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Discussion Starter #1
Randomly, this started happening Wednesday during my ride home. I opened the throttle up completely to pass a car and as soon as it hit 4k RPM it immediately started sputtering and would not accelerate past 4-4.5k RPM no matter what. This weekend I took a look and was able to repeat the problem easily. I noticed, however, that if the bike is in neutral (parked or not) it will rev up to 8k RPM or so, but also does the same thing where it starts sputtering out. It almost feels like someone came and installed a governor on the bike when I wasn't looking.

I tried a few things, but nothing helped:

1. Ran it with the gas cap open, just in case there was an issue venting.
2. Removed the pod filters and cleaned/re-oiled them - but also took her around the block WITHOUT the filters, no difference
3. Checked the battery voltage, that looked good (12.something, can't recall offhand, this was parked with the engine off)

Here's a video I took earlier, it's 4 minutes long but here's the interesting bits:

https://www.youtube.com/watch?v=yaygAnUWnMs

0:22: Parked, revs to about 5k RPM with throttle fully opened
0:42: Riding down the street, again limited to about 4-5K RPM
1:30: Pulled out onto the major street, 1st gear to 4k RPM no problem, 2nd gear to 5k RPM starts sputtering
2:55: While rolling along, I pulled in the clutch and was able to rev up to the red line without sputtering
3:20: Slowed down to lower gears and gunned it again, 3rd gear it sputtered at 5k RPM
3:40: Coasting into my drive way in neutral, and my dumb ass downshifted into 1st without the clutch. Whoops! :BLAM:

I just replaced the spark plugs a couple weeks ago with new ones (gapped them myself), the charging system was replaced last year with a TPE stator and new R/R. Not sure what to look for or test for aside from what I mentioned...any ideas?
 

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1986 VN750
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I'd pop the carbs off and inspect. Could be as simple as crud in one of them jets.
 

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Mine has done this once per season since I bought it.

1oz of Seafoam per gallon of gas always seems to cure it until sometime in the next season.

I suspect dirt getting into the jets, but I've yet to see the inside of my carbs. My bike did sit a while before I bought it, so I'll bet there's crud coming loose from the bottom of the bowls.
 

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FREEBIRDS MC CENTRAL NY
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Really should not be revvin to 8grand in neutral.
 

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Discussion Starter #7
Not making a habit of it, just trying different things to pinpoint the issue.

I'll try seafoam first, if that doesn't help I'll pull the carbs and clean them out. I cleaned them out a few weeks ago, but I painted my tank a couple weeks after that, so there is a chance something made it's way in.
 

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Alpha Geek
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I've had this happen on different bikes for different reasons. The easiest fix is to back flush the carbs through the vents as Wolfie so often suggests. A proper cleaning (removal and complete disassembling, manual cleaning not just carb spray) and seafoam can fix it sometimes. Don't get carb spray on the air cutoff diaphragms or slide diaphragms. Remove those first.

Another time, I bought a bike with torn slide diaphragms. OEM slides are pricey, but there's a guy making parts that replace the plastic and rubber with one rubber piece, and they work GREAT for 1/3-1/4 the price. You can find them on the Googles.
 

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Only reason I don't do the backblow.... If there's a pile of dirt in the bottom of the bowl, I don't want to launch it up through the carb. Although the backblow can get you off the trail if you're stuck.
 

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Discussion Starter #10
Looks like it was the carbs. I cleaned them, changed the jets (been meaning to do that for awhile now) and good as new.
 

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Discussion Starter #11
ugh.. problem came back, dangerously. I was out riding, pulled up to a red light to turn right into traffic and waited for a gap to make my move. Saw a gap in traffic and pulled out, tried to gun the throttle and.... *sputter* *sputter* *sputter* *sputter* between 2-4k RPM, barely moved... nearly got me killed and the car behind me started laying on his horn.

Pulled off the road and took side streets home, but I'm pretty well scared. Need to fix this once and for all. I'm going to pull the carbs off again and look at them to clean again, but with brand new jets I don't know how that can be the problem. There is no rust in my tank, far as I can tell anyway.. I'm going to pull the petcock off and see if it's clogged? I tried flipping it over to reserve but that didn't make a difference. Will also check the fuel lines as well.

Here's what I'm doing, please feel free to suggest additions:

1. Pull carbs, recheck jets and floats
2. Pull fuel lines, check for leaks/clogs
3. Pull vacuum line, check for cracks
4. Pull tank, check for rust / debris
5. Pull petcock, check filter screens
 

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Discussion Starter #12
Alright, did everything I mentioned above...

1. Carbs looked fine, considering I just cleaned them a week ago this isn't much of a surprise. Floats move freely, far as I can tell everything is fine with the carbs.
2. Pulled fuel lines off, both of them looked good. No cracks, no clogs.
3. Vacuum line is the same, looks completely fine.
4. Looked in the tank with a flashlight, silver as far as I can see. No rust or rust spots anywhere.
5. Pulled the petcock, the filter screens both look nice and clean. No debris, dirt, anything. Disassembled the knob side, and it looks fine.

I put the petcock back in the tank and set the tank up on blocked. I then hooked up my hand vacuum pump to the vacuum port, and hooked both fuel ports up to hoses connected to a small container. Pumped the vacuum handle and fuel flowed pretty freely from both sides evenly. So I'm assuming the fuel tank / petcock are in good working condition.

I checked the spark plugs, they're white/light tan.

I put it all back together, went for a test ride and noticed the problem very early on - especially when I gun it and accelerate fast. But even when riding at 20mph down the side streets I noticed some sputtering just while going a steady speed in 4-5 gear at around 2500rpm.

I tried pulling over and opening the gas cap, and then riding a few more blocks with it open - made no difference though.

Went home, tried adjusting the carb air mix screws. I had them at 2 1/2 turns out, but I figured I'd go through and readjust to see if it makes any difference. I turned the screws all the way in, then backed them out 2 turns exactly. Went for a test ride, and it felt a little better, but still sputtered and seemed to lag a bit in throttle response.

I tried 1 1/2 turns out, and again it seemed a bit better but still sputtered quite a bit. Tried 1 turn out and it was about the same, so I backed it back out to 1 1/2 turns. While it is a bit better, I haven't done extensive test riding on major streets to see if there is truly a difference.

On top of all of this, I noticed I had some kind of leak from the gas tank - I can't tell where, but it appears to be on the right side near the front. When I had the tank off I examined it and couldn't find where the gas could be leaking from, but when it's on the bike after a ride there is a steady drip from the front right by the bolt holding the tank on, dripping right onto the exhaust. It runs down the inside of the tank and drips onto the rear cylinder head, so much that there's a yellow/hold varnish stain.

Finally.. to top off my bad day, I went to go fuel up since I partially emptied the tank to pull the petcock, and spilled fuel all over the top of my tank - ruining my rattle can job.

I've had enough for the day, but if anyone has suggestions I'll check 'em out tomorrow. :BLAM:
 
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