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Discussion Starter #1
When trying to start ours (a 1990) when cold or even when warm and having sat for 20 minutes, it takes a massive amount of cranking to finally get started. Once it starts, it runs good, idles smoothly and has lots of normal power.

Note: Since we are in FL, the bike never sits, and is used very regularly.

Also noticed, was that is seems like the gas tank pressurizes while cranking to try to start. We heard a hissing sound after unsuccessfully trying to start, and found it came from the gas tank fill cap.

Any ideas? Thanks!
 

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Old Truck Junkie
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In many cases this is the sign of a low battery. Try jumping it with a car battery and see how well it starts. An MF gel battery ussually fixes this problem.
 

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2002 VN 750
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Do Not have the car runing when you jump it, you can fry the electrical system bad.
 

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Discussion Starter #4
In many cases this is the sign of a low battery. Try jumping it with a car battery and see how well it starts. An MF gel battery ussually fixes this problem.
Still does it with a battery charger in the "55 AMP Engine Start" mode connected to battery, so it does not appear to be a battery issue.

And besides, we had the battery tested about a week ago, and it passed with flying colors.
 

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1986 VN750
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Still does it with a battery charger in the "55 AMP Engine Start" mode connected to battery, so it does not appear to be a battery issue.

And besides, we had the battery tested about a week ago, and it passed with flying colors.
Check the plugs and plug wires. When I got my 750 it did this when it had NGK plugs that had been there for 18k miles. I threw the iridium plugs in and she started instantly - no backfires.

This should be your first step before trying anything else unless you are sure your plugs are in perfect order.

Edit: When I said it would do this - It could take a minute to get her started - after assaulting the neighborhood with several blasts that sound like a shotgun going off.
 

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Old Truck Junkie
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Another reason that I have come across on the back fire, is a little bit of water in the fuel. You can try some water treatment to remove moisture from gas. I use some cheap stuff called "heet." I buy it at Wal-Mart or auto parts stores. Many here like "sea foam."
 

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Try starting the bike with the fuel cap opened. Sounds like you might have a clogged vent.

+1 on checking the plug wires and putting in new iridium plugs.

A full tank of fresh gas with half a can of SeaFoam might be a good idea too...as a bit of crap in a carb can making starting difficult.

Backfires while starting are usually a sign of a weak battery. If your that sure your battery is good (is it an AGM?) it might be a bad wire, a loose ground, a clogged jet, or a clogged gas cap vent.
 

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1986 VN750
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thtanner: What is an R/R? And you must have got that bike cheeeeep since it was an '86, eh?
R/R is the Rectifier/Regulator, which is part of the charging system. I paid $1100 for her and have put about $400 in so far, making it around $1500 total.

She's riding great at the moment! Getting ready to go out here in about 30 minutes.. :)
 

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Linkmeister Supreme
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When trying to start ours (a 1990) when cold or even when warm and having sat for 20 minutes, it takes a massive amount of cranking to finally get started. Once it starts, it runs good, idles smoothly and has lots of normal power.

Note: Since we are in FL, the bike never sits, and is used very regularly.

Also noticed, was that is seems like the gas tank pressurizes while cranking to try to start. We heard a hissing sound after unsuccessfully trying to start, and found it came from the gas tank fill cap.
Any ideas? Thanks!
The hissing sound could be a blocked tank vent tube, which leads to a condition we often refer to as POOGS, -the phantom out of gas syndrome. See this link for the cure and prevention:
http://www.vn750.com/forum/showthread.php?t=17572

If new iridium plugs and the other suggestions made still don`t cure the hard starting problem, try fergy`s mod by wiring 12 volts straight to the ignition coils via a relay switch as shown in this link:
http://www.vn750.com/forum/showthread.php?t=17276

There is also a pick-up coil mod for moving them closer to the alternator rotor.
It is reported to help with the hard starting too:
http://www.vn750.com/forum/showthread.php?t=18550
 

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The "hissing sound" is a dead giveaway. There should never be above or below atmospheric pressure in the tank. You have a tank venting problem. As was suggested, try starting it with the cap open. If that helps, then check and see what you have for emissions equipment. If you have a CA bike (even if it was sold new in FL, it could still be a CA model, they sold them in many states), you will need to either remove or disconnect it. I completely removed my CA evap system, and air injection system. It is easy to do, and will relieve your bike of about 10-15 pounds of junk.

Remove your seat, and look at the back of the tank. If it has 2 fittings on it, with rubber hoses on them, it is a CA model. If so, get some more tubing of the same size, disconnect both hoses, and install 2 new ones. Run both these straight down to the bottom of the bike, and leave the ends open. If you have only one fitting, you do not have a CA model, make sure the one vent hose is open to the atmosphere on the other end. It does not connect to anything. If it does, disconnect it. If you still here the hissing sound and have starting problems, then that little rubber grommet under the gas cap is bad. Alcohol gas makes it swell up and no air can get through it. Removing it should solve the problem. ALL gas tanks need to be vented directly to the atmosphere. Doing anything else is going to cause problems.
 

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Discussion Starter #12
Update: My tank vent has only one tube at bottom of tank near seat. When I get the bike back, I will check & unkink vent line if necessary.

The other day I brought bike to Kawasaki shop, before I even started this post. They had not gotten to it, so I called them to put work (diagnostics) on hold, went & got some NGK Iridium plugs, and put them on the bike at the shop. It seemed to fire up fine!

So now instead of paying $109 for diagnostics, I discussed carburetor work. They wanted to clean, adjust, and sync the carbs for 3 hours labor, but I decided to go bare bones for now, and pay just 1/2 hour labor for just an adjustment & sync, and see how she runs w/ new plugs.

I noticed front plugs were quite a bit darker/dirtier than rear ones.
 

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It sounds to me like you have or had more than one problem. The tank venting is definitely something to look further into and fix if in fact it is a problem. The hard starting when hot problem is usually electrical, especially when you figure in the loud backfiring going along with it. As others have suggested, a good maintenance free battery goes a long ways to solving this. Rebuilding your starter motor has a great effect too. Weak connections and loose or corroded connections/grounds etc. can really drag the electrical system down and are more noticeable when the bike is hot. The coil mod can greatly enhance your cranking power going to the plugs and because it isn't a difficult mod, it may be worth you considering. The iridium plugs are also a good step in helping the hot start problem. Until you get the chance to see how it starts when it's up to temperature and has sat a few minutes, you won't know.

I think I'd hold off on the carb work and run a good dose of seafoam through a fresh tank of gas and see how that fairs. Good luck with it all and let us know what your progress is.
 

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Discussion Starter #14
Fergy, the hard starting "was" when cold, not hot. The Iridium plugs seems to have done the trick.

The only consequence of the tank pressure issue seems to be a small amount of gas getting past the fill flap gasket, especially when tank is full, so we will look into making sure vent tube is not restricted in any way.



 

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Discussion Starter #15
I bought a 1 foot section of 1/4" line, and hooked it to the vent at the front of the tank and routed it downward. The location of the other end of the line that was removed from the tank vent is unknown. It seems to run forward (to a carburetor?) instead of downward. I simply plugged the end of that tube with a bolt.
 
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