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Hey guys I just ordered my exhaust for my bike and am going to order the Suzuki 125 & 35 jets for the carb. I have been looking for a write up with pictures showing how to change the jets but have had no luck yet. I have no experience with carbs and have no idea how to change the jets so if anyone knows of a link to a write up that would be great.
Thanks,
Matt
Drain the fuel from the carb by shutting off the main tap and opening the drain screw at the bottom right hand side. The fuel will run out through the drain hose. Place a suitable container under it.
Ideally you should be able to change the jets without removing the carb from the engine. There's enough clearance under the carb for access using short handled screwdrivers. The bad news is that the four little M4 screws that hold the float chamber are incredibly tight and the chances are that you'll round them off before they come out.
I had to remove the carb and use an impact driver. Not nice in such a delicate instrument such as a carb. Once the float chamber bottom is off, turn the carb upside down, taking care with the float assembly. This is a very fragile component and any knock could throw out the fuel level setting.
If you're going to handle the carb a lot, remove the hinge pin (just pushes out), that hold the floats and needle valve in position, and put it somewhere safe.
Use good fitting screwdrivers on the jets, try the drivers on the new jets first to ensure they fit well before you attempt to remove the originals. They're not on too tight but, being made of brass they burr easily.
This photo shows the positions of the jets. The Main one also has a washer behind it that is easily lost. Watch out for it falling down as the main jet is withdrawn.
The slow jet is fitted inside a sort of tube.
Count the number of turns your mixture screw is out for. Screw it in completely counting the turns until it bottoms gently. Don't force it or the needle-like end will get damaged. When you have the new slow jet in, this screw will probably only need to be unscrewed by 1/2 to 1 and 1/4 turns out. This is because the slow running circuit will have a lot more fuel through it now, due to the bigger jet.
I couldn't find a picture of our carb, but this one is similar. The differences are that the idle mixture screw on ours is at the top of the carb, next to the inlet manifold and the slow-speed adjuster is also at the top.
http://farm4.static.flickr.com/3114/...e50dcdfe69.jpg
There are several tuning guides about, like this one (a bit complicated!)
http://www.factorypro.com/tech_tunin...m_engines.html
This is how I did mine without taking it out of the bike;
http://web.mac.com/danoaks/www.dirtly.com/Rejet.html
It's same website that forchetto found with reguard to the risers.
Brilliant little guide there, thanks. I notice they had trouble with the screws and have replaced them with allen headed ones.Quote:
Originally Posted by david3921
It was only after struggling with the original ones that I read a tip that could be useful when dealing with tight cross-head screws:
Dip the tip of the screwdriver in a little fine grinding paste, of the type used to re-grind valves. This increases their grip no end and prevents the driver slipping out.
Thanks guys! That seems to explain it pretty good...I just hope I dont run into any problems trying to tune it with the mixture screw.
Hey guys I was looking through the service manual and if you look on page 109 it says our carb has a 127.5 main jet and a 32.5 pilot jet. Does it really have a 127.5 main because I just ordered the 125 main and I wont want to use it if its smaller then stock.
I've noticed that. It's probably for the Brazil market for some reason. Mine came with 122.5 main and 32.5 for the slow jet. It's not an error as I have a brand new spare carb and it also has 122.5 main.Quote:
Originally Posted by firefightermatt
One thing I've got to try is raising the needle. In the manual it says it has various slots to be able to adjust the main needle height, but I don't think mine has these. To raise I'll try to do it packing the underside with a washer. It's a popular mod to improve mid-range pulling, to judge by the miriad of comments if you google for "jet needle mod".
Do let us know what main jet they nailed on yours.
Mine came with the 122.5, yours should be the same Matt.
I know next to nil about carbs but this is the same type that is on my Honda V65 Magna. I did tear mine down for cleaning but didn't take the diaphram assembly apart. I was too afraid of tearing it as they are hard to get and terribly expensive to replace. Like you said, on other forums they talk about shimming these types of carbs. I did notice on page 5-12 of the manual that they have the needle assembly laid out. The needle does have a clip (#14) and it does look like there are different grooves the clip can be moved to.Quote:
Originally Posted by forchetto
I've been meaning to richen the mid-range for quite a while. This is a popular mod all over the place, and it's acomplished by raising the needle in the carb. Most CV carburettors have non-adjustable needles, that is, there are no grooves on them. The way people do it is to insert washers under the head of the needle to raise it up 0.5-0.75mm. The jet needle and needle jet affects carburetion from 1/4 thru 3/4 throttle.
