Another carb question

[algie1100]

Hi All

 

I finely got my weak front braking issues resolved (thanks skydoc) and the bike (90) is running pretty good, but only getting in the upper 20’s in MPG.

Supposedly the cards were rebuild before I bought the bike, but I pulled the air filter to check that the sliders move back and forth during acceleration. It looked like there was gas gushing around on the #1 carb that I didn’t see on the others. I’m a total novice on carbs, but that didn’t look right to me.

A few other symptoms. When starting the bike the RPM’s start out around 400. If I use the choke the bike will die, so I just let it it idle a few minutes and can then ride it. I’ve run several cans of SeaFoam without a noticeable difference.

Any ideas, suggestions would be appreciated.

 

Thanks

Al

[Yammer Dan]

Sync them? Sounds like it could help.

[GeorgeS]

On that carb, drain the bowl, make sure the pump runs fuel thru the drain line.

 

Have you run Sea - Foam for a couple tanks yet ?

 

Maby the Float valve in that carb is sticking open. Sea Foam might, clean it up, worth a try.

[greg_in_london]

Before you take the carbs apart, check the float height - or rather check the float/fuel level. You can get an approximate idea of this by putting your bike on the centrestand and connecting a piece of clear battery overflow tube (use the end without those little slashes in :-) ) to the black pipe at the bottom of the carb.

 

Hold the clear pipe up the side of the carb/diaphragm cover (half way up the side is a casting mark) and loosen the drain screw (a combined flathead/crosshead screw - don't use the flathead mixture screw by mistake).

 

Fuel will flow into the pipe and find a level hopefully about half an inch below the casting mark I mentioned above. Ideally you would run the engine to be accurate here. Do this for each carburettor - if the flooding carb has a higher level than the others, then Bob's your mother's aunt (note for Americans: 'That's your problem then').

 

Yamaha changed the specified fuel level slightly for different models, so I can't be more precise - you'll need to check your manual, and if you do that, you may want to get the right tool, or at least use a glass tube fitted into petrol pipe. For troubleshooting, however, the above should be okay.

 

On a warning note, possibly because faffing with flexible pipe it's difficult to be precise, I'd recommend doing the test a couple of times on different days - it only takes ten minutes and reduces errors ('measure twice, cut once' etc)

 

**************************************************

 

If the above shows nothing, consider buying new needle nozzle o-rings and maybe the gasket for the jet block. If the nozzle o-ring has perished, I understand that you can get extra petrol escaping from the needle/nozzle area.

 

In the jet block itself, black rubber bungs prevent short circuiting of the main jet circuit. You'll have to check these if you take the carbs apart. I'm not sure if they're available, but I'm sure someone will have found a cheaper alternative, in which case, do you have any spare ?????

[Condor]

This is a dumb question, but couldn't you, after draining the bowl, inject pure Sea-Foam up into the bowl and let it sit for a while, and then drain it out??? Maybe a more potent way of freeing up the float valve if that's the problem...

[greg_in_london]

Hmmm... while I can't say that it WOULDN'T help - cleaning out SOME of the jets, if you squirted enough to fill the flat bowl, you would be closing the float and so not penetrating the bit you want to clean - unless it is grit that is holding the float valve open (which would affect all carbs and mean the filter had been removed).

 

Fuel levels shouldn't change much by themselves, but a quarter of a century is a lot of time for little vibrations to make pesky adjustments. I'd make the fuel level check first (it is part of the prescribed Yamaha maintenance schedule, after all...), but it would be a handy time to part drain and refill with seafoam if you wanted to. I presume you'd only treat the suspect one, or the bike wouldn't start again...

[5bikes]

Stuck open float on #1 carb. That's why it will start and run at 400 rpm, Using the choke just totally floods that cylinder and stalls the engine.

But if the float is stuck open my best guess you have other plugged ports that the seafoam can't get thru to clean them out.

Try taking the carb side diaphrams out, easy job and use spray carb in more jets/ports there.

You probably will end up removing the carbs and cleaning many more orifices in the float bowl area.

Did it sit for more than a few weeks at any one time?

Does it idle OK after it warms up?

Does it have power thruout the RPM range?

What is your MPG's?

[CrazyHorse]

I had this problem and it was the main nozzle that the needle slides into had unscrewed itself from the jet block and would actually pop out slightly from the venturi and pour fuel down the cylinder but it wasnt really noticibly popped out. Probably dumb mechanic (me) didn't tight it well enough on rebuild.

[algie1100]

Did it sit for more than a few weeks at any one time?

Does it idle OK after it warms up?

Does it have power thruout the RPM range?

What is your MPG's? __________________

I have 2 bikes and try to ride each at least once a week in the off season and trade the off in the riding season.

 

After it warms up it idles fine and runs fine, but the MPG is only in the upper 20's

 

Thanks for all the replies if I can get this sorted out I think this will be a really nice 2 up touring bike.

 

Al

[Yammer Dan]

unhook line to fuel pump. Mix 2/3 Sea-Foam 1/3 gas. Run thru fuel pump til you are sure carbs are full. Leave sit at least overnight. I would do two nights.