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11-05-2007, 10:11 AM Kevlar Joined on 11-05-2007 Visalia, Ca Posts 4 Too Lean? Hello, First off, thanks to William for all his clearly worded technical information AND his patience to put up with all us non-mechanical types. After having owned the 660 for 2 years now, I finally decided to look at improving the performance of this already capable machine. I started with the Hunterworks Tri-Fire CDI, exhaust end cap with no sparky, & K&N Drop in with outerwear. I also have the heavy 25" Big Horns with Bead locks. With just these mods I was able to reach 48 mph I next bought the Dynojet kit and under guidance from William, Prowrench, Tyrap, and others , I tackled the Rejet process. I followed DJ's instructions to a T, clip on 2nd groove, 155 main, a/f screw 2 turns out. I gained no improvement from the kit. I then learned DJ's 155 main = a Mikuni 145, so I went up to a DJ 165. I also turned the a/f screw out another 1/2 turn to 2-1/2 turns. Still no improvement. Next, I removed the airbox lid and BAMM! She got up to 50mph. (Btw, I think you should make a bumper sticker that reads GOT AIR?) So I fabbed up a counterfeit RAIS tube using An RV dump hoze (would like yours eventually) and I'm sitting pretty happy. All except now I'm wondering if all these mods are good for my engine. It seems to run hotter so I'm wondering if I'm too lean. My spark plug is a nice light brown. Is this normal or should it be almost white? Is there another way to check for a lean condition? Another question I have is about the a/f screw. Can you explain how it functions? I'm out 2 1/2 turns but I'm unclear of where it truly needs to be. Thanks and sorry for the long post 2nd Annual UTV Rally May 14-17, 2008 http://www.utvrally.com/forum/index.php    Report

11-05-2007, 1:22 PM wwlknsn Joined on 04-09-2006 Memphis, Tn Posts 154 Re: Too Lean? The modifications that you have done represent little risk for your engine even though the fun factor is increased substantially. A lean condition is indicated by lethargic performance. The most effective way to get your jetting correct short of having a dyno in your shop is to find the rich condition on each circuit and work it back a step or two for optimum performance. How do you do that? Start with your idle circuit, turn out your a/f mixture screw 3 full turns. Chances are that it will idle poorly. Turn it in until the idle smooths out just below a 'rich' setting. If best idle does not occur within 3 full turns from the seated position, then this would warrant a larger pilot jet. If your best idle occurs around 1.75 to 2 turns out, then leave the pilot jet alone. Assess pilot circuit which is simply the transition between idle and mid range circuits. See above. Chances are that you do not need to change out your pilot jet. If it doesn't stumble or cough off idle, then I would leave it alone. Move on to the mid range circuit. Put your clip 4 grooves down and run it. Likely to rich. Put it on the third groove. Still probably to rich. If so, the second groove will likel yield best acceleration. Move to the main circuit. Top speed performance should only be done with at least a 1/4 mile wfo run. Install the 175 Dynojet. Probably to rich. Go to the 170. Still probably to rich but getting better. You'll probably settle at the Dynojet 165 main but it takes your assessment to determine that. Remote tuning nearly impossible at best! A bleach white plug is an indicator of a lean condition. A tan plug for the most part is good to go. The a/f mixture screw is a tapered screw that simply fits in a passage way that provides fuel from the pilot jet to the idle circuit. The farther in the a/f mixture screw is turned in is leaner as less fuel gets past the taper. The farther out the screw is richer as more fuel gets past the taper. Given your modifications, your a/f mixture should be out about 1.5 to 2 turns. ww     Roostin' Rhino RAIS Power Tube    Report

11-05-2007, 2:00 PM Kevlar Joined on 11-05-2007 Visalia, Ca Posts 4 Re: Too Lean? Perfect, that sets my mind at ease. When you gauge the color of the plug are you looking at the porcelain or the tip of the electrode? I will to the a/f screw adjustment next and let you know. Here is a pic of my plug at current settings and mods. Copy and paste the link cuz for the life of me I cant figure this website out. http://i145.photobucket.com/albums/r237/kevlarzbucket/PB030006.jpg?t=1194297784 2nd Annual UTV Rally May 14-17, 2008 http://www.utvrally.com/forum/index.php    Report

11-05-2007, 7:54 PM wwlknsn Joined on 04-09-2006 Memphis, Tn Posts 154 Re: Too Lean? Reading a plug has value albiet a bit limited on a 4 stroke single. You can take a 2 smoke and jet accurately all day long by reading a plug. In reality, in order to accurately read a plug, you have to view the base of the porclein which is not the easiest thing to do short of cutting the threaded portion of the plug off. It's where 'chopping the plug' comes from. It should be a tan color at the base of the porclein lightening up slightly as you look out toward the electrode. The threaded portion of the plug will tend to look just like yours does. Basically charcoal in appearance.  The plug in the image looks fine and the only thing you can really say about it is that it looks about right. Beyond that, about the only thing you need to worry about is when it is going to foul a plug. It is, after all, a Yamaha and it is going to foul a plug on occasion. Put the plug back in and button it up. Then spend a bit of time following the steps that I provided. Find that richest point on a given circuit and work it back to a smooth run. Idle circuit first, pilot circuit, mid range circuit and finally the main circuit. Your jetting will be correct from bottom to top, no coughs, sputters or chokes and there will be little reason to look at the plug short of curiosity. ww  Roostin' Rhino RAIS Power Tube    Report

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