Suggestions on jetting

[clcorbin]

Gents,

One of the items I have to address on my bike to get it back up and running is the jetting. It is a 79F XS11. Here are the current mods that I know of:

Kerker 4-1 exhaust
High lift cams (I do not know what brand or lift)
Air box screen removed
K&N air filter

Currently, it has 130 main jets and the needle is all the way down (clip in TOP groove). And it is still running VERY rich. The plugs are BLACK. With a little bit of a crust of carbon on them. The exhaust is coated with a thin layer of carbon and is also absolutely black from the header flanges to the exhaust outlet. Fuel economy was only around 30-32 mpg. The bike does not have any issues starting, cold or hot. One bit that does play in this is that I am at fairly high altitude (about 5200 feet ASL) which does cause carbureted engines to run rich.

So, I have a couple of questions:
1) Does it make sense to anyone that I would be rich at this altitude with these mods?
2) What would be a good jet size to try on the main jet to get this thing closer to right? I can't waste too much money buying jets that are the wrong size.
3) Any ideas on things that could be causing it to run so rich?

Needless to say, any help would be appreciated!

[DiverRay]

Start with the float level. Set it a little higher than stock, (26.5mm) and then put the needles back too the center position. At 5K alt, the 130 should be close. These bikes seem to run best with the needles in the center position, no matter what the mod. You MAY want to check the needle and seat in the float valve as well.
DO make sure the vent tubes from between carbs 1/2 and 3/4 are open (the top lines on the carbs), and go to the two plastic fittings on the top of the air box. I don't understand what you are talking about with the airbox screen. The only screen I've ever seen in these is around the filter element.

[xs11widowmaker]

jets

My bike ran rich and very sooty for 2 years. I was told on here that the pilot jets should be the BS jets and not the VM jets. Whwn I changed over to the BS jets my problems were solved. If you go to Mikes XS sight you will see the differance. I hope this helps cause It worked great on mine.

[fredintoon]

Little rubber bungs

Hi Clint,
OK, mine's an '80 that feeds the slow running jet separately and does NOT need the little rubber bungs that block off the slow running jet passage.
BUT earlier model carbs feed the slow running jet from a side-drilled passage from the main jet chamber so that the slow running jet feeds off the main jet.
These carbs MUST have those little rubber bungs plugging off the slow running jet holes or they'll run really rich.
Sorry, dunno the exact year they switched over but it's a thing to check.

[clcorbin]

What rubber bung are you referring to? Where is it, inside or outside the carb?

[cywelchjr]

I understand it can be a screw on some, but it's inside the carb covering the idle jets. As I understand it, the change occurred DURING the 80 model year, so early 80's have the plug and later ones don't. Anything earlier than 80 should have the plug in there, either a rubber plug or a screw depending on what was there in the first place.

From my understanding of physics, without the plug not only would the idle be rich, but all through the range as the hole would allow extra fuel past the main jets as well. At least that was the case on my 400 which has the same carbs (in the earlier version with the plug) when the plug was missing. You can order the plug if you need it from MikesXS, all the XS models that use the plug use the same plug.

[bikerphil]

One of the items I have to address on my bike to get it back up and running is the jetting. It is a 79F XS11.

Which carbs are you running, early or late? 130 mains are way too small for the 79F carbs. I had a case once where the PO was running tiny mains and super huge pilots and these carbs were running way too rich that way. Check your pilot jet size. I 100% agree with needle in the center position. The early carbs have the idle mixture screw exposed, the late have them down in a tunnel. HTH

[fredintoon]

This thing

What rubber bung are you referring to? Where is it, inside or outside the carb?

Hi Clint,
it's the rubber plug shown as part of this #48-1408 kit from MikesXS:-
http://www.mikesxs.net/products-36.html#products
It seals off the access hole where the slow running jet is installed.
Carbs that should have 130 main jets need this plug to work right.

[clcorbin]

Ok. I'm on board now. My carbs have the pilot jet set about 1" down inside a tunnel next to the main jet. There is a screw and washer that seals this tunnel off from the float bowl of the carb.

So from what I am hearing, my rich running is probably caused to too large pilot jets and NOT a problem with the main jet. Correct? I did not look at the pilot jet number, so I can't say if it is stock or not. Per the factory drawing, it should be a 42.5 stock. If I drop it down, what would be the suggested size?

Thanks for the info!

[dragxs11]

Fred is talking about the pilot jet block off inside on the bottom of the carbs. If there is a passage between the main jet and pilot jet chambers you need the rubber block off plugs. See carb diagrams on Bikebandit.com for different years, or Yamaha parts website. If you bought rebuild kits and used the pilot jets from those kits, it's likely they are way to big. You can visually see the difference between stock and kit jets if you hold them side by side up to the light and look at the holes.

[dragxs11]

About 16! Since my local dealer only carries 15, I drill them out with a #78 bit(very small)
Bare in mind... I work on 80's, but I don't think the pilot size changed much through the years.

[bikerphil]

Ok, you're running the late model carbs. 120 main and 42.5 pilot should be good for your application. Rubber plugs over the pilot jet towers should be used. 130 mains are 4 sizes too large. Yer gonna have to experiment with your float height. 23mm is a good starting point. You can buy jets for a good price at Mikesxs.com.

[dragxs11]

I disagree Phil...
Is the idle speed adjust on the top rear, or bottom front of the carbs. Are there breather T's between 1&2 carbs and again between 3&4? If so, you've got early models.

[bikerphil]

Ok, I misread his post. I thought he said pilot screws down in a tunnel. Looks like he has the early carbs.

Corbin, I wouldn't go any smaller than 42.5 on the pilots. A 142.5 main would be good and start with a float height of 25mm. Gotta make sure you have the right type (BS30/96) of pilots tho.

[clcorbin]

A 142.5? It is running rich right now with a 130. I though the larger the number, the more fuel flows... Wouldn't a 142.5 just make the rich condition worse?