Consulting the Brasilian STX Sundown manual available elsewhere on this forum, I see that our Mikuni BS28 DOES have a grooved, adjustable needle. I also noticed that as well as fitting a larger main jet for South America, the needle is at the fourth groove from the top.
I opened my carb and the needle for Europe is set midway, that is on the third notch from the top. I set mine on the fourth as per manual. Does seem to run better.
I find that whenever a real improvement in combustion is made, be it ignition advance, an iridium plug, or like this, raising the needle, the idle speed goes up on its own, without touching the idle stop screw.
You can just about manage to do this job with the carb in situ, but it's not for the faint hearted. Took me about an hour. The problem is mainly replacing the rubber diaphragm correctly in its seating, and keeping it there while you struggle with the spring and cap. It wouldn't be so bad if it wasn't for the four cap screws also double as supports for the throttle mechanism AND the choke lever. It's easy if you have at least three hands...the obscenities muttered by me in the garage were enough to earn me eternal damnation.
There's just one tiny glitch in the carburetion left to tackle: after decelerating from high revs, blipping the throttle to change down makes the engine gasp. This does not happen if the deceleration is gradual and over a distance or when stationary, so it's not the idle speed mixture setting. I suspect it's that blasted ACV (Air cut-off valve, Coasting Enrichener, Transient Enrichment Circuit, anti-backfire valve...there are lots of names for them, I just call them bastards...). I had trouble with that before when a piece of foam from the air filter blocked one of the passages in that device. If you trawl various forums and sites you'll find the disabling of this emissions device a common mod. I'll report back when I get it sorted.
http://www.telecable.es/personales/a...eftsideACV.JPG
Hey forchetto, should I adjust my needle also when I change the main & pilot jets or is it not needed?
If you're getting the carb out, you might as well. It'll be easier on the bench and it does run better. The mid-range pull is more positive and, surprisingly it starts better and the cold "driveability" is vastly improved as well. Don't know why.
Well I finally got around to changing my jets today and it was a piece of cake until I striped out 2 screws on the needle cover on top of the carb.
Mine did in fact have the 122.5 main jet and 32.5 idle jet so that has now been increased to 125 main jet and 35 idle jet.
I moved the clip on the needle to the forth from top position, it was at the thrid from top.
My mixture screws was 1 3/4 turns out so I screwed it in and then back out 3/4 turn. I hope this is about where it needs to be.
I ended up replacing both the top cover and float bowl screws to hex head screws so I wont run into the stripping problem again.
Once the rain lets up here I am going to go ride and see if it made any difference.
That's exactly how I have it now, including the idle screw at 3/4 of a turn out!!!. Mine runs fine apart from a glitch when after decelerating for a turn or bend, I blip the throttle to change down a gear. The engine sometimes gasps. This doesn't happen when the bike is at a stand still, you can blip it as many times as you like and it never gasps. Only in motion. I've tried all sorts of things, including making the slide spring 10mm longer, as adviced elsewhere, but it remains there. I do hate these CV carbs...I'm still suspecting that ACV (air cut-off valve) on the left side...:confused1:
I confess that when I saw this picture thought very funny:lol8:, plus I really think it makes sense to raise the plunger to allow a whole equate the air too.:confused1:
http://images.orkut.com/orkut/photos...nuyuwDUNwn.jpg
That guy probably heard about the "washer" mod. I've never heard of that one, anyway the Qingqi's Mikuni has an adjustable needle.
I have solved the problem of the gasping at last. It seems that when I fitted a larger idle jet to improve cold running and low speed behaviour I overlooked the action of the ACV device (air cut-off valve), also called variously "coasting enrichener","Transient Enrichment Circuit",anti-backfire valve, etc. It's the lump on the left of the carb, just behind the choke lever.
