Carb Problems...

[petesmeats]

I got a little adventurous in the weekend and i took the carbs off the beast this weekend...

Put them back and the bike now runs a whole lot worse than before...

Symptoms

Lose power on full throttle but only from mid range revs up.
Sounds kinda fluttery.


I have had the fluttery noise before but after a replace of the spark plugs it went away.

While i had one of the carbs apart i kinda munched the small spring that goes above the jet needle and below the jet needle holder in the vacuum piston.

I made it so that it was functional again but is this a critical part???

Any information about what this spring does would be great...

I am also aware that the carbs should be balanced to get some of the "performance" (It is a honda after all) back. Around how much would this cost to get it done at a shop??

The original reason why i ripped the carbs out of the bike was because when i travel at 110km/hr the bike lurches a little bit... Not heaps just pulls then stops, pulls then stops... And when i throttle on it hesitates a bit...

I thought it might be an air filter thing but checked all the air components and they seemed fine to me.

any ideas or hints or tips or anything will be much appreciated so i can get my baby back to full noise again (Birthday on friday - Gaerne Shockwaves coming hopefully - Should probably test them out soon after i get them...)

Cheers in advance
Pete

[riffer]

Hi Pete,

I've been working on this part of my bike recently so I'll tell you what I know. Ixion or Motu will be around later to correct any of my mistakes...

The spring is a critical part. If you have a look at the carb again you'll see that it holds a rubber diaphragm down into the carb. This rubber diaphragm supports the jet needle, which is shaped like a javelin ie it tapers to a point. The pointed end sits in the needle jet.

The Venturi Principle dictates that when a fast moving fluid (air in this case) is accelerated past the top of an otherwise enclosed volume (in this case the float bowl, by means of the needle jet, emulsion tube and main jet), the pressure above that chamber drops (the “venturi effect”). The area of the carb throat controlled by the rising and falling slide is called a “venturi”. The venturi effect creates a low pressure above the needle jet (essentially, a weak vacuum), which draws fuel up from the float bowl (which is kept at atmospheric pressure by means of a vent channel above the carb intake). At small throttle settings, airflow going under the slide and above the needle jet is minimal so the venturi effect is minimal and little fuel can be drawn up from the float bowl. But, as the throttle opens, the volume and velocity of the air passing over the needle jet rises, so the venturi effect creates a lower pressure above the needle jet (therefore a stronger vacuum pulling fuel up from the float bowl). The slide, which is controlled by mass-airflow and differential pressures between the volume under it and the volume above it’s diaphragm (which gets it’s “pressure-signal” from a connecting channel above and upstream of the throttle plate), rises and carries the needle with it. The rising needle, with it’s tapered shape, exposes an ever-greater amount of the needle jet orifice to the venturi, allowing an increasing amount of the fuel to rise from the main jet.

However, I don't think the spring is your main issue. My guess is that when you put the tops back on the carbs you haven't quite sealed the diaphragms correctly. This would cause a weakening of the vacuum which will stop the slide moving properly. Take the carb tops off, and check the diaphragms are sitting properly on the top of the carb. Also ensure that when you put the carb tops back on that the springs sit properly straight - the ones in my carbs have a propensity to come a bit loose when you put them in.

Failing that, pull the tops off again, and check inside the carb venturi to see if all of the needles are still in there. Or that they aren't bent.

Good luck. I hope my suggestions help.

[petesmeats]

Yeah that does make a bit of sense...
I will check it out this weekend.
Is it a bad idea to continue riding it this way?
I am going to take my bike into the shop for a service next week and so will get the spring replaced then.
Should i also be getting him to balance them?
Is there anything else that i should get them to check?
From what i did with the carbs i cant imagine that i fixed the problem of surging at highway speeds. Does anyone have any ideas about this? I am probably due for a fuel filter change but am not sure if this would cause surging.

Thanks heaps for the help.
Pete

[limbimtimwim]

Are you double sure all the carbs are correctly in their boots?

