Trying to start for the first time ever...trying

Tried to start my cb450 project tonight with no luck. Here's what I know:

Fully charged battery, getting fuel and spark in both cylinders and electronic ignition is spot on.

Tried with electric starter, turned over a few times and backfired. Meanwhile the carb bowls are pissing out the drain tubes when the fuel is turned on.

Please help!

Finnigan said:

Meanwhile the carb bowls are pissing out the drain tubes when the fuel is turned on.

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There's at least part of your problem.

You can tap on the bowls. Hopefully they're just sticky or something is keeping the float valve from seating. It doesn't take much at all for them to leak by.

Fuck fuck FUCK! One cylinder has 120psi and the other has zero. Tried the compression test with the carb completely off and got the same result.

Am I looking at a complete teardown??

Drop a few drops of oil in the plug hole and see if that changes your number. If your exhaust valve isn't seating, it will cause bad compression too.

deviant said:

Drop a few drops of oil in the plug hole and see if that changes your number. If your exhaust valve isn't seating, it will cause bad compression too.

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Just tried that there's no change

Although, with the plug out and the stater going theres a ton of air coming out of the spark plug hole... Enough to blow my hair back

Finnigan said:

Just tried that there's no change

Although, with the plug out and the stater going theres a ton of air coming out of the spark plug hole... Enough to blow my hair back

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That's a good thing. If oil made the compression go up, then you'd be changing rings. Your fault is moving in the direction of the carbs. I'd recheck your valve settings.

This is the completely rebuilt engine right? What compression tester are you using because 120 is about right for the cheaper ones to read when the cylinder is healthy. 0 on the other means either the valves are partially open OR you broke the rings when you installed the cylinder or they are stuck in the piston. Just because it blows your hair back without a spark plug in the hole doesn't mean its making compression once the plug is in place. Leak down test will tell you right where the issue it is be it valves or rings.

Back fire from where? Intake or exhaust? Make absolutely sure that the timing is on, even E ignitions can be set up wrong.

And yeah +1 on floats, if the carbs have sat empty a while they may stick especially if they have laid on their side for a while.

I will never understand why somebody fails to mention they just rebuilt the entire engine before having issues.

Cam timing.

If it's you that built it, take it all apart and try again. You need the practice.

Zero is a 100% Valve open scenario///// The piston alone will make 10psi on starter.

The valves open make sense, i'll check those next

I have a strong feeling this is gonna become entertaining.

DohcBikes said:

I have a strong feeling this is gonna become entertaining.

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Yup.

Zero PSI usually falls into the "catastrophic failure" category.