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Discussion Starter · #1 ·
Bike is a 94 VT600CD VLX. Wasnt running when i got it so i will list all ive done as a process of elimination.

Stripped carb bodies COMPLETELY and soaked them a full 24 hours in Berrymans. Same soak time with jets.
Poked all holes in jets with a fine wire off a wire brush. Flooded carbs and jets with tons of carb spray and ten compressed air through all ports.
Installed new slides because one diaphram was torn so both replaced.
Looked up float height in service manual online and set at the prescribed 7 mm.
Set mixture screws at the listed setting of 1 1/4 out as initial setting.
Ensured air filter wasnt clogged.
Installed new fuel pump.
Looked up stock jet sizes and verified these ones are stock sizes.
Blew through fuel filter and it was easy to blow through so figured its not clogged.
Hit intake boots with starter fluid and no reaction so i assume no vacuum leaks.
Adjusted valves per the service manuals specs and procedure.
New air cutoff valves in carbs.

Now what its doing.. Starts easily and idles like a champ.
Will accept throttle to about 1/3 or so then starts sputtering like its starving for gas.
I took air ducts off the carbs to see if the slides were moving and they DID NOT appear to move. Ive had other bikes with CV carbs and i recall the slides would flutter even when at an idle... these ones dont do that. I also noted that i could feel air fluttering from those black plastic fittings just above the cutoff valves I assume those are vents of some sort?? I also noticed that if i took a hose and blew into those black plastic nipples the slides would raise. The hoses that were attached to them went down to a little square fitting on the rear right side of the plenum that sets on top of the front cylinder.

So now im wondering if somethings missing going to the carbs that goes to those black nipples to make the slides move?? Just where do those fittings go to?? And another observation is that viewing the cylinders with a colortune installed theres a awesome blue color but as i rev it up the flame dies out and then comes right back at an idle.

Im fairly well versed n a lot of bike stuff but this really has me miffed. I also thought about pick up coils failing at higher RPMs and if theres a possibility someone was in the right side cover at some point and got timing jacked up. Buddy had a honda magna that he got the timing marks on the gears in there off by one tooth and it acted weird too.I tried to find info about that in the service manual but didnt find that tidbit. Im out of game and would greatly appreciate as much input as is possible to help me get it running right. Thanks in advance...
CHUCK
 

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Discussion Starter · #2 ·
Also was wondering if theres a spec to do a fuel level check to see how full the bowls are getting. And if so, where alongside the seam where the bowls and bodies meet should i hold the tubing to see the level???
 

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1983 Honda vt750 Shadow
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If the slides are not lifting then that needs to be corrected.
Those nipples are for the secondary air filters I believe.
I don't have the same set up but it is what I remember hearing about.
 

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Discussion Starter · #4 ·
Swifty... So just what activates the slides to move?? I assumed the vacuum with it running sucks air out from the upper side of the slides. I made sure all the passages took plenty of carb spray and air, The little loop on the diaprams go around that little orifice which i assume sucks are out and thusly sucks the slides up. I also have the passage formed into the top caps lined up with that orifice so they can breath.

Im assuming said vacuum for he slides comes via that big hole at the top of the venturi at the engine side of the carbs. I used my shop vac for suction and no slide movement
 

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From what I can figure, it’s not vacuum per se, but the speed of the air flowing through the top of the bell causes lower pressure than what even the carb throat is seeing, which causes the slide to lift. During idle, mine are almost rock solid. Even with slow application of throttle they don’t move much. Give it a good rev or three, though, and they fly right open.
 

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1983 Honda vt750 Shadow
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On my older model there is a large opening in the front of inlet of the carb for air flow but on yours, maybe that is where the hose and air filter connects. It would be nice to have a description of that.
I believe it is the balancing for the CV operation.
The holes on the bottom of the slide provide vacuum to lift it.
 

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Discussion Starter · #7 ·
Based on the airflow arrows in the diagram all the holes up in the top chamber are open and lots of air and carb sprays been shot through them and i can confirm carb spray comes out below as does air. Im gonna take the compressor to the bike and grab my leak down tester. Even though i adjusted valve clearances doesn necessarily say the valves are sealing 100 percent.
 

