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Message started by mpescatori on 02/15/13 at 08:07:27

Title: Oddball jets and carb tuning
Post by mpescatori on 02/15/13 at 08:07:27

Hello all, I'm close to bolting everything back in place on my Savage and rolling her out for my "Groundhg Day" parade.
(Is it Groundhog Day yet?)

There's one thing though that really has me stumped.

I have a nice nifty lil' Blue Box of Jets as Lancer once sent me.

I looked at the jets in my carb, they are a #130 Main and a #50 Pilot.
#130 Main, given I've stripped out the airbox and replaced the filter with a 5" dia x 2" thick K&N, will probably be upgraded to a #150.
(I have all sizes from #147.5 to #157.5)

My issue is the Pilot Jet.

The Pilot jet currently in the carb (Mikuni BS) is "thin nozzle, no pinholes on the side". I'll call it #50a for further reference.

In my "Lil'Box of Jets" I have two other pilot jets, which are completely different.
- one has a thin nozzle, and SIX pinholes on the side; I'll call it #50b.
- one has a large nozzle and EIGHT pinholes on the side; i'll call this one #50c.

So, if they're all #50 Pilot Jets, why thin/large nozzles and 0, 6, 8 pinholes on the side?
Fuel flow obviously increases going from #50a - #50b - #50c.

I also have two #55 Pilot Jets in the same "b" and "c" configurations.
I am VERY puzzled, and so is my mechanic (Europe is EFI territory since the early Y2K, so carbs and jets are getting rarer and rarer)

I also have one spare needle in my blue box of jets; it is a wee bit longer and thinner than the one currently fitted to the carb,
BUT it hase 5 notches, whereas the OEM needle is smooth and has a circlip just under the white spacer.
(Yes, I have replaced the white spacer with the two brass washers provided)
So, if I wanted to replace the OEM needle with the new "notched" needle, where should I start measuring to fit the circlip?
From the top (where the white spacer was) or from the bottom (where the needle enters the main jet)?
This is important because needle height changes according to where I start measuring.

I hope anyone of you can give me a little coaching over the weekend, I plan to go back to the workshop next monday/tuesday and fix the carb :)

Title: Re: Oddball jets and carb tuning
Post by Serowbot on 02/15/13 at 08:50:02

I... don't... know.... :-?...

... but,... I'd recommend trying the #150 main,.. and leaving the stock pilot, and keeping the reduced spacer you already have...
(you're in slightly unknown territory here)...

I don't know the specifics of European model carbs,... but, I have a chart somewhere, of 80's model vs 95' and later model vs California models,... and they are not simply jetted different.... there are also changes in the slide needle and seat, and air needles... so it's not as simple as it looks... (the different size air jets seem to be used to actuate the slide needle at different points... likely to accommodate the small main jet?...)
On the whole,... it seems that standard US models tend to be a bit lean on idle mix screw, and on the main jet,.. but somewhat rich on the pilot...
So,.. I'm saying that your pilot appears to be the same as a modern US bike, but, very lean on top end...
The #150 main might just take care of it...

Best luck... ;)...

Title: Re: Oddball jets and carb tuning
Post by Dave on 02/15/13 at 09:04:34

Ground Hog day was a couple of weeks ago.....not sure what the little Whistle Pig forecast was.

The #50 Pilot Jets will all work the same in the Savage carb. On some carbs air is mixed with the fuel through those little holes on the side of the jet, and the jet functions as an emulsion tube. This does not happen on the Savage carb, and the only metering that occurs is through tthe little hole at the bottom.

