[Anonymous]

This board so hard.

[trinc]

you can fold the drain hose over on itself and zip tie it.

tim

[OldandReallySlow]

IMO, I don't think the drain hose would cause the problems he's talking about. First, the airbox isn't pressurized and second, it would just add more air to the mixture making the motor run leaner than normal. Vacuum leak would have to be either internal to the carbs or on the engine side of the carbs. That's just my .02 on it and since I'm not a physics major, maybe there is something I'm missing.

[The CyberPoet]

IMO... the airbox isn't pressurized and second, it would just add more air to the mixture making the motor run leaner than normal.

Well, here goes:

Vacuum created at the cylinder by the downstroke of the piston while the intake valve is open travels backwards through the system through the carbs (inducing them to mix in the fuel), and it doesn't suddenly stop at that instant. The vacuum continues backwards through the whole intake system right up to the air filter, where that vacuum coaxes additional air to get sucked in (the point of equalization). The air filter itself helps retain the vacuum pressure up a bit longer by providing a partial resistance to inbound air, thus increasing the vacuum duration event (and resulting in better fueling as a result usually). Opening a vacuum leak at the drain tube causes the vacuum event to reduce in time (which results in a leaner mix, as you surmised), as well as permitting unfiltered air into the mix.

I suspect the gobs of grease (as he put it) may have been causing the primary problems...

Cheers
=-= The CyberPoet

[Anonymous]

Tim: Good idea...done!

Cyber: I narrowed down the vacuum leak at the carb-airbox association. Even though the screws are tight, its looks as if the airbox boots are pretty worn and are a little demented from taking it on and off so much. Would it be better to just replace these 'rubber stacks' or just get a new airbox alltogether? (cheaper)

[The CyberPoet]

Cyber: I narrowed down the vacuum leak at the carb-airbox association. Even though the screws are tight, its looks as if the airbox boots are pretty worn and are a little demented from taking it on and off so much. Would it be better to just replace these 'rubber stacks' or just get a new airbox alltogether? (cheaper)

If it's the rubber stacks have seen better days in the center and/or carb end, replace them. If they're just not sealing at the airbox itself, you might be able to use some form of sealant (I'm thinking silicone or similar) to permanently affix them to it tightly. Unless the airbox itself is bad, there's no sense in replacing the airbox.

Cheers
=-= The CyberPoet

[Ivan]

If the boots are just the only problem with the airbox....

Just replace them, they aren't very expensive.

Ivan

[Anonymous]

Update:

So I was gonna get some new boots and a new drain tube...but then Keith got me a whole brand new airbox. Still the throttle response is poor.

So I am gonna do a carb sync, since the idle seems stable enough.

Using motion pro carbtune (the mercury kind)...

#1 - 2 - 3 carbs are all pulling mercury

#4 has no pull on the mercury whatsoever (vacuum leak?)

Even modifying the 3-4 screws has no factor.

My bike is possessed. And NO I will not take it in (cause I'm gonna beat this!)

[ThAzKat]

You go Joe, I am pulling for ya!!!!!!!

[Court93kat]

Hey Joe- have you checked all the rubber pieces under the black top on #4? There is supposed to be a small o-ring right below the spot you hook the synch tool. If one of those are missing, you will have problems. Also, check for a seal around the top of that cover. Just an idea. Wish you luck.

[The CyberPoet]

Using motion pro carbtune...
#4 has no pull on the mercury whatsoever (vacuum leak?)
Even modifying the 3-4 screws has no factor.

(A) Swap the mercury vacuum leads between 3 and 4, so you have three hooked to the #4 collumn & visa-versa. Still no action from cylinder #4 (now displayed on the #3 collumn)?

(B) Take off the vacuum connection from the tool to cylinder #4 and run a bit of wire through the actual metal tube the vacuum gets pulled through -- if there's build-up, it could be blocked. Q: If you put your hand over the carb and crank the bike, do you feel any air pulling over your hand into the carb?

(C) Look at the carbs connections between the carbs themselves. There is a rotation mechanism that is adjusted by the screws, normally consisting of a couple small flat plates, a spring, plus the screw. If they somehow got misaligned when the carbs were connected to each other, it could be holding the number four butterfly closed all the way (physically choking it); the position of the plates compared to the springs (stack order) should look the same as between 1 & 2.

(D) If you have a leak-down pressure tester, do a leak down test on cylinder #4 and check to see that it is holding pressure at all -- if it doesn't hold pressure for squat, it won't generate vacuum to speak of either. You can find a cheap pressure tested via HarborFreight (threads into the sparkplug socket, has a gauge, gets pressurized with air and you watch how that pressure holds/leaks over the next 2 to 60 seconds).

(E) If the exhaust header pipe for that cylinder is blocked or any of the valves are chipped/broken/bent on that cylinder, it also won't generate vacuum.

(F) Court's suggestion about the rubber seals within the carb are spot-on. Go look at the diagram for the parts fiche for the carb and consider simply replacing all the rubber seals from end-to-end for cylinder #4's carb. Swapping carbs with someone else temporarily (or buying a spare set of ebay) should quickly help determine if this is necessary.

Cheers
=-= The CyberPoet