Ok,

To chip in here, I agree you don't need the dyno jet kit. The jets from dyno jets are numbered differently, but you can match up mikuni jets and dyno jets in size.

The difference I found with the jet kit is the needles. But they were too thin for my setup. My machine would stumble between 1/4 - 1/2 throttle indicating the needle was too thin. I put the stock back in, and it is bang on. I am running 170/175 with the stock needles in the stock position. Now, mine is modified with the filter and pipe so it needs alot of fuel, but yours is essentially stock with the tabs removed.

It could be possible that the dyno jet kit makes a major improvement, but that may also be attributed to the airbox and filter modifications, along with proper jetting.

In my case, I didn't find any difference.

RM

 

In my case, I would rather take a beating then remove the dyno-jet kit. More crisper power (especially low and mid) and I picked up atv lengths in a drag. Before I piped it, fuel aconomy actually slightly picked up. Excellent product. Rennym, did you try adjusting your DJ needles?

 

cbus... you are really confusing me & others with saying a bog is lean & backfiring is rich, I think its the exact opposite. I have first hand experience with a lean condition that causes backfiring, just cover the air box with a lean condition & the trouble goes away. Also, I have experience with a very rich condition, just put a few extra spacers under the clip & the bike bogs/dies/runs out of gas, has deep tones emitting, lacks power, hesitates etc, all without backfiring. If you can't tell if the stumble is rich/lean just watch the tail pipe at night, I'm pretty sure flames coming out are a lean condition. I'm not saying your wrong/I'm right but I would be willing to swap ideas with anybody else as well.

I had good success with the dynojet kit with just airbox mods but had trouble dialing it in with no lid/full exhaust. I am using pos4-5 on the stock needles & may try filing the stock needles to mimic the dyno jet taper but not to the same extreme since I'm at the extreme rich position with the stock needles.....

 

Gary,



<< In my case, I would rather take a beating then remove the dyno-jet kit. >>



LOL.

I didn't bother to adjust the dyno jet needles, as I found success when I dropped the stockers back in.

I can see how the machine may have responded for you, as with every machine I have owned, I have found them to be lean. I jetted my 400EX up and it made a noticable improvement.

But in my case, with my mods, it's tough to compare the situations. Even different pipes are different to compare the jetting.

But for the $70 US (More than $100 CDN to me), I would spend some time with some Mikuni jets. Might as well screw around with $20 worth of jets. If it doesn't fix it, then bite the bullet and get the dyno jet kit.

RM

 

chimmer, a backfire is lean, a little popping in the exhaust header is not a backfire. That is a common misconseption. When I fried the carb slide and melted my air filter, that was a backfire. Backfire is when your air/fuel charge ignites in the intake track before it even makes it into the engine. Popping in the exhaust is from excess, unburned fuel burning off in the header, can't get that from running lean. As far as the book I mentioned before, its &quot;Motocross and Off-Road Performance Handbook, 2nd Edition&quot; written by Eric Gorr. Its a dirtbike book and mostly about 2-strokes, but the carb info works well regardless of what you ride. Eric's website is here Check it out, its got a good page on diagnosing jetting under Technical Articles, Carb Tuning. Also, read the Dirtwheels article about jetting from a couple of months ago.

 

cbus... I did not know that, thanks. That helps alot actually, I will try going much leaner on the needle &amp; see what happens. I guess the popping can cause fire out the tail pipe because that's what I had. Perhaps the poof noise heard after I turn off the ignition is a rich condition too. Funny thing is the way the condition improved when I covered up the airbox though. Jetting is a fricking mystery that only seems to be conquored by experience &amp; listening to others with the same. This menas I'll have to try pos 1 or two on the needle, I'll let you know how I make out.

 

The flames out the exhaust is a little confusing. Usually, jetting alone won't cause that. That usually has something to do with ignition. How is the spark plug, is it a fresh, new plug? On the Buell that I owned, I had a bad spark plug that failed in something like 20 miles. When that went bad, talk about fireworks in the exhaust! Covering your airbox made it run better, so I would richen it up. Maybe what's going on is you are lean enough to cause problems with the spark plug, so then your plug misfires, and then the popping and flames out the exhaust are from the unburned fuel on the misfire stroke burning in the exhaust. First and foremost, get a fresh plug in there. Ride it again and see what happens. Do the airbox trick and see if that makes it better or worse. If that makes it better, then richen it up. Go to the web site from my previous post for further/better details.

 

Your symptoms (covering the airfilter/airbox makes it run better), indicate you are too lean. This is a general statement.

You need to understand jetting and depending on your condition, understand what part of the carb needs to be adjusted.

At this point, it is safe to say you need to go richer. You may want to buy the next couple stages of jets. (remember you have two carbs so don't forget to ensure you have the proper number of jets). I wouldn't touch the clip position on your needle yet.

Next, read the jetting book. (I think there is probably good resources on the net which will describe it as well. Especially with all the dirt bike sites....) It will describe the carb operation, and what part of the carb is in play at what point in the throttle motion. The pilot at closed throttle, the needle in the middle, and the jet wide open. It should describe how to do a plug check, so you can verify your settings.

You can also read on this board, to learn the procedure to quickly change jets on the Raptor. The first round will probably be a couple of hours. The best I have heard is 20 minutes, but the guy had done it plenty of times.

My recommendation is to go up one size. Leave the needles where they are. Try one size bigger and see if that makes a difference. Also, ensure your filter is 'properly' oiled. (if needed, description on that can be found on this board as well)

Good luck,

RM