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post #1 of 47 (permalink) Old 02-08-2015, 06:44 PM Thread Starter
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Carbs

Hello
My engine has been running rough lately so I decided to remove the dash pots and have a look inside the carburettor

I did notice that the passenger side carburettor was different to the drivers side in that the little brass round jet bearing I think it's called was raised by about 10mm

I'm not that technically minded with carbs so I don't know if it's correct or not does in raise due to any setting on the carb or choke or is this a fault. ?
Please see picture any help much appreciated
Alec
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post #2 of 47 (permalink) Old 02-09-2015, 05:55 AM
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Hi Alec.
When asking a question it's always best to give your vin number and year model etc it makes trying to help a lot easier!!,
Also I have to say the car was running fine before right? And just started running rough?mmy guess is your carb question isn't the issue (.it must have run well with that jet at that setting) was your dash pots dry? Put them back on and refill the dashpot oil let it rest for a while and see how she runs.
Without knowing the model/year/ vin number etc it would be difficult to assist or advise what to check first,,,,,

Chris

Silver shadow MKII 1977 SRH31709
old English white
Chris
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post #3 of 47 (permalink) Old 02-09-2015, 10:26 AM
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Hi Alec.
When asking a question it's always best to give your vin number and year model etc it makes trying to help a lot easier!!,
Thank you Chris!! I used to think that people were being nitpicky when they said this, but after dealing with my two cars and those of others for 9 years now I have to say that having your chassis number is essential.

Based upon the avatar, if that's Mr. Hoar's car, it must be a Shadow II.

Depending on how rough you could have an anti-run-on/anti-dieseling solenoid getting wonky and stuck partially open. My Wraith II (LRK37110) could barely be made to run at idle and was extremely rough. It was eventually traced to a partially sticking anti-dieseling solenoid. It never hurts to take these off to check them. It also never hurts to give them a shot of WD40 or similar in the center to keep things gliding smoothly since exposure to dirt/collection of crud is not an issue. I've seen many revived and continuing to work correctly after a shot of penetrating oil, allowed to soak, and then a good number of on/off cycles by hand to make sure that everything is opening and closing as expected.

Brian

The opposite of a correct statement is a false statement. But the opposite of a profound truth may well be another profound truth.
~ Niels Bohr


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post #4 of 47 (permalink) Old 02-09-2015, 01:04 PM Thread Starter
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carbs

Thanks Chris and guyslp
Yes my mistake Its a silver shadow 2 1978 vin SRH32815
Now for the long story
The carbs have been tuned by su carb chap a while back all working fine
Then suddenly last week I was getting rough / missing idle and lack of power on driving
I only have basic knowledge of these things but willing to learn
So I cleaned all the spark plugs and found they were very oily on the drivers side . I had to remove the inlet pipe that goes to the side of the carb on the passengers side to remove the plugs I replaced the gasket with cut out one ,the type you cut to size yourself.
Still no difference
So I check all HT leads with multimeter and found one lead that had no resistence so changed that
Still no difference
So Blast! I bought new plugs and replaced them all and when I removed the gasket on the inlet pipe I noticed I didnt cut out the breather holes for it
At the same time I checked the pots for oil and found they were empty so I removed the pots to check for any oil in the chamber gave that a clean but noticed that the brass jet was raised up on the same side as the gasket was with no beather hole?
The other carb is level
So I was concerned I may have now damage this, causing it to suck up with excessive air suction ?
I have just learnt right or wrong that these jets are adjustable in height via the mixture control nut so maybe when it was set this was the correct height at the time
Lack of knowledge for me on this one
I think I have found the cause of the rough idle faulty ht lead ,wet plugs no oil in damper and gasket with no breather holes in
But due to lack of knowledge Im concerned about the height of the jet as the other is level not knowing if the gasket could of caused this to rise or this could just be the result of the carb guy tuning the carbs
I have been told on another forum that it should be level?

