Very strange carb problem.

[traffic903]

So I purchased a Chinese carb for my latest 044 project and it has a very strange issue. Once warm, at idle, it starts to idle rougher and rougher until it dies. This can take 5 seconds up to 45 seconds. Now for the weird part. If I hold the saw (and in doing so stop it from vibrating) then it idles fine.

This problem only occurs when the saw is left on the ground and is vibrating.

I have tried raising and lowering the metering lever and cleaning the carb with no luck. I swapped carb for an OEM from my other 044 and problem disappears. Should also mention that saw pressure tests fine, has heaps of compression (freshly rebuilt), has fresh fuel, no problem with hoses etc. Seems to be strictly this carb.

Can always buy another carb but just wondered if anyone had come across similar symptoms and found a fix.

Cheers.

 

[Thommo]

The spring under the metering lever could be a bit weak so it allows the metering lever to bounce

 

[Cliff R]

I have had absolutely ZERO success with the Chinese carburetors in any application, Quad, chainsaw, roto-tiller, etc, etc.

Just went thru all that crap once again with a 1988 Yamaha Warrior. They sell complete Chinese "knock-off" carburetors for $40. I went that route because the last guy that worked on the Quad broke the float, and stripped out the main jet brass sleeve inside the plastic housing (Mikuni straight slide).

Ended up buying two original unmolested cores and a high quality rebuild kit and building one carburetor for it....flawless!

The Chinese copy didn't do anything right, same as the carb I bought a few months ago for an MS-170, and every single one I've tried before that one no matter what it was for.

What makes it worse for me is that about 70-80 percent of the folks providing feedback for the Chinese carbs, no matter what application say they are perfect and zero issue with them. So far my success rate is ZERO across the board no matter what I bought one for. What I think happens here is that folks are a bit too quick to provide feedback, or they are just happy that the engine runs but really don't know it's not doing everything as well as it should........FWIW......Cliff

 

[Ozhoo]

A pressure test of the carb will likely show what's going on. Test to 6psi on the inlet and keep working things till it holds. If you need to, drop it in a cup of water while it's pressurized.

 

[HarleyT]

A new OEM carb cost $75 at the dealer, just get one.

 

[brandonstc6]

The aftermarket carburetors don’t always work, the Walbro carburetors are pretty reliable. I would find a good used one if I didn’t want to spend the money for new.


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[brandonstc6]

The aftermarket carburetors don’t always work, the Walbro carburetors are pretty reliable. I would find a good used one if I didn’t want to spend the money for new.


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[traffic903]

A new OEM carb cost $75 at the dealer, just get one.

Harley I am in Australia so that carb actually costs more than $200!! The other thing which is common here (especially in my area) is that the dealers have ZERO used parts inventory. I am sure it is so customers become frustrated with not being able to get parts for older saws, and so buy a new one.
I will look for a used oem on Ebay I guess, but who knows whether it will be ok.

 

[traffic903]

Thanks for the replies so far. I have not pressure tested it, but will do that next. Can anybody say with cetainty what the cause is though. I have adjusted the metering arm numerous times to no avail. The spring seemed stiff enough, but then it is hard to tell exactly. Someone more experienced in carbs could probably say for sure.
I have PLENTY of other running saws, and it's coming into summer here so I don't need this saw for cutting. This gives me plenty of time to sort the carb. And now it has become a bit of a challenge. Please keep the possible causes coming.
Cheers.

 

[HarleyT]

What happened to the original carb?

 

[traffic903]

What happened to the original carb?

No idea Harley. I bought the thing as a wreck. Spent some time chasing up the parts to finish it. Had to go China carb due to previously mentioned problem of cost. Was a full rebuild.

 

[traffic903]

Here's one for ya. Check out the pto side bearing situation!!!

 

[HarleyT]

If you see one here in the states, I can get it for ya and pop it in the mail, I think the shipping would be @ $15 or so.

 

[traffic903]

If you see one here in the states, I can get it for ya and pop it in the mail, I think the shipping would be @ $15 or so.

Mate that is an awesome offer. I thank you very much. I may just take you up on it as it appears there is nothing available down here used. Really appreciate it.

 

[L34]

If you see one here in the states, I can get it for ya and pop it in the mail, I think the shipping would be @ $15 or so.

Hi Harley,would you consider doing the same for an 038 May Carb?
Approx $380 for a new one here down under.
Cheers Chris.

 

[traffic903]

Update - pressure tested carb and it holds fine to 7psi. I didn't go above this. Should I keep going to find what pressure will cause it to pop?

 

[HarleyT]

Sure I see a Zama OEM for @ $68,

#1119 120 0605

 

[Poleman]

Traffic903, try sealing the Welch plug with clear fingernail polish and ever so slightly stretch the needle spring. I’m not sure what your AM carb looks like inside but a leaky Welch plug will cause an irratic idle. I fought this is the issue but it’s taking it out of the picture.
Like suggested earlier I think your issue from the saw idling on the ground which is a harsher effect and sharper vibration than when holding the saw which acts like a shock absorber.
I’ve used AM carb for years and still run them with a very low percentage being bad. Their cheaper to use and more affordable to others when I mod them to increase performance.

 

[traffic903]

Traffic903, try sealing the Welch plug with clear fingernail polish and ever so slightly stretch the needle spring. I’m not sure what your AM carb looks like inside but a leaky Welch plug will cause an irratic idle. I fought this is the issue but it’s taking it out of the picture.
Like suggested earlier I think your issue from the saw idling on the ground which is a harsher effect and sharper vibration than when holding the saw which acts like a shock absorber.
I’ve used AM carb for years and still run them with a very low percentage being bad. Their cheaper to use and more affordable to others when I mod them to increase performance.

Thanks Poleman. Will give this a try and report back.

 

[L34]

Sure I see a Zama OEM for @ $68,

#1119 120 0605

Thanks HT,I will see what happens if I can't get a cheap one locally.