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Discussion Starter · #8 · (Edited)
SWIFTY... i thought about when i used shop vac to see if slides reacted. I neglected to open the butterflies so i did it again tonight. holding throttle wide open slides did rise all the way up. Rather slowly but they did rise. Ive read on other bike forums that drilling the hole in the slides will make them more reactive both opening and falling. Any input on that? Any harm in drilling them out a bit larger???

ohm test on pick ups read 463 on each one and they are in spec according to the manuals range. Revisited valve adjustments and did a leak down test. No leakage. Since carbs were off i put my hand over the intakes and each cylinder sucked my hand pretty hard when i cranked it over.
 

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There is an article about jetting but it said it is better not drilling the slide holes.
 

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The only way to really verify that is to see them in operation while the engine is running. If your shopvac moves them smoothly, and they move freely with your fingers, there shouldn’t be much of an issue. Your carburetor also has three fuel circuits. Idle, main and high speed. You could still have a blockage of some sort in there, though the needle jet is pretty straightforward. In doing my bike, I fully cleaned out two sets of carbs. One still gave me issues, but the other worked fine…
 

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Discussion Starter · #13 ·
Was gonna put an add in the wanted section for a set of carbs but it says i have insufficient privledges to ost here, So, anyone with a good set for sale that will work on a 94 VT600CD VLX let me know what you have and what you want,Thanks.
 

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They’re not the easiest to find. EBay would be your best bet, followed by scouring bike salvage yards. What I was getting at was more you might have to go over those ones SEVERAL times before you clear out all the problems. I just had an easy solution, but I’m going to get back at those at some point…
 

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Discussion Starter · #15 ·
I
They’re not the easiest to find. EBay would be your best bet, followed by scouring bike salvage yards. What I was getting at was more you might have to go over those ones SEVERAL times before you clear out all the problems. I just had an easy solution, but I’m going to get back at those at some point…
I understand. I Would have to think that a total of 36 hours in berrymans, 3 cans of carb spray to flush passages after dipping, and enough compressed air to fill 20 dozen balloons should have all passages about as clean as they will be.
 

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1999 Shadow 750 ACE VT750CD3 Modified
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Those plastic elbows on the outside of the carbs are as @swifty2014 says for the secondary air filter, it supplies filtered atmospheric (outside air) pressure to the lower chamber of the slide diaphragms.
The holes in the bottom of the slide next to the needle provide vacuum from the venturi area of the carb throat through the slide to the top chamber of the diaphragm sucking the slide up against the force of the long wimpy spring.
This lifts the long jet needle from the needle jet and gas flows from the float bowl into the emulsion tube via the main jet and gets sprayed into the carb throat.
This operation is critical for running above about 1/4 throttle when it takes over metering fuel from the idle/pilot circuit.

I tried to kinda of simpify it, I hope it makes sense and maybe explains some of the behavior you have seen.

Lifting the slides with your finger should be relatively easy with no sticking and feeling only the resistance of that long spring.
There is magic for the right amout of fuel at the right time, but you shouldn't have to worry about that Honda did it for you and the basic system operation is dirt simple.
 

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I understand. I Would have to think that a total of 36 hours in berrymans, 3 cans of carb spray to flush passages after dipping, and enough compressed air to fill 20 dozen balloons should have all passages about as clean as they will be.
Ah, but that’s what they WANT you to think! 😉 On the other end of the scale, carbs can actually get physically worn out, though it’s rare.
 

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Discussion Starter · #18 ·
Only way i can get it to run and pull itself normally is to place 1 layer of tshirt rag across the oval opening of the plenum that sets on top of the front cylinder and then put the airbox over the rag and tighten down the clamp to trap the rag. Runs and goes like stink with that little added restriction. Take rag out of the equation and its back to its old symptoms.
I am tapping out on these carbs and will source another set when finances allow.
 

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...place 1 layer of tshirt rag across the oval opening;;; Runs and goes like stink
I think you can get a little more HP if you reverse the XL tag the other way. Right now it's in LX. Lags extra, you want to reverse it and have extra lag.

Who threw in that air box formula? See if I knew math, let alone the logic needed, the formula would have the 100% cotton briefs, choking the boxed intake area, meaning, a diaper at that opening and throttle up. No joy, put her see-thru panties on for less pleat meeting fiber, or heavy pleat meeting fiber is a cut pair of jeans.

Having the T-shirt right at the post suck, no way. You want the cotton covering the pre-suck, so the air cleaner catches it first, not a valve.

Signed,
Gotta fukwit the, "Degraders of Driveability" :D
 

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So increasing the vacuum fixes things, but you’ve tested for intake boot leaks and didn’t find any… That was with starter fluid. Have you tried an unlit propane torch? It could also be a valve issue of some sort.
 
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