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Discussion Starter #1
96 vn800
Mods- intake, intake ports cleaned up on the heads(nothing crazy) cobra pipes and EPA delete
Jetting is 52/175
Idles ok, backfires through the carb with light throttle.I would think it's a lean condition, but it dies on the choke. Pulls pretty good at wot. Any ideas
 

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Discussion Starter #2
Update, I turned the idle screw in to 1 1/2 out, was alittle better. Backfiring went down a little. So then I turned it to 1 1/4 out backfiring was a little worse
 

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Discussion Starter #7
It doesn't like 2 1/2. I have two shims and about 1 3/4 out runs perfect, but as soon as I go to put it on choke it dies
 

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First off, is it really backfiring through the carb? True backfiring, especially on bikes with electronic ignition, is very rare. True backfiring is either caused by a valve timing issue or by the ignition being so far out of proper setup that the spark plug fires when the intake valve is open and ignites the incoming air/fuel mix before the intake valve is closed. So in this case "backfiring" is probably not the issue.

With the mods you made, I bet what you hear is exhaust popping due to a lean fuel to air ratio on closed throttle on decel (light throttle). On way to know for certain, next time you hear the popping pull in the clutch. If the popping stops immediately, then you have proof it is not backfiring. Decel popping causes no harm at all to the engine, but a modded exhaust will cause the popping noise to be more evident. Turning the idle screw only slightly keeps the throttle plate slightly more open on decel and adds air to the mix, slightly reduces the vacuum through the venturi and reduces the fuel draw.
 

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Discussion Starter #9
It does it without moving too. Not as much. I turned the screw in and it doesn't pop as much. I noticed yesterday when I took it out, I did wot for a couple gears felt pretty good. When I let off and and went to ride slowly it popped a little bit. Still won't run on choke. I might try and put the 50 back in
 

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Discussion Starter #10
Also if I put it at 1 1/2 the popping is worse but it will some what run on choke. 1 3/4 runs better but won't run on choke. It kinda has me a little confused
 

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Discussion Starter #11
Alright I think I'm on the right track. I put the 50 back in left the two shims and it's almost perfect. Stays running with choke, I just have a very slight pop to take care of. I have the a/f screw out at roughly 1 3/4. I'll post back what I finally get it set at and what shim size
 

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carb school

got my bike out of the (harley) shop, and the symptoms OP is talking about still exist. I dont know about shims, or where the screw is. Id be happy to learn, Id just like to know if there is a sticky maybe that has pictures? Id like to see where the a/f screw is, what to shim, then sit around and try. Ive already spent so much on this thing, its time I learned carbs :-(
 

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The shims are small thin washers to put under the clip on the carb slide needle. Its a way to fine tune the fuel air mix on the low and mid range of the carb. The air mixture screw is usually a screw under a sealed cap or plug, preset at the factory. Sealed because to modify it or its setting means the bike will no longer pass emissions tests. Turning the air mixture screw out usually adds slightly more fuel to the air/fuel mix, which is one reason why turning it out enriches the closed throttle condition on decel that causes the popping.

To 94lTZ: if your bike keeps running on the choke, but will not idle or keep running without the choke applied, indicates two things:
1. If the choke on your bike is indeed a true choke, which closes off the carb venturi and causes the bike to run rich, means your carb is set way too lean for the mods made to your bike for the intake or exhaust mods,
2. If the choke on your bike is actually a fuel enrichener, then to apply the "choke" actually adds a lot more fuel at idle and low throttle without closing off the air intake. With the fuel enrichener "choke" applied the bike is sucking in a lot more fuel. This indicates your carb settings, idle jet, needle setting, is way too lean. Adjusting the air mixture screw can only marginally compensate, so the carb low speed and mid range jetting must be adjusted to add more fuel for the intake and exhaust mods made.
 

