Jetting Question

[trbig]

I was wondering if anyone out there could tell me who has the best prices for the main jets on the carbs. I want to try a couple sizes bigger. I seem to be running a bit lean. I am running the stock 112.5, (XJ) and want to try maybe the 117.5's. I am running an XJ head with the bigger valves on an XS motor, using the '78 XS cams. My pipes are getting blue, and after a decent ride (Maybe 50 miles) it is hard to start due to slow cranking initially while hot. You guys think 2 sizes is enough? Also poppping alot on deceleration.


Tod

PS. Someone asked me if I am getting better performance from this head setup versus stock, but I had no way to know. Last week, I got to ride a friend's XS Special, and mine does feel considerably stronger than his, but his bike does have many more miles on it than mine... so.. again, who knows.

[edgo]

www.mikesxs.com has jets at good prices. If you order more than $35.00 he ships free and it's fast.

Ed

[xj11john]

You might just want to check at a local yamma dealer or shop, take out time for shipping and there is no min. order.

I believe I've read they're only a couple of bucks apeice.

worth a look.

good luck.

[chevy45412001]

jets

i payed like 3.79 a pieace for them at local yammy dealer. wasn't worth searching all over for them. my XJ headed XJ / 4 pods and 4-1 header is running 137.5 mains that is just a bit to much though plugs look black i'm going down to a 132-135. but i have run my best 1/4 mile time with 137.5 might get a hair quicker. ( i hope bandit...lol)

[Firehawk]

Jetting Recommendations

Maybe that can help you out.

That's what I used. I'll find out early-mid next week as to how correct it is for a 1981 XS1100 at whatever elevation south-central Kansas is at.

According to that chart, for my bike:
1981 XS1100H
Stock main jets: 140

Stock pilot jets: 42.5

2 sizes for 4:1 exhaust (Mac)

3 sizes individual (pod) filters

2 sizes for no muffler

7 (main sizes) - 1 = 6; 140.0 + (2.5 * 6) = 155.0
2 (pilot jet size); 42.5 + (2.5 * 2) = 47.5

That's what I bought yesterday, and I just have to get through my midterms, and then head home to try it out.

[trbig]

Yeah, I'd read the jetting info beofre I asked, but none of them really apply to me. How many sizes do you go on the main jets before you start messing with the pilot jets? I recently changed those too, but back to stock. I had one messed up, and the new ones had more holes in them than my originals did, so I changed all 4. I was thinking this may be allowing a leaner mix also.

Tod

[trbig]

Ugh... never mind. I just read at the bottom of that jetting info about the 3 sizes to one on the pilot. Look before I leap... Sorry.
Sitting here, and the thought of jerking those carbs out again with the stock airbox.... sigh. I think I may just order the individual filters. By this, I am looking at maybe 5 sizes up on my main jets. My airbox doesn't move much, so I still have to manhandle the carbs and rubbers SEVERELY to get them back in. My only concern with the individual filters... and I talked with TC a bit on this... is the thought of those carbs just hanging there. It would seem like bouncing and bumps would really slosh the fuel and things around in the carbs. This is off the subject, but has anyone fabricated some sort of support for the rear of the carbs to take the place of the airbox's support? I have been off-roading in carb'd vehicles alot, and that fuel sloshing around will kill the motor sometimes. I realize I am not offroading with my bike...but just emphasizing a point. Anybody who has ridden on some of Oklahomas roads may understand!

Tod

[TopCatGr58]

Whoa there Firehawk!!

Hey Firehawk,

I just reread your post, and I think you have made a big mistake in your sizing!! You state your main jets are 140? I'm afraid you found the MAIN AIR JET size which is 140.

The Main Fuel Jet size for the 81H is 115 to 120 depending on whether outer 2 or inner 2 carbs, according to the manual! So.....
taking the richest 120, with 6 sizes equal to 15, total size should only be 135, not a 155. Those newer generation carbs don't share the supply with the pilot jets, so that's why they are much smaller than the 78-79 series 137.5 OEM main fuel jet size!

Sorry I didn't see this sooner, hope you can send them back for an exchange?
T.C.

[xj11john]

Trbig,

I have had indiv. pod filters on my xj1100 since i got it, never had a problem with gas sloshing or the stability of the carbs, the boots support them fine. Oh and the roads in Tennessee can be just as bad I'm sure

Just my .02, I very much like them, esp. when i pull the carbs

[motoman]

Hey ther Firehawk.......If you have blue pipes.your way to rich, specially in that short of a ride. If you have anything but Mikuni jets in the carbs, get rid of them. I'm at 5000ft. elev. and on my 81, running 24mm float levels(could drop em' a mm or to from that here) and 110 mains all across, pilots stock size(think is 42,5) and pipes stay shiny from head down(just don't use chrome polish on 'em, will cause them to yellow, thinkin you have a lean cond.) Run stock reccomendations for all jetting, sea level float setting, and Blu-Away on pipes and start over.

[xj11john]

motoman,

Anyone correct me if I'm wrong, but I believe blue pipes are caused by too lean a mixture.

[motoman]

Hey there John..............Blue/rich...........gold,yellow/Lean.......or forgot to not use chrome polish.

[trbig]

Well, I guess I was wrong too. I always thought that blue pipes meant that I was too LEAN (Running too hot bacause it was lean). I ordered my main jets according to this. My pipes are blue, bike acts hot after a decent ride of 50+ miles, and it pops alot on deceleration. BUT.... my plugs look perfect!?? Clean on the center and ceramic, but I light layer of carbon on the plug bottom/ seat.
Anyone else?? What color does a lean/ rich condition cause? I need to know if I ordered wrong. If I am too rich, I may try to stay stock and just put on the pods and see what happens. Looks like I may need to get a colortune.... Sigh.

Tod

[LoserShoes]

Rich means that there is not enough oxygen to completly burn the fuel, so you get uncombusted fuel out the exhaust valve.

Proper ratio most of the combustion takes place in the combustion chamber and only spent gases out the exhaust valve.

Lean means more oxygen then fuel so combustion happens more slowly, still burning as it exits through the exhaust valve. That is what burns valves and discolors chrome.

White plug insulator is lean. Shoot for light tan to be safe.

The soot on the bottom of the plug is from the rich mixture required to start the engine. That part of the plug never (hopefully) gets hot enough to burn off the soot.

The color gradiant for temperature for chrome starts at yellow and goes to blue, indicating the hottest temp.

Steve

[xj11john]

Oringinally posted by LoserShoes

Lean means more oxygen then fuel so combustion happens more slowly, still burning as it exits through the exhaust valve. That is what burns valves and discolors chrome.

Thanks Losershoes that is just what I thought, and I believe more O2= hotter flame from what I learned in welding class.