SuzukiSavage.com - Shortened air-filter pipe leads to sputtering

Moarpower

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Shortened air-filter pipe leads to sputtering
05/13/23 at 21:49:04

Hey guys,

I relocated my battery and reinstalled the stock airbox as an electronics and wiring box.

My setup is as follows

DR650 Cam
96.5mm piston
155/47.5 jets
Pod style filter
Straight exhaust with minor baffle

I originally had the pod filter on a 90-degree pipe that was about 10cm long. The bike ran great.

Now I have removed the longer pipe as it wont fit with the installed airbox. Same filter however the bike sputters at high revs, especially if accelerating quicky. If I don't climb the rev range fast it can still make it up to speed.
I have tried adjusting the carb from as little as 1 turn all the way out to 3 and it keeps presenting the issue, though it is very slightly better at 1 to 1.5 turns out and worse at 2-3.

I have a bigger pilot jet coming already but I doubt this is the issue

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« Last Edit: 05/13/23 at 23:28:03 by Moarpower »

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justin_o_guy2 Serious Thumper Offline What happened? Posts: 55279 East Texas, 1/2 dallas/la.	Re: Shortened air-filter pipe leads to sputtering Reply #1 - 05/14/23 at 03:38:20 Years ago I was reading about intake design. The only thing I remember is it said You need a volume between the filter and carburetor that is at least equal to the volume of the cylinder. I don't have a link, I probably searched Intake design theory
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Moarpower Senior Member Offline SuzukiSavage.com Rocks! Posts: 331	Re: Shortened air-filter pipe leads to sputtering Reply #2 - 05/14/23 at 04:21:27 But surely most people just have their filters mounted straight to the carb tho?! I probably need to adjust the needle or something
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LANCER Serious Thumper Alliance Member Offline Savage Beast Performance Parts Posts: 10593 Oklahoma Gender:	Re: Shortened air-filter pipe leads to sputtering Reply #3 - 05/14/23 at 05:20:44 Straight pipe wit minimal baffle ? Try a larger pilot jet. Re/adjust pilot screw.
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Moarpower Senior Member Offline SuzukiSavage.com Rocks! Posts: 331	Re: Shortened air-filter pipe leads to sputtering Reply #4 - 05/14/23 at 05:25:13 Yeah it's a drag pipe with an almost useless baffle in it. I really think it does nothing at all. I have a larger pilot jet coming but I thought that would only affect lower throttle ranges? . Any idea how I should set the needle with this setup?
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Dave

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Camp Springs, Kentucky
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Re: Shortened air-filter pipe leads to sputtering
Reply #5 - 05/14/23 at 09:01:52

The pilot jet has no affect on how the engine runs once you get over 1/4 throttle.

Make sure the pod filter you are using does not obstruct the oval shaped port at the top of the carb inlet. That port allows air to reach the area under the slide diaphragm....if you block that area the air jets and slide cannot operate properly.

155 main jet is likely too big and the engine will run too rich at higher throttle settings.

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Moarpower Senior Member Offline SuzukiSavage.com Rocks! Posts: 331	Re: Shortened air-filter pipe leads to sputtering Reply #6 - 05/14/23 at 14:07:57 Thanks Dave. The 155 had been able to be tuned to run well with the longer intake pipe. This issue has me stumped. Currently the the needle only has the brass clip on the top position with no washer
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Dave YaBB Moderator ModSquad Offline SuzukiSavage.com Rocks! Posts: 17804 Camp Springs, Kentucky Gender:	Re: Shortened air-filter pipe leads to sputtering Reply #7 - 05/14/23 at 15:23:33 Look at this thread: http://suzukisavage.com/cgi-bin/YaBB.pl?num=1347609265
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Moarpower Senior Member Offline SuzukiSavage.com Rocks! Posts: 331	Re: Shortened air-filter pipe leads to sputtering Reply #8 - 05/14/23 at 15:51:51 Wow thanks Dave The longer pipe is a more solid material than the rubber of the filter so this could be it !
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DragBikeMike

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Re: Shortened air-filter pipe leads to sputtering
Reply #9 - 05/14/23 at 16:21:41

Moarpower, can you post some photos of your installation so we can see exactly what you are wrestling with?

You mentioned that you are running the slide needle clip in the "top position" with no washers. Is there any chance your needle is being pulled out of the needle jet when the slide is in the uppermost position? Does your slide needle have any markings on it? Markings that would identify the needle, like 5C16 or 5C39? Is it possible your slide needle is some sort of aftermarket part, like from a carb kit?

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Moarpower Senior Member Offline SuzukiSavage.com Rocks! Posts: 331	Re: Shortened air-filter pipe leads to sputtering Reply #10 - 05/14/23 at 16:39:58 Thanks Mike. I'll take a bunch of images tonight.
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Moarpower

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Re: Shortened air-filter pipe leads to sputtering
Reply #11 - 05/17/23 at 19:00:30

Very frustrated by this issue!

I made sure the hole at the front of the carb intake was not blocked by the filter, even added a 10mm spacer to make sure.

All i did was fit a pod filter to the carb directly and its sputtering horribly when I try to accelerate quickly and wont go over 80kmph as it just sputters.

Low revs are fine and it will rev pretty well while stationary.

I pulled the carb and gave it a thorough cleaning and it still happens.

Is it really likely that the shorting of the intake runner caused such an issue ? If so is it a lean or rich issue that I have to figure out.

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ohiomoto Serious Thumper Offline SuzukiSavage.com Rocks! Posts: 2681 WTF is JOG?	Re: Shortened air-filter pipe leads to sputtering Reply #12 - 05/17/23 at 19:31:26 Make sure your slide isn't worn and sticking.
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Moarpower Senior Member Offline SuzukiSavage.com Rocks! Posts: 331	Re: Shortened air-filter pipe leads to sputtering Reply #13 - 05/17/23 at 21:29:15 how can i test that? With the carb out of the bike it moves up and down freely
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Moarpower

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Re: Shortened air-filter pipe leads to sputtering
Reply #14 - 05/17/23 at 21:32:12

Today i replaced the slide needle. The one that was in the bike only had one slot for clips. The new one had 3, the middle of which lined up with the single slot on the old one.

I tried on all 3 settings with next to no difference.

I also tried blocking different amounts of the air filter with tape, but again no change.

The bike takes of as quick as always but cant make it all the way through the reve range.

Could this issue be something relating to spark delivery at all ?
I just want to ride this bloody thing. Unfortunately I cant put the old intake pipe back on to see if it fixes things as its damaged and there is no longer any room for it. I will need to get a 90 degree runner

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