OutdoorKing Repair Forum Forums Repairs and Maintenance Questions on Walk Behind Lawn Mower Frames Question On Scott Bonnar Cylinder Mowers Scott Bonnar 24inch cut - Model 65

I have just picked up a 24 inch Model 65.
Model No. 65029.
5HP Briggs with numbers: - 131432 0177-02 81090807
10 bar cutting blade, spare 6 bar blade and low cut bottom blade.
Cutting reel needs a sharpen and bottom blade has only a season or so left in it, so I may replace at same time.

The machine has been left sitting for some time and has the usual problems - dirty dry fuel tank, perished fuel line, gunk in the carb.

I have cleaned the tank, replaced the fuel line, added a fuel filter to be sure, changed the oil, changed the plug and have pulled the carb apart and cleaned it.

I have reassembled the carb, reattached fuel tank and lines and have had the machine running.

Q1) There is fuel lecking from the fuel bowl gasket. I have replaced the gasket with the direct replacement (part number 27917) and fuel is still leaking from this area. Can someone suggest what I should be doing to stop the leak? I have had the carb apart several times and the gasket looks to be seating fine ( I have thouroughly cleaned both surfaces to which the gasket seats). Could I have reassembled the fuel float wrong?

Q2)Can someone advise of a proper workshop manual for this engine / carb? I have checked and there is nothing in the manuals area on this forum which I am subscribed to.

Hope someone can shed some light, cheers
Craig.

Hi Craig, the gravity feed fuel system on that engine has a float bowl, and fuel can only reach the level of the gasket at the top of the float bowl if the carburetor is flooding: that is, the needle is not sealing against the seat. Possible problems are: stuck float arm at the pivot; needle clip not properly installed on float arm; dirt between needle and seat; or damage to the needle or seat.

There is a general overhaul manual for older B&S engines such as yours. You can access it page-by-page for no charge, or buy a download of the whole book, here:
http://www.tpub.com/content/recoveryvehicles/TM-5-4240-501-14P/css/TM-5-4240-501-14P_70.htm
In case you are wondering what all those numbers mean, I gather that TM-5-4240-501 is a series of US military manuals, often adopted from civilian services. You can access any page in the B&S manual by adding one to the number at the end: 70 is Page 1, 71 is Page 2, etc, always followed by htm. If you want to read the book, it may be worth buying the download - there are close to 200 pages. I make extensive use of this manual on this site, but beware: it does not cover the Chinese or OHV Briggs engines.

Thanks grumpy, I will be sure to check this out!

Question though.. Even if I have a situation where by the fuel bowl is flooding, how come it seeps from the gasket seal rather than escape through an overflow?

Under normal circumstances (a good sealing carb) If I tip the machine excessivley back so that fuel is as high or higher than the gasket, the gasket should seal the bowl properly shouldn't it?

I understand I need to fix the root cause of why the bowl is flooding, I just can't understand why its leaking from an area sealed by a brand new gasket and two cleaned surfaces?

I'm thinking the casting may be ever so slightly warped in the corners where the screws attach to bowl to the carb body resulting in an improper seal due to low spots between the screws. Very hard to explain, only someone who has had a simalar problem would probably understand.

I will purchase a new needle and seat (although the one I have does not look bad) and try, but my hope for the leaking issues may be only half fixed. The seat on this carb can be simply unscrewed with a flat blade screwdriver.

Very frustrating!! Anyone else had this problem?

Craig.

It is not a great idea to have the float bowl gasket seal against pressure, because then you wouldn't know the carburetor was flooding. Fuel would go through the main jet and the discharge nozzle into the engine's intake pipe, without any external sign of trouble. That would be bad: if you left the fuel on when you parked the mower, it could hydraulic the engine. Chances are the starter motor wouldn't have enough torque to break the connecting rod when you next tried to start it, but it would be quite annoying if it did, and B&S rods are not very strong.

