My vac attack II will eventually start and idle but when I apply the throttle it stalls and then won't start again. It's fuel of good fuel and I've check the fuel lines and carb and choke. I DO have a wire that I THINK is the spark arrestor that isn't connected but can't find where it attaches.

It is possible that there is an issue with the idle control system in your car. The idle control system is responsible for maintaining the proper idle speed when the engine is running. If there is a problem with this system, the engine may start and then stall immediately. Boosting the battery can provide a temporary boost to the system, allowing it to start and run normally. However, if the idle control system is not functioning properly, the engine will eventually stall again.
Other possible causes of this issue include a clogged fuel filter, a malfunctioning fuel pump, or a problem with the ignition system. It may be helpful to have a mechanic perform a diagnostic test to determine the exact cause of the problem.

Sounds like a fuel blockage or your fuel pump is worn to the point that it can no longer provide the correct pressure.

Re-set the idle adjustment screw on carb? Also check fuel / air filter.

Does it have a good strong spark, good compression and is fuel getting into the cylinder.? More information is required.

Hi, Have you checked the fuel tank for water. Check the fuel filter and/or replace it. Check distributor cap for cracks and moisture. Good luck.

fit new pump ad float diaphragms in the carby
the fuel mix has become irrelevant as Stihl have an oil that is a 50:1 oil and covers all ratios and mixtures
do not use any e-mix fuels as that destroys carby components

Inspect the fuel line in the tank, it should be long enough to fall to the bottom of the tank whatever the operating position. It sounds like it may not be picking up fuel in a certain position.


I’m happy to assist further over the phone at https://www.6ya.com/expert/rolandw_c013176d62ee17ae

try to adjust hi speed/ low speed on carburetor

Yes it will use a fuel mixture of 40:1(3.2 oz of two cycle oil to 1 gallon of gas). Any fuel sitting over 30 days now is considered bad fuel. All the manufacturers schools this year and told us this. We are finding it to be true.
Good day.

Hey Jruthesq

The 850 is equipped with an Idle Air Control Valve (IACV) which supplies the engine with air when idleing (a necessity since the main throttle body valve is completely closed when no throttle is applied, thus the engine would lack air without the IACV when idleing). The IACV is suspended in a rubber mount on the front of the throttle body itself, and is easily removed and inspected/cleaned. If it's dead a good cleaning usually gets it going again. Also make sure that the air from the IACV is unhindered on its way from the IACV to the throttle body (it's actually common for the holes in the throttle body to be gunked up so bad by hardened carbon deposits that one sometimes needs a nail or even a drill to open it up again).

Just thought I'd mention this since you said that the gas needs to be feathered for the engine to start. When you press down on the gas the main valve in the throttle body opens up, closing the IACV and supplying the engine with enough air.

Oh and if your fuel pump relay is a green one marked 103 you should replace it with the new and improved red one. The relay is located under the fuse box cover under the hood. Remove the 4 torx srews holding the cover in place and you'll see the relays under there.

Good luck mate!