UK Monster Owners Club Forum » .: Technical :. » Engines, Clutch, Gears » Leaky carb

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Old 11-01-2020, 04:56 PM   #1
manwithredbike
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Leaky carb

I don't mean to be starting new threads unnecessarily and have read over some older ones related to this but i would like to pick your brains a bit if you don't mind. Carbs are something i generally leave well alone unless absolutely necessary bar the odd bit of tweaking at the idle adjuster and the occasional fiddle with the idle jet mixture screws.

I put fuel additive in the bike two days ago and ran the engine to draw it through the carbs. All good seemingly. Went out to the garage today to give it a quick start up and check that all was still good to find that the starter wouldn't turn the engine. I suspected a low battery but after a few presses, the engine suddenly turned and popped making a metalic clunk. On closer inspection, i noticed a petrol stain on the floor and found it was coming from the RH carb, on the front cylinder. Also noticed then that the oil level on the oil sight guage was way too high. Obviously petrol leaking from the carb, filling the front cylinder and onwards down to the sump. I pulled out the plugs, stuck the bike into 6th and on the axle stand to check that all was turning freely, as it was. Then i spun the engine on the button and it spat out a plie of petrol from the front pot. I done a rough compression test with my thumb, good compression, front pot same as rear one.
I removed the tank which was 3/4 filled with petrol mixed with additive just to stop more petrol from draining down as there's no tap on it..

A few things i'm not sure about now. Would the fuel additive been a contributory cause in any way or just coincidental?
Is it likely (as it would seen from previous threads) that it is a float valve sticking etc and as above, would the additive have contributed i.e will the problem be solved by draining and leaving dry till after winter, using normal petrol then?
Can the float bowl be easily removed without removing the carbs if need be?
Could there be any damage done elsewhere, the metalic clunk didn't sound too healthy?

Had just put new oil in about 100 miles ago so that's done now too.

Would appreciate any advice or thoughts you might have on it.

Many thanks in advance -- Phil
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Old 12-01-2020, 09:25 AM   #2
mickj
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You could try this, remove the plugs and try the starter. I'm sure I've seen on a post here that the carbs can drain through to the cylinders and fill the engine with petrol, this could give the symptom you describe if the cylinder was full of petrol when you tried to start the bike. The solution would be to fit taps.
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Old 12-01-2020, 11:15 AM   #3
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A reminder of the thread you are probably referring to in which you say you have seldom needed to do anything to carb'd bikes when laying them up and as stated back then- carburetted Monsters are a rather unique animal with their vacuum taps and pumps.

http://www.ukmonster.co.uk/monster/s...draining+carbs

So lets try and help- what was the fuel additive you put in?
I wouldn't have thought it would cause the problem but it is possible it dislodged some muck which prevented the float valve from shutting off.

If you removed the fuel tank there shouldn't have been any fuel draining from it as there is a tap but it is operated by vacuum not a manual shut off- this vacuum tap flows fuel to the vacuum fuel pump when the motor is turning so it can't keep filling the carbs- especially as they are higher than the pump and gravity prevents it.

Vacuum Fuel Tap:


Vacuum Fuel Pump:


Obviously in order for them both to work properly they require the associated hoses and the internal diaphragms to be in good order.

While the tank is off it would be a good idea to change the fuel filter as well as lots of owners don't bother.

You could also change the (very prone to cracking) plastic sender unit nut to a more robust Aluminium replacement:



But I know, owning an older motorcycle can be a never ending list of jobs and near constant tinkering to keep them running sweet

Anyway, I digress, as mentioned in the above thread, in my opinion you are far better off removing the carbs to work on them on a nice clean bench taking care not to mix parts between the two so I would say don't even bother to try and remove the float bowls in situ (others may disagree here but just the way I would do it).

