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2%er
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Discussion Starter #1
Hi, I was wondering if anyone can help me out with syncing my carbs? I'm pretty new to all this and slowly learning how to fix things, but for the sync, I don't really know what I'm doing. So I'm just trying to follow my clymers book and guides online and it seems like I've made everything worse. I apologise this is pretty wordy, just trying to be thorough as I don't have the experience to know what info to include or not.

So it's a 1986 Suzuki intruder 750, with pod filters and some sort of custom exhaust that I don't know what it is. I assume it had been rejetted from the previous owner as it had open filters when I got it and it ran okay. Not sure how to check for custom jets or whatever. It ran fine for a while (despite some other non-related problems) and then started stalling in 3rd gear. Checked the plugs and the back was fine but the front was sooty black, so rich I think. So I replaced that plug and gapped the same as the back one.

First I tried to set the idle to 1000rpm by comparing it by ear to a youtube video, seemed to work okay, but obviously not perfect. I ordered a tach to actually do the idle properly but it won't be here for a month.

Then I made a sync tool with 2 bottles and some water (I can't post links but if you put "bottle carb sync tool" in google images there's pics of it there) and hooked it up to the vacuum ports (made little brass adapters with o-rings on them) started the bike and right of the bat, one side raised the water level like crazy so I shut it off and fiddled with the idle sync a bit until it wasn't crazy one way or the other. Then I would get the water synced into the middle which was like super difficult, it was a matter of turning it like half a millimetre to get it just right.

Then when I tried the throttle sync at ~2000rpm, it was the same issue, super finicky tiny adjustments. And then when I finally got it right, I let the throttle off to idle, the water level on the front cylinder started dropping. So I did the idle all over and then the throttle and the idle just kept going out over and over. I finally just got them both to where they were sort of level but not really and tightened up the lock nuts.

Then I did the air fuel mixture. Basically screwed them in to the lean side til it started to get weak and sputter a bit, then out to the rich side 5-half turns til it did the same and then back 3-half turns to the "middle"

So now I guess the sync is roughly okay, but when I crank the throttle and let it off, it pops or backfires on deceleration. I'm not sure which cylinder it is, or how to check. The exhaust pipes are one on top of the other. I've tried fiddling with the idle screw a bit up and down, as well as the air/fuel screws each a bit up and down but it doesn't really help.

I also tried to put socks on the air filters to give it some more resistance or something (I read somewhere that might help) but it had no effect

Just checked the plugs and now both are kind of shiny black which is lean I think? Probably just from messing around with the air fuel though, right?

So now I just don't know what to check for. Do I need to take the carbs off and clean them? (I've ran seafoam in the gas for a few tanks prior to this, not sure if that counts as cleaning). Is there some other adjustment on the carbs I am unaware of?

Thanks
 

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Before you start, you have to make sure the throttle has plenty of slack, maybe 1/4" or more rotation at the grip. Then, the idle sync is adjusted at the front carb only, which is easier with the tank off and an aux tank providing fuel (or the tank tied over the bike with a longer fuel line). The throttle sync is done at the front carb, too, but, rather than turn the grip and hold to raise the throttles, I just slowly increase rpm, noticing which gets more vacuum, then adjust, repeat, until the vacuum tracks pretty well as the throttle is opened and closed. Once I have the idle and throttle cables locked down at the front carb, I then reduce the slack at the grip to about 1/8" rotation.

This engine is adjusted lean from the factory, so does tend to pop on deceleration. The pod filters make it even more lean, unless you change the main jets and, sometimes, shift the jet needle by replacing the plastic spacer above it with a thinner washer.
 

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2%er
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Discussion Starter #3
When you say slack in the cable, do you mean the throttle tube should turn 1/4" before it actually starts pulling the cable? I don't actually have an adjuster, this bike is pretty jacked up. I might just have to take the cable out of the housing to do the adjustment or something.

Is there any way to tell what jets and jet needles I have in it currently?
 

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Someone removed the adjuster at the grip? I didn't think that was possible. But, yes, the grip should have a lot of rotation, so one of the cables isn't pulling the throttle when you're trying to set the idle and idle sync.

The only way to check the jets is to take the bottom of the carbs off and look at the numbers stamped into them. The jet needles are connected to the CV pistons, and you have to take the top caps off the carbs to have a look. You have to be careful not to damage the diaphragms, and get them in the correct orientation when putting them back in. I can send you the parts fiche drawings of the carbs, if you PM your email address, so you know how they go together. Or, you can go here: http://www.partsoutlaw.com/oemparts/c/suzuki_motorcycle/parts

One other thing that can make for improper mixture is the fuel levels in the bowls. Easy to check with a clear tube that fits on the bowl drains.
 

