OutdoorKing Repair Forum Forums Repairs and Maintenance Questions on Trimmers and Brushcutters Two Stroke Trimmers & Brushcutters GMC Line trimmer not accelerating

Recently my 26cc GMC 2 stroke line trimmer has stopped accelerating on pressing the lever. It was working fine last week.

It starts fine and is still able to trim the grass since it starts with a decent speed. But the problem is I am not able to control the speed with the lever anymore.

Appreciate any suggestions. I shall try to upload pics once am home tonight.

Cheers
Dhiren

We need a description of what happens when you open the throttle. If there is an increase in the roaring sound from the air filter, but no change in engine speed, the problem is almost certainly fuel starvation: the fuel system is only providing enough fuel for the initial engine speed, and opening the throttle just leans out the mixture.

If fuel starvation is occurring, there are several likely causes: restriction in the fuel tank vent, or in the fuel line, or in the fine filter usually fitted to the carburetor fuel pump's intake cavity. Beyond that there are other carburetor malfuction possiblities, all of which require a full strip and clean of the carburetor, almost certainly with a replacement of gaskets and diaphragms.

It usually makes sense to follow a simple process:
1. Does the air filter noise increase greatly when you open the throttle?
2. If you answered yes to Q1, inspect and clean the fuel system upstream of the carburetor and see if the problem is cured.
3. If you answered yes to Q1 but the problem remained after you performed the cleaning in Q2, remove the cover from the carburetor fuel pump input chamber and observe the micro-fine metal mesh filter there. Remove and clean it very carefully, reinstall it, ande see if the problem is cured.
4. If you answered yes to Q1, and have now performed the cleanouts in both Q2 and Q3 but still have the problem, you should strip, clean, and re-kit the carburetor, following the instructions from the carburetor manufacturer's technical manual (usually available on line).

is the throttle cable working between the trigger and the carb, try squeezing the trigger and see if you can see the throttle move around the air cleaner area.

Only reason I ask this is you say nothing of it dying off when throttle is applied.

Thanks Grumpy and Joe.

@Grumpy:
//1. Does the air filter noise increase greatly when you open the throttle?

Answer to above is NO. The trigger simple gets pressed easily without any sound or speed changes. This is making me believe as Joe pointed out to check the throttle cable to the carb is indeed working.

how do i do this if the throttle is not moving on pulling the trigger?

thanks again

cheers
dhiren

I agree with Joe, if the intake noise doesn't increase, the throttle is not opening. You need to trace the throttle Bowden cable to the carburetor - you may need to remove the air cleaner to see where it connects to the throttle butterfly.

It appears the Bowden cable is disconnected either at the throttle lever or at the throttle butterfly on the carburetor. The carburetor end seems more likely. The cable inner is held there by a small screw, or it has a fixed fitting attached permanently to the end of the cable inner. When the throttle is released suddenly, occasionally the inner cable can get detached. Also, occasionally the cable outer can get out of position.

Another failure mode is if the whole throttle cable has become dislodged at the throttle lever end. The cable and its attachments are very simple, just trace it and inspect the two ends to see whether they are properly connected.

thanks guys. that looks like the problem. the inner cable was detached at the carburetor end. i have tried to fix it on to a screw as shown in attached pic. I believe this is the place it should go in. can you please confirm?

also while doing this I had to remove the throttle lever so stretch the cable enough. i seem to be having problem getting the throttle lever back with the right tension for the inner cable so that it stays on and would actually accelerate. pics attached. i couldn't take the pics just before removing the throttle since it just popped out after unscrewing the cover. I am not sure if i got the throttle spring etc assembly correctly fitted.

i have one more problem. the fuel line is cracked and would need to be replaced. both the fuel lines - one to the primer and the other one to the carburetor have cracked at the same time. glad i noticed it while doing the inner cable. any suggestion on where can i get the fuel line and step to install. looks fairly straightforward but would like to follow steps from experts here.

many thanks again.

cheers
dhiren

First, what you have done with the inner cable at the carburetor end appears to be correct. It seems to fit properly into the hole in the anchor fitting.

Second, those fuel lines look like they have gone hard and are discoloured. One has a strange kink as if it has been overheated. You can get fuel hose at a mower repairer, but there may be cheaper options if you measure the hose and then buy a metre of it.

At this point I have no idea how the upper end of your throttle system is supposed to work - I can't tell from those pictures. Let's see if someone else can help.

Fuel hose is geerally $2 a foot at the local mower shop, 1 foot of it will be plenty, and they should supply you with tygon line that will not perish, dry out or crack.

The cable connections look correct to me, I've got two of those whippers here for parts. Just make sure the outer cable is secured correctly at the control end.

Greg, my understanding is that he's now correctly assembled the carburetor end which was the original problem, but along the way he's dismantled the control (upper) end of the cable and now can't put it back together. Could you post a couple of pics of the upper end of an assembled one?

Certainly will, Cheers.

Woops, Sorry, my bad! Apologies all round. The GMC's I've got here have a different type of handpiece.

Looking at the pic of the upper end, the inner cable doesn't look to be able to fit any other way, and I would say that the other half of the handpiece has the locator for the outer cable. My suggestion would be to try assembling the handpiece with the other half first. You should be able to test the operation of it without having it fitted to the whipper.

The only cable adjustment I can see is the brass piece the cable goes through in the first two pics.

If all else fails, maybe strip it completely again, take a photo of all the parts, and I'll guide the reassembly.

Cheers.

Grumpy that's exactly what I have done:(

Greg I shall give it a try this weekend and get back.

Thanks for the help.

Its working fine now after replacing the fuel lines. I had to tape the cable inside near the hand end.

Thanks all again.

Cheers
Dhiren

As this thread s now complete I will close it, if anyone wishes to add to it please pm a mod.