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Carbs and Fuel System
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post #1 of 21 (permalink) Old 04-25-2011, 09:56 AM Thread Starter
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carb opinions wanted

1992 VN750 - all stock w/ Cobra exhaust

I'd like your opinions please:

I've been working on my bike after sitting for 6mo, replaced the stator (finally) and decided I had to pull and disassemble the carbs since the bike wasn't running properly.
https://www.vn750.com/forum/showthrea...d=1#post167113


While I had the carbs apart, First I removed the aluminum plugs on the AF mixture screws still sealed front the factory. My notes are at home, but one screw was 1-5/8 turn out, while the other was 2-1/2 turn out. I thought this was strange, so I mention it here. Also, both jets are labeled 132.... Aren't they supposed to be two different sized jets??

The last thing: If an exhaust gasket is bad and it's sucking air, that pipe will pop (after-burn) right? I expect it to pop all the time too probably right? Will this affect how the engine runs?? I'm gonna change the gasket, that's no problem... it's just for my information.


Thank you.

Last edited by spiral_72; 04-25-2011 at 12:01 PM.
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post #2 of 21 (permalink) Old 04-25-2011, 10:00 AM Thread Starter
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Ok, ONE more thing...... The float valve, front cylinder..... the tiny spring plunger on the needle where it contacts the tang on the float was stuck in. Am I thinking correctly that this would cause MORE fuel in that bowl? Would you expect that cylinder to run any richer due to the extra fuel in the bowl? With the plunger working properly, it only strokes maybe 3mm (1/8")
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post #3 of 21 (permalink) Old 04-30-2011, 12:02 AM Thread Starter
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So the bike continues to run bad. A buddy suggested I sync the carbs again..... so I synced the carbs closer than any human has ever on a VN750.

Same problem.

It acts as if it's running out of gas, but then picks back up.... sometimes it dies. Plenty of gas and the cap is open so it's not phantom out of gas syndrome. I adjusted the floats and checked them no less than six times before I put the carbs back together. THen I checked the fuel level in the bowls with the little clear fuel line trick. It's ok.

Same problem.

Then I had a thought. Thanks to someone on here (gotta look up their name) I had installed two clear fuel filters. Hmmm, so grab the flashlight... with the engine running strong I see nothing. Then I saw the fuel level steady drop in the filters. As soon as it got below the filter into the line it sputtered and died.

I'm pulling the tank for the 30th time. I guess I;ll pull the petcock and check the filter screen for debris.

1992 VN750 dark blue / black - stock
Cobra exhaust
Oversized front tire to correct speedo & improve handling
New stator and Vreg 4/11
Sealed battery
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post #4 of 21 (permalink) Old 04-30-2011, 06:57 AM
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More likely you don't have enough vacuum at idle to keep the petcock open. Check the vacuum pipe to the petcock.
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post #5 of 21 (permalink) Old 04-30-2011, 09:31 AM Thread Starter
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The tank is apart. I didn't see anything wrong unfortunately but I cleaned the petcock in the parts washer anyways.


Vacuum? That is valid, but don't you think I would have seen that when I synced the carbs? I'm using the yardstick and 6ft of clear tube with motor oil in it DIY gauge.

I wish I had a vucuum pump and I could check your idea! Hmmm.

1992 VN750 dark blue / black - stock
Cobra exhaust
Oversized front tire to correct speedo & improve handling
New stator and Vreg 4/11
Sealed battery
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post #6 of 21 (permalink) Old 04-30-2011, 10:17 AM
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Disconnect the vacuum pipe from the carb end and plug the carb nipple. Then put the free pipe end in your mouth and suck. It does not need much to open the petcock.
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post #7 of 21 (permalink) Old 04-30-2011, 07:09 PM
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Quote:
Originally Posted by spiral_72 View Post
1992 VN750 - all stock w/ Cobra exhaust

I'd like your opinions please:

I've been working on my bike after sitting for 6mo, replaced the stator (finally) and decided I had to pull and disassemble the carbs since the bike wasn't running properly.
https://www.vn750.com/forum/showthrea...d=1#post167113


While I had the carbs apart, First I removed the aluminum plugs on the AF mixture screws still sealed front the factory. My notes are at home, but one screw was 1-5/8 turn out, while the other was 2-1/2 turn out. I thought this was strange, so I mention it here. Also, both jets are labeled 132.... Aren't they supposed to be two different sized jets??

