Engine runs fine but is hard to start when hot

[Merkava_4]

Briggs & Stratton
92902 1801-01 77092901
Magnetron Coil Kit 591420
Yard-Vac Tornado Leaf Vacuum

The engine has the tank mounted Pulsa-Jet carburetor with the Automatic Choke and the Adjustable Mixture needle. All I did to the engine is convert it over to Magnetron ignition and change the carburetor diaphragm after cleaning the carburetor out. Engine runs fine, but is hard to start right after you switch it off. What I did is set the mixture needle to the 1-1/2 turns out bench setting, then after the engine was running, I adjusted the mixture further (between too lean and too rich) to achieve the highest RPM. Seems like it runs best at 2 turns out, but is hard to start after being ran for awhile.

I will say this: I am not familiar with this carburetor; it's my first time working on this type with the automatic choke, but I followed the instructions in the service manual very closely. Service manual says the choke valve plate is supposed to fluctuate as you're pulling the rope to start; which it does. The one possible variable that I can think of is that the flywheel is missing two cooling fins 180 degrees apart from each other. I don't know if that can adversely effect the Air-Vane governor or not.

The one thing I noticed about this carburetor is that it seems to be very similar in configuration to the more modern tank mounted plastic Pulsa-Prime carburetor; even the fuel tank has the same shape. The Pulsa-Prime carburetor however, is very easy to start after the engine is hot.

[KE4AVB]

Being that older of a L-head it might just be that valve clearances have closed up that much and needs re adjusting as the valves aren't fully closinf at the time they need to be when hot.

[bgsengine]

Briggs & Stratton
92902 1801-01 77092901
Magnetron Coil Kit 591420
Yard-Vac Tornado Leaf Vacuum
.

check for tank warp - pop the carb off, remove screws and diaphragm, if you can slide a .002 feeler gauge between carb and tank especially under the throttle shaft area, you need the tank repair kit, or a new tank or new carb or just retrofit the dang thing with a pulsa prime conversion kit (cant think of the part number offhand..)

(look closely at the tank you will see the groove where vacuum is supplied - then maybe you'll understand how choke is opened.. )

[bluemower]

the diaphragm spring closes the choke immediately after engine shutdown. When you attempt to restart a hot engine, a fully closed choke is not needed. Most likely you are flooding the engine with fuel. To partially open the choke during restart, more intake manifold vacuum is needed. If the engine is well worn, you may not achieve this goal. Here are the maintenance items that affect the intake manifold vacuum:
1. proper valve seating and valve clearance as mentioned by KEV4.
2. check the carburetor base for warping. Use a straight edge from the screw holes - across the small hole next to the choke rod compartment.
3. inspect the mounting surface on the fuel tank as described by BGsc
4. consider installation of the 391413 repair kit.
5. make sure the o ring is installed in the carburetor where it fits on the intake tube.
6. inspect the intake tube and gasket for defects.
7. look for excessive throttle shaft wear

Engines operated at high altitude are more difficult to start.
Engines equipped with the easy start system and the mcr are even more difficult to start.

Finally - some starting tips:
remove the air cleaner and manually hold the choke partially open - see if the engine starts
Place the throttle control to the idle position. This seems to be opposite what most engines need, but this will increase the intake vacuum. See if it starts.

[Merkava_4]

Well guys, the engine started on the first pull of the rope today and ran strong. I wheeled it over
the neighbor's house while it was still running. When the neighbor came out to hear it running,
I shut it off and told the neighbor I'm done. He insisted on paying me $50 but I would not accept
any payment. I told him if I took his money, I'd have to warranty it.