20Hp Vanguard running rich?

[TArrryan]

Hello Arbtalk

 

I have a 20Hp Briggs and Stratton vanguard engine powering a Countax A20/50 ride on mower. In the past month I have noticed it's been using allot more fuel than It did at the beginning of the year, one tank use to last the day but now I'm using more than 2 tanks a day on the same work!!

 

There is also a loss of power when climbing slops, this becomes more noticeable with the cutting deck engaged, after pausing the mower for a few seconds the revs will pick up again and you can carry on for a short distance longer.

 

I have also noticed a very strong petrol smell around the mower when it is running, I have checked for leaks and none have been found (the fuel line is only 2 feet long)

 

From looking inside the carb while It's running we can see one cylinder is getting more fuel than the other, The over fuelling cylinder has a very wet spark plug while the other spark plug is as dry as a bone. we have removed and cleaned the carb twice now with no change to the jets.

 

We have tried very hard to find the source of the problem and we are now beginning to lose patience with It.

 

Ill quickly list what else we have looked at.

The tappet clearances have been set correctly (we have the workshop manual).

A full service carried out (oil, all filters, spark plugs) with no change in performance.

Both cylinder have been checked for loss of pressure and are running at 160-170 psi.

Spark plugs have been swapped with no change.

Both cylinders are pulling in an equal amount of air.

There is no smoke coming from the exhaust (white, black or blue)

oil level remains constant.

 

There Is a fuel pump on the side of the engine but we do not suspect this otherwise the problem should be common to both cylinders.

 

Has anyone got any ideas?

[Simon R]

Check for a good spark on the problem cylinder with spark tester.... Possible coil breaking down under load........set air gap on ignition unit to about .008/.010 thou....

[GardenKit]

If one cylinder was not getting fuel I would expect to find a blocked jet and a drop in both power and fuel consumption.

 

Assuming that the jets are not blocked, because you have checked, and cleaned the carb, then I wonder if you have lost the spark to one cylinder (the wet one)

 

This would cause the loss of power, and the increase in fuel use as the one good cylinder will have to work harder to keep the revs up and so the governor will be keeping the throttle open more.

 

I think it will be as well to check the spark. Do this first by just using a spark tester. This will verify if there is a spark. Then you need to identify the fault. It could be a duff coil, but could also be a duff diode in the earthing loom. To test this, remove the engine cowl to expose the coils. Remove the earth wires from both coils and recheck the spark.

 

If there is still no spark, the coil is duff, if there are sparks on both then the earthing loom needs replacing.

 

Best of luck.

Edit.Sorry to Simon, I was writing this while you were posting

Edited July 3, 2012 by GardenKit