OutdoorKing Repair Forum Forums Repairs and Maintenance Questions on Engines Questions On Briggs & Stratton Engines 3hp B & S stops after 5 minutes running

Hi, I have a Rover Scott Bonnar 45 model no 80202 0880 01 80030303. Have cleaned out the carbe, new diaphragm, air cleaner, manifold and fuel tank gaskets, oil and no rubbish around the cooling fins. It starts and runs for about 5 minutes and then runs rough, loses power and stops. The only way to restart is to choke it once and it will go for another 5 minutes. Very frustrating. A couple of photos

The first thing to suspect, is a blocked vent in the fuel tank cap. To check this just loosen the cap temporarily and see if the problem goes away. If it does, you need another cap.

Will try that on the weekend.

Cap is clear and vented.

OK, that gets us a bit further. Now, the next important clue is that you've said it needs to be choked to restart, after it has stopped. If the choke had no therapeutic effects, I'd say the next most likely cause was a temperature-sensitive ignition coil (your engine has breaker points - it was made in 1980, and electronic ignition was fitted from 1983). However if choke is required, it is losing compression or starving for fuel, and doing so after a fixed time interval of 5 minutes. Let's assume for the moment that you didn't make any mistakes when you overhauled the carburetor.

This may mean the problem is temperature-sensitive rather than time-sensitive, which could fit for, say, lack of tappet clearance. Before we start to get desperate and re-do things you've done before you started this thread, I suggest you check the valve clearances. For that 80000 series engine, the required clearances are inlet 0.005"-0.007", exhaust 0.009"-0.011", measured with the engine cold.

I know it's a no-brainer but could it be a dodgy spark plug. I ask this because I had a smilar issue and it went away with a change of spark plug.

I checked the valve clearances today and they are within tolerances. I also tried it today and no change. I will pick up a plug this week, I also had that thought. Thanks

New plug, no change.

Have you verified that you still have spark when it shuts down? To make this check, have a spare spark plug handy when it stops. Immediately transfer the spark plug lead to the spare plug, press the plug base against the cylinder head, and pull the starter. See if there are sparks between the electrodes. Remember, you need to do this within just a very few seconds of it stopping.

When you've done that check, if you do have spark the next step will be to dismantle the carburetor and fuel tank again, so do the spark check first, and report back. Then we can talk about the next part.

Thanks Grumpy, tried a couple of things, noticed it runs very hot about the time it runs rough and stops, also noticed that the head gasket is leaking, will get a new one next week.

The symptoms fit an overheating problem. I note you have already checked the cooling fins. Did you check the fins right across the head, especially underneath the top of the cowl (the most important part)? Are the fins on the flywheel fan present and clear? Of course a severe head gasket leak could be the problem too, but such leaks have to have a cause. Unless someone has loosened one or more of the cylinder head bolts at some time, blown headgaskets on side valve Briggs engines are more often a symptom of overheating, than a cause of it.

It's leaking from between the intake manifold and exhaust, the fins are clear and present.

The gasket obviously needs to be replaced. When you do it, you will need to check both head and cylinder castings for flatness. It must have blown for a reason. One part or the other may be bowed, and if it has been blown for a long time, you may find a leakage path that has eroded the aluminium.