Date: 28-03-24  Time: 20:36 pm

Author Topic: Help needed - fuel problem  (Read 2751 times)

Andy1970

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Help needed - fuel problem
« on: 15 March 2017, 02:39:47 pm »
Hi everyone.


I've just got the Fazer all back in one piece and started it up for the first time today. It runs but I've got fuel pissing out of the carb breather pipe between carbs 1 and 2. I checked the exhaust downpipes, pipe 1 was cold, 2 was warm, 3 and 4 were hot. The fuel only leaks out when it's actually running, not when stopped, not even when the ignition is on and the fuel pump is running up.


The engine is a replacement that I got off ebay and this was the first time I've started it. I drained the carbs before taking them off last October and they've been stored in a shoebox indoors since then.


Any ideas what the problem might be?


Many thanks,
Andy

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Re: Help needed - fuel problem
« Reply #1 on: 15 March 2017, 05:07:28 pm »
after removing from the shoe box did you do anything to them or just refit and start up
carbs that have been dried and stored are best opened up to give a clean to check any residue, broken orings,blocked jets etc etc
if you have cold 1+2 then your running no fuel through so its time to pull them and inspect with the prospect of a rebuild kit needed
be sure to check all your jets and everything while your there

Disorderlypunk

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Re: Help needed - fuel problem
« Reply #2 on: 16 March 2017, 05:44:06 pm »
just had a thought - did you do a compression check on the replacement engine?
if the inlet valves are not sealing it can positive pressurise the carb venturi tube during the compression cycle causing pressure in the float bowl and pushing the fuel through the breather
that would explain no fuel in 1+2 therefore not firing and would explain why fuel only exits breather when running
also its a lot easier to compression check than to remove carbs
think about it and let me know as it is mearly a theory but in my head a sound one

Andy1970

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Re: Help needed - fuel problem
« Reply #3 on: 17 March 2017, 11:35:42 am »
Hi DP. I've had a think about your new theory and it seems to be logical. There's not much useful info on the net; most of the leaky valve info is about exhaust valves as the inlets don't generally seem to be a problem. I'll get a compression tester and check it out though.


Andy.
« Last Edit: 17 March 2017, 02:21:17 pm by Andy1970 »

Andy1970

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Re: Help needed - fuel problem
« Reply #4 on: 29 March 2017, 09:20:45 am »
Update on this. I changed the float valves in the carbs, and also checked and adjusted the valve clearances (all the exhausts were a little low, the inlets were mostly fine, other than two which were at the low end of ok). Unfortunately this hasn't fixed problem. It's not running on cyl 1 and fuel is still coming out of the carb breather on that side. I did a compression test, and the cold values are 175, 150, 175, 175. So it looks like No 2 cylinder might be blowing back through the inlet. I guess the next step is to take the head off and have a look at the state of the valves, unless anyone has any other simpler suggestions?

Fazerider

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Re: Help needed - fuel problem
« Reply #5 on: 29 March 2017, 09:32:48 am »

What are the fuel levels like in the carbs with the engine not running? (After turning the ignition off and on enough times for the pump to switch off).


Did you replace the whole valve in the carb? The O-ring around the valve seat is prone to cracking, fuel then pours around rather than through the valve.
« Last Edit: 29 March 2017, 09:58:35 am by Fazerider »

Andy1970

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Re: Help needed - fuel problem
« Reply #6 on: 29 March 2017, 09:53:15 am »
Hi Fazerider


Yes, I replaced the whole valve including the O-ring.


I haven't checked the fuel levels in the carbs, because I didn't think that a slight out-of-adjustment on the float height could be enough to cause this much of a problem. I did check that the floats weren't damaged or leaking while I had the carbs apart. I'll check the fuel levels at lunchtime and let you know what I find.

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Re: Help needed - fuel problem
« Reply #7 on: 29 March 2017, 10:17:01 am »


 I drained the carbs before taking them off last October and they've been stored in a shoebox indoors since then.


Any ideas what the problem might be?


Just a thought, but is the drain screw closed properly?
Another ex-Fazer rider that is a foccer again

Fazerider

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Re: Help needed - fuel problem
« Reply #8 on: 29 March 2017, 10:35:11 am »
The level check is at least simple to do and might give more info on where the problem is… but so far everything is pointing to Disorderlyponk’s theory being right.

Andy1970

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Re: Help needed - fuel problem
« Reply #9 on: 29 March 2017, 02:04:51 pm »
OK, so here's what I found out.


Firstly, the fuel levels appear to be spot on.


Cyl 1 is getting a spark.


