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Another Carb Question: Jet Needle Slide

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Need to understand the operation of the needle slide. What causes it to raise as you crack the throttle open?

According to a "Carb 101" site that was posted on this DR forum, the slide is the primary source of generating the mixture around 1/4 throttle. This is where my DR650 has it's major flat spot. I think finally I got my pilot screw set up to where it idles great, and picks up off of idle without any problems(Actually a bit rich, but still tweaking). But as I roll back on the gas, I hit that flat spot and the bike bogs and surges.

I believe that I am still lean in this throttle range. I've shimmed the needle up about .032, but that hasn't really made a huge difference. I tried removing the air box cover just out of curiosity, but as I expected, that didn't buy me anything.

Should I shim the jet needle up a bit more? Or is there somthing I can look at on the slide to make sure its functioning properly?

I've been playing chess with this bike for about a week now and think I'm getting pretty close to getting 'er running pretty smooth.

Any info appreciated.

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Vacuum is what allows the slide to raise. This moves the needle jet higher to allow more fuel to flow.

What mods have you done to the bike so far?

Did you make sure the black diaghram is not pinched and there is a good seal at the carb? It may be the slide is not allowed to move far enough or fast enough to allow enough fuel to flow at 1/4 throttle. The needle jet also controls the fuel flow at this point. Did you check to make sure the needle jet is free of debris?

Does this surge or bog appear in every gear at the same throttle opening?

Give us some more information about what you have done to the bike so far. I only have a little experience with jetting my 05 dr650se. I installed the dynojet kit with a 155 main jet, airbox mod, k & n filter, jesses extended fuel screw and k&n pre-filter, stock exhaust and the needle jet on the 4th clip. My elevation is 1100 feet asl. The power gain was noticeable.

Greg

Clearfield, PA

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I have't done any mods to the bike besides shimming the jet needle. It's brand new. ~425 miles. Owned it for only 2 weeks now.

Will take a good look at the diaghram. Where does it pull the vacuum from? Maybe I got a hose that's not hooked up correctly / fully / kinked?

As far as the behavior in different gears. Yes, it acts the same no matter speed or gear. I have paid allot of attention to this to make sure it is directly related to the throttle position, and it is for sure.

Will take a good look at the jet while I have it apart too (Kinda already on my list to do) :applause:

Thanks for the feedback.

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The engine that creates the vacuum, as the air is drawn through the carb.

There are three hoses. One that runs to the petcock, one to the air box (larger one that connects on the right hand side of the carb), and a smaller one that routes back towards the air box. I think it might be an overflow hose.

I would check the diaghram to to make sure its alright, that it's not pinched or torn. You might want to drop the fuel bowl and make sure there isnt any dirt in the bowl. Check the needle jet to make sure its clear of any debris.

If found this in a different jetting article. Too rich jetting (too much cutaway, needle position too high, too large a needle jet) can make the bike lunge and hard to control. If its too lean in this area, the bike will feel really flat and down on power, but will respond quickly to changes in throttle position. It may detonate (ping) under load too.

Try applying the choke at 1/4 while the problem is happening and see if the problem gets better or worse. You should be able to tell if the problem you are having is lean or rich condition. If the condition gets better then you are probably lean.

I hope this helps some.

Let me know how you are making out and hopefully those with more knowledge of the DR will add some suggestions.

Greg

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Dude, there's nothing wrong with the vacuum diaphragm. What you have done by altering the airbox cover is to further lean the bike out, if you haven't replaced the stock main jet with a richer jet.

If you still have the stock main jet in there, it doesn't matter what you do with the needle, it's still going to run too lean if you let in more air by altering the airbox intake.

The carb must be richened significantly on the main jet, and then raise the needle, open the airbox, and open up the exhaust, to make a big difference in power and how well it runs. I haven't done this yet to my DR, but I did it with my XR650R, and the difference was huge.

All the guys in here say to get the dyno-jet kit, which includes a grooved needle for adjustment, and rich main jetting. I haven't gotten it yet, but plan to.

But anyway, to answer your question, raising the needle richens the mixture, and lowering it leans it. But still the needle position probably won't do much with the stock jet since the stock jet is so small even fully open it's not letting in a lot of fuel.

When you open the throttle on a bike with a CV carb, like the DR has, all you're doing is opening a butterfly valve that then allows engine vacuum to raise the slide, via the diaphragm. I think all street legal bikes have this type of carb, while dirt bikes use a direct cable link to the slide, so when you twist the throttle, a cable physically pulls the slide up.

Don't give up on it, the DR650 is an excellent bike, and trust me it will run even better after it gets around 1500 miles on it. It's kinda slow to break-in, the engine is pretty tight when new.

L.L.

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I dont think he modded the airbox, or added any mods other than the washer shim. He took the side cover off the airbox to see if the problem got better or worse. He appears to have a 1/4 throttle flat spot. He was trying to get rid of this by shimming the needle.

I mentioned he should check the diaghram to make sure he didnt pinch it when he had it apart adding the washer shim. Might also want to check and make sure the diaghram wasn't torn or improperly installed in the first place.

I think all he wants to do is cure the 1/4 throttle flat spot he is experiencing in all his gears at 1/4 throttle.

Greg.

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Right on. Thanks a ton to both of you.

smashinz2002: Yeah, I knew what I was getting into when I took the air box cover off. Like I said, that was more out of curiosity. Pretty much affirmed that I'm running too lean at 1/4 throttle since it didnt change anything.

