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2001 Shadow Spirit - Dunnellon, Fl
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Discussion Starter · #1 ·
Can someone help answer a question about pilot jets? I bought a 2001 VT750DC a year ago. The only mod I have found is the exhaust, which appears to be similar to the Cobra 2 in. Slash Cut Drag Pipe Exhaust System. Can't find a name on the pipes to know for sure. The bike ran ok but seemed to be a bit sluggish. This past Oct it began having starting issues. Did some troubleshooting and decided to rebuild the carbs. They were nasty and had crud in both bowls along with a stuck float in front cyl carb. While cleaning them I found that the main jets are 105 and 108 per specs but the front cyl carb has a #48 pilot jet and the rear has a #40S pilot jet (might be wrong about which one was in which (beer)). Everywhere I have researched references using the same size pilot jet for both carbs. Anyone know why someone would have used 2 different size pilot jets?
 

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1983 Honda vt750 Shadow
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That 40S size is strange. Does it look like they were opened before? Maybe an aftermarket jet as many different companies sell jets with different size markings.The factory Keihin jets have a K which looks like a star pattern.
One manual I have shows this. See if those are your carb numbers
 

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1999 Shadow 750 ACE VT750CD3 Modified
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My first guess would be a box of mixed jets and bad eyesight.
My second guess would be to cover up the symptom of a lean situation with the one cylinder, probably actually caused by an insulator/boot leak.
Other than that I'm at a loss.
 

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1999 Shadow 750 ACE VT750CD3 Modified
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That 40S size is strange. Does it look like they were opened before? Maybe an aftermarket jet as many different companies sell jets with different size markings.The factory Keihin jets have a K which looks like a star pattern.
One manual I have shows this. See if those are your carb numbers
Any aftermarket pilot jets I've come across maintain the Keihin sizing and the 2, 3 stepping, so...38, 40, 42, 45, 48, 50......
Now aftermarket main jets are a bit more of a mess, I'm specifically thinking of Dynojet, but there are others and then you get, jets that keep the Keihin sizing but use the 2.5, 5 numbering stepping and they can really mess up a tray of almost identical looking Mikuni jets that follow that stepping progression, but have their own sizing related to it.
Oh yeah almost forget those pesky Solex mains. (-;
 

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2001 Shadow Spirit - Dunnellon, Fl
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Discussion Starter · #6 ·
That 40S size is strange. Does it look like they were opened before? Maybe an aftermarket jet as many different companies sell jets with different size markings.The factory Keihin jets have a K which looks like a star pattern.
One manual I have shows this. See if those are your carb numbers
Swifty: Someone had definitely opened them before. I even found what looked like gasket material (from a tube) coating the bowl edges and seals. The carb is the VDF2D model. The pic shows what was in there.
284253


My first guess would be a box of mixed jets and bad eyesight.
My second guess would be to cover up the symptom of a lean situation with the one cylinder, probably actually caused by an insulator/boot leak.
CSRoad: The more I think about it you may be right about someone trying to cover up another issue. Looks like someone tried a couple of cheap fixes without spending any real money.

I think I will order a standard rebuild kit with a pair of 40 slow jets and go from there. Then I can order a separate pair of 42 slow jets if needed because of the aftermarket exhast. I will definitelty check the boots and air connections for leaks. It just threw me off finding 2 different size pilot jets when all research mentions using the same size in both carbs.

Thanks for the feedback! ?
 

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1983 Honda vt750 Shadow
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Those are Keihin jets at least, but I never heard of the 40 with an S designation. Maybe an off road racing type fine tuning increment ???
I would recommend putting in the 42 jets. That way you add a little bit of extra enrichment with the exhaust and you won't have to turn the idle mixture screws out so far.
I had #40 jets in my old 1983 bike with aftermarket pipes and I had the screws out to about 3 1/2 turns. So I got creative and drilled them out with the smallest drill I had and they went from about .016' to .020". I only have the screws out about 1/2 turn now, but I lost 10 MPG. I didn't expect that. So I need to go in and put in #42 pilots. Just a little increase in bore size can really effect flow rate I found out !
This video was an education.
 