I tried running the bike with the sparkplug removed, first from Cyl 2 and then from Cyl 1. With the Cyl 2 plug removed the problem persists. This seems to rule out a leaking inlet valve in Cyl 2 since the pressure in the cylinder is able to excape through the sparkplug hole.
With the plug removed from cyl 1 something very interesting happened. The problem persisted, but also exhaust fumes were escaping from the sparkplug hole. I'm guessing that this means that there's a leak between cylinders 2 and 1? Possibly a failed head gasket.


Thoughts?


A.


 

Andy1970

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Re: Help needed - fuel problem
« Reply #10 on: 29 March 2017, 09:46:34 pm »
So I removed the head this evening, and there's no obvious signs of a leak between 1 and 2 cylinders. I'll check the valves for leaks either tomorrow or Friday, depending on when I have time.

Fazerider

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Re: Help needed - fuel problem
« Reply #11 on: 29 March 2017, 11:52:37 pm »
Very puzzling.
If an exhaust valve on cylinder 1 was leaky the gas in the exhaust system could blow back to the carb while on the induction stroke.
The only problem with that is that you measured good compression.

Disorderlypunk

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Re: Help needed - fuel problem
« Reply #12 on: 30 March 2017, 01:23:31 am »
yeah this is confusing me now -cant think about your probs too much rite now as i have my own lol (yep the C-head)
you obviously have had better luck removing your head than me but i managed to find original yam head gaskets from etjames in wales
http://www.ebay.co.uk/usr/etjames1921?_trksid=p2047675.l2559
for £35 if it helps save a few quid

Andy1970

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Re: Help needed - fuel problem
« Reply #13 on: 30 March 2017, 10:07:09 am »
OK, I checked the valve seals this morning by carefully filling the combustion chambers with engine coolant and blowing compressed air back up the inlet and exhaust ports (I used an old plastic bottle lid with a hole drilled in it to seal the outside of the port).


First prize goes to......Disorderlypunk! Both inlet valves on cylinder one are leaking.
Second prize goes to....Fazerider. The exhaust valves on cylinder one are also leaking slightly.


Of course none of the above explains the compression readings, which were ok on cylinder one and low on cylinder two. It's possible that there might also have been a slight leak in the gasket, but recent enough not to do any obvious burning damage to the head or block mating surfaces. Since the gasket's going to need to be replaced anyway I guess this doesn't much matter.


On the bright side, the allegedly low mileage engine which I bought off ebay is clearly otherwise in very good nick. There's still clear cross-hatching on the cylinder walls and the heads and pistons are very clean.


Hopefully the valves don't need anything more than lapping in.




Andy1970

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Re: Help needed - fuel problem
« Reply #14 on: 07 April 2017, 06:57:29 pm »
Update on my fuel overflow problem. I lapped all the valves, which took absolutely ages and then reassembled the engine and checked and re-adjusted the valve clearances. I started it up this afternoon and it's still bloody leaking. :'(


In desperation I disconnected the fuel pump and started it up again, and it ran absolutely fine until the carbs emptied. So it doesn't seem to be a back-pressure problem, but rather a problem on the inlet side of the carbs. I've already replaced all the float valves and seals, so I'm at a bit of a loss as to what the problem is.


Interestingly, when I dismantled the bike last autumn, I discovered that the wires to the fuel pump were connected in the classic bodger's "twist them together and wrap tape around it" method. This leads me to believe that the pump isn't exactly the correct one for the bike. It may just be that it's been replaced with a 98-01 pump at some point, or it may be a pump from a different model entirely. Does anyone know if the connectors are different between the different years? I know this is the case for some parts of the wiring loom, as my ebay engine had different connectors on the oil pressure sensor and the alternator.


My first worry was that I might have reconnected the pump backwards, but I'm pretty sure that it wouldn't run at all if I'd done that. The pump seems to be operating correctly, ticks a few times when you turn it on, then stops.


Next step is to try plumbing the fuel in direct from the tank to the carbs and see if it'll run properly then.

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Re: Help needed - fuel problem
« Reply #15 on: 07 April 2017, 07:28:24 pm »
AJ Sutton site says the pumps are different 98-01 5DM-13907-00 £514.98 & the 02-03 is 5RT-13907 £278.22 unfortunately there is no pic of the 02 pump.


