OutdoorKing Repair Forum Forums Repairs and Maintenance Questions on Engines Questions On Briggs & Stratton Engines B&S only starts with aerostart when cold

I bought an old Masport tiller with 3.5 hp B&S that hadn't been used for several years. After an oil change, new spark plug and air filter (and a new pull start rope to replace a broken one) I can't start the engine when cold. Aerostart does the trick to start it, and it then keeps running though it seems not as smoothly as it should; after it warms up for 5 minutes or so it starts well. The new spark plug got sooty very quickly.

There seems to be a fair bit of carbon on top of the piston (looking through the spark plug hole), but it doesn't blow any visible smoke. Compression doesn't feel great but I think it is acceptable; I don't have the means to measure it. I just want to till compost into the soil a couple of times all over the 1/4 acre block in preparation for landscaping before disposing of the tiller.

I suspect worn piston rings and am thinking of using some heavier oil I have at hand to get by for my needs without further expense.

Any comments, tips or advice would be greatly appreciated.

Have a look at the carb and see if it has a choke butterfly. If it does check to see if it closes when you operate the pull start. If it doesn't there is an issue in that operating mechanism.
Also if it does have this butterfly, there will be a mixture screw on the side of the carb. It may be set too rich. I'll refer to my manual for setting procedure. In the meantime, check the carb and maybe post a picture and I'll see if I can help there.
Cheers!

Thanks for your reply Unimog74.
I don't think there is a choke butterfly on my carby. I am including a couple of pictures to help identify things.
Cheers

Ok I see. When you operate the throttle control to choke, check to see that the choke slide at the outer end of the carburettor extends thus closing the airway off effectively.
Get the engine running as you have been and run it up to normal operating speed. See the large flat screw on the side of the carburettor? This is your mixture screw. Ideal setting is achieved by slowly screwing it in until the engine falters and then wind it out slowly counting the number of turns until it falters again. Count the turns back in half the number and that's where it should be set somewhere there. Fine tune this setting for best running.
See how you go and let us know.
Cheers.
Ps when you wind the mixture screw in, don't wind it all the way in hard, this will damage the seat.

Aerostart and its like are not good stuff to use on small engines, as you may realise. Difficult starting does indicate an engine problem, but it may be a simple one.

Your engine has the 'Pulsa-Jet' carby, with 'Choke-a-Matic' linkage operated slide choke.

As Unimog74 says, first check that the throttle control is fully extending the choke slide, at full throttle. Just pull the slide outwards, to see if it moves any further. Then check that the slide retracts fully, when the throttle is backed off.

If either condition isn't satisfied, first try adjusting the throttle cable. Loosen the cable clamp screw at the carby, slide the cable outer a little in the appropriate direction, and re-tighten. Check that the cutout switch, Item 3 in the diagram below, is still making contact when the throttle is fully closed.

If necessary, use pliers to carefully bend the link at point 2 of this diagram, to adjust this:


The next step is setting the mixture, via the mixture screw. The factory setting is 1.5 turns out from the closed [fully clockwise] position; it should start and run well enough to complete the adjustment as Unimog74 has described. Run it for about 5 minutes, before doing the final adjustment.

By the way, if you can supply the Model, Type and Code numbers off the cowling [those numbers stamped near the carby], we can direct you to an owner manual and parts list for your engine. Can't quite make them out well enough, in your second pic.

OK, thanks again for the help.
model number: 80212, type: 1715-01, code: 83030103

I'll only get to try out the directions provided on Saturday morning...I'll let you know how it goes.

Righto, your engine was made on 1st March 1983. So that will also make the machine a Mark I [inch pattern] Home Gardener [important if non-engine parts are required].

The engine Illustrated Parts List is here: http://bsintek.basco.com/MDEXResultsPages/PDFDisplayPage.aspx?fileName=Z6nkAJVJ1DajI

And the Operators Manual: http://bsintek.basco.com/MDEXResultsPages/PDFDisplayPage.aspx?fileName=flivAJX-nfBhU7y

It isn't very likely that worn rings are the cause of the starting problems on this machine. It is not advisable to use heavier oil in any case; Monograde SAE30 is the best for these engines. They invariably use oil, if run on multigrade.

Nor are ignition issues common, as this engine has the Magnetron electronic system, not the old contact points.
Unless a 'previous tenant' has altered the flywheel/coil stator clearance. A standard business card should just fit in the gap, if it's set correctly.

If it has been idle for some time, it's a very good idea to get all of the old fuel out of it that you can, and fill up with fresh stuff.

Success and joy!!

Thanks for the advice Gadge. I got to it this evening...The problem was the choke not closing off properly. Gently bending the linkage wire closed it off completely (It would only close to within about 2-3mm beforehand) and brought the success. since then I have also adjusted the mixture screw a little...it was set too rich (which might explain the sooting on the spark plug and carbon deposits on top of the piston?)

After that I set the magnet gap to a business card thickness and lubricated the pull cord clutch for good measure. Starts cold easily now. Still running a little more 'lumpy' than I think it should but that could be the gummy residue from the old fuel which I hope will improve as a bit of fresh fuel goes through and those residues dissolve. Cheers

I hope you did not put any lubricant inside the starter clutch.

The clutch balls need to be dry, and able to move very freely, for the clutch to operate correctly. Damage to the crankshaft can occur if they stick.

The only lubricant permitted here is a single drop of oil on the felt pad inside the clutch top section, which bears on the outer end of the crankshaft.

Thanks for that.
I was aware of the need to keep the steel balls and their chamber dry. I put about 4 drops of sewing machine oil (I wanted a very thin oil) onto the felt pad...hope I didn't overdo it.

Briggs recommend engine oil for this. However, 4 drops of a very light oil would be OK, as the drop volume is smaller.

On the subject of fuel, Briggs diaphragm carburettors aren't at all prone to gumming up. But E10 fuel is to be avoided.
Debris in the tank can obstruct the screens on the pickup tubes over time, and is the most common problem with them.

As the specific issue raised has been resolved, I'll now lock this topic.
If anyone should wish to add further info, please PM a Moderator.