FS400 Stalls on throttle.. Sounds like sucking in too much air

[champagnecharly]

mm oops.. 150bar could do a whole lot of damage.. and yes i meant cylinder compression.

 

ok 50psi on decomp. yet near impossible to start when decomp is pressed in.

 

Went to prime the bulb.. Note the bulb is not fixed to carb directly but by to hoses.. am sure you knew that already.. anyway.. airbubble still same size as when I received your last post.

[Rich2484]

Yes two hoses. I hate that design.

 

Ok so the fuel isn't leaking back down to the tank. That means its back to carb. Strip it. Clean it, and check the settings on it.

 

The manual I sent you should have the info on there. Have a really good read of it.

 

I'm out for a bit as the step daughter is in labour again now and we are off to hospital.

[GardenKit]

I'll stick my oar in here too.

Firstly don't be too worried about it sucking air, that is what its meant to do. But that air is in turn meant to suck some fuel from the carb jets and it sounds that this is not happening. Before getting too carried away with strip downs try running it with just a little choke applied. if this corrects it then the problem is most likely on the induction side, either fuel or air. Remove and overhaul the carb, checking the jets and in particular the metering arm height. While the carb is off check the inlet boot for tightness and the seal twixt carb and backplate.

 

Secondly, I personally can't see the point in running it without the clutch. The engine needs a little load to perform and the drive shaft, head and clutch provide this, with it removed the engine may appear to rev up properly even on a weak mixture. I have never had a running issue which was down to the clutch except for the inability to adjust the tick over due to an unwanted load if the clutch is grabbing. And anyway, and has been said, the clutch may not be at fault at all as it may be engaging due to a high tick over speed from a weak mixture. if it is sticking, as per the other thread you can sort it after the engine is fixed.

 

Thirdly, the primer bulb (or more correctly 'purge' bulb) works by creating a vacuum which draws fuel towards it from the tank via the metering chamber. it is not unusual to have a 'vacuum' bubble in the purge bulb. Once the engine is running the bulb serves no purpose except for the non return valve in the base.

 

Hope this helps to confuse.

[champagnecharly]

Hi Gardenkit,

 

I hadn't seen you post until just now.. Thank you. and yes now i am confused not confused so much about what you say just which direction to take....

 

I have taken the clutch off and run without and she runs great even when just twitching at the throttle which is where it was prone to issues previously.

 

I actually picked up a spares or repairs fs120 (yes am glutton for punishment) hoping my rotovator atachment would fit and then to dispose of the 400. seller claimed it was a carb issue so I thought it was an easy fix.. with this I was getting exactly the same engine issue as the 400.. however in this case the head hardly turned... So I removed the clutch.. and hey presto.. it works a treat..

 

So i came back to post my findings but only to have the element of load thrown in - thank you as v valid and important factor-.. .. So now I'm lost as to where to begin..

 

Back to the primer/vacuum bulb.. Yes air bubble didnt concern me. What is strange is that the vacuum disappears and it becomes much easier to press once stalled.

 

 

am now going to try swapping the clutches after a good clean. the fs400 was v loose where as the 120 was almost stuck together. what i also noticed is that the shoes had worn the metal on the cover on the 120.

 

well at least its a sunny day..

 

P.s> Rich.. so are you a Granddad now? Boy or girl? i hope all went well.

Edited May 25, 2013 by champagnecharly

[champagnecharly]

Finally received my parts. 10 days wait!

 

Clutch springs are 4-5mm shorter!! This certainly wont have helped.

[champagnecharly]

Well just received a pressure gauge.. tied it up to inlet on carb (not got/made blanking plate yet) and all seems air tight with no loss either way.

 

By connecting directly to carb. Can I presume it is not going to distort my results?