Carb Question/ Vacum and idlescrews.
Thread Starter
The Zebulon
Squid
Joined: Apr 2009
Posts: 5
From: East Bay,Nor-Cal
Carb Question/ Vacum and idlescrews.
Hello everyone, Im new to this forum and I hope that it turns out to be as cool as it looks. I have a 98 hawk and im about to get her running, yet again.
Heres my question. When tuning the carbs with the idle screws and a vacum gauge, I would asume that hooking up the vacum guage w/t a T connector to both carbs and resetting the idle screws tight, then one turn out, and half turns from there until the vacum gauge gives me the steady reading i want when I snap the throttle. This is how I do it on my 1966 elcamino, except I dont tweak the timing on my superhawk. Is this the correct way to get my bike tuned in?
I realy do appreciate any time taken to answer this. Im one of those guys that hates throwing money at mechanics.......... Thanks Zeb.
Heres my question. When tuning the carbs with the idle screws and a vacum gauge, I would asume that hooking up the vacum guage w/t a T connector to both carbs and resetting the idle screws tight, then one turn out, and half turns from there until the vacum gauge gives me the steady reading i want when I snap the throttle. This is how I do it on my 1966 elcamino, except I dont tweak the timing on my superhawk. Is this the correct way to get my bike tuned in?
I realy do appreciate any time taken to answer this. Im one of those guys that hates throwing money at mechanics.......... Thanks Zeb.
mildly retarded
SuperBike
Joined: Mar 2008
Posts: 1,278
From: Denver, CO
I personally don't know the answer, but many on here will chime in by tonight. Try looking for it in the manual. there is a factory manual in PDF format on this site for download. Its in the technical section.
Welcome!
Welcome!
Senior Member
SuperBike
Joined: Dec 2005
Posts: 1,689
From: South Lake Tahoe, CA, USA
When you say vacuum gauge, are you talking about a manometer to synch the carbs?
In that case, you use it to adjust the position of the 2nd carb throttle plate so that both have the same vacuum reading at idle. This is called synchronization.
Then set the idle speed.
The idle mixture screws don't affect vacuum. I think the base setting is 2-1/4 to 2-1/2 turns out from the seat on the idle mixture screws. Most people don't seem to adjust them much from there. I don't recall the exact procedure for adjustment. Something like turn it in, until the idle speed starts to change, then back it out 1/2 turn. But I could be wrong. The procedure is in the manual IIRC. You will need a special tool to adjust them on the bike.
In that case, you use it to adjust the position of the 2nd carb throttle plate so that both have the same vacuum reading at idle. This is called synchronization.
Then set the idle speed.
The idle mixture screws don't affect vacuum. I think the base setting is 2-1/4 to 2-1/2 turns out from the seat on the idle mixture screws. Most people don't seem to adjust them much from there. I don't recall the exact procedure for adjustment. Something like turn it in, until the idle speed starts to change, then back it out 1/2 turn. But I could be wrong. The procedure is in the manual IIRC. You will need a special tool to adjust them on the bike.
Member
Squid
Joined: Sep 2007
Posts: 41
From: Arizona
Well what exactly are you trying to do, if it is syncing the carbs then all you need is a set of dual gauge vacuum gauges and a phillips head screwdriver. If your carbs are all gunked up from sitting around for months then id pull them and clean them before doing anything else. Im not sure of you knowledge level but there are no stupid questions here. Ask away. More details will definitely help us help you.
If your going to be playing around with your mixture screws then i highly suggest taking the carbs off and removing and slotting the mixture screws with a dremel so you can turn it with a regular flathead screwdriver (removing them is tricky, i was able to do it with a small pick, tapping it around and around until loose).
I got this idea from someone else on this forum and it was totally worth it. The screw from the factory is "D" shaped and honda wants you to use their special 1/4" bit tool for use with a right angle carb adjustment wrench(or whatever the proper name for it is). The idea is that it is adjustable with the carbs on the bike, I've found that it is damn near impossible to tell whether you are actually turning the screw at all if you use the right angle wrench tool, regardless of whether the screw is slotted or not. So i just pull them and adjust, then reinstall, kinda of a pain but id rather be sure of what I'm doing.
If your going to be playing around with your mixture screws then i highly suggest taking the carbs off and removing and slotting the mixture screws with a dremel so you can turn it with a regular flathead screwdriver (removing them is tricky, i was able to do it with a small pick, tapping it around and around until loose).
I got this idea from someone else on this forum and it was totally worth it. The screw from the factory is "D" shaped and honda wants you to use their special 1/4" bit tool for use with a right angle carb adjustment wrench(or whatever the proper name for it is). The idea is that it is adjustable with the carbs on the bike, I've found that it is damn near impossible to tell whether you are actually turning the screw at all if you use the right angle wrench tool, regardless of whether the screw is slotted or not. So i just pull them and adjust, then reinstall, kinda of a pain but id rather be sure of what I'm doing.
Thread Starter
The Zebulon
Squid
Joined: Apr 2009
Posts: 5
From: East Bay,Nor-Cal
Great Response from everyone!! After reading a little and using the little bit of carb knowledge that I know I figured out that,(and please tell me if im wrong) My car has a vacum advance for ignition timing, my bike has an icm to handle that.... therefor, a Vacume gauge is um.. nill? I found my vtr manual and it said to use a tachometer, wich measures ignition pulse wich changes depending on motor load and fuel curve.
Heres my next question. Im still alittle confused about the sink, should i use a tachometer and follow the book, or should I use something else? And Do the idle screws controll or contribute to stachiometeric efficincie? I know the the jetting plays a major roll but vtr's dont run holly carbs, so im a little lost
I would also like to add a comment about Blkbrds reply. I was lucky enough to find the idle screws have already been noched. But i did'nt realize that the factory did'nt do it. Guess that's the benefit of buying an old race bike.....Thanks guys!!!!
Heres my next question. Im still alittle confused about the sink, should i use a tachometer and follow the book, or should I use something else? And Do the idle screws controll or contribute to stachiometeric efficincie? I know the the jetting plays a major roll but vtr's dont run holly carbs, so im a little lost
I would also like to add a comment about Blkbrds reply. I was lucky enough to find the idle screws have already been noched. But i did'nt realize that the factory did'nt do it. Guess that's the benefit of buying an old race bike.....Thanks guys!!!!
Last edited by Presidential; Apr 21, 2009 at 10:58 AM. Reason: i suck at typing
Senior Member
SuperSport
Joined: Dec 2005
Posts: 963
From: Sunshine Coast, Australia
You only have one idle screw.
What you are talking about in each carb is a fuel mixture screw.
The vacuum gauge is used to balance the airflow between each carb, by getting each butterfly open the same amount, ie. synchronized.
Do yourself a favour and get on the net to research how a CV carb works. As you say, they are not Holly's.
What you are talking about in each carb is a fuel mixture screw.
The vacuum gauge is used to balance the airflow between each carb, by getting each butterfly open the same amount, ie. synchronized.
Do yourself a favour and get on the net to research how a CV carb works. As you say, they are not Holly's.
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