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Discussion Starter #1 (Edited)
Hello everyone.
I'm really new to the forum here, so hoping someone can help me.

I've just bought a neglected 600 F2 1994 model which has sat for some time. I've replaced battery and got it to crank over.

It leaked fuel everywhere, so I took off the fairings, stripped it down to the head gasket. Replaced with a new one. Reassembled everything, and now fuel p***es out of the drain holes (just below the each exhaust outlet on the outer side of the engine block). There are drain holes there, so I gather this would mean I have a sticking carb float.

I'm assuming this as it can empty half a tank of fuel onto the floor in less than 3 minutes. That's how fast the fuel is coming out. I didn't feel like risking fuel near a hot exhaust any longer so turned it off. The bike starts everytime though. I'm confident there's now no leak on head gasket (coolant not contaminated, no oil in water).

I've taken carbs off and tapped throttle bodies. They sound different, indicating a couple are stuck?
Please see here for video.
I've got them soaking in carb cleaner at the moment.
Anything else I should try while I've got them apart?

Also, I've supposedly got a vacuum line coming off of cylinder 1. This isn't connected to anything. Cylinder 2 has a closed off port. Cylinder 3 and 4 don't have any pipes/tubes coming off them. Where do I connect the vacuum hose?

My fuel petcock does not have a vacuum line. Possibly aftermarket? It's got one pipe coming off which just simply goes to a T-Piece for the carb feed.

I'm hoping that once the floats are cleaned and working the niagra-falls effect of fuel escaping will stop. Anyone else had this?

Many thanks for any info.
 

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First question. Are you sure it's an F2? 2nd question, does it have a fuel pump? Reason: F2 used a vacuum operated fuel valve, and that's what the tube off port #1 should go to. If it's open, plug it. Your sucking in unfiltered air and ruining the fuel mix. The F3 incorporated a fuel pump, deleting the vacuum petcock, most likely to assist with the ram air. Do you have ram air?? You could have an F3 tank, etc. or a missmatch of F2 F3 parts as some are interchangeable.

Those small holes by the exhaust ports allow water/debris to leak out from the spark plug tunnels only. They serve no other purpose. If you're leaking fuel out of them then there is a more serious problem with the cylinder head. Are all the spark plugs tight? The only way I see fuel leaking out of those holes is if a spark plug is amazingly loose, sending overloaded fuel from the cylinder out past the spark plug (but if your getting all 4 holes leaking I can't imagine it would run at all), there could be a serious crack in the cylinder head, or the cam cover is leaking fuel diluted oil into the plug tunnels.

Definitley sounds strange to me:idunno:
 

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Discussion Starter #3 (Edited)
Hi IanDoohan. Thanks for your quick response.
I think it's an F2. It's a 1994 model so am I right in thinking the last of the F2's? Sorry, I'm a bit new to these bikes.
It doesn't have a fuel pump. It's purely gravity fed.
I'll plug the pipe at port #1 then. Sounds like I've got a mixture of F3 parts on there. Not an entirely bad thing I assume as I'd read somewhere that the diaphragm on the F2 petcock is prone to failing.
I don't have ram air either. There's no directed airflow to the air intake.
Spoke to a guy at a local garage today. He said he's seen something similar happen on a yamaha before where the carb floats stick so much that the entire fuel flow gets empties straight into the engine head and will try to flow out however it possibly can. Although this isn't supposed to happen under normal circumstances, it can mean the head becomes 'fuel washed' as he put it – explained that it removes the oil in the head as if you were cleaning it with a petrol mix.

I've checked & cleaned the float needles. The next is to check the floats themselves on the other side of the carb. I'll let you know if this solves the problem.

When I had the head and block apart to replace the head gasket, I cleaned all surfaces with a rag and petrol (nothing abrasive). Didn't see any cracks at all in either the head or block. It all looked in good condition. (attached 2 pics). Although the head was mucky in places (don't think it'd ever been apart, cleaned up well well when I was done).

Will have another look on Monday and see if I have more success.
One last thing about the vacuum line – Is it absolutely necessary? Was wondering if the carbs rely on this vacuum in any way?
 

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The vacuum line is only for the fuel tap that has the diaphragm on it. The vacuum from the engine opens and closes the diaphragm to allow fuel to flow from the tap. If you don't have the diaphragm on the tap to plug the hose onto then the hose is serving you no purpose, that's why I said plug it. Or remove it and plug the port on the head that it's connected to.

