Engine slow flame (backfire) and won't start. victor v40 4-stroke - SOLVED.

[Bender360]

Hi folks,
This is my first post so my apologies if it's in the wrong spot.
I have a Victor V40 4 stroke push mower that was working perfectly. Couple of weeks ago I was mowing away (it started perfectly cold) but eventually needed to empty the catcher. Throttled down to idle, took out the catcher, emptied, came back to a stalled mower. No big right? Um, yeah, big. It would not restart. I'm used to the habits of this mower and this was new. Normally it will start within 2 pulls even cold, hot is even easier. But this time no. After several pulls with half or even full throttle (no choke) it would not fire, so I tried choke one of two pulls then back to half throttle - no joy. But every few pulls I'd get a slow flame backfire (woooof wooof) sound. I thought I'd flooded it - and probably did using the choke when hot. So I left it for 30 minutes and came back to the same situation. So I left it an hour, then came back. Same woof woof, but I left it at 2/3 throttle and just kept going - eventually it started the fire once and woof woof still. After about 50 pulls (including pulling as it coughed - ie: keeping it spinning) it fired into life and actually ran normally. I finished the lawn then shut it off and immediately tried to restart it and couldn't. Same woof woof would occur. So at this point I'm thinking fuel, carbi, air filter.

I left it for a day, tried again with air filter removed (just to test if it was blocked), same deal (woof woof - but would not start cold). Okay, so I have a problem. Here's what I did to try to fix it:

1) Drained carbi bowl - tried to start, no joy. Same woof woof slow flame eventually (after say 5 to 8 pulls)
2) Pulled off carbi, cleaned all jets with carbi cleaner and wd40 with tube, cleaned needle valve for bowl, tested float operation - all good (i've done this before a few years ago so knew the process). Put back together without issue, but still same problem - no starting but woof woof backfire.
3) Drained the fuel tank and carbi, put in new stuff, same problem.
4) Checked sparkplug - can see visible spark on slow pull earthed to engine. Gap ok. Cleaned spark plug, reduced gab (a couple of thou). Same problem exists.
5) Swore at it a bit, poured a drink (two), had a think about it.

I'm kinda at a loss. If it was timing, why would it eventually fire up again the day it stalled? I agree it's presenting like timing or possibly
valve gap (or burnt valve) maybe?

If anyone has any ideas I'd appreciate hearing them.

Cheers and thanks.

 

[bertsmobile1]

Bender,
Most of the techs here are from the USA so V 40 will mean nothing to them.
For the rest of you, the V 40 was a GXV 160 clone out of China which Victa fitted , contry to their del with Briggs & Stratton that triggered the Briggs take over .
I think they came out of the Sanli factory but am not sure.

From what you have posted , t sounds very much like a blown head gasket.
Take the top cover off and look for tell tale oil leaks from the head/ cylinder joint line.
These engines had a lot of problems due to non existent quality control like a lot of the stuff source from China on a least cost basis .
If you got a good one they are great.
The other known major failure is the plastic gear on the cam shaft dropping a tooth or two which puts the valves out of time .
This is a little harder to test and can cause the head gasket to blow so you might have both.

To check the valve timing, remove the spark plug & rocker cover
The cover was siliconed on a lot of them so is difficult to remove without bending it out of shape so be careful.
Put a screwdriver down the plug hole so it touches the piston then slowly rotate the engine while watching the rockers moving the valves

Rotate the engine till the piston is nearest the head and both of the rockers are loose.
This is the firing stroke and the magnets on the flywheel should be just coming past the first leg of the coil
Both of the rockers should stay loose till the piston is almost at the other end of the stroke then the exhaust should start to open and remain open while the piston is coming back to you
Just before it closes the inlet should open and stay open for the entire time the piston is going back away from you.
If this is not happening then the cam is busted
Drain the oil and have a good look for little bits of plastic ( or metal ) in the oil

I don't think it will be a failure of the ignition timing key but wile pulled apart this far it will not hurt to remove the starter cup & nut / bolt that holds the flywheel on.
If you look at it end on there will be 2 rectangles cut into the shaft & flywheel that come together to form a perfect square and in that square is a aluminium key.
This can shear and allow the spark to happen at the wrong time.
This almost never ever happens with any Victa because the swing back blades take the shock of hitting some thing while mowing .
I have never seen one broken &I have pulled down better than 300 engines , but it is only another 10 minutes to check it and rule it in or out.

