Vintage 3.5hp Briggs and Stratton 148cc Engine won't go past idle

[volvofan94]

I’ve set the mixture screw 2 turns out from the fully closed (tightened) position. I’ve tried a variety of settings for the mixture screw, but none have worked to date. The tip of the mixture screw is in good condition. Looks like the manual says 1 1/2 turns for initial. Will try that then post back.

My carb doesn’t have the idle speed screw mentioned in step 4 of the Final Adjustment procedure. May have gone missing over the years. Will replace it.

 

[SmallEngineHead160]

Yes one & a half turns out should be your initial setting to get it running to make additional adjustments.
Sometimes if it won't stay running with the initial setting you may tweek it a 1/4 turn in or out but you should never have to turn the screw all the way in to get it to run.
If the engine only runs with the screw all the way in than that means you still have a problem with the carburetor.

If you want the engine to idle at a set speed than your gonna want to have that idle screw but as long as your starting/running the engine in the fast position it won't matter for now.

 

[Ocean909]

@volvofan94 I know you plan on selling this, so spending +$25 isn't ideal for your profit margin, but swapping out for a pulsa-prime may be less frustrating. There is no auto-choke, no adjustment, and its basically a direct swap. Just thought I'd add to your options.

 

[volvofan94]

@Ocean909, I like it, that’s the way I’ll go with the project! At this point I’m at my wits end with getting the Pulsa jet to work correctly. lol. Tried starting it yesterday, still no luck. Even checked the carb/tank mounting surface for flatness before starting the engine; it looked good.

I’m ~$40 into the project now, not a lot of money, but having the garage space back is plus at this point.

What are the part numbers for the fuel tank and pulsa-prime carburetor?

 

[Ocean909]

I believe the part number for the carb is 795477 the tank 494406. Searching for the tank # at the usual online suspects will get you the tank and carb combo. Couple of things to note. Its aftermarket so it may work may also be junk. Depending on your mower age you may need to cut the end of the breather tube or order the shorter one. You also may need the longer screw for the air cleaner. The mount on the tank may need a 6mm bolt.
Hope this helps

 

[SmallEngineHead160]

The modern pulsa-prime carb/tank is a good cheap alternative I have done it myself and it seemed to work fine the only issues are the ones that Ocean909 stated plus I would like to add that the pulsa-prime carbs do not have an idle adjustment screw so on a mower with a throttle control if you put the control in the idle position the engine could ither idle to low or the engine could stall. This can be worked around by just slowly adjusting down the throttle until you reach a proper idle speed.
There is a another fix but that involves changing out the control bracket that mounts to the engine and fuel tank with a correct pulsa-prime control bracket which with the correct governor spring is designed to only allow the engine to idle at a set speed.
Some of the aftermarkets where selling pulsa-prime carb/tank kits that included that control bracket but I don't know you if can still find those. You can find used control brackets on eBay but this may all be out of budget for you.

All this said, if the idle issue isn't a problem then the pulsa-prime is definitely the way to go.

 

[volvofan94]

Got the pulsa-prime carburetor and fuel tank kit ordered. $28 and it should arrive next week.

Hopefully the speed control bracket I have on the engine will work with the pulsa-prime carb setup. Looking at the photos of the pulsa-prime carb and tank online it should match up no problem. The mower has a handle mounted speed control (looks aftermarket) which connects to a cam that adjusts the throttle plate and controls the governor speed on the pulsa-jet carb. Hopefully those parts can be reused! Will keep my fingers crossed as I begin to install the new tank and carb.

 

[volvofan94]

Got great news; the new pulsa-prime setup worked well!! 3-4 primes and one pull later, the was engine running! Even fixed the handle mounted kill switch so it turns off nicely too.

I appreciate everyone’s help and suggestions with this project. Couldn’t have done it without your help.

Am I able to reuse the pulsa jet carb air cleaner on the pulsa prime carb? I’m going to purchase a longer screw to hold it to the tank through the throat of the carb tomorrow.

 

[SmallEngineHead160]

That's great news, yes you should be able reuse your original air cleaner

 

[Ocean909]

Glad to hear it worked out. SmallEngineHead160 is correct, the old air cleaner should bolt right on with the longer screw. Also Some of these replacement carbs have a small black screw blocking the threads where the air cleaner screw threads in.