corsa won't start

[bfowler]

Hey everyone! So first off the build:
Polini corsa
24mm polini carb with 112 main 38 pilot (brand new)
Naraku black manifold (brand new)
PG short exhaust
8.44:1 gears

Just can't seem to figure out why my scooter isn't starting. I built this scooter a while ago and it ran well for a couple months and then it all of a sudden decided it didn't want to start up anymore. I know scooters need spark, fuel and compression in order to run so I went and did some checks. First off I did a compression test and compression is at 120 psi with throttle wide open. Then I did a visual check for spark and I can see a spark coming out of the spark plug when I ground it to the engine case. Finally I went and checked for fuel. Carb fills with gas when I kick it over and I also tried choking the carb with my hand to start it up and my hand gets wet with gasoline so I know I have fuel. So we have fuel spark and compression but it still won't start up. Trouble starting can be caused by an airleak so I went and built myself a leak down tester. Pumped it to 7 psi and sprayed it down with some soapy water. No bubbles around the base gasket or head gasket areas. The only bubbles I saw were on the Naraku intake which is a bit sad for me since I bought it to replace the CT manifold and hopefully not worry about it leaking. Pics below. Also put on a fresh exhaust gasket and added some high temp hondabond. I am lost and any help is much appreciated!

[MrJumps]

Have you trid to see if the spark is consistent? It may spark then miss for a few sparks then spark again. Maybe go lower idle jet?

Thats strange, if spark is consistant its not eletrical and if it gets fuel to the bowl it should start. 120 compression is good, those leaks shouldnt keep it from starting. I found a bike started better with an airleak. But yeah thats weird, have you changed plug? Sometimes they spark but in the bike they act weird. I would throw a fresh plug in it, and use the kick started and give it heavy standing kicks. Not the regular throw down starting just good enough kicks strong heavy kicks. It should start right up if not you either have flooded it from a massivly large main jet or you somehow have a broken ring or something that is causing it to not run but still show compression.


Also out of intrsst how much did that compression tester run you?

[bfowler]

Have you trid to see if the spark is consistent? It may spark then miss for a few sparks then spark again. Maybe go lower idle jet?

Thats strange, if spark is consistant its not eletrical and if it gets fuel to the bowl it should start. 120 compression is good, those leaks shouldnt keep it from starting. I found a bike started better with an airleak. But yeah thats weird, have you changed plug? Sometimes they spark but in the bike they act weird. I would throw a fresh plug in it, and use the kick started and give it heavy standing kicks. Not the regular throw down starting just good enough kicks strong heavy kicks. It should start right up if not you either have flooded it from a massivly large main jet or you somehow have a broken ring or something that is causing it to not run but still show compression.


Also out of intrsst how much did that compression tester run you?

Compression tester or the leak down tester? (The picture is the leak down tester that I made) Compression tester I got from oreilleys for like $25-30 I think, was a while ago. I was originally using a BR8HIX plug but I didn't have any more lying around and I had some BR9s left over so I threw that a fresh one in and it still didn't want to start up.

pretty sure 7 is too high. I seem to recall 3-5psi. You will blow out seals, and gaskets. I've never seen a naraku leak, but the pressue has to go somewhere at that psi. I just read to not go over 6, and most reccomend under 5

I wonder if your timing is off? did you mess with the flywheel? make sure the naraku gasket is in place also.

I remember reading that you should use 6-7 psi when doing the leak down test. Checked both crank seals after I did the test to make sure I had everything in place and all seems to be well. Naraku gasket is in place. As far as flywheel I didn't do anything besides take it off to split the case and then put it back on when I put the cases back together. Really confused why my bike won't start.

[MrJumps]

I was talking about how much to make the leak down tester.

By chance do you have multiple flywheels or have you ran the motor with that setup before? The af16 and af18 flywheels are difrent. I just saw another member with that issue recently. His bike was getting all what yours is but it would not start.

But yeah ive never seen a Naruku leak so far thats a first for me.

I am very intrested in why it wont start. Do you have a scope to look at the piston and walls? If your pipe plugged up do you feel puffs from it when its turning over?

Anyway I hope these ideas help I am throwing darts but this is really strange for sure. Hopefully we figure this out soon.

[bfowler]

I was talking about how much to make the leak down tester.

