Author Topic: PD46A carb overflow trough inlet tubes (Read 5939 times)

hudecheck · « **on:** October 19, 2016, 04:55:07 AM »

Hi guys, I would like u to ask for a help. I have been struggling with my PD46A (Honda CB550F2 1978) carbs since one is still overflowing through inlet tubes like u can see in first pic in red circle. Yesterday I did many hours of changing all possible combinations since firstly was overflowing through 2nd carb then I change carb bowl+float+rubber tip valve on float to 1St carb and vice versa towns. Well then was overflowing 1st carb. Afterwards I replaced rubber tip valve back to 2nd carb together with float. And well still overflows only 1St carb. So this carb bowl is somehow reason. In the second picture u can see what I have spotted that this suspicious carb bowl has shorter overflow tube at the end of it... But overall this carb bowl is anyway looking totally same like the others.

Is very strange that even I set float very high or very low there was still overflow through this inlet tubes and not through carb bowl overflow tube. Du u have any tip what to do with this issue? Thanks a lot!

flybox1 · « **Reply #1 on:** October 19, 2016, 07:07:44 AM »

I would think someone at some time either swapped out for another float bowl, or replaced that carb body itself.
If they are the same carb body model, you should be fine. The overflow tube length out the bottom of the bowl is of no matter.
If fuel is flowing out that brass hole, then your fuel level is too high....which could be from a bad float valve, a stuck float, incorrect float height, or debris in your fuel preventing float valve seal.....
Check all of these and report if the symptom is still there.

hudecheck · « **Reply #2 on:** October 19, 2016, 02:58:21 PM »

Carb body cannot be as I wrote once I change 2nd carb bowl to to 1st one and vica versa then I was leaking there where was this "suspicious" bowl.

Please correct me if I am wrong but in case the fuel level is too high why is the fuel not overflows through overflow tube? And I checked them thoroughly - they are all ok - not clogged - very sure.

I am also sure that this is not by float valve, since I replace 1st to 2nd carb as well as floats and it was tight once it was placed in "good" carb bowl.

I honestly believe that I check all of you mentioned. I would be actually glad that at least there is flowing through the overflow tube but it's totally strange since this is not happening.

Do you know for what exactly there are those brass holes ("inlets") and how or to which are connected - are they connected direclty to fuel tubes? thank you for whatever tip

EDIT!!! Sorry I made a mistake to calling carb bowl as bank. So I correct it to carb bowl

!!!

hudecheck · « **Reply #3 on:** October 19, 2016, 03:07:15 PM »

One more question. Can this issue be somehow connected with petcock or tubes going to carbs from petcock? Thx

flybox1 · « **Reply #4 on:** October 20, 2016, 06:51:36 AM »

Quote from: hudecheck on October 19, 2016, 02:58:21 PM

Carb body cannot be as I wrote once I change 2nd carb bowl to to 1st one and vica versa then I was leaking there where was this "suspicious" bowl.

Please correct me if I am wrong but in case the fuel level is too high why is the fuel not overflows through overflow tube? And I checked them thoroughly - they are all ok - not clogged - very sure.

I am also sure that this is not by float valve, since I replace 1st to 2nd carb as well as floats and it was tight once it was placed in "good" carb bowl.

I honestly believe that I check all of you mentioned. I would be actually glad that at least there is flowing through the overflow tube but it's totally strange since this is not happening.

Do you know for what exactly there are those brass holes ("inlets") and how or to which are connected - are they connected direclty to fuel tubes? thank you for whatever tip

EDIT!!! Sorry I made a mistake to calling carb bowl as bank. So I correct it to carb bowl !!!