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backfires through the carb with light throttle
lean.
check your worse/better conditions
a Rich condition is better when motor is cold then gets worse as motor gets hot.
a Lean condition is worse when motor is cold then gets better as motor gets hot.
could be your pilot mixture screw is too lean that's causing the backfires thru the carb
 

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on the 800, even if your air intake is stock or is thunder mfg free flowing or hypercharger, the best carb pilot jet size is the stock 48, the 48 is adequate and just adjust the pilot mixture screw, I got a open air intake with k&n filter and v&h pipes and my pilot jet is a 48 , don't need a 50PJ on an 800
 

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Discussion Starter #16
Believe it or not it was backfiring/ popping through the carb but was rich. Made no sense, I could feel it popping with my hand. It had me a little confused on what to do and still has confused on why it was coming back through the carb. Went to a smaller pilot it i have it set up pretty good right now. It's set up at 50/175, two shims and around two turns out on the a/f screw. The bike runs great. Pulls really strong
 

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Discussion Starter #17
on the 800, even if your air intake is stock or is thunder mfg free flowing or hypercharger, the best carb pilot jet size is the stock 48, the 48 is adequate and just adjust the pilot mixture screw, I got a open air intake with k&n filter and v&h pipes and my pilot jet is a 48 , don't need a 50PJ on an 800
My bike has mildly ported heads. That's why I tried the 52 but ended up with a 50. Mpgs seem fair. Haven't went through a full tank yet
 

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Discussion Starter #18
got my bike out of the (harley) shop, and the symptoms OP is talking about still exist. I dont know about shims, or where the screw is. Id be happy to learn, Id just like to know if there is a sticky maybe that has pictures? Id like to see where the a/f screw is, what to shim, then sit around and try. Ive already spent so much on this thing, its time I learned carbs :-(
Tell me what's done to your bike I'm sure I can help
 

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nrg2brn, you said that you wanted to learn carbs and want pictures, so I will copy/paste a link to Russian wolf's scooterizing web page that has some pictures that might be of help.
http://www.angelfire.com/ak5/russwolf/documents/scooterize.pdf

the following might be of help for you, or maybe not, of what I know so far about the 800 carb, others can post what they know also that also might help you, can't hurt I guess.
- the carb on the 800 is a CVK36 , the 36 is metric size means millimeter
- the CVK36 carb is similar to the CV carbs on older model Harleys, the only difference is the main jet threads
- the main jet that Harley shops sell for their CV carbs have a different thread then the CVK36 Keihin carbs
- pilot jet threads on CV and CVK carbs are same
- when installing a Harley main jet into a CVK36 carb, you need to also buy the Harley emulsion tube that holds the Harley main jet (MJ)
- the stock (factory) MJ on the 800 is a Keihin 134 I think or a 135
- the main jets that are included in DynoJet Jet Kits are stamped with a star before their jet number, like this DJ134, the DJ stands for DynoJet and the 134 is their part number only and not the actual size of that jet
- 800 owners who buy the DynoJet Kit usually just want the adjustable #DNO106 needle in the kit, the DJ jets in the kit is for use all stock air intakes and too small a MJ size to use in free flowing aftermarket air intakes
- the DynoJet DNO106 needle in the kit has notches you place the e-clip, I think there is 6 notches on the needle,
- when putting the e-clip in notch #1, this lowers the needle into the MJ hole and leans out the midrange
- when putting the e-clip in notch #6, this raises the needle out of the MJ hole and riches out the midrange
- the DynoJet kit includes 2 small washers called shims, they can to under the e-clip to raise up (richen) the needle 0.5 notch, or above the e-clip which does not raise or lower the needle but is used to equal same size as 800 stock needle head
- the pilot jet mixture screw setting on a stock 800 is 1.75 turns out, 'out' is a counter-clockwise turn (to richen), and 'in' is a clockwise turn (to lean)
- the 800 stock Pilot Jet size is a 48
- at the factory they install an aluminum plug or cap over the hole for the pilot mixture screw, when adjusting this mixture screw drill a small hole and use a metal screw and pliers and just pull the plug off, the mixture screw is just under this plug/security cap
- on the carb intake rubber boot, there is 2 clamps, 1 is on the left side, leave that clamp alone, and 1 is on the carb side, that's the one you loosen to remove the carb from the boot

I hope others can add to this what they know to help you, because I surely missed something or got something wrong
 
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