Carburetor Drowning Issues

Good Day Guys,

I have recently bought a 93' RC36. When I bought it it was flooding badly and if you went slow it just drowned the motor to a halt. Got it home and took off the carbs and then set the floats, the one float did not look so great and I then went and tried to get spares. I could not find spares and bought (what I am guessing is RC24) set of carbs and they where not a direct fit to the current bike. I basically took everything that was better on the one set of carbs and put it on the other set of carbs. I then put it back on the bike and then switched it on and watched the carbs fill up with fuel. I went back to the drawing board and checked everything again and everything seems in spec. I can block off the floats one at a time (By gently pressing it up till the needle seats) and then it stops flowing, but for the life of me I don't get it, when I put it back on the bike it just fills up. Now it looks like it over flows from one of carbs and affects the rest but I am not sure, this is the first V4 I am working on and it seems to have a bit of separate rules for the V4 that don't apply from the inline 4 or V twins.

Now when I tested them there is a pipe running from the carbs that is not connected, but as far as I understand there is just an aux air intake.

The one notable thing is that the velocity stacks are off when I test but I don't think that should allow the thing to fill up (I mean I can see the fuel pooling up on the butterfly).

I am a wits end and any assistance would be greatly appreciated.

Regards,
Werner

PS: I have attached an image with the pipe that is not connected circled in red.

 

First up, that big pipe is the air vent for the diaphragm chamber. May just connect to the airbox somewhere, or a sub air cleaner, so it is supplied with clean but non-vacuum air.

Regarding the flooding, you need to be very sure that the tips of the float needles are clean and perfectly smooth, and then also make sure the seats in the carbs are also smooth and clean. These are all that stops the fuel from overfilling the bowls. I presume you have set the floats height with the float tang in contact but not depressing the needles? Are you sure all of the floats do, in fact, float???

You can clean the rubber needle tip with carb cleaner and a cloth with gentle twisting, and the seats with a q-tip soaked in cleaner.

Looks like the float valve sets are available but not cheap at USD34 per carb.

http://www.partzilla.com/parts/sear...3/VFR750F+A/CARBURETOR+COMP.+90-93/parts.html

Best of luck Werner.

 

I will cleant hem out again and see if that helps but I did chase carb cleaner through them. I set them to 9mm and it still flowed and then I set it to 11 and it still flowed.

So for sanity's purpose ... can one float that is stuck open flood the whole bank ? Reason I am asking is that I had one needle/seat suspect. I left the float bowls off and depressed that one to amke sure it seats then all went well. I then just replaced that one and set as the rest and the problem continued. Is it possible there is something in the throttle body that is leaking where ti shouldn't ? Maybe pilot jets that where not closed off or something ?

I really dont think its the needle and seat but I am starting to think that it is flowing from somewhere else.

 

I don't think there's a way for excess fuel to get to other carbs; they do share a manifold overflow but I assume that would be below the overflow height.


Sent from my iPhone using Tapatalk

 

Well currently I need to see if there is any way to trouble shoot cause I am thinking that there is one carb with a problem affecting the rest in some way. Mayb take off the intake from each carb and test them seperately so see if they stop with the needle set right and it it doesnt remove that one throttle body. Plus might be easier to work with one offencing carb rather than others and this is the only way I can think of singling them out as working or not.

Any suggestions ?

 

How about allowing the carbs to fill, then shut off fuel supply, and drain each bowl and measure the volume that comes out. Would tell you if one carb has much greater volume than the others.


Sent from my iPhone using Tapatalk

 

If your float bowls are filling up with too much fuel, then your float needles need to be checked that they are seating properly and that the float heights are properly set.

Could be some sediment or something in there as well preventing the needles from seating and sealing.

Did you complete rebuild the carb and put all new seals, jets, needles and seats in?? What do the vacuum diaphragms look like for the slides?

 

Just remember don't split the carbs off the plate, you will dig yourself into a bigger hole

 

I did that with my Magna ... if you have a manual, it's not so bad, but yeah - this is REALLY good advice and will save you a LOT of hassle.