Thanks Alec

Silver Shadow 2 1978
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post #5 of 47 (permalink) Old 02-09-2015, 03:29 PM
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Hi Alec

Yes, the jets are adjustable in height by the mixture control screw. The lower the jet, the richer the mixture. The height of the jet in the pic looks just plain wrong. As you suspect, they should be roughly the same height and slightly below the level of the bridge piece. My car is a 74 SY1 which has entirely different SU carbs so I cannot give any advice about the carbs on your car. If this had occurred on my car I would immediately suspect a failure in the jet/lever assembly. It is possible the one needle on your car is so badly worn that it would require the jet to be set in this elevated position, however if that were the case any person experienced in tuning these carbs would recommend new jets and needles were fitted. If you do not want to strip this carb down yourself, maybe a visit back to the SU guys is in order.

Regards

Geoff.
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post #6 of 47 (permalink) Old 02-09-2015, 06:54 PM Thread Starter
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Carb

Hello Geoff

Thank you for taking the time to reply

You have managed to put my mind to rest and have
learnt something new

To strip down the carb and retune is beyond me
So I will have to call in the su carb chap

Would the height of the jet have any adverse effect on the spark plugs

As I noticed one bank of 4 plugs were very wet oily ?

Thank you Alec

Silver Shadow 2 1978
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post #7 of 47 (permalink) Old 02-09-2015, 10:44 PM
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Hi Alec

The height of the jet would not affect just one bank. This is because each carb services two cylinders on each bank. From the drivers seat as you look to the front of the car, the bank on the right hand side is the A bank and the left hand side is the B bank. The intake manifold connects the right hand carb to the following cylinders - A1 B2 B3 A4 and the left hand carb is B1 A2 A3 B4. I would not like to guess at this stage as to the reason for the oily plugs on the one bank only.

I think you just need to chat to the su carb chap and see what his opinion is.

Let us know the outcome

Regards

Geoff.
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post #8 of 47 (permalink) Old 02-10-2015, 08:58 AM
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Hi Alec
Well it does seem something else is at play here and guy and geoff have highlighted a couple of things to think about those weakner valves could always do with a squirt of 3in 1 and it takes no time to do so I would do that and just check the spade connectors one at a time so you don't mix up the wiring whilst your at it.
Something iv done myself is just check your sparkplugs are seated correctly recently when I replaced mine I didn't quite have them fully seated (we all know they are a bugger to fit) so i had to borrow a better wrench set (mine is just a little to short and I didn't "feel" them tighten) and did them all again.
I have however fully rebuilt my carbs myself and had a chap come and balance them on the car once I had refitted them ( my settings was apparently very close) it's not a job I would advise everyone to try but I have to say if your a competent home mechanic with an eye for detail it is possible (if you drop screws use dirty rags to clean bits or don't think making notes is worth it then your not the kind of chap to try refurbishing carbs!!) it's a job for the methodical approach,,,ps I have a 1976 m11 shadow I do have photos of my carb rebuild but alas can't seem to see how to add images using my ipad.

Chris

Silver shadow MKII 1977 SRH31709
old English white
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post #9 of 47 (permalink) Old 02-10-2015, 10:03 AM
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Hi Alec

Quite a curious problem you have there. Even in the worst case scenario, a blown cylinder head gasket, you would only expect one or two cylinders to have wet and oily spark plugs. Worn valve guides would cause the same symptom, but why on only one bank, unless the one cylinder head has been reconditioned and the other not - highly unlikely, I had to smile at Chris's point about seating the spark plugs. I have done this myself, but only on the one plug. The problem is when you are screwing them in they hit tight spots giving the impression they are fully seated when in fact they are not. You do have to be so careful not to overtighten them and strip the threads, which exacerbates the problem. I always use anti-seize on spark plug threads.

I personally would run a compression test on all cylinders and also check the oil dipstick for any traces coolant which shows up as whitish foam. Also check the exhaust is dry - no steam in it.

Regards

Geoff

PS - The one thing Chris forgot to mention when carrying out any work on the car - loads of photos.
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post #10 of 47 (permalink) Old 02-10-2015, 12:19 PM Thread Starter
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Carbs

Thanks Chris and Geoff

Great Help

I have a much better insight .I did read the tech manual on su carbs hif just so I could at least understand how the jets are adjusted and could see how the lever arm works.

Thanks for the advice on the spark plugs

I think I will need the su carb chap in to have a look
I will get a compression test done aswell

Thankyou for all timing the time to help great site

PS How sunning is in Las Vegas not stop rain here in Cornwall uk

Thank you Alec

Silver Shadow 2 1978
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