HELP, I need a Briggs & Stratton "EXPERT"!

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I borrowed a friend's 2 man post hole auger (General Model 70). Sort of a semi-permanent loan. He's got no place to store it. It's got a 5 hp Briggs and Stratton Vertical shaft engine (model 130920, type 0382, build date is 6/8/76). When I got it home it was obvious that the engine hadn't been run in awhile, and the whole thing appears to have very few hours on it.
I am having trouble keeping it going. Below is a list of what I have done so far. This list is not necessarily in exact order, regardless of what I have done so far, the basic problem persists. I can cold start it and run it under no load or with a load and it seems to run fine, but after using it for about 5 minutes (under load), it starts to die (surging). If I choke it quickly, I can get it to keep going off and on for maybe a minute or two more, but it ultimately dies out. It will do the same under a no load condition, but it seems to take it a bit longer to occur. Not much mind you, and this may only be my perception of time. I have been running it without an air cleaner, but with the air cleaner screw in place. I have a new foam air cleaner on back order at a local shop. I'm not using it in a dusty condition, (been too damp) so I'm not really worried about dirt. I'm at a loss at this point. I really need an experts advise on this one. Right now, my thumbs are killing me from running a one-man (manual) post hole digger.
List of "repairs" to date:
Replaced spark plug (original RC-J8 was still in it) with a C-J8. Same heat range plug, just not resistor. Though the original still runs it as goo (or bad) as the new one.
Added a screw-in straight pipe generic muffler (original was non-exsistant).
Removed and cleaned tank-mounted (pulsa-jet) carburator. Replaced diaphram, and main fuel pickup tube. I also put some carb cleaner in the tank, and a bunch of nuts and bolts and shook it for quite awhile to clean it. Then flushed it with clean fuel.
It takes it about 3 turns out on the needle valve to make it run the best (by ear) in all throttle positions under no load. I can start it with only 1.5 turns, but it just doesn't run great at this setting.
The gas cap venting is ok, not clogged.
Originally cleaned and checked points (.020 gap) and condenser, but ultimately replaced them as problem persisted. Replaced flywheel key as the old one was slightly tweaked. Enough that I first thought that it might have been an offest key, but upon further inspection, this doesn't appear to be the case.
Pressure checked cylinder cold / warm 65 psi.
Removed head to inpect valves, and cylinder. Though there is some scoring on one side (bottom) of the cylinder, everything otherwise looked ok. Appears to be very clean, very little carbon build up, and crosshatch pattern on cylinder wall still very apparent. Valves appear to be seating as there is a wear ring all the way around them, but I don't have a valve spring compressor to do a more thorough check, or lap. Did not check valve to pushrod gap.
Resistance check from spark plug wire to engine ground reads 2870 ohms. I have not replaced the coil. Bill Lewis snipped-for-privacy@erols.com REMOVE both "nospam-" in return address to reply.
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Im no expert but a 65 lb compression is ng , the motor probably was at 130 new and as is has no power it could be valves or the piston.
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I agree that the presssure seems low. from what you describe it sounds like you are running out of fuel. I would double check the fuel cap vent. When it is about to die, take off the cap and see if it keeps running.
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Can not test compression on briggs. They give no specs in any manual I ever read as most units have a comprestion release. Do a cyl leak down test that is the proper test. your problem is one of 3 most likley you missed something when cleaning the carb or put something togeather wrong good chance the unit is drawing air between the carb & tank (one is warped)
or lastly the coil is cutting out when hot, when it quits you will have no spark until it cool down. Good luck

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Unfortunately my compression gage has a check valve that doesn't allow me to do a leak down test. I'll look at it to see if I can take it out of line. Otherwise, any suggestions on another method to do this test? This engine doesn't have a compression release.
The carb is so simple that It would be nearly impossible to assemble it incorrectly. I am open to the possibility that there may be some loose debris in the carb that my initial cleanings failed to remove. I may remove it and go over it again with an even finer tooth comb.
Interface between carb and tank is ok.

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yes it does have compresion release. On this briggs model it is built on the cam lob. Check the val clearance when cold. (all specs on briggs puts out are cold) You say in a later post it has some blow by in the carb? If valve clearance is good then check for seating of valves.
You may be able to make up a cly leak tester a basically it uses compressed air to the cyl via the spark plug hole. start at 100 PSI and make sure you have a good hold on teh carkshaft with pistion at TDC on comprestion stroke. If you dont have a good hold on the crank shaft it will rapidly spin the crank 180 degrees. Rememebr engines need 3 things comprestion fuel/air and spark. Figure out what it is missing when it dies will help you solve the problem. I still think it is carb related if it runs a few mins then dies.

