Petrol hedgetrimmer problem

I have a Hitachi CH62EA3 2 stroke hedgetrimmer.
It doesn't seem to rev as high as it used to. If the blade is pointing upwards, it runs at nearly full power. If the blade is pointing down, it barely revs at all.
I've checked there are no splits in the hoses, the tank filter seems clean & no air bubbles appear in the transparent fuel pipe when running. I don't think it's fuel starvation from the tank.
I've had the carb off & the diaphragm seems intact. I've sprayed carb cleaner in the airways that I can see. The carb is the common horticultural type with a priming bulb on the side. It primes OK & starts OK.
The plug is a good colour, but I'm certain it's fuel related.
These carbs should work at any angle, but mine doesn't any more.
Any advice gratefully received.

 

Bit of an odd ball fault, this one but something to investigate.....
Check the fuel pipes coming from the tank (one flow, one return) - I've had a couple of machines in recently where the fuel pipe has fractured just as it passed into the fuel tank, either through a grommet or direct through the plastic.
John

 

Thanks John. I'm fairly sure the pipes are not split as I've had both grommets out to remove carb & to ensure there's no kink in the pipes, & didn't see any issues. No leaks either. I agree it's an odd problem to have. Overall it's down on power (revs) even at the best position. When pointing downwards, it's only just running. Not fuel starvation from the tank as I can see the clear pipe is full of fuel & has no air bubbles.

 

Are there any adjustment screws marked H and L on the side of the carb, and what make is it?
We might get some sort of clue if applying the choke makes the engine pick up, but I'd be inclined to strip the carb down, and replace the diaphragms.
Carb cleaner is essential when cleaning the carbs out, and compressed air is a boon too. If you check the diaphragm under the primer bulb, there is a tiny gauze filter that's there to feed fuel to the needle valve behind it.
John

 

Thanks again John. I agree, it's likely a carb refurb is required. I just wanted to know if I'd missed something obvious. I'll have to remove carb to see what make it is & to order the correct kit. I assume ebay is a good place to start looking? I'm actually using brake & clutch cleaner (ran out of carb cleaner) but I have a compressed air supply.
Forgot to say I don't think there's any adjsutment other than tickover. I'll check if slight choke sorts it, but I doubt it will.

 

I get a lot of stuff from GHS Ltd and they do a great range of diaphragms and gaskets for Zama carburettors (owned by Stihl) so you should find something there, including a pattern part replacement if necessary.
Ruixing carbs are a bit difficult though.
Brake cleaner is just fine, careful with the compressed air as you can blow the welch plugs out without realising!
Generally if the primer bulb fill up within 3 presses then the diaphragm there is ok, but there is a pump diaphragm too identifiable by its very thin membrane and U shaped flaps.
John

 

Thanks John.
I'll strip it down tomorrow & keep you posted. BTW, I think it takes more than 3 pumps to prime it, so maybe the diaphragm is the issue...

 

Hi John. I've taken the carb off & here are the details: It's a Walbro WYL. Also has 212 945 stamped on it. I've googled Walbro WYL & it keeps coming up with K20 WYL.
GHS sell a kit for Walbro WYL 1-125 & 136-140, but mine is a 212. It also includes full strip down gaskets & imagine I just need diaphragms.
Help!

 

I've ordered this parts kit. I hope it's the right one as I have hedges that need cutting.
https://www.ebay.co.uk/itm/CARBURET...TSU-G22L-G23L-TR200-XE32-K20-WYL/133163151716

 

So many different choices out there.....absolutely ridiculous!
This looks correct, same as the Honda GX22.
Fingers crossed!
John

 

Cheers John. We'll soon find out! Have a great weekend mate.

 

I've stripped, cleaned & rebuilt the carb. All new gaskets, diaphragm, mesh filter & needle valve.
Runs with more revs & power, but still slows when trimmer pointing down.
It runs better with no filter so that's been washed & is now drying. Slight spray coming from carb mouth at times.
Plug cleaned & set at 25 thou gap.
Starts easily, plenty of fuel. No air appearing in clear fuel line. Fuel pickup filter appears clean.
I'm stuck.

 

REWIND
I've just used it in anger & it seems to be running much better than before & is usable now. The carb overhaul seems to have fixed it.
It doesn't rev up as quickly as it once did, but the fuel is old & there's probably too much oil in the mix given the blue smoke.
Thanks again for your help, John.

 

Well, I'm pleased you've got somewhere - this one certainly had me baffled!
You can ignore the slight spray out of the carb - all two strokes do this and its the reason that the air filter often has liquid in it as it's just part of the two stroke running procedure.
Consider a fully synthetic two stroke oil such as Oregon or Stihl and the mixture is lean at 50:1 mix. This should all but remove the smoke but the machine will be lubricated fine. In your case there could be a fair bit of accumulated oil in the crankcase but that will clear after a while.
Good luck with it and be safe
John

 

Hi John,
Unfortunately the old problem has returned. Yesterday I couldn't even trim a box hedge as the revs are so low when pointing downwards. Had to use a rechargeable trimmer as it had more power than my 2 stroke Hitachi!
I'm going to strip the carb down again & reassemble but don't know what I'm looking for. I'll also slacken off the blade bolts in case it's friction causing the problem, but that doesn't explain why it varies in speed depending on angle of use. The petrol is now new, not too much oil in the mix but it still slows drastically when pointing down, speeds up when pointing up & seems down on power all the time. It's been fine for the past couple of weeks but now it's unusable. No bubbles in transparent fuel line & it primes quickly. Stops when I put the choke on.
Any tips gratefully received.
Thanks mate.
UPDATE
I slackened the blade bolts, greased the gearbox, pulled apart then reassembled the carb & checked the fuel filter but no joy. Just the same.
When cold, the engine "bogs down" & can't be revved until it gets warm. It didn't use to do that. More induction noise than I remember too.