FCR overfilling ?

[stef]

Good morning,
I made some adjustements on my FCRs over the last few days, namely the needle clip position. yesterday, after a final adjustement, i filled up the petrol tank (was nearly empty), and went for a test ride.
it was crapistic.
so i thought, nevermind, i'll just go back to the previous needle clip position, which seemed not too bad.
I removed the air filters and to my surprise, i found the inlet pipe and carbs full of petrol ! i mean really full, and it was still flowing in ! so i disconnected the tank with the quick release connector, and the filling stopped.

now then, why is that happening ?
someone here warned me that this could happen if i removed the vaccum tap (which i did.. i sometimes think i know best and just ignore sound advice !)
but still, why arent the floats inside the carbs stopping petrol from pouring in ?

I take it that the extra pressure from the full tank induced the floods, but should this really happen ? should i fit the tap back , or just throw a match ?
thank you !

[Saint aka ML]

I only have stock pump but had the same issue. It is not float height. Honestly no idea what it was, there are two screws that adjust idle I stopped petrol doing that by closing them a bit and then rode down to MD.

Warning you will now have plenty of petrol in engine, possibly mixed with oil. My started as a surprise. Where I came home after using the bike 2 days earlier with no issues. Most of petrol from tank was in engine.

[utopia]

Yep, twas me who warned about that, though in fairness I was only repeating what I'd heard from Saint's experience, and I may have included an element of doubt as to whether there might be some other cause.
I guess the strength of the seal at the float needles would depend on such things as the head of fuel in the tank, the angle of the carbs, and suchlike.
And if you fit a manual tap, then there's every chance that one day you'll forget to turn it off, and the same thing will happen again.

[stef]

Yep, twas me who warned about that, though in fairness I was only repeating what I'd heard from Saint's experience, and I may have included an element of doubt as to whether there might be some other cause.
I guess the strength of the seal at the float needles would depend on such things as the head of fuel in the tank, the angle of the carbs, and suchlike.
And if you fit a manual tap, then there's every chance that one day you'll forget to turn it off, and the same thing will happen again.

yep, so i suspect some leaky float valves..which could also explain the permanent richness of the mixture..
got to open those carbs..

[Nottsbiker]

http://ducatitech.com/2v/fcr_faq.html

"I've got what I call the 70/20/10 rule. 70% of the people I sell carb kits to bolt the carbs on their bike and wheely into the sunset with a maniacal giggle never to touch their carbs again. 20% of the people will love the increased power but want to diddle about with the fuel screw or slow air screw to get idle "just right." Note that these two adjustments are easy to get to. The last 10% of FCR buyers seem all fubar'ed. They can see the potential for the carbs, but something just isn't right. They just need to take their carbs to a local shop with a dyno and pay them to make the bike and the carbs play together nicely."

I'm assuming you've read the above quotes about FCR's ;)

[stef]

http://ducatitech.com/2v/fcr_faq.html

"I've got what I call the 70/20/10 rule. 70% of the people I sell carb kits to bolt the carbs on their bike and wheely into the sunset with a maniacal giggle never to touch their carbs again. 20% of the people will love the increased power but want to diddle about with the fuel screw or slow air screw to get idle "just right." Note that these two adjustments are easy to get to. The last 10% of FCR buyers seem all fubar'ed. They can see the potential for the carbs, but something just isn't right. They just need to take their carbs to a local shop with a dyno and pay them to make the bike and the carbs play together nicely."

I'm assuming you've read the above quotes about FCR's ;)

yep, i did..
but i dont know were i can possibly take mine over here.. the local ducati shop is crap.
took me 3 weeks to get some valves shims, they couldnt sell me orings to service my mikunis, they'll probably laugh at me with my FCRs..and charge me for it.
as for a tuner with a dyno.. i'll be quicker building a dyno myself.

