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Discussion Starter #1
The EX / GPZ have the known problem that if the petcock and the float needle valve fail, the fuel could flow in the combustion chamber and into the crankcase. This I have experienced also :rolleyes:

The solution is also known: make sure the petcock and the float valve and seat are in top condition.

But what I have not found, is if someone has a modification for when one of the above fail, the fuel gets dumped outside the carburetor in stead of in the combustion chamber. Can anybody enlighten me on this?
 

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The carb vent is above the throttle so the overflow runs down to the intake valve.all the vent hose does is cause trouble if it gets plugged or blocked. .

Fog
 

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The EX / GPZ have the known problem that if the petcock and the float needle valve fail, the fuel could flow in the combustion chamber and into the crankcase. This I have experienced also :rolleyes:

The solution is also known: make sure the petcock and the float valve and seat are in top condition.

But what I have not found, is if someone has a modification for when one of the above fail, the fuel gets dumped outside the carburetor in stead of in the combustion chamber. Can anybody enlighten me on this?
@ducatiman has been working on this very issue there is a thread somewhere in carburettors if you wish to look there was some talk of supplying this with a carb set I think.
 

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Discussion Starter #5
Can you link the topic? Somehow I can't seem to get the desired results via the search option :unsure:
 

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Link is in post 4
 

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Discussion Starter #8
Cool, I did not know Ducatiman was also working on this. By change I was working on this issue today with a motorcycle buddy, in the same way. It's actually logical, the casting of the float bowls seem to be prepared for this feature.

What we tried was drilling a hole with a milling machine, with a milling tool of 2.8mm. Than we press fitted a 3.0mm brass tube in the hole. A 40mm tube extends about 10mm above the top of the float bowl.

With water the modification worked perfect, but with petrol the pressfit would weep one drop every few minutes. The petrol seems to be more prone to capillary action.

We pulled the tube out, chamfered the hole a bit, and refitted the tube with a bead of JB-weld. This is now hardening, so we'll know in a week or so the final result.

This does make me wonder what kind of press fit @ducatiman uses. Can you tell me what method you have used?


The waiting game...
 

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The method I used....applied a very light film of solder to the outside/bottom of the tube prior to pressing. Pressed when solder is cold, not hot. My theory...being soft, the solder defers to and allows pressing while deforming and filling any imperfections in the drilled slot.....meanwhile leaving a slight sealing ridge at the very top of the slot. Thus not leaking. I wanted to avoid the use of any adhesive.

To this point I've had no interest from anyone in doing these. Though I've got product on hand if called upon.

Researching (after discovering missing spill pipes from early 70's Honda carbs I was dealing with) revealed cracked tubes (thus "spilling over") are a fairly common phenomena on these oldies. Replacement is documented on Honda forums dealing with applicable older models, though methods vary. YMMV.
 

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Discussion Starter #10
Using an adhesive was also not my preferred choice. We figured that a press fit with -0,2mm on the hole would for sure seal off the connection with the tube. Especially seeing that we did not drill with a conventional spiral drill, but with a 3-tooth milling bit on a milling machine.

Alas, it works but not perfectly. One drop every 10 minutes will still stink out the garage overnight o_O

I'll keep your tip on the solder in the back of my head. For now I'll let the JB-weld set. Than I'll fill the bowl with petrol, and let it just sit in the garage for a week or so.

The next attempt would be with a tighter press fit, maybe with some help of some heat and shrink fit the tube in the bowl.

I'm surprised with the lack of intrest in your modification. Could it be that people don't recognize the danger for the engine in having liquid petrol on the inlet valves and combustion chamber? I've had multiple cracked spark plugs because of that :cautious: Off course that was before refurbishing the carbs 😊
 

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I'm surprised with the lack of intrest in your modification. Could it be that people don't recognize the danger for the engine in having liquid petrol on the inlet valves and combustion chamber? I've had multiple cracked spark plugs because of that :cautious: Off course that was before refurbishing the carbs 😊
I think it's more like people depend on the vac operated petcock and float valves too much how hard is it to turn the fuel off when parked. I do every time even for a 10mins stop. never had this issue.
 

