after rebuilt the carbs idle at 5k rpm

[mason79]

Hello Fellow Xsirs,

I recent bought a 79f standard from a one owner, shows 48k miles, it was full dress.

He advertised it for 1500 bucks, it was not running right because it was parked indoors in southern California in the 1998 and in October 2005 he decide to bring it back;

The short of it is; he had a dealer Kreemed the tank, new petcocks, carb holders, carbs rebuilt, trucked it home without really riding it, and parked it for another 6 months at which time he sold his home and bought a motor home to travel the states.

He is out of time and spent a whole week hassling with the dealer to stop the gas flowing to the air box and engine, while the engine was running 300 bucks later SOS.

It did not want to idle; and would stall the whole time it pumping gas on my legs.

they deliver the bike to my home, this was 2 weeks ago for 700 bucks.

The carbs came out, and here is what I found

1) #1 Diaphragm, off positioned, and not sealing; but they do desend at different rate, fixed they still drop differently.
2) # 3 float was filled with gas, fixed, this was the problem with the air box floods
3) found 150 mains, books says, 137.5 I made the change
4) pre synced the carbs as per this web site, using a bread wire.
5) mixture 1.25 turns out

So here’s my problem guys, and I do appreciated your help on this.

Engine starts and warms quickly, but the engines want to accelerate to 5,000rpm or so by it self right away, when I disconnect the vacuum lines to the petcocks it gets a little better, idles at 1500 rpm, turning the idle screw does little as well..

There is one thing I can’t figure out where is should go is a small tube/hose leading from the crankcase this tube exits just behind the starter connection, and this tube/hose is around a foot long and has a 2” bracket with a hole in it, does anyone knows where this goes and if it is the cause of the problem, please help!

[DiverRay]

Mason79,
The "bread tie" will get you started, but you will have to adjust some of the other screws on the carbs. I'll try to give you some information, in the order it should be done.
1. have a shop manual nearby, and read through the adjustment procedure.
2. check that #2 carb has the vacum line going to the advance unit under the left cover on the crank.
3. you DID change the engine oil? if not, you need to do it!!
4. back the idle screw out, and make sure the throttle cable isn't binding or holding the throttle open.
5. reset the idle (mixture) screws to 2 turns each.
6. rest the idle screw to one turn past contact, as a start.
7. restart the bike, let it warm up a bit and star tthe final adjustment from there.
don't forget, you need to check the valve adjustment, cam chain, and timing as well. they all affect the carbs, and the way the bike will run.
Good luck, and I hope it is running soon.
Ray

[mason79]

thanks i'll try tommarow

oils was changed, and some was placed in the cylinders, cough.

cam chain was done

valves seems quiet

how about that hose behind the starter connection, do you know where it goes? and thanks

[remccool]

Hopefully you didn't do what I did when I did the bread tie adjustment. I put it all back together and the idle was super high (about 6k), I had forgot to adjust the main idle (located on the airbox side of the carbs, between 2 & 3) from the all the open position used to set the butterfly valves using the bread tie method. I adjusted the Main idle adjustment and then it idled ok. Just a thought......

[DiverRay]

Sorry, forgot about the hose. It is a breather hose. It should be mounted on one of the airbox screws. The breather is for the middle gear assembly. You can just run it up and loosly tie wrap it to the frame, if need be. Just be sure it isn't someplace that water will drain into the hose.
Ray

[mason79]

thanks everybody,

i lied i took the carbs out today, again

no, the the idle adjustment i backed it down all the way,

2 turns out mixture, all the way close, 1/2 turn out, all the same.

could it be worn needle jets?

pilot system? stuck choke system?,

funny didn't do it before when it was flodding

let me ask, do you connect the fuel lines to the 2 upper ports or is that for the vacumm line which is connected to them now.
any more suggestions?

[John]

Your carbs, being 79's have two sets of T fittings between the carb sets.The lower fittings is for the fuel inlet, and the upper set of T's are for the bowl vents. They should be routed to the small nipples near the top front of the airbox, on either side of the big crankcase vent tube. If you have the fuel lines attached to the upper set of T fittings, then you're just dumping fuel into the carbs from the vent circuit. The small vent hose on top of the engine, near the crankcase vent is for the middle drive. It should be routed up under the fuel tank, and held by a bracket that bolts to the front mounting bolt for the airbox.

