83 Petcock leaking at ON, no vacuum tube

[JsWang]

Hi All,

My 83 Maxim did not have a vacuum tube attached to the petcock when I bought it several months ago. It ran, however I'm not sure how well it did since I have no reference for comparison. I rode it for short distances to the gas station and such a few times. There have been several times when strong gas smells were present when it was stored in the garage, and it was suspected that the culprit was a stuck open bowl in the carb. However, after draining the tank, and then later on cleaning the carbs, while putting the carbs back on, it was noticed the petcock is leaking at 'on' position. But it only leaked above a certain fuel level in the tank. I now think the petcock is the primary culprit. I will boil the carbs later however.
Sorry for the bad grammar.


Can someone help me diagnose the issue.
Was the petcock converted to gravity feed?
-I plan to take the petcock apart, how would I tell if it was?
-How would I fix the leak if it was?
-Should I convert it back to vacuum feed? If so, how?

Thanks

 

[Lou Ranger]

I think our fuel systems are gravity feed no matter what kind of petcock is installed.
What the vacuum operates is the tap - i.e. the vacuum opens a valve so that gas can flow down into the fuel line to the carbs. This would mean that the vacuum counteracts some sort of passive system (a spring??) which shuts off the tap when the engine doesn't run and there is no vacuum.

If your vacuum hose isn't even hooked up, then either the spring has weakened, the seal no longer seals, or the petcock you have is a conversion to a manually operated one.
If the later, then you have to shut off your gas every time you shut off your engine.

Another thing I have read on here is that the vacuum operates on just one line even though both carbs have an opening for a tube. On one carb, the opening is capped off and is meant to be that way. Presumably, if you have a replacement manual petcock, both openings will be capped?

Perhaps if you posted a picture of each carb and the petcock, someone who is familiar with both will be able to help more than I.

 

[JsWang]

Another thing I have read on here is that the vacuum operates on just one line even though both carbs have an opening for a tube. On one carb, the opening is capped off and is meant to be that way. Presumably, if you have a replacement manual petcock, both openings will be capped?

Perhaps if you posted a picture of each carb and the petcock, someone who is familiar with both will be able to help more than I.

By 'each carbs', do you mean each cylinder? Because the fuel line goes to the carbs, and the vacuum lines are attached to the engine. I will post a picture later today.
As far as I know from searching online and on this forum, I have a stock vacuum actuated petcock. It has Res, ON, and Pri. Right now, I can't shut off the petcock flow if the tank is filled up above a threshold leak level. The gas flows on both On and Pri; however, the flow rate at Pri is much faster than at On. Your comment about the weak spring tension with no vacuum tube sounds likely, but that would also mean the bike was ALWAYS flooding when it was shut off?

I'm just confused.
If the petcock is converted to gravity feed, then the On position should act as an Off switch. But I remember always riding at On, and the seller told me to use Pri only at start up.
If it was not. The bike should not run without a vacuum tube, if the petcock is functioning properly. Is it just rust clogging the spring-pushed vacuum-actuated valve? Could it be keeping the valve semi open, and allowing fuel to flow when the engine is off?

I plan to take the petcock apart this weekend. I'm more curious on how to identify what was done to it and what is wrong with it once i take it apart.

Thanks

 

[Lou Ranger]

By 'each carbs', do you mean each cylinder? Because the fuel line goes to the carbs, and the vacuum lines are attached to the engine....

No, I mean the carbs. The vacuum line goes from the black tube up to the petcock not to the engine. See the photos below - red arrows.

The petcock is not converted to gravity feed. There is no fuel pump so it is always gravity feed. If yours leaks with a full tank, it sounds like the weight of the column of fuel above is enough to overcome the spring (or whatever it is) that normally shuts off the flow in the absence of vacuum. The fact that it shuts off the flow if the tank is nearly empty indicates that the petcock is still functional but needs the part that applies pressure replaced or serviced.

 

[JsWang]

Oh. We are talking about the same thing for the tube. I consider that port on the boot a part of the engine, since it is bolted to it; engine intake, carb outlet, same thing. But on mine, are both plugged up. See pictures.

Ok fine. It's always gravity fed. But ours is supposed to be vacuum actuated open, rather than manual open (aka, prime).
Wordings aside, if the bike did not run on vacuum tubes, should I just restore the spring's elasticity and run the bike on prime?

I'll know more hopefully once I get it apart on the weekend.

Thanks

 

[Maxim-umm]

Sounds like it's rebuild time for your petcock. When you take it apart pay close attention to how the parts are aligned inside. Specifically the diaphragm. There is a little "port" that should face a certain direction. (sorry I can't be more specific, I did mine almost three years ago) If I get a chance I'll take mine apart today and take some pics since my bike is in pieces at the moment.

