455 rancher(2010)-What am I missing?

[Lexicon]

I worked on a 455 Rancher for a friend last summer that was doing the exact same thing. After I found I could not tune the issue away, I replaced the fuel line, filter, tank vent and kitted the carb making sure metering needle height was correct. Problem persisted. It was after this I realized the saw was still under factory warrantee, so being that I did not want my friend paying for more "darts" for me to throw at it (I like that saying Mattyo, fits perfectly!) I took the saw to GKS to see what they could do with it. They ended up replacing the entire carb... Saw runs fine now.

I see you stated you replaced the carb, but did you go with OEM (Zama) replacement? You said it was chinese, but a chinese Zama or another chinese flavor knock-off???

Original carb is Walbro WTA-1. soaked it in mineral spirits, blew it out @25psi, rebuilt it with new pump & metering diaphragms, needle, etc. no change in symptoms, ordered a Hipa WTA-29 equiv.. no change in symptoms...

 

[Mattyo]

you have compression and spark, but no fuel, just gotta figure that one out

 

[Terry Syd]

It is a strato saw and the strato valve starts opening at about 1/3 throttle. Is the strato system operating properly?

 

[Stump Shot]

Check your spark by having it jump a 5mm air gap. There should be a thick bright blue spark. If a very thin weak blue, white or pinkish spark or no spark your coil is bad. It will be enough to get it started and that's about it. If good spark is present move on to fuel related issues, these can be many, eliminate one at a time, if you can pressure check carburetor and fuel delivery system, this will help narrow down the possibility's. SS

 

[Mattyo]

make sure you have a brandy new oem carb. make sure you have a brandy new oem fuel line with NO holes in it. I would do these things first, then consider you have a bad coil.

brandy new oem carbs are $45 on ebay

make sure your impulse line is not clogged


a saw that won't come off idle .. a bog when you hit the trigger is usually related to not enough fuel on the low screw.... back the low screw out 1/2 turn and see if it improves, if not, back it out a full turn and see if it improves. if you have one with limiters they can be defeated. push the ring in that is around the needle.. while holding that with a small screwdriver screw the needle counter clockwise all the way out... remove limiter/ring ... reinsert needle

 

[Lexicon]

It is a strato saw and the strato valve starts opening at about 1/3 throttle. Is the strato system operating properly?

This is the reason I pressed on with this saw, to learn. Never heard of a strato engine before this post... 1/2 hour of googling & youtube vids, I can say that the strato passageways are all new (Piston & cylinder) with the exception of the actual intake manifold, the black plastic assembly with the clean air side lobes, item 14. As I understand it, there is no actual "valve" but passageways that are blocked or unblocked depending on piston position, is that correct?

 

[Lexicon]

make sure you have a brandy new oem carb. make sure you have a brandy new oem fuel line with NO holes in it. I would do these things first, then consider you have a bad coil.

brandy new oem carbs are $45 on ebay

make sure your impulse line is not clogged


a saw that won't come off idle .. a bog when you hit the trigger is usually related to not enough fuel on the low screw.... back the low screw out 1/2 turn and see if it improves, if not, back it out a full turn and see if it improves. if you have one with limiters they can be defeated. push the ring in that is around the needle.. while holding that with a small screwdriver screw the needle counter clockwise all the way out... remove limiter/ring ... reinsert needle

Appreciate the input. The impulse line is fresh new tubing and clear. Respectfully I think I'll stop short of buying another carb, think its a bit of a stretch 2 units with same fault. Ditto for yet another coil... Update after recent tuning attempts... saw is impossible to start without holding throttle open, and will not idle, also, while throttle is held open to maintain, there are small droplets spitting up through the fresh air ports in manifold (I have the air cleaner removed for now) from what I could glean from the Walbro carb support documentation, I concluded the original carb max fuel orifice must have been clogged, since thorough cleaning installing carb kit made no difference. Any labor-based actions I'm game. but I think I've thrown too many components at it even for the sake of learning...

 

[Chainsaw Jim]

I'm noticing there isn't any mention of changing out the oil seals. A bad seal will cause all this.

 

[Terry Syd]

there is no actual "valve"

There should be a 'valve' that controls the air into the strato system. From looking at a diagram of the engine, the strato valve sits just above the carburetor.

It needs to be closed at idle and then begins to open later as the throttle moves to about 1/3 open.