I know you've heard this before, but as you can see by the list below, I've tried all the Normal stuff. If the engine sits for any period of time and cools below 80 degrees, it won't start.

I've checked all of the following, but the '94 Yamaha YFM400FWF still won't start when cool. The spark plug gets saturated with gas after cranking - choke or no choke.

1. No fuel runs out of overflow.
2. Got good spark (OK) - NGK IRIDIUM DR8EIX - gap 0.28
3. Carb rebuilt (OK)
4. Rechecked float pin and seat (OK)
5. Pilot Jet set 2 turns out (OK)
6. Removed and Checked Choke O-ring (OK)
7. Adjusted intake and exhaust valves reset to spec. (OK)
8. Battery charged (OK)
9. Checked, Cleaned and applied Dielectric grease to All Wiring Connections.
10. Got good compression 118 psi cold engine. - 152 psi Warm

After I warmed the head with a blowing propane heater and it did finally start and would start easily when the engine was warm.

What else is there to check?

 

Jetting? Mods? Clean air filter? Intake leaks? Exhaust leaks? Fresh fuel?

Not sure on your specific model but is the carb gravity fed or is the a diaphragm type feeding system (these suck and could be the problem)

 

New K&L Carb Kit added, supposed to be same as OEM parts.
New Spark Plugs Tested.

I notice choke seal part (Seal) #34 was missing.
Could this be the problem?



I just got the part today going to put it in, I'll let you know

Here's the Carb Diagram.

 

Well, installed the missing choke seal - no help.
It still won't start when the engine is cool to the touch.

I fired up the propane heater, let it blow on the engine for thirty minutes and…
… it stated like a champ.

i checked the spark again and got the fire shocked out of me… Good Spark.

I talked to the dealer again… they don't have a clue either.

Still hunting for the solution… stay tuned.

 

If you spray a bit of starting fluid in, will it start and stay running? or will it just stall out. I

 

@yukon1975 - I don't use starting fluid. I afraid it will burn a piston.
I did squirt some gas in the cylinder way earlier in the process... No Start.

The BIG QUESTION is - Why will it start and idle smooth, when I heat up the cylinder with the propane heater???

 

I take it your using fresh fuel. sounds like the carb needs to be reinspected. perhaps still a bit gummed up in the pilot jet hole in the carb, not the pilot jet itself, or the fuel level in your bowl is not high enough, therefore only runs when warm, since it is not getting enough fuel to ignite in cold engine, but runs fine when hot since the gas evaporates fast in the warm engine.
check the float level-or if the float is stuck down a bit, try bending the float where it attaches to the needle down a bit?
it definitely sounds like a carb problem.

 

@yukon1975

The Kodiak went to the dealer today. The mechanic did a complete inspection of the carb.
Nothing much was wrong, but he didn't like the brass aftermarket main jet needle. He changed it back to the stock needle. He said most aftermarket needle sets were in spec.

He also changed the O-Ring on the Fuel/Air needle.

When I left he got it started after a lot of cranking and fooling with the intake.
It idles smooth just like it did when I would start it by heating up the head and spark plug.

He wanted to keep it over night and check some other things in the morning after it was completely cool.

Stay tune to the continuing saga.

BTW: The stator checked out as Good.