 

[JsWang]

That would be really helpful. thanks

 

[Lou Ranger]

Definitely yours is set up for no vacuum operation since both nipples are capped off. I have never had a petcock apart so I cannot help you with the mechanics unfortunately.

But I have talked to a lot of bike sellers who try to minimize their bikes' failings to buyers. I will bet that the PO had his petcock start to fail and he closed off both vacuum connections and then worked it like a manual - relying on the petcock spring to close off the flow and then turning it to PRI or RES when he wanted to go somewhere. He probably only filled the tank half way before each ride so that at night when he parked it, it wouldn't leak.

That's probably why your seller told you to use Pri only at start up. He was likely trying to hide the fact the fact that he had to do this cockamamie work-around in order to demonstrate the bike to you and still not have fuel dripping on the floor when you were deciding whether to make an offer on it or not.

I looked at a nice old bike just the other day and there was gas dripping. Guess what? It put me off totally and it was hard to focus on the fact that the rest of the bike maybe was pretty nice. Especially when he was having to make sparks with jumper cables in order to get it started. LOL

PS - recommend you invest $3 in an in-line fuel filter (like my 1st photo above) so any detritus in the tank will not get into your carbs

 

[JsWang]

Thanks for the inputs, the PO comment makes sense now you speak of it that way.

I know~ I know~ get a fuel filter~~~ lol I see that comment everywhere on this forum.

I already got a pkg of 5 off of ebay. Was planning on install them once I determine and get the appropriate line clamps. I think I will install them now anyways. Btw, are the filters from ebay okay? or is it that much safer/better to get one from the local hardware/moto store?

Thanks

 

[Lou Ranger]

I know~ I know~ get a fuel filter~~~ lol I see that comment everywhere on this forum ... Was planning on install them once I determine and get the appropriate line clamps. I think I will install them now anyways ...

I worried about line clamps until I actually got the filter and saw the one-way "fishscales" on the tubes. I installed it without any clips over a year and 13,000 kms ago and nothing has budged and not a drop of leakage.

I'm still on my first one so your pack of 5 ought to last at least 65,000 kms if Milton gas is just as clean as mine

 

[JsWang]

SWEET!! I'll install it together with my petcock assignment this weekend!

 

[JsWang]

Ummm... need help guys...
So I took apart the petcock.. I'm dumbfounded by what I found. Pictures Attached

No spring, no vacuum suction part, no rubber stud seal.

Any recommendations from any of you?
I plan to go to home depot and see if they have some kind of rubber that I can put in there...
Is there a hole that's perpendicularly drilled inside the main gas hole? Is that the reserve gas flow hole? If so, I'd have to somehow plug both of them, but with the ability to remove the plug at a later time in order to properly repair it if I wanted to.

Thanks for any advice you might have.

- JW

 

[Lou Ranger]

I've never seen inside a live tank or petcock, but from what I understand, both fuel tube inlet holes are in the brown plastic tower that goes up into the fuel. The reserve fuel tube's inlet is lower than the regular "ON" tube's inlet so it can take the last couple of litres out.
But unless you have all the internal petcock parts, you won't be able to choose one or the other and you might not be able to shut off the flow of gas when it's turned to "OFF" - unless you buy one of those in-line shut off valves - or keep the tank near empty so there is not a heavy column of gas above the open line.

If the petcock assembly itself is leaking and you just want to do a temporary repair until the rebuild kit arrives in Tuesday's mail, how about a square piece of rubber (like inner-tube material) with 4 corner holes so you can simply screw the petcock plates together and seal the join? In effect you would have an open path from the tank to the carbs and maybe they could overflow (?)

Sorry, I just don't know for sure. Hopefully another who does will better advise.

 

[JsWang]

Well here's what it's SUPPOSE to look like.. My front, and the casing look pretty much the same as the one in the video. Except the back innards are all missing. The gaskets, seal, and spring are all not there. Just a gasket layer made out of I-dunno-what.
I wonder how it even NOT leaked at all when I took the tank off the first time...

 

[JsWang]

Found kind of a hack solution.

Got some Rubber engine vacuum port caps. Cut down to a size where it's slightly longer than the length needed, so there is some compression to hold down the cap slight in the cavity when the case is closed; serving the same purpose as a spring. Shoved the front end into the petcock main hole, nudge the back end into the groove on the casing so it pushes the cap straight down.
Hope this lasts, I shall see.

Only downside I see is. As far as I can tell, when the petcock is in PRI, it draws from the reserve port. So I guess I don't have a reserve range anymore.

Right now the petcock holds, however the in line filter is leaking..I'll have that sorted out soon hopefully.