More Two Stroke Troubles ....

[fixerupper]

So I have a Komatsu brush cutter a BC3500DWM…and Its about 14 years old done a fare amount of work I pulled it out of the shed the other day to whizz over the bit of land behind our house , fresh fuel , new plug, new air filter …first pull starts up fine but it feels gutless, and slow, even grass laughs at it ….I’m thinking dirt in the carb …before I pull it to bits ..does that sound right ..the drive down to the business end seems ok and free and the gear case rotates freely, it fires up so I’m guessing the piston and cylinder is OK …what else can explain the problem …here is a photo …I took the air filter off to get a better look …the foam air filter was damp with two stroke ..is this normal ? there does not seem to be any adjustment on the carb apart from the cable stop screw ...am I missing something ?...I'm learning more about small two strokes ..than I ever wanted to know ....

...

 

[Screwdriver]

99/100 it will be a problem with the carb.

Cleaning it might help but you really need an ultrasonic bath to be sure. Old fuel turns to hard varnish and is very difficult to shift unless you're using a specific product/process. There are some tiny holes, apertures and patways in these tiny things and you need to make sure they are clear without poking at them with a wire. From the other thread, I learn that the diaphragm can also swell and degrade so you might want a carb kit before you rip it apart. I discovered the easiest method with my old Stihl was just to swap out the carb with a new (cheapo Chinese) one. Worked a charm.

 

[fixerupper]

Thanks Screwdriver .. that sounds good ....ultra sonic bath ...here never ....getting a carb kit local to here no chance ...any thing will have to come from China or Athens ...it's the thing about living in the back of beyond...

 

[eLuSiVeMiTe]

Thanks Screwdriver .. that sounds good ....ultra sonic bath ...here never ....getting a carb kit local to here no chance ...any thing will have to come from China or Athens ...it's the thing about living in the back of beyond...

Copy and paste from elsewhere but this is my method for cleaning carbs.
Some of the trials bikes I've bought have had pretty grim carbs as they stand for long periods.

Wife makes me do them on the BBQ hob now. Gets a bit smelly.

Quote.

I restore vintage motorcycles for a hobby and commonly "boil out" carburetors.

Here's what I do:

Use about 1 cup of WHITE vinegar to a couple of quarts of clean water, enough water to cover the parts (more or less vinegar, the exact amount is not critical). Strip the carb down to it's smallest individual components, being especially careful to remove the rubber parts and gaskets. Do *not* soak the rubber parts or gaskets, set them aside.

Place the carb parts into the vinegar solution and bring the mix to a soft rolling boil on the stove (it will smell a bit, so be prepared for this). Maintain this rolling boil for about 45 minutes or so, adding water if necessary to keep the parts covered.

After the initial 45 minutes, drain and replace the solution with clean water. Bring the water back to a soft rolling boil for another 30 minutes or so to rinse the parts.

You'll find the parts will be covered with a soft white powder... this is normal and it will brush off easily with a soft toothbrush or something similar.

Blow out the passages with compressed air and you'll be good to go.

Note this will *not* damage metal parts of any kind, including castings and brass.

 

[Pete.]

I'd loosen/remove the exhaust first and try it. If it runs well then it's a blocked exhaust, which is a lot easier to sort than stripping the carb.

 

[Rannsachair]

Carbs and modern fuels are becoming a real pain, I seem to be cleaning carbs regularly of bikes and outboards. I was helping my brother out last week picking up a new lawnmower and strimmer from my local forestry/gardening dealer and he said he used to hardly buy a carb and now buys in over 100 a year.

 

[andymfell]

/QUOTE]

attached illustrated parts list & carb service instructions

there is a idle mixture screw it is not meant to be easily accesible to stop unauthorised twiddling the screw needs a "jewellers type screwdriver" as it is recessed down inside the throttle barrel it could be under a nylon plug in the centre of the part that rotates when the throttle cable pulls on it

 

[fixerupper]

Oh thanks guys for your responses .. and big thanks andymfell for those pdf's . printing them now ..I'm going into town in the morning armed with the diagram, and order the repair kit and the gasket diaphragm kit from the shop I bought the brushcutter from...I might take some time, but better to have the new bits before I pull it in bits ....hopefully the " take it apart clean it and put back together" technique will work ...thanks again ...

 

[earthman]

Carbs and modern fuels are becoming a real pain, I seem to be cleaning carbs regularly of bikes and outboards. I was helping my brother out last week picking up a new lawnmower and strimmer from my local forestry/gardening dealer and he said he used to hardly buy a carb and now buys in over 100 a year.

Have you tried just using 'Super Unleaded' petrol, BP's Ultimate for example? Depends on where you fill up in the country but it should be free of ethanol, that's the substance that you are referring to, that causes problems?

 

[Rannsachair]

Have you tried just using 'Super Unleaded' petrol, BP's Ultimate for example? Depends on where you fill up in the country but it should be free of ethanol, that's the substance that you are referring to, that causes problems?

Thanks, will look into it, though I just checked that my nearest BP is 1.5 hours drive/ride away!

 

[eLuSiVeMiTe]

Have you tried just using 'Super Unleaded' petrol, BP's Ultimate for example? Depends on where you fill up in the country but it should be free of ethanol, that's the substance that you are referring to, that causes problems?

The fact my last bike needed premium for the octane level to stop knocking I would happily pay the extra for it for that reason. Even so I still cut the fuel and emptied the bowl if I wasn't gonna be riding for a while.

 

[eLuSiVeMiTe]

Carbs and modern fuels are becoming a real pain, I seem to be cleaning carbs regularly of bikes and outboards. I was helping my brother out last week picking up a new lawnmower and strimmer from my local forestry/gardening dealer and he said he used to hardly buy a carb and now buys in over 100 a year.

Point him at this
https://aspenfuel.co.uk/uses/

 

[grim_d]

Honestly I wouldn't waste the time rebuilding the carb if you can get a new one, the cost will only be marginally higher.

Most of them are made by or copies of Zama carbs, easy enough to identify and cheap as chips from China...I consider them consumables.

I'll replace primer bulbs when the ethanol rots them but I won't rebuild a carb on a garden tool unless I can't get a replacement cheap enough.

Have you tried just using 'Super Unleaded' petrol, BP's Ultimate for example? Depends on where you fill up in the country but it should be free of ethanol, that's the substance that you are referring to, that causes problems?

BP ultimate was ethanol free but if it still is I don't know, v power and momentum both contain ethanol.