rpm hang-up
 

while riding home yesterday my "bone stock" bird started acting up at a stop sign. now it happens when ever i crack the throttle.

basically when ever the throttle is revved the rpms climb and then hover at about 2000rpm before slowly returning to idle. my first instinct was to lube the cables, done. then adjust throttle freeplay, done. perusing the service manual couldnt find anything of the sort. perusing the forum couldnt find anything that i could put to use. what should i check next? oh yeah! it is an03' bone stock. no past issues

My dual-sport does that same thing when the carb jets get partially plugged and need a shot of carb cleaner sprayed through them - of course its a lot easier to get to the carb on it than the 'Hawk's carbs...

Check for a vacum leak. Check the line to the fuel petcock first. If that is it take a can of carb clean and spray some the carbs and see if your motor revs up at all

Have you removed the tank recently? Sounds like PVLIR but if you haven't moved any vacuum/fuel lines recently then I'd lean to either petcock problems or carb needing cleaned.

Mine does the same but I've yet to rip into her and do any maintenance. I plan on doing a good bit of stuff this weekend and I'll look into what mine does and report back. It's not annoying but I do notice it. At first I thought it was my riding style or position of wrists on the bars thinking that I was not letting the throttle return all the way back. Turns out that it's just hanging up for a secord then drops to my 1200-1400 RPM idle. It seems the hotter that day the more prone it happens which makes me think of throttle cable getting stuck from gunk getting hot and sludgey. Won't know until I tear into it this weekend.

It's probably not the throttle cable getting stuck. I've always blamed it on the air temp and air/fuel mix. As it gets warmer outside the air gets a little thinner causing a slight rich condition. Kind of like having the choke on for a second.

I may be way off, just what I have always thought. My '03 has done it since stock and every step along the way. Even after jetting. Just a quirk of the VTR I guess.

thanks for posting up. the weather here is 100+ every day. i feel well ahead of where i was yesterday. couple questions though. as far as i know there is no petcock only a fuel valve so i will assume they are the same. also my skills of abbreviation are not what they should be, what is "PVLIR"? if carb cleaner is sprayed into the carbs and the motor does indeed rev up what does that indicate?

With the carb cleaner he was talking about looking for a vacuum leak. I don't think he meant spray it "into" the carbs, this would cause the engine to rev for sure but tell you nothing. He probably was trying to say spray around the carb boots and see if they have any leaks. If the rpms go up and the only place you sprayed is the boots then you know it is leaking.

When asking about removing the tank it's possible(and easy) to put the vacuum lines back on wrong. If you put the little line on the bottom of the petcock instead of the back it will cause the bike to run poorly.

ahhh. some of the clouds are clearing. i am just getting ready to remove the tank, but have not done so in the two years that i have owned it. so that rules out any connectivity errors up to this point unless some how they have worked themselves apart. the condition just started the other day. something inside says "something just aint right":confused:

Depending on how many miles you have that could be the issue. Have you replaced the air filter at all?

I wouldn't tear into anything just yet though, try replacing the air filter with another OEM and consider running some "seafoam" through the bike. It works wonders, and if you do have a clogged jet or something similar it should clear right up with that.

ok time for my ignorance to become more apparent if not already so. what is "seafoam"??

It's a brand of fuel system cleaner. Well, it does more than that actually. I use it with every other oil change too, let the engine warm up, pour the amount into the oil fill port that the can tells me to, then run the bike for 10 mins before draining and changing the oil.

Find it at advanced auto and just follow the directions on the can.

please i beg you be patient with me! how does adding something to the oil

"pour the amount into the oil fill port"

have an effect on on the fuel sytem? and thanks for the tip on the air filter. start with the easy stuff first.:thumbsup:

ok i looked up "seafoam" and found there website. apparently it can be added to both the fuel system and the crankcase. kind of like aspirin for the bird


:boom:

seafoam is weird stuff, but GM actually uses it at their dealerships IIRC.. For whatever that is worth.

And the PVLIR I was talking about is as explained: Petcock Vacuum Line Inadvertent Relocation, can happen when you remove the tank, so that is not possible. (and it does have a petcock of sorts that is vacuum operated.

Spraying carb cleaner at the vacuum hoses while the engine is running is a time tested way to find a leak... :P My gut still points to this, or perhaps a bad diaphragm in the petcock. But I am no expert.

