OK..Stumped ( 357xp with "bog" )

[afleetcommand]

Freshened up a non running 357. Seals, a new ring, spark plug, fuel line etc....ditched the Walbro (As it would not run with it) and put on a Zama EL-42. Runs fine and will idle until the cows come home. But when you first give it throttle after letting it idle...even a second. It bogs, four strokes a bit before taking off up the RPM range. Like its pooling gas some where.

I notice there is no "notch" in the throttle plate.

First what am I missing??
Second, if this is a common issue; any one try a notch in the throttle plate to help low rpm issues coming off idle?

 

[EvilRoySlade]

Geez Walt, coming from you I'm sure you've looked it over good. So I'm going to guess at stuff.
Idle set a bit too low.
Any irregularities through the intake passage that could pool fuel.
I'd almost say idle is set too rich somehow.
Simply put, it seems you are lacking enough vacuum when pulling the trigger.

I'm curious what you find cause like I said, coming from you this is going to be educational.

 

[huskyboy]

I'd try a different carb and see if the problem still continues

 

[tickbitintn]

metering height or pop off pressure???

 

[afleetcommand]

I'd try a different carb and see if the problem still continues

Tried a different Zama....pretty much the same.

 

[huskyboy]

Tried a different Zama....pretty much the same.

Fuel must be puddling somewhere in intake? Thats all I can guess. The problem could lie with the Zama carbs themselves. Wonder if a walbro would do same thing?

 

[afleetcommand]

Fuel must be puddling somewhere in intake? Thats all I can guess. The problem could lie with the Zama carbs themselves. Wonder if a walbro would do same thing?

Two things have my attention...often regardless of brand there will be roughness introduced to the intake tract, like those little brass screens on 350's or the bumps molded into some Stihl intake boots....that would help as the old 357 is smooth. The other thing is the Walbro has a small hole in the throttle plate. I was contemplating putting a small notch in the throttle plate, but the question is where. Usually they are down stream of a jet....

 

[Simondo]

Freshened up a non running 357. Seals, a new ring, spark plug, fuel line etc....ditched the Walbro (As it would not run with it) and put on a Zama EL-42. Runs fine and will idle until the cows come home. But when you first give it throttle after letting it idle...even a second. It bogs, four strokes a bit before taking off up the RPM range. Like its pooling gas some where.

I notice there is no "notch" in the throttle plate.

First what am I missing??
Second, if this is a common issue; any one try a notch in the throttle plate to help low rpm issues coming off idle?

Walt.
I Picked up on 3 things in your description.....1 ....symptom happens even if ..." idles for a second"... could you even get fuel pooling that fast ? (yes /no, may lead you to other thoughts ) and still ..not.. go on to load up the motor under a prolonged idle ?
2..Waldro carbs were on the early to mid production 357 saws iv had dealings with so is there any difference in the intake compared to the intake used with the Zama carbs ? (might explain the lack of a notch )
3...Zama carburettor saws run fine in general so the carb design (if a working carb) is not known to produce your problem as far as i know.
Zama EL-42...shared fuel circuits ..H &L ?

 

[afleetcommand]

One thing is pooling might not be the right word...but if the throttle plate is shut....and it idles fine. Things are at "steady state". When the throttle is first opened regardless of time in idle it stumbles...sound super rich. THEN snaps to. and as long as you don't idle it its snappy. Interestingly enough taking the screen out of the muffler made things better. So its a signal thing is my guess. Wonder if there is a different part number for the Zama intake boot. And yes if you raise the idle to around 3k with the idle screw (not low speed...then it just acts lean) ...there is no "bog". Probably because now the plate is slightly open.

Crossed my mind to change ignitions as well...this weekend I am back on saws. Will try the "notch" and gutting that muffler deal with the internal tube. Swap ignitions as well to eliminate that as a concept.

 

[Simondo]

One thing is pooling might not be the right word...but if the throttle plate is shut....and it idles fine. Things are at "steady state". When the throttle is first opened regardless of time in idle it stumbles...sound super rich. THEN snaps to. and as long as you don't idle it its snappy. Interestingly enough taking the screen out of the muffler made things better. So its a signal thing is my guess. Wonder if there is a different part number for the Zama intake boot. And yes if you raise the idle to around 3k with the idle screw (not low speed...then it just acts lean) ...there is no "bog". Probably because now the plate is slightly open.

