Need engine troubleshooting help

shop deals on amazon
Rugged made
Advertise with us
Treestuff
Arborist Forum

Help Support Arborist Forum:

This site may earn a commission from merchant affiliate links, including eBay, Amazon, and others.
While i agree that it may be a valve issue as i find most briggs engines need a valve job when i get them, try removing the fuel shutoff elbow if you havent already and clean the gunk out of it. Sounds dumb but give it a try. I have found in rare circumstances a fuel elbow will let fuel down the line to start cold but then shut off and no pop on juicing the cylinder directly.
,
 
I still think you have an ignition issue. I have seen motors with enough spark to activate a light, but not enough to fire. To me, the fact that it won't pop with starter fluid is diagnostic of ignition issues.
 
The later B&S and Tecumseh engines have an internal compression release. There is a spring loaded pawl that rides on the crank and holds the exhaust valve slightly open for easier spin starting. When the engine fires and rpm increases, centrifugal force overcomes the spring pressure on the pawl and it moves out of the way. Because of this you wont be able to get a true psi compression reading on any of these engines.

Im with Morgaj on the ignition. I would also replace the wear parts ie; points, condenser, carb diaphragm etc if it uses the carb that sits on top of the gas tank. A valve touch up is probably a good idea as well and not too difficult. With this work completed you will have a good running reliable engine for many years to come.

Here is a short vid showing how to check the valves;
HOW TO Check The Valve Clearance On A 4 Cycle Flat Head Engine - YouTube
 
bullseye13 said:
While i agree that it may be a valve issue as i find most briggs engines need a valve job when i get them, try removing the fuel shutoff elbow if you havent already and clean the gunk out of it. Sounds dumb but give it a try. I have found in rare circumstances a fuel elbow will let fuel down the line to start cold but then shut off and no pop on juicing the cylinder directly.
,
Click to expand...

I removed the fuel shutoff fitting from the tank (on the second time through the fuel system) and totally disassembled it, flushed out the tank again and reassembled. This setup uses the gasculator with the glass sediment bowl and a fine screen to prevent debris from getting into the fuel line. On the third time addressing the fuel system, I removed this screen and instead installed an inline fuel filter. The one I used is transparent (not translucent white but clear as glass so I can see exactly what's going on)
 
I need to prep saws and load the truck now for a tree job tomorrow but if I have any extra time I'm going deeper into this engine. I will specifically be looking at the ignition system and valves too perhaps.

I don't believe this engine has a compression release but not sure. I am going to do a compression test cold, run it till it quits and then immediately do another test to see how the numbers compare. If a valve is stuck open, it should read close to zero. It just isn't acting like a valve issue but I'll investigate that aspect.

Thanks for all the ideas thus far. I'll report with additional findings. I have encountered some weird mechanical issues over the years and I never forget them once discovered. eg, I had a Ford truck that was losing transmission fluid with no evidence of leaking. And my motor oil kept being overfilled. So I concluded that the transmission fluid must be getting into the oil somehow. I was told by a number of other mechanics that it was impossible. I explained to them my trans fluid was going down but the engine oil was going up so it must be possible, but how? Well, I finally encountered an old geezer at a transmission shop that told me what to check and I solved the problem. (the diaphragm in the shift modulator had failed (no shifting issues, though) and the carb was sucking trans fluid up the line, dumping it into the intake manifold where it worked its way back to the oil sump. No the engine wasn't smoking like crazy, the truck shifted normally and so forth. So it was a strange issue but if I ever encounter it again, I'll look for the modulator issue. When I figure this engine out, I'll post the findings and maybe it'll benefit some other guy.
 
Usually when the valve lash is too tight, the engine pops and backfires before it shuts down completely. Pull the breather and check the lash with a feeler gauge for peace of mind however.

If its shutting down with no warning whatsoever, it has to be ignition? Compression and fuel issues usually result in surging, back-fires and other warning signs before the engine quits completely.

The cheap neon light in-line spark testers are real handy for this kind of situation. You will be able to see if you're getting a nice strong spark or a weak spark. About $5-10 depending on where you buy.
 
I would check for ignition first. If it runs good for 10 minutes there isn't anything major wrong mechanically. Low compression would cause low power and rough running, not a "shut the switch off" condition.

Showing spark outside the cylinder does not mean it is strong enough to spark under compression, and the timing light may fire under a weak spark condition also.

Coils for these are cheap and easy to find in my area (and usually the same from 8-12hp engines). You could also find a later model coil and flywheel and retrofit the more reliable solid state ignition.

Look over the points before you buy anything. Check the gap and condition.
 
Additional info

So I pulled the engine apart somewhat and here are my findings.

I checked the compression cold with a normal automotive compression tester (same one I use on saws). It read around 55/60 psi give or take.

I then started the engine and ran it until it quit. (18 minutes, not under load) It did sput a few times before shutting off but when it quit, it was abrupt.

I then checked the compression and came up with about 80/85 ish.

I then removed the starter cover and inspected the coil. Clearances appeared ok. It was close but not touching anything.

I then removed the flywheel and checked the points. They appear ok as far as condition and gap.

(the coil appears original due to white paint on it, so being it's 33 years old...)

So then I pulled the head. Both valves looked normal. No evidence of burning, feathering, etc. I then removed the keepers and pulled the valves. The stems had a bit of carbon on them but what I would consider normal. I cleaned the valves up very well and slid them back into the guides. I measured clearances and there doesn't seem to be ANY. When I put a .002 feeler in between the valve stem and cam follower and pushed down on the top of the valve, it was tight (couldn't pull it out). The engine was not cold or hot at this point, somewhat "warm".

Does anyone have the valve clearance specs? (I can't watch the YouTube video as I don't have broadband here) I'm guessing it should be around .004? give or take a couple?

The cylinder and top of the piston look pretty good, no significant scoring or looseness.

So that's where I'm at thus far...
 
I have a Craftsman shredder with one of those engines and the carburetor was loose on it. Caused it to do like yours until I found the loose carb.
 
Snapped a few shots of the old B&S book.
First pic: Valve clearances. Notice the aluminum and cast iron have different clearances.
2nd pic: a shot of the codes and their meanings.
3rd pic: the clearance/gap for coil laminations to flywheel.
4th pic Carburetor identification. I'll bet you have the Flo-Jet two piece.
5th pic: notice the emulsion tube and adjusting screw (yellow outlined area)
go all the way into the top of the carb body (purple looped area)
Most of that top comes off as a unit
BUT you have to unscrew that mixing tube assembly to remove the top
otherwise you will bend it if you force the top off
without first removing the tube and screw .

I saw a few in the shop that were damaged in that way and the kit to repair it
was 35~40 dollars 25 years ago.
I'll wager it's a scarce item by now.
-
on the spark. I allways test with a clip on plug like the one in this web pic.
http://ww2.justanswer.com/uploads/mobiletech/2012-02-07_223236_spark-tester.jpg
if the spark jumps that (bout 1/4"), you're probably in good shape for ignition.
haven't seen one pop that gap and not run with a good spark plug.

If I missed a page or the pics aren't clear, let me know and I'll try to get better ones.
 
THAT IS NOT a lot of slop for valve clearance. .008 intake /.012ex is about normal, some engines set at .010 &.020.
if you cant pull a.002
feeler gauge out you might have the crank in the wrong position. The reason you turn engine in reverse to check compression
is the compression release wont work in reverse rotation. I bet it was the ex valve you could not pull a.002 gauge out
of cause that is the valve held open by the comp release. I am also surprised you can get it started with 50# comp as we
mostly found about 60 # was the point were the would not start.
Wise Wood
 
wise wood said:
THAT IS NOT a lot of slop for valve clearance. .008 intake /.012ex is about normal, some engines set at .010 &.020.
if you cant pull a.002
feeler gauge out you might have the crank in the wrong position. The reason you turn engine in reverse to check compression
is the compression release wont work in reverse rotation. I bet it was the ex valve you could not pull a.002 gauge out
of cause that is the valve held open by the comp release. I am also surprised you can get it started with 50# comp as we
mostly found about 60 # was the point were the would not start.
Wise Wood
Click to expand...


The feeler gauge was pinched by both the exhaust and intake valve. To check the compression, I just pulled the rope so the engine would have been turning in the normal direction of rotation. (not backwards)

I'll grind the valves down to get some clearance and put the engine back together and see if it'll stay running. I want to try this valve thing first before I mess with ignition system so I can have a better idea of what the trouble was...

It'll be a few days before I get back to it probably.
 
I have a 6.5hp briggs mower that does the same thing unless you loosen the gas cap a bit, try that.
 
fearofpavement said:
The feeler gauge was pinched by both the exhaust and intake valve. To check the compression, I just pulled the rope so the engine would have been turning in the normal direction of rotation. (not backwards)

I'll grind the valves down to get some clearance and put the engine back together and see if it'll stay running. I want to try this valve thing first before I mess with ignition system so I can have a better idea of what the trouble was...

It'll be a few days before I get back to it probably.
Click to expand...

Now, I could be completely wrong on this, but I recall that flathead Briggs engines use insufficient valve clearance as their decomp system. The valves are held open just a little to bleed off compression until it starts running. Every one I've had apart never had any sort of cam mounted decomp like I've read in this thread. As far as adjustment, if any I've always read that the valves need to be replaced once they're worn and make the engine hard to start. Your compression doesn't sound that far out of range. The L head briggs was never known for making much.

I would buy the 10.00 spark tester and rule that out before going any further. Weak ignition can mimic all kinds of issues.
 

Similar threads

M
Carb hissing noise when engine is off
Replies
11
Views
529
muddtree
M
BadgerClaw
Ms 192 tc weird stalling after running
2 3 4
Replies
66
Views
3K
Hulpio
Hulpio
M
Homelite chainsaw woes
Replies
8
Views
905
OnlyHomelites
OnlyHomelites
Joe The Arrow
MS261cm Ignition module
2 3
Replies
47
Views
1K
atpchas
atpchas
P
Help on a Husky 262XP
Replies
19
Views
832
Bob Hedgecutter
Bob Hedgecutter

Latest posts

Back
Top