idles then dies with slightest throttle up, valve timing?

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650creature

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Hello all ,

starts, idles ,dies with slightest throttle up. Having trouble understanding why the book tells me to gap the tappets on cyl.1 when the cam lobes are up? Makes no sense to me , when the lobes are down on the right cyl., garenteeing that both those valves are closed as well.?
Yet, thinking i was understanding the words wrong, i adjusted the gaps when the lobes were up (on cyl.1 l.h. side) and promply had the kick starter kickback , should a took notice because not long after it started the carbs got blown off the engine.
Spark plugs are black, thing is running crazy rich ,they get dirty fast. Had a timing light on , said i was advanced, but when i retard the timing to line up the marks she dies.
Installed pma,pamco combo, did my best to transfer TDC mark, seems pretty close by feel. 77' d model
any help is much appreciated, thanks.
 
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You may want to back-track slightly and re-install your old rotor and stator.

Then do the valves, cam chain and timing.

The bike will run on the battery, no lights, for quite a while without a charging system. This will give you plenty of time to gets things working. Just keep charging the battery with a 2 amp charger as needed.

You don't need timing marks to do the valves.
1- rotate engine counter clockwise until the intake opens and closes
2- then with a straw or thin long screwdriver down the spark plug hole, gently continue rotation the engine until the piston comes to top dead center
3- at this point both the intake and exhaust valves should be loose for which ever cylinder you are working on. If not go back to step 1.
4- adjust both valves
- now do the same, steps 1 to 4 for the other side

Adjust cam chain, should have 1 to 2 mm of travel, anything less is too tight.

You do need timing marks for the ignition. So install the old system temporarily and once set it should never change. Saving the old system will always allow you the option of rechecking.

Now go back and clean the pilot circuit of your carbs. Lots of article here on carbs, Check the XS650 Tech section.

Good Luck.
 
thanks for the reply brian902.,

I have just completed doing all of that, also, after it acted the same, i dissengaged the cam chain and rotated the crank 360 thinking that that somehow had something to do with it. Nothing changed.

This problem has been a real challenge to figure out. I have gone through the valve timing many times, but it's still dumping excess fuel into the cylinder. It was idiling last night, lined up the fire marks with timing light, and still dies with slightest throttle crack. Took out the plugs and they were SOAKED.

I know it is getting way too much fuel and i'm convinced it's a valve timing issue.

Carbs are leaned out significantly. Speaking of carbs, could my float bowl have been damaged when the carbs got blown off?
 
Check to see your floats are set to the correct height and they are not leaking, gas in the float is a bad thing.

Bikes that idle and die when the throttle opens up are a sign the idle/pilot circuit is dirty.

Good carb section in the XS650 Tech section at the top of the page. Go there for carb type info.
 
Cleaned carbs, floats are good @ 25mm, needle clips in the middle, size 25 pilot jet with pilot screw 1 1/2 turns out, 128 mains.,
Gas is still dumping into both cylinders; seems to idle untill plugs get drowned.
TDC mark is lining up with FIRE mark, when timing light is hooked up.
Checking if choke plunger is somehow stuck though I doubt it's the whole problem, maybe a contributing factor.?
 
Idle timing spec isn't so it fires at TDC on this bike, it's supposed to fire 13°-17° BTDC.
 
did u eventually gap the tappets as per the manual?T that is important.
 
Thanks for the replys,
Tappets are gapped .002 intake .006 exhast. Tdc mark (on pma) is matching up with fire mark on sticker ,which comes before the tdc mark on the sticker.
Pamco timing plate is fully retarded.
 
Brian902 said:
Check to see your floats are set to the correct height and they are not leaking, gas in the float is a bad thing.

Bikes that idle and die when the throttle opens up are a sign the idle/pilot circuit is dirty.

Good carb section in the XS650 Tech section at the top of the page. Go there for carb type info.
Click to expand...

Pilot circuit seems clean, no dirt or peices or things., I am getting this black residue building up on and around the piston/mixing chamber though, it shows up very quickly after the bikes starts to idle.
 
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Valves are .004 and .006 but some go with .003 and .006.

Your intakes are too tight.

TDC for valve adjustments is just to make sure the piston is at the top when on the compression stroke. Any where near the top on the compression stroke is close enough for valve adjusting.

Easiest way to find the compression stroke; watch for the intake valve to open and close, the next time the piston comes to the top is the compression stroke, can be verified by placing finger over the spark plug hole and feeling the compressed air. Both valves will be loose and can be adjusted. Using a straw you can just feel when the piston is at it's highest position.

Easy eh!
 
From my Haynes manual: Inlet: xs650D ....0.05mm (0.002 in) Exhast: ... 0.15mm (0.0059. in)
Feeling the piston through the sparkplug hole , I know the piston is at TDC when both valves are closed on one cylinder and the exhaust valve open on the other cylinder ( with the intake just starting to open). It almost looks like its opening too soon???, part of the reason why I am getting blackish residue in my carbs so fast.?
Loosening intake valves to .004.
 
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Bike will not start with jet needle clip in the middle. But as soon as I moved the clip all the way down (letting in less gas) it would start .humm......
 
Moving the clip down raises the needle and lets in more gas. Raising the clip lowers the needle which makes the midrange leaner.
 
Okay here's the update; the engine will not start after I move the needle jet clip up at all. I will kick till my leg's sore, then pull the plugs and they're dry.:wtf: ,seems I am getting too little or too much fuel . The pilot jet is nominal at 25, and the bike is not responding to the idle scew. Anyone ever have a similar experience??
 
I think that if you move the clip up, this is lowering the needle to a point where they block the gas passage.
I think at this point, you have the tappet clearances and it was running at the beginning of the thread, I would put the carbs back the way they were when it was idling and look into some timing and electric things.
 
The bike was not starting so I replaced the size 45 pilot jets, and returned the jet needle e-clip to the lowest notch.
First kick starts up and idles for a minute.
Plugs are wet and when I turn the throttle a good spray of air/fuel gets blasted the wrong way through the carbs.
It has to be valve timing.
Re-aligning crank,cam and components.
 

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