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Discussion Starter · #1 ·
Hi, I read about the carburetor tuning in the service manual, it mentions that the CO meter is used to monitor the exhaust gas. Is it really necessary to have a CO meter to do it? Or, is there any way to do it without using the CO meter.

Thanks guys.
 

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Hi

Ideally yes for the meter as this accurately captures the readings.
Alternatively colortune.
The Colortune has a clear spark plug that lets you look into the combustion chamber while the engine is firing. The colour of the combustion flame tells you if the mixture is correct. With the carburettor mixture screw you can then adjust the flame colour to get the correct mixture.

Just found their u tube promo

https://www.youtube.com/watch?v=Y9t8XhFlKbk

good luck
 

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Discussion Starter · #3 ·
Thank you very much for the reply.

Just wonder what size of the park plug on Silver shadow would be?

14mm?

Thanks

Hi

Ideally yes for the meter as this accurately captures the readings.
Alternatively colortune.
The Colortune has a clear spark plug that lets you look into the combustion chamber while the engine is firing. The colour of the combustion flame tells you if the mixture is correct. With the carburettor mixture screw you can then adjust the flame colour to get the correct mixture.

Just found their u tube promo

https://www.youtube.com/watch?v=Y9t8XhFlKbk

good luck
 

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Discussion Starter · #4 ·
I did some search, and found the OE spark plug would be NGK BPR5ES, which is 14mm thread size.

BTW, what's the difference between BPR5ES and BPR5ES-11?
 

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I did some search, and found the OE spark plug would be NGK BPR5ES, which is 14mm thread size.

BTW, what's the difference between BPR5ES and BPR5ES-11?
Just for clarity, the OEM plugs were never NGKs but were Champions. In the case of the SY2 cars they were either RN 14 Y or XN 14 Y with a gap set to 0.03 in/0.76 mm. I don't think this changed from the SY1s and it's documented in the Owner's Handbook and, I believe, the workshop manual. NGKs are the "accepted standard" now and Crewe issued a service bulletin stating that BPR4EVX were suitable for all V8 engine cars. Some people have gone to the iridium plugs, which I think are real overkill for the older carbed cars, and NGK recommends the V-Power line for the SY series cars.

See the attached NGK Spark Plug Chart for an explanation of their numbering scheme. The -11 designation has to do only with the pre-gapped version of the plug and a -11 is pre-gapped to 1.1 mm. Typically we want the ones with no numbered extension since the lowest numbered extension, -8, has a 0.8 mm gap, which is a bit larger than OEM spec.
 

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Discussion Starter · #6 ·
Thank you guys for the info.

I hooked up a vacuum gauge to the intake manifold vacuum source, and after the car starts, I got a fluctuating reading of 15 in Hg, still in the green normal zone of the vacuum gauge, the fluctuation is about 2 in Hg, and it's changing pretty fast, like the jittering .

Would this relate to the carburetor balancing? or something else.

Also, the cold start idle rpm is just around 200-300, then the rpm would gradually go up to 600-700 as the car warms up. I remember the car used to cold start at 500-600 rpm and then gradually go up to 1100-1200, as the fast idle mechanism regulates. I did not tamper with the fast idle mechanism since I got this car. Something wrong with this symptom.

Thanks
 

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Also, the cold start idle rpm is just around 200-300, then the rpm would gradually go up to 600-700 as the car warms up. I remember the car used to cold start at 500-600 rpm and then gradually go up to 1100-1200, as the fast idle mechanism regulates. I did not tamper with the fast idle mechanism since I got this car. Something wrong with this symptom.

Thanks
I'll let someone else cover your first questions since this isn't territory I've covered myself.

However, what you describe as the idle behavior on your car is, as the saying goes, bassackwards. When you set the choke the fast idle cam should also be set. When the car is started cold the mixture should be enriched by the choke and the amount of fuel being fed through increased by the fast idle cam so your starting idle should be far faster than your normal "warm resting idle."

You can turn off the fast idle cam by giving the accelerator a quick punch with your foot to release it. The idle speed should then decrease though if the car is still cold and the choke is still closed it will remain faster than a warm resting idle.

You shouldn't have a slow idle with gentle climbing on a cold start if all the bits meant to assist with a cold start are functioning as intended.
 

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Discussion Starter · #8 ·
Thank you for the reply.

