question about carb slide springs

[Dan Hodges]

Slide Springs & Jets

Thanks for the input Dan.

After getting a chance to put 100 miles on the scoot last week, the spring lengthening did help, but not as I had hoped.

Before, the bike used to fall on its face when I would get under 3k rpm. It had nothing. Then I put some bigger pilot jets in and retuned. It was mildly better, and wouldn't die if I got out of the clutch early, but it wouldn't pull either. Now with the springs lengthened, it pulls. Still, when I hit 3k, it feels like afterburners kick in.

From what you are saying about the Dynojet kits, I probably need to get one.

When my bike was stock prior to 06 it had no glitches however with a header and I have three different brands on hand that I have used off and on since I bought the bike new, it always seemed cold natured and had a slight glitch under 3,000 rpm. Stock, it came with a #185 pilot air jet and I changed that to a #180 pilot air jet leaving the #142.5 pilot jet alone. With this and the mixture screws turned out 4 turns it worked fine in stock form with the header. It was only after I modified the motor that the glitch problem arose. I bought a new set of springs from Yamaha and when I compared them to the original ones I found that the original ones had sagged slightly. I put the new stock ones in and it made no difference. I stretched the original ones 1 inch and put them back in and it helped some but didn't solve the problem. I then got a new set of V-Max springs from Yamaha. When I took the ones I had stretched back out I discovered that they had collasped back down to maybe only one inch longer than stock. I put the Max springs in and they cured the problem glitch wise but on the dyno it was lean from about 3500 rpm to 5,000 rpm indicating the springs were too stiff and not allowing the slides to open quick enough. After that combo I put the DJ kit in using their recommended jet combo with their needles installed with the clip in the second grove from the top. In my particular case I believe it was the shape/length & taper of the needles that did the trick. Mention is made that during all of these trials and tribulations I installed a NOS vacum advance diaphragm that I had been saving for 20 years just to make sure I eliminated the possibility of the original one being bad, but that neither hurt or helped it. The function of the vacum diaphragm is another story and it's covered in the Yamaha shop manual. Mention is also made that I'm using the stock air box with 4 one inch holes drilled in the filter base plate with a K&N replacement filter. My timing is set at 40 degrees @ 4,000 rpm with the vacum advance plugged for the test and it doesn't increase anymore after that. I have a 79 ignition timing plate installed that allows me to check my ignition timing with a timing light from idle to WOT. A box stock 81 Special with the mixture screws turned out 4 turns from lightly seated will work fine but will be slightly cold natured. If you replace the #185 stock air pilot jet with a #180 air pilot jet (Mikuni jet numbers) everything will be kosher if everything else is factory spec. Somebody ask if I had made sure the springs were the problem before I used the DJ needles and yes I did and I have litteraly a shoe box full of every kind of spring I could get from Yamaha to prove it. Another carb problem that I have found from messing with other peoples Eleven is that the rubber in the carb diaphragms have become stiff and no longer supple and doesn't allow the diaphragms to move freely like they did when new. Generally speaking, all old Elevens need new diaphragms and the after market diaphragms are inferior to the OEM type. The emulsion tubes (needle jets) and jet needles themselves also can show signs of wear and these must be replaced if they are worn. All of this stuff not withstanding, a box stock 80-81 Eleven will like a stage I Dyno-Jet kit and if it has a good header and K&N pod filters the DJ kit is practicullay mandatory because you will never get it right with the stock needles. I have had a similiar carburetor experience with the family's big cubic inch modified FJ-1200. I prefer stock parts where applicable and I'm not pushing the DJ stuff but it worked for me. Just remember, if you are using DJ or any other aftermarket jets, the jet numbers do not correspond with Mikuni JET NUMBERS.