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2000 DRZ400S motor stumbles at constant rpm

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First post here after perusing for about a month. This forum seems like a great place with alot of great people who give great advice! What more could I want. So here is my first question about this yellow (so far a used lemon) 2000 DRZ400S with 15000 miles on it. I bought it on kind of an impulse buy from a friend in need. He is moving (I should say his wife wants to move) to Maine and he needed to sell one of his bikes. He has a loaded suzuki hog (looks like an all leather harley) and for his trail riding he had the DRZ. He bought it from a guy who did some mods to the muffler, chopped off the end of it, cut out the insides, did a bad brazing job putting the end back on so the tip could be screwed on. It is loud as HAIL! The bike had a miss in it, or a stumble, or a hesitation, not sure what to call it. I figured I would take it to a shop, get it tuned and timed and all would be well. Now $1000 later, it runs the same. Since I bought the bike, here is what was done: New 80/20 tires, stock muffler off of ebay, carb cleaning, ACCT replaced with the latest version of the ACCT (instead of a manual one) to reduce the tension on the chain, new cam chain, new plug, timed and tuned. Now it accelerates well as before, but at any constant rpm (street cruising at 25, 30, 35, 50, 60 mph) the bike jerks. I can hear the engine stumbling, missing, which cause the bike to have a little jerk in it. So here I am, a jerk who did an impulse buy, sitting on a twerking bike. Do these bikes have an electronic timing module that I could just replace as the next expense? Can the bike be hooked up to a computer and watch the motor miss to find the problem? I'm not sure how much more I want to spend on it as I have already surpassed its resale value. Please..any advice will be appreciated, from SELL IT NOW to replace the whatchamacallit and it will be fine.

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First post here after perusing for about a month. This forum seems like a great place with alot of great people who give great advice! What more could I want. So here is my first question about this yellow (so far a used lemon) 2000 DRZ400S with 15000 miles on it. I bought it on kind of an impulse buy from a friend in need. He is moving (I should say his wife wants to move) to Maine and he needed to sell one of his bikes. He has a loaded suzuki hog (looks like an all leather harley) and for his trail riding he had the DRZ. He bought it from a guy who did some mods to the muffler, chopped off the end of it, cut out the insides, did a bad brazing job putting the end back on so the tip could be screwed on. It is loud as HAIL! The bike had a miss in it, or a stumble, or a hesitation, not sure what to call it. I figured I would take it to a shop, get it tuned and timed and all would be well. Now $1000 later, it runs the same. Since I bought the bike, here is what was done: New 80/20 tires, stock muffler off of ebay, carb cleaning, ACCT replaced with the latest version of the ACCT (instead of a manual one) to reduce the tension on the chain, new cam chain, new plug, timed and tuned. Now it accelerates well as before, but at any constant rpm (street cruising at 25, 30, 35, 50, 60 mph) the bike jerks. I can hear the engine stumbling, missing, which cause the bike to have a little jerk in it. So here I am, a jerk who did an impulse buy, sitting on a twerking bike. Do these bikes have an electronic timing module that I could just replace as the next expense? Can the bike be hooked up to a computer and watch the motor miss to find the problem? I'm not sure how much more I want to spend on it as I have already surpassed its resale value. Please..any advice will be appreciated, from SELL IT NOW to replace the whatchamacallit and it will be fine.

 

 

open (or something) pipe and unknown jetting, plus the jerking on constant throttle sounds like a lean condition. 

 

the mcct is more desirable than the acct, as it won't prematurely wear out the timing chain. 

 

i would start with a clean air filter, freshly cleaned jets (of whatever size they are) and run the bike with the airbox door off, then on, then 1/2 taped over the intake hole in the airbox, to determine which way made it run the best. that should tell you where to start shopping for jet sizes. 

 

before i dove into that though, i would run the bike at idle and flood the area with propane or similar flammable gas to find out if there were any air leaks. 

 

checking the float height is easy also, with a section of fuel tube connected to the bowl spigot. 

 

if you want to check the stator's output (which i don't think is the problem here) there is a tutotial in the faq section. 

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Thanks ohgood...I have installed the stock muffler, so it no longer has an open pipe. I did read the posts here about the mcct vs the acct and decided to go with the latest version of the acct that I read puts less tension on the chain than the year 2000 acct. I don't expect to have this bike in 5 years and mostly road riding, so the acct is easiest for me. The carb was supposedly cleaned, the jets, the filter, timed, all that, by the shop I took it to. As far as the shop is concerned, the bike runs fine now (?!?). I have run it with the side box off the air filter after reading about opening up the box, no change in the miss at all. I'm not sure about the propane air leak test, I take it that if it is sucking air, the propane will increase the rpm. Could I use something like starter spray instead? Not sure how to 'flood the area with propane' without starting a fire in my garage!