The fast idle on my car is functioning, when I set the choke, idle stop screw is on the high step of the fast idle cam, and if I give the accelerator a quick punch, will release it. The initial low idle rpm is not right, just wonder what would cause it.

I also hear some hissing sound from the left bank carburetor area, I think it's coming from the weakening device, is this normal? Or, I have some vacuum leak?


Update on the vacuum gauge reading, when the car is fully warmed up with 600rpm, the vacuum reading would be around 20 inch Hg, with 1 inch Hg fluctuation.

Thanks

I'll let someone else cover your first questions since this isn't territory I've covered myself.

However, what you describe as the idle behavior on your car is, as the saying goes, bassackwards. When you set the choke the fast idle cam should also be set. When the car is started cold the mixture should be enriched by the choke and the amount of fuel being fed through increased by the fast idle cam so your starting idle should be far faster than your normal "warm resting idle."

You can turn off the fast idle cam by giving the accelerator a quick punch with your foot to release it. The idle speed should then decrease though if the car is still cold and the choke is still closed it will remain faster than a warm resting idle.

You shouldn't have a slow idle with gentle climbing on a cold start if all the bits meant to assist with a cold start are functioning as intended.
 

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If you hear hissing you've got a vacuum leak. Definitely nip that in the bud and hope that no one has adjusted the car "to make up for it."

These days most people replace vacuum hosing with black silicone since it holds up so much better to heat over time and doesn't become brittle and/or shrink. Any time you are replacing vacuum lines only do one line or line segment at a time!! Problems can arise by your either introducing a leak that wasn't there or eliminating a leak that was that others have tweaked to "work around" not knowing anything about vacuum leaks. If you do more than one segment at a time it is nearly impossible to determine where the culprit lies. If you start the car after each segment and things stay the same you know you're no worse off and probably haven't either induced a problem or solved one, either.
 

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Discussion Starter · #10 ·
Thank you for the info.

So, the weakening device won't make any hissing sound then?

Thanks


If you hear hissing you've got a vacuum leak. Definitely nip that in the bud and hope that no one has adjusted the car "to make up for it."

These days most people replace vacuum hosing with black silicone since it holds up so much better to heat over time and doesn't become brittle and/or shrink. Any time you are replacing vacuum lines only do one line or line segment at a time!! Problems can arise by your either introducing a leak that wasn't there or eliminating a leak that was that others have tweaked to "work around" not knowing anything about vacuum leaks. If you do more than one segment at a time it is nearly impossible to determine where the culprit lies. If you start the car after each segment and things stay the same you know you're no worse off and probably haven't either induced a problem or solved one, either.
 

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Thank you for the info.

So, the weakening device won't make any hissing sound then?

Thanks
That's the direct implication of, "If you hear hissing you've got a vacuum leak."
 

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Discussion Starter · #12 ·
Just found that vacuum leak point, fixed that, got some improvement, but not much, the vacuum gauge reading is still fluctuating 1 inch Hg.

Thanks

That's the direct implication of, "If you hear hissing you've got a vacuum leak."
 

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One way to check for vacum leaks is to spray carb. cleaner at any suspicious looking joints or pipes. If the car stumbles, you have a leak.

I have both a gas tester and a colourtune and the colourtune is the best way as you see an immediate change when you make an adjustment. For quickly checking a car I use the gas tester, but all adjustments are made with the colourtune, and I trust that more than the analyser. Apart from anything else on cars with dual (or more) carbs it's impossible to know which carb to adjust with the analyser. If your car is running rich it might be 'hunting', maybe try checking the mixture now, and correct it if required, then see if the vacuum gauge still fluctuates. I always find it's best to go round in circles; set timing, then idle, then balance, then mixture, then check timing again, then idle etc until it's all correct. No point trying to make one thing perfect when other things might be wrong, and adjusting those will have an affect.
 

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Discussion Starter · #14 ·
Very helpful input, thanks a lot.

One way to check for vacum leaks is to spray carb. cleaner at any suspicious looking joints or pipes. If the car stumbles, you have a leak.

I have both a gas tester and a colourtune and the colourtune is the best way as you see an immediate change when you make an adjustment. For quickly checking a car I use the gas tester, but all adjustments are made with the colourtune, and I trust that more than the analyser. Apart from anything else on cars with dual (or more) carbs it's impossible to know which carb to adjust with the analyser. If your car is running rich it might be 'hunting', maybe try checking the mixture now, and correct it if required, then see if the vacuum gauge still fluctuates. I always find it's best to go round in circles; set timing, then idle, then balance, then mixture, then check timing again, then idle etc until it's all correct. No point trying to make one thing perfect when other things might be wrong, and adjusting those will have an affect.
 