I also think mine might be related to air temp. Last night we had great riding weather here and actually had a few cool spots outside of the city limits. Bike never did the hang up. Only seems to do it on mine when I'm in the 90+ temps and even then its doesn't do it 100% of the time. I'd say maybe 10% in the low 90's and about 35% if its a real balmy and humid 96+ day here in the south.

Thinking about this though, my previous car did the same thing from day one off the showroom floor. It was just a trait of the car as everyones did it.

I'm not too worried about it until it seems like it might be affecting performance or idle. Unless of course someone thinks I should be :D

"Petcock Vacuum Line Inadvertent Relocation"= PVLIR

i learn something new every dam day.

i really didnt think about it during the much cooler morning ride. i will see what happens in the morn.

thanks

just thought i would post up about the morning and afternoon commute. my current state is definitely not temperature related. it was 66 deg F when i left and it happens everytime the throttle is closed at anything over 3000rpm. it is quite the nervous feeling while cornering because the revs dont drop the way they normally do. same condition existed on the way home when it was 102 deg F. glad the weekend is here.
cheers

Does it do it regardless of clutch position? Or just when the clutch is pulled in?

it does it regardless of clutch position. what about the choke? is it possible the "se" valve is not seating properly?

could be, but it's starting to sound more and more like a vacuum problem. Carb slides maybe.

well i wanted to see how things were functioning under the airbox so i removed it. i found that the "se valve nut" had cracked right where the threads end and the little flange seats against the carb body. the spring and needle were just kind of flopping around and not working as intended. so for now i will assume that this is the cause of the condition. so far i have not found a source for individual components of the choke. so more than likely i will have to buy it as an assembly. any thoughts? any cool mods while i have it apart?

over a month and now i am on the road again. still isnt just right. reason for the delay. i was sent the wrong air filter twice. while it was down i removed the pair system and added and routed vacuum lines for better access to carb syncing. the se valve repair did not solve the problem. so while inspecting for vacuum leaks i think the rear carb insulator band may have a slight leak, but never having had the carbs off. still a bit perplexed by it all. and while riding it today it i could not escape the feeling that i cant remember how it ran before. so the seafoam is going through and if anyone has any thoughts i would love to hear them

it's a lean indication. reading factory pro tuning guidelines:

idle hang then falls: lean
idle drops then rises: rich


i would spray some wd-40 around the carbs looking for a vacuum leak... if that tests ok i would try turning the air/fuel mixture screw out 1/2 turn.


tim

ref: http://www.factorypro.com/tech_tunin...m_engines.html

excellent stuff thanks

just to be clear we are talking about the "pilot screw"??? any idea's or links for the right tool for the job. the manual specifies a tool. and there are some pretty good horror stories about the process. the aftermarket was pretty good to my dirtbike in this area. how lean could it be? not a good idea to ride it in its current state?

From what you describe, an air leak is still likely I think. Most carb adjustments needed for the mixture tend to be minor when it comes to temp or altitude changes. You say it is not the temp that does it though.

You can try the mixture screws and see what happens. Just make sure you know where they were before you adjust them. I guess you could call them "pilot screws" as they work in conjunction with the pilot jet, but the common name is mixture screws. Motion Pro make a good tool for adjusting them. You will need to turn them out to add more fuel.

I would be looking for a fault though from you are telling us. Spraying around the engine works well for finding air leaks. I have used water with success. You will notice it immediately if it suck a bit in.

i am in the process of checking for air leaks. the tank is off. it has no effect at the rear carb or the vacuum ports. the front carb is more difficult to test with out removing the air box. so that will need to come off. is there anywhere else i should be spraying? did i mention the new air filter is a k&n. would that add to the possibility of a lean condition?

Most def. The K&N will require you to rejet the bike or make some allowances to richen the fuel mixture. if you dont want to re jet im strongly belive in flo commanders, read up on them it can richen your bike and sync your carbs without the hassle of rejetting...a bit spendy thou..

*Straps on flame suit.

thanks for posting up. i will pop the factory air filter back in and see if it has any effect. flo commander looks pretty cool i didnt actually see a price though. re-jetting(buy a hand full of bigger ones and try 'em all) looks to be about the same effort as adjusting the pilot screw without the proper tool.

cheers
man your 98' must be wheelin' wit all dat stuff