Carburettor Testing (Get it Going)

[Rustynutz]

Coming back to your original post Kam
10 to 12 seconds is fine, i've had them 4 seconds and they still run fine, just has to be seen holding then release when you blow the vent.

As far as air bubbles go, are you testing with the jets closed? there is a free passage to the low jet

more importantly is the check valve working? (see my first post)

and when you say you set the metering lever level? is that level or level with the gasket? as most carbs are measured from gasket.

 

[Rustynutz]

The function of the check valve is to allow fuel to enter the chamber and stop air blowing back, if this is not operating the carb will not function.

 

[roncoinc]

Coming back to your original post Kam
10 to 12 seconds is fine, i've had them 4 seconds and they still run fine, just has to be seen holding then release when you blow the vent.

As far as air bubbles go, are you testing with the jets closed? there is a free passage to the low jet

more importantly is the check valve working? (see my first post)

and when you say you set the metering lever level? is that level or level with the gasket? as most carbs are measured from gasket.

There is only one standard diaphram carb used on chainsaws that measures the lever to where the gasket sets..and it's not made by zama..
follow the link i posted,it will show you the correct way to set the lever..

 

[Rustynutz]

Well I spent ages following walbro's instructions to set an MDC level with the body! it was only when I got near the gasket level they worked at all.
search on the the net and found I wasn't the only one to notice this??? 0.012 below gasket for that one.

maybe zama got better service data?

 

[roncoinc]

Well I spent ages following walbro's instructions to set an MDC level with the body! it was only when I got near the gasket level they worked at all.
search on the the net and found I wasn't the only one to notice this??? 0.012 below gasket for that one.

maybe zama got better service data?

see post #43

posting erroneous info as opinion is one thing,posting it as fact without experiance is not cool..
RTFM man.. follow the LINK...

 

[kam]

I've been going over the literature on setting the metering lever
height and found that the Stihl manual calls for level with the carb body, and Zama calls for .012" below the body, so who should I trust ?

I was pressure testing with H and L needles set at 1 1/4 turns and now I tried with the needles lightly seated with the same results.

 

[kam]

Ok, the check valve seems to be working. I can blow on it and hear leaking air....holds when I suck on it.

 

[kam]

Rustynutz,

I'm sorry, just realized I hijacked your tread, I was looking for carb info centering on the metering and check valve systems.

kam

 

[Rustynutz]

No prob Kam that's the point of the this tread
Like I said some bubbles coming out of idle ports is ok, we are looking for leak's in gaskets, welch plugs that kind of thing, if your check valve is working and metering needle is setting and resetting and you have new everything in there then its down to metering settings, put a strait edge across and the arm should sit 0.0 to 0.012 under (no gasket) if that's set reassemble and test on saw
Just remember gasket first then diaphragm

let us know how you get on!

 

[kam]

It's running !!!!!

After setting the metering lever to .012" below the carb body, the saw fired. When I tried to start it again, it fired and jerked the starter handle out of my hands. After a few minutes of trying, and getting "kickback", I suspected a timing problem.

I checked the Stihl manual and it confirmed that a defective coil changes the timing. I knew that several models of Stihl uses the same coil, and on checking, my 026 had the same coil as the 036 PRO that I am working on. Swapped coils
and it started right away and responds to L adjustment. I can't do the H adj. till I find some wood to cut.

This is the first time I heard of a mis-firing coil. I always thought that a coil works or it doesn't unless heat related.

A big thanks to all the different ideas given. It brightened up my day. All my problems are not over yet, I still have to locate a coil and a clutch for this thing.

Thanks again

 

[Rustynutz]

Nice one Kam good to here you got life there, and sounds like your cab is running and had a good service! I usually give it 1/2 to 3/4 throttle, back off the high needle till it starts to chug then turn in slowly till you get a nice trigger response, this gives you a good starting point, then you can tweak from there on site, just remember not to go too lean (monitor engine temperature)


Your better going slower and richer than faster and leaner, the former bungs the plug up the latter melts the engine.

Not had of your coil fault before either, well spotted! I thought they just died or went intermittent.

 

[Rustynutz]

thanks guys for this most edifying tread
and yes I agree with Sefh3 should be a sticky in fix it up section!

 

[roncoinc]

After setting the metering lever to .012" below the carb body, the saw fired. When I tried to start it again, it fired and jerked the starter handle out of my hands. After a few minutes of trying, and getting "kickback", I suspected a timing problem. "



Sorry i truncated your quote but to get to this .012" below carb body metering lever thing..
it has me confused.i have never seen that have to be done.. now the gasket on that side is about 12 thou thick,are you sure you have the gasket and the diaphram in correct order ??
ALL carb specs call for metering lever LEVEL with carb floor..
fooling around with that to make up for a bad diaphram dont solve problems..
if that needs to be done SOMETHING is not correct..
AGAIN i will say,follow the manufacturers instructions..if they dont work SOMETHING is wrong !!

 

[Rustynutz]

mmmmm interesting these settings, just looked at my Walbro metering lever gage

WB -1.3mm below
WTA WA WT -1.5mm below
MDC HDA HDB MDC level
SDC 1.2mm above

now some of these are with and some without the gasket, I know if you set the MDC level with the body it wont run level with gasket runs fine, yet walbro said level with body not gasket, so that's how much they know!
I managed to find someone who fixes loads of these to find that setting and he said .012" under gasket is the sweet spot for the MDC, others may differ.

 

[a. palmer jr.]

The saw seems to run just fine at open throttle, it's when I try to idle it that it falls down. I kinda figured it might be loading up because it may have been set too rich on the L screw but I turned it in to about 3/4 turn and it didn't do any different. I think I'll take the carb back off the saw and check that gasket. Won't be around tomorrow but will start again on it Wednesday. Thanks for the replies.

I guess I could have mentioned it has a Walbro HDB on it.

 

[Rustynutz]

There little buggers if anythings set wrong, metering gap affects the idle circuit, sounds like yours is not pumping enough, that would give a lean top end (go like the clappers) but not enough to set the idle up.