Pic of 98-01 pump


https://www.ajsutton.co.uk/product/yamaha/5DM139070000/fuel-pump-comp-fuel-tank?uid=0





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Re: Help needed - fuel problem
« Reply #16 on: 15 April 2017, 01:41:28 pm »
Update on my fuel overflow problem. I lapped all the valves, which took absolutely ages and then reassembled the engine and checked and re-adjusted the valve clearances. I started it up this afternoon and it's still bloody leaking. :'(


In desperation I disconnected the fuel pump and started it up again, and it ran absolutely fine until the carbs emptied. So it doesn't seem to be a back-pressure problem, but rather a problem on the inlet side of the carbs. I've already replaced all the float valves and seals, so I'm at a bit of a loss as to what the problem is.


Interestingly, when I dismantled the bike last autumn, I discovered that the wires to the fuel pump were connected in the classic bodger's "twist them together and wrap tape around it" method. This leads me to believe that the pump isn't exactly the correct one for the bike. It may just be that it's been replaced with a 98-01 pump at some point, or it may be a pump from a different model entirely. Does anyone know if the connectors are different between the different years? I know this is the case for some parts of the wiring loom, as my ebay engine had different connectors on the oil pressure sensor and the alternator.


My first worry was that I might have reconnected the pump backwards, but I'm pretty sure that it wouldn't run at all if I'd done that. The pump seems to be operating correctly, ticks a few times when you turn it on, then stops.


Next step is to try plumbing the fuel in direct from the tank to the carbs and see if it'll run properly then.


If the pump is from a fuel injected model it will be higher pressure, the carb pumps are very low pressure (upto about 5psi max)  so it dosn't ruin the float valves.




Disorderlypunk

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Re: Help needed - fuel problem
« Reply #17 on: 15 April 2017, 02:24:35 pm »
if its the higher pressure pump would it not pump fuel constantly as it never hits the knock off pressure
doesnt this problem only happen when the bike is running
(my pump starts on ignition then stops when it reaches pressure and i assume starts up again when using fuel i.e. fuel line pressure drops)

Andy1970

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Re: Help needed - fuel problem
« Reply #18 on: 18 April 2017, 10:07:49 am »
The bike ran fine with the pump disconnected and a temporary tank plumbed straight into the feed to the carbs.


The pump had been shutting off ok, and it was only leaking when running, but as I've tried pretty much everything else at this point I've ordered a second-hand replacement pump off ebay and will give that a try.


Plan B, if that doesn't work, then I'll have the carbs off (yet) again and give them another clean. I think that the most likely culprit at this point is a valve which is sealing just well enough to stop the fuel at atmospheric pressure, but not well enough to stop the fuel when the pump is running and the engine is vibrating.


If Plan B fails then Plan C is to get the carbs cleaned and overhauled by a professional.




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Re: Help needed - fuel problem
« Reply #19 on: 18 April 2017, 12:37:37 pm »
i hope the old pump isnt the first prize lol

Andy1970

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Re: Help needed - fuel problem
« Reply #20 on: 27 April 2017, 10:36:52 pm »
Well, the new fuel pump didn't make any difference, so I went onto plan B. Removed the carbs again today, cleaned carbs 1 and 2 again, but also switched the floats, valves and seats between carbs 1 and 2 to see if the problem moved with the valves.

Put it all back together and thank foc it looks like the problem may finally be sorted. Running nicely on all four cylinders, and no longer pissing fuel everywhere.

Weather permitting I'll take it for a short shakedown run tomorrow, which will be the first time I ridden it since last autumn.

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Re: Help needed - fuel problem
« Reply #21 on: 27 April 2017, 11:39:38 pm »
The bike ran fine with the pump disconnected and a temporary tank plumbed straight into the feed to the carbs.


The pump had been shutting off ok, and it was only leaking when running, but as I've tried pretty much everything else at this point I've ordered a second-hand replacement pump off ebay and will give that a try.


Plan B, if that doesn't work, then I'll have the carbs off (yet) again and give them another clean. I think that the most likely culprit at this point is a valve which is sealing just well enough to stop the fuel at atmospheric pressure, but not well enough to stop the fuel when the pump is running and the engine is vibrating.


If Plan B fails then Plan C is to get the carbs cleaned and overhauled by a professional.


Or a 5 gallon can in a top box plumbed in directly.
Sorry not helpful I know, but would certainly make the bike handle weird with 50 lb weight of fuel up high slopping around.


I notice that BB made a comment about the carb drain screw or screws are the tight and sealed? just sometimes the obvious is easily overlooked.
Good luck and I hope you sort it soon as I'm sure it is trying your patience.


As it only does this while the bike is running could it be to do with a carb fuel shut off valve letting go with the vibration, I think this is called clutching at straws.
As I said 'Good Luck'.