Help, carb and rejetting issues - Kawasaki Vulcan 750 Forum : Kawasaki VN750 Forums
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post #1 of 23 (permalink) Old 03-21-2005, 10:28 PM Thread Starter
Art
 
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Help, carb and rejetting issues

Help, I hope somebody out there has more experience at souping up their 750 Vulcan than I do. I am trying desperately to dial in my carbs and feel that I am very close. I am running very fat main jets, bigger pilot jets, adjustable slider pins with clips set at 4 notches from the top and with 4 washers on top of the clips. Jet kit came from Factory Pro, but I have had to modify the main jets to get to the right size, i.e. drilled bigger. I know that I am close by inspecting my spark plugs after a hard run, they are almost the right shade of brown. I was experiencing a very lean condition untill moving the pins up from 3 notches to 4.
I have good start up, good midrange and poor wide open throttle. I have the pilot screws at 3.5 turns out and the bike does not smoke. I would say that I have good usable power until 7-8000 rpms. Then the engine feels like it has a rev limiter set. I thought I had a dirty fuel filter, it seemed worse when hot then when cold. I changed the filter, but no luck. I am wondering if I need to set the pins up one more notch, the problem with that is that I have yet to read anywhere of anyone running with this setup. The bike just acts as if it isn't getting enough top end fuel. Does anybody have any ideas?
Thanks in advance. Art
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post #2 of 23 (permalink) Old 03-22-2005, 01:46 PM
 
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Re: Help, carb and rejetting issues

Art,


I haven't re-jetted my VN750 yet, but have done several other bikes with CV carbs. I'm down to about 45 minutes from start to finish on my other bike. I am attaching a file that shouls help you out, but here is an explanation in a nutshell.

The pilot (or slow) jet provides the fuel at idle up until roughly 1/4 throttle. The most noticable effect of an incorrect mix from the pilot jet would be either popping on hard decel (lean condition) or rough running wet exhaust at idle.

The vacuum slide and needle take over from about 1/4 throttle to 3/4 throttle. The taper of the needle is the critical element here. I've never used the Factory Pro kit, (I'm a Dynojet guy) but I've never really had any problems in this area.

The main jets are what I suspect are causing your problem. These kick in from 3/4 throttle to full. Obviously if they are too small, you will experience top-end starvation.

A simple trouble shooting effort would be to wrap tape around your throttle and mark from 0 to 4 (quarters), and run it to see where your issue starts to turn up. That will tell you where to look.

From the looks of your intakes, I would suspect that you are providing the maximum amount of air the carbs can handle. With Dynojet jets, you should be somewhere between 130 and 144. This will vary depending on altitude and exhaust.

If you can't work out the Factory Pro, you can order DynoJet jets directly from DynoJet [www.dynojet.com] for $2 each plus shipping is 6 or 8 bucks. It would cost less than $30 to buy a handful of jets (step 2) and fine tune the carbs from there.

Hope this helped. Good luck.
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post #3 of 23 (permalink) Old 03-22-2005, 09:41 PM Thread Starter
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Re: Help, carb and rejetting issues

Thanks for the very informative info. I spoke with Factory Pro today and they pretty much confirmed your ideas on the main jets. I ordered a hand full of jets ranging from 150-170. The tech fellow figured I should be able to find a suitable jet within this selection. I must commend their tech support, they know their stuff and are very helpful. He figures that I am too fat on top end and I need to drop a few sizes, we'll see. I will post final details once I am satisfied with good results. Art
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post #4 of 23 (permalink) Old 03-23-2005, 01:05 AM
 
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Re: Help, carb and rejetting issues

I to have just purchased a Factory Pro Jet Kit (K24-1.0). It came with 132, 134, 138 mains. I have the 138's in now and it seems low on power still. With stock air system and cobra exhaust, Factory Pro says I should be using 134 mains. I don't get it. Some of you guys are using 144's?
BTW one other problem I have is the bike jerks in 5th gear (only) at all RPM's when under load??? Different problems?
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post #5 of 23 (permalink) Old 03-25-2005, 09:16 PM
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Re: Help, carb and rejetting issues

Well what we typically use is the 3.0 kit.
Factory Pro Tuning CRB-K24-3.0 carb kit

And I used 142's, most use 140's when they do the earshaves.

