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Message started by red2k1 on 12/27/04 at 19:39:17

Title: Mid-Range Power & the White Spacer (Backfire)
Post by red2k1 on 12/27/04 at 19:39:17

This article may be linked somewhere on this site, but thought it would be helpful to have it here.

Savage Backfire
(from January 1997 RIDER magazine's Tech Q&A)

Q) I purchased a new Suzuki Savage 650 last July. From the very beginning the motorcycle would backfire when decelerating or coming to a stop. I took it back to the dealer twice before the 600-mile service, and complained about it at the initial service. I have tried different grades of gasoline and they seem to have no effect. The dealer has told me that I should expect backfiring with the design of this engine and that it should decrease as I build up mileage. I have 900 miles on the bike now and backfiring doesn't seem to be decreasing. I have found other riders of Suzuki Savages that are having the same problem. - Jay Coney, Kerrville, Texas.

A) This column receives a lot of mail over the course of a month, and the single biggest gripe among our readers are problems with lean-running. late-model carbureted bikes. The poor old LS 650 really suffers at the hands of the EPA, and I certainly sympathize with you, Coney. We can fix it, but first let me explain the hows and whys.

When the throttle of any engine is rolled or snapped shut, some fuel is drawn through the engine and kicked out the exhaust without being burned. In abundance, this raw fuel vapor can be smelled, tasted - and when light is passed through it- seen. It's referred to as photo-hydrocarbons or more commonly smog. Yes, there are several other pollutants coming out of the exhaust, but the human senses can't detect them. The manufacturer of motorcycles have three methods of dealing with excessive hydrocarbons. Forcing air down into the exhaust port with an air pump and diluting the outgoing fuel vapor is one method. Kawasaki pioneered this method with their 'Clean Air System', which employed a vacuum-driven pump that puffed air through reed valves placed over the exhaust system. A 'cat' is nothing more than an oven which bakes the hydrocarbons, burning them off.

The most common method is to simply lean out the carburetor. The low-speed and midrange circuits of the late-model carburetor are not adjusted to give optimum performance - they're set up to produce a minimum hydrocarbon count on deceleration. What miserly amount of fuel they do deliver to the combustion chamber when the throttle is closed causes misfire and an audible afterfire in the exhaust pipe. Now, I haven't mentioned fuel injection or other exhaust gases. As I said, the bulk of complaints from readers of this column is deceleration backfire and also poor idling of carbureted engines. No doubt we'll get around to discussing other emission-control devices and their problems in future issues.

Getting back to your Savage 650, Coney, here's how we can specifically cure its problem. We need to richen those two areas of the carburetion curve that are factory set on the ridiculous side of leanness. Remove the diaphragm slide from the carburetor and look down inside its bore. Two small screws hold a plate over the slide needle.

Removing the plate, you'll see a small, white plastic spacer with a hole through it sitting on top of the needle. Throw that spacer away and reinstall the plate. A spring under the needle clip will now push the needle up to the plate occupying the space vacated by the white spacer. The distance that the needle has been 'lifted' is the thickness of the discarded spacer - and that's ideal. With the needle raised, more fuel will flow by it, meeting the actual needs of midrange running.
We can also fatten up the low end of your bike's carburetor by turning out the low-speed mixture screw. To gain access to this screw, you'll need to drill out the brass plug pressed in over it and yank it out with a sheet-metal screw attached to a slide hammer. You'll find that plug up high on the right side of the carb about where the mouth enters the carburetor. Usually Suzuki applies a splash of white paint over the brass plug so that it's immediately noticeable. With the engine warmed up and idling, turn the mixture screw out incrementally until you achieve the highest idle. There will be no doubt in your mind that you're making progress because the idle will come up and sound stronger. At this point, turn the idle adjuster knob out and bring the idle back down to a leisurely gait.

Just these two, relatively simple adjustments will not only eliminate the backfire, they will make an amazing improvement in throttle response and driveability.


Title: Re: Mid-Range Power & the White Spacer (Backfi
Post by Nightrain on 12/28/04 at 08:43:41

here is the percentage of throttle that the different jets manage. Note the overlap


http://www.dansmc.com/carb_jet_usage1a.jpg

Title: Re: Mid-Range Power & the White Spacer (Backfi
Post by rkutzner on 12/31/04 at 13:59:28

Only remove 1/2 of the spacer at first or at least replace with one or 2 #4 washers so that the dimple in the plate can do it's job. A few on this site have reported that removing the whole spacer causes an over rich condition in the mid range and even a raw feul leakage at idle that was corrected with putting some 'space' back in.

