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Discussion Starter #1
The bike has been running great over the past couple of weeks. The idle seemed to be on the low side until the bike really warmed up (heard that a few times here, so I didn't get worked up about it). Yesterday, after about 25 miles of riding home from work, I noticed a little hesitation, almost like I was running out of gas, and thought Oh $#*& now I have the phantom out of gas syndrome! But, it cleared up as quick as it came, bike never stalled. This morning on the way to work, she ran like a clock. On the way home things went into the toilet! About 5 miles into the ride it really started to idle rough (almost a full tank of gas) at a stop light. Pulling away I had to play with the throttle to keep it from stalling, then she fired up and went. At the next light, I noticed that the rpm's stayed high when I pulled in the clutch, and came down veeeerrrryyy slowly. As long as I was in gear and moving, I was able to keep going. Any time I needed to idle, the rpms would stay high and sometimes come down and sometimes not. The adjustment knob was useless, and I had to pull to the side of the road 3 times. I finally got the bike home. I already had Seafoam in the tank. I drained the carbs and filled them with solvent, let them sit for 15 minutes or so, then drained them out. Started the bike, and it seemed to idle ok, but a quick test ride and absolutely no power. It ran, but it felt like I was dragging a car behind me. Toward the end of the 5 mile ride, it surged a bit every now and then, but it was not good.

Okay so my limited diagnostic skills are telling me that I really need to pull the carbs and clean them out. Plugs are clean, both cylinders seem to be firing, no smoke, a little popping, compression is 170 - 175 on both cylinders, charging system seems to be working. I'm guessing fuel system at this point.

Like I said, I have limited diagnostic skills, so I am hoping to get some input from the more experienced folks in the group before I start wasting a whole bunch of time for no reason. I plan to pull the carbs and thoroughly clean them, and also take apart the petcock and clean the screen. I should probably also clean out the gas tank (in case there is some gunk hiding in there as well).

Does this sound about right? Am I barking up the wrong tree? Also, if I am heading in the right direction, what is the best way to clean out the gas tank?

As always, any help and input is greatly appreciated! Thanks!
 

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Discussion Starter #3
Is there an easy way to test this using a vacuum gauge? I picked one up when I bought the compression tester, but I have not used it yet.
 

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Thanks Lancer. I already have the hose cut at 45 deg. to avoid that particular problem. I am going to try spraying the carb boots like the thread says to see if it has any effect. The boots are held in place on my bike by wider hose clamps than stock. They might not be seating 100%. Something to check before pulling the carbs I guess.
 

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Chris, storm16 has had the same problem with his bike - idle doing crazy things like what you're describing (I test-rode it with the rpms at 5K as I was thinking about moving in first gear). I'll see if I can find the thread [Found it! http://www.vn750.com/forum/showthread.php?t=6614], but the consensus there was also "vacuum leak." There's about a zillion points, it seems, where a leak can be that might cause the problem, but here's a starter checklist:
1. Boots between the carbs and the engine - check all four clamps
2. Check that you put the carbs on the bike right - there's a little nob at the top of the front boot that should line up with the mark on the engine block; the rear boot is harder, but I believe it's something like nob s/b 15 degrees to the right of 12 o'clock. (someone check me on that)
3. Boots between the airbox and the air filter housing - they are deceptive, and will appaer to be all the way in when they are not. They have a sort of double-lip on each end - make sure they are all the way in (there should be very little play in them once they're seated properly).
4. Check the clamps on the boots from the carbs to the airbox - make sure the boots are fully seated and that the clamps are really cinched down.
5. Then check that the boots are fully seated up in the airbox. There's a little notch on each boot that should fit over a tab on the airbox itself.

Those are the main ones I can think of on half a cup o' coffee, but I'm sure folks have more to add to the list. Whatever it is, sounds like it "came loose" with riding - that is, all was well previously, so something wasn't quite seated properly or clamped all the way down and finally found its level, as it were.

Good luck!
 

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Discussion Starter #7
Thanks Cindy! I did a few searches here on the rev problem, but I guess I just didn't come up with the right combo of words. I'm heading down to the garage now to check all of the connections.
 

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Well you guys are the best!!!! :rockon:

I reseated the carb boots on the carb side, and the idle is no longer revving out of control. All of the other connections seemed to be seated tightly. I did notice an occasional hesitation on acceleration when opening up the throttle. It only happened once or twice. I also noticed a little popping at around 4K RPM when the bike was on the center stand. I'm guessing that there still might be a little air getting in. I'll continue to check.
 

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Well you guys are the best!!!! :rockon:

I reseated the carb boots on the carb side, and the idle is no longer revving out of control. All of the other connections seemed to be seated tightly. I did notice an occasional hesitation on acceleration when opening up the throttle. It only happened once or twice. I also noticed a little popping at around 4K RPM when the bike was on the center stand. I'm guessing that there still might be a little air getting in. I'll continue to check.
Well done! I think it's now official: you can no longer call yourself "inexperienced" at wrenching! :rockon:
 
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