Yamaha Maxim problem

[Scarbo]

I own a 1985 Yamaha Maxim 700 with an inline 4 cylinder engine. I've owned this bike for 22 years and it's been a great bike that I still enjoy riding.

Recently, I cranked it up and was letting it warm up. Before I knew it, it had dumped all of the gas in the tank on my garage floor. I've taken off the gas tank and checked all the fuel lines for any cracks or breaks, but don't see anything wrong.

I would appreciate any ideas of what might have caused this.

 

[seventyss]

Sounds like a problem with the hoses, if they are old and brittle they will crack and split. How long has it been since you started the bike? It could be a carb issue, maybe a stuck float, if that's the case the gas would flow out of the overflow hoses attached to the bottom of each carb. Also make sure that the screw that you open to drain the float bowl is closed all the way on each carb. You might be able to see what is going on better if you watch with a flashlight and a mirror. More info would be helpful.

 

[blkredlinedrvr]

Sounds like either the tank or one of the lines has a hole or one or more of your floats are stuck open. Does the Maxim use a vacuum operated fuel valve or regular on/off/res? I've never had luck with the vacuum operated fuel valves working for me.

 

[canyonman]

Does the Maxim use a vacuum operated fuel valve or regular on/off/res?

The 82 650cc I had did. I remember the gasket around the fuel valve on mine started leaking once.

If it was only leaking while running I would suspect a carb issue

 

[Canadian FJR]

Float is holed or sticking.

Canadian FJR

 

[meosborn]

My first bike was an '85 Maxim 700. What a great bike. Cracked intakes finally inspired me to move on.

 

[Scarbo]

Thanks for your replies. I checked all the fuel lines and didn't find any cracks or breaks. And I checked the drain screws on the float bowls and they were tight. This bike has an on/prime/reserve fuel cock. It tends to leak a little (mmmmm, kinda like it's owner).

So, it must be a stuck float. This has been such a dependable bike that it's never been in the shop, except to get new tires.

Well, thanks for your help.

 

[seventyss]

Sometimes a stuck float can be freed by tapping the float bowl with the handle end of a screw driver. I would suggest draining the bowls so the stuck float will be able to drop freely (hard to advise you on how hard to hit it, I will say it would be best to hit at the top of the bowl where it is attached to the top part of the carb). If the float is stuck you should see fuel coming out the bottom drain of the float bowl. There's probably an overflow tube in the bowl with a hole in the top that will drain fuel if the float is set to high or stuck. This is separate from the bowl drain screws but will be channel fuel out the same nipple. I would also suggest draining each bowl to see if there is any junk in the fuel. If there are any rust flakes coming from your tank it could keep the needle from seating completely. I don't know about Yamaha carbs, but I had a problem with gas leaking out of the fuel pipes that deliver fuel to each carb on a Honda CB750. The O-ring seals start leaking when they get old and hard. Is gas running down the outside of the float bowl?

 

[charismaticmegafauna]

This bike has an on/prime/reserve fuel cock.

You've just described an 'automatic' (vacuum controlled) petcock -- which would eliminate the external fuel lines (as the problem); if, as you said, the bike leaked out all its gas after you started it and while it was running?

You see, it takes engine intake vacuum to open that petcock (wnen in the normal, "run", position) -- otherwise, the petcock 'automatically' shuts itself off.

Could be? time for carb o'hauls -- needle & seat assys. Remember too: today's fuel blending may not be anything the designers' had in mind when they thought-up the plastic for the carb-floats -- many (plastic) carb-floats get heavier over-time.

Good luck.

 

[Scarbo]

I had started the bike and was letting it warm up, and was getting my helmet. The gas dumped out so fast that it had to have come from an overflow hose. The bike does have a fuel filter, but crud in the tank, and the lines, could be part of the problem.

I'll try draining the float bowls. No fuel has been leaking out of the bowls.

I'm sure it's probably time for carb overhauls, which is beyond my limited shade tree mechanic abilites. Unfortunately, the only Yamaha dealer in town doesn't work on bikes more than 10 years old.

Thanks

 

[03HiYoSilver]

You may want to Treat the Gas with SeaFoam first for it may clean out the varnishes in the Carb system.

Good Luck with your fix.

 

[charismaticmegafauna]

I had started the bike and was letting it warm up, and was getting my helmet. The gas dumped out so fast that it had to have come from an overflow hose.No fuel has been leaking out of the bowls.

Seems you've narrowed it down to the fuel lines between the petcock and the carbs (or the fuel fittings on the carbs where the fuel lines attach?).

Yamaha dealer in town doesn't work on bikes more than 10 years old.

Ouch..., why's dat...?

My FJR will soon be 8 years old -- a couple more years and they'd refuse to look at it...?

Thanks

You're welcome

 

[Leskid]

I had started the bike and was letting it warm up, and was getting my helmet. The gas dumped out so fast that it had to have come from an overflow hose. The bike does have a fuel filter, but crud in the tank, and the lines, could be part of the problem.

I'll try draining the float bowls. No fuel has been leaking out of the bowls.

I'm sure it's probably time for carb overhauls, which is beyond my limited shade tree mechanic abilites. Unfortunately, the only Yamaha dealer in town doesn't work on bikes more than 10 years old.

Thanks

If it didn't drain until the bike was running, that suggest the vacuum-operated petcock is functioning correctly. If it all spilled out on the floor as fast as you report, I'd have difficulty believing a single stuck float would cause that (as quickly as you report). Can you pop-off the tank and check to see the fuel supply hose is still attached to the carb rail assly? On my seca, it's between carbs 2 & 3

If that had somehow been popped loose, the fuel would just gush straight from the tank to your garage floor.

 

[Duezzer]

Pull your tank and add a length of hose so you can see whats happening ( gas and vac )

Fill tank, put vice grip or something you can pinch the line gas line off with

Fire up the bike see what and where the gas goes

Good luck

My guess is a stuck float my 550 Maxim did it alot

Carb cleaner helped