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Petcock or ???

marvinsc

marvinsc

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The bike: 1980 GS750 16 valve engine (not mine)

The problem: Carbs overflowing

The attempted fix: Owner bought another set of "good" carbs, same problem.

Sounds like a petcock issue to me. He is trying to sell the bike for $750 as is. Not gonna happen I don't think but if he goes down enough I might give it a shot. Does my diagnosis sound reasonable?
 
Well it's either the petcock or the carbs.....

Either way....it is fixable...
 
Sounds like a carb issue which quite possiably is being exposed by a leaking petcock. Doesn't really matter which since the bike needs to be serviced anyway and both are easy to fix.

Sorry to rant here but it amazes me that so few people actually service their bikes. First thing that should be done with ANY GS purchase, regardless if whether or not it's currently a problem, is to pull off the carbs and replace all the O-rings. 25+ year old rubber O-rings that live in gasoline should be replaced since they are sure to be hard and brittle - on their last legs. It's a ticking time bomb that can easily be disarmed with a little maintenance.
 
It has been said here many, many times, ...

in order for the carbs to overflow, you must have TWO faults. The petcock must leak and the inlet valves on the carbs have to leak.

Since the problem remained, even after the carbs were changed, I would guess that the petcock leaks and BOTH sets of carbs have problems. :eek:

.
 
The carb inlet valves are designed to seat and seal against the pressure applied by the fuel in the float bowls, not the head pressure generated by 4 gallons of gasoline a foot above them.

When new, they may hold against such pressure, at least for a while. But even though they may seal perfectly fine against the head pressure from the float bowl levels pretty much forever, eventually due to wearing they will not be able to suppress the pressure from gasoline in the fuel tank.

I doubt if there'd be any problems if the petcock were swtiched out. 'Tis possible it would still leak a tiny bit into the airbox if the float levels are WAY high, but as mentioned earlier, easily fixed.
 
The guy says He is firm at $750 or will part it out on Ebay next spring. I would hate to see that happen but I do think he is too high on a bike that is unrideable.

5052-motorcycleside2.jpg
 
marvinsc said:
The guy says He is firm at $750 or will part it out on Ebay next spring. I would hate to see that happen but I do think he is too high on a bike that is unrideable.

5052-motorcycleside2.jpg
Click to expand...
mention the time he'll spend stripping and fees he'll pay going e-bay. i bought my 850 w/ 15k miles for $300. keep in mind there's a better deal out there. leave him your number and be prepared to walk.
 
Griffin said:
The carb inlet valves are designed to seat and seal against the pressure applied by the fuel in the float bowls, not the head pressure generated by 4 gallons of gasoline a foot above them.
Click to expand...

What Griff said. It all boils do to pressure and the lift capacity of the floats. If there is more pressure at the head than the floats and seals have the capacity to hold back, your carbs are going to flood.

Replace the petcock and then clean the carbs...:-\\\
 
I'd pay $750 for a 16V 750 with a sound engine, a title, and nothing but carb problems, anyday. I wouldn't pay more than that, but I'd pay that. especially if it's as cosmetically clean as those photos. Strip of that godawful fairing, and that disgusting luggage and sell those on ebay for $250 and you've got the bike for $500.
 
doctorgonzo said:
I'd pay $750 for a 16V 750 with a sound engine, a title, and nothing but carb problems, anyday. I wouldn't pay more than that, but I'd pay that. especially if it's as cosmetically clean as those photos. Strip of that godawful fairing, and that disgusting luggage and sell those on ebay for $250 and you've got the bike for $500.
Click to expand...


Come get it, 2 1/2 hours West of you on I-24 in Paducah KY. I can get you the guy's contact Information.
 
marvinsc said:
Come get it, 2 1/2 hours West of you on I-24 in Paducah KY. I can get you the guy's contact Information.
Click to expand...

I'm on hold until I finish parting out this RF900. The ole lady has a "1 non-running bike in the garage" limit on me. If it's unsold a month or so from now I may check back with you.
 
Since you won't be watching the Browns on Sunday take a couple and fix the carbs. If anything you can turn the bike over for around $500.
 
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