Hey guys I’ve been having a very odd problem with my VN 750 that has left me on the side of the road twice now. If you have any insight I would love to hear it.
Since about two months ago the bike tends to stop running every 100-200 miles with fouled plugs (gas fouled not oil). Usually the front cylinder quits and the rear will keep going for a little while on its own before dying. If I keep the bike running on the rear cylinder only I get gas leaking out of the pipe connected to the front cylinder. Both sets of plugs look fouled but the front set is always worse. If I clean off the plugs or replace them it will start up and run until the plugs are too fouled again. I had the carbs taken off and cleaned, the mechanic said they were pristine and nothing was sticking or clogged. The carbs still have the plug over the mixture screw so that hasn’t been messed with. Air filters are clean and I’m not having trouble getting a spark to the plugs when I test it. I bought the NGK Iridium plugs last week hoping to fix the fouling and after a week they are fouled as well.
Further background info:
When I bought the bike last fall it was missing the idle adjust screw that mounts on the left carb. I bought the part last winter and had it installed this spring. There was a sheet metal screw in the hole between the carbs when they tried to install the idle adjust. I didn’t have this issue before this was installed but it seems like a long shot.
I have a standard lead-acid battery that the shop says is in fine condition and tested normal with the volt-meter. Electrical system tests recommended by Clymers came up normal.
I'd double check those air filters and ensure they are clean and oiled (not over oiled), then I'd check the air/fuel mixture sounds like it's way too rich. Remove the lead plugs from the mixture screws and set it yourself. Turn them all the way in then back them out about 2 to 2 1/2 turns.
Others on here will soon chime in as well with great advice too.
Definitely worth checking the petcock. The air/fuel mix screws I don't believe would be the problem since one, they're still sealed, and two, that mix is at idle and doesn't really come into play beyond idle. It does disturb me that you had the carbs professionally cleaned and they didn't remove the caps and the pilot screws. They obviously didn't clean the pilot jets, but again that shouldn't be associated with the rich running problem. You're sucking in some extra gas somehow. Maybe a stuck float or float needle not seating?
That sheet metal screw doesn't go all the way into the float bowl does it? :wow:
Mine did the same to me the past couple of weeks after me and a buddy cleaned the carbs. my idle screw side diaphragm was partially eaten up. I was procrastinating about putting it in, but I had gone on about a 150 mile trip weekend before last, and the bike was running fine a little lack of power but nothing to alarming. Got to where we were going, then when we went to leave, I started it up and it seemed flooded but it got back on the road just fine. Had to pull over because of rain but other than being a bit sluggish it did ok most of the way home. When me and my buddy finally split our separate routes my bike all of a sudden felt like it was running on one cylinder. I was glad to get it home. Pulled the plugs back wasn't bad but front was gas fouled like crazy. They are maybe only a month old and iridiums so I knew they where good. Cleaned them real well and threw them back in. Bike ran like a charm. Road it to work the next day and by time I got home it was acting sluggish again and the fronts where slightly fouled again.
This past weekend I finally took the five minutes to put the new diaphragm in and its like a new bike, haven't gone on any real long rides yet but the bikes never ran so well and I'm hoping it continues to do so.
But the point is as of right now I gotta say my whole problem was the diaphragm, which when we cleaned it I didn't think looked like anything urgent. I mean it wasn't completely eaten up just partially see through. It only takes a couple minute to check them and 33 dollars to replace them. Good luck bud hope you figure it out before it leaves you stranded again.
Thanks for the great ideas. At least it gives me a couple of new things to check out before throwing more money at the dealership.
niterider: How would I check the petcock? Just pull the hose from the carb to see if it's sending gas without the motor running? I would think the bike would smell like gas if that were the case.
Authority84: Not sure what you mean by the idle screw side diaphragm.
fergy: The sheet metal screw was in the hole between the carbs where the idle screw connects. I assume the PO put it there because the bike wouldn't run well without the idle screw. Why the idle screw was missing in the first place I don't know. The mechanic that installed the idle screw had to cut the sheet metal screw out before he could proceed.
Thanks for the great ideas. At least it gives me a couple of new things to check out before throwing more money at the dealership.
niterider: How would I check the petcock? Just pull the hose from the carb to see if it's sending gas without the motor running? I would think the bike would smell like gas if that were the case.After running engine remove the vaccuum hose and check for gasoline in it. It should be dry.
Authority84: Not sure what you mean by the idle screw side diaphragm.
fergy: The sheet metal screw was in the hole between the carbs where the idle screw connects. I assume the PO put it there because the bike wouldn't run well without the idle screw. Why the idle screw was missing in the first place I don't know. The mechanic that installed the idle screw had to cut the sheet metal screw out before he could proceed.
If you're pulling fuel through the vacuum port on the petcock, it goes directly into the intake bypassing the bowls on the carb. That's why Lance is recommending you pull a vacuum on the port on the petcock, with it in the on position, and if it allows gas through the vacuum port, there is your problem. Hope this helps!
I sucked on the vacuum hose last night without getting any gas to come through. Gas did end up coming out the vacuum nipple on the carb after a few seconds but I assume that is normal. Does this result point toward a ignition system issue?
It sounds to me like you may have a float stuck open and bowls are overflowing. Not sure about this, but it doesn't seem like you should be able to suck gas out of the vacuum port. Hopefully some of our carb experts will chime in on this.
It sounds to me like you may have a float stuck open and bowls are overflowing. Not sure about this, but it doesn't seem like you should be able to suck gas out of the vacuum port. Hopefully some of our carb experts will chime in on this.
If the float is stuck on that carb I'm going to have some words with the guy who told me he cleaned them and they were immaculate. I'll follow up on the float valve issue and let you guys know what I find out. Thanks for the diagnosis help. I would've been lost without you guys.
I got the bike into the shop this weekend and the official diagnosis is warn float valves that are not seating properly. Parts and service is going to come to $400.
When it comes time for the next bike I'm not taking any chances, whatever I buy will be brand new. There are just too many people out there that take lousy care of their bike and then get it running decent and sell it on Craig's List.
Thanks again for taking the time to give me a hand troubleshooting this. I should be riding trouble free for the rest of the summer. :rockon:
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