Need help figuring out proper jet size.

[pilcherdustin]

Ok I just bought a 2004 Yamaha Blaster this past weekend. The guy I bought it from said that when he bought the quad It was bored over and had a pro circut full exhaust system: Platinum pipe with 304 silencer. I have stock air filter with no air box lid.

Now right before I bought it, he went back to stock piston size. Everything else is the same. I guess a previous owner installed a 300 main jet. Is this to big for my current setup? It has been flooding out really easy on starting in the cold or when the engine is hot after driving awhile. Could the main jet size be contributing to this hard start issue?

 

[speedyslyder]

compression test.
free flowing gas from tank to carb
take the carb apart and clean it with carb cleaner
set float level and pay attention to cleaning the pilot jet and float needle
and if it was bored larger then a stock piston put in it with out a stock bore cylinder you got a problem

 

[Fast6hand]

Sounds like a carb cleaning is due. Once a cylinder is bored over, it can't go back to standard size piston, they only get larger.

I would check the float height along with the needle valve seat, and the needle valve tip it self. If it's sticking or not sealing properly it could flood the engine. As far as the jetting I'm not sure. I'm sure someone else will chime in. Oh and welcome to the plethora or blaster advice!

 

[pilcherdustin]

Ok I guess I should have clarified. He went back to stock cylinder and piston. He bought a new jug.

 

[Fast6hand]

Ok I guess I should have clarified. He went back to stock cylinder and piston. He bought a new jug.

I think that's good being you get more bores.

 

[speedyslyder]

what is the airscrew set at?
it has been really cold here not sure where you are but if you jet it know you will have to rejet for summer
or everytime you switch betwen 0 degrees to 100 degrees
you will need some genuine mikuni jets...and must plug chop to confirm numbers

 

[pilcherdustin]

Ok I just did a compression test with the carburetor off the engine and on cold engine i kicked it about 10 times and the most it ever read was 100 psi.

 

[speedyslyder]

Ok I just did a compression test with the carburetor off the engine and on cold engine i kicked it about 10 times and the most it ever read was 100 psi.

not sure about doing it with carb off?
i have never tried that
but if it is at 100psi...its need to be rebuilt/top end normal is 120psi /or your comp gauge is lying

 

[speedyslyder]

clean the carb put it back on
hold throttle wide open then kick it till comp gauge stops rising/also there should be a rubber o ring on the thread part of your comp gauge/and make sure release valve on gauge is not leaking.
if it still read 100psi..time to open up the top end and inspect/replace

 

[pilcherdustin]

Ok since the carb was off and I know its not putting any fuel/oil mixture into the engine so I put a couple squirts of oil in the cylinder. I kicked it about 10 times until the needle stopped moving. It got up to about 110 this time.

 

[pilcherdustin]

Not what could have happened. I bought it because he said the top end had just been rebuilt and it just finished breaking in. When I bought it Saturday it would crank like 2 or 3rd kick. It was in the 50's outside then and now its in the 30's. I drove it about 4 or 5 hours sunday and used 93 octane mixed with yamalube 2R mixed 32:1. It shouldn't have worn out that fast.

 

[speedyslyder]

if it is running like crap and compression is low as you say it is
then only 1 thing to do. rebuild.

take the exhaust off the cylinder and look up in at the piston
if it looks like crap then guess what its crap lol
you will be able to see a lil of cylinder as well

 

[speedyslyder]

Not what could have happened. I bought it because he said the top end had just been rebuilt and it just finished breaking in. When I bought it Saturday it would crank like 2 or 3rd kick. It was in the 50's outside then and now its in the 30's. I drove it about 4 or 5 hours sunday and used 93 octane mixed with yamalube 2R mixed 32:1. It shouldn't have worn out that fast.

if it had a airleak and was jetted improper and you rode it for 4hrs
then yes it could have done damage...

he might not have bored or hone cylinder/or even bought the wrong size piston

maybe a leaky head gasket/warped head..the list goes on

 

[pilcherdustin]

Once it's running it would idle all day long and as long as your in the power ban it will haul butt. Crazy fast.

 

[Blaaster]

This is sounding more like an engine with an air leak and a carb that needs cleaning.

Test for leaks and then plug chop the #300 jet.

 

[pilcherdustin]

Where could the air leaks be?

 

[Blaaster]

The main culprits are the reed cage, carby boot followed closely by crankshaft seals.

 

[pilcherdustin]

Ok now that I know where to look for air leaks, how exactly do I test for them?

 

[pilcherdustin]

Ok I did some research and am heading to home depot after class today to build a pressure tester. I looked at piston and cylinder walls through the exhaust hole and it had a few lines on skirt but piston looks great and cylinder walls look great too. So I'm hoping I have an air leak somewhere. Will keep yall informed.

 

[pilcherdustin]

Ok is this what the reed cage should look like. It doesn't really have enough of a lip to catch on the engine block. From pictures I see on the internet all I see are cages with flanges with screw holes.