Lean and Rich Symptoms in Motorcycle Carburetors
In your post you indicate that some of the symptoms you have read are contradictory. I will try and clarify between the two conditions and attempt to give you guidelines in troubleshooting between the two.
Motorcycle carbs have a few circuits that effect different throttle positions.
Idle Circuit -...
At a base level, carburetors meter the amount of fuel they let into the engine by the amount of air that is moving through them.
Vacuum is created by the piston moving in the engine and creating an open space. As the piston moves down, it creates an empty volume which pulls in air through the only opening it can find, which is the passageway through the ...
Carburettors are very crude in comparison to EFI systems, and so the amount of fuel entering the engine is simply a factor of the amount of air going in, which is controlled by the position of the butterfly (and hence by the throttle position).
At a completely closed throttle, there will therefore still be some fuel getting in, enough to keep the engine ...
Multi-cylinder vehicles with multiple carbs
To port this question over to applicability with cars. This is the same issue that has plagued older Ferrari and Jaguar mechanics over the years. The 'balancing act'. If you have a V12 and 6 or 12 carbs, getting them all balanced and uniformly restrictive in terms of allowing air into them can be ...
An air screw on a Keihin PWL26 only effects the idle circuit of the carburetor.
The idle circuit pulls through the pilot jet exclusively. The pilot jet typically can deliver no more than 15% of the overall fuel when the throttle is wide open.
The claim of 15% is based upon the inside diameter of the pilot jet and the inside diameter of the main jet.
The air ...
Carburetor Circuits Will Still Pull Fuel from the System
If the engine is running on a carbureted vehicle, off throttle or not, it will consume fuel.
There are three basic circuits in a most carburetors that provide fuel to the ICE.
Idle Circuit - effects fuel metering at low RPM conditions where the throttle plate is closed.
Gasoline sitting for two years in the float bowl of a carburetor will surely lead to some varnish. The hydrocarbons evaporate from the fuel and oxygen acts as an oxidation catalyst changing the remaining components into other compounds leaving varnish in their wake.
Varnish will coat and clog the inside of the carburetor. Float bowl, floats, needle and ...
Jetting a carburettor - short answer
You will require two things more than likely.
A size larger main jet
An adjustable needle jet
Smoothbore Carburettor Image
Your main jet sits in the float bowl, it's number 11.
Off idle and higher the main jet contributes more and more to air fuel mixture as you open the throttle to wide open where the main jet is 99%...
You have a carburetor on that bike. You may need to do some adjustments, if not, you will make the air fuel ratio leaner and that will be really hard on your exhaust valves.
The more oxygen you have in your air fuel ratio beyond 14.1:1 will increase your combustion temperature. This, in turn, can damage your exhaust valves due to too much heat....
You should avoid over-use of the choke if possible, as over-fuelling the engine will cause more carbon build up, shortening the life of the plugs and reducing the time before the engine needs a "decoke" to get rid of the build-up. Plus it wastes fuel! Of course, too little is just as bad...
I've always gone for the following, though I don't know if it's ...
More than likely what the problem is, your float in the fuel bowl is shot. When the float is shot (ie: doesn't float correctly in the fuel), too much fuel is let into the carburetor and causes the exact issues you are talking about.
You may be able to get a new float and needle valve (very likely), but you may just be better off buying a new carburetor. ...
JB Weld is gasoline resistant.
I would disassemble the carburetor and inspect suspicious cracked components prior to applying any epoxy to the surfaces.
Ensure components are absolutely clean
inspect gasket surfaces for anomalies and remediate any issues you find
validate suspected cracks
Back when I used to do this sort of thing to keep something on the ...
I'm not a watercraft Mikuni guy, but I've dealt with a few two-stroke carbs that work in this manner.
There's a few possibilities:
The internal filter screen is clogged, but I'm discounting this as it's just rebuilt, and I doubt that would cause the primer bulb effect anyway.
The fuel return is dirty or blocked. Verify with it running (after an ether ...
A free flow exhaust requires more fuel to the engine
The baffles created back pressure in your exhaust system that restricted the flow of the exhaust gasses. When you removed the baffles it allowed the engine to 'breath' easier due to the lack of restriction.
Restriction in exhaust systems are designed for several things.
to restrict gasses flowing into ...
The DT 230 Carburetor will fit on some DT200's
The 1999 model of your bike uses the Mikuni TM30x1 Flat Slide Carburetor
Older models use a different carburetor model. The slide is round.
Here is an image of the flat slide carburetor.
Here is an image of the round slide carburetor
Both of these carburetors are readily available on ebay and Google shop.
