Re-jetting

Hey everyone. I Removed the factory filter on my 83 seca turbo and installed a k&n filter, and put a k&n filter directly on the turbo itself. Is this a big enough change that i should re-jet or re-sync the carbs? Keep in mind that i am new to carborated vehicles. Is this a job i can do myself, or should i bring it to a mechanic? if i need a mechanic, Anyone got any suggestions in nothern minnesota?

 

I'm not too familiar with the turbo, but the K&N I installed in my 750 Seca leaned it out enough to require re-jetting. A lean mixture on a turbocharged engine is typically very unhealthy - the increased engine temp can combine with the the increased pressure and temp that is normal for a turbo, resulting in detonation (knock, ping, etc) - valve or piston damage follows soon after.
Listen to your bike when its running, check for abnormally high temp or symptoms of overheating, check your plugs using a plug chart, and definitely get a mixture check done if your still not sure - someone in your area may have a colortune plug, or you may be able to pick one up (e-bay?) for less than the cost of a shop visit. If your feeling bold, a 1/8th turn rich on the mixture screws may get you by 'til you can get a mixture check done. Lots of good info on jetting and tuning on this site, but beware: the process is not for the faint of heart or poorly equipped! Check Chacal's info (XJ4Ever), and if in doubt, you can always go back to the stock air filter. Good Luck!

 

Ok, thanks for the info.

Since i am new to the carborated life, i am to familiar with jetting. Are there people that can do this for me? any idea on pricing?

 

About the only people I would trust to re-jet and tune one of these bikes would be the owner/rider of one who has already done their own - bikes of this age are not really welcome at most bike shops and shop time can add up in a hurry for jetting and tuning. Your first step should be to try to locate someone from this site who is close to you and has a colortune plug so you can check your mixture, or to take your bike to a shop that specializes in older bikes with the specific instructions "Perform mixture check only!" If they say mixture adjustment is necessary, make them give you a firm price quote, and make sure it is written on the work order.

You've come to the right place - lots of guys here with tons of knowledge and who are eager to share it, now you just have to hook up with the right one. You may want to put your location in your signature line, or include in your request for help setting the mixture.

 

Thanks for the info. I live in bemidji minnesota, anyone live around these parts that could assist me in re-jetting my seca turbo?

 

Also, how do you know your bike is running lean?

 

Look at the spark plugs.

Do a forum search on "spark plug color."

If they're bone white on the insulators you're running dangerously lean.

They need to be like coffee with cream or even a brown paper bag.

Pull the plugs, take some pics of the business end and post.

 

Ok lets hope this picture go attatched to the message. I pulled the plugs and this is what they looked like. Am i running Lean? I took it for like a quick 5 mile ride, there was some backfiring going on? is that related to the plugs?

 

Looks rather lean to me.

Backfiring is often a symptom of a lean mixture. Were you getting these when letting off the throttle during shifting, or more under acceleration?

Going lean under load on a turbo could be pretty destructive.

 

i couldnt view your link....does it show up like this.....?

 

no, it does not. i cannot see the pic, but i trust those who say its lean.

if your bike is in total stock form, and has the original jetting in it, its already running lean with todays fuel (10% or more ethanol).

with the help of this forum, you can get it jetted properly, especially if the bike is running well now other than the occasional backfire and white plugs.

keep in mind that reading the plugs after idling wont tell you squat about the mid-top end jetting (same goes for the other way).

you will need to take the carbs apart and see what jets you have in there now. also, you need to see where the pilot screws are set to. record all this information before making changes, so you can go back if you run into trouble.

 

To see the picture you need to open a browser window and paste this URL in (Photobucket doesn't allow linking).

http://s1140.photobucket.com/albums/n56 ... ction=view¤t=2011-04-20122530.jpg

There are actually several circuits that affect mixture in the carbs. The pilot jets mainly affect idle and low RPM, the main jets mainly affect WOT and high RPM, and the needles and needle jets have the most effect in mid-band.