Crossed my mind to change ignitions as well...this weekend I am back on saws. Will try the "notch" and gutting that muffler deal with the internal tube. Swap ignitions as well to eliminate that as a concept.

Having no air bleed /notch ..is not a thing im used to seeing overall . I see the EL-42 has a hole in from the edge rather than a notch by the transition feeds like many carbs. Makes me wonder how the Zama carb performs like that as factory built unless the transition works slightly differently without the need for a edge notch.
Only prt no dif seems to be the -01 on the end of the parts ether side of the Walbro carb and changes to , -02 for the Zama.

 

[David Young]

how do you tune the carb are you still on the initial 1 and 1 adjustments?

could it be lean for an instant?

I love these teasers Walt thanks for putting it here. make sure to give us what the conclusion was.

How about a video?

 

[afleetcommand]

Video's on the way....just haven't had a split second to build them & edit them. Approx. 3 hrs per video. It was a case of not doing the basics....I rushed a vac test. Should have done a more complete eval. Funny beyond what I'm going to put on the video.....but the short version, It Went to a local shop from the owner to fix an idling issue...NOT the local Husqvarna dealer. They "fixed" the idle issue. (It was a County saw. I won't touch them at work....) They tried with what looked like a damn sheet metal screw into the auto decomp hole. It didn't seal well. even with the silicone that was also in the hole. I'm building the saw up from the bearings up now as I've got so much time into jerking around with the symptoms, I don't ever want to see it again. My own damn fault trying to squeeze an hour here and there hoping to fix things in time allotted....vs. rolling back and working from the basics and doing my own diagnosis. A teaching moment. One I seem to learn every couple of years. SO I stepped back and started from the beginning.... the carb was a little dirty nothing terrible...it had a new ( 372XT ?) long wire ignition. Suspect it was swapped out through someone else's attempt. Pulled the top end and everything is BLACK in there....too much fuel from tuning around an air leak I suspect. Might even be the case gasket allowing bar oil! ( Doesn't matter..cases came apart.) And that screw. Video's to follow....LOL

 

[Matt B]

Thanks for the brief wright up Walt, looking fwd to the video. Cheers, Matt.

 

[Mattyo]

Bog is technically too little fuel off idle.

But poor ignition due to either poor compression or an electronic issue can look like too little fuel.

Looking forward to the vid...

 

[afleetcommand]

No....bog in this case is over fueling. BUT when you see the issue it will give you a laugh

 

[Mattyo]

Too much fuel, too little spark? ...or... too little comp.

yep...I'm curious

 

[afleetcommand]

none of the above...

 

[tickbitintn]

Air restriction?

Sent from my XT1635-01 using Tapatalk

 

[Mattyo]

A completely plugged screen? Muff welded shut?

Now I gotta see this

 

[afleetcommand]

The rest of the story:

Now I have to keep the record straight....I know it's convoluted....but my saw world always is.
1) Customer sent it to a local shop because it wouldn't idle.
2) I don't have any idea what they attempted or accomplished. But they told the customer it needed a new carb and they couldn't get one.
3) Customer asked me to take on the saw and I refused unless the local dealer sent it to me. (How I work mostly, through one of a couple of dealers) The customer then asked the local dealer to get and fix the saw....so they retrieved the saw.
4) The local dealer called me as I was familiar with the customer and asked if I was interested in taking on the saw. And I stress they did not work on the saw, just did the paper work to get it into their system. So NONE of the goofy stuff happened there! I accepted the challenge...(They knew I would! I have a sybiotic relationship with them. I ask for projects....they oblige.)
5) I did as you see and returned the saw to the dealer who in turn returned it to the customer...everyone is happy.

Also I have no idea where the self tapping screw was added to the mix. I do know it wasn't added by the dealer, PROBABLY not the first repair shop..and I know enough about the customer to recognize ANYTHING could have happened there..

SO the local dealer is the "hero" in this story because they both orchestrated a solution AND got the parts......