More than likely, you have an air leak
If you haven't cleaned out and rebuilt a bunch of 4 carburetor banks in your life there is a good chance you have accidentally created an air leak in the system. Unmetered air will create the symptoms you describe.
The giveaway on most lean conditions is the falling idle. It idles high and is getting enough fuel but ...
Your carbs are clogged with varnish and bad gas
The remnants of gas that has evaporated are a gummy hard varnish inside of your carburetors. You have a bit of work to do.
You need to completely disassemble the carburetors and thoroughly clean all of the nooks, crannies, jets, fuel galley's and air galley's in order to get your bike back in working order.
These symptoms are typically caused by one or more blocked jets in the carburettor.
Small particles of grit can block any one of the jets in carburettors. The fuel still gets to the engine through the other jets but the efficiency is much degraded. The number and size of the jets varies by model.
I have no experience with Yamaha motorbike carbs but I ...
A carburetor is a carburetor: it doesn't matter what kind it is - it allows air to flow through it and meters the fuel to produce the optimal air/fuel ratio to allow the engine to run.
That said, you'll have two things to look at:
First, fitment. Will a different carburetor physically fit within the confines of the current carb? Will the carb output size ...
You will need about 25 feet of clear vinyl aquarium air hose and a screwdriver.
Cut the aquarium hose in half to make two lengths. Use each to make a water manometer to balance each pair of carbs (left pair and right pair). Then balance the inner pair and the outer pair using the same method.
The basic idea
The secondary venturi act as a second carburetor when there is a demand for more fuel. When an engine is designed the carb must be large enough to flow enough fuel and air for the entire RPM range. A single barrel (venturi) carb large enough for the higher RPM range may flow inefficiently at low RPM. A carb small enough to flow efficiently at low RPM may run ...
I'm not an expert on bike carbs, but if they are the same as car ones there will be two settings - one for mixture and one for idle. Once you have them balanced, you'll need to adjust these to get the right levels, while still keeping the pair balanced (i.e. increase the idle on both by the same amount, then check the balance, then decrease the mixture a bit,...
Your experiencing fouled plugs. Fouled plugs have carbon buildup that grounds the electrode of the spark plugs over the ceramic with carbon. The carbon buildup occurs because the AFR (Air Fuel Ration) is too rich. This makes the combustion process, when you fuel is burned, too cool. Since combustion is too cool carbon buildup occurs on your sparkplug and ...
How the choke works
The choke of a scooter consists of a dedicated choke nozzle in the fuel reservoir and two narrow drillings leading to the venturi (the pipe where the air goes through):
When the motor cranks and the choke is active, the slight underpressure in the venturi sucks in extra fuel through this drillings. When the choke is inactive, a piston (...
Those are the remnants of gasoline
When you let gasoline evaporate it leaves behind various elements within the gas that can't dissipate through evaporation.
These remnants can clog various galley's in your carburetor as well as clog jets.
Even if you are soaking your carburetor you will still want to physically clean out the jets and use compressed air ...
It sounds like your carb(s) are plugged and need cleaned. If the fuel in the carbs has ethanol in it, the carbs are going to be caked with crap. The floats could be ruined. There are a lot of things going on. Getting the carbs rebuilt or at the very least cleaned up, is going to be a must. All of the symptoms you saying are pointing to carb issues.
You are describing a lean condition
The more you open your throttle the more vacuum you are creating in your carburetor venturi and your intake manifold. When you are operating at higher RPM any unmetered air leaks into your system can become more obvious.
Unmetered air is air that is getting into your system after the fuel has been delivered. If you ...
Yes, you can bend the tab
The metering diaphragm enriches the entire range on every circuit. If the fuel level is higher it will require less vacuum under Venturi's Law to pull the fuel from the 'float'.
You can use the metering diaphragm float tab as a method to enrich all of the circuits and then adjust your low speed circuit with the fuel screw to lean ...
A few minutes of fuel leaking is more than you should expect. Usually, when you drain a carburettor, if the fuel lines are full as well as the carburettor, I expect about 10-15 seconds maximum. If it's running longer than that, it's coming down from the gas tank.
Follow the fuel line to the gas tank (as best as you can). Are there any valves that you can ...
Sounds like the carburetor, float, and/or float valve may be dirty.
NOTE: A service manual will be extremely helpful as you go thru this process.
There is no reason to take this carburetor apart and not rebuild it. So, get a carburetor rebuild kit, which contains the necessary seals/gaskets and other items needing replaced.
After disassembly, all of ...