Small Engine Mechanics Help Needed

[Ducatiboy stu]

I have been swearing at my ride-on for a few months now..

It has a Briggs & Stratton 16hp vangaurd single. Model 28Q777-0667-A1

The problem being it would start and run fine , then after 5-10mins of mowing it would start to backfire and die...

Let it cool for a few hrs, then the same thing

I have replaced the plug, ignition coil, cleaned the carby, but still the same prob...

And now it doesnt have any spark...

Any ideas

 

[Zizzle]

Is that a magneto ignition?

If not, does it have points or a hall effect pickup?

 

[kirem]

I have a similar donk on my Cox Lawn Boss ride on ,with a B&S 13HP.

My FIL gave it to me and it had never been serviced, so last weekend I gave it a new spark plug, oil and oil filter and new blades, it ran a bit better and cut a lot better, then I realised I had forgotten the fuel and air filter. So I replaced them and the bloody thing is like a new one.

It would carry on and backfire etc when putting under load and engaging the cuttng deck, now it doesn't miss a beat.

I did notice the fuel filter was only 1/4 full when running, now it is full.

I am now looking for any simple mods I can do to try and squeeze a bit more HP out of it.

 

[MVZOOM]

Stu, after you do the onsumables - ie.. airfilter, fuel filter etc - if they dont solve the prob, get the carb serviced or get a re-build kit. There are some pieces in it that will need attention and should solve the issue.

Cheers - Mike

 

[Ducatiboy stu]

Well I gave it a tune today, after working out which screw was the mixture, and cleaned the plug....again..

Also found that the plug lead was shorting against the block

Seems like it has been running rich and fouling the plug..

Was amazing how well it run, it even idled nicely

So.....I gave it a good hard run on the lawn, cutting grass that almost made it stall, and it handled it well

Then....... Guess what happened after an 1hr....it started playing up and stopped dead...and wont start..


I am very anal about maint on it, allways has new oil, filters, driveline chains are allways greased, along with belt tensioners adjusted and oiled....

The motor does not blow any smoke or use any oil....I only use 30w red oil in it..and if it looks slightly black, I change it

 

[felon]

Did it start again after it cooled? Check your fuel line is not routed too close to hot areas. Could be getting vapour lock.

 

[Ducatiboy stu]

Is that a magneto ignition?

If not, does it have points or a hall effect pickup?

Magneto ignition, trigered off the fly-wheel...just like a motor bike, it has a strong magnet in the flywheel, which trigers the coil. The magnet is strong enough to provide the pulse for the spark plug... basically it is a self energising system that does not need a battery.

The battery is only there for the starter motor

Did it start again after it cooled? Check your fuel line is not routed too close to hot areas. Could be getting vapour lock

does start after cooled, but fuel lines are not near hot areas... I have replaced all fuel lines and filter ( and hose clamps )

If it was vapour lock, it would not run for 1hr under hard running....

 

[Ducatiboy stu]

I have a similar donk on my Cox Lawn Boss ride on ,with a B&S 13HP.



I am now looking for any simple mods I can do to try and squeeze a bit more HP out of it.

One of these will do the trick

 

[vic45]

Well I gave it a tune today, after working out which screw was the mixture, and cleaned the plug.


Clean the plug again and check for another mixture screw. It might have two, low and high speed.
On B&S the high speed screw is (if it has one) under the bowl of the carburettor right in the center. The best way to adjust the high speed mixture is under load.

Also check to see if it has valve clearance, B&S suffer from valve recession and valve guide wear.

 

[Ducatiboy stu]

Well I gave it a tune today, after working out which screw was the mixture, and cleaned the plug.


Clean the plug again and check for another mixture screw. It might have two, low and high speed.
On B&S the high speed screw is (if it has one) under the bowl of the carburettor right in the center. The best way to adjust the high speed mixture is under load.

Also check to see if it has valve clearance, B&S suffer from valve recession and valve guide wear.

Cant see another mix screw, the bowl has the solinoid under it, so not relevant..

I do know about valve clearance.... made the mistake of setting them at " 010", which is what I thought, but found out that that they are very fine..ie 020-050"

Have set the valve clearances...


When you run morris minores, and 308's with solid lifters, valves clearance is ...well...you just have to know how to do it

Not to mention my old International Diesel......

 

[MVZOOM]

Well I gave it a tune today, after working out which screw was the mixture, and cleaned the plug....again..

Also found that the plug lead was shorting against the block

Seems like it has been running rich and fouling the plug..

Was amazing how well it run, it even idled nicely

So.....I gave it a good hard run on the lawn, cutting grass that almost made it stall, and it handled it well

Then....... Guess what happened after an 1hr....it started playing up and stopped dead...and wont start..


I am very anal about maint on it, allways has new oil, filters, driveline chains are allways greased, along with belt tensioners adjusted and oiled....

The motor does not blow any smoke or use any oil....I only use 30w red oil in it..and if it looks slightly black, I change it

This is what mine was doing. Removed plug, cleaned, ran nicely - then spluttered and died after a period of time. Carb rebuild kit = fixed.

 

[pokolbinguy]

Be very careful using E10 fuel in small
Motors aswell. We had all kinds of fun fixing our lawn mower, whippersnipper and chainsaw after using it. Causes the engine to gunk up and makes it all kinds of fun to start. Just beware!!

 

[mika]

There's no movement in the flywheel is there ? Or in the crank bearings resulting in an inconsistent gap to the magneto ?
The spark only dissappears when it's hot ?
If it's cold, and you're just pulling it over does the spark get progressively weaker ?
I'm thinking an ignition control module that's getting hot and failing.
I was thinking coil, but you said you replaced that ? Might be worth checking the resistance on the ignition lead if it hasn't already been replaced, multimeter and give it a good twist around while measuring to be sure.

 

[Zizzle]

There's no movement in the flywheel is there ? Or in the crank bearings resulting in an inconsistent gap to the magneto ?
I'm thinking an ignition control module that's getting hot and failing.

Both good points.

I've had a CDI give of the ghost before.

But they tend to be pricey to replace. I ended up building my own.