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Old 04-23-2011, 04:18 PM   #1
Pa. Vulcan
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Default Air/Fuel mixture adjustment help. Vulcan 800 rear cyl running rich.

2000 Vulcan 800 classic
Bike has 19K miles.
Hypercharger and straight pipes.

I don't know what jet size was installed with the HC.
Runs good but rear cyl is a bit rich. black soot in pipe and when reving up towards limiter on acceleration it often stays rev'd for a 1/2 second or so when I roll off the throttle.
I know there is a number of things that could contribute. I found no exhaust leaks and no intake leaks I could find. I am going to check valves soon, but in the meantime I checked the AF screw and found it 4+ turns out from bottom.
I turned it in approx 1/2 turn and I think it's better, but barely. Problem is that I can not tell the difference by ear between appox 3 to 4.5 turns on the screw when adjusting it. It doesn't seem to change noticeably between 2.5-3ish and about 4.5 turns.

So regardless the valve check in the future, how do I best set the mixture? Will a vacuum gauge be more accurate?
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2000 Vulcan 800 Classic
Cobra Pipes and highway bars. ~ Custom paint / side panels. ~ Kuryakyn hypercharger ~ Drag bars ~ Custom mirrors, levers, and Baron Dually pegs ~ Mustang saddle ~ custom/lowered taillight/plate holder ~ LED accents
2006 Vulcan Nomad 1600
V&H Pipes ~ Mustang seats ~ Luggage racks ~ dually highway pegs ~ Light bar
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Old 04-23-2011, 10:30 PM   #2
sfair
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Some questions:

1. How long have you owned the bike?
2. Has it done any long term sitting?
3. Who did the modifications?
4. How do the plugs look?
5. Is the problem the rpm hang?

Post back.
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Old 04-24-2011, 07:54 AM   #3
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sfair While you are looking at this thread I would like to ask you what causes the rpm hang Mine was doing that when I rejetted and stopped when backed up the number of turns.i am planning on doing a coyate air change on my 1500 and also want to know how many turns out you suggest to try! thanks for you're time! Mike
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Old 04-24-2011, 10:56 AM   #4
Pa. Vulcan
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Quote:
Originally Posted by sfair View Post
Some questions:

1. How long have you owned the bike?
2. Has it done any long term sitting?
3. Who did the modifications?
4. How do the plugs look?
5. Is the problem the rpm hang?

Post back.
Thanks for the reply. Answers and more info:
1) Since December.
2) The person I bought it from has two other bikes, so this one was not used as regularly as it will be now. He purchased it from someone who could not ride any more in 2005 and put about 5 K on it. So yes, it's safe to assume it has sat at least for the winters. here in NE PA.
3) The carb/HC install and pipes were installed by the first owner.
I did most of the 20K service over the winter (cables, brakes, replaced bearings chain sprockets, etc) I did not do the top end service (valves-etc) yet nor have I done a carb tear down. I did run seafoam through the carb procedure when I first got it.
Now that the spring weather is here I put ~450 miles on it so far.
I have been adding approx 1 ounce of seafoam per gallon with each fill-up as well as the appropriate dose of startron for the ethanol (approx 1/2 ounce per 4 gal)
I replaced the exhaust gaskets as they were both leaking, but particularly the rear. And properly torqued the exhaust. No more leaks.
I removed the EPA valve/hoses and installed caps on the corresponding reed valve and airbox connectors
The pipes had no baffles, I installed cheapie can opener type but was never happy with the sound so I recently installed HP-Plus baffles (free flowing).

4) Front looks normal, rear was sooty black.

5) RPM hang seems to be much less now that I have the AF mixture screw set at 3.5 (it was at 4).. It was doing it pretty consistent when reving 6-7K+, now it seems to do it occasionally, but not for nearly as long. Not sure if some amount of hang is normal or not.

