Stihl 025 Won't start

[Sam R]

When you replaced the carb did you also replace the intake flange gasket? Bad tank vent wouldn't keep it from starting. To check your impulse line if you don't have a mityvac or some other similar tool, is just put a little blob of any kind of grease right over the impulse hole coming out of the crankcase and then rotate the flywheel back and forth. Do full revolutions - if the grease sucks in or blows out, your impulse line is good. If it doesn't, that's a problem.

 

[ArchieBennett]

Sorry to all to start the "heated" discussion about fuel flow. I hope we can all remain friends.

I understand what the impulse is doing and how it is functioning inside the carburetor. Perhaps now better than I ever did before - which is a GREAT thing. It all is making sense to me now and I fully understand the carburetor and the miracle it creates. It is all pretty simple and straightforward science, really.

Sam - thanks so much for the glob of grease idea - it makes perfect sense, and is a free way to create the tool I don't have. I like it better than the soapy water as it does not cause me problems if it gets sucked in rather than blown out, and I can do it anywhere - including the hole in the gasket between the carb and the intake boot. That is the logically first place to check, and if I have it there I have it everywhere else necessary and can test open passage from there into the carb, which is the last step it is needed.

I will be doing that tonight if I get a chance. Let me do that to see what I get so I know if I need to double back or if we are moving forward given what we know. I will report back as soon as I get a chance to get back in my shop and do some playing.

Aaaand - since I just opened the emoji file... I have to use this one simply because I can:

 

[kenton.a.frank]

Wait a minute "does not draw fuel" Well you go on to say it "moves fuel" and then make reference to a fuel pump. Now if a fuel pump does not draw fuel, what exactly does it do? The impulse goes pressure and then vacuum. That moves the diaphragm. That pumps the fuel right? That draws fuel from the tank, right? When the flap allows vacuum to enter the fuel line it draws the fuel to the carburetor. I stand by my original post. No impulse=no fuel.
Before the fuel pump in saws we had to keep the saw level and turn the bar for certain cuts.

Isn’t that like saying the battery on a car is the “fuel pump”? The impulse powers the diaphragm which pumps the fuel much like the electricity from the battery powers the pump on a car. Arguing semantics here. Bored I guess.


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[Dengel]

Sorry to all to start the "heated" discussion about fuel flow. I hope we can all remain friends.

I understand what the impulse is doing and how it is functioning inside the carburetor. Perhaps now better than I ever did before - which is a GREAT thing. It all is making sense to me now and I fully understand the carburetor and the miracle it creates. It is all pretty simple and straightforward science, really.

Sam - thanks so much for the glob of grease idea - it makes perfect sense, and is a free way to create the tool I don't have. I like it better than the soapy water as it does not cause me problems if it gets sucked in rather than blown out, and I can do it anywhere - including the hole in the gasket between the carb and the intake boot. That is the logically first place to check, and if I have it there I have it everywhere else necessary and can test open passage from there into the carb, which is the last step it is needed.

I will be doing that tonight if I get a chance. Let me do that to see what I get so I know if I need to double back or if we are moving forward given what we know. I will report back as soon as I get a chance to get back in my shop and do some playing.

Aaaand - since I just opened the emoji file... I have to use this one simply because I can:

The only reason I mentioned the soapy water idea was bc the grease trick didn't work for me. Maybe my glob was a bit big, who knows. But pulling the spark plug and doing the soapy water bit worked a treat. You could even run a long length of tubing from the impulse nipple o the cylinder into a glass of water and look for bubbles. The long length of tubing would be your safety against sucking water back into the crankcase. And definitely pull the plug! Trying to eye things while fighting compression adds another layer of frustration you don't need at this point.

 

[HarleyT]

Looking back through this thread:

The intake boot is the rubber boot between the block and the orange handle, not the rubber boot going into the air filter.

For the hell of it, put up some pics of this thing....

 

[ArchieBennett]

So the blob of grease tells the tale (MAYBE)!

I put the glob over the gasket between the intake boot and the carburetor. It did not do a thing. Tried it twice for good measure. Then as I was doing it the second time, I thought to myself: "Self - the gasket won't hold tight enough to the intake boot to work without the carburetor and nuts squeezing it."

So I backed off one step and removed the gasket. Then there is the metal "gasket" that protects the boot. Same logic so off it came.

Then I put the grease right on the boot and nothing. "Hmmm..." Said Self. Kind of same story, so pull it back with with fingers and try again directly on the handle. There it worked! So I know I have impulse at least as far as the handle.

So logic says: If there is pressure squeezing the carburetor to the block, then the gasket is ever so slightly squeezed to the carburetor on one side and the metal transition plate on the other, the T.P is squeezed to the rubber boot, and the boot is squeezed to the handle on the other side of that. I should then have a seal everywhere needed, and the gasket is new. However life says there are no guarantees, and something is not working or I would have gas.

What is the answer??? $23 OEM Intake boot? It does not leak inside, and it looks good at the impulse hole area... Is there some other possible culprit??? Only other thought is remove the metal transition, but that must be there for some logical reason, and I don't see removing it if an engineer decided it should be there. Can a guy use RTV silicone there or is that asking for nightmares later?

