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Discussion Starter #1 (Edited)
Hello,
I just got a Yamaha V Star 250 off of Craigslist. Pretty low miles and in crazy clean condition. It will start up for a second and then die. It does turn over but as soon as I release the start button it dies. The bike does not start if I have the engine kill switch set to off.

Here is a video I made of the start up.

To note what I have done so far:
  • removed and cleaned carbs
  • Drained and added fresh oil and new oil filter
  • new spark plugs
  • fresh gas (no ethanol)
  • tested the sidestand switch
  • tried bypassing sidestand switch
  • tried bypassing kill switch (at handlebar)
  • checked the fuses.
  • Charged the batter and load tested it.
I feel like is something to do with the kill switch or sidestand just because of the way it stop right after turning over, but I don't know. Any ideas on what else to check? I am afraid it might be electrical.
 

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are you pulling the choke all the way out to start it

and are you sure the choke cable is connected to the carb mechanism?
 

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Discussion Starter #3
are you pulling the choke all the way out to start it

and are you sure the choke cable is connected to the carb mechanism?
Check and check there. It will only turn over if I have the choke all out so I know its working, plus I check to make sure the carb end of the choke was fully seated and screwed in. When I pulled the carbs, I inspected and tested the choke.
 

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the thing missing from your did-that list is the fuel pump

these bikes have one because the bottom of the fuel tank is lower than the float bowls, so the bike would run with a full tank of gas, but not all the way to empty

pull the fuel line off the carbs, turn the ignition on, and the fuel pump should run, at least for a few seconds, and spray gasoline out the hose.

If the fuel pump is not working, then unhook the line from the petcock and make sure it letting gas flow when you turn it on, then connect that line directly to the carbs, and if the tank is full, the bike should run.

if the direct connect fuel line does not make the bike run correctly, then I would think the ignition is dropping out when you release the starter button for some odd reason. An inline spark detector would let you see if the plugs stop firing when you release the starter button.
 

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It is either fuel, air or spark. Breathers clean? Choke stuck. Manually fill the carb with gas and see if it runs longer. A good squirt of gas in the sparkplug hole will run the engine longer than it is if you have spark.
Not sure the electrical setup but the equivalent of putting 12 volts to the coil should ensure spark.
 

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Discussion Starter #7 (Edited)
It is either fuel, air or spark. Breathers clean? Choke stuck. Manually fill the carb with gas and see if it runs longer. A good squirt of gas in the sparkplug hole will run the engine longer than it is if you have spark.
Not sure the electrical setup but the equivalent of putting 12 volts to the coil should ensure spark.
Breathers as in the air intake/airfilter? And by choke stuck do you mean stuck closed or open? I'll go try your suggestions and report back

Edit: Just tested the fuel pump again and yes it is pumping gas to the carb.
 

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the other possibility is you have really bad vacuum leaks, maybe the boots are not sealed to the carbs

if you have a propane torch you could turn it on m(un lit) and direct the gas flow at the base of the carbs, or where the boots connect to the heads - if the bike starts while you are cranking it like this, you have a vacuum leak. Carb cleaner also works, can make a bit of a mess though - but it should evaporate off.

another possibility is the timing is off (someone was messing with the timing chains) or something is wrong with the cams or valve adjustments

the fast way to check for that is to do a compression test on the two cylinders - if the compression is low the bike will stumble and will not run correctly.

Did the previous owner give you any history on the bike? Any previous problems? From the work you already did it sounds like it sat for a long time either with no gas in the tank or the fuel broke down and fouled out the carbs.

Have you looked in the tank with a flashlight, see any rust in there?

if the fuel filter was plugged you would get no flow from the fuel pump.

If the fuel filter is missing, and there is rust in the tank, it will get sucked into your newly cleaned carbs and block the passages again.

one more thing, the carbs should have a throttle position sensor, its used to advance the spark as the throttle is opened - if that is not connected or not reading correctly, the spark timing will be way off.
 

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Discussion Starter #9
1. Checked the boots, both are tight. The top of the top boot doesn't have a clamp or anything but seems tight
2. I did a compression gauge test and as it was cranking about 4 turns got to 30psi.
3. Bike is super clean, always garaged, no rust, inside of tank is clean, 0 rust. Did sit for years without being used. That's why I pulled the carbs.
4. The fuel "filters" in the tank? I didnt see an external filter anywhere.

as far as cams or valve adjustments, I don't know if that is something I can do. Maybe I need to just take this bike to the shop..

Where is the the throttle position sensor on this bike?
 

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the compression on both cylinders is only 30psi after 4 revolutions of the engine?!

it should be 150 to 180 after it stops climbing (might take several revolutions to stop increasing, but the first compression stroke should throw it up to 90psi or more.

30psi is nothing - if you did the compression test correctly you have a serious mechanical failure, like the timing chains both broke or are missing, or completely out of place from where they should be, or your valves are stuck open, or there are no rings on the cylinders....

?!?!!!
 