 

Ok, well here is what I have done and the results.

I got a big syringe (50ml) and cleared out the carbs of fuel. I then proceeded to push water through the fuel inlets but splitting the front and back carbs (they join at a T-piece). When I filled up the front carbs (They are set to 9mm float height as the manual says they should be) then the flow stopped and no water was coming out anywhere. So that was great news, for all intents and purposes the front was fine. (And I knew if I did the same to the back and it was fine then that theiry would be shot to shit)

I did the same the back as to the front and the water just when pissing into all the carbs. (I still dont know how it gets to all the carbs but it does) I then proceeded to open the 2 back carbs and I set their float to 11mm and then re-esabled and tested. I got a bit upset when a bit of water started comming out (but I assume that it was in the pipes and that the air rushing through pushed that out cause it didnt continue. They seated and the flow stopped.

I then proceeded to drain everything again and assemble everything as it would be on the bike and then the syringe took the place of the fuel pump.

I pushed alot of water in ... about 200ml or maybe just over and then .... it stopped. It would not let any more in. So I then went and emptied the float bowls to see that all of them had fuel in and it was all good.

It was a bit late at that point to put the carbs back on the bike but that will probably happen tonight and then I will test everything and see how it goes.But it does look like there is a small light at the end of the tunnel. Hoping it is not a train.

@Jeff_Barrett I replaced everything in the carbs from a known set of good carbs (The bike they where on was in a prang and written off but they where all good) My old parts I kept but in anything seemed remotely suspect I replaced it with the best part I could get my hands on. I did remove the top plate but not the bottom plate holding them together and I never removed both at the same time so the sync is not out (I tried to avoid that at all costs cause I remember doing the sync on my CBR 919 and that was not fun.)

 

Hey Werner sounds like you might have solved your own problem.

Only comment I'd make is that water being denser than fuel, your floats will have been sitting higher in this test than they will in petrol, so might be pushing harder on the seats. Still, a seal is a seal, so fingers crossed.

 

Yeah well the water was a better option than fuel cause the whole place was full of water and my wife would cut off certain parts of my anatomy if petrol was all over the lounge

I am thinking it should be fine now, cause at least with the water the problem was replicated. I think it would have been a different issue is it was not replicated with the water and it sealed up first time.

I am hoping to get it back on the bike today and test, weather permitting cause its kinda rainy and overcast here so might only happen tomorrow. Will keep you posted on the progress and once its up and running I will post pics. (Cause since I bought it, it has been needing a wash and a good clean up)

 

Got home all happy to put this puppy back together again and ... it does it again ... now I am really at wits end

 

Are all the floats loading up or just one?

Is your fuel pump putting out the right pressure?

 

Next step is to check float needle valves and seats. Dirt on the valve seat or a nick on the tip of the needle could be causing it.

 

@Jeff_Barrett: This is outside the bike with pressure I provide via a syringe. This is nt even the fuel pump yet. I just slowly apply pressure and make the liquid go into the carbs. All the floats are filled but I dont know where the extra is being pushed out from.

@Allyance: I checked them and replaced where needed s not sure what else I could still do on this front. I am out of carb cleaner, wuld acetone harm the needles cause i could then clean it out with that and a q-tip

I did read that there where carbs that the flat height was 13.7, might it be that my flats are nt set to the right height and that I have one that needs to be set higher ?

 

Ah, I thought you had reinstalled them ... you mentioned they were working on the bench earlier.

Then yes, I agree with Allyance about the float needles. When I do a set of carbs, I just replace everything so there's no guessing later. It's just done.

 

Well I did replace everything thats the problem. I think I am missing something.

I have attached pic from a website that had float heights... Maybe I fall in the after 93 category ?

 

What does the VIN plate say?

 

Are carb still off the bike? If so time to take out float, needle valve and valve seats. Spread everything out and examine every thing with an LED flashlight. As they used to say on Sesame Street, one of these things is not like the other! One valve is not closing all the way, tip damaged, seat dirty, tab on float bent, look and compare.