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Discussion Starter #1
My 04 EX-500 was recently "tuned" by a local shop. It's got a K&N drop in filter, and a full Hindle exhaust. Ive posted this question before, but it was mostly directed towards my flat mid range/top end problems AFTER the tune.

My current question is what could cause my idle problems though.

If I let it idle for a short amount of time and rev it, it does fine. Revs up normally, falls back down reasonable quickly, and doesn't bounce. Revs back down to a normal idle. But if I let it sit at idle speed for 30 seconds, or a minute or so....a reasonable amount of time AT IDLE... If I rev it, it will rev, then fall back down to only 500 rpms or so...idle extremely low for a second, then return to a normal idle. It does this to the point that if I let it sit for several minutes and rev it, it almost shuts down. Any help would be appreciated!
 

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second chimp in space
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are you saying that it runs better when cold?

Or is it that if the bike is warmed up it will do what you said also?

If it runs best when cold, then they set your idle screws too rich. I can tell you how to set them right if you want, or you can take it back to the people who botched the tune up.
 

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Discussion Starter #3
Honestly this idling problem happens whether the bike is warm or cold, it doesn't matter. If I let it sit at idle for any length of time and rev the motor, it will fall back down and attempt to stall...as if it's suddenly not getting fuel. Acts like it did once when I ran the reserve tank and all down to empty...wouldnt start til the carbs could fill the fuel bowls, and then it idled real low for 5-10 seconds. (Which is a funny story...I find it odd when you can run out of gas in your reserve tank when you never even switched to reserve. :hshot )
 

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second chimp in space
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I'll venture to guess that it's your hoses. Make sure the hose going from one of the carbs to the petcock isn't crimped. This hose provides vacuum that opens the petcock for you. If it's crimped, the petcock might not give enough gas. Try putting the bike on prime and see if that fixes the problem.

Also, make sure there is no pressure in the tank. Open the cap and see if the problem disappears. If it does, it could be your vent, which is part of the cap.

My bike had both problems, but they only manifested themselves on higher rpms, so this might not be it.

It may also be an air leak between carb and engine. Spray the rubber boots with a light lube (wd-40 or something) and see if that makes the engine speed up slightly. It shouldn't.

Or you could just have the idle too low... There should be a knob on the left or right side of the carb rack. Turning it sets the idle speed. Maybe the shop just set it too low...
 

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Discussion Starter #5
I'll check the hoses and the gas cap...

By prime...do you mean the choke? If I give it any choke, from having no choke, it starts to stumble and act screwy. Too rich.

Ok, so...petcock.. What is this? I know the petcocks on radiators and stuff....but I dont know about this. Is the petcock youre referring to on the gas tank, and the hose runs from that to the carburetor?
 

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the petcock is attached to the gas tank and is the valve that shuts off gas and allows you to switch to reserve. there should be a hose that connects it to the carbs. pinched hoses could be your problem.

but since you changed the air filter and the exhaust, did you have the carbs rejetted also? because if not, that is the source of your flat spots.

also, if you give the bike gas and raise the rpm and then chop the throttle, do you get backfiring? if you do, then that is an indication you are running lean and that the headers are not sealed correctly to the head.
 

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second chimp in space
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You switch to prime with the same lever that you switch to reserve. This switch is on the petcock, by the way. You should have 3 settings: normal (ON), reserve (RES) and prime (PRI). Prime just bypasses the regular vacuum operated switching of the petcock, allowing gas to always come out. This is useful in diagnosing and when you just put the carbs back on and need to fill them with fuel so the bike will start.

Using the choke when the bike is warm should cause it to stumble and die. Mainly on idle, though. Giving it gas disables the choke on most bikes.

What is your idle speed, by the way? 1000rpm, 1200rpm?
 

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Discussion Starter #8 (Edited)
Idle speed is about 1100 rpms. And by fuel switch is three position: Off, On, and Reserve. There is no prime as far as I have been told on this bike. If it is run with the switch in the off position, it will run for maybe 5 minutes or so, and then drain the bowls in the carbs and shut off. I ran the tank ENTIRELY down before and had to sit and crank the bike in 5 second bursts over a several minute period before it got enough fuel to start. It was definitely aggravating.

As far as the performance stuff goes. The shop claimed they probably wouldn't have to rejet due to the air temperature here being so high usually. (High 80's is norm).

I get minor backfires and popping when driving, but it only happens A)when shifting, which is rare. or B)If I hold it in gear and decelerate, once it passes down through a certain rpm range, say 5500-3000 rpms, it will pop and crackle til it approaches idle speed and then stop.
 

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second chimp in space
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Set your idle at 1200.

Air filter and pipe can kill your midrange-WOT without a rejet, but they don't affect idle much.

If you don't have prime, I guess you'll want to really make sure that hose isn't crimped.
 

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you are running lean, need to rejet. the temp there isn't going to affect it that much. it's not like you are talking extreme temperatures. the bike was already jetted to run at your temperature, then you changed the airflow on the bike which is going to run in the same temp. you pretty much increased all the things to do with air, and you aren't giving it more gas.

if you have flat spots an acceleration, you need to rejet.
 

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Discussion Starter #13
Sorry I haven't been able to get to it...I've been working 40 hrs +
overtime for the past several weeks now and just haven't had the energy to work on anything mechanical---I do that enough at work. Lol, but the second I get the chance, I'll pull my plugs and see what they read....I don't know why I never thought of that.

All work and no play make me a stupid boy

Anyways, within the next few weeks the bike is going back to the shop, for a full out dyno-tune, and I'm gonna tell them to order the jet kit if they need it. I think I'm also going to order a sprocket while I'm at it....maybe up 2 teeth in the rear. :D
 

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HalfLiterBeater said:
I think I'm also going to order a sprocket while I'm at it....maybe up 2 teeth in the rear. :D
:headbang
Do it. You won't regret it. Especially pulling off the line or doing freeway speeds at length. Go up at least 2 (should be a 43 for you) and it will be a different bike.
 

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Discussion Starter #15 (Edited)
I figure I might as well since I've already modded the hell out of it (and I can call what I've done "modded the hell out of" because all the 500's I see around here, and most I see in photos, are stock, or nothing more than a pair of slip-ons... Just ordered a Sunstar 45 tooth rear sprocket. They had a JT sprocket for like $8 cheaper, but it didn't look nearly as cool...it was stock-looking and dark metallic, the one I ordered looks like billet. Stock, I was told, is 42 teeth. So I went +3 in the rear.

Anyways, off to drink like a madman again and dream about pulling roll-on wheelies FINALLY! :alky :alky :twofinger
 

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If I remember correctly stock rear sprocket for '94+ is 41 teeth. I'm running a 44 tooth rear and it's nice. But the pre '94 have a 42 tooth stock. Newer or older 500's without a modded sprocket don't feel right to me because they lack the low end pull it gives. You'll like it.

My bike is a '91 by the way.
 

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Discussion Starter #17
So....you're telling me I may have just gone up 4 in the rear? Ahhh, you're right! I just read a spec sheet comparing the changes between models.... Uhhhm......UH OH! THIS is gonna be interesting.............. ROLL ON WHEELIES :headbang

I just might make this the last time I spontaneously order parts while drunk...
 

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Half - How's the sprocket been?
 

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Discussion Starter #20 (Edited)
Oni said:
Half - How's the sprocket been?
Fun. Fun as hell. Now I get just need to get the speedo/odo corrected. But I tell you man...the bike is fast now. REAL fast. :D

Oh and since I just noticed this is one of my old posts about the carb problems...I fixed it. The idle mixture was set too rich. A few turns on each carb and it idles smooth now.
 
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