 

[Bender360]

Bender,
Most of the techs here are from the USA so V 40 will mean nothing to them.
For the rest of you, the V 40 was a GXV 160 clone out of China which Victa fitted , contry to their del with Briggs & Stratton that triggered the Briggs take over .
I think they came out of the Sanli factory but am not sure.

From what you have posted , t sounds very much like a blown head gasket.
Take the top cover off and look for tell tale oil leaks from the head/ cylinder joint line.
These engines had a lot of problems due to non existent quality control like a lot of the stuff source from China on a least cost basis .
If you got a good one they are great.
The other known major failure is the plastic gear on the cam shaft dropping a tooth or two which puts the valves out of time .
This is a little harder to test and can cause the head gasket to blow so you might have both.

To check the valve timing, remove the spark plug & rocker cover
The cover was siliconed on a lot of them so is difficult to remove without bending it out of shape so be careful.
Put a screwdriver down the plug hole so it touches the piston then slowly rotate the engine while watching the rockers moving the valves

Rotate the engine till the piston is nearest the head and both of the rockers are loose.
This is the firing stroke and the magnets on the flywheel should be just coming past the first leg of the coil
Both of the rockers should stay loose till the piston is almost at the other end of the stroke then the exhaust should start to open and remain open while the piston is coming back to you
Just before it closes the inlet should open and stay open for the entire time the piston is going back away from you.
If this is not happening then the cam is busted
Drain the oil and have a good look for little bits of plastic ( or metal ) in the oil

I don't think it will be a failure of the ignition timing key but wile pulled apart this far it will not hurt to remove the starter cup & nut / bolt that holds the flywheel on.
If you look at it end on there will be 2 rectangles cut into the shaft & flywheel that come together to form a perfect square and in that square is a aluminium key.
This can shear and allow the spark to happen at the wrong time.
This almost never ever happens with any Victa because the swing back blades take the shock of hitting some thing while mowing .
I have never seen one broken &I have pulled down better than 300 engines , but it is only another 10 minutes to check it and rule it in or out.

Thank you for the awesome reply! This will be my weekend job, but at least now I have a few things to easily test and look for. Very much appreciate your help!
I'll post the results in the hope it helps someone else also.
Cheers

 

[Bender360]

Bender,
Most of the techs here are from the USA so V 40 will mean nothing to them.
For the rest of you, the V 40 was a GXV 160 clone out of China which Victa fitted , contry to their del with Briggs & Stratton that triggered the Briggs take over .
I think they came out of the Sanli factory but am not sure.

From what you have posted , t sounds very much like a blown head gasket.
Take the top cover off and look for tell tale oil leaks from the head/ cylinder joint line.
These engines had a lot of problems due to non existent quality control like a lot of the stuff source from China on a least cost basis .
If you got a good one they are great.
The other known major failure is the plastic gear on the cam shaft dropping a tooth or two which puts the valves out of time .
This is a little harder to test and can cause the head gasket to blow so you might have both.

To check the valve timing, remove the spark plug & rocker cover
The cover was siliconed on a lot of them so is difficult to remove without bending it out of shape so be careful.
Put a screwdriver down the plug hole so it touches the piston then slowly rotate the engine while watching the rockers moving the valves

Rotate the engine till the piston is nearest the head and both of the rockers are loose.
This is the firing stroke and the magnets on the flywheel should be just coming past the first leg of the coil
Both of the rockers should stay loose till the piston is almost at the other end of the stroke then the exhaust should start to open and remain open while the piston is coming back to you
Just before it closes the inlet should open and stay open for the entire time the piston is going back away from you.
If this is not happening then the cam is busted
Drain the oil and have a good look for little bits of plastic ( or metal ) in the oil

I don't think it will be a failure of the ignition timing key but wile pulled apart this far it will not hurt to remove the starter cup & nut / bolt that holds the flywheel on.
If you look at it end on there will be 2 rectangles cut into the shaft & flywheel that come together to form a perfect square and in that square is a aluminium key.
This can shear and allow the spark to happen at the wrong time.
This almost never ever happens with any Victa because the swing back blades take the shock of hitting some thing while mowing .
I have never seen one broken &I have pulled down better than 300 engines , but it is only another 10 minutes to check it and rule it in or out.

