow me to adjust the mixture.
When the mixture is correct, the choke rod is adjusted accordingly to where there is just enough slack so the jet remains fully home when the choke is off and the engine fully warmed up.

I would think yours is similar, but in your case to adjust the mixture the choke cable has to be temporarily disconnected to allow movement of the jet on both carbs vie the big nut at the bottom.
I would suspect there is a spring that holds the main jet in each carb hard up against the adjusting nut and the cable pulls against that spring when lowing the main jet to choke it.

Just so you know, the photo's are not mine, but I will post some photos.
My jet is much closer to the jet bridge, indicating that indeed your carbs are probably still set a little rich.

 

Note the photo with the red rectangle, that is called the jet bridge.
The green arrow points to the main jet and when I measured where my jet is from the surface of the jet bridge to the jet, I get .062 inches, that's about 1/16th of an inch.

Yours looks lower then that, indicating that your carbs are set too rich.
Keep in mind that I have a 3.4 litre, but the over-all adjustment should be similar in appearance when looking at the jet and jet bridge relation.

And about the lack of power, if there was no oil in the damper tubes, then when you stepped on the accelerator pedal to open up the butterfly valves, then you would have gotten a big gulp of fuel into the engine.
That would have caused the hesitation and lack of power.

EDIT:
I am also assuming that your photos of the jet/jet bridge is with the choke in the HOT/OFF position.
Is that assumption correct ?

 

That is great info Jeff, and thanks. In neither case was my jet ever even with the bridge... on either side... so explanation hints that these may have been both out - explaining the richness since I’ve had it, and the common soot on all plugs. Unless I hear otherwise from Jon, I’ll use his manual for tuning the carbs... should I go through a whole set up or just start with this Big Nut adjustment mentioned?

 

The jet will never be even with the jet bridge, no fuel would flow at all if it was.
The tapered needle in the piston would totally close the jet off _ or come near to it.

It just appeared that your jet was a bit low over all causing a rich mixture.

 

Looks like you have some progress, it could be a good idea to get some oil in the choke cable and make sure the inner cable is not bent slightly as it enters the outer cable, that should help with the stiffness.

Jeff is right, I always disconnect the choke cables during carb adjustment to ensure that there is no action on the carb, when you do reattach it, slide the choke lever just slightly off hot (only 1/8") then reattach the choke cable, that way, hot will always be off.

The initial set up for the jet is to set it level with the bridge (nut up) and then lower 2 full turns on the nut, follow the setup for the carbs on the SU site I gave you the link for, which essentially you richen the mixture until the highest idle speed is achieved, then lean it off until the idle just starts to drop, then back up to get the idle speed back but only just, you may have to play with the idle adjustment if the revs go too low or too high, you need to do this to both carbs a step at a time, and listen for an even hiss from both carbs, or get a gauge that measures the air flow through each carb and adjust the throttle adjustment screws.

If you start with the base setup, jet level with bridge and then 2 turns down, you need to loosen the interconnect between the carbs, then turn each jet a 1/4 turn at a time and let the idle settle, then another 1/4 turn etc.


Follow the instructions, they have more details than I can explain here


Good luck and let us know how you get on.