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Need help diagnosing rough idle problem

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Hello All,

 

Always greatful for the knowledge you guys share on here. I have searched the forum over and over again (for the last month or so) but can not find anything that fixes my problem.

 

Bike:

2002 Suzuki DRZ 400S

 

Issue:

Rough idle when started.

Idling at ~800 - 1100 rpms

Cannot idle higher than 1200rpms

Give it any gas and it chugges and then dies

starts up every time when cold, a little harder to start when warm

 

 

Things I have tried and checked:

spark plug is new and clean

cleaned carburetor

checked for vacuum leaks

tried to swap carb with a carb off ebay, no change at all, same symptoms.

changed oil

 

Things I have replaced on the bike recently

used gas tank off ebay (has line filter)

new stator (old one got eaten by bolt)

new regulator (because of a low voltage issue)

 

 

I dont know what to do next and was hoping someone might have an idea or has had this problem before.

 

Any ideas are welcome.

 

Is this a carb/gas/air issue? -or- Should I be looking somewhere else for the problem... (timing,compression,valves)

 

The bike ran great, and then sorta started chugging on the way home from 1mile round trip. from that point on, has had this issue.

 

Thanks!!!

 

Ryon

 

 

 

 

 

 

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Did you always have your idle set that low or is that the only way you can get it to run? Even 1200 rpm's seems really low, should be around 1800, I have mine set around 2000.

First guess would be pilot jet related but if you swapped carbs that's out. Does it run any differently with the choke on?

Next guess is something's up with the new stator or regulator you just installed.

Make sure your valves are in spec

Edited by Gsxrstuntdrz
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How long ago did you change the oil, and did/does it smell like gasoline?

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Rich , can you list what mods you have and what your jetting is please .Things like exhaust , if 3x3 mod done , mainjet /pilotjet sizes , needle and/or clip position . That will help a lot , greg

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Sounds like it's not getting enough fuel to run above 1200rpms. Check petcock and fuel supply. Verify good free flow of fuel to carb.

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Sorry for the delay, thank you for the replies...

 

This is almost a stock bike.

 

The only mods that I have found are...

 

It does have some holes (1 inch) drilled into the airbox from the top... about 4.

the air/fuel canister has been removed

 

 

Normal Idle rpms was 1500/1600 before this happened.

 

I have not jetted the carb(s) yet... I soaked my original carb in pine sol overnight ... came out super clean.. used compressed air... no change.

Ebay carb is being used as is... have not made any changes/cleaned that... assuming it doesnt somehow share the exact same problem as the other carb.

 

I have a jet set (moose racing) ... new in package.... has not been installed.

 

 

If i put the choke on (1/2 or full) it will die.

 

Idle screw is accessible, but have taken it all the way out to clean carb... put it back in 'approx' same location/turns... no change

 

 

Additional info;

I think this problem started on the ride home... and it continued that day... at which point I had to go back to work and parked the bike in the garage..

 

A couple days later... i pulled the bike out of the garage and pulled the carb to clean it.. thinking it was dirty causing the rough running. That is when i found the gas in the oil.

 

Gas Tank.... i had installed the used tank from ebay... i connected both lines from the petcock to the carb (gas + vacuum) ... Something failed... the float or the petcock vacuum ? .....and it did flood the engine with gas... So, I changed the oil twice to fix that...

took all the plugs off (3) to drain, and let it breath for a litttle while.... i dont smell any gas in the oil any longer...

 

So after finding the oil in the gas... I cleaned the carb anyways and put it all back together... Now it is as it stands.

 

Could this be the newly installed stator causing this issue as suggested? ... It seems like the bike is running similar to before i changed the stator.

 

(stator has been on about 1month before problems started)

 

Thanks much guys.. missing the trails.

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also....

 

I dont know if this helps... but..

 

When brought it home and it was running rough. It was still running 'half normal" ... as in , I could give it gas and rev it to 6k no prob.  The more i idled it.. the more it seemed to run like shit.

 

So thats when i turned off, and pushed it into the barn.

 

next couple days (1 or 2) later... was when i discovered the gas had now flooded the engine cylinder... which hadnt happened until then. (i think)

 

 

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Gas flow;

seems to be ok. I installed new fuel line from napa + line filter.

i've tried installing the the old tank again (and old fuel line) just to eliminate that combo.