And like riffer said, putting a diaphram cover on wrong, and maybe pinching the diaphram is bad.

[riffer]

A surging carb at cruise speed would tend to indicate an overly lean mixture, I think.

Have you changed the air filter or exhaust lately, or tweaked anything?

As for getting the carbs synced, how much can you afford?

[petesmeats]

Yeah that was one thing that i was wondering about...
The hose that goes from my air box to the frame does not fit nicely on there...
It is as if the carbs are sitting wrong and move the whole air box away from the front of the bike but when i had the carbs off i put alot of force behind pushing them back into place and am sure that they are definately in the right place.
The hose still attaches but only just, and i am not entirely sure that they stay in place once the tank is on.

I am thinkin though that the most likely thing is the diaphram not sealing properly...

Pete

[petesmeats]

A surging carb at cruise speed would tend to indicate an overly lean mixture, I think.

Have you changed the air filter or exhaust lately, or tweaked anything?

As for getting the carbs synced, how much can you afford?

Ok stuff is falling into place...

I have an aftermarket Neptune pipe on it... But i know that it was running fine UNTIL SOME BASTARD STOLE THE STRAP THAT CONNECTS THE CAN TO MY BLOODY FRAME, and the exhaust now rattles itself a little bit and rotates about the lowest connection causing the can to sit quite far out from the bike... I will fabricate something in the weekend that will fix it until i can go to the neptune guys and get the actual strap.

EDIT: Cant really afford much... I have no idea what sort of price i would be looking at but might be willing to pay if it is worth it... I am also aware that i am fighting a probable losing battle with a machine that is as old as me...

[riffer]

Aha - the plot thickens...

So, tomorrow you're going to pull the tank off, get at those carbs, and check the fitting of the diaphragms under the tops, and how the carbs fit into the rubber boots in the motor.

And then you're going to fix the wobbly exhaust.

It's all good. :yes:

[petesmeats]

Aha - the plot thickens...

So, tomorrow you're going to pull the tank off, get at those carbs, and check the fitting of the diaphragms under the tops, and how the carbs fit into the rubber boots in the motor.

And then you're going to fix the wobbly exhaust.

It's all good. :yes:

Yes it does sometimes it takes a little bit of someone else to make you associate certain symptoms with certain subtle changes in bike...

Thanks heaps all...
Pete

PS I'm intrigued about how much balancing would cost... Anyone know?

And around how much is a total service???

I am probably due to take the bike in for a pro to look at it and fix any small mistakes i have made with maintenance...

[petesmeats]

Quick update from yesterday...

I took the carbs off and checked the vacuum stuff and they seemed allright.
I then discovered that i had neglected to connect a bloody hose to the air box... My Bad.

I think it is running better but will know more in the morning when i ride it...

I also straightened up the exhaust so hopefully that straightens out that side of things (scuse the pun.)

I did however break the head off one of the screws on the carb vacuum covers... Dammit i will get it fixed proper next weekend...

Thanks once again for all the help.
Pete

[skaz]

hey man, what hose u forget to put on? it was probably that hayden bastard givin it a thrashing that made it run rough, how did ya manage to torque the head off that screw? gettin into it with ur impact driver or something? have u checked ur plugs? they should tell u if its running lean, put that .5 of a mech eng degree to good use.

[petesmeats]

Um yep shirley it was Hayden that broke my bike... I woulda said that i thrashed it more than him though seeing as he is scared to crash it...

I neglected to connect a hose that runs from the bottom of my air box to somewhere at the top of the head??? Not really sure where it goes cos i couldn't really see...

I'm getting my boots tomorrow. I am prob gonna head out for a longish ride on saturday to test them out. And i might pick up my bloody strap from somewhere if i can locate where they are based...

I torqued the screw head off by being really really ridiculously strong...

But seriously though i just turned the screw and it came off.

Welcome to KB By the way you filthy ginger ninja...

Oh yeah results come out tomorrow so i don't even know whether i am 1/2 an engineer yet... Heres hoping.