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

That yellowed fuel will not be helping matters, just making an observation. Fresh petrol is usually a purply pink colour.

I'm not seeing any dirt or problems, Stuart. Did the carb cleaner squirt out of the pump intake port when you sprayed it into the mesh screen on the long pickup pipe? Did you have any difficulty pushing the fine copper wire through the main jet? Can we see a picture of the mesh screen after cleaning please?

Joe, because the engine stopped running after being out of service for a while, fuel deterioration is a more likely source of the trouble than dirt build-up. However there was a reasonable accumulation of dirt in the small chamber right under the main jet. I can only see a blocked pickup pipe as the problem if something like gum developed right across the screen. This would be a likely scenario if there were 15% ether (MTBE) in the fuel during a storage period, but hopefully we don't have ether in the fuel here in Australia. Claggy yellow fuel, probably due to ethanol, blocking the main jet (with some help from accumulated particulate matter around the jet) seems like the most likely cause to me, at this moment.

Photos after cleaning. When spraying through the screen, a small amount of debris came out of the port on the carby body. After that it seemed to flow freely. I have fed some fishing line down the main jet with no apparent obstruction. Hopefully everything else looks OK and we can move towards re-assembly?

Before we talk about reassembly there are two points I'd like to clear up.

First, when you initially took the carburetor off the petrol tank, was there any petrol in the well under the main jet, where all the brown crud was collected? The function of the fuel pump is to continually pump fuel into that well, allowing it to overflow from that compartment and return to the main fuel tank. If that well was dry, the fuel pump was not working at all. If it had at least a centimeter of fuel in it, the fuel pump was working well enough for the engine to start and run, unless the main jet was blocked. Hence the answer to my question can tell us the cause of the engine not running in the first place.

Second, could you please look closely at the diaphragm, checking for thin spots or actual cracks or perforations, especially where the piston/cup bears against it. If it shows signs of deterioration it would be appropriate to replace it while the carburetor is apart.

Once those points are cleared up, it will be time to clean that rather claggy petrol out of the tank, and reassemble the carburetor. Here are the assembly instructions for the fuel pump:


Note that the diagram shows a carburetor with two plastic pickup tubes, which applies to a different version of the Pulsa-Jet that has a main jet mixture adjustment. Your version, with the second pickup tube incorporated in the metal carburetor body, has only an idle mixture adjustment. The actual assembly instructions apply equally to your carburetor.

Please refer also to the disassembly instructions when you are putting the fuel pump together. Carefully engage the dowel/roll pin on the body with the hole in the cover, and ensure the cover pulls down evenly as you do up the cover screws.

When you come to putting the carburetor back on the tank, and connecting the links, levers and governor spring, the process is just the reverse of disassembly. If you are unsure, please stop and say so - we'll work it out from first principles.

Yep, there was about 1cm of fuel in the well. I will replace the diaphragm as suggested and have cleaned out the petrol. Will start on re-assembly and check in when I get stuck with the levers. I am also replacing the throttle cable/lever so is how do you ensure that this is done correctly?

There is one more job I suggest you do before reassembly: checking the tappet clearances. That should be dead easy while the fuel tank is off, and it completes the engine reassembly phase properly.

The trickiest bits of reinstalling the carburetor, to me anyway, are the wire links and the governor spring. The governor spring has to hook onto the little tab on the end of the air vane which is under the cooling air cowl. Only the tip of that little tab can be seen under the edge of the cowl (circled in red in the picture below):


You unhooked it and the spring still looks good, so you'll put it back on without too much trouble.

For the levers, reversing the disassembly sequence given in the instructions is a good plan, but hooking them on is a sort of black art. You can put one end of each link on easily (probably the carburetor end), then to hook the other ends onto the operating levers you have to juggle things a bit. At least you have the advantage of doing it with the control panel and levers not mounted on the carburetor at the time. You can put the attaching screws between the panel and carburetor on after the links are installed. You can't do that when you are taking the carburetor off, say, a Honda, so in the latter case it takes practice.

The throttle cable and lever are assembled and mounted on the handlebar first. Then you connect the wire inner at the bottom end to the control panel speed control lever, followed by putting the bottom end of the cable outer under its anchor clip - see green circle below:



Finally you slide the bottom end of the cable outer back and forth under its clip until the movement range of the speed control lever on the handlebar matches the movement range of the speed control lever on the control panel at the bottom, and stops the engine via the kill-switch when you get all the way to the slow speed end - then you clamp the bottom end of the cable outer in that position. It is quite a bit easier to do this on your engine than on one with a coupled choke(Choke-A-Matic), because in that instance it has to be rather precise at both ends rather than just one end of the movement.

If you just do these things one step at a time, and post when you get even slightly stuck, it shouldn't be a hassle.

Well I wish I could send you a sound clip of a purring little engine! Some finished photos for you and the others whose patience and guidance helped an absolute mechanical numpty achieve something pretty good. I will continue with a little fine tuning and reel adjustment but, once again thanks.

One thing I forgot to mention was the fuel. I replaced the existing with new 95 Premium unleaded and although clear, it still has a yellow tinge rather than the pink of regular unleaded?

Hi Stuart, on a great resto and mate, you did it all yourself with invaluable input from grumpy. This is now a great archive for future restorers/repairers.
Well done, guys!

Thanks for posting that Stuart. A little Briggs of that generation is usually a sweet, purring little engine that lasts a very long time if you just keep it clean, especially the oil and the air cleaner element. Yours looks really nice. I personally favour OHV Honda engines these days, but that's a bit like buying a BMW instead of a Holden: it doesn't work any better but it makes you feel better. Incidentally the stripes on your lawn look impressive - it seems your mowing technique is good as well as the mechanical and restoration skills.

It sounds to me as if you now have some familiarity with your engine, which will give you the confidence to look after it and investigate anything that seems to be going wrong. This will make your mowing more enjoyable. Remember, we are here to help and will be glad to do so at any time. Meanwhile you've contributed an excellent detailed thread to our archives - it will most likely be a very popular one.

Incidentally, the chemical composition of 95 RON petrol as sold in Australia is somewhat different from 91 RON. The only disadvantages I know of from using 95 instead of 91 (which is what the manufacturer specifies), are first, it costs more, and second, it will usually have a higher proportion of cat-cracked constituents that are a bit prone to forming gum if held for long periods, especially in warm weather. (Gum in petrol makes it yellow - but other constituents can also do the same thing, including moisture absorption into fuel containing ethanol.) On the other hand if you buy 91 you need to read the information on the pump at the petrol station carefully to ensure it does not contain ethanol.

I will close this thread - if anyone needs to post to it, just send a PM to a moderator.