OutdoorKing Repair Forum Forums Repairs and Maintenance Questions on Engines Questions On Briggs & Stratton Engines Quantum XTL 45 Cat - Hard to start and shakey

Good morning all.
Have a Husqvarna mulch mower with a Briggs and Stratton XTL 45 model 127802 Type 1539-81 code 99122359 motor that will only start using aerostart intervention and will cut out if the air cleaner box is closed unless the engine is revved up. It also shakes slightly when running, which I thought replacing the sheer pin on the flywheel would have fixed due to timing alignment.
This mower/motor combination has no throttle or choke cables using only the governor from the rear of the motor. (Photos attached)
The carburettor is the Primer version and has no mixture screw adjustments at all. (Photos attached)
So far, I have replaced the o-ring at rear of carbie intake tube, new gasket on air cleaner box, cleaned internal of carbie of varnish and grime, replaced flywheel sheer pin (half sheered), checked intake tube gasket at motor and tightened, cleaned rust from magneto and coil, replaced spark plug and installed a new air filter.
Attempted to complete the compression test, which was only 35 psi, but believe this model runs some form of decompression, which makes it difficult to test but easier to start. If it doesn't have this, then my problem is obviously compression and new rings would be in order.
If it is compression, I believe these engines are not very well suited to having new rings installed or being honed for O/S rings and pistons (plus cost of doing so), but I could easily be wrong/mislead.
Have removed the carbie again and taken photos for reference purposes to attach here and will give it another clean. Appears I missed a small jet on the left hand side front of carbie intake (near air box) that looks like it is covered in stale fuel varnish.
Have also played with the governor spring to get full throttle, which appears may have bypassed the mowers ability to use it's auto-choke.
There was a lot of oily grime around both the top and bottom of the engine indicating possible seals blown, which could have been caused by the flywheel sheer pin throwing out timing. Neither have been replaced at this stage due to trying to determine cause of hard starting and running rough.
Couldn't find any information on the XTL 45 using searches on this forum site, so thought it may help others if I can find my cure.
Thank you for your assistance.
Regards
Daryl

the new gasket between carb and air cleaner box should fix your primer problems or is it the same since you replaced it ? with the air filter out and back fitted up try priming and look in there , you should be able to see if its working when all fueled up .
did you clean out the main jet ? it is the nut that holds on fuel bowl , if you look at it you see one lareger hole through it just above the nut part and in the top a tiny hole ? make sure they are clean and free the tiny one catches a lot of people . poke a jet cleaner or strip the plastic from a bread tie and gently poke it in untill your sure all clear . did you reset the air gap when you had flywheel off ?

take a job card or business card , put between the ciol and flywheel , turn until the magnets suck it too flywheel and lock it up there all set .

is it a blade bar cutter or bar with blades ? could be out of balance as they do when older and been sharpened a few times . check it and see if it balances on a screwdriver .
see how ya go there bushy , even old worn and smokey they still will start n run unless its valve clearance too but we go into that later .

, Dave

Thank you vccomm for your quick reply.
The new gasket between the carbie and air box didn't help, although I was hopeful it would. It is still hard to start, but at least it stopped the fuel flowing out of the primer button hole.
Neither did replacing the worn out o-ring on the intake port/tube or replacing the sheer pin on the magneto/flywheel, which I thought was the cause of the "Hard to start" issue. In my mind, the sheer pin replacement should have worked with regard to affect on spark timing.
The primer pumps fuel through the carbie and into the intake area, but I originally noticed that excessive fuel pumps on the primer returned fuel through the carbie to the air filter area if used to excess.
The main jets, along with every other orifice I had located, have been cleaned with Carbie Cleaner (again today) with no real effect to overall issue, and all holes in the main jet (nut) are clear.
There are no fuel leaks from either the bowl or nut area, which indicates a good seal for both.
Air gap on the coil was reset using a business card, which I normally use a pair of feeler gauges at 0.010" to complete.
I haven't tried to balance the single bar blade as yet as main issue is that the mower is hard to start. It gives an initial cough and splutter, like it wants to start, but fails to fully fire, unless helped using Nulons "Start you bastard", which has got me wondering why.
Appreciate your help.
Thank you.
Daryl