Stiletto_72: I have been playing with the choke and it does indeed make a noticable improvment, which again, tells us its lean. Will pay really close attention to the behavior tomorrow back and forth to work and bounce that against what you found in that article (Which is excellent info by the way.)

Dont worry smashin, I aint giving up. I love this bike and have a blast buzzing around on it, even when its not behaving. Thats why I'm pretty anxious to get 'er tuned up right and really rolling.

Thanks again fella's. Will keep ya posted on my progress. Heading the right direction for sure.

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I'm gonna have to classify it as acting surgy and lunging. It will kind of start to cut out and then lung to catch back up with it's self. This would say rich yes?

This kind of makes since because, here is CO, we get a pretty decent temerature swing between the morning and the afternoon (like 20 to 30 degrees), and it's almost always worse in the afternoon when its hot. The air is less dense when it's hot, therfore making the bike that much richer. You agree?

The only confusing thing is, that cracking the choke still make a difference (I think). Like I said before, it doesn't totally clean it up, but definately does something.

I think I'm gonna try taking my shim washer out from under the jet needle and see what direction that takes us.

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Update:

I took my .032 washer out from under the needle, and now (After a full night of scratching my head) have the pilot screw adjusted to 1 3/4 turns out.

Ended up here cause I figured it was too rich since it was surging and what not. Not too much of a improvement this morning on the way in..... unless.....

If I cracked the choke WIDE OPEN, it runs great. So that means it's too lean right? Well this doesn't make sense. I'm at 5000 to 6000 feet, its hot out, so I cant be THAT lean on gas.

Does the stock jetting need opened up THAT much? Thats insaine. How in the world can they be that lean stock and still run anywhere, much less 5000 feet elevation.

Thoughts please.

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I think you need to ignore the shim and pilot screw for now and start looking at the bottom side of the carb. As you said it works good with full choke. That has to tell you the bike is not getting enough fuel. Sounds like main jet is clogged or some other fuel delivery problem.

Check the float height and look inside the float bowl for sediment or something else blocking the jet. I bought a new inline 4 Zuki one time that had one of the carbs bad from some fuel deposits that had formed over the jet. Cleaned it up and all was well.

Good Luck,

Terry

99 DR650

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Been in there a couple of times and havent spotted anything ugly.

What do you think about it being a petcock issue? Hmmmm. :applause:

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Need to understand the operation of the needle slide. What causes it to raise as you crack the throttle open?

According to a "Carb 101" site that was posted on this DR forum, the slide is the primary source of generating the mixture around 1/4 throttle. This is where my DR650 has it's major flat spot. I think finally I got my pilot screw set up to where it idles great, and picks up off of idle without any problems(Actually a bit rich, but still tweaking). But as I roll back on the gas, I hit that flat spot and the bike bogs and surges.

I believe that I am still lean in this throttle range. I've shimmed the needle up about .032, but that hasn't really made a huge difference. I tried removing the air box cover just out of curiosity, but as I expected, that didn't buy me anything.

Should I shim the jet needle up a bit more? Or is there somthing I can look at on the slide to make sure its functioning properly?

I've been playing chess with this bike for about a week now and think I'm getting pretty close to getting 'er running pretty smooth.

Any info appreciated.

Out of the box the 650 is way to lean. I had the same trouble with mine at 700 ft. take the time to do the carb 101 throttle chop diagnostic test then correct the problem. stock my pilot screw was 3/4 turn out. I pulled the snorkel turned it 2 1/2 out. the best thing is to call Kientech Engineering(541) 472-0835 and talk to them. best thing I did and ordered the dynojet kit along with opening up the top of the air box.

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If its the vacuum petcock acting up, you can bypass it by running with the petcock set to the PRI position. This will allow fuel to flow without relying on engine vacuum to open the valve.

Give that a try and see how it runs.

Terry

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i know this is an old post but it brings up a good point. the float level will change the mixture through the entire range. i swapped out my pilot jet with another and the bike ran like total crap. i found out that it was a pilot for a two stroke. but while i was changing the pilot out, i accidentally messed my float level up. it was very rich(too high). i was getting horrible mileage 85 miles til reserve and it was very sluggish(which is what happens when rich). so i readjusted the float level to 15mm and it ran considerably better but now it had a surging at low rpms and cruising. it was a tad too lean(which causes the bike to act quickly to throttle inputs and also to surge and buck). so i upped the level to 14mm and this has been where i've stayed. super smooth cruising, clean and smooth acceleration, and good gas mileage. and my plugs finally have the nice tan color to them which i've been trying to get since i got the bike.

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yeah, check yer float height...it was off from the factory on my 350 and caused all sorts of grief the first two months that i had it. surge, starve for gas and die. took it to a zook dealer and had the floats set and it ran like a different (although still super lean) bike.

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search the forum like you have been and call Jesse @ Kientech Engineering

(541) 472-0835 get the extended fuel mix screw, it makes setting the mix easy then you will be able to tune the beast. were your at you should be at 1 1/2 turns out to start and If you haven't done this yet, you are some were around 1/2 turn out give or take 1/4 turn way to lean for good responce. this bike is choked down for our tight emission laws. less fuel hotter exhaust two spark plugs all to burn fuel with little pollution. The only way to do it with a carb type engine.

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