Effect of leaning out jet needles?

[BigRed]

Hey, folks.

My bike is running way rich. With help from another member (thanks, Rob) I got a colourtune done to try to get my idle mixture right. After seeing the carbon continue to build on the plugs, I tried leaning the screws some more, and notice that they were only out about 1/2 turn to start with. Do I need to re-jet, or can I just try leaning my jet needles? The bike's an '80SG, and the engine's from an '82XJ. I'm not sure what the carbs are from, but I know the jet needles have five slots to choose from, so I think that means I've got a dynojet kit.

Will leaning the jet needles adjust mixture in all RPM ranges? Should I try lowering the float height first (it's on-spec right now)? Or, should I just bite the bullet and buy some smaller jets.

I'm getting about 140km when the low fuel light comes on.

Thanks,
Brian

[Olsen_XS]

I would try the float height in the chambers. Effects the whole trottle range. Had the same symptons on mine, adjusted more than 2 mm higher, with carburator upside down. Made all the difference, now it is a little on the lean side, and I will probably move back the level a mm or so.

[BigRed]

Thanks; I'll try that tonight.

[tinman905]

If you tell us a bit more about your bike ,stock or with what mods. What # jets do you have in the carbs now. It's difficult to help without more info. If you have a Dyo Jet kit your needle should be set at the second groove down from the top. Also check what air jets you have they should be #190 if it's a Dyno Kit.

[BigRed]

Just got it back together, and about to go for a test ride. I lowered the floats 1.5mm and checked my jet sizes: 115 main, 47.5 idle, and 170 air. The bike's got Mike's XS pod filters, and a 4-1 Kerker exhaust. I didn't check the jet needles this time, but IIRC, they've got five grooves, and they were set from on the middle one.

Thanks!

[natemoen]

Stock main is 137.5 and if I understand correctly (which I totally might be wrong) wouldn't you need to go to a higher number for pods?

[79XS11F]

Hey Brian, Standard needle jets have 5 clip positions with the middle one being the stock position. The DYNO kits also have 5 positions. Stock needles are an alloy color. DYNO needles are brass. On my 78 engine back in 79 The main jet was up sized from the stock 137.5 to 140 and the clip on the needle lowered one position for use with a 4 into 1 Kerker. with not much of a baffle in it. The engine ran very well with that set up. Floats were left stock.
If your engine is still running rich increasing fuel jet sizes will not cure that issue.
I just put the air box back on my modified bike with the above jetting and color tuned her. She is also rich in the middle range where the needle comes into play. I will be returning the needles to the stock position and checking it again tomorrow.
I went back to the air box because everything I have read about CV carbs says the BOX must be there if you want a decent tunable mid range. Since putting the box (drilled) back into play the engine is running MUCH better. When i did not have the box on and the PODs off I could see the slides popping up and down with no consistency at all. Very hit and miss. I am pretty much convinced that if one really wants POD air filters and a good running engine, different carbs are required.
Rob

[motoman]

Agree with 79XS using pods. With the jetting stated, guessing you have the later carbs.

[petejw]

hi bigred,
just re read your post,
you need to identify what carbs you have,
if there off an 80 model or the xj model,
they have different pilot jets,

if there the 80 model, the pilots should be 42.5 not
the 47.5 which would make you way rich, the the air pilot
jet should be 185 not 170, that would also make it richer,
leave the float levels and change the air and fuel pilot jets.

with regards to pods if you have the early model carbs with the upper 'T' vents, then the air box is best, if you have the later model carbs where
the vent is situated at the back of the carb bell then pod filters are fine.

[T99Ford]

Guessing he has later model carbs, as his main jet is a 115. The later carbs can have a pretty good midrange with pods, although you do have to tune it right.

[petejw]

just checked the carb specs on the xj,
which appears to be what you have,

if youve leaned the carb floats out 1.5mm the bike
wont run well at all, try putting the floats back to stock
or slightly on the rich side.

[BigRed]

another 3mm?

So, know that I know I have XJ carbs, I checked the XJ service manual for float height specs. They don't specify a float height measurement like the XS manual, but rather a wet-check fuel level in the bowls. Turns out I'm still 3mm too high, as the fuel is right up to the bottom of the flange. No wonder it stalls when I stop!

I'm going to double check that pilot jet... 2s and 7s can look alike, so maybe I do have a 47.5.

Thanks a lot for the help guys!

[petejw]

the float height is the same for the later
model xs carbs, they can b set at 23mm.

[BigRed]

Well, I finally got around to checking the spark plugs after lowering my floats. I must have non-stock floats or something. After my wet-check, I saw that the fuel level in the bowls was 3mm too high. I lowered it 2mm to leave it a little rich to support the 4-1 Kerker and pods. That leaves it just within spec, as the manual says 3mm +/- 1mm (distance between bottom of bowl flange and fuel level. The float height measured with the bowls off is about 26.3mm. It runs great, and the plugs look way better (clean/tan) now. The RPMs still drop when I stop really hard, but it's not as bad as it was. I may try dropping the float height another mm, but I suspect that'll lean me out too much, and I'll need to re-jet.

I'm looking forward to seeing if I can get more than 140km before the fuel light comes on!

[79XS11F]

Check the spring action on the needle valves.
Rob