 

i've changed gas and tried superunleaded ... which i usually never use.

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@Gsxrstuntdrz

i will remove the stator and check it..... if that could be the problem. i have been reluctant to do so thinking it was fuel/air/carb related ... let me know your thoughts.

 

regarding the regulator... i connected the old one to test... no change.

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Fuel in the oil .....the o ring on the needle valve is most likely shot...item 18..https://www.thumpertalk.com/shop/oem.php?partcategory=787963&manufacturer=5&category=5&year=2002&model=27331..  . O rings can be sourced at automotive shops.

Return the moose jet kit and get the JD Jetting Jet Kit 

Do the 3x3 mod.....

 

 

Edited by Craigo 485sm

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Replace the petcock, then pull the carb again and replace the valve body O-ring(it is on the part that the needle valve goes into). Your petcock is toast and it is still allowing fuel to the carb, the o-ring is bad allowing fuel to the cylinder. Until you stop the flow of fuel it will continue to flood the cylinder/crankcase. Put a manual Raptor or Pingle petcock on it...the oem vacuum ones will fail again and they are expensive. With a manual one you will shut the fuel off every time you turn off the ignition...it becomes a good habit. 

 

Read this thread on petcocks:

http://www.thumpertalk.com/topic/841228-new-pingle-on-the-way-some-questions/

 

and this one on the carb which shows the o-ring(picture #5) in question(btw you must use a Vitron o-ring that is fuel resistant):

http://www.off-road.com/atv/tech/atv-tech-basic-carburetor-cleanup-52101.html

 

Like Craigo said, put in the JD jet kit:

https://www.thumpertalk.com/shop/JD-Jetting-Jet-Kit-DR-Z400S-SM-JDS005-p2006766373.html

 

Modify the holes in the top of the air box to equal a 3"x3" opening. While your at it, get the extended fuel screw:

https://www.thumpertalk.com/shop/ThumperTalk-DRZ400S-SM-Extended-Fuel-Mixture-Screw-K1002-p2006766350.html

 

Change your oil again & go ride............... :ride:

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@Motor7 and Craigo ... ok, change oil, replace o-ring , JD jet kit, and petcock, make the 3x3 mod ... parts ordered.

I will report back with my results in a few days. Thank you for your time.

 

Do I need to change the oil multiple times to get 'all' the gas out? or just fix the problem and change the oil and I am good?

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@Motor7 and Craigo ... ok, change oil, replace o-ring , JD jet kit, and petcock, make the 3x3 mod ... parts ordered.

I will report back with my results in a few days. Thank you for your time.

 

Do I need to change the oil multiple times to get 'all' the gas out? or just fix the problem and change the oil and I am good?

 

I would run it with some cheap dino (mineral) oil to operating temp for several minutes , then do an oil change, should be ok then....

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UPDATE 5/16

-----------

 

I have replaced the petcock, replaced the o-ring, replaced the jets, changed the oil (once), moved the idle screw in 3/4 turn (clockwise...inward), took off the air box cover in lieu of pending 3x3 mod.

 

The engine is still running the same as before. I can not tell of any change to the rpms,power,etc.

When I give it gas it wants to sputter/choke out/die.

 

Should I change the oil again?

 

When I first started it up, after making these changes... It sounded a little better for approx 10 to 20 sec. I saw it idle at 1600 for 5sec or more. Then it quickly started running like it has been.

Is this problem still a sign of gas in the oil? If so, shouldnt the idling be getting progressively better after each oil change?

Before the oil change i did smell some aromatic hydrocarbons in the oil.... It doesnt seem to have that gas smell any longer.

 

Here is a youtube video of the bike idling... as it stands right now.

 

 

When the video starts... the bike has been running for about 5minutes already...

Choke is off at the beginning... I put the choke on the 1/2 position in the video... then choke off again.

 

 

What can I try next?

 

Change oil again?

 

Check stator for damage ... check continuity?

 

Drop off at mechanic shop?

 

lol... thanks guys!!1

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SOLVED..

 

It was the stator.

Apparently, I didnt use enough loctite. and the bolts backed out of the flywheel again... causing the new stator to be damaged.

 

It now was red loctite on the bolts to keep things in place.

 

Thanks to everyone that offered help!!!!

 

 

special thanks @Gsxrstuntdrz  for figuring it out.

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