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I know this is an old thread and you've probably figured the situation out by now, but two different-sized main jets are factory spec for the dual carb shadows. Honda did this as a matter of handling emission requirements and temperature differences between the front and rear cylinders while running.
 

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1999 Shadow 750 ACE VT750CD3 Modified
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That may well be, but if you say to hell with emissions and you tune for performance IME you still end up with some main jet stagger with the twin carb VT750 ACE and Spirit.
I've seen it blamed on the head temperatures or the exhaust port differences, all I know is if you tune properly on each cylinder, you are still stuck with it.
 

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I know this is an old thread and you've probably figured the situation out by now, but two different-sized main jets are factory spec for the dual carb shadows. Honda did this as a matter of handling emission requirements and temperature differences between the front and rear cylinders while running.
He knows this. Was talking about 2 different sized PILOT jets.
 

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I just put a kit in each of the carbs of my 2002 vt750 ACE. I’ve had the bike since August 2004. Never opened the carbs until now. Over 18 years. I pulled the carbs because gas was squirting from the vent hose. I turned the cabs upside down and blew into the fuel inlets. One carb allowed me to blow into it, the other didn’t. Fuel shut off valve was fouled. One main jet was marked 100 and the other 110. I didn’t keep track of which carb the jets came from. The jets on the kit I bought have no markings. Typical of Chinese aftermarket parts. I’ve reinstalled the carbs and will start it up tomorrow. I hope I don’t regret using the Chinese jets. Those carbs are a PITA to take off and reinstall. If I decide to buy 100 and 110 jets, does anyone know which carb gets the 100? Front or rear?
 

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I just put a kit in each of the carbs of my 2002 vt750 ACE. I’ve had the bike since August 2004. Never opened the carbs until now. Over 18 years. I pulled the carbs because gas was squirting from the vent hose. I turned the cabs upside down and blew into the fuel inlets. One carb allowed me to blow into it, the other didn’t. Fuel shut off valve was fouled. One main jet was marked 100 and the other 110. I didn’t keep track of which carb the jets came from. The jets on the kit I bought have no markings. Typical of Chinese aftermarket parts. I’ve reinstalled the carbs and will start it up tomorrow. I hope I don’t regret using the Chinese jets. Those carbs are a PITA to take off and reinstall. If I decide to buy 100 and 110 jets, does anyone know which carb gets the 100? Front or rear?
The rear cylinder gets the bigger jet, because it runs hotter.
 

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'83 VT750C; ‘21 SV650A
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I decide to buy 100 and 110 jets, does anyone know which carb gets the 100? Front or rear?
Even after 18+ years, unless your fuel is mixed with sandpaper, there should be nothing wrong with the stock jets that required replacing them. They’re just tubes with holes in, so as long as they’re clean, they’ll work. And probably better than the Chinese replacements, though again, how they can get a ‘tube with holes in’ wrong, is beyond me.
 

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Even after 18+ years, unless your fuel is mixed with sandpaper, there should be nothing wrong with the stock jets that required replacing them. They’re just tubes with holes in, so as long as they’re clean, they’ll work. And probably better than the Chinese replacements, though again, how they can get a ‘tube with holes in’ wrong, is beyond me.
I think the point is that the bike has an aftermarket, straight thru exhaust. The bike will definitely benefit from larger main and pilot jets.
 

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The rear cylinder gets the bigger jet, because it runs hotter.
Well, that makes sense. I rechecked the jets and they are 105 and 110. Not as big of a difference as originally thought, but I don’t want to chance the rear cylinder running even hotter with unknown jet sizes so I think I’ll pull the carbs off and reuse the original jets. Everything else on the bike is original. Thank you!
 

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I think the point is that the bike has an aftermarket, straight thru exhaust. The bike will definitely benefit from larger main and pilot jets.
Nope. In most cases, the stock jets will do just fine, and the exhaust probably still has baffles of some sort. Until you touch the intake, you’re pretty safe. Especially since ‘lean is mean’, so running things a bit leaner will usually make more power.

Also, the key words here were ‘suddenly started’, and that a dirty carburetor was found. Anything caused by jetting size would be more immediate. A gradual decline more points to blockages or buildup of ’stuff’ in the fuel passages.

In any case, we’ll see what happens!
 
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