My thoughts on the clunk you heard are that if your battery was getting down while you had the starter pressed and the motor 'blew back' (hence the 'Pop!') then it was probably caused by the Sprag catching it- whether or not it has done damage partly depends on the condition it was in before- repeated turning the motor over until the battery dies while attempting to start it is a sure fire way to kill the Sprag clutch.
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Old 12-01-2020, 03:24 PM   #4
Darren69
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It sounds like you have hydraulic locked the engine by filling it wilth fuel. If it didnt fire you'll have been lucky to not have done any damage, if it did then it probably would have wrecked the engine. My guess is the fuel ckeaner washed the dirt down to the float valve causing it to stick open. Drain the oil, fill with fresh and turn over with the plugs out to make sure all the fuel is out. Check the float valves are working ok.
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Old 12-01-2020, 03:48 PM   #5
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My 900SS did exactly that the fuel filter started breaking up and blocked float valve. On the side stand it drained tank, same symptoms. Carbs strip/clean and engine flush seems to have been okay for many more thousands. If battery and starter is strongwomen the crank has been known to twist causing big time issues. Hopefully you goy away with it.
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Old 12-01-2020, 10:03 PM   #6
manwithredbike
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Thanks all for the replies and for the tips etc.
Flip, I figured someone would pick up on my recent post about not working with the carbs every year, and here i am a few days later!!! lol
I only removed the tank after the event so it was on the bike when the leakage happened. The additive was called ethanol shield, recommended and sold by a local biker who uses it in multiple bikes every year. I figure that possibly the vacuum tap is not sealing given the amount of petrol in the bottom end and in the front pot, much more, i suspect, than a carb full. Something i need to check and sort. Might consider also fitting a manual tap as an added safeguard.
Looks like i will just bite the bullet and take the carbs off and clean them and replace any thing that looks dozed/perished etc. I will also change the petrol filter, good advice, i had already changed the sender unit nut a few years ago (to a new plastic one) so that's fine for now.
Hopefully emzedder, there's no damage done, particularly a twisted crank!! Will find out when i get it up and running again, but it seemed to be turning smoothly after i took the plugs out and spun it on he button.
I'll get at it later in the week, fingers crossed.
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Old 13-01-2020, 01:18 AM   #7
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I think it's called the Law of Sod!

I've always used Putoline Fuel Preserver in my bikes and Lawnmower (which starts after a couple of pulls each Spring after spending the Winter in the shed) without any issues although I do tend to ride my bikes when the weather isn't too bad during the Winter just to give them a run out.

All I do when I know I'm not going to use them for a couple of weeks or more is make sure the tank is topped up as near to the top as possible (with Esso Premium which apparently is Ethanol free still) after running some preserver through.

This is the fuel preserver:
https://www.ebay.co.uk/itm/NEW-PUTOL...EAAOSwrj9d2-LL

Obviously the percentage of Ethanol in fuel effects carburetted motors a little differently to fuel injected ones as the cabs cannot compensate for the change in mixture like the injection ECU can but the real danger is the fact it is so corrosive and hygroscopic during periods of lay-up.

Putoline also make this although I have no experience of it but it seems to say the right things in the sales blurb:

https://www.ebay.co.uk/itm/Putoline-...YAAOSwkedd7sGN

I have said many times, in my experience Ducati's more than most bikes, don't like long periods of being layed-up not being used and this is probably more true of the carby bikes and unfortunately this is becoming even worse with fuel containing Ethanol.
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Old 13-01-2020, 09:44 AM   #8
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I use a fuel saver from Briggs & Stratton ( the lawnmower engine manufacturer ) . Its cheap ! I always find that the bikes seem to run better as I use the tankful of fuel saved petrol after the winter layoff, which makes me suspect that it does have carb jets/fuel injector cleaning properties and might also also explain the carb leak in this thread.
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Old 16-01-2020, 11:42 PM   #9
manwithredbike
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I just got round to looking at the bike tonight. The vacuum tap is shot, passing unrestricted so obviously that, along with a leaky float valve has flooded the engine, though i'm not sure which came first.
Plan is to replace the vacuum tap and now that the tank is off, pull off the airbox, battery box, coil pack etc and take the carbs off and give them a clean and maybe replace the float valves with some neoprene tipped ones. Might also replace all the pipes and tubes in and around the carbs too while they're off. They're all at least 22 years old now.
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Old 17-01-2020, 08:10 AM   #10
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That’s almost exactly what I did, I sent Luke and Craig an email asking for everything here but for my 900:



Then a day or two or later this lot arrived:



I also replaced the diaphragms in the vacuum pump but they came from Allens Performance.

https://www.catalyst-findit.co.uk/in...78s30susleo0k1

http://www.allensperformance.co.uk/
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Old 07-02-2020, 03:50 PM   #11
manwithredbike
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Finally got round to getting the bike up and running today. Ended up doing a few wee mods while the carbs were off.
I fitted a manual tap to the fuel line between the filter and the vacuum tap, just as a belt and braces - and so that i can lift the tank off a bit more easily in future without having to drain it first.
Also fitted a £6 vacuum tap with a modded bracket. The ducati one was priced at £80 from a well known parts dealer which i thought was a bit steep. The cheap one seems to work 100% fine.
I also modded the idle screw on the carb, brazing an extension on for easy adjustment. I find that i'm always tweaking the idle speed depending on time of year, type of journey so now i can just reach in behind the oil cooler and turn it up or down easily without fiddling with a screw driver. Hoping that storm Ciara goes away soon so i can get out and about for a spin soon.
Trying to post a few pics, will see how that goes




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Old 07-02-2020, 03:59 PM   #12
manwithredbike
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Cheap vacuum tap with a small angle bracket to fit in same position as original tap
[IMG][/IMG]

Idle screw with extension brazed on
[IMG][/IMG]

New handy idle adjuster behind oil cooler
[IMG][/IMG]

New in-line fuel tap
[IMG][/IMG]
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