Other thoughts: I'm not sure of this makes as much difference as I think it does, but I also have been driving it differently now that I am used to it. When in between gears, so to say, I leave it in the lower gear to keep RMS up rather than bog down by shifting up. Example, criusing a back road at 50 I'll leave it in 4th. Especially now that I lowerd the RPM by ~200 by installing 17/40 sprockets. But I am not sure how much difference that will make. I have a lot of engine experience from my youth working on cars in the late 70's - early 90's, but bikes (working on them) is somewhat new to me. I'm *assuming* lower RPM will exasperate any symptoms associated with running rich, like fouled plug(s) or valves.
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2000 Vulcan 800 Classic
Cobra Pipes and highway bars. ~ Custom paint / side panels. ~ Kuryakyn hypercharger ~ Drag bars ~ Custom mirrors, levers, and Baron Dually pegs ~ Mustang saddle ~ custom/lowered taillight/plate holder ~ LED accents
2006 Vulcan Nomad 1600
V&H Pipes ~ Mustang seats ~ Luggage racks ~ dually highway pegs ~ Light bar
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Old 04-24-2011, 11:24 AM   #5
sfair
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Since you have auto experience, let me run this by you.
Your rear cylinder may be running rich because of the combination of mods that have been done. Because of the firing order, the timing of that order, the design (or lack thereof) of the intake, you could be suffering from charge pile-up in the intake.
Just like on a small block Chev, there are some uneven fuel distribution problems with the stock intake manifold but when you install a single plane, one of the back cylinders really starves for charge and the other has excess. If you remember the old Holley "Z" series of intakes, it had a balancing port that helped that issue by pulling excess charge from one cylinder and feeding it to the other.
When you alter exhaust and intake systems (air cleaner included) the tuning is upset and some other problems may be introduced.
Factory systems usually offer some leaway, but as combinations are altered, the softness of the allowable tune starts to narrow and various systems become more critical to the correct operation of the engine. You did mention something about bogging....

Now, what you are going to have to do is:

1. Ensure that all carb functions are in order.
2. Tune the jetting so that the bike idles clean and you may have to split the difference on the main jet to obtain the best plug reading on both front and rear cylinders.

I do not usually delve into questions on modified bikes because it is difficult over the internet and a lot more complicated than most realize. It can be a bag of work too if one wants to make sure the tune is spot on!

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Old 04-24-2011, 11:29 AM   #6
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Quote:
Originally Posted by mikeyger View Post
sfair While you are looking at this thread I would like to ask you what causes the rpm hang Mine was doing that when I rejetted and stopped when backed up the number of turns.i am planning on doing a coyate air change on my 1500 and also want to know how many turns out you suggest to try! thanks for you're time! Mike
If you can catch Pat C. attention, he just had this problem and maybe he can help.
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Old 04-24-2011, 08:03 PM   #7
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Just my .02 as far as my experiance.
RPM's hanging up normaly mean the m/j is too small for the application which means its running lean.
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Old 04-26-2011, 09:23 AM   #8
Pa. Vulcan
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Quote:
Originally Posted by sfair View Post
...you could be suffering from charge pile-up in the intake.
Just like on a small block Chev, there are some uneven fuel distribution problems with the stock intake manifold but when you install a single plane, one of the back cylinders really starves for charge and the other has excess. If you remember the old Holley "Z" series of intakes, it had a balancing port that helped that issue by pulling excess charge from one cylinder and feeding it to the other.
I know exactly what you're talking about and it makes perfect sense. [lilght bulb] I had not even considered that similarity.


Quote:
Originally Posted by sfair View Post
Now, what you are going to have to do is:

1. Ensure that all carb functions are in order.
Agreed. That is next on the list. Hopefully the weekend or so I'll get the time.

Quote:
Originally Posted by sfair View Post
2. Tune the jetting so that the bike idles clean and you may have to split the difference on the main jet to obtain the best plug reading on both front and rear cylinders.
Been reading up on the CV carbs, so i'll order a jet assortment and after a good cleaning and inspection I'll work through the jets, needle adjustments, etc, if needed.