Mine runs great with a 1/2 spacer.  Local conditions will determine YOUR proper amount of 'space' to remove...but just tossing it all is assuming too much and may cause you other problems.

IMHO  ;)

Title: Re: Mid-Range Power & the White Spacer (Backfi
Post by red2k1 on 02/08/05 at 16:16:28

Have to agree with rkutzner on the spacer. Have now had the chance to test with three different spacer conditions: none, 1/2 and 1/3.  For my bike and where I ride, the 1/3 spacer proved to be the most driveable and the best compromise in terms of lost mpg. --- am running a 155 main.

Title: Re: Mid-Range Power & the White Spacer (Backfi
Post by bobo383 on 02/08/05 at 18:56:58

I agree with red2k1 agreeing with rkutzner.  My bike flooded at idle with the spacer totally out.  

Half spacer is good for my bike with a 155 main and hollowed-out stock pipe.

Title: Re: Mid-Range Power & the White Spacer (Backfi
Post by bobo383 on 03/11/05 at 20:24:44

You're right, low and mid range performance stunk.   I've since put on a sportster muff and got my power back.  Sure do miss the loudness though.
Just for kicks while I had the muff off I ran with the open header for about 10 minutes.  LOUD!  So loud it was near painful.  Ran OK, but not good.  

The sportster muff is the best performance I've had so far, and no backfires with a 155 main and half-spacer.  Sounds decent, but not loud.

Title: Re: Mid-Range Power & the White Spacer (Backfi
Post by tarheel365 on 03/21/05 at 05:45:28

I looked at the carb specs post and noticed the older savages had a 155 main...i have an 87

does that mean i still have to go up a jet to change to a sporty muffler?

is it difficult to remove the brass plug?  

thanks

Title: Re: Mid-Range Power & the White Spacer (Backfi
Post by bobo383 on 03/21/05 at 07:27:36

You're probably OK with your 155, just try it and see how it runs afterward.  If it backfires or has lousy throttle response you can jet up or play with the spacer thickness on the needle.

I drilled out my brass plug and pried out the remains.  I went a little too deep, hit the mixture screw and boogered it up.  But there was enough of a groove to be able to remove the screw and cut a new groove for a good screwdriver bite.  It ain't that hard, just pull out the bit often to make sure you're not going too deep.

Title: Re: Mid-Range Power & the White Spacer (Backfi
Post by Savage_Rob on 04/15/06 at 22:11:13

Below are some photos by Steelwolf from his white spacer mod to help anyone doing this.

http://suzukisavage.com/images/uploaded/SteelWolfCarb01.jpg

http://suzukisavage.com/images/uploaded/SteelWolfCarb02.jpg

http://suzukisavage.com/images/uploaded/SteelWolfCarb03.jpg

Title: Re: Mid-Range Power & the White Spacer (Backfire)
Post by BC-Savage on 04/28/11 at 13:22:40

hi Guys;
Correct me if I am wrong, but it looks like from the photos above, The Spacer, Main & Primary jets can all be accessed via removing the top cover of the carb. All the time never removing the carb from the bike.
That makes it a lot simpler job.

Title: Re: Mid-Range Power & the White Spacer (Backfire)
Post by verslagen1 on 04/28/11 at 13:45:33


080967192B3C2B2D2F4A0 wrote:
hi Guys;
Correct me if I am wrong, but it looks like from the photos above, The Spacer, Main & Primary jets can all be accessed via removing the top cover of the carb. All the time never removing the carb from the bike.
That makes it a lot simpler job.

Yep, you're wrong... or half wrong which is the same as half right.  Which one do you want to be?

Only the spacer can be gotten to from the top.

Main and Idle mixture jet are gotten to from the bottom.  Also can be done with carb installed.

Title: Re: Mid-Range Power & the White Spacer (Backfi
Post by verslagen1 on 04/28/11 at 22:19:54


6B6A047A485F484E4C290 wrote:
iS 4 5/8 OK, or should I be looking to re-jet enabling me to get that mixture sCrew closer to 3?

No, it's very likely that you loose the screw going down the road.  Go up to the next size.


Quote:
Also, I asked this in another thread, does the 86 carb have the white spacer too?

