What's on your bench today?

[spudulike]

Turned out to be over fuelling so fitted carb kit but no differences still the same over fuelling,

 

These carbs have a slide with a tapered needle on it which slides up and down in the main jet, to cut down the fuel you lower the slide via the idle speed adjuster or via the hidden screw:sneaky2:

 

That being said, it sounds like you have a setup issue and over-fuelling may be caused by a leaking needle valve so check this out by pressure checking the carb and make sure the gaskets and diaphragms of he carb are in the correct order.

 

This may help - http://www.jonsered.com/ddoc/JONI/JONI2004_AAaa/JONI2004_AAaa_TBC230,D,S_.pdf

[GardenKit]

Further to what Spud said.

These carbs are not prone to over fuelling. All fuel has to pass through the main jet and is not forced through in any way. The fuel flow is controlled by two methods, working together. Its the airflow through the carb from the piston on the induction stroke that creates low pressure adjacent to the needle and tube. The lower the pressure (higher flow), the more fuel is drawn to mix with the air. The airflow is regulated by the rotary valve which also rises on a ramp as it rotates, lifting the needle and allowing more fuel out at mid and high throttle.

So the only logical causes of over fuelling would be an incorrect, or missing, main jet, or possibly (and most likely) a damaged rotary valve which has stuck at the top of the ramp allowing too much fuel at low throttle.

 

These rotary valves are cheaply and easily replaced. The main jet cannot really be faulty unless the O ring has failed, or the jet has been lost whilst servicing.

[woody paul]

These little 22cc engines were about the most reliable engine I have ever encountered. They just keep going and going.

I have sold thousands over the years and service hundreds each year, yet have only once had to replace a crank seal and have never changed a bearing.

So this makes me ask what caused the seals and bearings to fail in the first place and wonder if that cause is also responsible for other. as yet unfound problems.

 

I have had engines that are simply worn out and have low compression which then causes exactly the symptoms you have, so its worth testing the compression. They will work down to 110 psi after a fashion, but are really a bit too far gone at this figure.

 

Similar symptoms will also be found as Spud says, from a poor carb, but as there is no slow speed circuit on the barrel carb its less likely. A poor mixture however will cause the engine to stall at tick over.

 

Yes very good engine, but has had a lot of work in the years I ve had it. What is the max psi I am looking for out of interest.

[GardenKit]

You should be seeing 140 to 150 psi if the engine is really good, but more likely to see around130 on a working, but worn, engine.

[adw]

Came in a bit late on this one but just one suggestion, block muffler causes back pressure and blowing fuel back through the carb.

[spudulike]

Had the fun of servicing an HT131 pole pruner a week or so ago. I was told that on full extension drive was being lost intermittently. So.....started stripping it down and what a job. Springs, sliders, bearings, bushes.....what a mare. Three of the strange slider bearings just fell apart, bits were stuck in the tube, a couple of loose circlips, all stripped and a bucket of bits.

 

Ordered the parts, serviced the four stroke power-head and waited.

 

The parts came in eventually, I am guessing not many people service these things. After a while examining the parts, the parts list and scratching my head, I put it together, stripped it, put it together, stripped it and eventually worked out how the unit goes together, how the sliders and springs fit together and how it all hangs together.

 

Got a sense of achievement getting it all back together and working again - think it was pretty shagged and must have been interesting using it as it was with only two of the five bearings complete.

[woody paul]

Would not think it muffler problem as rev's ok and then cuts out when you back right off to tick over and if you take plug out it soaked in petrol.

[monkeymoreton]

I have this same issue with hedgetrimmer I'm probably going to replace with a Chinese carb as I have been quite lucky with them so far

 

Sent from my LG-H850 using Tapatalk

[GardenKit]

Would not think it muffler problem as rev's ok and then cuts out when you back right off to tick over and if you take plug out it soaked in petrol.

An engine with a blocked exhaust would give totally different problems, it would start OK and tick over well but would be unable to rev out.

 

If this machine will rev out OK and can operate in the high to mid rev range but only dies on speed approaching tickover then it is possibly that it is just set too rich on idle. So adjustment of that hidden screw may be required.

 

Assuming of course that the compression is OK, otherwise you will be trying to tune out to compensate for wear. This simply does not work. Have you tested that compression yet?

[woody paul]

Compression test done and only 100 psi so knackered ?.