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

[champagnecharly]

Hello again,

 

SO after the issue with the clutch. that I havent yet got around to.. I have been having another issue which is stalling when reving her up.... not neceseraly full throttle but when revs increased. The times it happens (most of the time) it can be noticably heard and it sounds like a bag of nails. More specifically it sounds almost hollow like hungry rumbling belly if you see what i mean. It sounds like it is sucking air. Compression is fine 5 pulls and upto 130-150psi although when decompression switch is in it only goes to 50-70 (is that normal)

I had changed the carb, gaskets, rings last year but hadn't got it back together until recently. Admittedly filter etc is not back but that makes little/no difference.

 

Anyone any ideas what it could be? I'm wondering if perished seals could do this by allowing air through when vacuum pressure is up.. but would that not show a leak?

 

Anybody any idea?

[Ray1]

It could be an air leak somewhere, it also could be an air leak causing the head to keep spinning even when the LA screw is wound right out. How old is the machine and do you know its history? I hope its not a spares or repairs ebay special that you've picked up.

[Rich2484]

Ok. Going on the other thread you have started.

 

I know its not stihl ones but the Kawasaki strimmers can give all sorts of funny running problems when the clutch goes.

 

It may not be the problem but my advice would be to sort the clutch out and then try again. Work one issue first then go to the next.

[Ray1]

I would sort the running of the engine out first, Completely remove the engine from the shaft and remove the clutch from the flywheel. Then find out what the problem is with the engine, a pressure and vac test is the only way, if you've put in new rings, a test should have been done at that stage to test the integrity of the base gasket, crank seals and the crank case seal. Go at that for a start.

[Rich2484]

I would sort the running of the engine out first, Completely remove the engine from the shaft and remove the clutch from the flywheel. Then find out what the problem is with the engine, a pressure and vac test is the only way, if you've put in new rings, a test should have been done at that stage to test the integrity of the base gasket, crank seals and the crank case seal. Go at that for a start.

 

Yeah and spend hours stripping an engine down when the clutch could a fault all along. What's the point in starting to stip it to pieces again when there is already one issue that needs sorting.

 

Pressure and vac testing a strimmer is a pain. Especially the fs400. He crank seals can go on strimmers. But then so can everything else.

[Ray1]

Yeah and spend hours stripping an engine down when the clutch could a fault all along. What's the point in starting to stip it to pieces again when there is already one issue that needs sorting.

 

If you remove the clutch from the flywheel you eliminate all problems with the clutch, with the clutch removed the engine will either start and run as it should or show exactly the same symptoms.

[champagnecharly]

Thanks guys..

No no history..As for age not too sure. and well it wasn't mean to be spares or repair. Supposedly fully working.. or so the seller's father in law had told him. One of them! I didn't find out until after the courier had collected it and I started her up! By then it was all a bit late.

 

So air leak. or clutch.. mm chicken or egg.. I'm hungry so which ones chicken?

 

IF the kawaski clutch can cause this issue.. would it not be wise just to take clutch off and then see? it would remove that factor would it not? even more so if an air leak can cause the clutch to play up i end up chasing my tail..

 

Ok so the chicken is the engine.. thats what i shall go for ( or so I thought now undecided again).. and also makes sense given the clutch hasto come back off...

So if its an air leak. Could an air leak on the fuel line do such a thing? The fuel line seems brand new but wasnt changed by me and although it is fairly snug, i wonder if it is tight enough!? One thing that makes me wonder is after stall "sometimes" I check to see how the primer bulb is and there is not very much pressure there an di can hear it gurgle as if its sucking in/out air...

 

mmm didnt realise how much there was to do to do a pressure and vac test.. maybe i'm not all that peckish after all..

 

Hold lets just recap and please excuse any repetition.. if it could be a clutch issue. by removing that would it not rule that out as a problem? I.e if it still occured with no clutch on it would show it was an airleak.. Just seen ray you posted the same thing.. Rich, Do you agree?

[champagnecharly]

oh and how much will a pressure test through sparkplug tell me? As mentioned 130-150bar (not consistent) and 50-70 with decompression out.

 

With regards a vac test what exactly do i need?

 

ohh on a positive note.. it has a good spark!

[Rich2484]

Yes it would. By removing the clutch and starting it up (clamped in a vice not just held or left on the bench)

 

I don't think its an air leak in the engine crank case parts. Have you removed he fuel cap and tried it? Is the fuel primer bulb the right one. Had one once that was the wrong size bowl and not sealing around the carb. This meant it leaked air around it. And didn't stay pressured up.

 

Give the bulb squeeze and fill the line and bulb with fuel. Then just leave it and watch it for a few mins. See if the fuel goes back down the line quick or the bulb empties quick.

[Rich2484]

oh and how much will a pressure test through sparkplug tell me? As mentioned 130-150bar (not consistent) and 50-70 with decompression out.

 

With regards a vac test what exactly do i need?

 

ohh on a positive note.. it has a good spark!

 

This bit o don't get.

 

Think you mean a compression test. 130-150 bar (personally I think you mean psi) bar would blow the engine to pieces is good. And with the decomp in 50 is also very good. The decomp is exactly what it says on the tin. Allows the compression to go so its easier starting and better for the recoil and you.