If you think all is right, then please perform the clear tube test for each of your carbs, and show us (picture) the results.

hudecheck · « **Reply #5 on:** October 29, 2016, 03:15:38 PM »

Sorry for quite time to reply but I couldn't sooner.. I did this test ad the level seems to be good in all cases, see figs. I am seriously thinking to just basically clog those he'll tubes

flybox1 · « **Reply #6 on:** October 29, 2016, 06:40:14 PM »

Out of the pictures you posted, only the top one has accurate fuel level. The others are too high.

alacrity · « **Reply #7 on:** October 29, 2016, 11:55:59 PM »

It's possible that brass tube has split partly where it bonds into the body of the bowl. A leak here from fuel st the proper level will chase into the tube and look like your level is too high. Ez test. Remove bowls dry thoroughly. Set up on level support so you can see under them (set in partly open vice jaws for example),fill with whatever- I use acetone-- and see if the liquid stays in or leaks out

hudecheck · « **Reply #8 on:** October 30, 2016, 09:43:19 AM »

To flybox1: is it too high? But out of the sketch you proposed the split line between bowl and carb body is still acceptable and this is where is in my case. Anyway I can still lowered it but according the PD46A standard which is 14,5 cm I am so I need to go above the standard like 15cm..Can others heights have influenc to the first one (carb)?

To alacrity: sorry it's a little bit hard to imagine what you mean by this. This test you are proposing.. How should I hold valve rubber tip if there are no bowls mounted?
By the way the brass tube is most probably not splitted since once I remove bowl 1 and replace it it to carb 2 and bowl 2 to carb 1..then carb 2 is the one where leaking through the tubes is occurring.

flybox1 · « **Reply #9 on:** October 30, 2016, 10:41:16 PM »

Yes, yours are too high.
The goal is 3mm below the split line.

KLCruiser · « **Reply #10 on:** November 02, 2016, 09:41:34 PM »

I just had the same problem on my '77 CB750K after cleaning the carbs. I did two things and the issue seemed to resolve itself. First I set all the float heights to spec. And second, the previous owner for some reason had capped the ends of all the overflow tubes coming off the overflow nipples. And it occurred to me that the overflow tubes probably need to breath as gas enters to bowls otherwise air pressure may push it out elsewhere, which it did, same place as in your case. I just pulled the tubes off for now, made sure the overflow tubes in the bowls were clean, ran a guitar string through and then blew them out. Put it all back together and seems to have fixed the problem.

strynboen · « **Reply #11 on:** November 03, 2016, 05:46:39 AM »

fuel height is far to heigh..you are over floting the carbs..its so simpel as that

hudecheck · « **Reply #12 on:** November 09, 2016, 01:53:20 PM »

Hi guys, so I was playing quite lot with this and you were probably right. I took 1st carb bowl off (carbs were in installed position on engine) and just were playing with the height till the moment there was no leaking through tubes. Anyway its strange since manual for PD46A specifies the height 14,5 mm which I precisly did in case of all but you are saying that its too high, which is obvious now. So I will then take off whole carb assembly and set them perhaps to 15 or a bit more milimeters. Thx for support so far. I will keep you posted for others who could be potentialy dealing with this.

Just one strange thing - I have learned that if I have high level in carb of fuel does not necessarily means that fuel will go through overflow tubes but can go through those tubes I am struggling wiht...

flybox1 · « **Reply #13 on:** November 09, 2016, 02:04:11 PM »

If you set your float height with the idea they need to stop overflow, then you run the risk of lowering the fuel level enough that you will be running lean.
Refer to the clear tube test diagram i posted above to double check you have adequate fuel level in the bowls.
If each bowl tests good, you should have zero fuel leakage from anywhere...AND, you'll have enough fuel in the bowls.

Glad you're making progress....just check your work

hudecheck · « **Reply #14 on:** November 13, 2016, 03:49:57 PM »

Well, I gotta say I was not successful in the end

. They were leaking in the end!

So then I set all carbs to 15 mm (instead of 14,5mm) but after some moment of fuel open the inlet tube start leaking again :/. I starting to hate it.

I wanted to ask you. There was again leaking of fuel of in #1 carb so I just set this one even higher - lets say 18 mm and eventhough there was leaking in the end through inlet tube. So the question is - is this flow through inlet tube connected rather to non-equilibrium of heights of all floats to this one or just bad setting of this one float carb #1? I dont understand if this is connected to equilibrium and I set all of those to same level there is this bloody leaking :/. Thx for support and sorry for not that good explanation but its quite hard to describe..

