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Discussion Starter · #1 ·
Afternoon all!



I have been reading up on baseline adjustments of the fuel-main adjustment screws, I believe Larry's book recommends 2-1/2 turns out from an initial soft seating of the needles. I have read that some find 2 full turns out is adequate, one was at 1-5/8 turns out...seems to be pretty widespread from all of the posts I have read. I understand that every bike is different, there are different displacments etc...I am trying to dial her in better and this is an item I would like to be more clear on.



I ask the following because the exhaust smells a bit rich--and it seems to go through my tuning tank about 16-oz's rather quickly. I will check the plugs when I get home tonight and post some pics as a follow up. Average temp is around 35 deg F too which I know will 'rich' up the mixture.



Several Questions:

1) should tuning be done with the bike on the center stand?

2) Is plug coloring the end-all be-all evidence and best way to check the 'burn' and confirm if the bike is rich or lean?

3) Is the ideal color if one had to compare colors, similar to that of a nicely roasted marshmallow?

4) How much adjustment should be made to 'fine-tune' these carbs...a blade width or more per adjustment?



I did a stupid thing too and forget to add an inline filter to my tuning tank, and might have some dirt in the main jet--when I crack the throttle she's sluggish, you can hear the tug-of-war between cylinders, then when she gets above 3k, she sounds amazing! The sync looks good on the home made manometer...though that too is slightly off.



Thanks for your input!
 

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Afternoon all!



I have been reading up on baseline adjustments of the fuel-main adjustment screws, I believe Larry's book recommends 2-1/2 turns out from an initial soft seating of the needles. I have read that some find 2 full turns out is adequate, one was at 1-5/8 turns out...seems to be pretty widespread from all of the posts I have read. I understand that every bike is different, there are different displacments etc...I am trying to dial her in better and this is an item I would like to be more clear on.



I ask the following because the exhaust smells a bit rich--and it seems to go through my tuning tank about 16-oz's rather quickly. I will check the plugs when I get home tonight and post some pics as a follow up. Average temp is around 35 deg F too which I know will 'rich' up the mixture.



Several Questions:

1) should tuning be done with the bike on the center stand?

2) Is plug coloring the end-all be-all evidence and best way to check the 'burn' and confirm if the bike is rich or lean?

3) Is the ideal color if one had to compare colors, similar to that of a nicely roasted marshmallow?

4) How much adjustment should be made to 'fine-tune' these carbs...a blade width or more per adjustment?



I did a stupid thing too and forget to add an inline filter to my tuning tank, and might have some dirt in the main jet--when I crack the throttle she's sluggish, you can hear the tug-of-war between cylinders, then when she gets above 3k, she sounds amazing! The sync looks good on the home made manometer...though that too is slightly off.



Thanks for your input!
[1]yes,always safer in the maintenance stand,and its easier
to get to both sides

[2]not really,but its a good guide.a morgan carbtune would be a tad betterhttp://www.carbtune.com/index.html

[3]a tan colour

[4]bear in mind these carbs are 30 year old,so it could be in half or 1/4 turn increments

hth
 

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Adjust a bit and then take a plug spanner/wrench out on a ride with you.Stop after the engine is hot and check/adjust again.Check again when you get home.



I am lucky as I have a Colourtune device,



http://www.gunson.co.uk/item.aspx?cat=673&item=1853



They are too expensive IMHO for what they are but do work.
 

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Rick, you mentioned "backing them out" to make the mixture leaner. On these carbs, you have to turn them in to lean the mixture. These mixture screws control the fuel flow, not the air flow as on some carbs.



I would try a half turn, then as Shep says, check your plugs again and adjust. You can also adjust for highest RPM at idle, but you really need a more sensitive tach than the bike's to do that.
 

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I have been reading up on baseline adjustments of the fuel-main adjustment screws,


Just for clarity: what you're adjusting is the idle mixure. It only controls the mixture at idle. Well, actually it plays a part at increased throttle too, but it's a very small part.
 

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Just for clarity: what you're adjusting is the idle mixure. It only controls the mixture at idle. Well, actually it plays a part at increased throttle too, but it's a very small part.


The term,"Idle Mixture Screw" is misleading.It's a ,"Mixture" screw and sets the mixture of air and fuel ratios at all engine revolutions.This is different from the amount of fuel used at different engine speeds.





http://en.wikipedia.org/wiki/Air-fuel_ratio
 

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The term,"Idle Mixture Screw" is misleading.It's a ,"Mixture" screw and sets the mixture of air and fuel ratios at all engine revolutions.This is different from the amount of fuel used at different engine speeds.





http://en.wikipedia.org/wiki/Air-fuel_ratio
I don't think so,,,,If that is the case, why do people change jet sizes?



You can turn the idle screws all the way in and the bike will work fine,,except at idle.
 

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I don't think so,,,,If that is the case, why do people change jet sizes?



