Rich front - lean rear - Kawasaki Vulcan 750 Forum : Kawasaki VN750 Forums
Carbs and Fuel System
From the gas tank to the carbs
All fuel system discussion

Reply
 
LinkBack Thread Tools Display Modes
post #1 of 23 (permalink) Old 03-13-2007, 02:58 PM Thread Starter
Junior Member
 
Reno2door's Avatar
 
Join Date: Jan 2007
Location: Southeast (Fl, Al)
Posts: 16
iTrader: (0)
 
Rich front - lean rear

VN750 cylinders (not human body!) hee-hee-hee....Anyway!

I have hunted for but have not found the answer to my question. I hope someone can tell me where to start the troubleshooting process for this:

Bike: 1994, 60K miles, have run Seaform through tank three times in last 700 miles or so, replaced vacuum line on petcock within last 200 miles. I have done the Grambo Trick on the cam chain tensioners and I do have after market exhaust. The Kaw shop drilled out the jets. Still have pop on deceleration but it is worse some time than at other times. Ran out of gas the other day with only 6-8 miles on reserve. Could hear gas sloshing but it wasn't enough to run. Put in about 1/2 gallon and it cranked right up. Missed after fillup so I put in Seaform which straightened out the miss. Runs okay, keeps up with the pack at Interstate speeds but there must be something wrong because:

My front cylinder is running very rich...dark carbon buildup on plugs, black smoke on startup and when "getting down on it."

The rear cylinder is apparently running a little lean... plugs are basically grayish, not really any brown there.

This began with the last set of plugs I put in the machine around 300-400 miles ago. The set I removed at that time were all grayish-brown without any sign of deterioriation. I am getting ready to put NGK iridiums in and would like to know where to begin with the troubleshooting. I see that there are SO MANY things to check a flow chart would be helpful but at this point any guidance on the simpler side of life would be greatly appreciated.

Thanks in advance for any help!!

Reno
Reno2door is offline  
Sponsored Links
Advertisement
 
post #2 of 23 (permalink) Old 03-13-2007, 03:04 PM
Members who have donated towards server costs
 
Crobins365's Avatar
 
Join Date: Jul 2006
Location: Kennett Square, PA
Posts: 3,505
iTrader: (48)
     
Have you done a carb sync yet? Seems like the simplest explanation for the two cylinders running at different levels.

C
Crobins365 is offline  
post #3 of 23 (permalink) Old 03-13-2007, 04:19 PM
Members who have donated towards server costs
 
93VN750's Avatar
 
Join Date: May 2006
Location: Tampa, Florida
Posts: 1,766
iTrader: (2)
 
Send a message via Skype™ to 93VN750
Did this problem start right after the shop drilled out the jets? Or did it develop some time after that?

How does it idle?

Jon

93VN750, under re-construction
vn750.com Member # 828

Rick's Stator and R/R
MF AGM Battery
Coastered
Degoated
Shaved & Jetted
Iridium's
MAC Tapered Staggered Pipes
Battery/Temp/Clock Gauge
Stainless Steel Brake Lines
Dunlop D-404's
23,XXX miles and holding pending gasket change (underway!!!)
93VN750 is offline  
 
post #4 of 23 (permalink) Old 03-13-2007, 05:13 PM Thread Starter
Junior Member
 
Reno2door's Avatar
 
Join Date: Jan 2007
Location: Southeast (Fl, Al)
Posts: 16
iTrader: (0)
 
The jets were drilled several hundred miles ago, so it has developed over time.

This problem actually has shown up since I rode it from Mobile, Alabama to Tallahassee, Florida. This was also the first time I had used reserve gas setting since I have had the bike (bought used at about 52K miles last March 2006.)

The plugs were normal on removal in Tallahassee but when I returned to Mobile, I trailered the bike back. It cranked without problem to load onto the trailer. The first time I tried to start it (about a week later), it wouldn't, ran the battery down and while charging the battery discovered the vacuum line cracked on the petcock and replaced it. It started fine after the battery was charged but it must have been deteriorating ever since then because after less than 100 miles it got to where it didn't want to start. So I pulled the plugs and found them fouled like now. Replaced them with standard plugs and have been riding it since then, probably about 600 miles or so. Pulled them today to put in the iridiums and found the carbon buildup on front ones, which is different that the last set because there was unburned gas on the front ones the last time. But when we pulled the plugs the last time it had not been riden in several days, just started up and electrical connections cleaned up. I ran it 150 miles or so Sunday (day before yesterday). Haven't run it since Sunday.

The idle is a little sporaic. Typically, when cold I have to adjust the idle up a little until the bike gets good and warm and then I have to idle it down again. If I watch my tach when idling it fluctuates as I understand is normal between 50 rpms (1000-1050).

It is a little hard to start when warm. Many times will crank it over 2-3 times (don't touch throttle), then it will backfire and start the next time. Only other times it back fires is on deceleration and that is not consistent. Seems to depend on how much I have it wound up and how quick I back out of the throttle.

I have not done the carb sync but have just assumed they would have checked that when they drilled the jets.
Reno2door is offline  
post #5 of 23 (permalink) Old 03-13-2007, 07:28 PM
HAWK
 
Ccspinner's Avatar
 
Join Date: Feb 2006
Location: Chicago land
Posts: 2,576
iTrader: (9)
 
Send a message via Yahoo to Ccspinner
With a dealer I would assume nothing. The backfiring when starting is usually caused by a week Batt. Why did they drill out the jets and not replace, you can't be sure what size they are or that they are correct when you drill them out.
That is a cheep way to do it, If they drilled out one jet a little big you will have one richer that the other, it does not take much to make a big difference.