I'm still trying to understand how 1/2 a tank of gas could leak out the spark plug tunnel. That's driving me crazy. The only connection between those holes and the inside of the engine is the spark plug. If your spark plugs are properly installed then there is no way for fuel (or oil) to have access to those tunnels. The only other possibility is the engine is so diluted with fuel, AND the cam cover gasket is pinched or not on correctly over the spark plug tunnels. Check that too.

I've never seen anything come out of those holes except debris, spiders, or built up grime that plugs them up. That is a crazy mystery.
 

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Discussion Starter #5 (Edited)
So, spent a few hours cleaning the carb, making sure everything worked and that I could see nothing obviously wrong. I checked that none of the jets were blocked, all the float needles move and that the floats themselves can move freely.
Just put everything back together and still no change :mad:.
You can see what I mean in the pic, and what I've tried in the video.

^ Also, should mention things IanDoohan said to check above, I've checked the plugs. They all seem tight. I've plugged the hose on port #1, had everything apart and checked the gasket was seated, installed and sealed properly.:idunno:

Can someone help?! Please.
 

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Have you pulled the spark plugs? I still can't figure out the path that fuel from the carbs can take to get into the spark plug tunnels. It almost sounds impossible. Does this only happen while its running? Or can you duplicate it without having to run the engine. Those small holes travel to where the spark plug is. If you remove a spark plug cap, then remove a spark plug and take a piece of safety wire and pass it through the small hole you will see it pop out by the spark plug threads. That's it!? It just doesn't make any sense. Can you do the couple things I've just asked and post very well lit detailed photos so I can see in the spark plug tunnel? You're high tension leads from the spark plugs must be saturated with fuel. That would probably instantly blow up once you started the bike up. I just don't get it.

And the carbs slides will make that noise and all probably feel the same depending on the condition of the diaphragm rubber. Once the cap is on with the spring tension they will all most likely work normally.
 

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Discussion Starter #7
No fuel leaks when the engine isn't running. Ok, hang on. I'll go back out and try as you suggest with the wire. I'll put the results on here later!
 

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Discussion Starter #8
Ok, done all that. Not any further forward though. (I'll do this in 2 posts so I can attach all pics). Removed plug from cyl#1 as that's the worst leak. Plug is clean, HT lead is clean & not covered in fuel. Holding the camera as best I can, you can just see down into where the plug was removed...
 

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Ok well done. Now that we are understanding how that hole functions, the question is how is fuel from either the tank or the carbs getting in that space????? Is your engine oil diluted with fuel? I hope someone else see this post and offers suggestions. There is no way for fuel to get in there. And looking at my 900RR head (very similar) I've been reminded that the drain passageways are in the EXHUAST side of the head, making it even more impossible to have fuel from the carbs getting in there.



Are you running it on the side stand? Is it at all possible that's its leaking from the carbs, running down the cylinder head and more near #1 giving the IMPRESSION it's leaking from the drain hole?

I love a good mystery, but this one is just plain nutty!

And the reason you took the head off was suspicion of a head gasket leak? Did you use a new head gasket? I see a lot of Red sealant around there.
 

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Discussion Starter #11
Yes, the bike was leaking this way when I got it. I wondered if it was a head gasket, so I put a brand new one in there. I've checked all the carbs. From where they connect there is no sign of any drips. It's bone dry. You can literally watch the fuel spit from those drain holes when the bike is running. I agree, it's weird the fuel is getting in there. I mean, the fuel would have to be there for the spark plug to function, however how is it getting to the drain hole. Think I'm going to have to take the head off again aren't I?

Failing that, an engine transplant?
 

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And we're sure it's fuel because you have to refill the tank afterward? I only ask because there are cooling passages in the head, and if it were cracked internally somewhere it's possible for coolant to leak out there, or water. I know I sound like a broken record here but your sure it's fuel leaking and not water? You're running an ethylene glycol coolant in the system now? If the previous owner left plain water in there and it froze it could crack the internal cylinder wall cooling jacket and leak coolant, but the fuel thing just has me puzzled. And with it only doing it while running doesn't make much sense either. If you have a gravity fed fuel tap and leave it on, with a sticking float needle you would still have the leak, engine running or not. Are you turning the tap off after you run it?

Aside from swapping to a used head, I would try and duplicate the symptom without the engine running. Is there a coolant hose hooked up wrong? Having the water pump pumping fuel into the head somehow:idunno:

I'm running out of ideas.
 