The last thing: If an exhaust gasket is bad and it's sucking air, that pipe will pop (after-burn) right? I expect it to pop all the time too probably right? Will this affect how the engine runs?? I'm gonna change the gasket, that's no problem... it's just for my information.


Thank you.
Main jets are both #132.
Jet needles are different.
For 1987-2002 (latest year specified in my Clymer manual) the front is N53A. Rear is N53B.

Gordon

1991 VN 750 -"Cosmic Lady" or "Bad Girl"?
Purchased May 16, 2008
Approx.19,300km (12,000 miles)

H-D windshield
Relocated R/R
MF-AGM battery
Fiamm Freeway Blaster horns
F&S luggage rack and engine guard
Kury Offset Hiway pegs
July 13, 2016, Riding on the DARKSIDE now, Classic Radial 165/80-15


TOP TEN THINGS A NEW RIDER/OWNER SHOULD DO. Click on link.
https://www.vn750.com/forum/11-vn750-general-discussion/9127-top-ten-items-you-would-suggest-new-owner-do-his-new-ride.html
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post #8 of 21 (permalink) Old 04-30-2011, 08:58 PM Thread Starter
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Quote:
Originally Posted by pappa View Post
Disconnect the vacuum pipe from the carb end and plug the carb nipple. Then put the free pipe end in your mouth and suck. It does not need much to open the petcock.
Yessir, it works like a champ! Actually that's how I've been draining the tank. Suck on the vac line and pinch it with vise-grips. (I use an old line with a union, I did NOT pinch the line on the bike).

I cleaned out the tank since I didn't see anything wrong with the petcock. I had almost no tiny stuff I would call rust.... just barely enough to turn the bottom of a filter off-white. I did have some very large pieces of paint though. Most was flake sized, some pieces, one piece was 1/4" x 2" long ribbon...... I don't know where it come from. It's all back together now, but still runs bad.

I took it on a short trip. It did ok I guess, but stumbled a lot with a hesitation around 4500 in neutral, but I can power through it most times. Under load I have hesitation/stumble around 3000 that cannot be powered through. On the return trip I was annoyed and give it WOT from a rolling a stop in 1st gear. The engine come to life, full power and haulin' *** and it stayed that way to 3rd gear till I let it off.

Last thing, if while riding I shift really early, like 2000rpm through 5th gear, she acts pretty good.

1992 VN750 dark blue / black - stock
Cobra exhaust
Oversized front tire to correct speedo & improve handling
New stator and Vreg 4/11
Sealed battery

Last edited by spiral_72; 04-30-2011 at 11:00 PM.
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post #9 of 21 (permalink) Old 04-30-2011, 10:13 PM
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do the tank cleaning and maybe line it with a tank liner of your chosing... many will jump in here.. I am not a fan of adding other filters to the lines going to the carbs but it shouldnt be an issue.. some will disagree with me here...you may have to clean your carbs again as well.
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post #10 of 21 (permalink) Old 05-01-2011, 02:11 AM
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One thing about putting filters in the fuel lines between the petcock and the carbs; make sure the hoses don't arc up to the filters, then back down to the carbs. If the filters are higher than the petcock outlets, you're gonna starve your carbs once the fuel in the tank gets below a certain level.

Jim

J.D.
Kerrville, TX
'95 Vulcan 750 "Therapy II",
aka "Raggedy Ann"
'95 VN750 project
'03 VN800B "The Little Black"
'04 VN800E Drifter project
'93 VN1500A custom project
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