OutdoorKing Repair Forum Forums Repairs and Maintenance Questions on Engines Questions On Briggs & Stratton Engines Rover - Briggs and Stratton Quantum 45

Hi Guys,
I normally don�t have a tendency to find many four strokes that are not completely stuffed at the local recycle centre however I recently bought this fairly decent condition and complete Rover with a Briggs and Stratton Quantum Engine. I haven�t worked on a quantum before as all the ones I have ever seen were completely stuffed usually by running out of oil.
The codes for this mower are Model: 12F802 Type: 0875-01 Code: 95061956
I managed to get the mower going by simply cleaning the spark plug however it smokes a little when it idles and full speed. The smoke is black which makes me think the rings might be ok. The smoke definitely is not blue which as I understand is typical of stuffed rings.
The mower runs rough however I am hoping I can turn this into a decent mower.
This afternoon I plan to give the carby and good clean and replace the air filter to see how that goes.
I am thinking valve clearances might be an issue due to the small amount the engine smokes when running. Could I please confirm the expected clearances for this engine?
I�d appreciate some pointers before I get going on this one. For reference I have included some photos of my new challenge.
Thanks
Peter (Just changed my username, the last was a bit boring)

Hi Peter,

Here is the Operator's Manual for your engine:
http://bsintek.basco.com/BriggsDocumentDisplay/29lpAFKT9FzXFix2.pdf

Here is the Illustrated Parts List:
http://bsintek.basco.com/BriggsDocumentDisplay/18hruJXHnfBhU7y.pdf

The engine was built on 19 June 1995.

Black smoke is usually petrol smoke, so your engine is probably running very rich, and this may be the source of all of the complaints you listed. The simplest causes, and very likely ones in this case, are either a clogged air cleaner element, or a choke that is not opening fully when the speed control is moved away from the choke position. You can easily check both potential causes by temporarily removing the air cleaner box, and looking at the choke plate or the linkage on top of the carburetor which operates it, while moving the speed control from choke to run. You should see the plate rotate to full choke in the choke position, and to wide open in the run position. If the choke is opening fully, briefly run the engine without the air cleaner and see if the smoking has been eliminated.
Post-Edit: See later posts in this thread: this mower has the primer version of its carburetor, which does not have a choke. Testing the mower with the air cleaner filter element removed is the first diagnostic test that should be carried out.

Incorrect valve clearance is unlikely to cause black smoke, though it is not impossible. For the 120000 series engines, inlet tappet clearance should be 0.005"-0.007". Exhaust tappet clearance should be 0.007"-0.009".

Please let us know what you find.

The absolute most common cause of a quantum running rich is a dirty air filter.

Pete, your quantum is a primer carb model, so a good carb clean and new filter should see you right. Your model has no choke so dont go looking for one. Be careful not to damage the gasket between the carby and the air filter housing as it wont let it prime properly and make cold starts nearly impossible.

bigted, the IPL shows that model and trim coming with three optional carburetor versions: primer, manual choke, and auto choke. I can't reproduce that page from the IPL, but the workshop manual also says models 12A700 through 12W800 have a Walbro LMS carburetor, in all three versions:


I should have looked at the pictures more thoroughly: as you say, this mower has the primer version of the carburetor.

Well. I didnt get time to pull the carby off as I was working on a few other units on the weekend.

I did however replace the air filter as the current one was just about blocked up solid with dirt. I am surprised the engine started at all. I'll put a photo up tonight.

So for now the mower is running so close to perfect its not funny. I will however be taking the carby off as instructed and giving the mower a good once over. I'll also check the valve clearances this week to make sure everything is ok.
Grumpy, Joe and Bigted, I appreciate the pointers as always.
I do find it strange how people can throw a good unit in the bin.

I ended up taking the carby off and giving it a really good clean. With the exception of some stale fuel build up everything looked ok. The set-up was relatively easy to put back together after consulting the manual for the quantum engine.
I did end up replacing the gasket between the carby and air-filter simply because it crumbled upon removal. No other components in the carby needed to be replaced. The needle seat and Bowl O Ring were already in good condition. With the air compressor and carby cleaner it shined like new.
List of maintenance
Carby clean, new air filter, spark plug, 4 new blades, primer gasket.
Upon testing the mower smashed through knee high grass with ease.
I rate this as one of the better mowers I have worked on. The rover frame is also very robust for an older unit.
Grumpy, Bigted and Joe, thanks for the assistance. Hopefully I can find more quantum�s to fix up.

Jaffa, my view is that in general older Briggs engines, and older Rover mowers, may tend to be better than newer ones - so I don't think you should be surprised to have been pleased with yours. I will exclude some of the newer Briggs engines from that: the small OHV ones look rather promising to me.

I'll close this thread.