need help with a 3.5 BNS rally push mower

[sullidog]

Hi. I'm currently working on a rally push mower with a 3.5 BNS classic engine. It starts on the first pull! My problem is that it will run fine for a few seconds, then it starts to miss, (it doesn't miss that bad) It's just driving me crazy why it might be missing. Here's what I did:
Replaced spark plug
cleaned air filter
cleaned carb bowl
replaced gas cap
changed oil
cleaned exhaust
cleaned valve box
cleaned deck
replaced governor spring
put in fresh gas
The only thing I can think of is to clean the mixture nut, but I'm not sure how to get it off. Do I just keep turning it like a regular screw, or is there another way to get it out?
Thanks!
Troy

[Richard Martin]

Troy,
I see in your tag line that you are operating as a small engine repair service. I recommend that you take some classes or get some certification. Try www.educationdirect.com (http://www.educationdirect.com). Been there, completed that.

[Bob Minney]

Yes it unscrews-careful not to bend needle
maybe a pin hole in carb diaphram-might be worth doing rebuild
pretty simple and parts are not too $

older bs engines have points and condensor to check

also if manual choke- check operation, make sure it is opening completely, could be causing rich mixture

[khouse]

bob is correct. rebuild the carb. go to napa and buy a small container of soaking carb cleaner. soak carb 1 hour. spray it all down with braklean spray. then blow out with compressed air. install the new kit. install the needle about 1.5 turns out to start. after it warms up turn the needle in till the engine starts to run poorly then note the position of the needle. then open it up till it runs poorly and note the position. then place the needle half way between. your done.