Older B&S 3.5hp B&S lawnmower. Choke-omatic. Won't start unless I pour gas into carby, then once going will continue to run easily. Would a loose intake tube be the culprit! It is loose. I have throughly cleaned the carb, diaphragm is OK. The needle in the mixture screw is a little stepped at the tip, I have adjusted the mixture screw 1.75 turns as per specs. Still won't starteven if I richen mixture a little. It does seem to be lean when I try to start mower, so air leak I am fairly sure. Good compression/spark. Thanks.
mrfxit,
Feb 22, 2:36pm
Sounds like you are on to it
Would be good to replace that needle & pop in a new carb diaphragm
tonyrockyhorror,
Feb 22, 2:40pm
It certainly won't be helping having a vacuum leak.
fishdoc,
Feb 22, 2:56pm
Thanks. What is the usual fix for loose intake tube! Are they threaded or pressed in. Tube feels threaded, when I hand tighten, the tube is about half a turn out of usual position.
ceebee2,
Feb 22, 4:22pm
Its carboned on the thread / remove carefully and clean the thread before screwing back in with loctite.
fishdoc,
Feb 22, 7:22pm
Thanks for your help
alfred011,
Mar 3, 4:04am
With those old B&S carbs alot of people remove carb from tank and the spring and cup washer fall out these parts fit in the carb side not in the hole in tank,make sure that the small spring is attached to diaphragm on oposite side to chohe pull rod.Check the gasket under the engine cover and the oring in the carb as they will suck air .The main jet should be pointed with no step as this will cause problems also the throttle shafts get very worn and will suck air stuffing up the mixture setting.wash out air filter and lightly oil turn out mainjet 2.5 turns start motor with full tank of gas ,put on full throttle turn mainjet in until engine starts to missfire then screw out til it missfires then go back to about middle position with mainjet.When you fit carb to tank hold ccarb upside down fit tank to carb then flip over and put the screws in.
jenny188,
Mar 3, 5:59am
Have a 3.5 in the shed. Smokes sightly but sill runs. Most get hard to start with low compression, oftenwith crankcase seals, sometimes in combination with worn rings. First word of your post may have said it all "OLD"
fishdoc,
Mar 3, 7:28am
Thanks for advice. Mower going fine now. I'm advised by a small engine mechanic that the spring and cup washer (as in post 8) do go on/in the petrol tank side of the diaphragm. Found some good clips on you tube. Thanks again.
jmma,
Mar 3, 3:22pm
Wrong, as in post 8, goes carb side of diaphram. Get a new mechanic (o:
Thank you for that info and link, much appreciated, apologies to alfred011
mrfxit,
Mar 3, 9:15pm
Correct
fishdoc,
Mar 4, 2:27am
Thanks guys have just started playing with mowers as a new hobby, so thanks for your help
flat_white_ltd,
Mar 4, 2:43am
On a side note,. those choke-omatic carbies generally don't like starting unless the tank is at least 1/2 full.
fishdoc,
Mar 4, 3:16am
Thanks, have seen your website, very impressive and thanks for your advice
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