can't get this 250 to start

[Oaklandish]

my brain is racked... this is the 8th pregen 250 I've tried to restore and this one has me stumped.

valves are in spec
spark plugs are new and have spark (I tested each one on the outside of the cam to see if it was actually getting spark)
new gas
I've swapped the clutch and kickstand sensors with some from an operating bike
carbs have been cleaned and I've tried two different sets
compression is good
motor turns manually and it turns if attempting to start in gear (I have the bike on the center stand and the wheel spins when cranking in gear)
new battery
I've also swapped the cdi into another bike and it works
new oil and filter

when I hit the starter it seems to crank normally but never ignites. I can hear it trying to ignite when I crank and give a little throttle.
I feel like this has to be something little that I'm missing...
any suggestions?

[Motofool]

Originally Posted by Oaklandish

...........
I feel like this has to be something little that I'm missing...
any suggestions?

Have you verified that fuel reaching and filling up the bowls up to the specified level?

[TnNinjaGirl]

Air leak in carb boots?

[Oaklandish]

Originally Posted by Motofool

Have you verified that fuel reaching and filling up the bowls up to the specified level?

yes. I drained them today to make sure the new gas is getting to the bowls and drained them again for that very purpose

Originally Posted by TnNinjaGirl

Air leak in carb boots?

I'll check tomorrow...

[Motofool]

Originally Posted by Oaklandish

yes. I drained them today to make sure the new gas is getting to the bowls and drained them again for that very purpose..........

.......... up to the specified level?
You need to connect a U-tube to the drains.
It is common to accidentally alter that level during manipulation and cleaning.



Also, for start ups, these engines are sensitive to the idle regulation.
Of course, you cannot adjust it now, but you can check that the butterfly valves are at least a hair opened.

If really stubborn, you can remove the air filter and spray some WD-40 or carburetor cleaner or starter fluid down into the airbox while cranking up.

Use an auxiliary car battery rather than imposing too much cranking to the little one in the bike.

[Oaklandish]

Originally Posted by Motofool

.......... up to the specified level?
You need to connect a U-tube to the drains.
It is common to accidentally alter that level during manipulation and cleaning.



Also, for start ups, these engines are sensitive to the idle regulation.
Of course, you cannot adjust it now, but you can check that the butterfly valves are at least a hair opened.

If really stubborn, you can remove the air filter and spray some WD-40 or carburetor cleaner or starter fluid down into the airbox while cranking up.

Use an auxiliary car battery rather than imposing too much cranking to the little one in the bike.

both of the carbs I'm using work fine in other bikes...

[jkv45]

I'd confirm ignition (I know you said you checked for spark, and have it, but at this point...) by spraying Starter Fluid into the carbs while cranking.

If you have ignition under compression you will get some popping. If you don't, you have an ignition issue. If you do, you most likely have a fuel issue.

First make sure you have a strong battery. Voltage while sitting should be 12.7-8V (fully charged). 12.5V is 75%, 12.0V is 25% charged. While cranking you should still have around 12.0V.

[Oaklandish]

Originally Posted by jkv45

I'd confirm ignition (I know you said you checked for spark, and have it, but at this point...) by spraying Starter Fluid into the carbs while cranking.

If you have ignition under compression you will get some popping. If you don't, you have an ignition issue. If you do, you most likely have a fuel issue.

First make sure you have a strong battery. Voltage while sitting should be 12.7-8V (fully charged). 12.5V is 75%, 12.0V is 25% charged. While cranking you should still have around 12.0V.

it's 12.75.
this is my 8th pregen (12th total) that I've restored. I check for things like that first.

[jkv45]

Originally Posted by Oaklandish

it's 12.75.
this is my 8th pregen (12th total) that I've restored. I check for things like that first.

OK - so does it pop or not with starter fluid?

[Oaklandish]

Not sure if you'd consider it a pop. It makes the normal crank sound deeper like its on the verge of igniting. Similar to cranking with the throttle open

[TnNinjaGirl]

Is there any restriction in the exhaust?

[jkv45]

Spraying the Starter Fluid in is a little tricky with an airbox - did you lift the carb slides (EDIT: and open the throttle plates) when you sprayed it? It would be a lot easier to get a good shot into the cylinders without the airbox in place.

You should get some amount of popping and short running if any amount of Starter Fluid reaches a good spark.

[Foxrider64]

Is it possible the coils are reversed? If they are going to the wrong cylinders the bike will desperately want to fire but will only burp because the ignition cycle is not timed with the piston position.

[MR2Aaron]

Maybe a dumb question, but you've checked to make sure that the cams are properly timed, right?

[alex.s]

Originally Posted by Foxrider64

Is it possible the coils are reversed? If they are going to the wrong cylinders the bike will desperately want to fire but will only burp because the ignition cycle is not timed with the piston position.

the wiring harness doesn't allow it when used with stock coils. the lengths just wouldn't work out. you would need to modify the harness where the two split off at the mid-section on the right side and swap them there. otherwise the left side coil wiring would never reach the right side.

it sounds like the crank position sensor isn't working. it's the little green connector with two wires leading from your stator. it should read between 100-300ohm resistance. too high or too low reading means a short or break and will keep the cdi from triggering spark.

you can also check the voltage going to the coils. it should be V+ until the cdi triggers, in which case it drops to V- and the field collapses into the spark plug. so if you don't see voltage when not cranking, or don't see the voltage drop when cranking, you know what the issue is.