so it sounds like the primer is working , but they dont push fuel , air only and into the bowl that in turn pushes up the fuel through a hole in jet tube .
so it tries to start but just coughs n wont quite make it ? then starter spray n off she goes huh . and low on comp' you almost think ?
remove the plug lead and be SURE to secure it away from the plug . sit it up so you can get to the blade , turn it until you feel resistance and see how it feels from there . when you feel comp' back a little , see if it sort of bounces back when it gets compression . is it smokey at all ? there is some numbers on coweling that tell its date/age , how much work has it done . might just need valve adjustment too .


oops , just checked , its 99 . so its 16 now sort of , so could be time for some real servicing , did it get worse slowly or just didnt like to play one day .
if it is of any help , most times i just get rid of the bail bar and brake set up , move the kill switch to the throttle plate and fit a cable , its all there and just needs to be fitted and parts moved

Thank you again vccomm for your quick reply and, you may have just confirmed my suspicions, as there is no resistance when rotating the blade at all with regards to compression. As such, tomorrow morning, I'll pull the head off and see if there is any issue with carbon build up on the valves caused by the sheer pin issue putting timing out. If there is no excessive build-up around the valve heads, then it has to be wear of the compression rings from age. Smoke wise, when running, the oil rings must be pretty good as there is little to no smoke from oil burn. Excessive oil and associated grime, at both ends of the crankshaft, would indicate the seals will also need replacing with a new set of rings.
As this belongs to a customer, can I get away with just a set of rings without knowing the full history of the mowers use? Maybe a changeover motor would be best option then rebuild this one as a future replacement for me or someone else?
Your assistance has helped confirm my suspicions.
Much appreciated.
Regards
Daryl.

Bushy260 most commendably gave the 'magic numbers' in the OP.
1999 manufacture should be US-made, but we have our suspicions about any engine with a 'plant number' [the last two digits of the Code] in the 50's being early Chinese-made examples. The early Chinese engines had a few quality control issues...

2002 is the changeover year [for their small sidevalve engines] that Briggs give, but there is reason to believe that this may not be definitive.

The partly sheared flywheel key will be due to the blade striking some solid object - always an issue with this blade type. And it's one reason that that key is a 'designed weak point', and made of soft alloy.

Replacing the key, as you say, will have fixed any spark timing issues.

And it sounds like the primer is working OK - as vccomm says, what it does is to pump air into the float bowl vent circuit.

The usual reason that these Walbro carbies leak fuel out through the primer bulb hole, is that the needle/seat float valve is leaking. This can be due to muck, or to the soft neoprene seat having gone hard with age - and the age of the machine makes me suspect the latter.

For sure, take the head off to check for deposits - but it's not common to find much on the valve sealing faces.

Compression issues due to rings are not super-likely - as vccomm has mentioned, lack of tappet clearance [especially on the exhaust valve] is the next most common cause of hard starting in a Briggs, after carby and ignition.

Time to check these too, while the head is off - it's easily done, since the cowlings will all be off anyway.

Thank you Gadge for your reply.
The factory number is 59 according to the code reference.
I thought the partly sheered flywheel key would have fixed the rough running issue, but it didn't. Machine still has the wobbles when running, but the motor seems to be rubber mounted on the frame bolts, indicating this was an expected standard.
The primer leaked fuel when I first picked it up from my customer and put fuel in it, but this issue has since stopped after the initial carbie clean.
There appears to be very little compression when turning the blade by hand and, with compression test result being so low, after 3 pulls, only registering 35 psi, was a poor result.
Not sure where to turn, except compression rings, or lack thereof.
There was a lot of oil gunk built up at both ends of the drive-shaft with my thought being incorrect timing adding pressure to both magneto and pto seals due to sheering of flywheel pin.
Photo of oily gunk build-up on top of motor (under magneto) is now attached here for reference....

