help me with my 1981 seca 750

so i recently picked this Yamaha seca wasn't running
so i cleaned out the carbs and it fires right up
problems i have a across are its leaking gas from a hose that comes from the air box and it runs fine but after a while it stars to idle really low till it completely shuts off

anyone have any idea on where to look to fix this problems ?
or anyone live here is SLC who has experience with this bike ?

so where does this go and why is it leaking gas ?


this is were it comes from


thanks

 

at least one of your float needles are stuck open or your float height isn't set correctly and your petcock isn't shutting off correctly for you too be leaking gas from your air box. The hose from the airbox should connect to your crank case (its a vent for the crank case) but you don't want to hook it up until you fix the leak or you will end up with gas in your oil. have you checked your valve shims and done a running synch and carbtune or plug chops to set your mixtures.

 

leaking gas usually means a stuck or mal-adjusted float in the carbs. that hose is probably the airbox drain. you probably have gas in your oil now, too.

 

i did not do anything of this
how bad is it when there gas in the oil?
is it as simple as to drain it and replace it with new oil?

 

Gasoline dilutes oil so yes, it's bad to run it that way. You said you cleaned the carbs but that's a 31 year old bike and needs new float needles among other things. To get that bike running how it should there's a laundry list of things that need to be done, all of which you can/will get help with on these boards. If you have a fair amount of mechanical aptitude and patience it's rewarding in the end.

Getting the gas out of the oil is as simple as changing it, but don't run it again until you fix the leaking float needle or needles.

Welcome and good luck.

 

sound good man i will remove the carbs again ans do it right with new replacement parts its was just a pain in the ass getting those air boots back on

 

When you buy a "Sitter", ... there's usually no two ways about it:

You got some work to do.
We'll be happy to help.

Knock-off what you need to do, ... one thing at a time.

Here's Job-1. The most important thing for you to do.
Get a Genuine Yamaha Factory Service Manual. The "Factory Book."
Specific to your Bike.

This is also Job-1. Call it Job-1A or 1B.

Until you get the FLOODING issue resolved, ... Install a Shut-Off Valve right next to your Petcock.
Costs 6-Bucks Online

http://www.amazon.com/Briggs-Stratton-6 ... B0038U3JKM

Costs $11.95 at a Lawn Mower Shop or ACE Hardware.

Stop the flow of Gas.
Badda-bing; badda-boom.

Very simple insurance against a Crankcase full of gas.
OPEN during running or tuning.
CLOSE it when you stop.

If you go to the Drug Store after you buy the Gas Valve and buy a small bottle of Black Nail Polish, ... you can "Paint" the whole Red area of the Valve and the two miniature hose clamps, ... Black ... and make the Fuel Shut-off Valve virtually disappear.

Here's what it can look like. This one's on my bike.

 

i will start tearing it apart and will update with photos so i can get help and learn since i know nothing about bikes

 

You'll get better at getting those boots on, trust me. Also I believe the aftermarket float needles are 1mm longer than stock so you will need to reset your float levels. And even if they aren't you need to check the level anyway. Don't try to shortcut this, it's a downward spiral if you do.

Lots of good tutorials here:

http://www.xj4ever.com/

Also the FAQ section on these boards are awesome.

If you put you general location in your profile you might get lucky and another member might be close and able to help.

 

ok so i took the carbs out now anyone know what is the float height on xj750 ?

 

Wet set them. Follow the link I posted above. Should be 3mm below the carb body,

 

You can save a lot of time by picking the winner of the Clear-tube test and setting the remaining three to that "Measured" height.

I made a Float Height Tool by gluing a Toothpick to the Slide on a Machinists Ruler.
Color the Toothpick so its easy to see.

After selecting the Carb with the Correct Height; "Measure" the HEIGHT frpm the Body to the Tip-top of the Floats with the Tool.

Use that Height to set the remaining three Carb Floats too using the Tool which is set to the Height of the Correct one.

Be sure the Tool is "On-the-flat" and the Rule is square.

Repeat the Clear-tube test to verify the accuracy.

 

ok will try my best but honestly i am lost lol
need to start doing some more reading
will take pics and hopefully you guy can point things out

thanks guys

 

http://www.xj4ever.com/


this is awesome dude i see what i did wrong lol

 

Here is the link I was referring to:


http://www.xj4ever.com/setting%20fuel%20levels.pdf

You don't need such an elaborate set up as in the picture, just be sure the carbs are level. I just had mine on the workbench and used a small level to make sure they were level. Then use some sort of a portable gas tank. I used a small gas can with a hose running to the fuel pipe on the carb assembly. Works best with two people.

Again make sure they're level.

 

upside-down floats?

 

yeah the one on the left side was upside down



ok you guys so i come back to the first topic i cant seem to find where this hose goes too
there already one in into the crank case but what about this one

 

I just looked on my bikes and it appears to just be a drain line, it runs on the back side of the drive shaft

 

yeah kind of figure thanks man !!


so i adjusted all the floats and ran great but after a little while once it was warmed up it started to idle low till it eventually dies anyone know what to do next ?

it turns back on after it dies
sometimes with a little bit of throttle

 

The Mixture Screws might need to be raised -- JUST A NUDGE.

Visualize the Hand of a Stop Watch.
One complete TURN = 1 Minute = (60 seconds).

Yon may need to add but 3 or 4 Seconds of Richness.
A "Tweak"

 

yeah man thanks man i turned it about one and a half and sounds pretty good

also i have a oil leak i believe its from the oil pan does the whole exhaust come out are they bolt on or welded?

also i wanna replace the spark plugs my question is does it have to be a Yamaha spark plugs or can i just put any that fit ?

 

Yamaha does not manufacture Spark Plugs.
Yam isn't in the Oil Business; either.

Until such time as you have the Engine "Dialed-in" and running just right; go to any Auto Parts Store and get NGK, Bosch or Champion Spark Plugs.

Removing the Exhaust can try the patience of a Saint.
Before you embark on removing the Exhaust, ... pinpoint the leak.
The Exhaust is Bolted-on.

Your Drain Plug may be leaking.
The Oil Level Sensor could be the source of the leak.

Treat every single Fastener you have to remove with penetrating oil.
Those Fasteners are SOFT!
Prone to seizing.
And would rather Break before getting taken-out..

 

^^^^^^^^^
thanks alot man i did not know that
so what kind of motor oil should i do a oil change with 10-40?
how do i replace the oil filter ?

i will look closely where the oils is coming from so far i know its on the left side by the gears

 

was also wondering are all bikes really hard to push while in neutral?seems like my rear tire is stuck or are they just really hard push because of the weight just wondering ?

 

put it on the center stand in neutral the rear tire should spin freely both directions if not check your brakes and bearings. same with the front

 

Its the weight, it won't be like pushing a grocery cart