Question about 1991 Yamaha XJ 600

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I installed a jet kit and now the bike will idle wildly

I installed a jet kit and now the bike will idle, once I touch the throttle, the bike will rev up to about 3000 to 3500 rpms for about 8-10 seconds. If I put a load on the motor, the idle returns back to normal. The problem seems to worsen and the bike get hotter...
The bike runs fine other than it is a little on the weak side until ou hit about 2500 rpms then it really smooths out...

Thanks for any suggestions...

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You have an air leak(s) between the carb an the cylinder. The rubber seals and fiber gaskets are 19 years old and have become hard. Disturbing the carb has caused the old hard rubber to crack and let extra air into the mix. Fix the air leaks and the problem goes away. I have seen some guys smear silicon seal on the inside & outside of rubber manifolds. Often, 15 seconds or so in the microwave will make the rubber instantly soft again but only for 10 minutes or so. Just long enough to re-mount and clamp down. Obviously, new parts would fix the problem You can try Babbit's. Generally, if you can find a part anywhere, Babbit's is where it will be.

Go to the site below where you can see a parts diagram for your specific bike. You will select the actual brand, year, model, etc., once you go to the site. Part numbers and prices are also shown. You can order parts from this site. In the event no price is shown on a particular part, the part is not in stock. www.babbittsonline.com/pages/parts/viewbybrandand/parts.aspx

Go to this site and you can download a free PDF service manual.
www.carlsalter.com/motorcycle-manuals.asp Most all of the manuals are in English but some are not. There is no way to be sure without doing the download. You can always delete it if in a foreign language.

I installed a jet kit and now the bike will idle w - 02af4b9.gif

Can I get a Very Helpful rating for this answer? Thanks!

Posted on Jun 27, 2009

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Through experience over the years I've found that the Super B used on a Big Twin Harley should be jetted 29.5 on the slow jet with a 70 or 72 on the main jet. If used on an Ironhead Sportster, slow jet of 26 with either a 66 or 68 main jet.

The way to tune the carb slow speed circuit is to allow the engine to warm up and adjust the idle mixture screw one turn off the bottom. Then try to rev the engine. If the engine does not rev cleanly, try coming out a half turn on the idle mixture. If it seems to help, continue until it revs cleanly. If this is the case, you slow jetting is too lean, install a richer jet and repeat the above procedure. Once you get it tuned to where the engine revs cleanly with the idle mixture screw at one turn out, you low speed jetting is correct.

The high speed jetting is not quite as simple to set as this has to be done on the road. I usually find a long uphill run to test the jetting to keep top speeds reasonable. At about 55-60 miles per hour, roll the throttle on in high gear. Feel the way the engine pulls. If it pulls good, back off on the throttle about 1/8th turn. If it pulls better, it's just slightly lean. If when you roll the throttle on, the engine starts spitting back through the carb and doesn't run well, you are way lean. Either way move upwards on your jet size one step at the time and retest.

If the bike seems sluggish and blows black smoke when you do the "roll-on", you're too rich. Install leaner jet one step at a time.

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