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15

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. Background Motorcycle carbs have a few circuits that effect different throttle positions. Idle ...


15

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 ...


15

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 ...


12

Background 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 ...


11

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 ...


10

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. Throttle Settings 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. Secondary ...


9

I wouldn't 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....


8

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 ...


8

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 ...


7

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 ...


7

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 ...


7

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 ...


6

Don't worry, you're not the only one who had to endure this pain... I had an old KZ650 I pulled the carbs from what it looks like a similar design. Like yours, it was older and the plastic air intake tubes were very stiff. Here is what I had to do. Pull gas tank off and disconnect from carbs. Pull the seat off to access the air filter and air box. Pull ...


6

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 ...


6

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. ...


6

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 ...


5

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 ...


5

You said that it is leaking from somewhere "under the tank" and then jump directly to the carbs. If it is the carbs, you'll probably have to tear into them. If it is from under the tank, there are a few things you can check: Is the tank intact? You may have rust burrowing through the tank and causing leaks. This is bad. Should be visible in the fuel ...


5

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 http://www.natenewz.com/2010/06/13/carburetor-...


5

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 ...


5

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 ...


5

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. ...


5

You have two separate idle settings on your carburetor. One is for the choke idle and the other is for your off-choke idle. When you start your vehicle in the morning the idle setting will be fixed on the last termperature of your vehicle, so if you drove home the night before and the engine was at full operating temperature you would have that idle ...


5

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 ...


5

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 ...


5

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.


4

Two main reasons: Already some races require restrictor plates to keep the speed down, so swapping out the carburetor for modern fuel injection would increase the need for restriction. It is easier to inspect and monitor a carburetor, therefore it is more fair for each team since it is harder to cheat (or at least easier to get caught). However, from ...


4

Found the culprit the jets were fine, however the float bowl was full of residue and water, as well as the jet carrier bolt being snapped in half so the jets were moving along to where they were not able to fuel the cylinder. After a full strip down, rebuild and calibration its now firing on both cylinders correctly.


4

A shop manual (particularly one with colour photos) will offer some spark plug diagrams / photos, to compare against your plugs, but they're not particularly useful. As you said, claims are contradictory. The problem is, that a symptom of too lean/too rich is that it doesn't run as well as it should. That's both ways. So a too-lean symptom for one person is ...


4

I need to get a carb kit and just haven't gotten around to it. A carb kit for a 1975 Honda may be harder to find than you think. You'd better start searching for that now or maybe even a used carburetor, if you can find one. My guess is the obvious one: Something did not seal when you worked on your carburetor. Pull it apart again. You missed something, ...



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