Maybe one good news is that I had very bad idle and after all possible variants of this issue I just yank out pressed in pilot jets and found out that these were after US celaning and all the sprays through still very badly gunked..So after proper setting the floats (hope once) I hope there will be much better idle.

hudecheck · « **Reply #15 on:** November 15, 2016, 12:47:02 PM »

OK guys after some hours of playing around with this issue I just arrived to the point that I just decreased the height of the fuel in carb #1 cca 3-5 mm lower than others unfortunately that was only solution how to avoid this issue of overflowing through the inlet tube - Ive found that was flowing through inlet tube of main jet, emulsion tube respectively. Which is in the end no surprise since this is heading more deeper to the bottom of the bowl.
Maybe one more detail, which has helped slightly - the emulsion tube in this carb was quite loosen so I tighten it and leaking was diminsihed - anyway mentioned decrease of level of the fuel was necessary.

Maybe this help to someone. I will keep you posted if the problem appears even despite this adjustement..

flybox1 · « **Reply #16 on:** November 15, 2016, 12:55:18 PM »

Id certainly keep looking for fix, and not a bandaid to your issue, but if thats what you have to do, please keep an eye out for an overly lean cylinder on the one you lowered (read: check plug color often)

hudecheck · « **Reply #17 on:** November 15, 2016, 02:23:40 PM »

TO fylbox1:
Yes you bet that I will be watching this which I know I have to do so but thx for reminding anyway. I dont like such a "half-solutions" so I will be handling this definitely. I have got contact to one guy who is quite expert in such carbs so I will discuss it with him for sure

.

Right now I have found leaking in oil pump cover during the syncing the carbs

so perhaps bigger issue appeared so not to get bored

Bodi · « **Reply #18 on:** November 16, 2016, 06:09:51 AM »

This is plenty odd. To overflow out of the main jet hole, the bowl has to be pretty much 100% full, well over where any reasonable float setting would limit it.
The top of the overflow brass tube inside the bowl is below the level where fuel would come up through the main jet: I can't think of any way this can happen without fuel also pouring out of the bottom nipple.
You've done everything I would suggest: the clear tube test shows that the float valve is working, you've confirmed that the overflow tube is clear...
A crack in that brass tube would make no difference to the clear tube check. It would cause a dribble from the bottom nipple with correct float level as fuel seeps through the crack.

If the bowl has been sealed - ie the overflow drain and the atmospheric vent (generally though small tees and vent tubes between 1/2 and 3/4) are both blocked - you will get leaking into the throat when fuel is flowing in and raising the bowl level. The pressure has to be relieved somewhere.

Deltarider · « **Reply #19 on:** November 16, 2016, 07:23:26 AM »

Makes me wonder what the fuelline is connected to...

flybox1 · « **Reply #20 on:** November 16, 2016, 07:29:22 AM »

Quote from: Deltarider on November 16, 2016, 07:23:26 AM

Makes me wonder what the fuelline is connected to...

+1
I had to look for it too, Its visible up in the first photo.

Deltarider · « **Reply #21 on:** November 16, 2016, 07:35:56 AM »

Quote

Quote from: Deltarider on Today at 07:23:26 AM

Makes me wonder what the fuelline is connected to...

+1
I had to look for it too, Its visible up in the first photo.

But... that's the vent tube, isn't it? Something else... could it be that the PD carbs - being NOT original for a CB550F2 that had the 069A carbs - are not compatible with the intakes and as a consequence are angled thus that leakage can occur? Just a thought. But first make sure you've connected the fuel supply line to the right nipple.

flybox1 · « **Reply #22 on:** November 16, 2016, 08:09:04 AM »

Its been a few years since ive worked on PD46s, so I cant say for sure, but if it were the vent, there would be an immediate issue with bowls not filling fast enough

Bodi · « **Reply #23 on:** November 16, 2016, 10:25:47 AM »

Plus they wouldn't stop filling. That does look strange but the fuel rail is at the bigger dead-end bung visible at the outside of the body, I think the fuel tee is just really long and it's connected properly. The vent is the smaller undrilled bung?

hudecheck · « **Reply #24 on:** November 16, 2016, 05:09:06 PM »

This what you are saying sounds to me suspicious. I have been also surprised of too much simplicity of this carb from connection point of view in comparison for example cb750 dohc I also have.
I connected like it originally was and believe it's right I hope. Take a look in schematics. Where suppose to be in this case vent? Thx

News:

Author Topic: PD46A carb overflow trough inlet tubes (Read 5939 times)