OutdoorKing Repair Forum Forums Restoring, Customising and Modifying Tech Talk SB Model 45 - Clutch and Engine Problems

The burning question is whether either the lint-covered mesh screen at the bottom of the long tube (the fuel intake screen), or the small brass item at the bottom of the shorter tube (the main jet) was actually blocked rather than obstructed. If so, that will have been the cause of the problem. If they were merely obstructed, it will be necessary to clean them both properly then go on to Problem 4. Both because we don't know the answer to that, and for practice and thoroughness now that we've gone this far, I suggest we should go the rest of the way anyway. Of course the first thing you need to do is to clean out the little well in the top of the fuel tank below the main jet, if you haven't already done so. Then, turning to the carburetor itself, step 1 is to clean both the mesh screen and the main jet with carburetor cleaner, which comes from your local auto shop in a spray can and may be called carb cleaner, throttle body cleaner, or some similar name - the counter jockey can point you to the right stuff. Wear safety glasses when you use it. In the case of the mesh screen, you might try squirting it across the screen first in the hope of blasting some of the remaining crud off and out rather than through and in. You will later need to squirt some directly through the screen, but it's best to do that during our pursuit of Problem 4, because of where the displaced crud has to go. In the case of the main jet, just squirt cleaner through the tiny hole in the center. After doing that, push a small strand of copper wire through the hole to verify that it is clear, then give it a short second squirt with the carb cleaner. I recommend that you do not dismantle the carburetor further except in pursuit of Problem 4, which I will now get into.

The Pulsa-Jet carburetor has a built-in fuel pump, which is subject to two main forms of deterioration, particularly during periods when it is unused. The first is blockage from the same crud you've seen in the Problem 2 investigation. The second is deterioration of the rubber-like diaphragm which is the heart of the pump. From the crud you had in the carburetor it sounds as if you may have used fuel that contains ethanol, and if so there is a good chance the pump diaphragm is damaged - we'll find that out.

On what might be called the back of your carburetor is the fuel pump cover, circled in red:



You need to remove that cover and dismantle the fuel pump - carefully:

Note the roll-pin (circled in yellow) which is being used as a dowel to locate the pump cover accurately. You will have to lift that side of the cover by using something like the sharp edge of a knife blade - which would be easy except that you'd prefer not to ruin the diaphragm (which acts as a gasket) and have to replace it - though you may have to do that anyway.

The objective when you open the pump chamber is to take pictures of the components, inspect them, and clean the compartment and the components with carburetor cleaner. You will also need to squirt carb cleaner through the screen on the end of the long tube (see Problem 2 above) in the hope that it will blast straight out into the pump cavity, carrying the crud with it. (Remember about wearing the safety glasses.)

Aside from getting the crud out, we want to know if the pump diaphragm, component 3 in the diagram, will sit flat with its little flaps laying flat on the ports they have to seal (one port is on the carburetor body, the other on the cover). We want to know whether the flaps were sealing before the cleaning operation, and also after it. There are two main issues in whether the pump works or not: whether the flaps seal, and whether the little cup, or piston (Item 2 in the diagram), is stuck in the bore.