need help my b&s 21hp vtwin will only run with choke on any advice?

tomsch · Oct 23, 2012

I have a 21 hp briggs and stratton vtwin engine that will only run with the choke on. Any help with this problem would be appreciated. Thanks

murphy1244 · Oct 23, 2012

tomsch said:
I have a 21 hp briggs and stratton vtwin engine that will only run with the choke on. Any help with this problem would be appreciated. Thanks

Somewhere your sucking air. What have you done to it?Or a fuel blockage

V1Rotate · Oct 23, 2012

Can you give us more info? What kind of machine is it? How long has it been since it has run? Is the fuel fresh? Have you changed the fuel filter?

tomsch · Oct 29, 2012

It is a craftsmen lawn mower. I have cleaned the carb 3 times,changed fuel filter,put new gaskets & o ring in,etc. I have not checked for vacum leak yet. Thank you for the information. I will try that and see what happens.

stevess · Oct 29, 2012

not sure of your model but you may want to check to see if there,s a throttle cable adjustment. My ariens would show it was running on choke but was actually running on fast because the cable had moved. Does it require alot of cranks to start?

tomsch · Oct 29, 2012

It does have a throttle cable. I will have to check that. It does not require a lot of cranks to start. It starts good. The model # is 407777 Briggs & stratton. It is a nikki carb.
Thanks for the information.

mostly_gas · Oct 29, 2012

Sounds like you have a lean condition. Causes include low fuel in float bowel( plugged needle jet, plugged fuel line, fuel pump), plugged jets in carb, vacuum leaks, and low compression (valve adjustment stuck or worn rings) and bad fuel (water, other contaminants). You need to verify enough gas is getting to to the float bowel. Try pulling air cleaner and put hand over carb several times to see if that clears the jets.

Ilikeurtractor · Oct 29, 2012

My experiences with "needing to have the choke on to run when warm" have been gummed-up carbs. I even had one snow-thrower that had such long, narrow ports in it that I couldn't even clean the gum/varnish out of them and ended up buying a new carb to fix the problem after only 1 summer of gas had sit in it. I had to take needle-nose pliers after it to pull the needle free from its seat. I've also ran into another engine recently that ran great after 15 years of old gas in the tank upon startup. So I suppose it depens on carb design a lot and probably fuel quality. Seems like ethanol may also contibute to carb varnishing but the verdict is still out on that one. It would be great if they could economically make fuel-injected small engines to help alleviate these issues. Needless to say, I'm a big fan of diesel engines

bigdeano · Oct 29, 2012

I have a B&S opposed twin engine that the needle valve was closing by itself from the vibration. The spring wasn't strong enough. I ran it with the choke on for a long time until I figured out what was happening.