Stihl 020T C1Q-S16A carb issue - help please

[Rob Rhind]

Hi
I have two Stihl 020T chainsaws - 1996 and 1998.
Having trouble with one of the C1Q-S16A carburetors. This is the older style carb without the accelerator pump. As have the two working saws have narrowed the running problem down to the carb. Problems starting, idles high and bogs down/stalls on acceleration.
I have stripped carb, sonic cleaned it and used compressed air to dry it. Fitted a new service kit, not that there appeared to be much wrong with the one already fitted. No improvement, in fact now the saw not starting at all and neat fuel ejected through exhaust.
Any ideas please as can't find anything to replace the C1Q-S16A. Can't see anything else I can do to clean/service the carb. Using compressed air to blow through the holes in the unit wouldn't have done any harm, would it?

Thanks

 

[SteveSr]

Using compressed air to blow through the holes in the unit wouldn't have done any harm, would it?

Great way to kill a carb with compressed air. The check valves, designed for little more than atmospheric pressure, won't handle compressed air at all. You need to verify that the main nozzle check valve is still present and functioning. If it was a rubber disc it is long gone!

If it is spitting gas through the exhaust it is likely either assembled wrong (metering gasket and diaphragm) or the metering lever has not been properly set (assuming that you used the new one in the kit). Was the carb service kit OEM or Aftermarket?

@lone wolf ?

 

[DND 9000]

This C1Q-S16A carburetor was replaced with the C1Q-S32 carburetor.

Did you check the height of the metering lever from your existing C1Q-S16? Should be flush with the carb body. If it is not possible to get this carb back working you need a new one. The C1Q-S32 can be used as a replacement part (1129 120 0650). This carb has a compensating cover on, but a cover for non compensating versions is also included. So if your saw does not have the compensating parts (air filter parts) you have to use the non compensating carb cover.

 

[Rob Rhind]

Thank you for the replies.
I was on here way back in 2014 - too far back for me to have remembered not to use compressed air on the carb as advised at the time.
As I had recently rebuilt an old Airmate WW39 compressor just used it without thinking. Gave the carb a thorough blowing including straight into the jet ports with jets removed. I was wary of the welch plug, having just replaced it and nothing exited the carb body as far as I could tell. anyway after a night to dry out I tried to fire her up again with the very small amount of fuel left and guess what, she runs and idles. Always find these saws struggle a bit with high idle as fuel runs low but seem to have sorted this out. On this basis I can confirm that it would seem that compressed air appears to be useable on the early C1Q - S16A(11291200601) non compensating carb.
All the subsequent carbs made are the compensatory type as far as I can tell - C1Q-S32(1129 120 0650), C1Q-S61{C1Q-S126} (1129 120 0651) - now superceded by 1129 120 0653. Lots of cheap copy 1129 120 0653 carbs on sale here on ebay UK; some are less than £10 to buy. Is it possible to replace the compensating cover on a 1129 120 0653 with one off my C1Q-S16A together with associated gaskets and it will work on my 020T? Surely is cannot be that simple

 

[stihl86]

Using compressed air is like Russian roulete. The odds are on your side.
Until they aren't, Your choice.
All the carbs are in the C1Q family. All should share the same body.

 

[DND 9000]

The 1129 120 0653 carburetor can be used as a replacement part if you use the end cover 1129 121 0800.

 

[lone wolf]

Great way to kill a carb with compressed air. The check valves, designed for little more than atmospheric pressure, won't handle compressed air at all. You need to verify that the main nozzle check valve is still present and functioning. If it was a rubber disc it is long gone!

If it is spitting gas through the exhaust it is likely either assembled wrong (metering gasket and diaphragm) or the metering lever has not been properly set (assuming that you used the new one in the kit). Was the carb service kit OEM or Aftermarket?

@lone wolf ?

Where do i start? Do you have a good running carb you can try so you know for sure it is in fact the suspected carb and the saw is good? Thats why I keep extra carbs. you could be there for days.

 

[SteveSr]

Gave the carb a thorough blowing including straight into the jet ports with jets removed.

This is a GOOD way to break or blow out the main nozzle check valve.