Chad Falstad "Hawk"
Vroc #17649
2011 HD Ultra Classic "angel"
2001 Nomad 1500 Sold March 2012
2001 VN 750 "Sold June with 2008 with 21,000""Serinity"
Ccspinner is offline  
post #6 of 23 (permalink) Old 03-13-2007, 08:00 PM Thread Starter
Junior Member
 
Reno2door's Avatar
 
Join Date: Jan 2007
Location: Southeast (Fl, Al)
Posts: 16
iTrader: (0)
 
So you suggest I put new jets in...okay. This motor is supposed to have been bored to "1 over" so what size jets would you guess would be appropriate?
Reno2door is offline  
post #7 of 23 (permalink) Old 03-13-2007, 08:21 PM
Members who have donated towards server costs
 
Crobins365's Avatar
 
Join Date: Jul 2006
Location: Kennett Square, PA
Posts: 3,505
iTrader: (48)
     
I think I lost track of the time sequence,but see if this is about right:

"Several hundred" miles ago, the shop drilled out the jets
You rode the bike from AL to Tallahassee after that, and everything was ok - plugs were normal
Trailered the bike back to AL - bike wouldn't start and you found the vacuum line on the petccok cracked. Replaced that. Rode 100 miles, pulled IR plugs and found them fouled "like now" (Carbon front, gray rear) only at that time there was also unburned gas on the front plug
replaced with std plugs - rode around 600 miles; pulled 'em and now they're carbon fouled front and gray rear. But no unburned gas on the front ones.

I agree that the drilled jets sound highly suspicious, but so does the cracked vacuum line since everything appeared fine on arrival in FL, but has deteriorated since. How was the bike held down on the trailer? That is, where were the tie-downs located? If you can recreate that scenario, it's possible that other lines, hoses, etc. were "tweaked" on the trailer ride back. How does the vacuum line look on the rear cyl?

C
Crobins365 is offline  
post #8 of 23 (permalink) Old 03-13-2007, 08:25 PM
Members who have donated towards server costs
 
93VN750's Avatar
 
Join Date: May 2006
Location: Tampa, Florida
Posts: 1,766
iTrader: (2)
 
Send a message via Skype™ to 93VN750
I doubt that boring it 1 over would require new jetting. In fact, unless you have changed the air intake system, air filters, air box, etc., you shouldn't have to rejet.

If you do not get more air in, then you can not get more air out so mixture shouldn't be changed over stock.

I would pull the carbs and make sure that everything is in order. The diaphrams are both good, slides are free to move, all air & fuel passages are clear, and put in a set of new factory jets, of stock flow rating.

I would sync the carbs and set the idle mixture screws.

Having made sure the fuel system is right, another possibility is that your front coil has an issue and is not putting out correct spark. You could switch the coils and see if the problem follows the coil.

The hard start when hot is probably your battery. Really need a good MF AGM style battery with our electrical systems.

And yes, assume the dealer does nothing they say and you will do yourself a favor.

Jon

93VN750, under re-construction
vn750.com Member # 828

Rick's Stator and R/R
MF AGM Battery
Coastered
Degoated
Shaved & Jetted
Iridium's
MAC Tapered Staggered Pipes
Battery/Temp/Clock Gauge
Stainless Steel Brake Lines
Dunlop D-404's
23,XXX miles and holding pending gasket change (underway!!!)
93VN750 is offline  
post #9 of 23 (permalink) Old 03-13-2007, 08:58 PM Thread Starter
Junior Member
 
Reno2door's Avatar
 
Join Date: Jan 2007
Location: Southeast (Fl, Al)
Posts: 16
iTrader: (0)
 
The rejetting was because of new exhaust. I can't tell you the brand but it takes all exhaust to right side of bike. I am going to find out brand now. That was the purported reason for the popping back was the new exhaust.
Reno2door is offline  
post #10 of 23 (permalink) Old 03-13-2007, 09:23 PM
Geek
 
rnewell's Avatar
 
Join Date: Mar 2006
Location: New Jersey
Posts: 872
iTrader: (0)
 
Just putting exhaust on doesn't require new jets. I agree with everything Jon said.

Ron from Jersey
2005 VN750
HellFire windshield
Kaw extended backrest
Cobra exhaust
Re-located stator wires
Side bags
15,000 Miles July/2012
It's PAID OFF ! May 2009
rnewell is offline  
Sponsored Links
Advertisement
 
Reply

Bookmarks

Quick Reply
Message:
Options

Register Now



In order to be able to post messages on the Kawasaki Vulcan 750 Forum : Kawasaki VN750 Forums forums, you must first register.
Please enter your desired user name, your email address and other required details in the form below.

Once registered, your User Name"cannot be changed". We can make exceptions within 7 days, but after that, it is set in stone.

User Name:
Password
Please enter a password for your user account. Note that passwords are case-sensitive.

Password:


Confirm Password:
Email Address
Please enter a valid email address for yourself.

Email Address:
OR

Log-in










Thread Tools
Show Printable Version Show Printable Version
Email this Page Email this Page
Display Modes
Linear Mode Linear Mode



Posting Rules  
You may post new threads
You may post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are On

 
For the best viewing experience please update your browser to Google Chrome