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Discussion Starter #1
I have been reading through other posts but am still not sure what is going on with my bike. I rode it yesterday with no problem and then I started looking over it more cause it was backfiring. I found one of the tubes that is supposed to be connected to the carburetor not on it. so I attached that and also took off the bar that is attached to the front for the highway pegs. When I went to start it, it would turn but never start. I had to give it some throttle and then hold the throttle for it to stay on. I tried adjusting the idle and it worked a little but would still die after about 30 seconds. now it just clicks constantly. I took the battery and had it checked at auto zone and they said it was good, i don't really trust them though. Hopefully someone has an idea what the cause of this is. I'm a car person and this is my first bike so please bear with me.
 

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Linkmeister Supreme
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What is the battery voltage now, after the test at Auto Zone?
If it hasn`t been charged up since the test, and is below 12.5 V, you may just need to charge it up a bit to get started. The vn750 like a fully charged battery to start.
You can boost a mc battery too, with any 12 volt battery or your car.

If you don`t have a sealed battery, (one you don`t have to add water to), get one now, and save yourself a lot of headaches. You want Maintenance Free-Absorbed Glass Matt, (MF-AGM) technology. See link below in my sig line, and the Vulcan Verses for more info. lance328 has posted links to Ebay for the Deka battery online for about $55 IIRC. Check your plugs too. NGK Iridiums, p/n DPR7EIX-9 are recommended here.

Which line did you reconnect to the carb?
A small vacuum hose to the middle nipple on the petcock?

Or a vent hose going to the right "ear", where the air filter lives? If that hose is pushed all the way in and "bottoms out", it plugs the vent and the engine will stumble and quit. Pull the vent hose out and cut the end off at a 45* angle, so it won`t be plugged by pushing in too far again.

Let us know what you find after checking the above suggestions, and if it starts.
 

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Calif Rider
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Like Hoss said about the hose you hooked up. Everything was fine until you hooked it up, undo it and go from there. The backfiring maybe all you need is an adjustment of the the air mixture screw, or a leeking exhaust gasket. Find what cylinder is popping and listen for an exhaust leak on that one, and if not try adjusting the air mixture screw out this sometime helps on the popping.
 

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If you jump from a car battery, don't have the car engine running.
 

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Discussion Starter #5
I jumped the battery with my car an was able to get it started, with the choke on. When i put the choke off it idled for a couple min and died and could not start it again. Am going to replaced the battery tonight. The hose that I connected was a vent hose to the air filter. I dont think i bottomed it out but I will make sure when I connect it back up.
 

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Discussion Starter #6 (Edited)
Well I put in a new battery and that fixed the clicking noise but now i cant get it to idle. If I apply some throttle it is fine but the minute I let up it idles at around 800 rpm then dies. any thoughts?I dont see any idle adjustment knob on the side like the manual says.
 

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Ok, if your starter turns the motor over, and it will run a little, then the starter is working and you have spark. Open the drain screws on the bottom of each carburetor, and see if gas drains out. If it does, you have gas in the carbs. Assuming you have compression, I'd say there is about a 99% chance your carbs are plugged up with what used to be gas, and will need to be removed, disassembled, and thoroughly cleaned. If the caps have been removed from the idle A/F mixture screws, remove the screws, and the springs, spray some Gumout in the holes where the adjustment screws were, then spray a little WD-40 on the adjustment screws, to lubricate the threads, and prevent the o-rings from getting damaged. Put the screws back, turn them in till they seatlightly, then back them out about 2 1/2 turns, and see what happens. Hopefully it will now idle. If not, you will have to go ahead and clean the carbs.

BTW, if the hose you put back connected to the back of the right side air filter housing, it was the carb float bowl vent hose. Go ahead and remove it, and blow into it. It should not be plugged. You can leave the end unhooked for now, it is supposed to be vented to the atmosphere. The air filter housing just serves as a holder for it. You can even get a longer hose, and run it out the bottom of the bike somewhere. Jerry.
 

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buy a new battery and spark plugs
He already bought a new battery. New plugs may help, but for now, the old ones can be cleaned and regapped. Unless they are broken, in which case new plugs will definitely help.

Also make sure there is a spark to all 4 plugs. The Vulcan 750 will run with just one plug per cylinder firing, but it does not run well. Make sure there is gas in the float bowls, and that the carb float bowl vent is clear. If that stuff checks out, I'm almost certain the problem is with the carbs or choke.

I would start by removing, disassembling, and thoroughly cleaning the carbs. Make sure you get everything back right, and look for anything wrong while you have them apart, including with the choke assembly and cable. When you reinstall the carbs, make sure you get everything back in place properly, and have no air leaks. Removing and replacing the carbs is not a real easy job, but with time and patience, it is not that bad.


Also, try running it with the gas cap open, just in case the tank vent might be plugged up. This is a fairly common problem on bikes with the CA evap emissions crap on them. Jerry.
 

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Discussion Starter #10
Well here is a little update, I took the carbs out and gave them a once over with some carb cleaner. I know I will have to get them cleaned and rebuilt but I think I will have that done by a professional. I put them back in and still had the same problem, after talking with some friends they had advised me to look for an air leak. I ended up getting it to idle for a few seconds and sprayed some starting fluid where the carb attaches to the engine. I got a massive acceleration from the engine. I think that is the problem. the clamps are worn and the hose could have some cracks. I am going to replace both and see how it goes. I figure I will send my carbs to carbworx since it is way cheaper than anything local.
 

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Discussion Starter #11
So I got the parts in and went ahead and installed the carb (havent sent it out yet, was to eager to ride) and the bike will run perfectly......with the choke on. When I take the choke off it dies. I rode for 3 hours today with the choke on and had no problems (besides running out of gas on the other side of my subdivision) Any ideas?
 

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I think the carbs need to be disassembled, checked for worn parts, the metal parts soaked in carb cleaner, and all the orifices blown out with compressed air.
 

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I had a 93 that had sat for 10 years, after cleaning the carbs, new battery, all the usual stuff it still wouldn't start. Turned out to be the choke plunger was broken and had to be replaced. Once that was done the bike ran like new! Just a thought.
 

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I assume the backfiring is on de-cel.
Common prob with these bikes as others have mentioned. No big deal.
Start by setting your air screws 2 1/2 turns out. You may (like I did) have to go to 3. I don't like any more cause the screws may fall out!!

As far as the carbs go, it's time to bite the bullit and do a good cleaning.
From what you decribed, your pilot jet is definately plugged. Very common on bikes that have sat for some time. The small holes in the needle jet are probably also plugged.

By running with the choke on, you are probably getting less mileage than a Mack truck!!!!!!!

Have fun:beerchug:
 
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