Harley see below for a picutre. I understand exactly what we are talking about. The boot is center of pic. Imp. hole is to the lower left of it.

 

[ArchieBennett]

I'm sorry, lower right...

 

[SteveSr]

Is that an OEM fuel hose or aftermarket? Aftermarkets like to kink. Looks sort of like an OEM but installed UPSIDE DOWN! The long part from the mounting flange goes IN the tank! I think you have your answer. Look inside the tank when it is empty. The fuel pickup should drag the bottom of the tank. I don't think it will reach the bottom if installed backwards.

 

[ArchieBennett]

It is oem, and it is right side up. It drags bottom.

 

[giver]

Is the lever for the needle valve hooked in to the diaphragm?

 

[SteveSr]

It is oem, and it is right side up. It drags bottom.

That hose still don't look right. Sure its the right one? All of the ones I have seen have the wide spaced ribs in the tank. This one also has a very large flange near what is now the carb connection... which is about the same diameter as the fuel pickup. Looks like it would be awfully hard to install this so it wouldn't kink and cut off the fuel? @HarleyT should be able to settle this.

 

[SEAM]

Yupp, you are trying to connect the filter end of the fuel line to the carb... that one is too wide for the carb nipple and will draw air.
Invert the hose so the "S" shaped section goes in the tank and you are probably ready to saw

 

[backhoelover]

Said he used compressed air to blow out carb wonder if he blew the nozzle check disc out??

 

[Sam R]

I was gonna say, something is definitely wrong about that fuel line. It has that big ring around the pickup end so it's easier to fish out & hold with your tank hook. And with it set up the way you have it should be leaking fuel, it might appear to be coming from somewhere not the fuel line but as SEAM said it's not going to fit snug on the inlet of the carb.

 

[Sam R]

Said he used compressed air to blow out carb wonder if he blew the nozzle check disc out??

Good point. I think any diaphragm carb manufacturer will advise against this practice for just that reason. They're not as simple as float bowl carbs, diaphragms can be very tricky devils.

 

[Okie]

Said he used compressed air to blow out carb wonder if he blew the nozzle check disc out??

Good point. I think any diaphragm carb manufacturer will advise against this practice for just that reason. They're not as simple as float bowl carbs, diaphragms can be very tricky devils.

Most all carbs can be damaged using direct injection of high pressure compressed air into passageways, can cause welch plugs to start leaking or sent into orbit un-noticed.

I use low pressure air usually around 25 lbs and do not direct inject into any carb passages.
I learned this, do not use high pressure direct injection of air lesson the hard way when working on all sizes of carb's from 4 barrels to one barrels, finding that I had caused additional carb problems during rebuilds using high pressure compressed air to clean carb passageways.

 

[Sam R]

Most all carbs can be damaged using direct injection of high pressure compressed air into passageways, can cause welch plugs to start leaking or sent into orbit un-noticed.

I use low pressure air usually around 25 lbs and do not direct inject into any carb passages.
I learned this, do not use high pressure direct injection of air lesson the hard way when working on all sizes of carb's from 4 barrels to one barrels, finding that I had caused additional carb problems during rebuilds using high pressure compressed air to clean carb passageways.

Good point there Okie. Also, when working on diaphragm carbs I'd like to add it's a good idea to use non-flammable brake parts cleaner if you blow out a port or something like that. The flammable stuff I think has alcohol or some solvent in it that'll ruin your O-rings and other non-metal parts that can't be seen nor removed in most cases. I can't really vouch for the bigger stuff, I specialize more in the 2 strokers but I have rebuilt a few automotive carbs, never used anything stronger than a spray can of carb cleaner in terms of PSI to blow them out.
And I'm definitely there with you, in my earliest days working on 2 strokes I definitely broke a few things I could have saved. Once I spent so much time hammering out a welch plug that by the time I got it all back together the metering side leaked so bad I think more gas came out the sides than went through the venturi

 

[SteveSr]

I was gonna say, something is definitely wrong about that fuel line. It has that big ring around the pickup end so it's easier to fish out & hold with your tank hook. And with it set up the way you have it should be leaking fuel, it might appear to be coming from somewhere not the fuel line but as SEAM said it's not going to fit snug on the inlet of the carb.

Wonder if he got a small barb fuel pickup with the new big barb hose? This way the fuel pickup will fit the carb end of the hose but not the tank end which would be very loose.

 

[SteveSr]

It is oem, and it is right side up. It drags bottom.

Remove the fuel pickup from inside the tank and then the fuel hose and post pictures of BOTH disconnected. The fuel hose should pull out from the TOP (outside) of the tank. If it doesn't you have another clue.

 

[Sam R]

Wonder if he got a small barb fuel pickup with the new big barb hose? This way the fuel pickup will fit the carb end of the hose but not the tank end which would be very loose.

That's a good point. If the tank has a hole that big in it the fuel pump won't work too good even if he's got positive impulse.