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Old 01-15-2012
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Yamaha 6hp No Start

I have a 2006 Yamaha F6 4 stroke engine. The engine will start first time, first pull. Thereafter, once warm/hot it is unlikely/impossible to re-start. I have cleaned carb and coolling which improved re-starting but still totally unreliable for a guaranteed hot re-start. Any suggestions?
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Old 01-15-2012
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my guess is that its running too lean,what does your spark[s] look like!
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Old 01-15-2012
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Quote:
Originally Posted by sbl372 View Post
I have a 2006 Yamaha F6 4 stroke engine. The engine will start first time, first pull. Thereafter, once warm/hot it is unlikely/impossible to re-start. I have cleaned carb and coolling which improved re-starting but still totally unreliable for a guaranteed hot re-start. Any suggestions?
I used to have the same problem with 4 stroke off road motorcycles, generally after being dropped. Some possibilities:

1.Marginal pick up or ignition coils or plug that start to break down with heat

2.Float level too low or high. Try shutting off the fuel at re-start. If it finally fires it may be being flodded.

3. Float that is leaking, causing over rich condition which may allow cold start
but not on hot re-start.

4. Check all hoses and connections for air leaks. Hoses close to the block may develop cracks from the heat.

5. Check for debris in any air bleed jets in carb, possibly causing an over rich condition when hot

6. Make sure carb is tightly bolted to the manifold flange.

7. A stretch, but make sure the valve clearances are set properly. Perhaps try the above items first.

Let us know what you find.

Dabnis
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Old 01-15-2012
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Quote:
Originally Posted by sawingknots View Post
my guess is that its running too lean,what does your spark[s] look like!

Just saw this, could be. You might try choking it on the hot re-start, but if that doesn't work it will probably really be flodded.

Dabnis
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Old 01-15-2012
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choking a engine that has been running too lean doesn't seem to work for some reason,my second guess would also be a weak or marginal coil
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Quote:
Originally Posted by sawingknots View Post
choking a engine that has been running too lean doesn't seem to work for some reason,my second guess would also be a weak or marginal coil
Right, maybe just richening up the idle mixture temporarily would be easier. An overly lean idle mixture can make for hard starting. But then an overly rich mixture may be more acceptable to a cold engine and then troublesome after it gets hot. I tried everything on the 4 stroke motorcycles and it didn't seem to matter too much when they were hot. I have kicked until I couldn't stand up any more, not a pop, nothing, then on the next kick it would fire. Never could figure out why. If you can do it, take the plug out when the motor is hot, ground the base and pull it over as hard as you can. The spark should be a bright buleish white color. Or maybe just put a new plug in and try it?

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Disconnect the fuel line. Start. Run for 30 seconds. reconnect fuel line.
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Old 01-16-2012
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Gee I have a 4 hp,did not they started easily at all.Ps if there are any carb. adjustments ,unable to locate.
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Quote:
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Gee I have a 4 hp,did not they started easily at all.Ps if there are any carb. adjustments ,unable to locate.
IIRC, the only adjustments allowed anymore are idle speed and mixture. Not familiar with your particular engine but they may be right on the carb. The speed adjustment will probably be right on the end of the cable fitting. Mixture may be a small single screw and may be hard to see?

Dabnis
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You need to eliminate the ignition circuit as the cause of the problem. You could easily have a heat-related problem with the coil.

You can hold the ignition lead (with something insulating! Don't zap yourself!) near to the block and watch the spark when cold cranking. Note how far it will jump. Repeat when hot. If the spark is much weaker or intermittent, there is your problem.

When you do get it started, how does it run? Any roughness and reluctance to rev up? How is the idling when hot?
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