Sometimes, when the moon is full, my exhaust emits a strange tone. It only happens when I'm cruising along. All other performance is fine. High speeds at full throttle, fast acceleration and strong bottom end. But when I'm cruising, doing my thing for an hour or two on a long ride it can be a bit distracting. It sorta just skips or grumbles a bit almost like its rich. My response is to either gear down and make way more noise (fmf powercore 4) or accelerate which just ends up making me shift again. It's audible right in the sweet spot... you know the one, around 4500 rpm... :P


I am a carb thinkerer so it's been on and off a few times in my possession. I have been su****ious of the carb boots but spraying carb cleaner doesn't invoke a reaction from the engine so I am not rushing out to get new ones yet. The carb itself is clean, I've checked the jets and the float is fine. I have a YOST fuel mix screw, which probably has a different taper than stock. I doubt this would cause that much of a difference, but this is why I'm asking you people... Maybe I'm wrong

Any ideas are appreciated

Thanks

 

Reach down and open the choke (it is actually an enrichener circuit, not a true choke), that will richen the mix slightly. If it smooths out you have a lean spot. If not, you might be a tad rich. My bike would kind of miss, but not a true misfire, at cruising rpm over 6000. I found if I pulled the choke it would smooth out... lean. On my bike I had the stock carb with the needle shimmed about .030", but that was too lean even with the Dial-A-Jet. I got the KLX300 adjustable needle and solved the problem. The DAJ covers the fine mixture and altitude/temp changes.

 

If its a miss it might be the 09+ rectifier ground problem -

KLX World: KLX 250 Rectifier ground mod - possible fix for ~6500 RPM stumble

 

I did this just because, knowing it cleared up when the enrichener was opened, but it didn't take away the hesitation. So if the ground doesn't work, but the enrichener does, it's the jetting at the needle.

 

Exactly. I spent a week to two chasing fuel for the "surge" on my bike before I finally gave up on it and just accepted it as a quirk of the bike. Couple of months later the ground mod thread was opened and I had the problem resolved in 20 minutes. Others have reported that the ground mod did nothing but adjusting fuel delivery fixed the problem.

Luckily there are forums like this so we don't drive ourselves mad blindly chasing gremlins in the machine

 

Just to double check, I'm supposed to zap a wire right onto the brass connector thingy on the end of the black and yellow wire, and run that new wire to a ground on the engine... right? I will try this first as it seems like the easiest solution, but my cruising issue is not around 6500 rpm... it's when I'm doing 40km along the seaside in 3rd or 4th at 4500 rpm. (I have a loud muffler and tall gearing, I like to keep the revs down in the city)

as for a lean surge.. I'm running a 128 main, 38 pilot with the dyno jet needle clip at the 3rd spot.. This is the noticeably best set up for power and performance. My air/fuel mix is usually around 2 1/2 but I adjust it as I go depending on elevation and temp. When I knock it down to 124 main there is the same cruising issue. When I lean out the air fuel screw there is the same cruising issue. I have not tried putting the clip in the 2nd spot yet on the needle... I tried that with my '10 SF and didn't like the results

One more thing I'm curious of is my air filter. Its the stock sponge and I have some blue spray oil for it that is really waxy. I pilfered it from my buddies KTM tote and it said it was good for all air filters. Would there be a problem with using a "high end" air filter oil such as this? Perhaps at low rpms the suction is restricted from too much oil or something like taht? I had serious issues on my TW200 when the air filter was over oiled. Bogged out at high speeds because the vacuum (backpressure?) was decreased and couldnt pull through the filter

 

the surge isn't necessarily at 6500, mine was closer to 5000-5500. It seemed to be more about holding a steady cruising RPM in the mid range than any one certain RPM.

And yes, you want to ground the box (rectifier) not the wire going into it. Adding a wire is the best bet but if you had to cut, make sure you ground the end coming out of the box and not the end that heads into the wiring loom as that is the existing ground. Failure to do so will result in the battery not being charged.

 

Your running the bike way too lean for the altitude your at. Put in the #132 jet, set the needle clip one notch lower than stage 2 (which is raising the needle in the main jet). You will pick up a little over 1 hp (over your current setup) and your AFR will range between 14.5:1 down to 13:1 @ WOT. Still too lean but the best we can do with the DynoJet kit. Enjoy !

 

That would be the prime spot for the Dial-A-Jet. The fuel adder works based on fluid flow characteristics and acoustic wave patterns, don't know much about the latter, but do understand the former. Lean draws a vacuum, rich does not. Lean vacuum will suck additional fuel in through the jet mechanism as needed. It is infinitely variable where the brass is not. It can fill in the lean spots.

My brother and I both have the KLX300 needles and 128 Mikuni jets. He rode his as it was and it had some flat spots, adding the Dial-A-Jet smoothed out the flat spots. I did the same in 1989 with my 86 Nighthawk S, added the DAJ system to it and it took out the mid range flat spot. Did it again in 1997 on my KLX650, it actually had an incredible effect covering a variety of modifications and environmental conditions.

It is well received in the ATV and Snowmobile markets, not so with the bikes. I attribute it to the newness of the other industries, where bikes have been established for over a century. Brass is how jetting was done. In the other industries the riders were more open to a different possibility. I saw that same possibility back in the 80s and eventually acted on it. What sold me was the similarities to the fixed jetting Mikuni power jet, so I took a chance and did it again and did it again. I bought the one my brother used - told him to stick it in. He did and found the difference.

It won't adequately cover all the ranges with stock jetting. It requires you jet in close, but lean. My 650 was close with stock, the 250 wasn't. Now it is and the DAJ is there to cover for the lean spots. The 650 has had the air box lid cut (too loud without one), a full reverse cone exhaust installed, and a big bore Vulcan piston 678cc installed; gone from sea level to over 5000 feet in the mountains of WV; and has been ridden from 20 to 95 degrees without any jetting changes other than the DAJ kit. I don't have any gauges to test, wish I did and could. All I have is looking at the plug, the tail pipe, the exhaust color/smell, and mpg. Plug is perfect tan, tail pipe end is good color, no exhaust smoke color, and a jump from 50 mpg stock to 60 mpg with modifications. Nothing numeric, but it seems burning less gas and good plug color is a reasonable hint of good mixture.

Worth a try? I don't know, but I'll do another one on my street tracker when I finally get it done. A few guys on the KLX650 group have also had good experience with them. I've only read one rider actually having bad experience using one (claims it didn't work, nothing damaged), seen more negatives about jetting and bore kits. The others that claim the Dial-A-Jet doesn't do anything have not run them, they just say it won't work - yet Mikuni does a similar thing with their power jet... who do you think knows more - some guy who's not used the part or the company that made your carburetor actually using similar technology? Check out Thunder Products - Performance carburetor and clutching for snowmobiles, motorcycles and ATVs.. Read the media stuff in the menu on the left. Nothing to lose doing a bit of investigation. The owner of the company, Lon, is easily accessible with a phone call to ask questions.

 

so it would seem that a dial a jet is in order... but until then I guess I'll pull the damn thing off again and bump it up to 132 and #4 on the needle