[utopia]

Then again, there is now a very strong suspicion that the float valves are leaking. This would need attending to first, before doing any set-up, and you may then find that you're one of the 70 or 90% of FCR users who don't need a dyno (at least not desparately).....its a 9 to 1 shot, which is pretty good odds.
The leaky float valves may also account for the difference between the cylinders (there was one, if I remember correctly), due to the different angle/attitude of each individual carb.
And you'll have to get the new float bits mail order anyway, so you may not need the local dealer at all.

A quick thought....you could have a day out at a club day at the local race track, and ask around the paddock for a nearby dyno tuner. If there's one nearby, then it'll be well known.

[stef]

Then again, there is now a very strong suspicion that the float valves are leaking. This would need attending to first, before doing any set-up, and you may then find that you're one of the 70 or 90% of FCR users who don't need a dyno (at least not desparately).....its a 9 to 1 shot, which is pretty good odds.
The leaky float valves may also account for the difference between the cylinders (there was one, if I remember correctly), due to the different angle/attitude of each individual carb.
And you'll have to get the new float bits mail order anyway, so you may not need the local dealer at all.

A quick thought....you could have a day out at a club day at the local race track, and ask around the paddock for a nearby dyno tuner. If there's one nearby, then it'll be well known.

erm, local race track ?
this is normandy. i guess le mans is only a couple of hours drive..yeah, why not.
but you are right, it may all be sorted with the leaky valve fixed (assuming it's a leaky valve.)

[Saint aka ML]

I can tell you this my crabs were fixed by MD with no new parts or even opening them. My crabs are now also the 10% before that they were the 20%

[stef]

I can tell you this my crabs were fixed by MD with no new parts or even opening them. My crabs are now also the 10% before that they were the 20%

maybe they miss the sea ?

anyways. i took the bowls off, and apart from one side of the carbs that was at 7.6mm instead of the recommended 9, there was nothing wrong with the valve. i did the test of blowing in the petrol intake to check for leaks, but found none.

the plot tickens.

[crust]

Mine did this, went to start bike one day and nothing.

Thought battery was flat, charged it, nothing, checked everything, took plugs out and she was full.

I examined the float needles carefully and the float seats, couldn't see anything wrong, so re-assembled, still leaked.

In the end I replaced the float seats and set the float heights exactly, problem solved.

[gary tompkins]

maybe they miss the sea ?

anyways. i took the bowls off, and apart from one side of the carbs that was at 7.6mm instead of the recommended 9, there was nothing wrong with the valve. i did the test of blowing in the petrol intake to check for leaks, but found none.

the plot tickens.

The error on the float heights could have caused the running problems. One cylinder would run richer in the low to mid range due to float bowl overfilling.

Float height setting can have a big effect on how an engine runs.

[stef]

umm ok,
i am a little surprised that 1.4mm off could be this troublesome, but then again, why not.
i'll reassemble and check asap. and i'll refit the vacum tap.

[Dookbob]

Don't forget that Crust also replaced the float valve seats as well as resetting the float heights in order to solve the same problem.

[DavidT]

I'm afraid I don't have much to offer on the topic other than to share my woes. *I've just got my old Mong back this week with rebuilt motor and new 39mm FCRs. *The last time it was returned to me, on my first outing the carbs were flooding so badly that neat petrol was running out the exhaust pipe. I sent it back to the shop, and despite rebuilding the carbs to check for crud in the float valves it did the same thing 3 times over the next while. *Eventually the supplier had the carbs back for inspection and somewhat reluctantly admitted the valve assemblies were faulty and replaced them. *This week I have had fuel running out the air breather hose. *The supplier again suggested crud in the valves or that it might be the fuel pump over pressurising the system. *I ran it today without the pump (disconnected the vacuum hose and plugged it so I reconnect at the roadside if needed) - ran out of petrol before the tank was properly empty, I think, because of the lack of head and later suffered possibly an air lock in the hose. *Reconnected the pump and all seems well.

I'm in much the same boat as Stef - I would quite like to take it to someone who knows what they are doing and get them working 100%, but certainly don't have anyone local. (Any recommendations from anyone for a good Dyno shop in Scotland or Northern England?). If it wasn't for the fantastic lift at wide throttle openings I don't know if I would be willing to persevere. Although I did get 53mpg tonight on a 100 mile round trip, so...