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30 psi? Will not run with that. Make sure tester is tight in the sparkplug hole and the throttle is wide open when you turn it over for 6 to 8 cranks. If compression is 30, that's your problem. If you are using the cheap Harbor Freight tester, don't trust it. I had one telling me 15 psi on my new running lawn mower. You need at least 90 psi. If it really is 30 psi you have a timing issue or broken/stuck valve and least likely is a piston/ring problem. If both cylinders are reading 30 then I would bet it is out of timing.

Sent from my VS996 using Tapatalk
 

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I agree with bucfan, 30 psi is such a serious failure I would:

1. make sure the compression gauge is working properly, throttle open all the way, crank several revolutions...
2. do a wet test after the dry test if the pressure is still very low, to see if its valves or rings that are bad
3. test both cylinders

if the low pressure results are the same, Im afraid this craigslist experience is going to set a new golden rule for buying used bikes: If a bike is not running then always do a compression test on the engine. Bring your own battery or jumper cables if you need to. If the owner wont let you then walk away.
 

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It only has 198 miles?! I would bet money on carb issues if it has set for any amount of time. Did you clean ALL parts? jets? Carb atomizer (tube that runs through the center of the carb)
 

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You know what i read these threads and you guys helping out with problems and you guys are awesome! I hope i never need your help but i am glad you are there if i do. Thanks bucfan11 KCW and Les just off the top of my head.
 

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Discussion Starter #15
It only has 198 miles?! I would bet money on carb issues if it has set for any amount of time. Did you clean ALL parts? jets? Carb atomizer (tube that runs through the center of the carb)
Yes I cleaned the carb pretty thourogly.
As for the psi being low, that is what I though so, yeah that would do it. I did another test today and while the psi does climb, it takes quite a few cranks just to get 60.
Also, yes thanks to everyone for weighing in.
I am afraid I might need to just take it to the shop now. I don't know if I can competently do any engine work other then light maintenance.
 

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Good luck and keep us informed. Just checking to make sure you did the compression test correctly, if not readings will be off.

How do you perform a compression test?
The process to perform this test is really easy. The engine should be HOT during testing. If you are working on a non-running motorcycle, you can test while cold, however values can be 10-15psi lower in some cases.

Turn petcock to OFF position and run motorcycle until it runs out of fuel. For fuel injected models, remove the fuel pump fuse.
Remove all spark plugs.
Remove ignition fuse, if equipped.
Hook up compression tester to a cylinder. Use a dab of grease or Vaseline to lube the threads and O-ring on adapter. This will prolong O-ring life.
Hold the throttle all the way OPEN.
Crank or kickstart the motorcycle until the needle stops climbing. Usually 3-4 kicks.
Record the result and compare to value in service manual.
Repeat steps 4-7 for all remaining cylinders.

Readings should be similar to this:

Engines will need at least 100psi to run, and they might not run well at this low on compression. Most healthy motorcycle engines will have 120+psi. I would investigate further with any readings under 110psi. Readings on all cylinders should be within 10% of each other.
 

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sorry if I did not give enough info on doing the wet test

the first time you check the compression, if the pressure is low it could because of valves leaking (stuck open, not timed correctly, or burnt on the face) a blown head gasket, a hole burned thru the cylinder (from running lean and hot), a cracked head or cylinder, or worn, broken or missing rings.

If you inject about a teaspoon of oil into the spark plug hole, and run the test again, if the pressure comes up, then its worn rings or highly rusted cylinder walls keeping the rings from seating, because a little bit of oil will only improve the seal between the rings and cylinder wall, it wont fix any of the other listed failures - so if the wet compression is much higher, then all those other things on the list are eliminate

You have to inject the right (small) amount of oil - do not take an oil bottle and drizzle some in - if you put in too much the oil will fill the entire combustion chamber, and when the cylinder tries to rotate past top dead center it will hydro lock, and could cause damage.

BTW, compression testers should really come with a valve-stem attachment thing so you can put it on an air compressor and validate the gauge is reading correctly.
 

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With only 198 miles I have a hard time believing it has engine failure. Does this engine have a decompression valve for easy starting? If so, you compression reading will not be accurate. Before I took it to a shop or tore into the motor I would find out. I am still leaning on carb issues.
 

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I just looked at my XV250. It has only one carburetor, so it is unlikely you cleaned the "carbs". It has a fuel pump, which is not electrical but vacuum operated. That means it will only work when the engine is turning. I didn't see a TPS, and since the bike is carbureted I don't think it has one. My guess is that the idle speed is set way too low, so the engine dies as soon as the starter quits turning it over.
 

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^ thats a good question for CatManFoo: did you try giving it some gas as you release the starter?

If the compression test was done correctly then 30 or 60 psi is too low for the engine to run, and there is a mechanical problem.

If the compression test results you got are wrong and you take it to a shop, they can do a compression test with their equipment and confirm its low. If they find its not low then something else is still wrong.

test equipment failure is a rare but possible problem - if you check something with a meter for example, and it says your battery is at 72V, you immediately get a different meter and check it again, because that would be an impossible reading on a 12.5V battery

but if your meter is broken and it reads 4V.. then it could be 4V (dead battery) or it could be a bad meter... in this case your compression gauge could be faulty

and its weird but at this point that would be a good thing!
 
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