[DiverRay]

on the Standard, the fuel lines connect to the bottom ports, that face the airbox, and the vacum lines connect to the top, or front ports. the vacum lines should be connected to the intake boots on # 2 and #3 carbs, and the vacum for the advance unit is on the #2 carb itself.
Ray
You can look at the online parts cataloge at the Yamaha site, and see how things are supposed to be connected. It does help sometimes.
http://www.yamaha-motor.com/sport/parts/home.aspx
Ray

[mason79]

thanks again xsirs,

okay everything is connected fine then,

has anyone expereinced this problem of the idle climbing to 5k?

when i upplug the vacuum to the petcocks it goes to 2k, and i

know the flow to the bowls is stopped.

i'm thinkin this leans it out, i set the floats leaner than it was,

could it be a the pilot circuit,

this has been a crash course on fussy carbs to say the least

any more suggestion?

the carbs are off the bike now

[TopCatGr58]

Hey Mason,

Welcome to carb hell!!! One thing that sticks out to me is that you stated that they REPLACED The PETCOCKS, not just rebuilt them!? Are you sure they used vacuum controlled petcocks required by the Standard, or did they perhaps put on SPECIAL petcocks that supply fuel thru both ports, and don't use vacuum to make them flow!?!? The vacuum lines go directly to the intake boots, and IF fuel is leaking from the petcocks, then it's getting sucked into the intakes, which could contribute to the elevated idle/throttle when the vacuum lines are connected!?

But, also, when you disconnect the vacuum lines from the petcocks, are you plugging the lines or just leaving them sucking air?? Have you checked the ignition TIMING? Wondering if when connected, the increased vacuum might be applying too much vacuum to the advance mechanism ?

Remove the Pilot Jets, and make sure they are the ones with several holes in them, NOT SOLID WITHOUT HOLES. IF solid, they are the wrong type, and too rich! Also, does it have the proper pilot jet tower plugs in place? If not, also too rich getting fuel directly thru bowl instead of thru the shared port in the MAIN JET TOWER!

Again, make sure the vacuum advance is connected to the #2 carb BODY PORT, not the intake boot!! Let us know what you find!
T.C.

[mason79]

Great,I don't feel alone knowing the XScessive heavywieghts are splattering their grey stuff for me, without high-sideing it.


in the prepurchase state, it would want to stall from the flooding, the only thing i can think i did different is the float levels maybe 3/32" lower/leaner.

and the mains from 150 to 137.5 is top end stuff.


the petcocks have run, prime and reserve and the vacuum lines are clear plastic(i could see), no fuel direct to the intake runners, the tank is off to the side on run with no leaks, i suppose this is proof enough the diaphram holds shut.


they are sucking air, so i leaned it out right?

no chance to check timing, first flooding and now wild revving. not a perfect enviroment for a t light.

the advance line is connected to the carb body, thanks

wouldn't a maxed out advance top out at 2 to 3 thousand rpm?

i will look at the pilot jets now,

but what are tower plugs?

thanks

[mason79]

pilot jet caps are the screws covering them right? well i got them. going to the carbs, will let you all know and thanks a bunch for helping me keep one on these monsters on the road instead of the heaven.

[mro]

No load, and as engine warms up rpm keeps climbing?

lean condition?

pilot needle, spring, washer, o-ring.
no or worn/damaged o-ring can increase idle
damaged/worn needle ??? vac leak(s)???

Had similar prob when I got my 80G, but went through the carbs as posted here, then made a vac gauge to sink carbs. Got the parts from MikesXS. Just new gaskets and needles


mro

[TopCatGr58]

Originally posted by mason79
thanks everybody,

i lied i took the carbs out today, again

no, the the idle adjustment i backed it down all the way,

2 turns out mixture, all the way close, 1/2 turn out, all the same.

let me ask, do you connect the fuel lines to the 2 upper ports or is that for the vacumm line which is connected to them now.
any more suggestions?

Mason, Just reread this, and I thought John addressed this, but the UPPER T fittings on the carbs are VENTs, they are NOT TO HAVE ANY VACUUM hoses attached to them. Just connect a hose to them and leave them open to air!! The only vacuum lines with actual vacuum in them should be to the 2 petcocks and the vacuum advance! IF vacuum lines are attached to the vent holes, it could be pulling fuel thru it!?

Since you have the carbs off, instead of using a bread stick tie, use the small holes in the top of the carb body where the butterflies close, and set them so that the edge of the butterflies are just partially covering the same hole to bench synch them. Then turn the main idle screw so that they all close. Also check your throttle cable for proper slack, make sure the throttle body isn't hanging on the ring clamps that hold the carbs or filters on!
Let us know!
T.C.

[Ken Talbot]

Originally posted by mason79


no, the the idle adjustment i backed it down all the way,

2 turns out mixture, all the way close, 1/2 turn out, all the same.

Hang on a second, Mason, the screws that you're talking about as being 2 turns out or some other amount are NOT idle screws. They are pilot air screws. Your idle is controlled by a single screw located down low between carb #2 and carb #3. You might have to get down on your knees and look up under the bank of carbs to see it. It has a large round head about 5/8" in diameter that you can grip with your fingertips. This is where you adjust the idle speed. The bread tie pre-sync is guaranteed to give you an excessively high idle speed because it sets the butterflies open a crack. At proper idle, the butterflies will be completely closed and fuel will be supplied by the low speed circuit only.

If this is not your problem, you might have no slack in your throttle cable, and might have been trying to adjust it with the adjustment at the top end of the cable. That adjuster is only for cable slack, not for idle speed.

????