David Mcfadzen
Member
Please help, i have had recently a fair bit of idle hang, especially when i have been cruising slowly, it will actually idel up after i have let go of the throttle up to 4 grand untill the cluch starts to engage then idle back down to 1800 were it is set. Or i can quickly hit the choke and it will idel right ba k down. Tonight i took off the carbs again and cleaned + re-set the fuel screw to 2 turns out, raised the main needle to 4th notch down both washers on top thinking it was from running lean. This did help with the hard "warm"starts but not with the idle up on its own after i let off. It doesnt apear to have any tears in the boots or anything so yet again i am baffled with my viper. Anyone have any suggestions would be greatly appreciated.
super1c
Super Moderator
The idle hang on a viper is and has always been a mystery!!!!! I tried every cure on this site with mixed results. The scoop on the idle hang is the pipe is soooooo tuned that at a certain RPM the pipe runs so well it doesnt no enough to idle down. When warm it is worse. I have had best results with turning idle down to 1200-1000, she will shake like a washer on spin cycle at those idle rpm's but it takes care of it for the most part. You already have fuel screws at 2 so thats good. I have gone as far as 2 1/4 and it helped some but not for the most part. Best cure i found is just blip the throttle a few times comming into every stop. same effect as hitting choke really quick just easier. As long as your sure you dont have a lean idle as in a air leak this is the way to go. To check for a air leak get some carb cleaner or starting fluid and spray it at carb boots and all around. If the idle goes up you have a leak there. But my money is just the normal PIA idle hang!!
David Mcfadzen
Member
Thsnks for your imput and yes i have sprayed carb cleaner and no difference in idle, i might just put new needle and seats to see, also would increasing my pilot's from 145 to 150 help? If this is how its going to be im going to have to put Electric start in the old girl to help with the sore shoulder.
super1c
Super Moderator
Those sound like main jet sizes. This is from total memory but some guys did go up a jet size on the pilot from 45 to 47.5. it's one size up regardless if I got number right. I did this and did not like it. Got to be a bit to much and had a slight bog on take off. Your start should have nothing to do with this. I do recommend e start either way! LOL. Best mods I did to my Vipers. But a viper starts very easy cold or warm. If your having a hard time starting when warm crack the throttle a bit when you pull and it will fire in half a pull. Another Yamaha quirk!
brethren
New member
When the idol hangs, try flipping the fuel enricher (choke). If the idol goes down you are running a lean idol. Most common cause is partially blocked pilot jet. In this case you need to take out the jets and get very thin wire and run it through them. You can use guitar string or strip some stranded automotive wire. You can also kink the wire to scrape the inside of the pilot jets. If the idol still hangs after a good cleaning, turn the fuel screw out in quarter turn increments, but not more then 2.5 turns out. I have also read that there is an O ring that dries out behind the fuel screw.
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BornYamaha
Member
Listen to Super1c. He is spot on. Tried all the things he mentioned. Even up 2 sizes on pilots for a while. That helped a little but was too rich and hurt mpg alot. Cleaned carbs within an inch of their lives. I also understood that it had to do with the pipe.
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super1c
Super Moderator
As long as your sure there is no air leak, which you said you didn't have it's just the viper idle hang. I will state this again "ITS NOT A LEAN CONDITION" and is not a symptom of dirty carbs. Just do the screws at 2, idle down to 1200 and blip throttle comming into a stop. The pipe hangs up and wont idle down when warm.
I had a viper that had the same idle hang you are talking about and it ended up being a crack in the manifold, might be worth checking.
02Viper24
New member
Every time my 02 and 03 had this problem I just cleaned the carbs really well and it was fixed. The carbs on these are very finicky.
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pete_man26
New member
Hmm.. little off topic but ever since I put my 835 together with the BB pipes i'm having a similar issue. I know I'm super rich because plugs are soaked and loads up after idling if I bring it up to engagement and whack it. Never new it could be because of a really good tuned pipe.
brethren
New member
I found this thread, might be worth looking into
http://www.totallyamaha.net/forums/showthread.php?t=99826
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The Viper motor idles up because it can 
A well respected engine tuner did an article on this topic some time back using his own knowledge as well as input from Yamaha Techs. Several factors were cited including the pork-chop crank, the flow of the tuned pipe, being a triple, etc.
Seriously I would be a lot more concerned with your fuel mixture just off idle and up through mid-range on this motor.
That said 4K is awful high, so it wouldn't hurt to check the intake, carb sync, the carbs themselves, etc. (most mentioned above) to make sure all is in order.
I like to set the Vipers down to around 1200 - 1300 rpms at idle. Don't overlook any of the carb circuits and air flows.
A well respected engine tuner did an article on this topic some time back using his own knowledge as well as input from Yamaha Techs. Several factors were cited including the pork-chop crank, the flow of the tuned pipe, being a triple, etc.
Seriously I would be a lot more concerned with your fuel mixture just off idle and up through mid-range on this motor.
That said 4K is awful high, so it wouldn't hurt to check the intake, carb sync, the carbs themselves, etc. (most mentioned above) to make sure all is in order.
I like to set the Vipers down to around 1200 - 1300 rpms at idle. Don't overlook any of the carb circuits and air flows.