1981 Briggs & Stratton 3HP Engine

The_Ruppster_86

The_Ruppster_86

New Member
#1
#1
Looking for some help from the Briggs "gurus" out there...

I have a '81 B & S 3HP Horizontal engine with a "Pulsa-Jet" carb.

Model: 80202
Type: 0855 01
Code: 81010703

Background:

I picked this engine up several weeks ago non-running. It had no spark but had good compression. A couple of days ago I cleaned the points, 2 leg armature, and re-gaped everything to B & S specs. Then I had spark! I purchased a new spark plug to B & S specs, new diaphragm, needle and seat kit, and gaskets. Carb was removed and cleaned thoroughly with carb cleaner including the fuel pipe screens. Next, I cleaned the tank of most rust using the "metal BB" method.

Note: The previous owner removed the governor from the engine.

Today I went to reassemble everything and do a test run. The engine runs without the choke and throttle set to at least half way. If I let go of the throttle the engine dies. The idling screw is closed almost all the way for most RPM. However, the engine still doesn't seem to be reaching its fully designed RPM with the throttle opened all the way.

What could be limiting my engines RPM and not permitting it to idle without the throttle half way open?

Any help would be appreciated!
 
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oldfatguy

oldfatguy

Active Member
#2
#2
did you check the main jet ? From what you describe it sounds like a fuel problem from a clog in the carb. It also could be a vacuum leak from a bad gasket or a worn throttle shaft. Also recheck the flywheel key in case it moved.Usually if you take the jet out and clean it and poke through the passages behind it that will solve the problem.
 
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The_Ruppster_86

The_Ruppster_86

New Member
#3
#3
Thanks for the reply oldfatguy. I will take the carb off and give it another good cleaning, especially the jet. I read on another small engine repair forum that two carb to block gaskets are required. After running it for several minutes and inspecting it, I had a small leak from where the carb mounts on the block. I suspect it is because I'm only using one gasket. Also, I'll re-check the flywheel key and report back. Thanks
 
D

Dual-500

Member
#4
#4
Flywheel key?

EDIT: Ok I re-read it and oldfatguy gets credit for suggesting checking the flywheel key.

In which case, I hereby second the motion.
 
creia

creia

#5
#5
The Ruppster did a pretty good of explaining the situation, however I'll add my .02 cents as well.....
As Jeff already mentioned, he (purposely) picked up a non-running engine (got it REAL cheap from another local OldMiniBikes member with a heart of gold:thumbsup: that has become his friend and kind of a minibike mentor to him:wink:- the carb gasket/rebuild kit cost nearly what he paid for the entire engine!) strictly for the fun, challenge and interest of getting it running.
My observation/conclusion is that the engine is running EXTREMELY rich, based on the following symptoms:
1. Never need to choke it even on a "cold" start.
2. To run at all, the mixture screw cannot be adjusted out more than about 1/2 to 3/4 turn from fully seated.
3. To get it to fire and run, you always have to open the throttle plate about 75%, and continue to hold it there. (If you let it return to the idle position the engine dies).
4. Always has a fuel smell coming from carb.
Re: Flywheel key condition/position
That checked out O.K. as he saw it when he removed the flywheel to access the points.
 
Neck

Neck

Growing up is optional
#6
#6
You say the smell of raw gas is always present? Is the engine sneezing back through the carb during the compression stroke like maybe the intake valve is not closing? Oh yeah.....Is it smoking black?
 
creia

creia

#7
#7
Hello Neck- Thanks for the reply.
Re: Fuel smell
Only right after it has been run, and it lingers for awhile.(presumably until it evaporates) If you pull the filter off and look down the throat of the carb you can see a little bit of gas on top of the choke slide tube if you pull it out
Re: Valves
You bring up a good point that I've also thought about. I do not think that it is "sneezing", however I wonder if the valves are not seating properly. (seems to have good compression when pulling the starter cord though:confused:)
Re: Smoking black
A little bit, however, surprisingly little based on how rich it appears to be running.:confused:
 
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Neck

Neck

Growing up is optional
#8
#8
These engines do have a passive compression release, which means the cam is ground so the intake valve does not close all the way until the piston is well on its way up during the compression stroke. But it should be open just a little, so not to lose too much compression while running. With valve/seat wear the valve may be staying open too far during the compression release cycle and blowing back through the carb, and making a double carburation pulse, thus running rich. You should pull the breather, or valve spring cover off and measure the intake and exhaust valve clearance at top dead center to see if it is within spec.
 
creia

creia

#10
#10
On or off it runs the same. Also, I would estimate that the engine is only getting up to about 50% of maximum rpm at full throttle.
Thanks for the help,
Michael.
 
Neck

Neck

Growing up is optional
#11
#11
OK then, check your valve clearances. One other possibility, has someone messed with the carb? Does the carb paint match the engine paint? Got any pictures?
 
creia

creia

#12
#12
We will look into checking the valve clearances. I know where the access plate is on the side of the engine behind the breather tube. Never done it before, however, we have a couple of Briggs repair manuals so we will study up on the procedure. Any words of wisdom?:wink:
RE: Carb matching the engine
There's not much paint on the carb, however, there is enough to confirm a match I believe.
Re: Photos of engine
Great idea- I'll have The Ruppster post some as he is MUCH more adept than I!:shrug:
 
D

Dual-500

Member
#14
#14
Neck said:
These engines do have a passive compression release, which means the cam is ground so the intake valve does not close all the way until the piston is well on its way up during the compression stroke. But it should be open just a little, so not to lose too much compression while running. With valve/seat wear the valve may be staying open too far during the compression release cycle and blowing back through the carb, and making a double carburation pulse, thus running rich. You should pull the breather, or valve spring cover off and measure the intake and exhaust valve clearance at top dead center to see if it is within spec.
Click to expand...
If this model has the "Easy Start" cam timing device that could well be the problem if it's sticking.
 
creia

creia

#15
#15
The engine still has the original decal/sticker on the side of the recoil shroud, and it reads "Easy Spin Starting" is that what you are referring to Dual 500?
All good analytical questions guys, and we sincerely appreciate the interest and help! I hope to get some answers to these, and start ruling some of them out, once we study our repair manuals and figure out how to do it:hammer:
Some have asked about the history of this engine (i.e., modification, repair, etc.)- I do not have a clue as this engine (and MANY others) has sat on a shelf (and not been run) at this OldMiniBikes group member's home for for years.:laugh:
 
D

Dual-500

Member
#16
#16
There's an easy start (maybe it's called something else) device that is mounted on the camshaft beside the exhaust lobe on later model engines. It's a long shot that it could be stuck but just about anything is possible.

What it does is increase the duration of the intake valve timing to reduce compression for startup. When the cam starts rotating after the engine fires up, the device is designed so the centrifugal force of the cam turning will null out it's effect - it moves so it doesn't contact the intake valve tappet any more while engine is running. Pretty clever design.

I don't know if the model you have has this or not. Not sure when they came up with it - maybe 70's or 80's. Some of the other guys can advise you on it - if your engine has it or not.

ONe is shown on this video: http://www.youtube.com/watch?v=t5kTrADx31Y The metallic thing on the inside of the plastic cam timing gear.
 
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Neck

Neck

Growing up is optional
#17
#17
Dual-500 said:
There's an easy start (maybe it's called something else) device that is mounted on the camshaft beside the exhaust lobe on later model engines. It's a long shot that it could be stuck but just about anything is possible.

You wont find one of these on an 81 Briggs 3 horse, I guarantee that!
Click to expand...
 
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