Bender,
Most of the techs here are from the USA so V 40 will mean nothing to them.
For the rest of you, the V 40 was a GXV 160 clone out of China which Victa fitted , contry to their del with Briggs & Stratton that triggered the Briggs take over .
I think they came out of the Sanli factory but am not sure.

From what you have posted , t sounds very much like a blown head gasket.
Take the top cover off and look for tell tale oil leaks from the head/ cylinder joint line.
These engines had a lot of problems due to non existent quality control like a lot of the stuff source from China on a least cost basis .
If you got a good one they are great.
The other known major failure is the plastic gear on the cam shaft dropping a tooth or two which puts the valves out of time .
This is a little harder to test and can cause the head gasket to blow so you might have both.

To check the valve timing, remove the spark plug & rocker cover
The cover was siliconed on a lot of them so is difficult to remove without bending it out of shape so be careful.
Put a screwdriver down the plug hole so it touches the piston then slowly rotate the engine while watching the rockers moving the valves

Rotate the engine till the piston is nearest the head and both of the rockers are loose.
This is the firing stroke and the magnets on the flywheel should be just coming past the first leg of the coil
Both of the rockers should stay loose till the piston is almost at the other end of the stroke then the exhaust should start to open and remain open while the piston is coming back to you
Just before it closes the inlet should open and stay open for the entire time the piston is going back away from you.
If this is not happening then the cam is busted
Drain the oil and have a good look for little bits of plastic ( or metal ) in the oil

I don't think it will be a failure of the ignition timing key but wile pulled apart this far it will not hurt to remove the starter cup & nut / bolt that holds the flywheel on.
If you look at it end on there will be 2 rectangles cut into the shaft & flywheel that come together to form a perfect square and in that square is a aluminium key.
This can shear and allow the spark to happen at the wrong time.
This almost never ever happens with any Victa because the swing back blades take the shock of hitting some thing while mowing .
I have never seen one broken &I have pulled down better than 300 engines , but it is only another 10 minutes to check it and rule it in or out.

Hi again,
Sadly I'm still in no go city.
I'm attaching some pics to help explain what I'm seeing (or not seeing) as I still can't find the problem.

When I looked at the outside I thought I had a blown head gasket. (Side pic with head assembled).

I removed the spark plug and rocker cover. I checked valve movement for all cycles - it is correct from the perspective the valves open and close when expected to.

I found TDC (both rockers loose) and noted flywheel position re timing. To me this looks slightly off, but I'm a little confused as there are three magnetic points on the flywheel and it lines up with two of them at tdc loose valves. (Rocker cover off pic).

Next I checked the flywheel key location - I couldn't tap the flywheel off. I suspect a little corrosion on the shaft and I didn't want to force it. I will to tap it off from underneath with a rubber mallet when the rain stops. I took a pic of the key position from above with nut and cup removed.

Next I removed the head. The head gasket appears fine - no blow-by on head or cylinder side. (Pics accompanying). There is a little scoring on the bottom of the cylinder, but it's very minimal.

I checked the valve seats, they look okay. No pitting I can see, though I didn't remove them so I can't be certain.

I'm borrowing a compression tester as I can turn the flywheel with one hand with the spark plug in tight. Should I be able to do this? I can feel clear resistance and compression, but I'm not sure if that's a clue.

I double checked the carbi float is working correctly as I thought maybe it's flooding and just pouring in fuel. It's definitely working correctly.

The compression is a grey area for me. I think it should be stronger, but I don't have a number to give you yet.

From the pics, does anything jump out at you that I've missed or got wrong? The three magnetic points on the flywheel have confused me, but the key looks like it's in the right position so I think it's just my being confused.

I appreciate any incite you or anyone else can give.

Cheers and thanks!

 

[Bender360]

THIS IS SOLVED.
For anyone interested, the problem had nothing to do with compression, head gasket or timing. The issue was the spark plug - yep, the friggin spark plug! Even though I had decent spark - it was CLEARLY visible during the day AND re-gapped it AND cleaned the contacts, it was definitely the problem. I pulled one off a two stroke chainsaw, put it in the mower, and it started second pull. Spark was one of the first things I tested, but I didn't factor in a faulty plug.
So there you have it. A faulty plug will give a weak spark, which IS enough to give partial ignition, but not enough to burn the fuel properly. I would have thought that an old wives tail, but I've just done some research and it's a known thing.
Thank you Bert for your awesome attempt at resolving this. Now excuse me, I have a jungle to mow! hahahaha