Yes, all models have the white spacer.


Quote:
And if I remove the spacer do I likely need to re-jet?

yes, maybe.  Raising the needle will add more fuel sooner.
Best to follow procedure and tune for the top end 1st then adjust the mid range.

Title: Re: Mid-Range Power & the White Spacer (Backfire)
Post by Russian Savage on 04/29/11 at 22:53:27

Ok just finished half of this mod. I pulled the brass plug, use a very very small steel drill bit and drill a small hole into the plug, try to get all the way through but don't hit the screw behind it. Then put a small drywall screw in it and twist using a hand screw driver. Just get it caught in there then grab it with a wrench and pull HARD. It takes a good bit of force but it will pop out.

I turned the screw out about 1.5 turns and fixed the backfire problem COMPLETELY! (My bike backfired on turn off before this)

I did want to do the white spacer mod as well but failed. >:(

The reason why I couldn't do it is frustrating. I lifted off the tank which was really simple, take the seat off then undo the screws and pull! I managed to remove the hoses and work on the top. After stripping all four screw on the diaphragm cover I drilled these screws out. I later replaced them with stronger, better screws. After finally getting the diaphragm out I tried to get the two screws inside it and stripped those too. I have the exact screwdriver for the job, the screws were just in TOO tight and were made of soft metal. I could not find a way to get them out without risking damaging the diaphragm so I just cleaned the carb and put it back together.

I really would like some help trying to find a way to fix this problem without spending much money. How to get those stripped screws out?

Title: Re: Mid-Range Power & the White Spacer (Backfire)
Post by azmav on 05/27/11 at 08:37:28

The only way I have found and has been recommended here on this forum to remove screws that are being screwy;-0, is to get a cheap impact driver at Harbor Freight or Auto Zone, etc.  When you hammer on the back side of it, it will force itself down into the screw head and ratchet out the screw. You might have to work at it to reach down in there, the tool will likely not fit so you will have to rig it.
787C6D7A6D667C6D7E080 wrote:
Ok just finished half of this mod. I pulled the brass plug, use a very very small steel drill bit and drill a small hole into the plug, try to get all the way through but don't hit the screw behind it. Then put a small drywall screw in it and twist using a hand screw driver. Just get it caught in there then grab it with a wrench and pull HARD. It takes a good bit of force but it will pop out.

I turned the screw out about 1.5 turns and fixed the backfire problem COMPLETELY! (My bike backfired on turn off before this)

I did want to do the white spacer mod as well but failed. >:(

The reason why I couldn't do it is frustrating. I lifted off the tank which was really simple, take the seat off then undo the screws and pull! I managed to remove the hoses and work on the top. After stripping all four screw on the diaphragm cover I drilled these screws out. I later replaced them with stronger, better screws. After finally getting the diaphragm out I tried to get the two screws inside it and stripped those too. I have the exact screwdriver for the job, the screws were just in TOO tight and were made of soft metal. I could not find a way to get them out without risking damaging the diaphragm so I just cleaned the carb and put it back together.

I really would like some help trying to find a way to fix this problem without spending much money. How to get those stripped screws out?


Title: Re: Mid-Range Power & the White Spacer (Backfire)
Post by LANCER on 10/14/11 at 08:21:05


7D786A686A636A0F0 wrote:
The only way I have found and has been recommended here on this forum to remove screws that are being screwy;-0, is to get a cheap impact driver at Harbor Freight or Auto Zone, etc.  When you hammer on the back side of it, it will force itself down into the screw head and ratchet out the screw. You might have to work at it to reach down in there, the tool will likely not fit so you will have to rig it.[quote author=787C6D7A6D667C6D7E080 link=1104205157/15#28 date=1304142807]Ok just finished half of this mod. I pulled the brass plug, use a very very small steel drill bit and drill a small hole into the plug, try to get all the way through but don't hit the screw behind it. Then put a small drywall screw in it and twist using a hand screw driver. Just get it caught in there then grab it with a wrench and pull HARD. It takes a good bit of force but it will pop out.