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I have a custom ON/OFF petcock on my EX/GPZ. Turn it on when I ride, turn it off when I park the bike. I don't have a reserve tank anymore but it really does not affect the bike IMHO, I have two trip odometers which makes it a piece of cake. I store an old two stroke race bike with 100 octane gas in the bowl, it has a custom flat side carburetor on it, I turn off the gas and that is it. Every 3 months or so, I kick the bike over, usually it starts on one kick (has stuck clutch plates, but thats another story.) Have been into the carburetor a while back due to eliminating a working/winning combo in favour of trying some dry brake BMW fuel line I had kicking around - I had to remove an inline fuel filter which let some debris get into the the bowl and flooded it out. Upon inspection, I could really not find any offending debris, but I was amazed how clean the bowl was without any porosity or any other nasty surprises due to long term storage with gas in the bowl. You results may vary,
 

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The next attempt would be with a tighter press fit, maybe with some help of some heat and shrink fit the tube in the bowl.
I tried another method and variants... a slight "belling" out of the measured inserted length prior to pressing. The bare brass tubing so soft, I believe it too easily deflected. Thus the solder method was born. I experimented with silver solder, but finally opted for softer, regular old tin/lead stuff. Tubing is quite intact and sealed.
Regardless, I believe the JB weld should hold up, though other options do exist and open to experimentation.
 

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PRC® aerospace sealants were the first elastomeric products capable of resisting deterioration from long-term exposure to jet fuel. Since then, sealants such as PR-1422 and Pro-Seal™ 890 have become acknowl-edged industry standards for sealing fuel tanks in virtually every aircraft in the world.

This stuff stays flexible, Don't know what chance a regular "Joe" type has of procuring it. Never really thought about the tubes before. Cheers
 

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Discussion Starter #15
Sounds like a great sealent, but just as you say, it seems to be hard to get for a regular "Peter" :) Would that stuff also be resistent to ethanol? In aviation fuel there is no ethanol added. To bad there is also still lead added to aviation fuel, otherwise I would like a couple of drums for my bike ;-)

Thanks Ducatiman for the info. What kind of length have you experimented with? I took a piece of tube of 40mm long and pressed it 5mm in the bowl. With these dimensions the tube extends 10mm above the edge of the bowl. In retrospect I'm beginning to wonder if a length just under the main barrel of the carb would be less prone to splashing. Or perhaps the sideways hole like you showed on the Honda carbs? What's your take on this?
 

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PRC® aerospace sealants were the first elastomeric products capable of resisting deterioration from long-term exposure to jet fuel. Since then, sealants such as PR-1422 and Pro-Seal™ 890 have become acknowl-edged industry standards for sealing fuel tanks in virtually every aircraft in the world.

This stuff stays flexible, Don't know what chance a regular "Joe" type has of procuring it. Never really thought about the tubes before. Cheers
Sounds like a great sealent, but just as you say, it seems to be hard to get for a regular "Peter" :) Would that stuff also be resistent to ethanol? In aviation fuel there is no ethanol added. To bad there is also still lead added to aviation fuel, otherwise I would like a couple of drums for my bike ;-)
I'm no expert on jet fuel. I do have forced air heaters that will burn kerosene, diesel, or jet fuel. But if you try to put gasoline in them, it will cause a massive explosion.
Make of it what you will.
 

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I've used JB Weld on the exterior of automotive carbs, so I agree JB will probably hold up. But I suspect a dab of blue loctite would be easier, less messy to apply and also work. I've used blue locktite to good effect on fittings exposed to hot engine oil, but I've never tried it on a fuel system fitting. In their technical data sheet they claim its a sealant as well as a threadlocker. https://dm.henkel-dam.com/is/conten...Blue-242-Carded-Tube-0.20-fl-oz-2018-04-09pdf
 
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