Kawasaki Vulcan 750 Forum : Kawasaki VN750 Forums - View Single Post - Reduce or Eliminate Popping / Backfiring
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post #4 of (permalink) Old 01-15-2006, 04:43 PM Thread Starter
Vulcan Verses
Vulcan Verses
 
Join Date: Jan 2006
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The carb screws come from the factory covered by a little round piece of soft metal - like a plug. VERY CAREFULLY drill or poke a small hole in the plug, then stick a sharp point (like an awl or a pin) in and pull it right off.

If it looks like it has a little metal seal over it.. Yours was sealed by the factory...it's just a lead cap...you can remove it by carefully drilling a real small hole and prying it out with an icepick. I used a dremmel with a small bit...I added a plastic tube to the drill so it would create a stop..so the drill bit only sticks out about an 1/16 th of an inch..( you don't want to drill out the screw behind it) Just be carefull ...the carb body is soft metal...so don't use much pressure prying it out

There is a small diaphragm on the side of each carb that is supposed to richen the mixture during decelleration. Over time, diaphragms get old & crack or develop pinholes in them. Try replacing the one on the rear carb,I beleive that will solve your problem

In reading this thread it seems to me that we need a "standard" way to count turns. When using a round screwdriver on a round screw, the only reference to "a turn" is the slot of the screw (and if it's phillips, there goes the reference). There is some instruments I calibrate at work that I need to reference the # turns in or out, like a carb screw. First, I place reference marks on the screw in a place that wont rub off (the side of the screw head). I use two different color paintsticks (like red and yellow) to make small dots 180 apart. Then I set an "outside" reference - a small piece of wire and some tape or such. You wouldn't believe how far around the circle my eyes will move the starting point without this outside reference. When I start counting, it is now a simple matter of starting the adjustment with the red dot aligned with the reference, then watching as the red dot pass the reference again and saying one. Actually the piece I work on has four scribe marks for reference, and a built in pointer, but you get the idea.

Access to the adjusting screws is not good. I could not get my smallest screwdriver in there, so I made one from some heavy wire. I put a nice flat tapered end on it and bent the other end 90 degrees. Now I know I have positive connection with the screw, and I can count the turns accurately.

I'm currently happy with 3.5 turns from the beginning, or adjustment screw's bottom. That half a turn made a difference for me. I also found the screw will fall out of it's boring with just a little more than 5 complete (360) turns, on my bike. I was thought if I go close to that setting, then I would need some putty to hold the screw from falling out fill in the hole with, similar to someone's idea of using tape. But, I'd need to find a putty that wouldn't make a mess while trying to remove it. It'll still pop, esp. when I twist back the grip quickly, but not loudly

With this subject coming up again I'd like to offer a word of caution for those that are going to turn the mix screws in first. The metal is soft on the seat so don't bottom it out too hard, a light touch should be enough. If you don't think you've hit bottom but the screw has stopped, back it out a half turn and try again. If it stops in the same place your probably there. Also count the turns you make in, as a point of referance. For what it's worth.


Use some RTV gasket silicone over the screws to hold them in. When you pull it off it should come out in one piece.

Don't know if you may be referring to the popping that comes from the 'Coasters' or not. Any way here is a link to some info on it. There is more than this one but this is start. I'm sure others have more info as well. http://members.tripod.com/diverex/coaster.html Also check out www.shermscycleproducts.com

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I think the original discussion is now talking about apples AND oranges. Apple: The Vn750 exhaust *POP* is created by air induction to the exhaust system as designed by Kawi's EPA junk...period. Orange: After installing my Jardine exhausts, I immediately took it to the street before readjusting the carb screws out. The engine produced a new sound like a "kak-kak-kak", or maybe some would say a slight "pop". I believe this may be "the pop" the fella at the store was referring to, suggesting we use a richer jet. But, that's exactly what we all have been doing, more or less. Usually, the suggestion given by all us Vn750 riders is to just readjust the carb's pilot screw outward, and I believe this works well enough, and there's no urgent need for a larger jet. However, I have bumped up my main jet and raised my needle using a thinner needle. Now I have an exhaust that rumbles nicely, doesn't sound like a cat coughing up a furball, and still burns correctly during all the different engine speeds. Lance
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I beg to differ...a few posts have mentioned that they still got occasional popping after they "coastered"...which is bypassing the Kaw Epa junk I believe. After turning out the airscrew...it seemed to vanish. You also mention that one doesn't need to rejet the carbs...but then say you did and the bike runs better....??? Knifemaker
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Well most of this talk about mixture settings and carbs is above my pay grade but I do know I had popping on decel before coastering and after the coasters on decel no popping. I have V&H Cruzers with no rejetting and bike seems to run fine. Dats about all I know. Phil
For the complete lowdown on coasters, see Ray Warriner's excellent write-up:

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Bob, I'm pretty wrenchless myself. Don't worry, you can do it! You don't even have to get coasters. All you need is a couple of marbles of the right size. Pop the hoses off of the reed valves, stuff a marble in the hose to block it, then re-attach the hose. Five minutes max. No one will know, and you've accomplished the same thing as coasters! And if for some reason you ever want to go back to stock, just remove the marbles. Jim "Pick" Foster
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I used copper caps from the plumbing dept. at home depot. I didn't want the marbles to shatter and get in my engine. It's still a 5 minute job. Warren
I plugged my reed valves with two 5/8" diameter plugs I got from Advance Auto. They fit perfect.

You will NOT have to remove the airbox IF you 'coaster' using 5/8" good quality PLASTIC chair leg end covers found at any good hardware store. Black plastic... Just remove the hoses, Permatex on the cover, and voila'... Should cost ~$1.49, almost invisible on the left side, totally invisible behind right ear, no hassle removing reed covers..takes all of 5min, works as well as anything out there, and leaves your reed switch covers stock in case you want to revert. Tech tip o' the day...
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