I turned the screw out about 1.5 turns and fixed the backfire problem COMPLETELY! (My bike backfired on turn off before this)

I did want to do the white spacer mod as well but failed. >:(

The reason why I couldn't do it is frustrating. I lifted off the tank which was really simple, take the seat off then undo the screws and pull! I managed to remove the hoses and work on the top. After stripping all four screw on the diaphragm cover I drilled these screws out. I later replaced them with stronger, better screws. After finally getting the diaphragm out I tried to get the two screws inside it and stripped those too. I have the exact screwdriver for the job, the screws were just in TOO tight and were made of soft metal. I could not find a way to get them out without risking damaging the diaphragm so I just cleaned the carb and put it back together.

I really would like some help trying to find a way to fix this problem without spending much money. How to get those stripped screws out?

[/quote]

Yes, Habor Freight has a small size impact driver for less than $10 and comes with a few driver bits, one of which is longer and fits the screws down inside the slide.  
It has been reported here that the tiny screws found inside computers work perfectly and are made of much harder metal so will not strip so easily.

Do not turn the pilot screw on the carb out more than 3 turns or it is possible to loose it on the road as mentioned.
When out 3 turns it is time to move to a jet one size larger and then adjust the pilot screw again starting at 1 turn out.
With a properly sized pilot jet for your engines setup, the pilot screw setting should end up being in the 1-2 turns out range when the engine is running at its highest rpm.  Then readjust idle rpm for 1100 rpm.
As long as the carb is CLEAN inside and everything is working properly then the carb will respond to jetting & tuning efforts.

Title: Re: Mid-Range Power & the White Spacer (Backfi
Post by LANCER on 10/14/11 at 08:56:42


5149484D4354534613210 wrote:
So first off, this guide is great.  However i'm having a heck of a time tuning everything just right.

Like many of you, i stripped all 4 screws on the top so I had to get a counter screw.  I even snapped the choke cap in half somehow from overtightening... so this has been quite the odyssey.  

Basically I got rid of the spacer, and went to 2 washers at first.  This had limited success, no matter how I set the fuel/air screw.  Today I went down to one washer, but it seems things only got worse.  Realistically I should aim for 3 washers, but I'd like to make sure that's the right course of action.

My main question is does turning the air/fuel screw out (counter clockwise) add more fuel to the mix?  With my one washer currently, turning out more makes the pop on shutdown even LOUDER.  I'm waking up dogs a mile away.  Kinda fun, but I don't really wanna be imitating Uncle Buck.  

Looking to reduce the backfire on shutdown at least, ASAP.

Thanks,
Phil



find stainless screws for the top for ease of use and providing a secure seal with the diaphram.
3 washers on the needle provides a good midrange fuel supply for most stock engines with most nonstock mufflers

you mentioned testing washers on the needle & adjusting the pilot screw together.  
keep in mind that the needle controls the midrange fuel circuit (1/4-3/4 throttle) and the pilot jet & pilot screw control the low throttle range (idle- 1/4 throttle)
adjusting the screw will make very little change on your midrange.

do the pilot circuit first, then needle and then main jet
set idle at 1100 and test drive
ALL ADJUSTMENTS MUST BE DONE WITH ENGINE FULLY WARMED UP or the setup will not be the most efficient for your engine when fully warmed.
go ride a few miles prior to jetting/tuning

**turning the pilot screw OUT will richen the mixture.

Title: Re: Mid-Range Power & the White Spacer (Backfi
Post by redsticksavage on 10/20/12 at 15:39:39

Today I did the 1/2 spacer and 1-1/2 turn of air mix screw mods, still running stock airbox, jets, and pipe.

The bike runs much better, before I had to run on 1 notch of choke all the time. Before the bike would frequently backfire on decel and when turned off.  Now it only backfires when I sharply decel.

Much improved but still not perfect.

Some hints I borrowed from this forum:

1. Remove the carb from bike and put it in a vise with wood and duct taped faced jaws.
2. Get the $5 harbor freight mini impact screwdriver, those screws on the diaphragm end of the carb are tight.  This tool has a Phillips tip that fits nicely all the screws on the carb without stripping.  And yes, impact in the form of repeated light but firm taps was needed to remove the ones on the diaphragm cover.

