Please help, I need some gurus to give me direction!!

[Mango]

I posted about this earlier but I bough a project 79’ 400 that had a screw embedded in the head. I did a top end with a new head and that went fine. Compression went from 90L, 120R to 150 L and R. I went through some issues with the carb but it has been cleaned with a full rebuild (compressed air and carb cleaner, didn’t mess with air screws). It only starts with starter fluid and not for very long. I checked timing which was off and now fixed-still won’t run. Then checked float height in carb and all jets are stock and clean. Next was spark plug cables which I cut the ends off both ends to ensure good contact- still no start without starter fluid. Could this be the coils being bad? It’s giving symptom of not getting fuel but I wonder if it’s just not getting spark. Also spark plugs were wet after trying to start. Any help is greatly appreciated!

 

[Mango]

Also curious about vacuum, I know it is necessary for fuel ti be pulled into the engine but how do I know if I’m getting it? I have compression but they are different from my understanding.

 

[Mango]

Also when I say rebuilt carb, I mean new jets and components.

 

[tstidham]

If it firing with starter fluid, then the coils are working and you have a fuel problem. If you have the vacuum style petcock, you want a vacuum line from the right side carb mount nipple to the petcock and a cap on the left side. There should also be an off, run and prime position on the petcock, put it on prime.

 

[Mango]

The spark plugs wet so I’m assuming it’s getting fuel. Kinda at a lost what to check next, but I’ll keep tinkering.

 

[tstidham]

Sounds like it's flooding the engine with gas if the plugs are wet. After you cleaned the carbs, what did you set the idle jet screws too? Usually it's around 1.5 to 2 full turns out. Also make sure the idle speed screw is turned out for as low an idle as possible. If it has the butterfly open too far you could draw fuel from the main circuit instead of or in addition to the idle circuit.

 

[JPaganel]

Also curious about vacuum, I know it is necessary for fuel ti be pulled into the engine but how do I know if I’m getting it? I have compression but they are different from my understanding.

If your engine is turning over and has any compression at all, you have vacuum.

An engine is basically an air pump. It sucks air in at one end and spits it out the other.

The "fuel system", such as it is, is the petcock. Petcock is a vacuum-operated on/off valve. If you have it in ON, it is closed until vacuum is applied (engine turns over). If you have it in PRI or RES, it's just open, and vacuum doesn't matter.

There is no fuel pump, and vacuum (from the nipples on top of carb holders) plays no role in fuel flow. Fuel flows into carbs by force of gravity, and is pulled into the engine by the incoming air going through carbs.

If you put the lever on PRI, and no fuel comes out, the petcock or the fuel strainer is clogged and you need to clean it all out.

If you put the lever on ON, there should be no fuel coming out unless there is suction on the tube. Suction is created when the engine runs, so if it won't run, you won't see it. You can use a syringe or a rubber bulb or a vacuum pump to test that. You can also just suck on the tube, but that tastes bad, and if your petcock leaks, you will get gas in your mouth.

If the lever is ON, and there is suction, and there is no fuel - your petcock is stuck, or something is wrong with the diaphragm. You need to rebuild the petcock.