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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 Watch out for it falling down as the main jet is withdrawn.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