# Bad stutter at 1/4 throttle



## gusguy (Aug 18, 2009)

I'm starting this in hopes of getting more traffic to my problem. I'm at my wits end with this machine. It spends more time with the body panels off than on and it's getting old. I kinda took over this thread but it has all my information,  Wheel speed sensor/ carb issue - Page 2 - MudInMyBlood Forums. 

Recap-
started breaking up out of the blue between 1/8 and 1/4 throttle
valves were adjusted today and it still acts up
does it stock cdi and dynatek
tried adding and taking away shims on needles
tried stock intake and 3" snorkel, runs worse with snorkel
158F 160R keihin jets
carbs have been gone through multiple times and should be clean
plugs are black
runs good after 1/4 trottle

Is it possible for the needles to wear out or something related to them. Any help is greatly appreciated


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## DaveMK1 (Nov 8, 2009)

You don't have any hairline rips in the diaphragms do you? Or possible they aren't sealed completely?


Sent from my iPhone using Tapatalk when I should be doing something more productive.


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## gusguy (Aug 18, 2009)

I looked them over pretty good last time I had them apart and didn't see any rips. Also made sure they were seated correctly. It sounds like it's dumping fuel down the cylinder and the plugs are black so that's what makes me wonder if something is worn out. The bike has 4900 miles so stuff is starting to wear out


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## gusguy (Aug 18, 2009)

So I got the right size fitting for my compression tester today. According to my cheap oriellys tester I'm at 50 psi front and rear. Is it possible this could be a voltage regulator issue or some other electrical problem. I'm reaching for anything here so any suggestions are appreciated


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## dman66 (Feb 20, 2011)

Did you check the fuel enricheners ( CHOKES ) ? Sometimes just the way the choke cables are routed to the carbs,the cables could pull and engage the chokes. Are the needles stock or Dynatec ? Have you tried tapeing up half the intake snorkle to see what results you get ? From what you are describing,it sounds like too much air into carbs on the idle end of the carbs or blocked pilot jets,which I believe u said they were # 40 pilots - where are the pilot screws set at ? Sorry for 20 questions.......


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## gusguy (Aug 18, 2009)

It's doing this with the stock intake on. If the chokes were stuck on wouldn't it be rich across the entire range. Stock needles with dynojet springs and pilot screws are at 2.5 turns out. The best way to describe it is it sounds like I'm in reverse with the stock cdi with out pushing the overide. The more throttle you give it the louder it pops and sputters untill you get going faster. It does this with stock cdi and dynatek


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## gusguy (Aug 18, 2009)

Another thing I just noticed while running it in the garage, after running for 5 minutes the rectifier started heating up. Wasn't hot but was pretty warm. Is this normal? I get 12.6V at the battery with it turned off and 14.6 with it running.


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## 2010Bruterider (Jun 20, 2010)

I'm pretty sure the rectifier is air cooled. So sitting and idling, I could see it getting warm. Your voltage sounds like it's doing the job.


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## gusguy (Aug 18, 2009)

So what about the coils? Is there any way they can fail at certain rpm's and be fine at others?


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## dman66 (Feb 20, 2011)

Even with stock opening,the chokes could act this way. Ive done the cable routing issue before.Is there new dynojet holes drilled into the slides as to where the plastic needle retainer could be sitting over one of these holes ? Have you checked the coils and replaced spark plugs ? With the quad running and the headlights on,is the voltage still at 14.6 - this regulator should not be an issue cause you would have higher voltage like 16 - 18 vdc if the reg. was bad,but you could try turning on headlights to high beam and turning on rad. Fan manually to see if it would clear the stumble - this actually worked on my old bayou 220 and had the stutter through whole range of throttle. And do you have a service manual to check specs ? If not I believe I could point you to a free one.


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## gusguy (Aug 18, 2009)

There are dynojet holes drilled but they've been there for 2 years so I don't think that has anything to do with this. I don't know how to check the coil packs but I do have a volt meter. I'm on my 3rd set of new plugs just to make sure it's not that simple. I turned the lights on in the garage with it running and ran through the rpm's and at no point did the lights flicker


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## dman66 (Feb 20, 2011)

If you have tried and checked all I have recommended before in the previous thread and this thread, then start from the beginning. But you did not report that you have retried all recommended. like covering the intake partially to see if the idle - 1/4 throttle clears up. i still think there is an issue with the pilots are blocked or carb could be dirty. alot of us reported that we cleaned our carbs multiple times with no effect,then do it again only to find something we missed.With all he mods you have now, did the quad run smooth all through the throttle. Check the carb vent line on the left side of the carbs to insure not blocked or full of water - easier yet, pull the vent line off the carbs and run her to see if problem corrects. Check the gas tank check valve to insure it works. And check the over flow carb bowl check valve to insure it works. You really need a service manual,cause there is a lot to check,and typing all of it is a lot of work. I took an hour to look for answers for ya,and keep coming back to my recommendations. We've all been through this stuff,stick with it, we will figure it out.


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## gusguy (Aug 18, 2009)

This has turned into another one of those threads where I don't really know what I did but it appears it's moving in the right direction. One of the last things I did earlier was check the coils and the stator and they were all good, so I put the stock cdi back on and went through the rpm's in neutral in the garage. The stutter was almost completely gone so I put the dynatek back on and it only stuttered a bit, almost like the famous dynatek stutter. So I pulled the carbs to switch to 42 pilots and that has almost eliminated all the stutter. It doesn't make sense cause I didn't need 42's last winter but this is where I sit right now. I put on a few miles after the change and it seems to be right. It was -18 when I pulled it out of the garage and went tearing down the highway wot. I don't know what that equates to in windchill but it iced my beard over immediatly. Gotta love the north woods. Dmann I appreciate all your effort and knowledge in trying to help me getting this heep going again.
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I also pulled the vents and blew them out. I don't know what changed the problem because I pretty much had my hands on everything on the top end but I diffinetly think I'm moving in the right direction. And that's 18 below zero for you southerners


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