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Discussion Starter · #1 ·
The bike idles poorly after changing the main jets. Pulls great mid to full throttle which is great but when I got back it idled worse than before, it was hunting. Up to about 1800, down to almost stalling. Was never this bad...
Anyway I thought I'd balance the carbs and I had the home-made rig with the two bottles, vacuum lines from each carb go to a Gatorade bottle half full, between the bottles is a hose that goes to the bottom of each bottle. This way you can visually see which carb is pulling more than the other.
So it showed the front carb was not doing so hot, the rear carb was sucking more than the front and that's why I saw bubbles once the one bottle ran out of air. I tried turning the adjuster screw and it didn't change anything.
I have no idea what's going on here.
 

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First thought is the carbs may not be seated all the way home in the rubber manifold. draw a sharpy line round the carbs then pull them up and check how far both are pushed in.
 

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i tried sinking with a homemade setup but after unsuccessful attempts i just turned the sinc screw a 1/8 adjustment at a time 1/4 is to much. rev it to 3000 and watch it drop, it would hang at 2000 for a second then fall to 1200 well i repeated about ten times having to remove the airbox each time until the rpms dropped from 3000 to 1200 evenly.
 

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Discussion Starter · #4 ·
It has to be what gt alex said. I didn't change anything other than the main jets and to do that the carbs come off, so... Yeah. I'll have another look tomorrow. Thanks.
 

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If the engine idled fine before the jet change...then you've got a vacuum leak. Could be the rubber manifold or one of the vacuum hoses. Remember too that idle vacuum is very much affected by the cam timings which in turn are affected by the clearances set during adjustment. Getting the clearances within the spec 'should' provide enough sync adjustment to balance the carbs...but sometimes it won't. Having both jugs making the same vacuum pulses requires them to have nearly identical valve adjustment clearances unless there is something mechanically wrong like a leaking valve seat.
 

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an alternative way to "balance" the carbs is to use light shined through the closed throttle plate area... I like using that method... so much easier and accurate "enough"!
... and funny thing about these carbs is that the secondary throttle plate is actually opened by a spring... (I bypassed that on mine, making it solid with a screw, throttle response becomes "crisper")...
 

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Discussion Starter · #7 ·
Update... Waiting for a new spark plug boot. The resistor failed in the front cylinder (not bad for 20 years) and the front isn't working as a result. SHould be here tomorrow. In the mean time, does anyone know what the NGK part number would be for spark plug boots for an SV?
 

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I just unscrewed the insides of the plug end and replaced the resistor with the same length of silver solder rod on both leads.
 

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an alternative way to "balance" the carbs is to use light shined through the closed throttle plate area... I like using that method... so much easier and accurate "enough"!
... and funny thing about these carbs is that the secondary throttle plate is actually opened by a spring... (I bypassed that on mine, making it solid with a screw, throttle response becomes "crisper")...
I take it yours is fuel injected because I'm not aware of a secondary throttle plate on the carbs, I will have to go have a look at my spare bits and see what you are saying.
 

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I take it yours is fuel injected because I'm not aware of a secondary throttle plate on the carbs, I will have to go have a look at my spare bits and see what you are saying.
yes, I guess you are correct... I was referring to the 2nd cylinder carburetor which is opened by a spring....
there is not a secondary throttle plate on the Gen. 1 bike.
only a secondary cylinder or 2nd cylinder.
 

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Discussion Starter · #12 ·
So anyway, got the bike running, still trying to balance the carbs w/ the homemade rig: Two bottles about 1/3 full, hose between the two, vacuum lines off each carb go to a respective bottle, turn the screw to get the fluid even between the bottles. Rear carb sucks all the fluid through, screw doesn't seem to have any effect at all.
Used a vacuum gauge in the end; got both carbs to draw about 10 in/Hg at idle. Does that seem right?
I'm also not sure if I have the throttle cables reattached correctly. Is there a stock setting for these?
 

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when looking at the slides check both move smoothly as the revs go up and down, sometimes the vacuum slides can stick.
 

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i have an idea and correct me if i'm wrong.could the idle knob be set to low.check if the throttle cable cam is contacting the idle adjustment stop.
 

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That seems like not enough vacuum. I would expect to see 18-20 in/Hg, though I admit I'm an FI guy, not a carb guy.
 

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You aren't going to get a lot of idle vacuum being the intake pulses are so infrequent at idle speed. Best to balance around 3000 or so which gives a lot higher readings and more represents the normal working environment. Many gauge sets have a damping orifice or adjustable screw doing the same thing....but if damped too much the needles become very unresponsive. Better to speed up the engine than over-damp the meters.
 

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Discussion Starter · #17 ·
Okay, I've gotten them as close as I can get them with actual vacuum gauges. Problem now is the bike idles at 2100 rpm. The adjuster screw is backed all the way off. Screw adjuster for balancing carbs still has zero effect. Throttle cable has slack in it (both sides).
Taking the carbs off now to look for anything obvious.
Bike has a DynoJet kit installed, clip third down from the top, DJ 150 mains, pilot has a "40" stamped on it, I didn't mess with anything but the main jets and the air screw, which I set to 2.5 turns out. I've got a track day coming up this weekend, I'm really hoping to get this to behave before then.
 
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