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Yes starter fluid will work to check for air leaks

Your running lean, I would start by finding out what size jets are in there and which needle you have. Look for a red or blue dot on top of the needle. What throttle opening does it miss at?

Edited by Gsxrstuntdrz

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It seems to miss at all throttle positions. I have tried it at a constant 20 mph, 30 mph, 40 mph, pretty much all throttle positions. The speedo jumps from 20 to 19 to 21...all without moving the throttle, as if the needle is moving around in the jet. I will pull the carb top off later and see which needle is in there. What color needle do you think I should put in there if it is running lean?

Edited by EnduroDo

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Thank you! I'll give that a try and report back (if I don't sell it first!)

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Thank you! I'll give that a try and report back (if I don't sell it first!)

 

While your in there take note of what main jet, pilot jet, and needle clip position it has as well.

 

Do you know if it has the 3x3 air box mod and/or been re-jetted? If not you will most likely find that is has stock jetting, which is a 142.5 main jet, 22.5 pilot jet, and a non adjustable needle (only one clip position and no color marking on it).

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What did the shop actually do for $1000..??...tuned and timed?.. that don't add up ...the timing doesn't move and how did they tune the carb without a jet kit.?

Unless it has one installed or they fitted one........Take the bike back and complain..

Edited by Craigo 485sm
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I pulled the gas tank off to get at the carb last nite and found that the petcock does not stop the flow of gas in run or res position. I had to drain the gas tank in order to set it aside or it would have drained all the gas out the petcock. Is this normal...where is the off position on these? Would this cause engine misses? I know this is a vacuum petcock, but how does it shut off? And who invented the vacuum petcock...sounds like a solution without a problem..some new engineer who had to produce a new idea to get a bonus?! 

 

The side of the carb needle had a number on it 5DH37. I didn't see any obvious color, except maybe a light blue tinge in a ring under a magnifying glass. And it had only one clip position. What needle should I put in this carb?

 

No air box mod that I can see, except I just kept the side panel off while riding it with no change in this problem.

 

What is an extended fuel screw? Do you have a part number for it?

 

The $1000 was for things I put on and things the shop did...2 new tires, tuneup (he called it a tune-up, maybe just a new plug- should it be iridium?), adjusted the carb, re-install all the turn signals (gave him a box they were in from last owner), new cam tensioner, new cam chain, new oil, new radiator fluid, new brake fluid (the bike sat for a couple years), new seat, new grips, luggage rack, windshield, lower front forks, lower back shock (via adjustment) to bring the seat down a bit.

 

We have 2 bike shops in town, and I don't want to cause alot of trouble for either one. I think this guy has done all he is capable of and I don't want to press it as I may need a tire change or some other things done again. If there was a suzuki dealer I would take it there but its a 2 hour drive.

Edited by EnduroDo

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It sounds like you have a faulty petcock if it allows fuel flow when on "res" or "on", which is normally an effective "off"......Prime is the position that allows constant fuel flow..

Yamaha FUEL COCK ASSY 1 (5LP-24500-01-00)

 

Did you remove the needle from the slide.?..only one clip position indicates the stock needle is fitted..

I would suggest this .....JD Jetting Jet Kit - DR-Z400S/SM and doing the  3X3 mod

 

 

ThumperTalk DRZ400S/SM Extended Fuel Mixture Screw

Edited by Craigo 485sm
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Thank you! I will order a new petcock, mixture screw. After installing those I will look at needle options if the problem persists. Are there any other options for the needle? I am a street rider mainly, not a racer. Yes I pulled the stopper off the top of the needle to take a look at it, the spring hit the rug and luckily I found it!  Hope this helps. I like the bike, but hate the ride!

 

How is it that we can replace the vacuum petcock with a free-flowing one, without affecting carburation? What is the purpose of a vacuum petcock? Why did Suzuki do this?

Edited by EnduroDo

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When you pull the carb to make your changes you should also replace the float valve needle and seat/o-ring. Just to be sure you do not fill your engine with fuel. Be sure to note what jets are in there. If stock air/fuel screw is still installed it may be covered by a small brass cap/plug that must be drilled to remove it.  Check the ACV diaphram for cracks or general age and stiffness. Should flex easily. Don't lose the small o-ring at top of carb under black top cap. +1 to suggest the JD Jetting JDS005 kit. New petcock is good. Be sure to cap off/plug the vacum nipple on the carb. Vacuum flow petcocks have been around for years on many diff bikes. It was invented because so many riders would forget to turn of the fuel flow and flood their engines. Good idea but faulty design. The rubber parts age and crack causing the petcock to allow fuel to pass.

