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9

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 ...


9

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 ...


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 ...


6

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 ...


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 ...


5

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 ...


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

Jetting a carburetor - short answer You will require two things more than likely. A size larger main jet An adjustable needle jet Smoothbore Carburetor 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 ...


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 ...


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

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 ...


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 ...


4

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 ...


4

The back pressure and flow change of the exhaust will have an effect on the combustion and mixture. Usually with a free flowing exhaust, you have to rejet the carb a little richer and with a free flowing airfilter, doubly so. Running it without an airbox is making it worse, the mixture is already lean and stuffing more air down the bores isn't going to help ...


4

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 ...


4

Depending on the application, there are lots of options for changing over to EFI from carburetor. Your best bet, especially if you're not a professional, is to find a system which is plug-n-play. Trying to find one which is compatible by retrofitting it from another vehicle would not only prove difficult, but would be very frustrating when it comes time to ...


4

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 ...


3

Simply cranking the car for 10 - 15 seconds should prime the carb. Crank the car for about 15 seconds Stop for about 15 seconds Pump the accelerator petal twice Crank the car again, if it doesn't start immediately keep cranking the car for a maximum of 15 seconds. Stop Wait at least 2 minutes, this is to prevent damage to the starter. Then go back to step ...


3

If by "spark plug was dirty" you mean "black and sooty" then you're running rich and need to either lean out your mixture or double-check your air cleaner and make sure it's good. I know my old 73 CL125 would occasionally accumulate an impressive amount of dead leaves and pine needles around the screen of the air filter. Only took a few seconds to pop off ...


3

The drain screws for the four carberetors are located at the bottom, outboard side of each carburetor. The drain screws are item #23 in this parts diagram. You can drain them by removing the side covers, placing a rag underneath the carburetor and with a reasonably long Phillips screwdriver, unscrewing the drain screw until fuel flows out and into the rag. ...


3

This is a two cycle engine This particular motor (and most Derbi's) is a 2-stroke engine and as such has multiple places where an air leak from the reed valve (intake track after the manifold) all the way through to the head gasket, base gasket, spark plug AND crank seals can give you a low-compression issue. Things to check Reed Valve* - The reed valve ...


3

I'm not sure if the answer is still relevant, but I own the XR650L big red pig and may say that it's rather safe to mess with the carb of this bike even if you don't have specific skills. It's very forgiving unless you do something really wild. I used to ride about 500 km on my with mixture being extremely lean and was lucky enough to have my engine ...


3

The 1998 XL650 has a fuel petcock that has a safety feature on it, as do many other bikes of the gravity feed carb era from about 1980 to present. Since you are running an XR650 you should not have the vacuum line. There is a vacuum line that runs from the manifold side of the carb to the petcock on the XL650. When the engine is turned over and creates ...


3

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. ...


3

I had a similar issue with my Craftsman mower. Turned out the needle valve was sticking. Once it started, I could tap the side of the carburetor with a small hammer and it would then keep running. Replaced the needle valve and it's been running fine all summer.


3

Twisting the throttle opens the butterfly valve in the carburetor which allows it to suck in more air. With the increased air flow, the carb should also suck in more fuel. So, if enough fuel isn't supplied the engine can't handle the extra air. I don't know enough about your bike to offer a solution, but this is one possible cause.


3

The two hoses in question can be identified by using a can of carburetor cleaner with the red hose attachment and squirting into the nipples for the hoses to see where the fluid emerges. I suspect the nipple on the top of the carb by the auto choke could be a vacuum line. This is frequently where they are placed. The vacuum line may need to goto a ...



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