Fuel leak. Dagnabit!

[jmink427]

I couldn't for the life of figure this out till now... I had fuel leaking out of the right carburetor vent (overflow). With the petcocks turned off. I knew that the left petcock leaked but not the right... This has been driving me crazy.. I thought I would look in to it today a little closer..Well I think I found the problem... There are two fuel line that go between the carburetors.. Didn't know they existed there till I really looked.... So the left petcock leaks and the fuel run between the carburetors through one of these lines or both to the right carburetor where the needle and set are bad and leaves a puddle on my shop floor... Does this sound right? I'm going to order rebuild kit s for the carburetors and petcocks tonight and maybe a 30 tooth rear sprocket....... will the stock length chain work with a 30 tooth or will it be to long?.....

 

[xjwmx]

I got a petcock rebuild kit from these folks.

http://www.z1enterprises.com/

I think they were recommended by bluebikerblan, who seems to know his rubber (seals), maybe by trade. Haven't installed it yet. It says made in Japan, which is good. If you buy from there, pay attention to their information about their shipping.

If you have to take a link out of the chain, it's easy without special tools. Just remember to measure once and cut twice, or is that....? You can't cut it back on. Remember that.

 

[bluebikerblan]

I couldn't for the life of figure this out till now... I had fuel leaking out of the right carburetor vent (overflow). With the petcocks turned off. So the left petcock leaks and the fuel run between the carburetors through one of these lines or both to the right carburetor where the needle and set are bad and leaves a puddle on my shop floor... Does this sound right?:confused

Yup....there's a crossover line between the carbs so that regardless of the petcock source the fuel can leak out of either or both carbs....

BS 38 type I (584) 76' & 77' ...at least if this type leaks, they do so externally through the vent tubes and hoses. (not into the carb throats & possibly the crankcase). [The two tubes hanging down are vent tubes, there are two more on the bottom of the float bowls]

BS 38 type II (2FO) 78' & 79'....throat vents (the two larger vent holes) can unfortunately leak into the throat and thereby into the crankcase.

BS34 BS series type III (3G1) also throat vented but fed by a single fuel line into a "T" which also serves as the cross-over supplying fuel to either/both carbs. Petcock open or failed can also leak through carb throat vents into the crankcase.

Point 1....seems to me to be that one shouldn't count on his carbs serving as a Petcock!

Point 2....an excellent case can be made for manual petcocks in good condition! Blue

 

[xjwmx]

BS34 BS series type III (3G1) ... Petcock open or failed can also leak through carb throat vents into the crankcase.

When the '34 leaks it seems to leak out of an air jet and back into the air box instead of getting into the intake. one less worry.

ps - if you want both the sureness of manual cutoff and the convenience or safety of vacuum operation, you can add an inline 1/4" valve. It's on the rack next to the external fuel filter

 

[jmink427]

My has both the vent tubes and the crossover going between the carbs and then individual ones running done from the bowls.....How would this vent? Is this not right? My bike is a '75.

 

[sreimer]

You can also cheat the needle and seat by using a drill bit by hand and very gently twisting it backwards in the seat and massage the needles with your fingers and some carb cleaner. Work about 90% of the time

 

[Ccrider]

Off subject question.
Did u add that choke or enrichiner linkage? I have the same carbs but don't have the choke linkage like u have?

 

[5twins]

The side vent hoses vent the area above the fuel in the bowl so a vacuum does not form and stop fuel flow. The nipples on the bowl bottoms are for overflow.

 

[bluebikerblan]

Off subject question.
Did u add that choke or enrichiner linkage? I have the same carbs but don't have the choke linkage like u have?

75' carbs were 447's unlinked with an enrichener circuit (choke) on one carb only. They did have the crossover tube link between carbs and two manual petcock fuel feed lines. External vent lines out the side & bottome vents just like the type I's as 5 twins explains. Two throttle control cables also....

Sorry, this is the only photo I have of a pair of 75's but your's should look like these?