David

[Capo]

Fuel level affects the mixture and is critical, I prefer to use a clear hose connected to an adaptor on the float bowl drain, this gives an accurate indication of the actual level.

I'm surprised (and somewhat intrigued) that the float valves could be faulty either in design or manufacture, this form of carburetor fuel level control is simple and has been around for a while now.

If I could get my hands on one to study, I could comment further

[Kato]

OK first the over fuelling is not an uncommon problem on poorly set-up FCR's, you first need to make sure they are spotless inside and a good quality filter is used between tank and carb, the smallest particle will stop the valve from closing fully and allow fuel to flow through the carb, next make sure you have the float level spot on, .5 mill makes a huge difference, third make sure your pump is not pushing more than 3.5 psi, I made a re-stricter so I have 4psi pre and 3psi post pump.

These carbs are very very fussy about set up but once you get it right they will deliver the goods as countless racers and specialist tuners will testify too.

[Dookbob]

Fuel level affects the mixture and is critical, I prefer to use a clear hose connected to an adaptor on the float bowl drain, this gives an accurate indication of the actual level.

I'm surprised (and somewhat intrigued) that the float valves could be faulty either in design or manufacture, this form of carburetor fuel level control is simple and has been around for a while now.

If I could get my hands on one to study, I could comment further

That sounds like a good float level check system Capo, But could you tell me please when using this system where you take your correct level to be, I would assume that it's somewhere on the bowl flange. Or is this check only for comparing one carb against the other after setting the floats in the normal manner. I am referring to the Mikuni carbs, not the FCR,s in this question.

[Saint aka ML]

OK first the over fuelling is not an uncommon problem on poorly set-up FCR's, you first need to make sure they are spotless inside and a good quality filter is used between tank and carb, the smallest particle will stop the valve from closing fully and allow fuel to flow through the carb, next make sure you have the float level spot on, .5 mill makes a huge difference, third make sure your pump is not pushing more than 3.5 psi, I made a re-stricter so I have 4psi pre and 3psi post pump.

These carbs are very very fussy about set up but once you get it right they will deliver the goods as countless racers and specialist tuners will testify too.

Kato do you have the huge restrictor like on other ducs or some kind of home made contraption? I was told to make one. How it was explained re it working seemed easy but building one well another story.

[Capo]

That sounds like a good float level check system Capo, But could you tell me please when using this system where you take your correct level to be, I would assume that it's somewhere on the bowl flange. Or is this check only for comparing one carb against the other after setting the floats in the normal manner. I am referring to the Mikuni carbs, not the FCR,s in this question.


I used this method when setting up Amal GP with remote float bowl,
According to the Mikuni manual, the correct level is 1.5mm above the bowl flange.
The valve seal is tested at 5 psi.

[Dookbob]

I used this method when setting up Amal GP with remote float bowl,
According to the Mikuni manual, the correct level is 1.5mm above the bowl flange.
The valve seal is tested at 5 psi.

Thanks for that, I have made a note of it, this sounds like the way to go to get a final check on the level after doing the adjustments. I suppose you would have to turn the engine over a few times after fitting the " sight glass" to the drain in order to top up the float chamber after filling the glass.

[Dookbob]

Fuel level affects the mixture and is critical, I prefer to use a clear hose connected to an adaptor on the float bowl drain, this gives an accurate indication of the actual level.

I'm surprised (and somewhat intrigued) that the float valves could be faulty either in design or manufacture, this form of carburetor fuel level control is simple and has been around for a while now.

If I could get my hands on one to study, I could comment further

If the FRC float valve needles are rubber tipped like a lot of them are , maybe a dose of ETHANOL could render them knackered.

[urbanfireblade]

Be sure to get a good seal when connecting the clear tube to the bottom of the float bowl drains, i had my bike idling when i done this check and fuel started leaking out the connection.