Carb Issue

[redunshee]

Having an issue with the carb not returning to idle quickly. Takes a few seconds then it will idle fine. Checked linkage and it seems fine. I rebuilt carb but wonder if the metering lever isn't set correctly or is it a pump side issue. Its a Zama C1Q carb. Also I'm cheating a little casue its a Stihl FS90R trimmer and not a chainsaw.

 

[xtremez]

When I’ve run into those issues before it’s been an air leak.

 

[Dean-O]

Adjust the valves. However if the cam pin has movement you can adjust the valves and it will run better for awhile. But depending on how bad the cam pin is it will start running bad again over time and the valves will go out of adjustment.

Only true fix is to buy a short block, which is not cost effective. Or buy a new FS91. Whenever an FS 90, 110 or 130 comes in shop first thing I do is break it down and check cam pin because all those models are now 10+ years old. If cam pin has slight movement I call customer and tell them I can adjust valves and advise to “run it until it dies” because it’s not worth putting money into. If it has a lot of movement then toss it and buy new one because short block+labor is not cost effective because you can buy a new FS 91 for less money.

 

[angelo c]

Adjust the valves. However if the cam pin has movement you can adjust the valves and it will run better for awhile. But depending on how bad the cam pin is it will start running bad again over time and the valves will go out of adjustment.

Only true fix is to buy a short block, which is not cost effective. Or buy a new FS91. Whenever an FS 90, 110 or 130 comes in shop first thing I do is break it down and check cam pin because all those models are now 10+ years old. If cam pin has slight movement I call customer and tell them I can adjust valves and advise to “run it until it dies” because it’s not worth putting money into. If it has a lot of movement then toss it and buy new one because short block+labor is not cost effective because you can buy a new FS 91 for less money.

Why not just replace the "cam". Ain't all that difficult?

 

[Dean-O]

Why not just replace the "cam". Ain't all that difficult?

Because the cam pin goes into a hole in the short block. The hole gets wallowed. That is the reason the cam pin has play not the cam pin itself. If you replaced the cam pin and the entire “cam” as you quote it would fix nothing and have the same problem.

 

[angelo c]

Because the cam pin goes into a hole in the short block. The hole gets wallowed. That is the reason the cam pin has play not the cam pin itself. If you replaced the cam pin and the entire “cam” as you quote it would fix nothing and have the same problem.

Got it. Have only done about 10 of these. Have only replace the "cam" follower. Haven't had the shaft/pocket bugger out yet. Have had the "decomp" spring waller out and the plastic go to heck and ruin the valve timing a few times.
Thanks