Enrichener circuits were on each of the paired and linked carbs starting with the 76' and after models of the Mikuni BS Series. Best, Blue

 

[bluebikerblan]

Not to beat a dead horse but here's a couple of diagrahms from "The Carb Guide
(of 5 Twins & Grizld) that I took the liberty of coloring a bit so I could follow a bit easier which gives a bit of a suggestion as to how things vent in cut away view. Credits to TRG and probably a lot of others too! Hope nobody minds my coloring up the scans???
Homey can't photo shop. Best, Blue

 

[jmink427]

75' carbs were 447's unlinked with an enrichener circuit (choke) on one carb only. They did have the crossover tube link between carbs and two manual petcock fuel feed lines. External vent lines out the side & bottome vents just like the type I's as 5 twins explains. Two throttle control cables also....

Sorry, this is the only photo I have of a pair of 75's but your's should look like these?

Enrichener circuits were on each of the paired and linked carbs starting with the 76' and after models of the Mikuni BS Series. Best, Blue

So my carbs should only have one crossover tube on the lower side ports and the upper side ports should just be run down like the ones on the bottom of the fuel bowls... Mine are tied together like the lower crossover ones... hisa means I should have four tubes from the carbs running down behind the engine.... 2 overflows and two vents. I also have fixed my petcock leaking problem temporarily when shut off...Should have a new one in a couple of days..... Here is a pic of it... Needs to be on "I fixed it dot com".

 

[bluebikerblan]

You got it.....just like the linked 584 set above add two fuel feed lines on the vertical inlet tubes and two more float bowl overflow vent tube on the bottom ports (These are
often joined to a small Y connector so that there's just a single line to drain float bowl
overflow drain lines.....should be good to go. Best, Blue

 

[jmink427]

well, alright then.. Thanks Blue...

 

[XSLeo]

Jmink, Those carbs look an awful lot like my 76-77 carb set.
The float bowls have a metal barb for the overflows, mine are plastic.
The enrichener bodies look like they are brass. Mine are alloy.
Some of the other parts look like brass plated.
Perhaps they are not XS650 carbs. Or mine aren't.
Leo

 

[bluebikerblan]

Jmink, Those carbs look an awful lot like my 76-77 carb set.
The float bowls have a metal barb for the overflows, mine are plastic.
The enrichener bodies look like they are brass. Mine are alloy.
Some of the other parts look like brass plated.
Perhaps they are not XS650 carbs. Or mine aren't.
Leo

Leo.....the reason that the carbs pictured above in a post by Jmink (with the photo shop red circle) look like 76' 77' 584 type I's is.....that's what they are. That's a picture (1 of 3) posted earlier in this thread by me. [Jmink just blew that photo up and repeated it for the photoshop red circle].

The enrichener's are alloy also btw, the "brass color" is paint....part of an Oldskoolcarbs rebuild I had done. Pictures are also by Oldskoolcarbs. The carbs are actually OEM to a 77 D I think. Blue

 

[XSLeo]

The thing that threw me was the brass color and the float bowls, the metal overflow barbs. On the three set of Bs38 carbs I have they are plastic.
Leo

 

[bluebikerblan]

According to the Australian site's history, the float bowl overflow nipples changed from plastic to brass in 76'. As you know they were eliminated altogether and vented through the carb throats with the type II's (2F0) of 78 & 79. My best guess is that all this "can't be vented or overflow drained externally" must have been driven by the US EPA standards fuss of the 70's. Same constraints which forced the crankcase gas vents to be fed to the intake airboxes.

http://www.xs650.org.au/XS-TX650 Carburetor Evolution.htm

 

[jmink427]

Alright got the petcock changed. That job was a little more work than I thought it was gonna be.. Some PO had put one of them on and used JB weld as a gasket... So I got all that of and cleaned up and I see why know... I guess when they repainted the tank they got out of control with a DA sander or something and gouged the surface where the pet cock mounts... So fired up the ole' Syncrowave 250 put some the material back where it was suppose to be... I checked everything with air and soapy water all looks good. Just took about 2 hour longer than it should have... Some people just shouldn't be allowed to work on machines!!

Before

After

 

[sreimer]

Very VERY MUCH AGREE!!!!! They do make fuel injected bikes these days that run just like a car. No carb or electrical problems to deal with and if new enough even come with a warranty! Why would you want to mess around with a 30 year old bike if you have no tools and no experience or aptitude?

 

[jmink427]

Very VERY MUCH AGREE!!!!! They do make fuel injected bikes these days that run just like a car. No carb or electrical problems to deal with and if new enough even come with a warranty!

What would be the fun in that? I would rather fix stuff!