Carb purge bulb air leak woes

[kram]

What should I be looking for? The purge bulbs appear intact and the leaks are within the carbs themselves. They are not purging/sucking fuel into the carb.

 

Had one apart, cleaned the non rubber parts/passageways with carb cleaner and reassembled to no improvement, all looked clean inside. This was from a newish saw with very little use (training before my CS31 and blocking down a handfull of trees). Husq/McCulloch Cs340.

 

Genuine carb is £60 and more than its worth so rather repair this one.

Genuine Husqvarna Carburettor 14mm Air Bore - 586 93 62-02

WWW.GARDENHIRESPARES.CO.UK

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Genuine part suitable for some of the following makes & models; Husqvarna 120 Mark II, 230, 235, 235e, 236, 236e, 240, 240e,  Jonsered CS2234...

 

The other is from a Stihl kombi engine, I have not got the carb off yet, the purge bulb is cracking but still holds suction against my hand. It has not been maintained...

Mycelium air filter? Behind the air filter is clean but havent pulled carb off yet, Im not sure how throttle linkage comes off.

 

Third is a BG86C blower, carb appears fine as it starts easy enough but looses power after a short time at full throttle and believe that may be a clogged exhaust/spark arrestor. The air filter is clean, sparkplug is new.

 

 

 

Edited December 5 by kram

[spudulike]

Never seen a spark arrestor on a BG86.

In my experience, purge/primer issues are usually sorted by working out which part isn't sucking, blowing or sealing....usually pretty frustrating little feckers at best.

Testing with a Mityvac often helps me.

[Mick Dempsey]

You should be looking for new equipment.

[adw]

The Husqvarna models listed all have a remote purge bulb rather than the bulb being integral to the carb, these items are purge bulbs not primers, so when the bulb is depressed fuel in the bulb is returned to the tank, as the bulb re inflates it draws fuel from the carb, the cycle then repeats itself, due to this system you can purge the bulb all day without flooding the carb. Bulbs that re inflate quickly without drawing fuel means the bulb or the hose is split, bulbs that will not re inflate either have blocked filter in the fuel tank, or the screen in the carb is blocked, or the hose is trapped, or some carbs have a non return valve in the carb itself which may not be functional, finally tubes incorrect connected.

[Mark_Skyland]

This might sort out your stihl blower issue, its a very common problem.

If the gasket isn't holed then its either put it in an ultrasonic cleaner and hope for the best or buy a new carb. On the Stihl's sometimes the plugs fall out of the plastic plate under the primer bulb which can cause the same issue.

 

[kram]

15 hours ago, Mick Dempsey said:

You should be looking for new equipment.

Very helpful reply. These are spares but we would like them fixed.

 

13 hours ago, adw said:

The Husqvarna models listed all have a remote purge bulb rather than the bulb being integral to the carb, these items are purge bulbs not primers, so when the bulb is depressed fuel in the bulb is returned to the tank, as the bulb re inflates it draws fuel from the carb, the cycle then repeats itself, due to this system you can purge the bulb all day without flooding the carb. Bulbs that re inflate quickly without drawing fuel means the bulb or the hose is split, bulbs that will not re inflate either have blocked filter in the fuel tank, or the screen in the carb is blocked, or the hose is trapped, or some carbs have a non return valve in the carb itself which may not be functional, finally tubes incorrect connected.

The bulb and hoses are not split, the air leak is occuring inside the carb.

 

12 hours ago, Mark_Skyland said:

This might sort out your stihl blower issue, its a very common problem.

If the gasket isn't holed then its either put it in an ultrasonic cleaner and hope for the best or buy a new carb. On the Stihl's sometimes the plugs fall out of the plastic plate under the primer bulb which can cause the same issue.

 

Thanks I will have a look.

The YT video I saw, suggested a blocked exhaust and it does seem to have some resistance when I blow through it, I think Im going to boil exhaust in caustic for half hour as that should remove any carbon deposits.

 

The blower starts up fine, after the initial warm up, it will run at 100% throttle without issue for about 30 seconds. After that, above 80% throttle it will bog down and loose power. The cylinder and piston look good, viewed from the exhaust port.

When I checked spark plug the gap was large so replaced it and ran better for a few minutes before it started again.

He bought a new one after a couple of days before I had a chance to look at it.

[kram]

Watched a video yesterday about a Stihl trimmer. The leak was an oring on the accelerator pump section of the carb, and the video implied its a common problem (also states that orings are not available from stihl and proceeds to seal it up, but any engineeering supplier should be able to get small viton orings if you can measure the size accurately)

 

I've just located the accelerator pump section on the cs340 and selectively dunked it in a cup of water. When the acc pump is submerged, it will suck up and squirt water. Theres a tiny circlip that I cant easily remove at the moment so will get it apart later on.

Acc pump is behind the throttle shaft in the hole, below the blue line, which is where I had it submerged.

[kram]

The cause of the Mcculloch Cs340 problem is comfirmed. Shrivelled O ring.

 

 

@Mark_Skylandwould you know if accelerator pump O rings are available? I suspect I will need to go to an engineering supplier. The bore is 5mm and piston OD measures 4.94mm, and ID for the oring is roughly 3.2mm (measured the piston, not the O ring itself). Slot width roughtly 1.2-1.3mm and old oring is a little under 1.2mm thick.

 

 

Edited December 6 by kram

[Mark_Skyland]

I cant get a parts list up for that machine but I very much doubt that you can buy that part, it probably only comes with a carburettor attached to it.

 

[kram]

I wont claim to know how to specifiy O rings... Will message some friends about it tomorrow. Something like this may do.

 

FKM O-Rings Metric 1mm-6mm Cross Section 1mm-253mm ID Rubber Oil Resistant Seals

WWW.EBAY.CO.UK

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Material: Fluorine Rubber(FKM). Cross Section(CS): 1mm 2mm 4mm 5mm 6mm. Features: Good oil resistance, wear resistance...