Sorry, no photos of oily gunk build-up from bottom end as main concern was initially to get it going.
I am starting to have a total dislike for these "self-controlled" no-throttle no-choke versions, but they seem to be coming more popular mowers.
Head will be taken off tomorrow for a look, but I'm at a loss. At 16 years, compression may be an unexpected issue, but may be the ultimate solution????
Appreciate your help, assistance and advice.
Thank you.
Daryl

Hi Darryl, Remove the muffler and remove the valve cover. In there you'll find the valves. Check the clearances at TDC, the valve clearances will more than likely be closed up causing your valve to not remain closed lomg enough thus causing your low compression issues. Valve clearances are (Inlet: 0.005-0.007, Exhaust:0.007-0.009 inches)
As for the vibration issue, check the crank by spinning the blade and see if it is spinning true, keep your eye on the bolt in the centre to see if it deviates away from centre at all as it spins around.

Thank you bigted for your reply and information provided. I'll have to check the valve clearances tomorrow as I work on these machines at home and don't have a shed with today being rather stormy. My enclosed area is small and full of machines, so I use an area outside to do any mower work. Appreciated all the assistance provided and will update on results to help others looking at similar issues.
Regards
Daryl.

i almost always ask the customer if they REALLY like the bail bar setup and no throttle as it is easy enough to fix just by moving the kill tab to the throttle plate and the brake goes bye bye maybe 1 out of 5 like it the way it is , most didnt know you can do it .
most of then have oily looking gunk too if they work hard as yours seems to look like it does and probably was parked because of the vibrations . it scares people LOL then they forget it and it wont start after a while sitting with old fuel , while your at it fit an inline tap and advise them to run it low on fuel when season is done then less damage .

Thank you vccomm for your additional information and suggestions. I had considered getting an in-line fuel shut-off as I don't like the idea of any machines not having one installed. Seems its just a way of saving a lousy pittance rather than consider customer convenience. On the other side of the coin, I guess it keeps fuel in the whole system for these units with no choke, but this has a primer so that, I suppose, makes this side of the argument rather mute.
Wouldn't moving the cut-off switch over to the throttle plate involve extra cost of adding a throttle control assembly just to stop the machine, as speed is self-governed with the only change being removal of the spring loaded brake handle and assembly? At least it keeps the magneto clean of rust
Will check on these options after checking the valve clearances and if I can get the mower running without a rebuild due to increasing potential costs of repairs.
Appreciate your assistance.
Regards
Daryl

Hi bigted. Finally got back to the mower. Removed the head, muffler and valve cover. The intake has zero clearance and the exhaust has a reasonable 0.011" or a tighter 0.012" gap. Piston and cylinder wise, both have a lot of oily carbon build-up, and some was loose and wettish and each revolution of the piston drags a little oil into the cylinder. From what I've read and watched on youtube, I believe the only way to do the gap for the intake, which is also (possibly) why it's hard to start, is to remove the valve and file down the end until I get the 0.005"-0.007" gap needed. Gueess there's not much that can be done about the exhaust gap, unless I replaced the valve. Getting almost to a rebuild at this point. I have attached photos of the piston, cylinder, head and valves. Not sure if they will help, but cylinder seems to be okay.
Thank you for your assistance.
Regards
Daryl.

The exhaust valve gap can be closed up by lapping the valve. You be surprised how quick it closes up sometimes.

And when filing the intake stem to increase clearance keep it as square as possible. I usually rotate the valve as I file them down which helps keeping it squared. After the initial filing lap the valve and re-gap as needed. BTW it will not take a lot of filing either to over do it.

Now to that blown head gasket check your head and block for warp-age as it looks like it has been ran extremely hot. I had several from a local nursery here they are constantly clogging the cooling system.