I was wary of the welch plug, having just replaced it and nothing exited the carb body as far as I could tell.

Welch plugs are notoriously HARD to get to reseal properly. Even the factory (Zama) doesn't trust them not to leak even though they have the proper tooling to insert them while the rest of us don't. They back them up with some sort of proprietary sealant. Forget about using nail polish or Seal All as these WILL NOT hold up to modern fuels.

For this reason I try to NEVER remove welch plugs. The odds of stuff being under there to cause blockages, especially after a trip through the US cleaner is not very high. If I find one in a high value NLA carb with deteriorated factory sealant I will run a fine bead of low viscosity super glue around the joint and let it cure for several DAYS! before returning it to service. Cyanoacrylate (super Glue) is the only stuff I have found that has excellent gasoline AND ethanol resistance.

Leaking welch plugs will usually cause a rich to over rich condition as fuel gets sucked directly from the metering chamber into the venturi through the welch plug leak. Attached is a Stihl tech note for a welch plug leak tester made out of an Irwin clamp if you would like to verify your workmanship.

 

[stihl86]

Good info. Proprietary for sure, but good info.
But some still wont believe it.

 

[Rob Rhind]

Thank you for your further comments.
I have two 020T saws and know they both run fine on the good C1Q-S16A. Swapped and refitted so many times now and as already mentioned saves a mess by undoing fuel tank cap to relieve fuel pressure before removing fuel pipe fromcarb. I also use a hex bit to block off the fuel pipe while carb off. This made it easy to prove that the other carb was the problem. Stripping and sonic cleaned the carb + a new fitting kit did not cure the issue. Carb was clean and existing kit seemed good anyway. As I don't like giving up on stuff, left me no real choice but to try the welch plug. I took care removing and there was no sealer used or certainly no evidence of that. Made myself a tool to fit replacement......

Seemed to fit OK but again no improvement on running so last resort was compressed air. Perhaps I was lucky and no damage done and apparently the original issue with the carb now resolved. Looking at the Zama parts schematic I could not see anything vulnerable to compressed air, welch plug aside - http://www.zamacorp.com/tclist.html?cnum=C1Q-S16A
Perhaps I missed something and was very lucky as made sure I gave all apertures/holes attention with the compressed air.
1129 121 0800 is the C1Q-S16A cover part. Has anyone else successfully converted a 1129 120 0653 style compensating carb to useful working non compensating variant just by fitting this cover and the associated gasket and diaphragm?

 

[lone wolf]

Thank you for your further comments.
I have two 020T saws and know they both run fine on the good C1Q-S16A. This made it easy to prove that the other carb was the problem. Stripping and sonic cleaned the carb + a new fitting kit did not cure the issue. Carb was clean and existing kit seemed good anyway. As I don't like giving up on stuff, left me no real choice but to try the welch plug. I took care removing and there was no sealer used or certainly no evidence of that. Made myself a tool to fit replacement......
View attachment 813055
Seemed to fit OK but again no improvement on running so last resort was compressed air. Perhaps I was lucky and no damage done and apparently the original issue with the carb now resolved. Looking at the Zama parts schematic I could not see anything vulnerable to compressed air, welch plug aside - http://www.zamacorp.com/tclist.html?cnum=C1Q-S16A
Perhaps I missed something and was very lucky as made sure I gave all apertures/holes attention with the compressed air.
1129 121 0800 is the C1Q-S16A cover part. Has anyone else successfully converted a 1129 120 0653 style compensating carb to useful working non compensating variant just by fitting this cover and the associated gasket and diaphragm?

Just get the 90 degree elbow and drill a hole in the black plastic mounting plate is all you have to do and it will be better.

 

[Rob Rhind]

Just get the 90 degree elbow and drill a hole in the black plastic mounting plate is all you have to do and it will be better.

Thank you lone wolf.
Is there any write up or thread on this please.

 

[lone wolf]

Thank you lone wolf.
Is there any write up or thread on this please.

No but its simple just look at it. Get an elbow put it on put greese or white paint on the end so when you put the mounting plate on it will leave a mark then take it off center it and drill.