Depending on what's been done to the carbs before, you may have adjustable needles in the carbs. Adjustable needles have the needle held in by an e-clip that can sit in one of several grooves. Raising the needle (by using a lower slot for the clip) will enrich the mid-band mixture. Even if you don't have the multi-slot needles, you can raise the needles by installing a small washer under them as a spacer.

To get to the needles, you remove the carb "hat" and the spring underneath it. The needle sits in the middle of the slide and it should be possible to pull it straight up and out of the slide without removing the slide or the diaphragm. There may be a plastic spacer above and/or below it. If you need to remove the diaphragm, some silicone grease around its edge is a good idea to keep it in place and sealed when you put it back. Silicone grease is available in the plumbing department of your local hardware store.

Edit:

By the way, mid-band is adjustable by raising or lowering the needle (as described above), or by switching to a different needle/needle jet set.

Pilot jets are adjustable by screwing them in or out. They are located under a blank cover at the front of the carb body (unless someone's already removed the covers).

Main jets are "adjustable" by drilling them out, or they can be replaced. They are not expensive, nor hard to find, but there are a couple of different numbering systems, so it's not always easy to tell which ones you have or which ones you need. To get to them you need to remove the float bowls.

Contrary to what you may read elsewhere on this forum, pilot jets by themselves cannot handle all the adjustment of mixture that's needed for proper delivery of fuel across all engine load situations.

 

To view the picture, right click on the link and copy it (copy shortcut, copy link address or something similar, depends on your browser). Then paste it into your address bar and remove the /

 

Ok, well via filter restriction i got my bike running at decent mixture. However i would still like to rejet here soon. I have mikuni carbs, any idea where i can buy the parts? also how do i know which size to buy, or is a guessing game. And how do you know that you have the right mixture? Like ive said, i am new to carborators. Thanks

 

Jets and other parts as well as a basic set of rejetting guidelines can be found in the XJ4Ever Catalog; click the banner in the upper right of this page ot look in the "Supporting Vendor" forum.

 

Ok so according to chacal's guide lines, i think i figured out what size jets to buy. could you guys look through this and let me know if i picked the correct size. Where i am is 1343 feet above sea level

Main Jet

+4 main fuel jet sizes for individual pod filters (no airbox)

Old jet size1&4 #127.5

Old jet size2&3 #132.5

New jet size1&4 #129.5

New jet size2&3 #134.5

HCP6933 Aftermarket Mikuni MAIN FUEL JET #130

HCP6934 Aftermarket Mikuni MAIN FUEL JET #135



PILOT FUEL JET

Increase the pilot fuel jet size +1 for every +3 main fuel jet size increases.

Old #32.5

New jet size: stay the same?

MAIN FUEL JET SIZE CHANGES NEEDED PER TYPICAL MODIFICATION:

Typical Intake Changes:

+2 main fuel jet sizes for single K&N filter (inside a stock airbox)

or

+2 main fuel jet size for drilling holes in the airbox with stock filter

or

+4 main fuel jet sizes for individual pod filters (no airbox)

PILOT FUEL JET SIZES CHANGES NEEDED PER TYPICAL MODIFICATION:

Pilot fuel jet size changes are related only to the change in main fuel jet sizes according to the main fuel jet size formula described above. Note that this pilot fuel jet rule is for the main fuel jet size change BEFORE any main fuel jet altitude compensation is factored in:

Increase the pilot fuel jet size +1 for every +3 main fuel jet size increases.

- Decrease pilot fuel jet size by 1 for every 6000' above sea level.

Additional changes:

- Add up all the main fuel jet size increases and subtract 2 sizes.

- Decrease main fuel jet size by 2 sizes per every 2000' above sea level.

- Under a mis-match condition, such as when using pod filters with a 100% stock exhaust, or 4-into-1 header with stock filter and air box, then subtract 2 main fuel jet sizes.




Is there anything else i am missing? Thanks for everyones help. This will be my first re-jetting job. So i need all the help i can get

 

just to clarify: what i meant by

Old jet size1&4 #127.5, Old jet size2&3 #132.5

was Old jet size in cylindar 1&4 and Old jet size in cylindar 2&3