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Discussion Starter #1
I wonder if any of you experts might comment on this issue that just popped up on my 1996 VN750 (8.5K miles) I've been driving it fairly regularly for a year now with no issues; bought it from an older gentlemen who didn't rid it much.

On the way home from work Friday evening I noticed the engine running rough (actually sounded like a cylinder missing) as I was heading down a short stretch of road to my house. Its downhill and requires little to no throttle. As I pulled in the driveway and stopped at the garage the engine was idling low and rough and stalled. I shut it down and finally got a chance to check it out this morning.

It cranked up Okay but I noticed the same rough running at idle but seemingly smooth and normal at RPM above about 2K. I pulled each plug wire off in turn to try and isolate the cylinder. I could hear that all four plugs were firing but noticed little or no change roughness when I pulled the rear plugs, so it appears the rear cylinder is at issue.

I then pulled the seat off and checked battery voltage just to eliminate that: 12.2 V ignition off, 14.3 or so volts when I rev to 4K so that appears to be fine. Then pulled the tank checked fuel flow while sucking on a piece of tubing connected to the vacuum fuel valve - fuel flow was excellent from both sides.

At this point I'm thinking some bad fuel or some dirt in the rear carb that has messed up the idle jet. I am planning on pulling the carbs and and cleaning them up then installing all new fuel and vacuum lines to the carbs. Any Ideas or suggestions?

Thanks in advance for any input,

Scott
 

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Calif Rider
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725 Posts
You said you heard that all the plugs were firing. Did you visually check that you have a spark at each plug in the rear. A wire could have come loose at the rear coil. This happened to me just a few weeks ago,and my bike ran like yours in now because of the loose wire.
 

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Discussion Starter #5
Thanks for the replies fellas. I could hear the "clicking" of the spark jumping as I disconnected the wires and held the plug wire near the plug tip. I could hear it on all four. Plus, I'm thinking that if it was the wires it would run ragged at all RPMs not just idle.

I use sea foam periodically... but I did get caught in a Major rain storm a week ago. Its possible some water got into the tank somehow. In looking at the bottom of the carbs I see what looks like an allen screw and a nipple out the bottom. Is that how they are drained? I tried loosening that screw its in there tight... sure would hate to strip the thing.
 

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Old Truck Junkie
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Don't strip it. Just go with the water treatment. I use some called "heet." There are others. Run the engine after putting some in the tank, also when running at high rpms 5k or so, turn the petcock lever to reserve and run it for a few miles. Don't forget to turn it back to on.
 

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Discussion Starter #7
I just drained the tank... by removing the petcock. About a tablespoon of water was in it. I then poured in a couple cusps of fresh gas and some sea foam and sloshed it around and drained that. If there was some water in the tank it certainly could have gotten into the crabs so I want to drain them.

Before I put it all back I want to replace the gas lines and vacuum line, they look old.. probably the original equipment. Where is a good source of new gas & vacuum line?
 

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Old Truck Junkie
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An auto supply store should do. Take the old hoses with you for sizing.
Go ahead and use a bit of water remover. You can use sea foam, but water remover is a lot cheaper. That is up to you.
 

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Discussion Starter #9
Thanks fellas. I drained the carb bowls also. Now for some new fuel and vac line and fingers crossed.
 

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new owner
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I'm in the same boat (was just going to post a thread for comments) We had some very heavy rain here, its been raining almost every day for a couple weeks so the bike has not got any use in about a week and half. Last monday we got 4 inchs in 3 hours.. its also been very HIGH humidity. And yes the bike is outside at all times (wish it wasnt, but it is). I took it for a ride last thursday and it was running "odd" i couldnt put my finger on it, but it was strange.It was just to a parts store a few blocks away so it was a short ride. Saturday I took it out and it was still odd, I thought maybe it was missing but under power it felt fine. It did surge/miss a couple times at a steady speed.

That worried me so i drove in town as i didnt want to die out on the road. it seemed to run fine at lower speeds but have that wierd 2 seconds of good, 1 second of bad hicup.

I felt it was moisture and drove it a bit and after 15-20 minutes it seems to be running fine now. So I'm going to assume it was moisture.

My question, is where? In the tank (it seems from this thread you guys think that may be it). I know i have had cars with moisteure in the Cap (distributer) that cuased this type of problem. But I'm assuming that wont be the case here.. (as this has elecetronic ignition (right?).

Guess i will get some fuel line stuff and put in tank for mositer and hope that was it..
 

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Discussion Starter #11
Just wanted to update everyone on this issue. I drained and cleaned out the tank and let it dry out out, drained carb bowls and installed new fuel lines. Re-installed tank and filled with fresh gas (I never use 10% ethanol gas unless there is no alternative) and some sea foam she started and ran perfect.

I noted the gas that I drained has a sort of yellowish tint to it.... the water could have been in the tank for a while. It might be a good idea to do this every couple of years or so.
 

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My question, is where? In the tank (it seems from this thread you guys think that may be it)
I've had a similar problem a few times. Washed the bike and water got into the tank, not sure how, I'm fairly careful rinsing around the tank lid. Anyway the bike would run like junk the next day. The water would buildup in the carb bowls and required them to be drained. I started using Sea Foam, based on recommendation here and have not had a problem since.

Another item on moisture. I've been told that the 10% ethanol they add to the gas around here actually absorbs water from the air. I have a friend who works in a marina, he said ethanol has been causing all kinds of problems with water in tanks. Sea Foam used regularly seems to keep thins running good.
 
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