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Discussion Starter · #15 ·
Update, got the colortune, and it turns out that the bank A is running rich.

The wired thing is despite how much I slackened the adjusting screw for the mixture on the bank A carburetor , it's still running rich(the yellow flame visible from the colortune). Screw the adjust screw in will enrich the mixture, I slackened the screw all way out, it's still rich, :(

Any idea what would cause this issue?

I have not checked on the bank B yet.

Thanks
 

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Discussion Starter · #16 ·
Update, similar situation on the bank B, rich all the way even with the adjust screw fully screwed out.

The color of flame is more blueish that the bank A, which is purely orange, though.
 

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Hi Covenant

Are you definitely turning the right screw. There are two - the volume screw and the jet adjusting screw. I am sure you are, so I will continue/

Remove the 4 setscrews and pull off the vacuum chamber (figure 12, chapter K in the SY1 workshop manual). Remove the long piston spring and pull out the piston. Make sure you do not mix parts between the two carbs and never rest the piston on it's side as it may bend or offset the needle.

You will now be able to see the jet. With the adjusting screw fully loosened, the jet should be proud of the bridge piece by about 1/8". As you turn the adjusting screw clockwise the jet should move downwards until it is about a quarter of an inch below the bridge piece. If the jet does not move then cleaning may free it off. Another possibility is the spring holding the jet in position may be tired and not exerting enough force to hold the jet firmly in place.

If everything looks ok and the jet is moving up and down with the adjusting screw, run your fingers along the piston needle. Check for any steps or ridges in it denoting uneven wear. Even if you detect no ridges, it may be the jet and needle have worn smoothly and therefore causing the rich mixture.

Ultimately, recon kits are cheap, so it may be worth just reconditioning the carbs and fitting new needles.

Geoff
 

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Discussion Starter · #18 ·
Thank you so much for the info.

I am turning the right screw, not the volume adjust screw.

The mixture is so rich that, it even causes some cylinder misfire, especial at cold start. I found one cylinder has this issue by means of the colortune.

The misfire justifies the fluctuation of reading of the vacuum gauge, I believe.

Also, fuel is sipping out of the fuel bowl lid, the fuel level could be too high.

The bank A fuel bowl is sipping more badly than the bank B, which is consistent with bank A running richer than the bank B.

Will the fuel level at fuel bowl also effect the rich mixture?

Thank you.

Hi Covenant

Are you definitely turning the right screw. There are two - the volume screw and the jet adjusting screw. I am sure you are, so I will continue/

Remove the 4 setscrews and pull off the vacuum chamber (figure 12, chapter K in the SY1 workshop manual). Remove the long piston spring and pull out the piston. Make sure you do not mix parts between the two carbs and never rest the piston on it's side as it may bend or offset the needle.

You will now be able to see the jet. With the adjusting screw fully loosened, the jet should be proud of the bridge piece by about 1/8". As you turn the adjusting screw clockwise the jet should move downwards until it is about a quarter of an inch below the bridge piece. If the jet does not move then cleaning may free it off. Another possibility is the spring holding the jet in position may be tired and not exerting enough force to hold the jet firmly in place.

If everything looks ok and the jet is moving up and down with the adjusting screw, run your fingers along the piston needle. Check for any steps or ridges in it denoting uneven wear. Even if you detect no ridges, it may be the jet and needle have worn smoothly and therefore causing the rich mixture.

Ultimately, recon kits are cheap, so it may be worth just reconditioning the carbs and fitting new needles.

Geoff
 

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Hi Covenant

Re: Will the fuel level at fuel bowl also effect the rich mixture?

Very definitely. You have identified the most probable cause. Check out page K15 of the workshop manual for setting the float levels. Bear in mind you may have to renew the float needle and seat as well.

Geoff
 

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Discussion Starter · #20 ·
Hi, Geoff

By proud of as in "With the adjusting screw fully loosened, the jet should be proud of the bridge piece by about 1/8". "

do you mean the jet should be ABOVE the bridge piece by 1/8'' ?

Thanks
 
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