# McCulloch 835AV won't cold start



## vbr666 (Oct 8, 2009)

Hi.
Recently, I had to dismantle and blow out carburetor holes on my 35cc mac (with zama c1q-m28d carb) as they were clogged.

I did it successfully, but I've changed my carb settings because it was necessary to remove both L and H needles out.

I'm now trying for at least 4-5 days to correctly adjust the carb, to work good in either cold or hot engine temperatures.

The problem is that when I successfully adjust needles to run smoothly when hot, it won't cold start.
I've cleaned the spark plug, pressed 3-5 times on the primer pump, closed yellow air intake handle to half open (choke) and started pulling on the cord until I fell of my legs out of exhaustment.
I sometimes have to pull it about 30 times just to get into the "zone" when you feel lesser resistance when pulling and know engine is getting really close to fire up (and sometimes even then it won't start except to run shortly for second or two and then die).
But at the same time, on same carburetor settings, if I press the accelerator to the max and start the engine, I can start it much easier and after it warms up, it will run smoothly both on idle speed or acceleration (both with same carb settings as above where it didn't want to cold start after 30 cord pulls).

So I tried different carb settings, making the mixture richer or leaner, opening L needle much more than it was possible before I pulled out limiter caps on it and then adjusting T - throttle screw to accomodate settings to more fuel intake when idle, but it wouldn't want to cold start (easily) - ever again.

I changed all membranes and that needle with it's lever recently (following zama carb manual: (zamacarb.com/pdfs/TechGuide_2007.pdf). I've already said that it runs very smooth once heated up, but until you heat it up, it's torture to start the engine cold.

I've also tried with 'default' settings:
Close the L needle to fit on it's seat and totally close the fuel intake, then open it one turn back (counterclockwise). I've also tried with half a turn (but then it's too lean), and more than one turn in steps.

To take the chainsaw to the service would be too expensive, it's an old saw and I'd like to adjust it myself again, as I've once succeeded in doing so (while limiter caps were still on), but it now looks like it was either lucky shot, or something has changed in between (some damage to the carb?).

What could cause the engine to run smoothly (and start smoothly) when hot, but can't start when cold?

*edit:*
*alright, here is the video of it's behavior:*
drop.io/095qjz3/asset/my-movie-mp4

*(just copy the link above to the browser, I still can't post links as I don't have permission yet).*
so in the vid I pulled the cord about thirty times before it showed "life signs" and started firing up for a sec and then choked. then I pressed accelerator to the max and successfully started it and after that, it was running smooth.


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## 30yearTech (Sep 14, 2006)

In your video after you pull the choke lever down, you push it back in slightly. This may be the reason it's hard to start. You are likely partially opening the choke butterfly and not getting a rich enough mixture to easily start the engine. Try pulling the choke all the way down and see if it will pop off a little easier.

Best of Luck...


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## vbr666 (Oct 8, 2009)

I knew it wouldn't work, but I had to try it anyways.
No, it won't start when the choke is on full (butterfly closed).
On my movie, if you've noticed, I'm turning the saw off by pulling the yellow handle to the max, thus shutting it's air intake (closing butterfly).
That is the only way to kill the engine as it's stop switch (electronics and/or circuitry) has failed and won't work from long time ago.

Full choke makes problem the same, after about 30 pulls on the cord, it starts warming up and you feel lower resistance on the cord and the engine starts working for a moment then dies.
It repeats this behavior until you press the accelerator to the max and heat it up a bit, then it works smoothly again.


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## geogrubb (Jul 28, 2006)

My $.02, I the setup is like a weedeater, 1. Since the tank is below the primer try pumping it 8-10 times to circulate the fuel to make sure there is fuel in the entire system, the primer just circulates fuel from the tank through the carb and back to the tank. 2. Fix the off switch, shutting it off with the choke is flooding it which makes it hard to start (3-4) pulls when warm and even harder after the engine has cooled since the excess fuel will have pooled in the crankcase in the form of a liquid rather than a gas. Have a good one. Geo


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## geogrubb (Jul 28, 2006)

My $.02, If the setup is like a weedeater, 1. Since the tank is below the primer try pumping it 8-10 times to circulate the fuel to make sure there is fuel in the entire system, the primer just circulates fuel from the tank through the carb and back to the tank. 2. Fix the off switch, shutting it off with the choke is flooding it which makes it hard to start (3-4) pulls when warm and even harder after the engine has cooled since the excess fuel will have pooled in the crankcase in the form of a liquid rather than a gas and if it isn't like a weedeater you probably shouldn't prime it at all when cold as it was already primed when you shut it off by choking it to death. Have a good one. Geo


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## vbr666 (Oct 8, 2009)

thanks for the advice!
I'll try fixing stop switch.

In the mean time, if anybody else has got any other advice, suggestion, idea what else would cause tough cold start, please don't hesitate to post it here.

Any help is much appreciated!


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## vbr666 (Oct 8, 2009)

geogrubb said:


> My 2. Fix the off switch, shutting it off with the choke is flooding it which makes it hard to start (3-4) pulls when warm and even harder after the engine has cooled since the excess fuel will have pooled in the crankcase in the form of a liquid rather than a gas and if it isn't like a weedeater you probably shouldn't prime it at all when cold as it was already primed when you shut it off by choking it to death. Have a good one. Geo


hi again.
I tried fixing the off switch yesterday.
Unfortunately it doesn't work and I don't know why.
There are two wires which I replaced because they were damaged badly.
I connected new wires exactly how old ones were connected.
I did not damage contacts, everything is as it was and it still does not work.

If I understand how the off switch works, it's simple electromagnet which is activated when the red button connects two metal contacts inside the handle.
when it's activated, the electromagnet reacts with flywheel which is also used for starting the chainsaw engine (using cord connected to it) and magnetic force from electromagnet stops the flywheel from turning, thus stops the turning of piston inside cylinder.

from that part (electromagnet?), there are two things coming out:
1. spark plug cable
2. the stop switch wire contact (1 side of first wire is connected to this contact, other side of first wire is connected to 1 contact on red button; 1 side of second wire is connected to metal armature of the electromagnet and other to the 2nd contact on red button)

I'm guessing that this electromagnet is functioning normally because the spark plug is functioning correctly (remember that spark plug cable is connected to the same device as the off switch wires).

*So, if both the electromagnet and switch button wiring are functioning, what else could cause it not to work when activated?*

If you need any picture of how this is connected or how it looks like, or video, just tell me, I will do it, possibly tomorrow.


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