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Off Idle Hesitation

drf256

Dr. Richard Cranium
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I'm having a strange hesitation issue with an 024-026 conversion.

The saw is ported. Comp currently 230 and timing advanced 6*. Brand new WT194 with the metering lever set .020 above the factory setting. Saw has passed pressure and vac test. Brand new OEM fuel line and filter.

The saw runs like a beast with no hesitation at all from idle to WFO initially. Let the saw keep idling for a bit,
and the idle rpm's drop slightly. Then pull the trigger and the saw wants to die. Get the revs up, and it runs fine again with no hesitation. Let it sit idling and it repeats itself.

My guesses are that the saw gets hot at idle and cools down after a few revs. I'm also wondering if my metering lever adjustment may be causing the saw to start flooding at idle and then get a sudden dump of fuel. I've run the metering lever above flush on a few ported 026 and it's generally helped performance.

Thanks.

@Terry Syd ?
 

Deets066

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Did you try it with metering arm at stock height (flush)
 

Deets066

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A ported saw usually needs richend up on the low numa
 

drf256

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The reason I raised it was because I was having some issues with it leaning out on the top end.

I made the cardinal mistake though, I changed two things at once.

The flywheel was swapped for an 026 one with better cooling fins. I also lifted the lever because of reading that it was helpful in this model with any performance mods and because of personal experience.

I think I'm gonna drop the lever back to stock. What I'm not getting is why there is such a big difference when it sits idling for a while. If I cut and wait about 10 seconds, I hit the throttle and all is well. If I set the saw down and wait 30 seconds, it wants to die when I hit the throttle.
 

drf256

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I'm thinking that's it.

I've read that phrase, but don't get exactly what happens when a saw "loads up".

So is my higher than normal metering lever causing the issue? Would that make the idle ports leak fuel into the case?

I'm still able to adjust the L and it still makes an RPM difference.
 

Brewz

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It sounds like you are getting fuel buildup when it idles for a while, and when you hit the throttle again, it sucks it up and floods the combustion chamber.

Just fault finding this out loud here.......
With the metering lever bent up, you will be opening the valve to feed fuel into the wet end of the carb sooner and for longer for each cycle of the motor. This will result in more fuel across the board
Perhaps with the metering lever bent up, it is delivering more fuel to the carb than the saw consumes at idle.
This will slowly fill the wet end with excessive fuel
Hit the throttle and main jet on the H circuit sucks in all the excess fuel and floods the saw.

Just a theory
 

Terry Syd

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The reason I raised it was because I was having some issues with it leaning out on the top end.

The lever height has nothing to do with the top end fuel mixture. The metering system is only used to control the idle and transition, if you want to understand that fully, then remove the pump diaphragm from the carb and start the engine with the choke on. You can run the saw, but don't let the revs drop to idle or the engine will stall.

Raising the metering lever has decreased the pressure on the metering valve seat. In other words, it works similar to decreasing the length of the metering spring. It makes the idle RICHER and brings in the 'ramp' of fuel off of idle sooner. If you set the metering lever at stock height it may fix your problem (that is, if it is 'loading up' by being too rich at idle).
 

drf256

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What was it doing at the top end mate?
It leaned out the last time I used it.

I have the timing advanced. I swapped the flywheels. Please take a look at the original thread for pics.

I'm not sure whether or not the magnet position is exactly the same on the flywheels. There's a possibility that I was more advanced with the 024S flywheel off the bat. Also, it's clear that the 026 flywheel is designed betterer.
 

Terry Syd

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I took a look at the difference in the fly wheels. What were they thinking when they designed the 024 fly wheel, "we don't want it to run too cool". Crikey, it is an air cooled two-stroke, they run stronger when they are cooler. An air cooled two-stroke can loose up to 20% on a dyno between a 'flash' reading when cool and a heat soaked engine. (That is important information to know if you are getting in a drag race...)
 

drf256

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Yes. The design is awful and a detail I initially overlooked on this build.
 

Basher

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Waiting on your reply on setting the lever back to flush, Terry nailed it on the metering properties, raising the lever does not affect WOT, the orifices limit the amount of fuel the carb can flow.
 

bikemike

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I'm having a strange hesitation issue with an 024-026 conversion.

The saw is ported. Comp currently 230 and timing advanced 6*. Brand new WT194 with the metering lever set .020 above the factory setting. Saw has passed pressure and vac test. Brand new OEM fuel line and filter.

The saw runs like a beast with no hesitation at all from idle to WFO initially. Let the saw keep idling for a bit,
and the idle rpm's drop slightly. Then pull the trigger and the saw wants to die. Get the revs up, and it runs fine again with no hesitation. Let it sit idling and it repeats itself.

My guesses are that the saw gets hot at idle and cools down after a few revs. I'm also wondering if my metering lever adjustment may be causing the saw to start flooding at idle and then get a sudden dump of fuel. I've run the metering lever above flush on a few ported 026 and it's generally helped performance.

Thanks.

@Terry Syd ?
Fuel may be pooling up in the intake boot bellows
 

jmssaws

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It's just a touch fat. Lean it out a little doc
 
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