You can turn the idle screws all the way in and the bike will work fine,,except at idle.


People change jet sizes because they have changed the fuel to air ratio by altering the Air intake parameters.



Think about this.How can the Fuel to Air Ratio be corrected if wrong at higher engine revolutions when the engine is under load?Where is the adjustment?There is none.
 

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People change jet sizes because they have changed the fuel to air ratio by altering the Air intake parameters.



Think about this.How can the Fuel to Air Ratio be corrected if wrong at higher engine revolutions when the engine is under load?Where is the adjustment?There is none.
That is why you change the jet sizes.
 

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That is why you change the jet sizes.


No.Its to increase or decrease the amount of fuel supplied,not change the fuel to air ratio.



I'll correct the above.It's to allow for the change in Ratio as well but the ratio must be set by the mixture screw.
 

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No.Its to increase or decrease the amount of fuel supplied,not change the fuel to air ratio.
If you change the jets to a larger size on a bike with a stock air box, air filter and stock exhaust,,you will be changing the ratio of fuel to air.
 

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I think you are both right, but Allen is a little bit righter. My limited knowledge of carbs led me to think that the mixture (idle mixture) screw did essentially control the fuel at idle. But of course it also contributed to the richness of the mixture at higher RPM's as the idle circuit is still in play. But at higher RPM's the secondary jet is exposed by the vacuum piston and contributes the vast majority of the fuel to the mix. The role of the vacuum pistons in the carbs is to moderate the mixture for different load conditions.



I will defer to wiser minds now.
 

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If you change the jets to a larger size on a bike with a stock air box, air filter and stock exhaust,,you will be changing the ratio of fuel to air.


I concede.You are correct.The jet size will determine the Ratio and amount of fuel at higher revs/load until the slides take over as well
 

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I pulled my plugs after a long weekend ride (where the bike did well) and the colour was a sort of light brown/grey sort of colour. Is that good?



I did notice though that after doing say around 300km at 110km/h when you pulled up to stop it didn't idle very well.



But this morning on my 50km trip at various speeds it was fine when idling. I guess this is a heat thing, vapour lock or something.



My new IGN CDI has just arrived, oh yeah! Job for the weekend, or tonight maybe.



We did around 1200kms on the bike, awesome riding. Very little cars and great weather. I can also reccomend upping the presuure in our tyres to 36psi rear, 34psi front. This was reccomended by my mates mechanic expert/racing brother. It made a huge difference to the cornering.



Cheers



Curt
 

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I concede.You are correct.The jet size will determine the Ratio and amount of fuel at higher revs/load until the slides take over as well
If the idle jet continues to provide fuel throughout the whole rpm range, it would, as Blue said, make some difference.



I am still not convinced that the idle circuit does continue to feed fuel at higher rpms though. I think that is why the rubber plug is in the low jet tower,,so that when fuel starts to flow through the primary jet it bypasses the idle jet. I don't know this for sure but I do not know why else the rubber plug would be there.




When the idle jet was plugged solid on one of my carbs,,the only thing that was noticeable was that one cylinder did not work at idle.



The idle jet does feed fuel at high rpm when the throttle is closed during deceleration,,then it feeds unmixed fuel because the air cut-offs are in action.
 

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Discussion Starter · #18 ·
Rick, you mentioned "backing them out" to make the mixture leaner. On these carbs, you have to turn them in to lean the mixture. These mixture screws control the fuel flow, not the air flow as on some carbs.



I would try a half turn, then as Shep says, check your plugs again and adjust. You can also adjust for highest RPM at idle, but you really need a more sensitive tach than the bike's to do that.


All good tips guys...thanks, and you are correct in the direction I need to turn them! thanks Blue Fox!
 

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Discussion Starter · #19 ·
Adjust a bit and then take a plug spanner/wrench out on a ride with you.Stop after the engine is hot and check/adjust again.Check again when you get home.



I am lucky as I have a Colourtune device,



http://www.gunson.co.uk/item.aspx?cat=673&item=1853



They are too expensive IMHO for what they are but do work.


thanks Shep...maybe you could share your experience with the Colourtune? It seems like you bought one, may have tried it, and feel back on your experience? Maybe you were disappointed...if money wasn't an object...are they worth it?
 

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Discussion Starter · #20 ·
Rick, you mentioned "backing them out" to make the mixture leaner. On these carbs, you have to turn them in to lean the mixture. These mixture screws control the fuel flow, not the air flow as on some carbs.



I would try a half turn, then as Shep says, check your plugs again and adjust. You can also adjust for highest RPM at idle, but you really need a more sensitive tach than the bike's to do that.


I do have a digital 'Tinytach' that will get you plus or minus 10 rpm...when you said adjust for highest RPM at idle, would I use the large idle adjustment knob, or are you saying adjust the idle mixture screws for each carb?
 
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