By chance do you have multiple flywheels or have you ran the motor with that setup before? The af16 and af18 flywheels are difrent. I just saw another member with that issue recently. His bike was getting all what yours is but it would not start.

But yeah ive never seen a Naruku leak so far thats a first for me.

I am very intrested in why it wont start. Do you have a scope to look at the piston and walls? If your pipe plugged up do you feel puffs from it when its turning over?

Anyway I hope these ideas help I am throwing darts but this is really strange for sure. Hopefully we figure this out soon.

Leakdown tester was about $25 I think. $15 for the pressure gauge and $10 for the various other stuff like the hose, clamps, teflon tape and the t connector.

And no this is my only flywheel. Same flywheel that it ran previously with. Keep the questions coming really want to figure this out

[Rip_City_Spree]

Did you clean the jets to make sure there is no obstructions? What is the idle screw set at on the carb? I ran nearly an identical setup except with a pg long andi think I was running a 34 pj or close to it. Did you try putting some premix in the spark plug hole the try it? My corsa started with all kind of air leaks.

[bfowler]

Did you clean the jets to make sure there is no obstructions? What is the idle screw set at on the carb? I ran nearly an identical setup except with a pg long andi think I was running a 34 pj or close to it. Did you try putting some premix in the spark plug hole the try it? My corsa started with all kind of air leaks.

The jet I used was brand new. I used to use an oko carb so I had to use pilot jet and main jet were a little bigger. I did do a visual check before installing and I can see a light all the way through on the jets. The idle screw is set so that the slide on the carb is all the way down. When I installed the throttle cable I adjusted it so that at no throttle the slide is all the way down and at max throttle the slide is all the way up. And then idle screw adjusted to make sure the slide is all the way down. Is this correct? I'll try to put some premix in and start it up and see what happens.

to my understanding its not about how much pressure it holds, its how long it holds it over a matter of time. so it doesnt need to be high. after 7psi i would go back through and make sure your seals are all in place and correct

After I did the leak down test I went through and checked both seals, both still in place. The air held pretty well but i could definitely see air bubbles coming from the naraku in the picture.

[MrJumps]

Adjust your idle a half turn in and try and repeat for at least 3 full turns. If its all the way closed your idle is set at off... play with the throttle as you goto start it.

[1man8scoots]

Check to be sure your reed cage is sealed. If it's leaking that bad you need to check why. Naraku don't leak like that unless it's not tight enough. Check the torque and tighter it as you check for leaks.
It won't start if there's a leak at the cage and if it does start it will die.

[1man8scoots]

Also it's very possible your engine is flooded. Remove the plug, place a paper towel over the spark plug hole and kick it hard 10 time and check the rag for gas.

[1man8scoots]

Finally, 120 psi is exceptionally low. I'd check the head torque.

[bfowler]

Retightened the head bolts to 8 foot pounds in a cross pattern. But yes 120 compression does seem really low, especially since I have a malossi stuffer crank as well.

If the engine is flooded wouldn't the spark plug be wet every time I remove it? What else can I do to check if the engine is flooded and also how can I unflood it if it is flooded? I did notice a long time ago that I would sometimes see gas leaking onto my left engine side right around where the clutch is which was coming from the carb. And now that I'm reading more about engine flooding I'm thinking maybe it is flooded. Because a couple of times when the scooter was running it died randomly and wouldn't start for a while which eventually led to it never starting again. I don't think it was a seize because I always had a temp gauge on and temperatures never broke 350. And through some posts here I see that flooding can cause scooters to randomly die and have trouble starting up again

Will retighten the naraku bolts to make sure that wasn't the reason for it leaking, hopefully it is though. Even so the leak from the naraku is so tiny that it should still be able to start.

[tazland001]

Its been a long time since I did a compression check on that motor but if I recall the compression zone for that engine is 120-160. Your at the lowest end so your prob going to have to open that top up and take a look. I doubt it is the intake. But I could be wrong.

[bfowler]

Its been a long time since I did a compression check on that motor but if I recall the compression zone for that engine is 120-160. Your at the lowest end so your prob going to have to open that top up and take a look. I doubt it is the intake. But I could be wrong.

Think that's the only option at this point. I don't have tools to rebore the cylinder after I take it off though. How much of a necessity is reboring?

[bfowler]

Yeah just can't seem to figure out why it won't start. I have compression fuel and spark. Have tried two different intakes as well as 2 different carbs. Did the leak down test. I'm out of ideas