Kawasaki VN750 Forum banner

New bike, having air and fuel issue

12K views 110 replies 8 participants last post by  michiganteddybear 
#1 ·
Hello group, pretty new hear, I have recently picked up a 1985 vulcan 700, the bike has been well for best use of words "custom" built, I bought the bike as a project as I can't seem to get the bike to properly run. I have had the bike starting and running which adjustment to mixture, but dies shortly after. Reading up here about these bikes I've gathered that the carb jets are pretty maxed out from factory and changing the exhaust or airfilter set up sometimes results in changing the jets. So this bike I have has straight pipes and no air filter box but has k&N filters directly on the carbs. Any recommendations of what I need to check, or things I should do to try and get this "custom" bobber running properly? Thanks in advance
 

Attachments

See less See more
1
#2 · (Edited)
Might need to rejet and possibly clean carbs. Read upon the earshave on the Vulcan verses. Can you get me some close up pics of the rear exhaust where it comes off the head?
 
#3 ·
Certainly planning on having them properly cleaned, I read about the earshaving, and im kind of thinking they need to be resized because when the bike would start and run you couldn't give it any gas or it would bog out and cut off, the plugs show sign or it running lean as well
 

Attachments

#4 ·
I guess your buddy that you got this from couldn't figure it out either. That may be why he was finally willing to let you take it off his hands. lol Your only other posting (under Newbie Check-In) doesn't tell us too much about your wrenching and/or riding experience so it will be a little difficult for one of us to tell you exactly what to check or change initially but we will do our best as we always do. If we know you have some experience wrenching on bikes it is easier to direct you. Make sure you tell us all the changes from stock that you are aware of which could be difficult if you are not totally familiar with a stock VN 700. You explained about the filters and pipes already. Do you know what jets are in it at present? They may have been changed previously.

Good luck and post a few more pictures if possible.
 
#6 ·
I can say safely that for sea level, open pipes, and an earshave, you need 42 pilots, 142 mains and 2 shims under the needle. With 40 pilots my rear cyl would drop out at idle when warm. Spent a year and 2 carbs figuring that one out.
 
#7 ·
Yes I am curious as a former member here(named Wolfie)and I have been thinking of doing the exhaust like that and would like to see the manifold.sweet bike
 
#8 ·
I Apologize for not mentioning, I have mechanical experience with automobiles both fuel injection and carb, but have only had time to get my hands into a few bikes. Mechanically speaking the motor is stock as far as internally along with the carbs, so still running stock jets. Your correct I'm not exactly sure the original specs and layouts of a stock vn700 to really tell what has been changed and what hasn't. I've been doing my best to read up about it though I've checked fuel delivery and seem to getting plenty of fuel to the carb I truly believe the bike is leaning out honestly based on the plugs seeming burnt, a redish brown tent to them. As far as pictures go I will take some when I get off work to show the pipes placement specifically for those that are curious
 

Attachments

#27 ·
No need to apolgize for anything. Now that we know you have mechanical experience we can eliminate some questions and understand what you are telling us is happening and what has been checked so far. You understand carbs and you know how to read the plugs. We do have several VN 700 owners here so they can help identify a lot for you although the 700 and the 750 are almost identical. I believe if I remember correctly the number change was a technical issue and not a full production issue at the time. I was thinking the new jets should be 142 and 42 with two shims each but did not get a chance to confirm that before someone else helped out with the answer. I am still running straight stock so I never made the change.
 
#13 ·
Do you know if any work was done to the rear manifold to flip it or not?and where was the overflow bottle put?
 
#18 ·
They would have had to flip it over unless the pipe snakes under the motor.that is also the rear motor mount as well.that's what I am curious about
 
#19 ·
For what it's worth, the best jet prices I've found were at Power-Barn.com. Shipping seems to get wacky if you order more than three pair (goes from a USPS envelope to a >$25 FedEx option) but you could probably get around that with a phone call.
 
#24 ·
One carb per cylinder (2). One Pilot and one Main jet per carb (so you'll need two of each total). Don't forget the needle shims. You'll need two per carb (4 total).
 
#30 ·
Hardly Davidson couldn't compete, but all the big four did was tune em better so at under 700cc they were as fast or faster than the 750.
 
#31 · (Edited)
Sure doesn't look like a stock gas tank. Looks good though. Wonder what the tank is from?

Wolfie always told us Arctic Cat jets were the same, and normally quite a bit cheaper/easier to get. I settled on Rocky Mountain ATV to get mine 3 years ago, but ended up not needing them. They're now showing all the mains for $2.99, but on their pilot sizes they jump from 38 to 50, at $4.99.

https://www.rockymountainatvmc.com/p/898/32873/Pro-X-N424-22-Series-Keihin-Pilot-Jet-

https://www.rockymountainatvmc.com/p/898/25596/Keihin-99101-393-Series-Main-Jet
 
#34 · (Edited)
Could be wrong, but I think the tank looks longer and has a better swoop to it. If I knew what it was I'd probably look for one. Stock tank looks more stubby toward the rear, and yours probably holds more gas.

edit: First pic in post #3, definitely looks longer, but looks like the stock cap. Modified stock tank maybe.

edit 2: rear mount point looks same as stock, tank ends about the middle of the rear head, but possibly less space between triple tree and front of the tank.

or I'm being fooled by an optical illusion.
 
#37 · (Edited)
Yeah, I keep thinking... How the heck do you get a longer tank in the same sized space?

I guess someone changed the lines on a stock tank, the way the tank should have been done. Probably wouldn't be hard to weld the stock mount tabs onto the right tank either.

Maybe it holds less gas than stock. :)
 
#36 ·
Looks stock in front and someone played with the back.I'm liking your bike more every time I see it,Enginewolf
 
#46 ·
Okay beginning the carb jet change out taking it over to my shop, took some pics of everything for those that wanted to see more
 

Attachments

#48 · (Edited)
You are correct. Eye the rubber diaphragms real good for cracks, and make sure they seat right under the cap. Don't mix parts between carbs, at least the needles are different sizes. (pretty sure)

I'm thinking they may have put a skin on the tail end of that stock tank. Unless I'm still totally tricked. The work might be seen on the bottom somewhere.

Hard to see but it does look like they flipped the left side exhaust manifold, to exit right.
 
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top