Suck and blow

[Coffinator]

http://www.youtube.com/watch?v=VMIC1wUzUj0

So what do you think? Look like a bad exhaust valve to me..

 

[Biker Dash]

An exhaust valve not seating properly would do that. It could also be an excessively dirty valve sticking open a bit.

 

[Coffinator]

Yeah. It runs ok on everything over 3k. Under 3k there is a lot of misfiring on one of the cylinders. Guess the motor has to come out..-_-

 

[marsmax85]

Sounds like my ex wife ! she had a few screws that were loose !!

 

[Boostmax]

A valve wont stick and un stick repeatably at different RPMs. The in and out pulses are normal in my opinion. If the bike runs OK above 3kRPM, there is no need to pull the engine. Sounds like carb issues to me.

 

[SpecOps13]

A valve wont stick and un stick repeatably at different RPMs. The in and out pulses are normal in my opinion. If the bike runs OK above 3kRPM, there is no need to pull the engine. Sounds like carb issues to me.

I would tend to agree. Atleast do a Compression test before pulling the motor. Plugs all out and throttle wide open when doing the test. Harbor Freight has a compression tool cheap...

 

[Coffinator]

Yeah I'll do a compression test.. But air going in, instead of out?=|
I don't know if that can happen without anything sucking the air back in.. Unless a non-firing cylinder pushing cold air instead of exhaust causes the same effect. I don't know..

 

[Coffinator]

Got 150-150-180-200 on the compression test. Its not horribly low i guess, but the difference between the cylinders is like 25%.. I don't know how much difference one should accept before doing anything with it? Uneven idle, and does not really run properly under 3k, unless im going uphill =O. Whattaya think?

 

[Suave Cowboy]

Bump. I had a problem similar to this, though it didn't suck at all, just had an occasional pop at idol out of one cylinder... Never figured out what it was!

 

[Rand-5107]

You need to do both wet and dry compression tests. If your comp. comes up after a few squirts of oil , your rings may be stuck or bad.

 

[Dr.n2o]

Curious to see what you come up with after tests. Just shootin' from the hip here but I'm curious how many other vmax's are doing this. The 70* v of the motor and firing order.....could just be overlap from exhaust stroke to intake....?

 

[sdt354]

Got 150-150-180-200 on the compression test. Its not horribly low i guess, but the difference between the cylinders is like 25%.. I don't know how much difference one should accept before doing anything with it? Uneven idle, and does not really run properly under 3k, unless im going uphill =O. Whattaya think?

Pull the pipes, inspect the exhaust valves. 150 to 200? this could be carbon buildup on the valves. 200 is high for a stock engine.

 

[Rusty McNeil]

With cam timing, duration and overlap there is always a little bit of reversion on both intake and exhaust sides of the motor.
The exhaust valves are still open some at TDC on exhaust stroke, so when the piston starts coming back down there is a little bit of "suck" before the exhaust valves are completely closed.
More noticeable at lower rpms's and idle.

I'm not saying yours is good or bad....just putting it out there....

Bike sounds good BTW.

 

[jwood]

A valve wont stick and un stick repeatably at different RPMs. The in and out pulses are normal in my opinion. If the bike runs OK above 3kRPM, there is no need to pull the engine. Sounds like carb issues to me.

I say carb issue as well...or the VBOOST is stuck open....