The needle is called the "Jet Needle", and the little brass orifice that it slides up and down in (and the Main Jet is screwed into the bottom of) is called the "Needle Jet". The needle jet you have with the clip positions will provide more fuel flow if it is thinner. As the slide raises the fuel flow is controlled by the size of the needle blocking the jet.....with less needle there is more hole available for fuel flow. If you want the needle to operate similar to the original one - you need to measure down from the single clip needle and find a diameter at a specific point - then find a similar diameter on the needle with the adjustable clips....then measure up from that point to find the clip position you will need to match the existing stock needle. Needles come in lots of sizes and the tapers can be different, and some are even double tapers......there is no way to know if a different needle will work well in the Savage. The way they are chosen or changed is to start with a known needle and do everything you can to get the pilot jet, main jet, and slide cutaway as close as you can with a specific jet needle and needle jet. Then if you find you need a bit more or less fuel at a specific throttle setting - you could choose a needle that is thinner or thicker or has a different taper to provide the change you want.
http://www.jetsrus.com/a_jets_by_carburetor_type/needle_mikuni.html

Title: Re: Oddball jets and carb tuning
Post by Serowbot on 02/15/13 at 09:46:19

Here's some general tuning tips that work for any carb'd car or bike...

If you can get the smoothest/ highest idle speed, by setting the idle mix screw between 1 and 3 turns out from closed,... you have set your idle mix, and your pilot jet is the right size... (if you have to go more than 3 turns out,.. go up one step on pilot jet)..(if it seems to make very little difference turning the screw, you are probably rich on the pilot, and can go down a step)...

To test the main, accelerate from 30 or 40 mph, in 4th or 5th gear at full throttle for several seconds, then reduce throttle by about 1/8,...if power increases for a second, you are lean on the main jet. Go up one jet size and test again.

If your main is good, and your pilot is good,... but you have surging at steady low speed... try pulling out the enrichment knob, one notch (do this with a fully warmed up engine)... if you get some acceleration, set your needle up a notch, or reduce the spacer...
... if it bogs instead of accelerating,.. you are either rich, or good... increase the spacer, or set the needle down a notch, until surging goes away, but you still get some bogging with the enrichment valve pulled out a notch...

There are other ways to test jetting, but this way is pretty simple and seems to get me close... for seat of pants tuning...
:-?...

(keep in mind,.. that changing the pilot, affects the needle and the main,.. and changing the needle setting, affects the main,...
Jets are additive... (the pilot doesn't stop when the needle starts, and when you are up to the main, the needle and pilot are still serving up fuel)... getting them all balanced takes some experimentation...

Title: Re: Oddball jets and carb tuning
Post by verslagen1 on 02/15/13 at 10:07:06

Not absolutely sure, but think your "130" jet is a Euro number. Versus our "145" due to differences of cc's versus ounces metering. or something like that.

Title: Re: Oddball jets and carb tuning
Post by Serowbot on 02/15/13 at 10:18:37

312235342B2620222976470 wrote:

Not absolutely sure, but think your "130" jet is a Euro number. Versus our "145" due to differences of cc's versus ounces metering. or something like that.

That's right... I remember reading that somewhere...
I forgot... :-?...

Title: Re: Oddball jets and carb tuning
Post by mpescatori on 02/16/13 at 07:55:33

Thanks all...

One thing I forgot to say, this carb was rebuilt and set up for me by Lancer way back in 2009...
And as the enrichment screw and other parts seemed to be messed up beyond repair (stripped threads, his own words), I actually bought a new carb from someone named Oscar (ODVELASC) and had it shipped to him. What I eventually got was a Mikuni carb which ran fine (albeit jetted for a K&N in the original airbox, and with the paper element idle was overrich) but some details were different, i.e. no thumbscrew to empty the bowl but an "L" shaped nozzle controlled by a miniature screw.

I tried getting to him but he must be TDY away or something, so I posted on RSD.

So... jets appear to be more or less OK, but the pilot jet issue really has me stumped.
Are you telling me that regardless the number of pinholes, those are ininfluential on a Mikuni BS? Only the main nozzle works?

OK...

Thank you !

BUT

Please keep them coming, you never kw when somebody might come up with a bright idea! ;)

:)