CARBS: Needle and Needle Jet

[srsupertrap]

Here is another Self Service article written by Joe Minton that addresses the subject of the carb jetting and the role of the carburetor Needle & Needle jet.

The article has some advice for GS1100 owners with 4-into-1 exhaust systems as well.

PS: I do not have Part 1

http://www.mediafire.com/?5bmfmxmngyf

 

[Steve]

I find it interesting that he starts his carb tuning with the idle circuit, then progresses to the needle, then the main. :shock:

Other articles I have read on carb tuning always started with the main jet and worked toward the idle mixture. The theory there is that, since all the gas goes through the main jet in the first place, if you tune the idle and needle mixtures, then install a larger main jet, the idle and needle circuits will be getting more gas, too, so you will have to re-tune them. :?


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[KEITH KRAUSE]

I've much more often than not adjusted the jet needle first after making what I feel are close initial adjustments for the pilot circuit.
Almost everything I've read says to do the main first but I've learned it just doesn't work many times or there's more trial and error involved. In most recent years I usually just go straight to the needle and then go with the largest main I can that doesn't create any bogging during a top gear full throttle roll on from approx' 60 mph. If I have to choose between a perfectly operating jet needle circuit or lose a couple mph at absolute top end, I always choose getting the needle perfect.
Works for me.

 

[Matchless]

Yes, I am amazed at the wealth of excellent information cropping up. I have closely followed all Keiths posts on carburation before taking mine apart and now when reading these 'older' articles, posted by srsupertrap, from the early 80's the picture is becoming very much clearer to me. I am only a hobbyist, but like to know and understand what I am doing before actually attempting it and have learnt over the years that the more you know, the more you realize there is still to know and and maybe more so vice versa.
I also now see how Keith's vast practical experience comes into play and he can go straight to the problem knowing that skipping a specified step will not have much direct or noticeable impact in a specific circumstance. I would think that a perfect stock bike being tuned compared to fitting a set of carbs from a breaker that may have been tuned for another type of bike or messed around by a PO would not be a problem for people like Keith, but moving away from stock can become a night mare for most of us weekend mechanics.
The theory in these articles are very informative if one is contemplating moving from stock or have been unfortunate (fortunate?) in acquiring a non-stock and poorly performing machine. I have never fully understood the airbox issue and the reason for moving to "pods" and the subsequent resulting carburettor problems and if the benefits are actually worth the problems that can or will be created, but have a better insight now, than I had before. Its like changing from big stock flashers to tiny after market flashers that a motor vehicle cannot easily see, which immediately pushes up the risk factor sky high, which is then not considered, but increases the social standing factor in the owners opinion, I think..., but I also think I should better stay away from this!
Anyway what I was trying to say is thanks to Keith and people like srsuperstrap and all the others who are prepared to share this very useful information with all of us. This forum is already a goldmine and will continue growing.
Thanks everyone.

 

[KEITH KRAUSE]

Thanks. We all try to help here.
Rejetting can be difficult. Some mods are a poor match and it won't matter what you do, you'll have issues.
One of the most common "carb" problems has nothing to do with the carbs. It's assuming the bike is in good mechanical condition and in otherwise good tune. People just want to go straight to the re-jet but if you skip all the other basics, like compression, valve clearance, cam timing/ignition timing/spark quality, clean carbs, leak free intake, etc, you may blame the jetting and set yourself up for frustration.
It's difficult to have patience or maybe even the time/money to do things right but shortcuts often waste more time and money than if you just did the basic checks/adjustments and do it right. If you find something wrong, fix it, don't try to compensate for it.
If you really pay attention, just read some of the horror stories here that suggest taking shortcuts and you'll see how much time is lost ending up with a poorly running bike and the owner blaming the pods, etc, ready to sell it.

 

[Guest]

One of the most common "carb" problems has nothing to do with the carbs. It's assuming the bike is in good mechanical condition and in otherwise good tune. People just want to go straight to the re-jet but if you skip all the other basics, like compression, valve clearance, cam timing/ignition timing/spark quality, clean carbs, leak free intake, etc, you may blame the jetting and set yourself up for frustration.
It's difficult to have patience or maybe even the time/money to do things right but shortcuts often waste more time and money than if you just did the basic checks/adjustments and do it right. If you find something wrong, fix it, don't try to compensate for it.
If you really pay attention, just read some of the horror stories here that suggest taking shortcuts and you'll see how much time is lost ending up with a poorly running bike and the owner blaming the pods, etc, ready to sell it.

Never better advice.