300/440/550 440-550 built motor not starting for the 1st time =(

C

ChevyAndVW

Location
Dudley, MA
i recently just build a 550 motor. (mild ported, 44mm BN carb. pjs pipe/manifold. jetsport intake. boerd 1mm over. jetsport head. etc) and went to fire it up and got nothing. it turns over and gas vapor r coming from the carb. took and plugs out and cranked it and gas vapors were coming more from the rear cylinder than the front. tried a little bit of starter fuild and still nothing. i mixed the gas 32:1 just for the break in point. its getting spark and seems to be getting fuel. im pretty sure its a carb issue. but just wanna get this going until i get a sbn. i also turned the screws to stock specs to start there... any ideas or carb adjustment specs would be greatly apperciated thank you
 
eeerieski

eeerieski

Location
NW PA
does it have compression? I know it is freshly rebuilt but that is one thing that's easy to check. It might also be the CDI, while it has spark the spark may just be weak. Don't use starting fluid, use premix out of a spray bottle.
 
C

ChevyAndVW

Location
Dudley, MA
it had 770 in the front cyliner and 100 in the back. my tester could be wrong as well and the motor was oviously cold. could a false reading be because the starter wasnt spinning the motor fast enough? and the cdi ran the previous 440 motor no problem
 
munki63

munki63

Epoxy is my duct tape
Location
Canada
does it even sputter? or just keep turning over?

1st I would check your filter in your carb make sure its clean, Make sure your plugs are in good shape, Check if your getting a constant spark, If your not its most likely your ecu, If your getting a constant spark there is something wrong with your carbs, check your plus line first....always start with the simple stuff
 
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C

ChevyAndVW

Location
Dudley, MA
the spark is good and the ecu ran the previous 440 no problem. the gas mist is blowing out the carb and when i turn it over with no plugs in it blows out the cylinders. most the rear tho....
 
2

2XLR8

X-
Sounds like massive blowby causing problems in the crankcase making it very difficult to carburate. If the clearnce is more than 7 thou it could have problems with the single ring pistons. The starter has to crank fast and you must reach near maximum compression by the fifth compression stroke, if it takes like over 10 strokes to get maximum compression then blowby is the issue you did say 70 psi. Even if your gauge was not acurate I cant see it reading half of what it should
 
cookn

cookn

Kamikaze
Location
where you live
you have issues. 70 psi is wayyy to low especially with your jetsport head. it should run around 180 psi on a stock deck height cylinder. did you put new pistons in on the rebuild. I would question if they are even the right size. I've heard people running at 100psi but never 70. something is definitely out of spec. was the cylinder bored?
 
munki63

munki63

Epoxy is my duct tape
Location
Canada
If its not even sputtering you not getting fuel or spark one or both of the two, even with compression being out 30lbs...which is not good to start with, even if your timing is way out I think you should get something
 
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