Quote:
Originally Posted by sfair View Post
I do not usually delve into questions on modified bikes because it is difficult over the internet and a lot more complicated than most realize. It can be a bag of work too if one wants to make sure the tune is spot on!
Understood. Appreciate the assist.

Another Q.
When setting the AF mixture the other day, the (el-cheapo) vacuum gauge, no dampening, was bouncing a good +/- 4psi at idle. Is that normal with these single CV's? I can find no vacuum leaks anywhere, checked twice. Once with propane and once w/starting fluid.
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2000 Vulcan 800 Classic
Cobra Pipes and highway bars. ~ Custom paint / side panels. ~ Kuryakyn hypercharger ~ Drag bars ~ Custom mirrors, levers, and Baron Dually pegs ~ Mustang saddle ~ custom/lowered taillight/plate holder ~ LED accents
2006 Vulcan Nomad 1600
V&H Pipes ~ Mustang seats ~ Luggage racks ~ dually highway pegs ~ Light bar
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Old 04-26-2011, 09:52 AM   #9
sfair
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You need to restrict the vacuum to your gauge to stop the bounce. You can partially pinch off the hose with a clamp, insert an old jet into the hose, make your own restriction, etc. in order to get a good reading.
To my knowledge, those carbs do not have a replaceable needle seat, so if the seat is worn, damaged, etc. and a new needle does not work correctly, then there could be big trouble. Maybe someone makes a kit to install one??? I do not know.

Post back with your results.
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Old 04-30-2011, 12:36 AM   #10
Pa. Vulcan
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Ok, pulled the carb tonight.

Findings:
Carb to intake boot was loose. The clamp on the carb side was not tightened at all. Carb was actually pulled out of the boot slightly (1/8" or so)
Carb was filthy. I wondered why the float drain was so slow (drip....drip....drip) When I removed the bowl the bottom was caked with brown goo.
Main jet: 170
Slow: 48
Not sure if the needle is stock or not. It was marked 008X and had 6(If I recall correct) grooves. Clip was on the third groove from the top and there were 3 washers on top.
Floats measured 16mm I adjusted to 17.5 just in case.
A lot of crud in the bottom (accelerator?) diaphragm.
Plugs: Front was slightly rich looking this time. Rear more so as last time.

So I cleaned every thing good. Made sure to blast cleaner through all passages.
reinstalled needle the same as it was. Tightened boot properly when putting back on bike.
Set pilot/AF screw to 3 turns out.
Fired it up and went for a ride. Idle and low speed still seems rich, a little hesitation on throttle, less when warmed up, but still there while somewhat intermittent. Sometimes bogs/idle drops upon pulling in clutch after slow speed , such as at lights/stop signs.
higher RPMS run great. Both higher rpm to wot is better (probably just from the cleaning. And steady cruising at mid rpm's is smoother. So some progress there.

Tomorrow I'll put a few miles on and also do a idle drop adjustment on the pilot.
Seems odd to be acting so rich at slow speed. From reading it seems a lot of folks go up to a 50 slow jet. This has a 48, well, unless someone drilled it or something.

ETA: Should the needle have any play? It has a fair amount of up/down play (bounce) with the retainer seated on it as well as some side-to-side(wobble)
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2000 Vulcan 800 Classic
Cobra Pipes and highway bars. ~ Custom paint / side panels. ~ Kuryakyn hypercharger ~ Drag bars ~ Custom mirrors, levers, and Baron Dually pegs ~ Mustang saddle ~ custom/lowered taillight/plate holder ~ LED accents
2006 Vulcan Nomad 1600
V&H Pipes ~ Mustang seats ~ Luggage racks ~ dually highway pegs ~ Light bar

Last edited by Pa. Vulcan; 04-30-2011 at 12:45 AM.
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