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Discussion Starter #1 (Edited)
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.
http://www.vn750.com/forum/showthread.php?p=167113&posted=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.
 

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Discussion Starter #2
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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Discussion Starter #3
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.
 

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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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Discussion Starter #5
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.
 

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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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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.
http://www.vn750.com/forum/showthread.php?p=167113&posted=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.
 

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Discussion Starter #8 (Edited)
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.
 

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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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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
 

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Discussion Starter #11
Thank you.

I put the filters directly on the carb inlets with a piece of 1" tube. So the filters are mounted vertically right ON the carb. From there, the tube makes a 90 degree turn to the petcock. The top of the arc on both tubes is slightly above the petcock. I have a full tank of gas to the filler neck and the lines are not kinked.


I called the local parts store. The have clear 1/4" fuel hose in stock. I'll rework it tonight (I hope) with the clear tubing, and at least that'll tell me something.

It's possible the fuel isn't making it to the bowls like you mentioned cause the arc is higher than the petcock.... The clear fuel line should tell me that.

Man I hope I don't have to pull the carbs again. I swear the floats were set PERFECTLY according to the manual. They exactly halfway between the two nubs on the bowl casting without depressing the spring plunger on the valve. I did the clear tube off the bowl in reference to the screw thing just like the manual says. I don't have the fancy special tool part number KAW#12345 but the tubes filled up and give me a reading close to what I would expect.
 

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Discussion Starter #12
I might make a video of what's happening. I dunno if that will help anyone or not.
 

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Discussion Starter #13
The clear fuel line was not installed last night...... maybe tonight. Heck it's supposed to be running for a trip this weekend. THAT'S not looking too promising.
 

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Discussion Starter #14
If anyone is interested in installing clear fuel line, find something with the fiber reinforcement (mine doesn't). This stuff sucks man. There's no room to work, and it's very difficult to keep the line from kinking. AAAH!

I have one line on, the front one is being a royal pain. I've pulled it, cut, rerouted it at least four times and it still kinks. I plan to work on it more tonight.
 

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Discussion Starter #15
Alright, very quick details. I installed the clear fuel line, pulled a vacuum on the petcock and no fuel moved. I rerouted the lines, did some other stuff, etc. No luck. I dropped a line from the petcock into a jug and it works great....

Long boring story short, the fuel was not moving into the carbs, because the air was trapped from leaving..... the bowl vent was plugged.

I dunno how long I've been fighting this particular problem, but I took her down the road and it's smooth as glass from 900rpm - 7000rpm. It starts good, runs good and everything is right again.


Thanks for all your help. I'm just glad it's done.
 

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Um...lemme guess; mud dauber in the vent line? Dunno why I didn't think of the possibility of it being plugged; it's happened to me more than once. I'm still trying to figure out how mud dauber nests got built in the fuel lines and vent lines of a freshly rebuilt set of carbs sitting on my desk in less than a week. Now I gotta open 'em up again...
 

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Discussion Starter #17
HA! So they got mud daubers in TX too eh?

I had a spider (I think) build a nest in the vac connector on brake assist on my truck. It took me quite a while to figure out what was wrong. The neighbor found it accidently when he sucked on the fitting with his mouth...it come out, right into his mouth.... I almost threw up man.
 

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LOL; been there before! Yeah, we got 'em over here, too; I think the three most common variants are nationwide. We've even got an annual Mud Dauber Fest every March in Luckenbach. I found a honey bee stuck in a carb vent line once, too, but it's usually been a dead mud dauber; this last time it was just the mud.

At least they're not aggressive, altho they'll sting if you handle 'em. What we have to watch for around here are wasps; they can build one of those paper nests on a bike under a cover in a single day, and when you pull the cover off...

Jim
 

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HA! So they got mud daubers in TX too eh?

I had a spider (I think) build a nest in the vac connector on brake assist on my truck. It took me quite a while to figure out what was wrong. The neighbor found it accidently when he sucked on the fitting with his mouth...it come out, right into his mouth.... I almost threw up man.
That was prolly a dauber too. They kill spiders, carry them back to their nests and lay eggs in them. If you bust open a big dirt dauber nest it will be crammed full of spiders!

http://farm5.static.flickr.com/4032/5083819463_f0be680e00.jpg
 

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Discussion Starter #20
I've always wanted to take this bike to the dragstrip. I have a three tracks within 30-45 minutes prob'ly. Last night I realized I forgot how fast the VN750 is. I've never been on a sport bike, but this KAW begs to be run and I never do it. I putt around at 1/4 throttle or less 99% of the time. The bike doesn't complain about it, but it seems bored till I give it some gas.

Maybe not though. I'm still a beginner and haven't mastered the launch yet. Give me a 5mph rolling start though and the KAW will hit 70mph in nothing flat. It's definitely built for the 0-60 trip.
 
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