SuzukiSavage.com - sputtering in the mid-range

Tocsik

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sputtering in the mid-range
06/16/14 at 09:24:59

I live in Denver (so, roughly 5280 altitude) and I'm new to this motor.
Bone stock for now except one of the PO's already removed the brass plug over the mixture screw. Bone stock meaning stock airbox and muffler. I do have the Raptor petcock installed already.

It feels kinda cold-blooded in that it runs better with the choke pulled out some for several minutes when riding on mornings that are over 50 degrees and I get some backfire on downshifts and the big kapow when I shut it off on warm days.

I notice it sputters in the mid-range almost all the time but pulls great in the higher RPM's. I turned the mix screw in while counting the number of turns and it was about 3 turns out. I backed it out the same and added a 1/4 turn to see if anything changed but it didn't.
I figure I need to clean the carb but thought I would toss it out there for feedback before digging in. I have my Dyna muffler in hand and now I think I should have it running smooth with the stock set-up before switching pipes so I have a better idea if re-jetting will be necessary.
At my altitude, what's the recommended number of turns out for the mixture screw as a starting point?
Any suggestions regarding the mid-range sputtering (other than cleaning the carb)?

Thanks.

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Serowbot YaBB Moderator ModSquad Offline OK.... so what's the speed of dark? Posts: 28660 Tucson Az Gender:	Re: sputtering in the mid-range Reply #1 - 06/16/14 at 09:30:07 You are really high there... I'd put on the muffler and leave the jetting as is... It may work really well... Some folks at that elevation have had to reduce jetting, rather than increase... Install... then jet... (you'll see an improvement or a worsening.. and this can clue you which way to go)...
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roadwarrior

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Re: sputtering in the mid-range
Reply #2 - 06/18/14 at 05:32:29

hiya i have just cured my backfire issue all together and the bike runs great now with no embarrassing backfire on down shift or rev.

on the side of the carburetor there is a little cover with three screws and behind this is a vacume diafram it shuts off fuel supply to the engine when coasting in gear or when you let go of throttle after a rev.

simply take of the cover and there is a spring so be carefull not to lose it as you take the cover off.

then remove the diaphram and place a small washer that fits over the brass centre piece,but not so wide that it hinders the diaphrams action (in and out). put the diaphram back in and the spring,cover. job done in ten mins.

what this does is allow fuel to pass through on down shift like normal bikes so no back fire and no dog farts.

im happy i finnaly got it sussed as i rebuilt this bike from bits n bobs as it was stripped and layed to waste. misses loves it and so do i now its noticably better on acceleration and performance too. hope this helps bud

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Dave

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Re: sputtering in the mid-range
Reply #3 - 06/18/14 at 06:12:51

roadwarrior wrote on 06/18/14 at 05:32:29:

on the side of the carburetor there is a little cover with three screws and behind this is a vacume diafram it shuts off fuel supply to the engine when coasting in gear or when you let go of throttle after a rev.

The TEV (Throttle Enrichment Valve) actually opens to allow more fuel to flow when there is a high vacuum (coasting) and the throttle is closed. By placing a washer behind the spring you are making the valve flow less fuel during periods of high vacuum.

When you are coasting with the throttle closed, the high vacuum can pull a lot of air past the throttle plate - but very little fuel can flow as the needle is blocking the needle jet. The only fuel that flows is from the pilot circuit, and this is not enough fuel to make rich enough fuel/air mixture that the spark plug can ignite in the cylinder on each stroke - and a lean unburned fuel/air mixture goes into the header and is either ignited by the next time the mixture does ignite in the cylinder and the flame travels into the header pipe - or the hot header pipe ignites the mixture. The TEV valve is supposed to supply enough extra fuel to make the mixture rich enough the spark plug can ignite it.

Placing a washer behind the TEV diaphragm either reduces the amount of fuel flow supplied by the TEV....or eliminates it. This may reduce the backfire frequency - by not allowing more fuel into the exhaust and thereby creating a mixture that is too lean to burn.

If it works for you....great. The replacement Mikuni roundslide carb does not have the TEV, and you can control the backfire easily by keeping the throttle open just slightly while you shift gears or decelerate. It also works on the stock carb - just keep your right hand on the throttle slightly so that you create the throttle setting you would have for a fast idle, and the backfires will be reduced.

Dave

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roadwarrior

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Re: sputtering in the mid-range
Reply #4 - 06/18/14 at 09:27:46

hi dave i appretiate the info and yes style of riding can get round the issue but i built the bike for the misses to learn on so i dont want to confuse her yet lol. from what i can tell it seems to work the other way around and shuts fuel of when on downshift and throttle off position. as you know the back fire comes from lack of fuel so placing the washer there means it cannot shut off the fuel flow entirly so it does not back fire and does not do the dog fart gun bang when turned off lol also it picks up better and rides much smother now even tickover is better it can run lower where as before i had to have the tickover high. but its def worth a try for anyone suffering this issue as its 100% cured the savage shes a 1989 one if that helps Roll Eyes

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Tocsik

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Re: sputtering in the mid-range
Reply #5 - 06/19/14 at 16:59:47

Tocsik wrote on 06/16/14 at 09:24:59:

I live in Denver (so, roughly 5280 altitude) and I'm new to this motor.
Bone stock for now except one of the PO's already removed the brass plug over the mixture screw. Bone stock meaning stock airbox and muffler. I do have the Raptor petcock installed already.

It feels kinda cold-blooded in that it runs better with the choke pulled out some for several minutes when riding on mornings that are over 50 degrees and I get some backfire on downshifts and the big kapow when I shut it off on warm days.

I notice it sputters in the mid-range almost all the time but pulls great in the higher RPM's. I turned the mix screw in while counting the number of turns and it was about 3 turns out. I backed it out the same and added a 1/4 turn to see if anything changed but it didn't.
I figure I need to clean the carb but thought I would toss it out there for feedback before digging in. I have my Dyna muffler in hand and now I think I should have it running smooth with the stock set-up before switching pipes so I have a better idea if re-jetting will be necessary.
At my altitude, what's the recommended number of turns out for the mixture screw as a starting point?
Any suggestions regarding the mid-range sputtering (other than cleaning the carb)?

Thanks.

__________________________________________________

Thanks for the replies.
I have the Dyna muffler on now but the bike still isn't running right. My morning commute is about 24 miles and even after half way (engine nice and warm) it ran better with the choke pulled out to the first click. I had to push it back in at stop lights because it wanted to die with the choke on when warm. Idled great with the choke in at the stop lights.

This sounds like it wants a larger main jet, right? At 5280 feet altitude, our air is already thin so bikes tend to run rich from the get-go.

The header pipe was perfect chrome when I got the bike with about 2800 miles. It now has about 3100 and the first 6 inches or so is starting to yellow/golden. That seems quick!

Any suggestions greatly appreciated. I really want to like this bike.
I have been searching and reading to gain insight but couldn't help starting a new thread to get some advice.

Did a bit (lot) more reading. Maybe white spacer mod? Even though the bike is stock with the exception of the Dyna?

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roadwarrior

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Re: sputtering in the mid-range
Reply #6 - 06/20/14 at 02:51:17

hello bud i would make sure your carb is clean to begin with then screw the mixture screw all the way in then unscrew it 3 and a half turns. also if you get a lot of backfire i would do what i said earlyer as mine runs sweet now bud. i fixed another savage yesterday doing the clean tune and washer in the diaphram on side of carb. let me know how it goes please bud as i seem to on it with this even though dave is in disagreement with me. its a simple cheap fix and it works a treat my savage is great at all speeds now

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