Strimmer woes

[Prajna]

So, my favourite Cheapanese strimmer doesn't like to start unless it gets a sniff of brake cleaner in the carb. It's fine once it's warmed up and runs great once it's started but when it's cold it won't fire without a squirt of brake cleaner. I've stripped the carb and cleaned it and cleaned the air filter. What next? It's an Aowei AW-BC430B, if that makes any difference. I do like it, seriously, it has electric start and has done heaps of heavy brush cutting and hay cutting with barely an issue.

 

[Prajna]

Forgot the obligatory photo:

 

[johnik]

what has it got for a choke, if it,s a rubber squirter bulb thingy, they can crack and stop squirting ?

 

[Prajna]

what has it got for a choke, if it,s a rubber squirter bulb thingy, they can crack and stop squirting ?

The primer bulb is fine. It has a plastic disc thing that covers the air intake for a choke; flip it closed for choke and open for run.

 

[Pigeon_Droppings2]

I tend to strip the carbs and clean/blow them out...only to find that the petrol hose has an air leak . I also seem to remember there's a little "draw" hose linking the carb to the engine which can get blocked sometimes.

The hose trick has happened to me 2 or 3 times!

 

[DAPPH]

Do a compression test both dry & wet .
Make up a brazed sparkplug with the ceramics & contact removed and use a proper compression tester dial with a pressure release screw in it.
Expect to se 12 to 15 psi on a dry well worn machine and around 18 psi after you pour a dessertspoon of engine oil in the sparkplug hole roll it about to get an even run of oil on around the piston head , refit the tester & pull over four or five times with out the air filter being fitted & throttle wide open . Once you have proved it's OK . with the air filter still off , get it running like you've been doing , build up the rpm then slap a thick card over the air intake , till it nearly stalls . repeat this exercise four or five times that should drag any crud out the carb & jets .

 

[Prajna]

I tend to strip the carbs and clean/blow them out...only to find that the petrol hose has an air leak . I also seem to remember there's a little "draw" hose linking the carb to the engine which can get blocked sometimes.

The hose trick has happened to me 2 or 3 times!

Thanks PD, I'll check for leaks.

@DAPPH I don't have any kind of compression tester but compression feels fine.

 

[frank horton]

It’s a bit like easy start….
once they weaned on it they can never get off it without a eng rebuild…
I have an eng that like a little more fuel than the choke system allows…
so I have a small squirt bottle with petrol in it…..
drilled a tiny hole near the carb inlet…..
works every time…..
would like an electric start strummer tho…..

 

[Prajna]

It’s a bit like easy start….
once they weaned on it they can never get off it without a eng rebuild…
I have an eng that like a little more fuel than the choke system allows…
so I have a small squirt bottle with petrol in it…..
drilled a tiny hole near the carb inlet…..
works every time…..
would like an electric start strummer tho…..

It's a cracker, this one. I should do a review, really. There's a square plastic box as a cover over the starter switch that gets knocked off in seconds, then ever after you knock the starter every time you put the strimmer in the car or shed. Really the start button should be isolated when the stop switch is off and it would be much more convenient if the start button was on the handle near the stop switch rather than on the back of the machine where it gets knocked every time you look at it. The start button fell to bits too (you might notice the yellow insulation tape holding it on in the pic).

Another almost brilliant feature of this design is a lock button for the strimmer head. Save you having to find a hex key or tent peg to lock the head so you can swap discs or string head. Damned cool except that strimmer dust leaks past the button and ends up packing under the button so that it no longer works until you knock the dust out.

Apart from those two issues I think it is a fantastic little strimmer and it has kept up with the 45cc Kawasaki in both the amount of work it's done and the size of broom and brambles it has knocked down.

I love it.

 

[Prajna]

Two stroke? Does it have a spark arrestor in the exhaust? They can get clogged and affect the running - especially if runing on the wrong mixture or cheap lube.

Good call. I'll check that. Mix is always pretty close: I'm the only one who uses it and I mix 5l every time, 25:1 2T oil. It should have a spark arrester 'coz it's needed here in Portugal, which is always on fire.

 

[dobbslc]

25:1 might be a bit to much oil depending on what type you use. My strimmer (or stummer ^) chainsaw etc run at 40:1 fully synthetic, it may just have oiled up.
Dump the exhaust in a mixture of costic soda for 30 minutes then blast it out with water.
Assuming it's not made of alloy.
New plug and give it a try. Worn crankshaft oil seals also cause running trouble like this though...