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On 12 Apr 2004 01:00:45 GMT, snipped-for-privacy@aol.com (PAUL100) wrote:

my original post stated that the cap vent was ok. I had already checked it. Though earlier, I did loosen the cap while running to allow fuel flow, to no effect. Bill Lewis snipped-for-privacy@erols.com REMOVE both "nospam-" in return address to reply.
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On Sun, 11 Apr 2004 16:47:15 -0500, snipped-for-privacy@webtv.net (m Ransley) wrote:

I agree, it seemed low to me however the following source, states that anything above 60 psi should be fine. http://www.repairfaq.org/sam/lmfaq.htm (http://www.repairfaq.org/sam/lmfaq.htm#lmcomptst is the specific reference. ) I have not been able to find any other specification on this engine regarding a cylinder pressure check. I still need to do a "wet" check, and a hot check. The original check was done while warm/cold. Bill Lewis snipped-for-privacy@erols.com REMOVE both "nospam-" in return address to reply.
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Sounds like the motor is leaning out the hotter it gets. You may want to check the intake manifold to block gasket and bolt, the carb to intake manifold gasket and bolts, and the diaphram gasket. All of these can make an air leak when hot. I have had a similar problem that was caused by a small piece of crud that was moving around in the carb blocking one of the orifices every now and then after the motor ran a while.
Just a couple quick questions, do you notice the engine running very hot after about 5 minutes of use? Was your compression test hot or cold, dry or with oil? And lastly, can you borrow a carb to swap on just to see if thats your problem?
Good Luck...

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I will check possible leakage between carb and cylinder head as suggested. I tried to buy a replacement o-ring that seals the carb to the manifold tube, but was unable to obtain. P/N on B&S site is defunct. It seems to be making a good seal though. Diaphram gasket was already replaced (see original post). Engine never seems to get excessively hot. Compression test done cold. Will try wet and hot. I tried my one possible source to borrow a carb or a coil. no luck.

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<--- snip --->
bill,
i had similar symptomps with a b&s mower engine. did the same thing, clean the valves, carb filter and so on. still ran lean. turned out the problem was the "butterfly" in the carb did not open all the way (choking) because the speed adjuster "loop" (the spring-loaded on the carb) was catching a plastic tab on the carb.
regards, richard
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On Sun, 11 Apr 2004 16:14:30 -0400, Bill Lewis

the same thing you describe. I also did pretty much the same stuff you did, except I changed the needle valve seat and needle.
At one point when the engine was running, I happened to run my hand past the head and felt hot exhaust where there should be none. It turned out the head gasket was bad. Make sure you retorque the head correctly. Also, check it again after running a while.
Gary Dyrkacz snipped-for-privacy@comcast.net Radio Control Aircraft/Paintball Physics/Paintball for 40+ http://home.attbi.com/~dyrgcmn /
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I suspect dirt, rust or water in bottom of carb. sediment bowl, possibly in gas tank also.
Another long shot is that it does not have enough valve clearance and when valves heats up, one does not fully close. When it dies, quickly see if it has any compression, place palm of hand on flywheel screen and turn clockwise by hand, compare compression with what it has before starting.
Walt Conner
>> I can cold >start it and run it under no load or with a load and it seems to run

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I will try to check valve clearance when hot. I have noticed that upon restarting I get a bit of blow back through the carb indicating a valve problem. A hot compression check might tell me more.
wrote:

Bill Lewis snipped-for-privacy@erols.com REMOVE both "nospam-" in return address to reply.
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To check valve clearance: With the engine cold, look for a cover which is about 1 inch by three inches. It is held on by two small bolts which take a 5/16 wrench.
This cap exposes the springs, and bottoms of the valves. Turn the flywheel until the valves open, and close. So you can see what they are doing. Leave the flywheel in the middle of the "valves closed" part of the turn.
Use thickness gages to see if there is enough clearance between the bottom of the valve (on the end of the spring that has the washer on it) and the lifters. The place you slip the gage in is between the spring "washer" and the near edge of the opening. Should be at least .010 for intake and .020 for exhaust. I know my descrip isn't very good. Wish I could draw you a picture.
Second thought came to mind. Be sure the engine is clean. Dust and crud under the flywheel cover blocks air flow, and the engine might be overheating.
--

Christopher A. Young
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I am not sure I saw the original post. It would be valuable to know what the model number of the engine being discussed is. I know of no B&S engine that has valve clearances mentioned in the below message and certainly not OHV engines as this seems to be, accutally clearances of these amounts may make it impossible to start some B&S engines.
Walt Conner
.>The place you slip the gage in is between the spring "washer" and the near

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He said it was a vertical shaft 4 HP engine for a post hole digger. As for the valve clearances, that's what I learned in a small engine repair course years ago. I've found they work nicely.
The clearance is between the narrow end of the valve shaft, and the lifter that comes off the camshaft.
What is impossible is when the engine warms up, the length of the shaft grows longer, and then the valve refuses to seat. Then it won't run.
The original poster was having trouble that the engine died after about five minutes, and sometimes closing the choke would help.
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Christopher A. Young
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Small B&S engines use an easy spin cam grind which depends on proper valve clearance to work, also, excessive valve clearance adversely affects engine breathing hence, performance.
All aluminum block, flat head B&S engines that I am aware of, call for .005 - .007 for intake and .007 - .009 on smaller engines .009 - .011 for larger engines for exhaust clearance.
The old cast iron block B & S engines did call for clearances .007 - .009 for intake and .017 - .019 for exhaust.
You are right that one cause of dying after a few minutes of running is not having enough valve clearance.
Walt Conner

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He said the enigine is like new. How could he have lost valve clearence unless the seats or valve faces got beat out?
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OP said motor was like new but compression was 65lb . Well 65 lb makes it probably a 1 hp junk, worthless unless he put it back together wrong.
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