Hi guys, I took apart the carbs on my 2006 vmax, replaced jets and gaskets. Put it all back together and proceeded to sync the carbs. Found that I have no pressure in carb1 (left rear), see picture attached. Also found that the black plastic "cylinder" in the diaphragm assembly behaves different in that same carb - it "trembles" while the other 3 are "steady" - see video here: https://www.dropbox.com/s/zuocb3433lubcx1/2020-03-31 17.42.15.mp4?dl=0. Two possibilities come to mind: vacuum leak in carb/intake1 or (hope not) compression problem in the cylinder. Some more info that may be relevant: when I did the carb work I also took apart the intakes and replaced the rubber joints that connect the output of the carbs to the intake, the rubber joints in the cylinder 1/2 and cylinder 3/4 vboost connections , and the o-rings in the connection to the cylinders. How could I go about diagnosing this? Thanks!
No pressure in intake for carb1
- Thread starter rafcastro
- Start date
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Pull the spark plug, do a compression test and then a leak-down test. That will rule-out some compression issue. Were you experiencing any irregular operational behavior before you tore-into the carbs?
Also, to check the liquid gauge, hook it to another cyl & confirm the gauge works as it should.
Also, to check the liquid gauge, hook it to another cyl & confirm the gauge works as it should.
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MaxMidnight
Well-Known Member
If it was OK before you worked on the carbs then it won't be anything to do with the cylinders.
You need to go back over what you have done.
I assume that you haven't left the cover off the intake barb and that the slide diaphragm is seated properly or not split?
You need to go back over what you have done.
I assume that you haven't left the cover off the intake barb and that the slide diaphragm is seated properly or not split?
Thanks for your replies. I know the pressure gauge works right because I used it just a couple of days to sync carbs on another bike. I also hooked it to another cylinder to eliminate the possibility of a bad gauge. I agree it's probably not a compression problem in the cylinder, because I know I sync'd the carbs at least once before doing the carb work and everything was fine.
Fire-medic, could you educate me on what is a leak-down test? MaxMidnight, what's the intake barb?
I suspect I'll have to go back into the carb in question and see if I did something wrong, but was wondering if there was a way of narrowing down the problem before doing that - like, could it be a vacuum leak downstream of the carb? Is it possible to determine that?
Fire-medic, could you educate me on what is a leak-down test? MaxMidnight, what's the intake barb?
I suspect I'll have to go back into the carb in question and see if I did something wrong, but was wondering if there was a way of narrowing down the problem before doing that - like, could it be a vacuum leak downstream of the carb? Is it possible to determine that?
The intake barb is where you hook-up the balance hose.
A leak-down test is done, both pairs of valves closed, and you charge the cyl head with pressure, and measure the pressure after a bit of time, giving you an idea of how-well the cyl is sealing. Air escaping from the carbs is obviously an intake side leak, air escaping from the exhaust is a exhaust valves leak. Air escaping from the oil filler is a piston rings leak.
The time-honored method for checking for an intake leak is to use something like starting fluid, and spraying it around the suspected area of the leak, engine-running. If the revs suddenly increase, you've discovered the source of a leak.
A leak-down test is done, both pairs of valves closed, and you charge the cyl head with pressure, and measure the pressure after a bit of time, giving you an idea of how-well the cyl is sealing. Air escaping from the carbs is obviously an intake side leak, air escaping from the exhaust is a exhaust valves leak. Air escaping from the oil filler is a piston rings leak.
The time-honored method for checking for an intake leak is to use something like starting fluid, and spraying it around the suspected area of the leak, engine-running. If the revs suddenly increase, you've discovered the source of a leak.
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William_
Member
Could there be something stuck in the hole where you connect the carb balancer? Probably not the issue but worth a check?
RempageR1
Well-Known Member
Place your hand on top of the intake of that carb to see if there is a vacuum. If the guague goes to the top, likely the issue is not the cylinder or the manifold. If it doesn't you do need to look in that area.
Is #1 firing?
Did you try backing the sync screw out while it's running?
Did you try backing the sync screw out while it's running?
[email protected]
Well-Known Member
I'm thinking the same. Maybe just way out of synch after tearing into the carbs.