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Discussion Starter #13
It smells like fuel and is colourless. (The stuff in the tray in the video was me draining other hoses checking things).
Just tried putting some on a rag. I can set fire to it and it'll burn quite happily, so I can assume it's definitely fuel.

When I drained the coolant which was in the bike, it was this flurorescent green compound, so I'm guessing it was antifreeze of some description.

I've got ethylene glycol coolant in there now. It currently doesn't smell of fuel.

Drained a bit of oil too. The oil looks and feels like oil still, not like petrol.

I couldn't see any cracks in the head when I had it apart. This doesn't mean there aren't any I guess. I haven't inspected it like a manufacturer would do with a microscope. With what I'm able to do here, it looked ok.

According to all the workshop manuals, and t'internet, I've got all the cooling hoses correct. I've triple-checked these now.

I've tried leaving the fuel tap on after I stop the engine. The leak stops. The leak only runs when the bike is running. Turning the fuel tap off when the bike is running shuts off the fuel because when what is in the pipes has been used, the bike will cut out.

Think I'm going to look at the replacement head route.
 

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Yeah that's a bummer. I hate not figuring out a solution or cause to problems. It's just mind boggling. Good luck anyhow.
 

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Discussion Starter #15
No worries. It's just a pain in the a, that's all.
That, and the time involved.
I'll post on here when I've got the replacement head and changed it. Just in case anyone else ever has this happen to them.

If the replacement head doesn't cure it... well, I'll either find a match or clean the bike and hang it on the wall. :idunno:
 

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Discussion Starter #16
Just took the head off the engine and I've got water in the cylinders, so we can assume the head does indeed have a crack somewhere.

Do I also assume I need a new engine at this point?
If I drain everything, the damage is probably already done though.

Anyone want a large, expensive paperweight? :mad:
 

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Just took the head off the engine and I've got water in the cylinders, so we can assume the head does indeed have a crack somewhere.

Do I also assume I need a new engine at this point?
If I drain everything, the damage is probably already done though.

Anyone want a large, expensive paperweight? :mad:
You will notice a bit of coolant on the Pistons because it's inevitable some will be in there upon removal. But I'm assuming your talking about a considerable amount? The water would be getting pushed out through the exhaust more so than past the rings so as far as the extent of the damage I wouldn't know. But if the oil didn't seem milky or diluted then the lower end may be ok. I guess an EBay/used head wouldn't be a bad idea, but you could spen a couple quid and have yours checked before you buy another one. I know if it were mine I would want to know exactly where it failed and would want to see the cracks, if there were any. How's the condition of the rest of the bike? Probably get a complete motor for pretty cheap:idunno: I wouldn't throw in the towel yet.
 

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Discussion Starter #18
Hmmmm. Ok, won't give up quite yet :thumb:
Just seen a replacement head on eBay for about £65 ($96). Won't rush in though, want to take a good look at the head I suspect has failed first for cracks. Will post pics on here if I find anything. Hopefully someone will be able to confirm if it looks out of the ordinary.
 

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Discussion Starter #19
Just wanted to say a huge thanks for your help IanDoohan. I've had a chance to look at the old head now. (By the way, I'm never using gasket seal again – that stuff gets everwhere!).

The only thing I can see is that the valve spring retainer is either missing or has pinged off somewhere inside the head, perhaps causing internal damage. The result is that one valve sits higher than the rest. This can't be good and has probably been that way for a while.

Having removed the follower caps on each valve, I'm also missing the shim on this valve too. I wonder if it's just exploded upward somehow, scattering various bits across the head.

It might be a fair bet to say this has caused a bit of internal damage? I can't see anything else obvious, at least externally. If this lot had been bouncing around the head at pressure, I can only assume it could wreck something and possibly cause the leak seen from out of the drain holes?

I've got a new head off eBay and am fitting it. I've got to wait for a replacement shim and new exhaust stud bolts, but will post the results on here when it's all reassembled.
 

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Well you're very welcome. More encouragement than anything;)

That valve looks like it's dropped the 2 retainers are still visible, is there any damage on that piston's crown? I'm still really stumped about the fluid leaking out the drain holes, and a missing/lost shim would also have a hard time coming out from under the "bucket" as they're called. But it is nice to see you found something. Take some fluid or air and and try and see if you can get it to come out somewhere other than the drain holes. That may lead you to where it's leaking into the spark plug tunnels. More so out of curiosity as you have the new head anyhow. Keep on it, hopefully you'll be up and running soon:thumb:
 
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