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Discussion Starter #1
Guys me an my buddy are fixing his bike, we took the carbs out to clean them up due to a sticking bowl, got that taken care of, also cleaned up the jets as they were cloged up, but the bike won't start, when we crank all it does is give us is a super loud bang thru the exhaust and also give us a mild one thu the carbs, we have a new battery on the bike hooked up to a chargers to ensure sufficient voltage/amps to achieve proper cranking speed, any ideas???
 

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Dual Sport idiot
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How did you clean the jets? If you poked anything through them you probably damaged the orrifice. Means you'll need to replace them.
No other thoughts right now, I'll think about it at work.
 

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Mine was doing this same thing. I think all I did was put in Iridium plugs and then an AGM battery after that... I think the plugs made it start even if it took a little bit of cranking... and the AGM battery made it start as soon as you pushed the button.

All of which points to spark, so check everything that has to do with spark. Even before the Iridium spark plugs I thought I had good spark but it still didn't start. Those plugs made a lot of difference. You should check for spark first though, maybe check that the coils are getting enough voltage and check your spark plug wires and all.
 

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REBUILD your starter, it's grabbing too many amps....

DT
 

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Linkmeister Supreme
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You didn't mention how old the bike is, or if it has had a tough life, lived mostly outside etc. If you're cranking the engine with a wet cell battery, it might not have enough juice to overcome the old and weak wiring. Check all the above and see if you can get your hands on an AGM battery. You'll need it.
 

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Discussion Starter #7 (Edited)
Guys, I'm not sure of what kind of battery this is, but I know it is new, the bike is a 1995,the jets look good w/o damage, and just to justify buying a new starter...why would the starter be the issue??? and and why do I need a new battery??? along with iridium spark plugs??? the bike is a 1995... bike has been kept inside of the garage, also I checked spark with a spark tester and it shows a spark jumping about a 7/16 gap.
 

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why do I need a new battery??? along with iridium spark plugs???
Until you've experienced it, mere words fall short of adequately explaining the difference. The AGM battery has more amps, is no maintenance (no pulling the seat every week to check electrolyte levels), and won't leak acid over your electronics and frame. The iridium plugs, while initially pricey, last for 100,000 miles or more and are virtually lifetime plugs. Get both and your bike will start if the air fuel mixture is correct.
 

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Discussion Starter #9
I understand the easiness of having lifetime plugs and 0-maintenance battery, but how does that relates to the backfiring, I'm not worried about the no start-the air/fuel mixure at this time, my main concern right at this time is why is it back firing, it appears as if it was out of timing...
 

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Calif Rider
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Is the choke working properly? Are the plugs getting all wet after cranking the engine over for awhile? These carbs are really tempermetal about just a little dirt getting into them. Is the fuel tank nice and clean? Maybe the fuel petcock is cloged or not working properly. It works on vacuum, check for crakes in the vacuum line.
 

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Discussion Starter #11
just so there is no confusion, the bike backfires while cranking, it does not starts, it just backfires while cranking
 

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Linkmeister Supreme
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I understand the easiness of having lifetime plugs and 0-maintenance battery, but how does that relates to the backfiring, I'm not worried about the no start-the air/fuel mixure at this time, my main concern right at this time is why is it back firing, it appears as if it was out of timing...
The timing is not adjustable. There is no distributor or ignition points, it is electronically controlled. As far as I know, the only way the timing can change mechanically is if the cam chains and gears become so worn that the chains jump a cog.

If your new battery has plugs on top to allow adding water, it is a wet cell, not maintenance free. I started my bike last week after it has sat for 3 or 4 months w/o being started. My MF battery was new in April, and cranked the engine over for several seconds until the vacuum operated petcock let fuel fill the carbs, then it fired right up on Seafoam treated fuel that has been in the tank since my accident 28 months ago.

Pull all the plugs and examine them for wear and if they are wet. If any electrode edges are rounded off by spark erosion they will need more power to create a hot spark. The Iridium plugs have a harder electrode surface and resist rounding off for up to 100K miles.

Not sure about backfiring, but it may be caused by too lean fuel mix I think.
 

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Discussion Starter #13
I agree, lean air/fuel mixture will cause backfiring when decelerating and pinging while accelerating, but w/ the choke wide open the mixture it is really rich... like I said the problem is while cranking...I know there is a tech/mech in the forum that has my answer...
 

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have you played with the idle screw make sure it didnt back out of the adjuster on the carb mine did and i had the no start backfire just like that took me a while to find the problem
 

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1986 VN750
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AGM battery and iridium plugs solved my problems. Same with just about everyone else here. Do not bother running a standard battery with cheapo plugs.

Pickup coil gap mod and pickup coil relay mod also greatly improve ignition.
 

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@Matthew Wellington: When I purchased my vn it came with a 'new battery', but after a few months it started dying every time I parked it. New battery solved the problem. If your bike starts with a jump, it means you've got low voltage or insufficient cranking amps from your battery. Try cleaning your battery terminals and take your battery to a car-parts store for a health check.
 

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talking about no maintenance batteries, can someone give me the reference/part number of the one needed for the 750 please.
also, i currently run with standard NGK's , are the iridium that much better ?
 

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1986 VN750
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talking about no maintenance batteries, can someone give me the reference/part number of the one needed for the 750 please.
also, i currently run with standard NGK's , are the iridium that much better ?
Yes the Iridium are *that* much better on our bikes (our ignition isn't exactly the best, so anything helps). NGK Iridium Plugs #7803/DPR7EIX-9

Here is a list of batteries: Batteries - Vulcan750.net Wiki
 
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