http://www.harborfreight.com/7-piece-reversible-impact-driver-set-93481.html

3. I replaced the diaphragm screws with Metric no 5 screws and used some anti seize when putting it all back together.
4.  Inside the diaphragm are 2 Metric no 3 screws that I also replaced as I nearly stripped the Phillips head on one before I again used the HF impact tool-no need for impact, just needed a well fitting Phillips bit.
5. I followed the forum advice and went to Ace where I found a black no 4 nylon washer and a white no 4 nylon washer, they were both identical except in color and both were about 1/2 the height of the stock washer. I used the white one.  While there I also picked up 4 no 4 brass washers as 4  together were the same height as the stock washer.  So I have these to play with if the white nylon washer doesn't work for me long term.
6. I drilled the brass plug with a very small bit and chucked it in my drill with only 1/8" sticking out and drilled a small hole that a 2-1/2 drywall screw could bite into.  It took me three screws before it came out.  I only used one screw per attempt to ensure I had a good bite into the brass since all this is happening at the tip of the screw. I also filed the tip down a little to avoid having it bottom out on the delicate air mix screw.  Not having a dent puller, I simply latched some vise grips onto the screw stuck in the plug and use a hammer and large screw driver against the face of the vise grips and sent the vise grips with the screw attached and brass plug attached flying away from the carb that was still mounted in the vise.

Note: I did compare these metric no 3 and 5 screws to computer case screws but the thread looked finer on the stock screws so instead of using computer case screws, I just bought replacements at Ace.

Thank you all for sharing your experience and making this job relatively easy for me.

Title: Re: Mid-Range Power & the White Spacer (Backfire)
Post by ROAD WARRIOR on 01/31/13 at 06:26:13

I have a 2012 s40 and replaced muffler, rejeted and used 2 washers replacing the white washer in carb.  It still back firers.  Will try going to 1 wash.

Title: Re: Mid-Range Power & the White Spacer (Backfire)
Post by Dave on 01/31/13 at 06:52:36


770B0E6E3D0 wrote:
I have a 2012 s40 and replaced muffler, rejeted and used 2 washers replacing the white washer in carb.  It still back firers.  Will try going to 1 wash.


The Savage will always backfire.......You should not be jetting with the goal of completely eliminating a backfire......it will never happen.  You need to jet with the goal of having the bike run smoothly, with good power and fuel mileage.

Title: Re: Mid-Range Power & the White Spacer (Backfi
Post by Ponzo on 07/01/14 at 19:32:55

After taking out the white spacer I forgot how the plate was installed... what's the proper way to install?

Title: Re: Mid-Range Power & the White Spacer (Backfire)
Post by verslagen1 on 07/01/14 at 19:35:41

holes over holes with the dimple pointing down.

Title: Re: Mid-Range Power & the White Spacer (Backfire)
Post by Ponzo on 07/01/14 at 20:00:04

That's what I thought and did. The backfire is gone but now on deceleration the motor stalls.. I'm not too sure what to do.

Title: Re: Mid-Range Power & the White Spacer (Backfi
Post by verslagen1 on 07/01/14 at 20:34:30

what did you put in place of the white spacer?

did you readjust the idle mixture?

did you readjust the idle speed?

Title: Re: Mid-Range Power & the White Spacer (Backfi
Post by Ponzo on 07/01/14 at 20:43:39


2B382F2E313C3A38336C5D0 wrote:
what did you put in place of the white spacer?

did you readjust the idle mixture?

did you readjust the idle speed?


I put two #4 washers and I did adjust the idle mixture and speed. It has a great idle.

Title: Re: Mid-Range Power & the White Spacer (Backfi
Post by verslagen1 on 07/01/14 at 21:24:07

turn the idle speed up a little.

doin' it by ear or meter?

Title: Re: Mid-Range Power & the White Spacer (Backfi
Post by Ponzo on 07/02/14 at 06:09:47


73607776696462606B34050 wrote:
turn the idle speed up a little.

doin' it by ear or meter?


  I'm pretty sure I got it fixed this morning by doing what you said and I turned up the idle speed and seems to be fixed. Thanks for all your help!!

Title: Re: Mid-Range Power & the White Spacer (Backfire)
Post by edsbike on 06/20/15 at 13:40:00

i did the air screw adjustment 1.5 turns out what a difference i noticed no backfire no hesitation while going 50 mph wanted to do the spacer but the last screw on the top of the carb stripped so its put it  off for a while untill i have more time

Title: Re: Mid-Range Power & the White Spacer (Backfire)
Post by Ultimafuego on 09/22/15 at 10:10:46

I ended up replacing the white spacer and the washer on the spring with nylon washers from ace hardware.  This gave me the best result.  I am running a harley sportster muffler and jets are 155/55.  The back firing gone almost entirely. Love it.

