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Old 10-01-2010, 04:31 AM   #1
vcand
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Default vt1100 Carb Sync Problem

1998 Honda Shadow
vt1100c2

Hello everyone!

I have 3 questions that I'd like to ask (sorry for the length, I tried to give as much detail as possible).

Background:
About a year ago my carb slides went. I just now had the time and money to replace them. While replacing them I cleaned the gunk out, cleaned out the jets, etc. I put the carbs back into the bike, and after quite a few starting attempts, it turned over and ran. It sounded a little "off" (kind of stumbled in its idle). So I decided that I would check the sync of the carbs (under the assumption that changing out those slides and cleaning everything may have offset it somehow). I built one of those manometers out of a yard stick and tubing. I used 20 feet of tubing, and I attempted to sync with both water and sea foam.

What I am finding is that as soon as I start the bike (warm of course), it pulls all the solution into the left port. When I crimp the left hose (to see the vac strength on the other side), it gently pulls the fluid that way but never really makes it there. I've checked the attachment between the manifold and carbs, no leaks and the clamps are tight. Plugs are good, sparks, new fuel filter, new fuel.

I did mess with the adjustment screw to see if I could correct that vac variance, but if I go too far in either direction it starts stumbling again; so I found a happy medium between the two extremes where things sound fine. One last observation, when I started the bike today, the left side smoked until it was warmed up, I don't know if that is due to adjustments or due to the fact that I sucked in a lot of Sea Foam the day prior and it may have been burning out.

1) So my first question is, does anyone have any ideas what to do in this situation? I tried searching for answers on the net and the closest situation/solution I found involved a car. What the person said to do was, disconnect the linkage between the two carbs. Then turn the idle screw (on the weak side) IN until the idle goes up, then turn the screw OUT on the strong side until the idle comes back down. Once that is done, reconnect linkage and sync again. I am not sure if this is relavent as they were talking about some 60's car.

2) The tires on the bike were bougtht about 6 months prior to the slides going (so it's been about 1.5 to 2 years and < 500 miles since I bought them), but they sat unmoved, outside, on the concrete, for the past year. Now the PSI hasnt dropped too much and they never went flat. Should I be concered about the integrity of the tires (ie. should I put a new set on)?

3) A friend of mine had a virago (I think 535), and it had sat for a year. When she got it up and running, within a few days something with the cam went and the motor locked up and was no more. According to her, it's something common with yamaha's, but should I be woried about something similar or anything else that I should check out before taking a ride?

Thanks for any help or advice.

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Old 10-01-2010, 08:48 AM   #2
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First of all,I am going by what bikes I have,and they are much older than your bike. My apologies if this does not apply to your bike.
I am wondering if you are using the idle mixture screws to adjust your synch?
These screws are used to adjust the synch to some degree,but if the bike does not run correctly,there is another synch screw [on my bike it is at the top area of the carbs and very hard to access even with the fuel tank removed] It is also possible that a special tool is needed to adjust the synch
A manual for your specific bike would have this info,or maybe your Honda dealer could let you peek at theirs. You could always buy a gallon of motorcycle oil before you ask Maybe someone more familiar with your specific bike can be of more help. Good luck.
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Old 10-01-2010, 11:20 AM   #3
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+1 on when slumlord advised - you need a manual, or at least a good diagram to see how your sync is set. If you're unsure of what a proper sync is, see my last post in this thread: http://www.motorcycleforum.com/showt...755#post745755
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Old 10-01-2010, 01:20 PM   #4
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Quote:
Originally Posted by slumlord View Post
First of all,I am going by what bikes I have,and they are much older than your bike. My apologies if this does not apply to your bike.
I am wondering if you are using the idle mixture screws to adjust your synch?
These screws are used to adjust the synch to some degree,but if the bike does not run correctly,there is another synch screw [on my bike it is at the top area of the carbs and very hard to access even with the fuel tank removed] It is also possible that a special tool is needed to adjust the synch
A manual for your specific bike would have this info,or maybe your Honda dealer could let you peek at theirs. You could always buy a gallon of motorcycle oil before you ask Maybe someone more familiar with your specific bike can be of more help. Good luck.
Thanks. My bike is the same. I have independent mixture screw on each carb and a center linkage with a screw for sync. To get to that screw I have to lock the throttle open, and stick a long flat head into it. I'll see if I can track down a book. thanks.
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Old 10-01-2010, 10:50 PM   #5
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There is an information site called dansmc.com look at topic 54 on the "motorcycle repair course",and it discusses in general how to synch carbs. You may also be interested in the special tool illustrated there that lets you adjust and lock the synch screws.
Wintersol is a very modest person,and it is good to know that he built his own tooling to synch his bike as it lacked the test ports. My hat is off to him.
Vcand, I never would have thought to lock the throttle open to get to that screw. It just shows how much a guy can learn on this site.
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Old 10-02-2010, 05:10 PM   #6
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Quote:
Originally Posted by slumlord View Post
There is an information site called dansmc.com look at topic 54 on the "motorcycle repair course",and it discusses in general how to synch carbs. You may also be interested in the special tool illustrated there that lets you adjust and lock the synch screws.
Wintersol is a very modest person,and it is good to know that he built his own tooling to synch his bike as it lacked the test ports. My hat is off to him.
Vcand, I never would have thought to lock the throttle open to get to that screw. It just shows how much a guy can learn on this site.
Yeah, I found several sites that said to use a hacksaw blade, too much work for me
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Old 10-02-2010, 05:13 PM   #7
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Ok, so here's the latest. I bought a manual, went through its weak description of how to do the sync, it's the same thing I'm doing. It says to hook up the adapters, connect the hose, sync till its within specs (by the screw I'm already using). It does not address my problem of the vac being WAY off on one side.

Should I just crank the hell out of that screw in either direction until I get the pressure up, or is the extreme pressure difference a sign of another problem (like a vac leak or something)? The bike use to run fine and was sync'ed well until I had to replace the vac slides, now it's all out of whack.
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Old 10-02-2010, 11:41 PM   #8
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If the throttles are visibly very close, but the vacuum is very different, it is likely you have a leak somewhere. You may have a diaphragm improperly seated, or maybe one of the boots isn't seating well.
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Old 10-04-2010, 08:08 AM   #9
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Quote:
Originally Posted by WintrSol View Post
If the throttles are visibly very close, but the vacuum is very different, it is likely you have a leak somewhere. You may have a diaphragm improperly seated, or maybe one of the boots isn't seating well.
+1
And while you are checking the diaphragms hold them up to a light and carefully check for holes. Also,my bike ran a lot better once the new exhausts were in as that balanced the exhaust backpressure
There is one more thing ,a warning actually , about the diaphragms. The main jet needle that moves with the diaphram and slide is confined by a screw that caps the needle and captures it. My bike was running lousy,and I finally pulled the carbs. I heard a loose part clank,and it was one of the capture screws! Worse yet,the screw would not thread in to capture the needle once again,because the vibration and the loose screw ruined the threads. I would recommend that you use blue [mild setting strength] Locktite to hold the screw in place.New diaphragms are very spendy.

Last edited by slumlord; 10-04-2010 at 08:24 AM..
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