Stumped

[2-Strokes 4-ever]

My 03 RM250 won't idle consistantly.

-All new motor with only 25 hrs.
-Good reeds.
-Float height is correct, jetting is good, carb is clean.
-Muffler freshly repacked.
-Powervalve clean and working properly.
-Timing right on.
-No air leaks in air boot, intake manifold, main seals, cylinder-to-reed cage, reed cage-to-carb junctions.
-Good plug.
-Fresh 93 octane mixed at 40:1

I warm the bike up, ride it around to operating temp, set idle and back out air screw till peak RPM, but no more... (2 turns.) Good idle.
Run it hard in the tight woods and when I stop, high idle (rrrring.....ning....ning...ning.) Very hard to start when warm and idling fast.

Even my friend and excellent mechanic is stumped.

Would a faulty TPS cause these symptoms? It's about all we can think of that's left to check.

Thanks guys

 

[wake_rider]

All symptoms lead to an air leak somewhere. Have you done a leak down test? If it's giving symptoms whenever hot, expansion comes to mind...

 

[wake_rider]

What might have been tight and leak free while cold, might change characteristics while hot.

 

[dirt bike dave]

Sounds like it idles a little lean when it is hot.

If it's important to you that it idle smoother when it is hot (as opposed to just warm), I'd turn in the air screw and maybe consider a bigger pilot jet.

However, you will probably lose some throttle response, and it may be a little rich when it's only warm.

IMO, these are the kinds of compromises we face when running a light weight, highly tuned MX race bike on the trail. Basically, Suzuki did not give much thought to the hot idle when picking the carb and porting for your bike. Making it idle smoothly when hot is likely to cost you either $ or performance somewhere else on the curve.

Oh, and anything you can do to help it run cooler might help the idle issue.

 

[2-Strokes 4-ever]

Haven't done an official leak-down test, but it may need to be looked into. I could live with no idle at all, or even a high idle, but the hard-to-start-when-hot thing is no good... LOTS of kicking! Playing havoc with the new autoclutch too.

Again, ever hear of a bad Throttle Position Sensor causing these symptoms?

*Also... when it's hot the idle gets real high, but within 10-20 seconds it starts slowing down as I sit and wait for the group. Stock pilot is a 48, JD Jetting says run a 45. I've run the 48, the 45, even a 42... when the bike is hot these pilots make no difference in the high-idle issue. The bike did this before a lower-end rebuild (just 4-5 rides ago), but I lived with it... still doing it.

*And, the motor's never been hot enough that it's boiled over.

 

[dirt bike dave]

A two stroke that is hard to start hot is just not right!

I can see how a bad TPS could be temperature sensitive and might cause these problems. If it's not too expensive, might as well replace it at this point.

Other things to try: Race fuel, one step hotter spark plug, maybe a carb slide with 1mm less cutaway, the thinnest oil your auto clutch will tolerate... Just throwing out ideas and bandaids in hopes something short of a new carb will make the difference.

 

[2-Strokes 4-ever]

Hmmm. A mechanic had an idea, disconnect the TPS because he said they often make the midrange blubber. My midrange was blubbering until I leaned the needle one more clip (leaner that JD Jetting recommends.) Maybe he's onto something... can't find out tonight though, 5 acres of grass to cut.

BTW dirty bike dave: This bike's been doing this long before the autoclutch install.

 

[High Lord Gomer]

I blame it on you even considering an auto-clutch. It probably started when you first started thinking those evil thoughts about an auto-clutch.

Auto-clutches are the debil.

 

[helio lucas]

usually the TPS is nothing more than a potentiometer (variable resistor). you could silmply measure with a ohm tester (multimeter is good) and compare with the service manual values if they state any?!?
just unplug it and test the bike with out the tps...
in a more extreme and desperate case you can put a resistor in place of the tps, even a potentiometer and see how it runs...

just a idea :cool:

 

[2-Strokes 4-ever]

Thanks to all. Hard to find time to work on the RM right now, but I'm gunna start the bike and spray contact cleaner at potential leak areas first, then try disconnecting the TPS. Kinda hard to get the bike good and hot here at home though.

 

[2-Strokes 4-ever]

This 'won't idle' issue is driving me nuts!

First off... I must of sucked some dirt in somewhere, only 20 hrs on an all-new motor and the piston was scuffed badly :bang: . A worn top-end was part of my previous jetting issue. She runs well through the RPM range, but I'm at my wits end with the non-idling issue... just as before, I warm the bike, set the idle (spring almost bottomed out), and the air screw (1 & 3/4 turns out.) Once bike is real warm (coming out of some tight, technical trail) she's idling super high. I disconnected the TPS with no change.

I noticed the V-Force reeds were pretty worn and replaced them. Strange question... do reed petals have a curve to them?... should they be installed with a certain side up/down? When I hold the reed block up to the light I see gaps where it seems that the petals should be tight to the plastic block. If the petals have a slight curve to them maybe a few should be turned over for a better seal?

I'm wondering if the motors lower-end is loading up with fuel because the reeds don't appear be tight/sealing well.... I wonder this partially because when I re-start the warm motor it blows a lot of smoke at first.

 

[RM_guy]

The reeds need to be flat. If you can see daylight under them then they should be replaced. Turning the over is not the best fix because they still won't seal well and now they'll be bending the opposte way and will fail. That's what's been causing your hard starting issue and may help the idle too.

 

[whenfoxforks-ruled]

Fatten your oil ratio! Your leaner ratio mix, may seemingly be okay, for put putttimg around, but when its up to operating temperature, you do not have enough protection, hello scuffed cylinder, unless you seen the dirt, in the rubber intake, reed or on top of the carb slide?. The seemingly hotter story at idle, does back up my opinion! THAT is exactly when, the cylinder is scuffing.

 

[2-Strokes 4-ever]

Reeds are brand-spankin' new.

 

[TWRT]

when I re-start the warm motor it blows a lot of smoke at first.

Are you loosing transmission fluid? maybe a worn oil side seal?
just throwing out ideas.

Dave

 

[2-Strokes 4-ever]

Hey, I'm open to thoughts and ideas. No loss of tranny fluid.... seals are good, only about 30 hrs on all new motor.

I've been advised to look more closely for an intake leak, perhaps just a pinhole in intake boot? Someone said to check powerjet for a clog (this would effect idling issues?)... And to make sure all the electricals are well grounded. Guess I'll look at float height, again. The brand new reeds not sealing tight against reed-block has me puzzled too.

*BTW... years ago on a different bike I had a stator going bad that caused hard starting (a warm motor made the stators elec output lower.) It got so bad kickstarting it wouldn't work, but bump starting generated enough juice to get it to fire until it quit alltogether. Hmmm.

 

[2strokerfun]

My bold prediction: won't be float height.

 

[whenfoxforks-ruled]

Try backing off the screw torque a tad, and see if the reeds lay flat? Over torqued will buckle. And be sure to use some blue loctite.

 

[helio lucas]

http://www.amazon.com/gp/product/B001DDBOVW/?tag=4samnew-20

this is the link of a spark plug tester. most of the times when the ignition is weak this is a very usefull tool to diagnose it.
i can say, "check for a air leak!" but your carb idle screw almost bottomed may indicate something, either a carburation problem or the slide stop is worn.
air filter with too much oil? exhaust pipe tail pipe (the one with around 28mm diameter) slightly blocked, maybe with carbon?
bad left crank seal? spray wd40 or carb cleaner around all the engine where a leak might develop and check if idle rpm changes?

when starting hot, do you need to open the throttle or you need to pull the choke to start it?
i can see a bad float valve cause hard starting on certain conditions...