Title: Re: Mid-Range Power & the White Spacer (Backfire)
Post by Dave on 09/22/15 at 13:31:41


58617964606C6B78686A620D0 wrote:
I ended up replacing the white spacer and the washer on the spring with nylon washers from ace hardware.  This gave me the best result.  I am running a harley sportster muffler and jets are 155/55.  The back firing gone almost entirely. Love it.


Those jets are awfully big.....how much black smoke comes out the tailpipe?  Do you get about 40 mpg?

Title: Re: Mid-Range Power & the White Spacer (Backfire)
Post by Ultimafuego on 09/23/15 at 07:22:00

I have not checked the MPGs after the mods yet.  Before molesting the bike from stock it was at 53mpg on a road trip down I-75 at about 70-75 mph.  No black smoke at all.  I originally had the metal washer on the spring and 2 metal washers between the circlip and the plate but it was causing hesitation at low cruising speeds that were solved by pulling the enrichment out. I had to play with it a while to get it right, but the jets are about as good as it gets.  I think they are pretty high too but i may jet down a step and see where its at with the needle adjusted right now.

Title: Re: Mid-Range Power & the White Spacer (Backfire)
Post by funkspieler on 08/21/17 at 14:20:23

This mod has transformed my wife's 05 Boulevard.  I sanded the white washer with 120 grit until it was roughly half the thickness.  It went from popping several times an hour to popping about once a week, and only when transitioning from uphill to coasting downhill.  Power has also improved noticeably.  I thought this bike was a real dog but now it is a pleasure to ride.  Many thanks to the OP.

Title: Re: Mid-Range Power & the White Spacer (Backfire)
Post by BullGary on 10/15/17 at 20:38:53

Just did this mod. I found the original spacer was 2.85mm thick, but I had read to grind it in half down to 2.5mm, which doesn't add up. In any case, I took it down to 1.47mm-slightly over 1/2. After running a bit and shutting it off, boy did it give a huge exhaust backfire. I'm hoping that's just from the mixture screw needing fine tuning.

Title: Re: Mid-Range Power & the White Spacer (Backfire)
Post by Dave on 10/16/17 at 02:10:46

The spacer and needle position do not affect the bike at idle.

Open your idle mixture screw a 1/4 turn more.

Title: Re: Mid-Range Power & the White Spacer (Backfi
Post by ohiomoto on 10/16/17 at 07:52:15


3538373A3C2B6B6E590 wrote:
...

**turning the pilot screw OUT will richen the mixture.
------------------------
:-?

Is this confirmed?  Every carb I've ever worked on was the opposite.  Opening the the pilot screw lets more air into the system and leans the idle mixture.


EDIT:  I found a reference and LANCER is correct.

"The pilot circuit has two adjustable parts, fig 2. The pilot air screw and pilot jet. The air screw can be located either near the back side of the carburetor or near the front of the carburetor. If the screw is located near the back, it regulates how much air enters the circuit. If the screw is turned in, it reduces the amount of air and richens the mixture. If it is turned out, it opens the passage more and allows more air into the circuit which results in a lean mixture. If the screw is located near the front, it regulated fuel. The mixture will be leaner if it is screwed in and richer if screwed out. If the air screw has to be turned more than 2 turns out for best idling, the next smaller size pilot jet will be needed."

http://www.iwt.com.au/mikunicarb.htm



Title: Re: Mid-Range Power & the White Spacer (Backfire)
Post by Dave on 10/17/17 at 09:55:04

Ohiomoto:

The stock CV carb has an idle fuel mixture screw......turning it in restricts the flow of fuel, turning it out improves the  flow of fuel.

The Mikuni VM carb has an air mixture screw....turning it out allows more air to flow - which reduces the amount of fuel flowing at idle.

Title: Re: Mid-Range Power & the White Spacer (Backfi
Post by ohiomoto on 10/17/17 at 10:58:12


5B606D7A6B677C7A6169647B080 wrote:
Ohiomoto:

The stock CV carb has an idle fuel mixture screw......turning it in restricts the flow of fuel, turning it out improves the  flow of fuel.

The Mikuni VM carb has an air mixture screw....turning it out allows more air to flow - which reduces the amount of fuel flowing at idle.
-------------


Yeah, I just learned that yesterday.  Everything I've ever owned (mostly motocross bikes) had a VM carb or similar Keihin.   Even my old Triumph had a VM on it.  Learn something new every day.  :)  

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