Warning: another of my anecdotes. I once saw a qualified motor mechanic trying to fit a K-Jetronic fuel injection system to a V8 Holden in place of the carburetor. He didn't bleed the fuel line properly, so when he switched on the ignition the system didn't reach full pressure, so fuel sprayed out of an injector, into the intake manifold. Then when he tried to start the engine, it was hydraulicly locked by petrol in the cylinder. That wasn't a big problem - car engines have strong connecting rods - but he needed to get the petrol out of the cylinder. He did the obvious thing, and removed the spark plugs, then cranked it. Unfortunately he had not disconnected the distributor low tension lead, so some of the loose spark plug leads sparked to ground while half a litre of petrol squirted violently out of a spark plug hole. The ensuing fire was unhelpful to the general condition of the car. It would have been seriously nasty if anybody had his head under the bonnet at the time.

No worries, but the an answer to the original question the carb shouldn't be leaking from the gasket right?

No, the carburetor should not be leaking from anywhere. If it leaks from the top of the float bowl, the problem is just about certain to be flooding - but any petrol leak is hazardous and needs to be fixed immediately. That is especially true of ride-ons - a fire right under your backside is low on everyone's list of preferences - but even on a walk-behind mower, a fire under the fuel tank can ruin your day.

So I have two problems, a leaking carb and a flooding float bowl. I will try and source and replace the needle and seat but what about the bad seal? Could i try two gaskets to try and take up the low spots? I will post a picture soon.

As mentioned the surfaces are clean and the gasket is brand new. The corner castings of the float bowl do however seem to be a tad ditorted. The four screws (1 in each corner) hold the body and the float bowl togethor. In the centre of the float bowl there is a section which seals higher than the rest of the casting. When the screws are tight the centre section bottoms out and the corners will bend. This was like this when I purchased the mower second hand and after been sitting around for years. Surely someone who plays with small engines a fair bit may know or can relate to something like this?

Here is a link to a perfect website explaining the small two piece flo jet carb I have.

Step 15 says "Check the flatness of the upper body and straighten the corners as necessary (#15)."

Now how do I straighten the upper body without breaking the corners?. I have had clamps on it to try and bend it back but i'm worried I'll break it if I bend it too far.

http://www.google.com.au/imgres?imgurl=http://outdoorpowerinfo.com/repairs/images/briggs_small_two-piece_flo-jet/_briggs_small_two-piece_flo-jet.JPG&imgrefurl=http://outdoorpowerinfo.com/repairs/briggs_small_two-piece_flo-jet.asp&h=480&w=640&sz=20&tbnid=6AQen4LG3Lup5M:&tbnh=103&tbnw=137&prev=/images%3Fq%3Dbriggs%2Bcarburetors&zoom=1&q=briggs+carburetors&hl=en&usg=__q_MHvumoy4AtH_3Sp-xGlvSGt-E=&sa=X&ei=jQbYTJemNYOWsgOx3rWOCw&ved=0CCcQ9QEwAg

Have answers..

http://www.perr.com/tip9.html

get some gasket silicone and seal that fucker up, no leaks, no mess, and no need to bend anything

Those sources look pretty good to me, but I always find myself impressed by really excellent photographs like those. I'm somewhat in tezza's camp: I tend to try sealing small leaks that are above fluid level by using a non-hardening sealant. It usually works satisfactorily. Of course if you have access to a cheap replacement carburetor that does not have any problems, that is even better.

This is what I will attempt.. Otherwise if someone has one thats working and wants to let go of it let me know..
Cheers.

If the carburetor body is distorted more than say 0.010", I would try filing away the high points (that is, the screw tabs) without filing the sealing surface, so that the tabs just barely bottom against the matching part when the gasket is compressed the right amount. The tabs have bent because there was originally clearance between them and the matching part, and some heavy-handed person over-tightened the screws, thus bending the tabs down. In other words, soft sealant to fill gaps of less than 0.010", and careful filing to fix bigger problems. Never bend castings, it often results in fractures.

As this thread is over 12 months old I will now close it for the archival value....If any member has anything to add, please send me a PM.