Carburetor Rebuilding With Pictures

[Bobpaul]

CARB CLEANING

1992 70 HP Johnson

Cover is removed exposing carbs. Once carbs are uncovered, remove the linkage so you can unbolt them from the motor. Each carb has 2 nuts, which must be removed.



The next three photos show the best way to remove these hard to reach nuts so that you don't end up losing them. Take a stiff piece of wire and make a 45-degree bend at the end of it. Loosen the nut and place the wire in the center of it. Then continue loosening the nut so that when it spins off, the wire will catch it and you will not drop it down into the motor. Using this wire method I removed these carbs in 5 minutes and it will work for any hard to reach nut. When putting the nuts on, simply reverse the procedure using the wire.







The next picture shows the 3 carbs laying in a tray lined with white paper towels. Mark each carb as you take them off. Mark the body and the bowl of each carb. I mark mine with a single line for the top, a double line for the middle and 3 lines for the bottom. (I, II, III)



The next picture shows the carb separated. The main body to the left with the float still in it and the bowl to the right with the gaskets still on it.



This picture shows the float removed with the needle still attached.



This picture shows the float with the needle still attached and the needle seat removed and laying there. You're not able to replace the needle seat on all carbs, but these unscrew and you get new ones with the factory carb kits.



This picture shows the low speed adjustment needle with the tension spring on it. Common adjustment for this carb is to screw the adjustment needle in all the way until it's lightly seated, then back it out 1 1/2 turns. Notice the glaze from the dried up gas in the bottom of the bowl. This is what builds up in the main jet and the low speed pick up tube that causes poor/lean running conditions.



This picture shows the top of the carb body with the welch plug removed. The plug seals the cavity of the idle circuit. Inside the cavity are 3 tiny holes. As the throttle plate is opened in the carb, it passed these tiny holes and allows gas to be pulled in at idle to off idle speeds. The large brass fixture to the right is where the low speed adjustment needle is screwed in. Do not try to remove it. The small brass fixture at the bottom left is where the primer link is connected. Another item you don't try to remove.



This view of the carbs shows the left one with the welch plug removed and the one to the right still has it in. I don't recommend you remove these plugs unless you know how without damaging the interior of the carb and you also know how to replace them so they're airtight. Those 3 tiny holes can be cleaned from the inside by inserting a small wire, slightly bent, to remove any blockage. Then some compressed air or a can of carb cleaner with the plastic tube. I bend the end of that plastic tube so it squirts into those tiny holes from the inside.

[Bobpaul]

This picture shows the main pick up tube with the low speed pick up tube inside it.



This picture shows how I insert a fine wire into the low speed pick up tube before cleaning, to insure carb cleaner gets into it. It speeds up the process in case of a sludge blockage.



This picture shows what I used out the of the carb kit. New gaskets for the bowl and the interior stem, a new manifold gasket, new float, needle, seat and seat gasket (that's the little round white gasket sitting on the float), new rubber o-ring for the low speed adjustment needle, new gaskets for the bowl plug and one at the carb top where some carbs of this style have an air jet.



This picture shows a VERY CRITICAL ADJUSTMENT.

The float must sit level to just slightly higher than level when reassembled. This is when you hold the carb body upside down after you've put the float in place. To get the float to sit level you can bend the tab connecting the float to the hinge pin that the needle is connected to. It doesn't take much to get it to sit level. Lift the float and put something sturdy and thin under the tab or over the tab, then put pressure in the direction you need to bend it. DO NOT put pressure on the needle when adjusting the float, that's why I say lift it. You'll know what I mean if you do it. I didn't take out the main jet from the bowl because I doubt any of you would have the tool to do it. After soaking the carbs in a can of cleaner, just wash them in clean water then blow dry with compressed air or force compressed carb cleaner through all passages, especially the main jet in the bowl and the low speed pick up tube.

**I may have forgot a thing or two because I'm familiar with doing this. Make sure if you are using this guideline, that if you have any questions at all make a detailed post and ask them in the repair forum on the BOC and I will help you get any questions cleared up. Use numbers with pictures when asking to help clarify and it will make the process quicker.**



Here are some pictures of the before, including dirt dobber nest that was in the carbs and after the cleaning.







One more very important thing: Do not reconnect your fuel lines unless you first purge them with clean gas and clean out your gas tank. To do otherwise could render all this work a total waste of time.

NOTE: For those of you that would like a hard copy of these instructions Click here to download them. They are in a zip file, so you'll have to unzip them and open the file in Adobe Acrobat or some other .pdf reader.