OutdoorKing Repair Forum Forums Repairs and Maintenance Questions on Engines Questions On Briggs & Stratton Engines Vanguard Twin B&S 14hp power loss

G'Day kind viewers.
I have a problem with my 14 hp V Twin OHV Vanguard (model 294777 type 0035-01).
This motor runs my 4 wheel steer MTD White. The carb is a Aisam single carburetor.
The engine has been well looked after and given its required servicings.
It's is relatively fresh and has done less than 150 hours.

The problem; gradually the mower began to faulter under load and would blow a small amount of blue-grey-black smoke while running rough. If you took the load off by disengaging the blades, the motor would begin to run well again.
These symptoms gradually worsened untill even short grass would make the mower faulter.

I have changed the plugs, filters, cleaned the fuel pump diaphragm, gave the carby a basic clean out, installed an in line fuel filter, changed the fuel and checked the valves (which I closed the gap a fraction).

After my servicing, the mower ran quite well for half an hour untill beginning to display its problems again.

The mower shop would be the place to send it, but this time of year they have a line of broken mower jobs stretching out the door and down the street. I was told that I mightn't see my mower till Xmas. So I have had a good read of many posts, questions and answers on this site, and thought I would try the site for any possible solutions to my woes.

Any help would be gratefully received, and I am happy to write-up my success/failures on the site for other peoples future references.

The grass is currently 13cm tall and we have just had 3 inches of rain. It's becoming urgent !

Check you valve clearances again. Just to be sure that a lock nut has not come loose etc.



Id say with your fuel cleaning, its been ok and now its not again. Id be getting into that carb. Can of carb cleaner, compressed air and squeaky clean it. Lay it all out on a nice clean old sheet. Continually chean your hands.


(you might be able to get a new one on eBay Ex USA for a good price too)

Your symptoms seem to be closely in line with those for a blown head gasket. Essentially, after warm-up your engine is effectively running on one cylinder.

The engine you have is notorious for blowing head gaskets. They always seem to blow between the combustion chamber and the oil drain hole or pushrod chamber, sometimes passing through the cavity around a head-attaching stud. There have been suggestions that a common cause of the problem, is overfilling the sump with oil.

I suggest you check for signs of heavy blow-by: remove the dipstick or oil filler cap, run the engine and see if gas is blowing out of the hole where you removed it. If you have heavy blow-by after 150 hours, and the engine has not been seized up, it is very likely one of your cylinders has blown its head gasket between the combustion chamber and the pushrod chamber.

In its early stages, a Vanguard with the characteristic blown gasket tends to run satisfactorily from cold then leak worse and worse as the engine gets warmer. Then, as the gasket damage progresses, it leaks right away from a cold start.

It is quite easy to fix, but it is not a good idea to run it under load in the meantime. It will erode the top of the cylinder and/or the underside of the head, and make a small job into a big one.

Thanks to both RBob and Grumpy for the help replies.
Blown gasket was off my radar, so I will go start it this morning and double check. I might as well do a compression test and see how both cylinders compare. There is no oil around the base of the oil filler tube, so I'm not sure that there is much blow-by if any.
I redid those valves last night (4 to 6 thousandths). Valves were a little loose but not by much at all.
The plugs were very dark . I gave them a clean up. The carby is next.
I will let you know what happens.

Ordinarily if a Vanguard or Intek has loose tappets the decompressor doesn't work and the starter can't turn the engine over, so I doubt your tappets are involved in this problem. Remember that the decompressor affects compression test results, but if the head gasket is leaking at the time, there should be a difference between cylinders. Unfortunately in the early stages of the disease, the gasket does not leak from cold, and of course you can only find symptoms when it is actually leaking. The "check for blowby" test only works when the engine is actually misbehaving.

Incidentally it seems to be fairly commonplace to remove the head, inspect the gasket, and not be able to detect a problem, but if it is reassembled with the old gasket it still has the problem, whereas a new one cures it. With practice, really close inspection around that center stud does show some slight blackening, but nothing spectacular - in fact nothing most people would notice.

Anyway, whatever it is, you should be able to find it before long. There are no complicated parts involved. I can't match the symptoms to a carburetor fault, but without actually seeing and hearing it, there is a lot of guesswork involved. I look forward to finding out what was wrong.

Oluoot,

I have similar issues with a Kawasaki engine and it came down to faulty spark plug on one cylinder. I would also check that you have the correct plugs installed.

It is a cheap fix replacing plugs as you can get new ones that are faulty.

I was going on the assumption that it was OK then when warmed up its playing up and doing it all the time now. hence carb.
But if its Ok when cold i agree with grumpy, its unlikely to be the carb.

Plugs were something i did not think of.

Alright fellas this is what is going on with this mower of mine.
I replaced the plus again (just in case in case).the carby got a carefull clean and inspection. Valves are right still.
I ran it from cold and got about 20 minutes of grass cutting done before it started the rough running and spluttering.
I throttled back to an idle and ran it for a couple of minutes and then on throttling back up to running speed, it coughed, missed and belched a load of black smoke.
I took out the right hand side plug and took a compression reading of 95psi. Replaced it and took out the left side. The Mower wouldn't start and a compression reading taken off the starter motor turning it over read 165 psi.
It looks as though the head gasket is going to be the culprit.
Time to clear a floor space and see how this thing comes apart.

I think you are now a long way further ahead, Oluoot, and are headed in what is most likely the correct direction. You can get a free download of the B&S workshop manual for that engine here:
http://www.4shared.com/get/EUOFwobA/272144_Vanguard_Twin_Cylinder_.html

The illustrated parts list and operator's manual are also available as free downloads. Parts list:
http://bsintek.basco.com/BriggsDocumentDisplay/Z6orvIVJ1DajI.pdf
Operator's manual:
http://bsintek.basco.com/BriggsDocumentDisplay/msvuAQ-K_ny7tH217FzoPu.pdf

Meanwhile there are literally dozens of internet discussions about blown Vanguard head gaskets you can find with a simple search. You might care to look at this one:
http://forums2.gardenweb.com/forums/load/tractor/msg1119005310306.html

Thanks again Grumpy (et al.). I loaded up that manual on the iPad and went through it the other night. Mate, there is some detail in that document. Here I was thinking I might be going into this head gasket job blind.
Still raining and grass still growing. I've toyed with the possibility of dragging the Allan Oxford sickle-bar out of the shed! Although I got over keen and began a resto on the Greenfield while sorting out the White. In the meantime the Grassmaster is holding the green hordes back.
The head-job starts next week. That doesn't sound quite right, does it?
Once again, thanks on a brilliant site and resource base.
Will keep you posted.

Thanks Oluoot, we've never had a Vanguard head gasket job documented in detail so far. If you can take some pics as you go along and post them here it will make this into an important archive that can save other members a lot of frustration and self-digestion of the liver and other organs in future.

I'll leave this thread open in the hope that you'll be able to help us.