Details on parts and such here.
http://autos.groups.yahoo.com/group/.../Ear%20Shaves/

RB

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http://autos.groups.yahoo.com/group/CNY-Riders/
For Central NY, Northern PA riders & visitors passing through

Quote:
Originally Posted by Lex1982
I to have just purchased a Factory Pro Jet Kit (K24-1.0). It came with 132, 134, 138 mains. I have the 138's in now and it seems low on power still. With stock air system and cobra exhaust, Factory Pro says I should be using 134 mains. I don't get it. Some of you guys are using 144's?
BTW one other problem I have is the bike jerks in 5th gear (only) at all RPM's when under load??? Different problems?

Red Baron
Binghamton, NY
Alright Already, Lets Ride!!
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post #6 of 23 (permalink) Old 03-29-2005, 11:10 PM Thread Starter
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Re: Help, carb and rejetting issues

Ok, I think that I have finally found the right combination, after having the carbs off approx. 4 times and the bowls off nearly three times that amount. I am now running 170 main jets on both cylinders and have found that I have more usable power at all ranges than ever before. I was concerned that the bottom end was slow to come on, but after test riding other smaller Vtwins I believe mine is ok.
It actually runs strong from 1/4 throttle to WOT and cruising the interstate is no problem. Special thanks to cman for his input. If anybody needs any smaller main jets let me know, I now have several. Thanks, Art
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post #7 of 23 (permalink) Old 03-30-2005, 10:43 AM
 
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Talking Re: Help, carb and rejetting issues

Art,

As I said in my e-mail, if you installed the larger pilot jets you are probably too rich on your mixture screws. 3.5 turns out on the mixture screws seems excessive with the larger pilot jets. Your bottom end should be the easiest to dial in since the shaft drive on this bike prevents any gear ratio errors.

A few sugesstions: (Let the bike warm up completely before trying.)
1. The right way to set the mix is to find a downhill grade, power to the crest, downshift and drag the engine down the hill. If your exhaust doesn't sound like an old percolator coffee pot, you're too rich. Understand that when you go from on throttle to off, you are purposefully creating a lean condition. It's the way carburation works. If your bike isn't popping, you're not creating that lean condition (this doesn't occurr on a stock setup because you aren't pumping enough air through the engine).

2. Get a clean sheet of copy paper and clip at a 45 degree angle to the end of your exhaust. Rev the bike from 0 to 1/4 throttle. If the paper starts to change color, you're too rich.

I think either of these will show that you are too rich on the screw setting. Turn the screws in until they are LIGHTLY seated. Back them out two turns. Go make a run. Adjust accordingly.

Just a guess, but you will probably end up at 2 1/2 to 2 3/4 turns out. You'll definitely feel the difference through your Levi's tag. On the other hand, if you don't re-adjust, you'll probably never need your choke again!
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post #8 of 23 (permalink) Old 07-09-2005, 09:36 PM
 
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Re: Help, carb and rejetting issues

WOW ! This is the best info I've read on rejetting the VN750 carbs !!!

Hey Art, What elevation above sea level do you live?
I'm in Dallas TX at a humid 485' ASL & am wondering if I need as big of main jets as you when I do the ear shave & carb rejet.
What exhaust are you running? Mine are V&H Cruzers.

Thanks,
Bill
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post #9 of 23 (permalink) Old 08-30-2005, 11:43 PM
 
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Re: Help, carb and rejetting issues

Mine is really screwy... I have a 700 I am running 45s for the Pilots and 145s for the Mains, front cylinder is at the second clip position from the bottom and the rear is at the third from the bottom. It works great!!! I was always surprised by this set up though because everyone else has 50cc on me but I still require more fuel???????


John Auten
Rising Sun, Md.
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post #10 of 23 (permalink) Old 10-09-2009, 09:49 PM
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I am having the same problem that this guy is on my 700... Runs alot better than before but at 7-8K It falls out... I am running Factory Pro 140 in front and 142 in back. Got the needle clipped up 3 notches. Any idea on where too go form here?
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