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dead spots with high-end

By 4strokeOnly,
in DRZ400/E/S/SM

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4strokeOnly

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I've got the stock "S" carb. I know, I know... FCR is great and all, but I'll take the improved efficiency being that I put so many miles on it.

The problem I'm having: Under medium-hard acceleration I experience slight dead spots in the high end and when cruising at high rev's I experience minor surging. The surging feels almost identical to what you would experience if you were about to run out of gas and had to switch to reserve, but not as severe.

I have a stock pipe, 3x3 and a dynajet stage 1 jet kit. Could anybody offer some advice on what to check or adjust? I don't have an expended fuel screw and the brass plug is still in place, so I suppose I'll have to start there.

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4strokeOnly

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It sounds like a "lean surge". I'm not overly familiar w/ the DJ kit, but post your jetting specs. and altitude and you'll surely get some help w/ the issue. The guy I ride w/ had the same issue w/ his bike and the DJ kit.

Well, the thing is... I didn't do the jet kit, so I don't really know. Previous owner did the 3x3 and DJ kit right before I bought it.

Would all the stage 1 DJ kits be the same?

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stringburner

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The way I understand it (and keep in mind it's just what i've read here, and what part of it i've retained :excuseme:), the Stage 1 kit is for bikes w/ unmodified airboxes (no 3x3). The Stage 2 is for bikes w/ modified airboxes (w/ the 3x3). But I think the stage 1 will work w/ the 3x3 w/ the right jetting. You're going to have to find out what the jetting is. It's a shame you don't have an extended screw. At least you could rule out the pilot jet, and move on to the main. From what I just read doing a search on "lean surge", some people cured it by adjusting the fuel screw, going up a size on the pilot jet, or going up a size on the main among other things. Some threads also ended up unresolved. :confused:

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4strokeOnly

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The way I understand it (and keep in mind it's just what i've read here, and what part of it i've retained :excuseme:), the Stage 1 kit is for bikes w/ unmodified airboxes (no 3x3). The Stage 2 is for bikes w/ modified airboxes (w/ the 3x3). But I think the stage 1 will work w/ the 3x3 w/ the right jetting. You're going to have to find out what the jetting is. It's a shame you don't have an extended screw. At least you could rule out the pilot jet, and move on to the main. From what I just read doing a search on "lean surge", some people cured it by adjusting the fuel screw, going up a size on the pilot jet, or going up a size on the main among other things. Some threads also ended up unresolved. :excuseme:

Hmm... so if I get the carb apart and look at the jets, would they be engraved with the size?

The previous owner also put the carb back together with the stock screws... :confused: so this should be fun!

I am pretty sure its a stage 1 though and after reading this: http://www.dynojet.com/pdf/3110.pdf I think you're correct on the stage 1/2, which may explain my issue. I might be able to get a hold of the guy and ask, but its a long shot. Can I just use a stubby screwdriver to adjust the fuel screw?

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stringburner

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Hmm... so if I get the carb apart and look at the jets, would they be engraved with the size?

The previous owner also put the carb back together with the stock screws... :confused: so this should be fun!

I am pretty sure its a stage 1 though and after reading this: http://www.dynojet.com/pdf/3110.pdf I think you're correct on the stage 1/2, which may explain my issue. I might be able to get a hold of the guy and ask, but its a long shot. Can I just use a stubby screwdriver to adjust the fuel screw?

Yep. The jet sizes are marked on the jets. You'll only be looking at the main and pilot, and the position of the needle...unless he changed a wrong jet.

You'll get some more responses from guys w/ DJ kits (I hope), but you're still going to have to remove the carb. since it obviously needs adjustment.

You can use a stubby screwdriver or angle screwdriver to adjust the fuel screw, but it's going to be a lot more time consuming i'd think. It's a tough spot to reach. You'll need to remove the anti-tamper plug either way.

Grip the float bowl screws w/ a small pair of locking pliers/vice-grips/channel-locks contraptions really good on the shoulder of the heads. Crack them loose, then extract them w/ the Phillips screwdriver. Shouldn't take but a couple minutes to break them loose that way.

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CobbMtn03Z

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did you get the rest of the kit from the PO?

see what jet is missing...

Seems like the PO half-assed doing the rejet, not drilling the fuel screw.

or just cut the 3x3 and said it had a kit...

was the bike at a higher altitude before you?

lean surge at the top = too small of main

might try raising the needle (lower the clip)

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4strokeOnly

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did you get the rest of the kit from the PO?

see what jet is missing...

Seems like the PO half-assed doing the rejet, not drilling the fuel screw.

or just cut the 3x3 and said it had a kit...

was the bike at a higher altitude before you?

lean surge at the top = too small of main

Ok, I mis-spoke, the plug for the fuel screw is removed. I worked with the guy who owned the bike before me and he's a competent guy, but may have used the wrong jet kit.

I do not, however, have the jet kit, so that's out of the question. I'll have to pull it to check the jets.

So, what jets SHOULD I have for sea-level, 3x3, stock pipe (although I'm fixin to put on the E-header I have), E-cams

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4strokeOnly

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I had this problem and swore up and down that it was carb related until i took Eddie's advice and changed my old worn out chain. The chain looked fine but when i replaced it a lot of vibration and those sporadic dead spots on the higher end went away.

I have about 3-4000 miles on this chain. EK 0-ring chain. I take real good care of it and it looks pretty damn good. What the usual life for a street (mostly) chain?

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herdman14

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My 2007 SM seems to have a surging problem too when you sustain speeds around 70mph. Though it's intermitent. I have the 3x3 mod, full yosh exhaust and DJ kit with the 155 main, #2groove on the needle and the screw out 2.5 turns. I followed the instructions for the DJ stage 2. It was cold out the day it was doing this and it was the first time I rode it at those speeds for an extended period of time. I'm interested to get it back out soon to see if I notice it again.

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4strokeOnly

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Thanks Eddie

Tape over the airbox did the trick. Pulled much better on hard acceleration and I couldn't detect any high rev surging either. I'll know for sure on the way to work tomorrow, but I think its definitely running a tad too lean.

I shall pull the carb out this weekend and give see what I'm in for.

Anybody know what size screws the carb has so I can order some nice socket caps before I tear it down? I'll search too, just thought I'd ask while I'm here.

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npm

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on my 03,

140 main, 142.5 w/pipe

25 pilot

2-2.5 turns on screw

4th position on needle

Eddie gave me the same recommendation and it works well. The main jets in the DJ stage one kit only go up to 136 (as I recall) so if the PO didn't buy extra jets it is likely too lean. I had to buy the main and pilot after I bought the kit. Fortunately my local shop had a whole box of Mikuni jets.

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