 

Don't give up on your bike. You will get it sorted out and ride HAPPY! :D

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Thanks Jim. I'm a bit confused by this vacuum petcock thing. If it is not properly working, and is leaking gas via gravity when in the ON or RES position, why would I want to replace it with a gravity feed petcock, as it now IS a gravity feed. I ordered the yamaha petcock, but now am wondering if I really need it. Could it, in failing, be causing the carb to starve for fuel intermittenly, causing a misfire, like what I am experiencing? Maybe the problem is at the source...the fuel tank, not downline in the carb?

 

What is generally used to stop off (plug) the vacuum line...some kind of clamp on the hose or a screw in the hole? Sounds like a pretty important thing to get right.

 

Also, how important is it to use the iridium plug in this bike?

Edited by EnduroDo

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Thanks Jim. I'm a bit confused by this vacuum petcock thing. If it is not properly working, and is leaking gas via gravity when in the ON or RES position, why would I want to replace it with a gravity feed petcock, as it now IS a gravity feed. I ordered the yamaha petcock, but now am wondering if I really need it. Could it, in failing, be causing the carb to starve for fuel intermittenly, causing a misfire, like what I am experiencing? Maybe the problem is at the source...the fuel tank, not downline in the carb?

What is generally used to stop off (plug) the vacuum line...some kind of clamp on the hose or a screw in the hole? Sounds like a pretty important thing to get right.

Also, how important is it to use the iridium plug in this bike?

Yes your broken petcock is now technically gravity fed, but there is no way to turn it off so it is constantly allowing fuel into the carb. If the float needle seat fails you will flood the crankcase with fuel. The Yamaha petcock Craigo linked to will have settings for ON, OFF, and RESERVE.

To cap off the vacuum line you can silicone a screw in the line

Iridium plug is nice but not necessary

Your problem is not anything to do with the petcock, just a coincidence. Jet kit is what you need

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Thank you! I will order a new petcock, mixture screw. After installing those I will look at needle options if the problem persists. Are there any other options for the needle? I am a street rider mainly, not a racer. Yes I pulled the stopper off the top of the needle to take a look at it, the spring hit the rug and luckily I found it!  Hope this helps. I like the bike, but hate the ride!

 

How is it that we can replace the vacuum petcock with a free-flowing one, without affecting carburation? What is the purpose of a vacuum petcock? Why did Suzuki do this?

 

If you click on the wording for the item it will give you a direct link...

ThumperTalk DRZ400S/SM Extended Fuel Mixture Screw

Yamaha FUEL COCK ASSY 1 (5LP-24500-01-00)

 

You will need to cap the port on the head when you install the manual petcock..

What is the purpose of a vacuum petcock? Why did Suzuki do this?...For set and forget purposes , the theory is you don't have to remember to turn off the petcock  when the bike is stopped as it doesn't allow flow without the engine running, unless on "prime" ...(all is rosy until the petcock malfunctions, like yours is atm)

 

Changing out fuel petcocks has no effect on jetting

 

 

Here is a guide for the 3x3 mod and jet kit install...

 

Edited by Craigo 485sm

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Thanks for all the great info...I'll get to work on it once I get the parts. Talking with a local shop yesterday I was told that one of his friends had a miss in his DRZ 400 and after lots of fixing this, fixing that, new plug, etc, he went to an iridium plug just to try it and the problem went away. Maybe he had a faulty new, regular plug, but just in case I just bought one of those.

I've got another question...I can't believe that this bike ran this way when it was new, with the stock carb, needle, jet, etc. Why shouldn't I just get a new stock needle and jet, maybe they are just worn out?

Edited by EnduroDo

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What's the update?

 

My 2007 DRZ 400S is all stock, no mods, had a similar "jump" at various speeds. I just changed out the stator and it runs great. 20K + miles on the bike. This bike seems to need  really strong electric to run good. 

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Redshift...no update yet except I have the jet kit in hand and trying to decide when and how to do it. If that doesn't work, time for a new stator. I hate throwing parts at a problem. Even more I hate throwing mechanics at the problem!

 

Craigo...what do you mean by "You will need to cap the port on the head when you install the manual petcock"

 

Does that mean plug the vacuum tube on the carb?

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