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ZAMM Fanatic
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Carb sync is over-rated. As long as carbs aren't GROSSLY out of sync it matters little (IMHO) that more charge (air+fuel) is being delivered by one carb versus equal amounts from each carb.

You can balance your carbs perfectly at 800 rpm (cold idle) and find at 1200 (hot idle) rpm they're out of balance. So where, then, is the perfect rpm to balance them? When idling? At mid throttle?

There's no balancing to be done at WOT, and without a load you would redline the motor trying.

Maybe someone who's worked at a dealership and had factory training can comment, or maybe it's in a manual somewhere.

FWIW, my background is from balancing Webers, Strombergs and SU's on sports cars, and again, the general strategy I and my mates adopted was "get it close" and fuggedaboudit!
 

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2%er
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Discussion Starter #6
Yeah theres like an adjuster barrel or whatever there but nothing to screw it into. Its just duct taped to the cable and the angled connector thing. I'm looking at replacements on eBay now. In the meantime I'll see if it helps just taking it out of the housing.

Is the fuel level in the bowls something I can check with the carbs still installed? I'd like to try all the options before I have to get into that hard stuff.

One thing I have going for me is it worked okay until I started messing with it, aside from the rich front cylinder, so I'm hoping the jets and stuff are okay and its just fine tuning the sync that's needed

How do I tell if the carbs need to be cleaned?
 

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Carb sync is over-rated. As long as carbs aren't GROSSLY out of sync it matters little (IMHO) that more charge (air+fuel) is being delivered by one carb versus equal amounts from each carb.

You can balance your carbs perfectly at 800 rpm (cold idle) and find at 1200 (hot idle) rpm they're out of balance. So where, then, is the perfect rpm to balance them? When idling? At mid throttle?

There's no balancing to be done at WOT, and without a load you would redline the motor trying.

Maybe someone who's worked at a dealership and had factory training can comment, or maybe it's in a manual somewhere.

FWIW, my background is from balancing Webers, Strombergs and SU's on sports cars, and again, the general strategy I and my mates adopted was "get it close" and fuggedaboudit!
Carb sync is fairly critical on these V-twins, since each cylinder is fed by only one carb. One cylinder pulling just a little harder than the other shows up as increased vibration, especially at highway speeds, and more backfiring on decel. The way the throttles are set up, once you get them adjusted at any open throttle position, they are matched throughout the range. You rarely run them at WOT; not for long, anyway. Most operation is in the lower to mid throttle range, where lack of sync is most pronounced.
 

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Is the fuel level in the bowls something I can check with the carbs still installed? I'd like to try all the options before I have to get into that hard stuff.

One thing I have going for me is it worked okay until I started messing with it, aside from the rich front cylinder, so I'm hoping the jets and stuff are okay and its just fine tuning the sync that's needed

How do I tell if the carbs need to be cleaned?
Yes, if you connect a clear tube to the drain and turn it up alongside the carb, then open the drain, the fuel will rise in the tube to the set point of the float (if the petcock is open, of course). The rear carb should measure 7mm below the bowl seat, there is a notched area that shows the line on the right side of the carb. The front should be 17mm above the bottom of the bowl; there is a reference casting to measure from, and many happen to have a thin line cast into the bowl that points to the spot on the seat. See this photo:

Since it is running, I would just run a tank or two treated with a good fuel system cleaner; many like Seafoam, others Techron - there are others.
 

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Good info, WinterSol. My lack of motorcycle tech'ing experience is showing. I've never dealt with carbs that didn't feed a common manifold.

In the auto/lawnmower world I've never run into a driveability problem due to float level problems. Only pinholed / sinking floats. And debris clogging needles and seats.

The one that really burned my bacon was a solid, foam-like float out of a Piaggio scooter. I tested it in water. It floated. But in gas it sank. It took a senior lawnmower mechanic to show me the error of my waze after I'd pulled that carb on and off the scooter for the 4th or 5th time...
 

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Float levels can affect the mixture, but only a small amount; if the bike is already tuned lean, a lower float level will make it more so, but it has to be really low to notice while riding. I like to have everything within spec, so any anomalies reveal themselves.
 

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2%er
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Discussion Starter #11 (Edited)
Do I check the float levels when the bike is running or something? I tried warming it up for 5 mins and then turned it off to check with a hose on the drain plug (on the front carb) and like just a few drops of gas came out. Nowhere near that line.

Also I couldn't figure out how to get the hose on the back carb drain. There's like a chrome tube in the way that goes into the engine
 

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Do I check the float levels when the bike is running or something? I tried warming it up for 5 mins and then turned it off to check with a hose on the drain plug (on the front carb) and like just a few drops of gas came out. Nowhere near that line.
Having run the bike, the carb should be filled, and opening the drain screw should let gas fill the tube. Make sure the drain is opened fully (without actually removing the screw). A couple turns should be enough. If the drain is blocked with hardened, dried gas, it could require a good soak with a cleaner to make it flow, or even removing the drain screw all the way to clear the drain with a soft wire. See below.