The idle circuit has a fuel jet and TWO air passages to feed it during normal running. As modern bikes are very lean jetted due to emissions, the high vacuum created during deceleration causes an over-lean condition that leads to backfiring in the exhaust. The air cut-off valve reacts to the high vacuum cutting off one of the air ways and so enriching the idle mixture momentarily and avoiding popping in the silencer.
As I've already made the idle circuit richer with my idle jet (nš35) the mix is now too rich during deceleration and this gives what is called a "rich stumble". This is why this only ever happened after prolonged deceleration and not during a quick down gear change or when standing still.
I've blocked off the vacuum passage from the carb to the valve by blocking the tiny hole in the valve lid with a piece of rubber. I have photos if anybody gets this problem.
I have this problem but now is not happening always. :lol8:
Once when I got out of the avenue to enter the district and the engine died as I had not control the bike, it cost me a few centimeters of skin from my knee.:eek2:
Quote:
Originally Posted by forchetto
In Brazil gasoline is mixed with alcohol. The carburetor has a cuba where gicleurs that interconnect the same passage of the air, so if you have a gicleur with 14.8 times less area that the passage of the air mixture is 14,8:1.
This would be the ideal proportion for the use of pure gasoline, the alcohol was 9,5:1 and our gasoline with 24% alcohol with which we use today is somewhere around 12,5:1.
Good deduction Sherlock Holmes...:icon10: I'd never have thought of that, but of course you're probably right. Brasil does use sugar alcohol in their fuel and explains the larger main and idle jets.
As I pointed out on message nš10 on this thread and the solution on a later message, I'll repeat it complete with photo:
"There's just one tiny glitch in the carburetion left to tackle: after decelerating from high revs, blipping the throttle to change down makes the engine gasp. This does not happen if the deceleration is gradual and over a distance or when stationary, so it's not the idle speed mixture setting. I suspect it's that blasted ACV (Air cut-off valve, Coasting Enrichener, Transient Enrichment Circuit, anti-backfire valve...there are lots of names for them, I just call them bastards...). I had trouble with that before when a piece of foam from the air filter blocked one of the passages in that device. If you trawl various forums and sites you'll find the disabling of this emissions device a common mod. I'll report back when I get it sorted."
I have solved the problem of the gasping at last. It seems that when I fitted a larger idle jet to improve cold running and low speed behaviour I overlooked the action of the ACV device (air cut-off valve), It's the lump on the left of the carb, just behind the choke lever.
The idle circuit has a fuel jet and TWO air passages to feed it during normal running. As modern bikes are very lean jetted due to emissions, the high vacuum created during deceleration causes an over-lean condition that leads to backfiring in the exhaust. The air cut-off valve reacts to the high vacuum cutting off one of the air ways and so enriching the idle mixture momentarily and avoiding popping in the silencer.
As I've already made the idle circuit richer with my idle jet (nš 35) the mix is now too rich during deceleration and this gives what is called a "rich stumble". This is why this only ever happened after prolonged deceleration and not during a quick down gear change or when standing still.
I've blocked off the vacuum passage from the carb to the valve by blocking the tiny hole in the valve lid with a piece of rubber. See photo.
What may happen now is that the exhaust backfires a bit under deceleration. To cure this richen (turn anticlockwise) the idle screw a tiny bit or until the backfiring is acceptable.
http://www.telecable.es/personales/a...limination.jpg
Does anyone know for sure if the 3rd hole on the bottom of this plunger is supposed to be open and NOT Covered by the plate on the inside? I just need some more verification that I have the plate in correctly?Quote:
Originally Posted by Luis Carlos
Thanks
Andrew
Here in detail the needle and the venturi. A hole called gicleur vacuum, the venturi interconnects the part above the diaphragm to the area of the engine intake. When the pressure is low in this area, the diaphragm is sucked into that hole, and raises the venturi
http://i37.tinypic.com/2pzbnsk.jpghttp://i34.tinypic.com/2cghs2e.jpg
http://intrudeiros.blogspot.com/2009...rgman-125.html
Thank you so much for the SUPERFAST Response with such great details! - Awesome much appreciated and will definately help others! Great JOB!
Andrew