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Steven P

Carb Kit or Chinese carb?

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From my experience with replacement chinese carbs you are better off rebuilding the OEM one. That being said, how much tuning experience do you have and are you tuning with a tacho or by ear? I had issues with some of my chainsaws bogging and it turned out to be my inexperience of tuning saws that caused that. 

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I don't care how experienced you are at tuning carbs, nobody can tell a 500rpm difference when the top end is revving at 12,000rpm.

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4 minutes ago, Joe Newton said:

I don't care how experienced you are at tuning carbs, nobody can tell a 500rpm difference when the top end is revving at 12,000rpm.

I don't mean it like that, but tuning the idle on smaller engines to be leaned out  then richening it up to bring the rpm back down is often missed. Tuning the top end is a piece of piss (top end on a bg86 blower is 7200rpm btw). I'm not on about a 500rpm difference on top end but balancing the H&L jet with the LA correctly. I learn't that I didn't have it right but now I know and it could be something the OP missed. 

If you have a tacho the process on a bg86 blower is: 

Turn the LA screw to set idle speed to 2700
Lean out L screw by turning clockwise until highest rpm is reached. keep winding out LA as you go so it is set to run lean/fast at 2700rpm meaning that the engine slows down if you turn the L screw either way. 
Once you reach that "sweet spot" then turn the L screw anti-clockwise until the RPM is 2500. It is now running slightly rich at idle. 
Pull the throttle and set the H jet so the RPM is around 6900 and then check that hasn't effected the idle (it shouldn't)

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Chinese carb all the way. Got them on lots of different engines, from a ts410 to gx390s. Much quicker to swap it out than mess around fitting expensive rebuild kits that may or may not solve the problem imho. 

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Thanks Paddy, this is my third e-bay special, first 2 just needed the carb diaphragms freeing up and they came to life again (1 of these is in bits again to change the fuel tank - another story, on hold till i get a screw extractor). Both needed the carbs adjusting too. I didn't get them ideal but near enough - you can hear if the machine is struggling to idle, or racing and set the screws somewhere in between. Likewise while waiting for a service kit (lockdown) for the saw (had from new) had to adjust that as the filters got bunged up and back again working OK. Hoping I can set this one up as easy once carb is fixed... but as always, good to get a reminder what to do. The LA adjust will come later, just getting the thing to idle well would be nice (nice thing about this blower is a throttle lever - same effect as the LA by holding the air valve open and so much easier to fiddle with as I adjust the fuel screws.

 

 

Still 50-50 really, guess if you get a better copy you'd be OK? but how do you know quality I wonder, or just take a chance.

 

 

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Depends on the cost of the carb kit and the cost of the AM carb. I have used Chinese AM carbs here and there but they can be very sensitive on the L screw adjustment, some like the ones on MS200Ts are unusable and un-tunable. 

If the carb is damn cheap, buy the carb and if it isn't too hot, take the parts off and fit them on your OEM carb.

Mostly OEM carbs can be rebuilt, there are exceptions that I have found where nothing works but it is relatively rare.

How sure are you it isn't an issue elsewhere?.......carbon in muffler/exhaust port, dirty air filter, low compression, dirty fuel filter etc. The carb may just need a bit of carb cleaner down the H&L screw holes and a retune!

 

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2 minutes ago, Steven P said:

Thanks Paddy, this is my third e-bay special, first 2 just needed the carb diaphragms freeing up and they came to life again (1 of these is in bits again to change the fuel tank - another story, on hold till i get a screw extractor). Both needed the carbs adjusting too. I didn't get them ideal but near enough - you can hear if the machine is struggling to idle, or racing and set the screws somewhere in between. Likewise while waiting for a service kit (lockdown) for the saw (had from new) had to adjust that as the filters got bunged up and back again working OK. Hoping I can set this one up as easy once carb is fixed... but as always, good to get a reminder what to do. The LA adjust will come later, just getting the thing to idle well would be nice (nice thing about this blower is a throttle lever - same effect as the LA by holding the air valve open and so much easier to fiddle with as I adjust the fuel screws.

 

 

Still 50-50 really, guess if you get a better copy you'd be OK? but how do you know quality I wonder, or just take a chance. 

 

 

Personally I would buy a rebuild kit and give it a go. If you're that worried money wise then buy a chinesium rebuild kit for £1.50 or whatever silly price they go for and stick that in it and see what happens. You could buy a Chinese carb and find it's just as rubbish as your faulty one and it could send you on a wild goose chase (been there, done it)

I used to buy a lot of cheap Chinese tools from chainsaws to pole saws and hedge cutters and they were okay but the carbs were always a pain in the arse. They leaked, the primer bulbs always cracked and the diaphragms would usually last a year before going hard and wrinkled. I also had a Husqvarna brush cutter that was built in the 90's. I took it to bits to clean it up and the plastics and rubbers were just as good as the day it was made whilst the Chinese tools fell apart and went crispy within a couple of years. By all means buy a Chinese carb but an oem rebuild kit will last much longer and there isn't much in the OEM carbs that can be permanently fubar'd. 

 

Do you know what carb is fitted to it? I think its a Zama C1Q on those and chinese rebuild kits are £5. When I have got cheap kits I have found the parts to be cheap too mind. The needle was thinner, the spring was weaker and the overall quality of the cut out parts was poor, bits of junk hanging off the seals and holes not ligning up perfectly. Made me realise what's in the cheap carbs though. 

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39 minutes ago, spudulike said:

Depends on the cost of the carb kit and the cost of the AM carb. I have used Chinese AM carbs here and there but they can be very sensitive on the L screw adjustment, some like the ones on MS200Ts are unusable and un-tunable. 

If the carb is damn cheap, buy the carb and if it isn't too hot, take the parts off and fit them on your OEM carb.

Mostly OEM carbs can be rebuilt, there are exceptions that I have found where nothing works but it is relatively rare.

How sure are you it isn't an issue elsewhere?.......carbon in muffler/exhaust port, dirty air filter, low compression, dirty fuel filter etc. The carb may just need a bit of carb cleaner down the H&L screw holes and a retune!

 

Thanks, I've been through it easy bits first. Exhaust is clear, no spark arrestor on this one and inside the exhaust is OK, new air and fuel filters (proper genuine parts), new spark plug, cylinder looks good, it's as tight to pull over as the hedge trimmers (similar sizes), new fuel + quality 2 stroke oil (which run the other machines OK).

 

So the next step is the carb itself, I've blown carb cleaner through it - though not down the L & H holes, I never thought of that (maybe I should have thought more, that makes sense). If it is coming off to clean it... my thought is for the time, effort and costs, put a new unit on or strip and build the old unit back up is it worth putting an after market carb in (loath however to pay as much for a carb as the whole machine did for an OEM one). Maybe it isn't worth it.

 

Yes, I think your right, Zama C1Q.

 

 

Thanks, I think I have made my mind up, I'll rebuild it, bit of a project for the next week or so. First though, a bit of a spray with the carb cleaner. Might get carried away and do the hedge trimmers too, chainsaw is a bit noisy for night time, that can wait.

 

 

 

 

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Rebuild it with an original carb kit. Doesn't need to be stihl branded, often it's just a Walbro or Zama carb. Buy it from them and you automatically get some peace of mind, especially if it's still not running after repair. 

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I think the OEM Zama carb in made in China anyway .

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