Stihl 038 cold starting problem

[Rubicon]

Hi guys. I have an 038 that simply refuses to start when left outside in the cold for a few hours. Bring the thing inside for half an hour, starts great.

It has great compression, strong spark when cold, new gas, new fuel line, new fuel filter, new carb kit, new plug, new air filter.

I recently repaired the impulse hose, as it was split where it connects to the carb. I cut the split portion of the impulse hose and reconnected it to the carb. It had run fine since then, and still does run fine, except that it simply refuses to start when cold. If I dump a small amount of fuel directly in the carb opening, it starts and runs great.

I replaced the air filter assembly as I thought maybe the choke plate wasn't closing all the way and causing the no start problem. That wasn't it.

Any ideas guys? Thanks.

 

[Max_arbo]

my experience, 5-7 pulls to start in 15-20 degrees...

 

[Dadatwins]

I would change the pulse line, if it split on one side, the other side might be shot also, and it is not pulling fuel as it should. You might also check the carb boot while you have it apart, if the pulse line is bad might as well change the boot while you have it apart. good luck.

 

[Lakeside53]

If the saw runs when you dump gas in the carb, then the problem is directly related to the delivery of gas either to the carb or from the carb to the engine. Cold exacerbates the problem of starting, so you may have a marginal condition that "just" works at room temps, but not at cold.

A few things - impulse hose - as discussed, and choke. The choke MUST operate correctly such that the engine can pull (vacuum) gas from the carb. Make sure it fits well and operates fully.

Tank gas pressure.. check your tank vent. In cold conditions, the fuel may have formed a slight negative pressure when it cooled. When you bring it inside, it makes a positive pressure (also try shaking the tank vigorously just before starting). It's hard to check without a vacuum and pressure tester, but unscrew the plugs in the vent line and see if they are clean. Also, over time the vent tube closes too tight around the screw (s) and makes for a slow vent. It's just a piece of fuel hose so replacement is often the best course of action.

 

[stihltech]

start

Does it have a fast idle when the choke is on and in the second position up?

 

[Rubicon]

Yes, the fast idle works fine.

The air filter/choke assembly is new, and the small "flapper" that actuates the choke works well.

This is very frustrating. It seems that if the intake boot or impulse line were cracked/split, the saw would not run well at all even when warm, due to an air leak.

Thanks guys. Any more ideas?

 

[Lakeside53]

Yes, the fast idle works fine.

The air filter/choke assembly is new, and the small "flapper" that actuates the choke works well.

This is very frustrating. It seems that if the intake boot or impulse line were cracked/split, the saw would not run well at all even when warm, due to an air leak.

Thanks guys. Any more ideas?

yes, same as before, the tank vent.. there are only a small number of things that can affect fuel delivery...

 

[buck futter]

they hit the nail on the head, cold engines need more gas ( a rich condition)
I rememeber being an early teen trying to start my toys in the winter and saying to my dad it won't start. He would always reply "choke it"
It sounds like the choke may work fine but look for an air leak, if you get really desperate you could try smearing copius amounts of grease on the boot and any junctions, it is not a fix but may point to where you need to look. You may also try to turn the low side out a quarter turn perhaps it will help a little. Cold engines need more gas, you put in more air when its cold try a little more gas.

good luck


Buck

 

[Rubicon]

UPDATE

I finally got around to working on this thing, and here is what I(you) found.

The impulse line which was previously split at one end, was starting to deteriorate. I replaced it.

The intake boot had a few small cracks in it. It wasn't leaking, but I replaced it anyway.

The fuel tank vent was a mess. The owner had installed his own vent tube and installed a set screw into it, trying to replicate Stihl's vent system. The problem was that the set screw was too large for the tube and was basically blocking the tube shut. With a small pressure tester, I had to pump 25 psi before the pressure would bypass the set screw. Needless to say, I ordered a new vent assembly.

I am happy to say that the problem is now solved. The saw now starts well when cold. A big thank you to everyone who helped in diagnosing the problem. Very much appreciated. Thanks!