Difference in Carbs between 79 and 80?

[TheNewGuy]

I have a 79 XS1100 Special and I would like to buy a DynoJet Stage 1 kit for it. I noticed that the kit on the DynoJet site is for 1980-83 XJ and XS 1100 models. It is possible to put this kit in a 79 XS? If so, has anyone installed it and is there any noticible power gain?


The Kit can be found at: http://www.dynojet.com/pdf/4101.pdf

The Referring page is: http://www.dynojet.com/jetkits/yamahajets.shtml

[TopCatGr58]

The 78-79 carbs are considerably different in how they use the main jets and idle circuit. They get their fuel metered via a channel, but draws from the main jets, that's why they are so much larger (137) than the 80-83 series which have seperate Pilot jets and Mains (110-120) usually!!

Others have used the Dyno-Jet kits, will let them chime in with their experiences!
T.C.

[dragxs11]

I used the stage 1 dynajet kit and noticed better bottom end right away. My bike is an 80 sg, and I put the recommended 124's in from the kit. However, I think I'm to rich on the top end. It charges out of a stoplight like a racehorse, but my dads almost stock 80G has better top end. It's taken me awhile to believe this, but after working on jetting another bike, I have learned more about the symptoms. Also, when I drop from 5000ft. down to 1500ft. She gets lethally fast, suggesting that I'm rich up here in Reno. My 2 cents.

[TheNewGuy]

Hmm...

Well then, does anyone have any suggestions for getting a little more power out of my 79 XS11? I plan on putting on a 4 into 1 exhaust. Right now it has aftermarket exhaust with a set of 2 into 1 Jardines. (The PO put those on). I don't think he re-jetted the carbs though, and the bike is still running a stock airbox. I don't mind the stock airbox I would like to re-jet for the exhaust with a stage 1, maybe later a stage 3 and put on some velocity stacks. But right now I'm having trouble finding the proper kit for this bike...

[TopCatGr58]

Hey there NewGuy,

You haven't told us much about your 79 machine. The Jardines 4-2 are going to flow about as good as a 4-1! Both are less restrictive than the OEM pipes and mufflers!

How many miles on this engine? Have you done a compression check, are they low with slight improvement after a squirt of oil= worn rings?!?! Stock is ~142+ 14PSI cold at sea level.

What are you expecting with this increased HP, pulling the front wheel up with a flick of the throttle??

Have you read the Notes regarding the Stage1 and Stage3 kits? Stage 3 looks like what you would want IF you are going to change your intake/filters!

Intended for motorcycles with stock or mildly tuned engines using a well designed aftermarket pipe and individual air filters. In most cases power increases of 10-15% can be achieved. However driveability may be compromised particularly with short stroke, high rpm motors.

Another option would be to get a bank of 80-81 carbs and swap with your 78, no problem doing that, a couple less vent hoses even!

Some folks sing the praises of Port and Polishing the head!?

You might also try new coils/wires/plug caps?

Have you gone thru all the tuneup steps, cam chain adjust, carb cleaning and synch, ensured no vacuum leaks!? Just some thoughts?
T.C.

[Meista007]

I would also like to kmow where to get stage 3 kit for my 79 special.

[TopCatGr58]

Hey there Meister,

At the beginning of the thread, it was noted that they make the Stage 1 and 3 kits ONLY for the 80-83 XS/XJ's, they don't offer them for the 78-79 carbs! You'll have to get a bank of 80-81 carbs to put the Jet Kit in!
T.C.

[pgg]

All 'performance' jet kits do is alter the airjet, fueljet, fuelneedle combination. Easily acheivable by swapping sizes and tinkering with the original components. You get the same results.

[pgg]

I would'nt read much into the sweeping '15% increase' statements either. That'll apply to the hordes of North American spec japanese bikes that were restricted and strangled to death with emission controls. Of course opening up the fuel and air jets will give a boost.

I heard a story from my local bikeshop ( they're well established, experienced, tied in with the race scene and generally clued up - unlike a lot of other bikeshops) They recently dynojet kitted an aussie spec CBR600. The bike consequently ran crappy and sluggish. They discovered the American dynajet kits' jets were more restrictive than the originals! They junked the kit, bunged back in the originals, and the power kicked straight back in.

An example of the advertising blurb not ringing true in all cases.

[Dennyz]

Here is some jetting guidelines I wrote up a while back and recently updated.

Jetting.html