My first attempt at a valve adjustment on a flathead Briggs and Stratton side-valve motor.
Biggest surprise was it started first pull, after 5 x pumps on the primer bulb, although it still has the shakes, it started without "Start you bastard" down it's throat.
Left it for about 3 hours and it started again on 2nd pull.
Still have to check the blade to see if it, or the driveshaft are bent, but inital "hard to start" problem seems to be sorted. Thank you.
So, let me say,a big "Thank you" to bigted, vccomm, Gadge and AVB for your assistance and input with regards to these issues.
vccomm, carbie gaskets and all seem to be good now after replacing and no fuel leaks.
Gadge, looking at the cyclinder, it appears in reasonable condition.
bigted, I eventually got the inlet valve out and filed it down. Seemed like the pushrod was also sticking to the valve making it harder to get the feeler gauge in to check, but ended up with clearance maxing the 0.007" limit (or slightly over with a tight 0.008"). Clearance on the exhaust valve is noiw showing more around 0.010" without touching it. Close for my first attempt at this. Compression test now reading around 77 psi, which is up around 40 psi after valve filing. Good advice. Thank you.
AVB, I don't have the suction tool for lapping, so it was put back together without doing this. I did consider using toothpaste, which is like a mild abrasive, to do this, but cleaned the edges of the valve head with a small toothbrush size wire brush. Re-used the existing head gasket, and looking at the carbon build-up on it, it really should be replaced, which could increase compression further.
Photos attached of compression test to help others understand what the difference can be.
Thank you all for your assistance.
Regards
Daryl

Well, mowed a section of the yard. Started the mower for the third time on 2nd pull, so inlet valve clearance of 0.000" seems to have been the main issue of both low compression and hard to start. As for the wobble, increasing the engine revs has reduced this as well. Maybe it was running too low?

I usually allow +- 10% of the gauge readings as that is within most gauge tolerances but 65-70 psi is normal for these engines as they do have bump decompression. This is usually on the exhaust valve so that more clearance on that valve decreases the bump and increase compression at start-up.

Briggs don't publish minimum compression numbers because this decompression but I have through experience found around 70psi is a normal good reading for these L-heads.

Good work there Bushy, that's another one rescued from the scrap pile for what is really a fairly simple job. I've done quite a few of these now and can get them done in 45mins-1hr.
Now to look at the crank and make sure it's not bent, if it's not then you probably just need to sharpen and balance the blade.

Thank you AVB for your information on compression. Is comforting to know that compression is about average, saving owner the cost of a rebuild.
Thank you bigted for your compliment on my first valve clearance adjustment. Checked the blade and one side had more meat on it than the other due to the way it had been sharpened. Didn't notice any significant variation on the driveshaft, but looking back over the photos of the single blade, it looks like it was slightly bent/twisted. I fixed that slight bend/twist by accidentally bending it more when I was running it around my yard and clipped a lump of concrete and now the blade needs replacing altogether. It may be me, or maybe someone can tell if the blade is bent in the two attached photos. In the first photo, the left hand side of the blade seems to have the same crisp angle as the right hand side, which also has more meat on it. The second photo is taken from the opposite side view, the blade was not moved, just me walking around to the other side, and the angle on the right (previously being the left in first photo) is still looking bent/twisted when compared.
On the shakey issue, the motor is rubber mounted and, without the blade attached, the engine still is a little shakey. Maybe a better way to describe it would be that "It has a slight sideways vibration".
Apart from the new blade now needed, it is back in working order. :-)
Thank you to all who have contributed in helping me get this mower working.
Much appreciated.
Daryl

Mulching blades which this appears to be are hard tell if only slightly bent from looking at an image. If one is bent more than normal it will show up as you rotate it through a full rotate and seeing if one side lower than the other based on a reference point such as the edge of the mower deck. They also can be harder to sharpen correctly on some grinders.

Since you have hit something with it and these are usually fairly reasonable to replace or at they are here I think that be your best bet. You may even be able a better aftermarket blade cheaper than the OEM version. What I sell here to my customer is usually a little thicker and heat treated than the OEM blades. I don't what is available in your part of the world but a little research probably will payoff for you.

Thank you AVB for your comments. New blade purchased and installed, but had to be genuine Husqvarna blade, which was $45-50, as I couldn't find an after-market match for genuine part number 531 00 50-45. Still has a little sideways vibration, but as mentioned, the motor is rubber mounted, so I guess that could be normal.
Starts first time, after I replaced the flywheel key (sheer-pin) again.
Thank you to all Forum Members who have contributed to this post and I hope it may help others with similar issues.
Have a great weekend.
Regards
Daryl