Me and my buddy are building a minibike and I got this old engine thats been sittin in our barn for a while. i tore it all apart, cleaned it up and got new gaskets and such for it. It'll run, but only for a little bit, It will run good for maybe 30 seconds tops, then cut out. It wouldn't be hard to find parts or instructions online for carb adjustments, 'cept I cannot find any ID #'s or even a make or model on it. I'd say its prolly right around a 5hp motor. Carb's got a float bowl on it, with adjustment screw on that. There is then another adjustment screw on the side of the carb. It will run good when it's choked but afterwe open up the choke on it, it'll run for a bit and die. Anyone know why this is happening, and howto adjust those screws to get her to run good. We've tried so amny combinations of adjustments on those 2 screws, and none seem to help any.

 

The mixture is too lean to run, when you open the choke.
What setting is the mixture adjustment on the bottom of the carb? This is the 'run' jet.
I would start at 1-1/2 to 2 turns from 'bottom. (Dont' force the adjuster. Forcing the jet down onto the seat will damage them both.)
Make MINOR adjustments to the carb. Once you get it running, turn the bowl jet about 1/8 of a turn one way, then wait a minute to see what change(s) are made to the way it runs.

The jet on the carb is the idle jet.

There should be some numbers stamped on the shroud if there isn't any ID plates.
Look near the cylinder head, or on the sides.

EDIT: From the settings you have on the run jet, just open it up (counter-clockwise) 1/8 turn and see if it runs better. If it still shuts off, turn another 1/8 turn.

 

There should be a jet on the bottom of the bowl. Turn it in by hand until it stops, then back out ~1.5 turns. Then once it it's running, turn in till it sputters, then out 'til is sputters, then find the "happy" spot in between. Any idea what brand it is? MAybe take some pics for us.. How did the cylinder look? Was it scored at all? Does it smoke? Are the valves good? I built a 5hp briggs one sumemr that we could get ~7 out of,... I shaved the head and advanced the timing... That thing was wicked on our mini bike.. I'm 6' and 260 pounds (280 then) and the thing would throw me back pretty good on take off, and still run 25mph...

 

Float level too high???? Running outta fuel???

 

Did you check the fuel filter? You may have to pull the carb off to get to it. Also,This worked on our lawn mower when it was running rough.
Pour rubbing alcohol into the gas and let it run. It might help,it might not.

(Disclaimer:If the engine blows up due to the following,I'm not responsible,Try at your own risk.)

 

Thanks guys i'll check into all of this when I get home and see what happens.

To answer all of the answers that I can for you guys....Cylinder and valves looked good. Getting plenty of spark, replaced the coil on it a few years ago, and haven't played with it since. It smoked a lil but it seemed to stop after a bit. I did notice when I pulled the plug it was damp, like it was flooded or something, but I wasn't sure as to howto adjust the fuel/air on it till I just read your posts. I have no clue as to what brand it is, I'm gonna take a swing in the dark and say a Briggs but not positive. Theres no markings or engravings on it that I could find, granted I didn't look real hard. There's plenty of fuel in the tank....how is the float level adjusted? I wish I could get pictures for you guys, but I don't have access to a digital cam. The gaskets leaked at first, but I got some new ones and some gasket seal stuff and that ended that. I'll give it a shot of alky and see what she does. Also, the idle jet BLueOval was tlaking about, is that the screw that just adjust what the idle speed is, or are you talking about the other screw on the side that actually is a jet? I should have mentioned that there actualy is 2 screws on the side, one is a jet, and the other is the idle speed screw. the jet looks as if it controls some sort of a pilot line that runs through the carb and exits near the end of the carb nearest the engine. Thanks a bunch guys.

 

As for the two screws that are on the side of the carb - yes, one is the idle mixture screw. . . the other, the idle speed screw.

The one that is the mixture screw, adjusts the mix between fuel and air. This adjustment should be in the range of 1 to 1-1/2 turns out from bottom. Be very cautious turning the jet in to 'bottom'. (This 'caution' is for both jets. If you turn either one/both in too tightly, you could/will ruin the jet; the mixture screws, or both.)

The idle speed screw . . . I'd set it so that when you have the carb adjusted properly, you can let the engine run very slowly, but not 'pulsing' for the lack of a better term. Going from idle to wide open should be smooth, with no hesitation. (The idle speed screw goes completely through it's mount, and touches part of the linkage. That's the best way to tell you, without pictures.)

Like pfogle said, "Then once it it's running, turn in till it sputters, then out 'til is sputters, then find the "happy" spot in between."
I'll add. . . make the adjustments a little bit at a time. Verrrrrry slowly. And make note of where the slot is on the jet's screw head, for a visual reference.

Your carb description sounds like the engine is a Tecumseh. Tecumseh engines (and others) had the 'run' jet on the bottom of the bowl. (OLD Briggs & Stratton engines had them there, too. But, that was eons ago.)

The float level is adjusted by disassembling the carb bowl and bending a tab on the float.
(If you haven't done this procedure before, you could lose any ground you've made in getting the engine to run.)
Try the mixture settings before taking the carb apart.
From your first post, it sounds exactly like the run mixture is too lean. This is why the engine will run when you have the choke closed. You are sending a richer mix to the combustion chamber. (Open the choke and you 'starve' the engine of fuel.)

Let us know how you make out.

 

Haven't had time to check into it yet, been painting the truck.....But thanks a ton, when I get to it, I'll post the results