Not running quite right????

[turftech 1]

Hi all, I have a 3HP briggs flattie. It has the pulse jet carb, with the tank mounted beneath. It had sat for a long time, I got it with a used Bonanza. Anyway, I took it apart, cleaned it, cleaned the head, cleaned the carb, etc. It runs, but it is hard to start, and it dies a lot, especially when throttling down. The idle is set pretty high. It also backfires when throttling down. I'm not sure if the needle valve needs to be adjusted in or out. Any ideas?

 

[71dodge]

somthing with the carb or the spark get a new plug clean the flywheel and clean the carb again

 

[turftech 1]

Haha, great minds think alike, that's what I did. Maybe my magneto/flywheel gap is off, anyone know what it should be for a 3hp flattie? I think that my mixture is off though too, all but positive. just not sure which way.

 

[jeep2003]

make sure the pickup tubes are not leaking sometimes the brass part cracks . and make sure the upper part of the gas tank the little bowl holds gas. also make sure the gasket carb to block is good and tight. If you compression is low it will be hard to start. if it is low check your valve clearances. i usually set the mixture screw out 1 1/4 turns and work from there. To clean the carb i usually go at it with carb cleaner in all the passeges then shoot it with compressed air. but take the diaphram out or itll probrobly screw it up. If its running your probrobly fine spark wise but it could be the plug. Make sure the connector is grabing the plug tightly and the top of the plug isnt loose

 

[doubletrouble]

my guess is carb or ignition. If its old and has points, check them and replace. They are cheap to do.

 

[Richard Trotter]

If the gas cap is is plugged and not vented, it can make the pulsajet do all kinds of weird stuff.

 

[The Restore Kid]

Hi all, I have a 3HP briggs flattie. It has the pulse jet carb, with the tank mounted beneath. It had sat for a long time, I got it with a used Bonanza. Anyway, I took it apart, cleaned it, cleaned the head, cleaned the carb, etc. It runs, but it is hard to start, and it dies a lot, especially when throttling down. The idle is set pretty high. It also backfires when throttling down. I'm not sure if the needle valve needs to be adjusted in or out. Any ideas?

Backfiring? That's a weird one.. I would almost say valves like Jeep said.. Usually a back fire in one of these motors means valve not seating properly. It's usually the intake valve that needs work being that is the floater that relieves compression anyways.. If it's just a little off it brings the whole show to a screeching halt... I think I would START with your needle though.. the best way to adjust one would be to.......... from the sounds of your motor, Get it running so it stays running.. and slowwwwly back the RPM's down to about as slow as it can manage to stay running.... I''d probably start with like 1 1/4 to 1 1/2 turns out on your fuel screw... then when you got your motor stumbling and kinda running at a slower speed... start screwing your fuel screw back IN to lean the engine out... When the fuel screw is right the engine will smooth out and pick up RPM's because the amount of fuel is matched to the amount of air the motor is trying to burn.... On most carbs you would do that first on the IDLE speed side, THEN set your high speed main fuel afterwords... BUT being it's a briggs you're kinda screwed there. I would say get the engine running at a fairly good speed.. Should be idle but I'd go slightly higher to get your fuel matched to a higher RPM where it wants to run and pull... Those Briggs carbs are a bitch because you only have the one screw.. It sounds like you are probably too rich right now so it can't burn all the fuel and it has a hard time.. You will KNOW when you get it right or pretty close because running 700 RPM's and stumbling and smoking will turn into 800 RPM's and smooth right out and sound nice.. I'd say get it running about a high idle speed and slowwwwly turn your screw in until the motor smooths out and sounds good. :thumbsup: Go too far and the engine will be too lean and get hot, have no power and want to die too... There's about a 1/4 to 1/8 of a turn in between right, too rich and too lean.. After playing with it enough you'll see how it works.. Those pulse jets are junk though.. You can run it lean and it will SCREAM once you get the engine GOING wide open.... BUT being it is real lean... you will never GET it going wide open because it will have about ZERO power.... OR you can feed it a healthy amount of fuel and it will take off like a bat out of hell until it starts hitting those high RPM's... in which case it will start stumbling and loading up again... They are a real bitch to get any performance out of. The newer Butterfly Choke type carbs they build Raptor carbs from run a LOT better for some reason.. Not sure what they did but it worked. I just use carbs about like your Kohler has and forget the whole nightmare though. :doah: Because I'm a huge Briggs fan but their carbs suck... :doah: lol.. Gap between the flywheel and coil isn't your problem.. If they are too far away they will NOT run, but I run mine so close they are damn near touching and will literally squeeeeze it right down so there IS NO gap abouut.. all that will do is give you a hotter meaner faster spark. It MAY set the curb just a minuscule amount advanced, but it's SOOOoooooo small it will never make the engine not run.. Only better usually.... :thumbsup: