B&S 5hp Help
 

Have a '77, 5 hp, B&S with a pulsa jet carburetor. Replaced points w/magnetron coil & ran it 3 times & on last run it had a loud squeal followed by puff smoke then off. Believe the starter clutch miscued which caused the squeal as well as sheared shaft key. Replaced key, cleaned starter clutch, have cleaned carb many times, spark plug appears damp from fuel, pulled head & there was minor carbon on valves. No compression when testing, but not sure if this is typ w/a pulsa jet carb. Pressure does come through carb

Cannot get the engine to start again & not sure what to ck next. Suggestions appreciated

No compression when testing??? How did you determine that?

This Briggs & Stratton.... what equipment are we working on?

Used compression test device, zero reading. Just not familiar w/this style carb, so not sure if have an engine or carb issue.
Engine is on tiller

You need compression.... carb has nothing to do with it. By your first description, the sqealing and puff of smoke seems to lead me initially to a seizing motor and/or a busted rod. I guess when you had the head off, you didn't see anything unusual?

lube the crank where the pull rope rewind comes through to eliminate that noise.
check for stuck valve if the piston moves up/down.

Did not see anything odd w/head off. Carbon deposits around exhaust which cleaned off. Head was clean & no abnormal wear in cylinder. Rods appeared to move well & smooth no binding. The exhaust valve did not rotate as smooth as intake valve, just figured prob dirtier. Prob going to ck springs & valves/rods next & adjust as necessary.
The starter clutch appeared that may have failed. The cap/cover was pushed up & the bearings slightly damaged the faces on the spindle. Cleaned clutch well, reassembled, greased shaft before install.
When testing compression on an engine w/a pulsa jet carb, does the test work just like on engine w/a typ carb w/bowl? Or is there a spark issue even though started before the glitch. Have spark though now which is why considered compression issue
The exhaust valve stem was slightly sticky, but opened/closed fine. Cleaned valves & ckd gaps, exhaust was correct, but intake was zero gap. Otherwise no issues w/valves
Tks

These are pretty simple engines. Here is a pretty good vid.
https://www.youtube.com/watch?v=y8EdlO8JVvY

I had one on my log splitter that the upper bowl rusted out on and couldn't find a tank for less than $100. I purchased an old Craftsman tiller with the same engine on FB/MP for $50 and used that engine.

Or you can try one of the Chinesium replacements from Scamazon. I'm not sure of the model you have so this may not be the correct one.
https://www.amazon.com/299437-Carbur...%2C154&sr=8-14

I don't know that engine specifically, but for lack of compression, my troubleshooting steps are generally about the same for most any of them.

Question 1 - does it have a compression break for starting? If yes, look there first.

Question 2 - if you pull out the spark plug and look in the hole with a flashlight, can you see the piston go up & down when the motor turns over? Is the head of the piston chewed up or dented? Does it have a hole in it?

Question 3 - are both intake & exhaust valves moving? Generally, you need to pull a valve cover to see this. Sometimes you can see it through the spark plug hole.

Question 4 - With the piston at top dead center, do you have clearance under both valve stems? An out of adjustment lifter will kill compression pretty quickly if it removes the gap. Gaps are generally pretty small, like the thickness of a piece of paper to 5 times that amount, with the exhaust being looser than the intake. But zero clearance means that the valve doesn't close all the way. If you can't spin the lifter with your fingers easily when the valve should be closed, then you likely have a problem there.

Question 5 - Does air blow out of the side of the engine head due to a failed head gasket?

Question 6 - Is air blowing out of anywhere else that it should not?

Why did you replace the points with magnatron?
points work just as good, I have multiple engines that have points style ignition systems, chain saws, boat motors, transfer pumps, tractors, tillers vintage cars & trucks etc. etc.
all work just fine without electronic ingnition, just saying.

Since you have the head off, and saying the valves are opening and closing as the piston is moving up/down, you pretty much have to have compression unless the piston has a big hole in it.
A pulse jet carb is no different than any other carb, hell you can take a carb off and set it on the work bench and the engine will run as long as you squirt a bit of fuel in the intake port with a squirt bottle.
A quick way to check compression (with the head on of course) is put your finger or thumb in the spark plug hole and pull the rope starter, if it blows your finger/thumb away and sucks it slightly on intake stroke, you have compression.
You are missing something,or you are not telling us enough information to help further.:bigthink:

I would venture to guess that your engine has automatic compression release (ACR) which operates at very low rpm by holding the exhaust valve slightly open. Assuming that you are turning the engine by hand with the head off to observe the valves, are you sure that the ACR is not causing that action that you see on the exhaust valve?

If your observation is truly a slightly sticking exhaust valve and not ACR operation, then a slightly sticky exhaust valve is not a good thing under any condition.

When the head is back on and rpm's increase, even with just the pull starter, and temperatures vary, you can have no clue how much that valve is fully closing or sticking.

My thoughts are, confirm valve operation is correct before firing the new parts shogun.