 

[Prajna]

25:1 might be a bit to much oil depending on what type you use. My strimmer (or stummer ^) chainsaw etc run at 40:1 fully synthetic, it may just have oiled up.
Dump the exhaust in a mixture of costic soda for 30 minutes then blast it out with water.
Assuming it's not made of alloy.
New plug and give it a try. Worn crankshaft oil seals also cause running trouble like this though...

Manual and filler cap both advise 25:1. It's done a ship load of work in the last few years, so oil seals could be less than optimal. I'll clean out the exhaust though and see if that helps. I also notice that it can be a pain to start when it's really hot too. I always let it cool off when it's like that; opportunity for a fag and a break anyway.

 

[Prajna]

Leave out the fags! - you would have more energy to get it started!

Electric start. No effort.

 

[Moose McAlpine]

What's the spark plug like? Coked up worn plug can make it hard to start from cold like that.

 

[Prajna]

What's the spark plug like? Coked up worn plug can make it hard to start from cold like that.

Plug looks great to me (though I claim no expertise in sparkplug analysis). I did try a brand new plug, to no effect.

 

[DAPPH]

Thanks PD, I'll check for leaks.

@DAPPH I don't have any kind of compression tester but compression feels fine.

Just try the card trick then

 

[DAPPH]

Just try the card trick then

But it does sound as though the piston & barrel are well worn often giving a bit of excess crankcase pressure that normalised to about what it should be once it gets running .
Can you see the cylinder walls and around a port when you take the spark plug out ?
If so what do you see?
Nice and shiny same all over no scores on the cylinder wall or lighter matt grey or scores on the cylinder walls . . if you remove the silencer look in that access point too for the same things . Anything but nice a clean scratch free shiny cylinder wall or an even coloured piston free of scores or quite dark brown tar marks indicates wear or problems .


One thing I didn't ask , off load when it is running hot on full throttle does the exhaust / machine noise stay constant or does it warble up and down a little ?

Variations beyond a certain point indicate wear in the cylinder & piston and slight crankcase excess compression that blows back through the carb a tiny bit so making it pulse /warble on each stroke of the piston . If such a thing becomes really bad it will also blow some atomised fuel with oil back out the crank case , through the carb and wet the inside of the air filter .

 

[Prajna]

But it does sound as though the piston & barrel are well worn often giving a bit of excess crankcase pressure that normalised to about what it should be once it gets running .
Can you see the cylinder walls and around a port when you take the spark plug out ?
If so what do you see?
Nice and shiny same all over no scores on the cylinder wall or lighter matt grey or scores on the cylinder walls . . if you remove the silencer look in that access point too for the same things . Anything but nice a clean scratch free shiny cylinder wall or an even coloured piston free of scores or quite dark brown tar marks indicates wear or problems .


One thing I didn't ask , off load when it is running hot on full throttle does the exhaust / machine noise stay constant or does it warble up and down a little ?

Variations beyond a certain point indicate wear in the cylinder & piston and slight crankcase excess compression that blows back through the carb a tiny bit so making it pulse /warble on each stroke of the piston . If such a thing becomes really bad it will also blow some atomised fuel with oil back out the crank case , through the carb and wet the inside of the air filter .

Ah, the air filter does get a bit oily. It doesn't get much chance to idle because the idle adjust bracket has broken off. Been meaning to stick it back on or fab a replacement. This is all the kind of info I was fishing for. I have charge of four or five strimmers, about ten chainsaws, and currently three gennys, so learning a bit about small engine maintenance and repair is probably a good investment of my time. Thanks.

 

[DAPPH]

That oily filter will now make the fuel to air ratio too rich and after a while of tinkering you'll not be able to have it running well . The extra rich fuel air mixture will also be likely to be too rich for hot starting .... the symptoms you said of hot starting .
Giving the shot of highly volatile cleaner temporarily overcomes that problem but in a two stroke it's usually not for too long .

 

[Prajna]

That oily filter will now make the fuel to air ratio too rich and after a while of tinkering you'll not be able to have it running well . The extra rich fuel air mixture will also be likely to be too rich for hot starting .... the symptoms you said of hot starting .
Giving the shot of highly volatile cleaner temporarily overcomes that problem but in a two stroke it's usually not for too long .

I regularly clean the air filter since I had problems with hot starts and cleaning the filter fixed that.