[Foxrider64]

Originally Posted by alex.s

the wiring harness doesn't allow it when used with stock coils. the lengths just wouldn't work out. you would need to modify the harness where the two split off at the mid-section on the right side and swap them there. otherwise the left side coil wiring would never reach the right side.

I've seen some strange things done to harnesses so I figured I'd ask. Worth a shot right?

[extremez31]

I am having the exact same issue with a 94' I am building. Mine starts via push start but it takes 3-4 attempts. and once the bike warms up it starts on its own.

I just rebuilt the carbs because I thought that could be the issue.

[cuong-nutz]

@Oaklandish, any updates?

[Oaklandish]

Originally Posted by Foxrider64

Is it possible the coils are reversed? If they are going to the wrong cylinders the bike will desperately want to fire but will only burp because the ignition cycle is not timed with the piston position.

I'm sure the coils are not reversed because they are on two separate sides of the bike. I don't think polarity matters either but I have them hooked up stock.

Originally Posted by MR2Aaron

Maybe a dumb question, but you've checked to make sure that the cams are properly timed, right?

I checked when I inspected the valves, I use TDC instead of visually guessing when the valve is decompressed.

Originally Posted by alex.s

it sounds like the crank position sensor isn't working. it's the little green connector with two wires leading from your stator. it should read between 100-300ohm resistance. too high or too low reading means a short or break and will keep the cdi from triggering spark.


you can also check the voltage going to the coils. it should be V+ until the cdi triggers, in which case it drops to V- and the field collapses into the spark plug. so if you don't see voltage when not cranking, or don't see the voltage drop when cranking, you know what the issue is.

I will give the sensor a read tomorrow.
I never checked the coils after I ignited the plugs outside the case and visually saw spark because that satisfied my concern in that area. I'll check them as well. it seems like I had spark outside the motor and now I don't.

[alex.s]

maybe theres something wrong with the exhaust you are using? you sure it doesn't have a rat or something in there?

[n4mwd]

First off, its always the carbs. Unless its something else - like the battery.

As to why you had spark and now you don't, its probably a loose wire because of all the work you've been doing. Or it could be that all the cranking has drained your battery so that the ECU wont fire under load.

The coil polarity does matter, but not enough that it wont start.

I hate carbs. It looks like a new EFI group buy may be taking place real soon if you hate them too.

[n4mwd]

Originally Posted by extremez31

I am having the exact same issue with a 94' I am building. Mine starts via push start but it takes 3-4 attempts. and once the bike warms up it starts on its own.

I just rebuilt the carbs because I thought that could be the issue.

Sounds like a bad battery. See my Ninja battery blog.

[extremez31]

After two hours of tinkering I finally got the bike to start on its own.

Here's what I did

I took the plug boots off the wires, I saw that they were a mess so I cut them down slightly and reattached them.

I replaced the plugs with the colder start versions CH8 I believe

I then attempted to crank and heard the bike attempt to start but it wouldn't

I verified the idle air screws were at 2.5 turns and decided to turn it down to 1.75 turns. Then attempted to start and I got more popping but again bike wouldn't start.

I kept adjusting the idle air down and it kept getting better until I was at full lock. The bike wanted to start but still couldn't.

I verified I was at full choke and I was. I came to the realization I'm getting too much air. I took all the preload off the butterflies using the idle adjuster and the bike fired right up.

Has anyone needed to fully tighten the idle air screws to get a bike to start?

Now that I got it to fire, I feel better so its time to start tearing it apart.

[n4mwd]

Originally Posted by extremez31

I replaced the plugs with the colder start versions CH8 I believe ... I took all the preload off the butterflies using the idle adjuster and the bike fired right up.

I recommend putting the correct plugs back in so you don't burn a piston.

Based on what you found, it sounds a lot like your carb boots are leaking. Either they aren't on right, aren't tight or might be cracked. They are rubber so cracking is a definite possibility. Also, the clamps squish the rubber to the point where they can't clamp tight. If the boots are not cracked, etc, then wrap the ends tightly with CLOTH electrical tape X 5 windings. This gives more diameter and allows the clamps to clamp tighter.

Did I mention that I hate carbs?

[jkv45]

Originally Posted by extremez31

I replaced the plugs with the colder start versions CH8 I believe

Just for reference, the stock plug is a NGK CR8HSA. Not sure what the difference would be if you had a CH8 - but it could be a different reach - which you wouldn't want.

A colder plug (CR9 - higher number for NGK) is for high RPM running or when you are making more power than stock.

A hotter plug (CR7 - lower number for NGK) is for consistent low RPM/low load running.

Stick with NGK in the stock heat range to avoid any problems.

http://www.ngksparkplugs.com/tech_su...2.asp?mode=nml

http://www.ngksparkplugs.com/techinf...tnumberkey.pdf

[n4mwd]

Also make sure you are running NGK and not Champion or some other brand.

Your life will be a lot simpler if you stick with NGK for this bike.

[extremez31]

Please forgive me. The plug that was in the bike was a CR7, I replaced it with the colder plug CR8 not CH8. My memory gets worse as I get older.