Also I couldn't figure out how to get the hose on the back carb drain. There's like a chrome tube in the way that goes into the engine
It is tight in there, isn't it? I use long, thin pliers to get a tube on mine. I'm a modeler, so have several of the type called hemostats, with locking teeth at the handle end. Also, having the right frame cover off helps a lot. That chrome tube, BTW, is the coolant line from the water pump.

If you have issues with dried fuel in the carbs, a good cleaning may be necessary. Before you have the carbs off to clean, though, a trick used by many Intruder owners is to disconnect the fuel line at the petcock, put the fuel line in a jar filled with Seafoam, and start the engine, to fill the carbs via the fuel pump. When the engine dies (with some smoke), the carbs are full with the cleaner. Let it sit a day or two, drain the carbs, and start it again with the gas tank connected; it will really smoke for a while, but should run as gas reaches the carbs. Now try using the drains; at the least, the soak in Seafoam will have softened the deposits, so you can clear the drains with a copper wire. Sometimes, removing just the bowl may be needed, if you can get the carb turned enough to get the screws out; then you can clear the drains more easily. These are JIS screws, not Phillips, and a Phillips screwdriver will strip the heads, so be very careful. Trust me, removing the carbs for cleaning can be a real pain, as you should not disconnect the sync cable between them, but get them out while tied together. The Seafoam soak (or your favorite fuel system cleaner, like Techron, or Lucas) can work, if the carbs aren't too blocked, which yours shouldn't be.
 

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2%er
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Discussion Starter #13 (Edited)
Okay I think I'll do this while I wait for a new throttle cable to arrive. Opened it up at the splitter and it's totally frayed in there. I'm surprised I'm not dead.

So to clarify, when I bend the tube around, the gas level should be at that notched line on the side? Or it should be above the line by 17mm?

Edit: oh and the cable says it should be here this week, but I doubt that. Is it okay to go back to syncing with the old cable (slacked this time) and then just swap out the part that goes from the splitter to the handlebars? I don't seem to need to change the cables from the splitter to the carbs, they seem in good shape. Or will I need to do the throttle sync again no matter what, when I change the cable?
 

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So to clarify, when I bend the tube around, the gas level should be at that notched line on the side? Or it should be above the line by 17mm?
On my front carb, the cast line on the bowl, that I highlighted in the photo, points to the spot on the bowl seat that is 17mm above the diamond-shaped bit, which is the reference line. If you don't have that line on your bowl, just measure 17mm from the reference, and mark the bowl seat, above the screw that holds the bowl on.

I would think that the new cable comes complete, with the splitter, but you can just replace the front part, and leave the cables that connect to the carbs. You do have to be careful to get the cable ends properly seated in the bit that holds the three ends together inside the splitter. If you do keep the rear throttle cables, then, no, you shouldn't have to redo the sync, since those are the cables you are matching with the sync. It wouldn't hurt to check, since all you need to is sample the vacuum.
 

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2%er
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Discussion Starter #15
Good point on the simple check for vacuum.

Should I be checking valve clearance while I'm doing this stuff? I see it in the maintenance schedule. Not sure what it accomplishes?
 

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Yes, if you have the tank off, you should check the valve clearances, if only for peace of mind. If the clearance is too large, the valves clatter, and you may lose a small amount of power, but if they are too tight, you risk burning the valves and valve seats, because the valves aren't closing tight enough to prevent combustion gases from leaking.
 

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Discussion Starter #17
Ok, so... The valve clearances were out. some were probably 0.008" or more. so i set all of them to 0.005".

The sync went much better with that and the throttle loose. So idle and throttle sync are pretty well matched now, but there is popping on acceleration now though. I am going to mess around with the AF screws a bit as I feel that might help but is there anything else to look for now that its on accel, not decel?

Also going to check the float levels, I forgot, heh
 

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Discussion Starter #18
okay got rid of the acceleration popping now there's deceleration popping when I shift. ugh. Also there's like a new clicking sound on the left side of the bike somewhere. I give up for today, it too hot and my brain is cooked
 

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Popping on decel is normal for this engine; it goes lean, and you get pops in the exhaust. There are 'transient enrichment valves', AKA coast valves, which kick in when the vacuum gets high enough, but they only reduce the pops. Turning the pilot AF screws CCW about 1/4 turn often helps, but nothing really eliminates it.

Clicking on the left side could be a small leak at the header gasket. Or, a spark leak at the plug boot.
 

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2%er
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Discussion Starter #20
Okay yeah the spark plug wire came out of the plug boot thing so I shoved it back in and taped it. I guess I'll need to replace the wires. Will riding with the clicking like that damage it? Should I not ride til the wires are replaced?
 
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