Kawasaki VN750 Forum banner

1 - 12 of 12 Posts

·
Registered
Joined
·
13 Posts
Discussion Starter #1
I have an 86 Vulcan 750 that has a hard time starting about half the time, and not always when cold. I cut off the exhaust, which may or may not be the culprit, but putting them back on is not an option. I suspect not enough spark; the plugs are new, but I notice that the right front plug wire has spark jumping from the wire to the spring-wrapped throttle cables occasionally. If I move the wire away from the springs, the spark stops and the idle speed goes up a bit. However, even with a slab of rubber wedged in to keep spark from jumping that gap, it's still intermittently hard to start. I know this is all very vague, but I'm looking for a place to start. Advice?
 

·
FREEBIRDS MC CENTRAL NY
Joined
·
16,076 Posts
What type of battery ya got? These bikes like agm batteries.try hooking up a jump box to it and see what ya got.does it backfire loudly when flying to start? I would lengthen the pipes some too as you need some backpressure

Sent from Motorcycle.com Free App
 

·
..have a vulcan good day!
Joined
·
4,508 Posts
What type of battery ya got? These bikes like agm batteries.try hooking up a jump box to it and see what ya got.does it backfire loudly when flying to start? I would lengthen the pipes some too as you need some backpressure

Sent from Motorcycle.com Free App
x2 on this..... ODD nailed it.
And replace Plug wires.....

:smiley_th

Past Copy & Pasted Individual posts from the verses…...


All 750 Spark Plugs = 12 mm threads – use 16mm thin wall socket – Book Spec: torque to 13” lbs
Torqueing, depending on if you use the suggested "Anti-Seize" your value may vary. I religiously do and go with 12 ft-lbs (144 in-lbs). Installing plug dry and torqueing, I'd probably go with a slightly lesser torque (10 ft-lbs ? ) (Steel Plug threads –torqued into Aluminum Heads).
Plug Wires: Dennis Kirk has 7mm wire for $2.99 in a 72" length the part # is 20- 21.
Ad two NGK end caps part # 20-306 @ $3.30 and two end caps part # 20- 789 $2.40 each.
(Requires approx.. 60”) Spark Plug Wire Replacement:
2 x 11.5" long
1 x 14.5" long
1 x 20.0" long
You should consider buying NGK plug ends if you haven't already. They are great looking and my directions are based on using them.
Dennis Kirk: [email protected] or 1-800-328-9280
2 - Part# 20306 – NGK Spark Plug Cap XD05F $3.30 a piece.
2 - Part# 20789 - NGK Spark Plug Cap LD05FP $4.80 a piece.
******** All NGK caps are made for Stock 7 mm wire. *********
Make sure you use copper core wire and not carbon core. 7mm is stock size, you can use 8mm but is
harder to install with little to no (factual) gain.
2- LD05FP and 2- XD05F are what NGK suggest to use on our VN750 bikes. :
**********************************************************************************
The DPR7IX-9 Spark Plug advantage: The advantage is (they claim) "Longer life, lower fuel consumption, smoother running, Improved ignition efficiency-giving enhanced power and acceleration" The part that matters really is the "improved ignition efficiency" as iridium can "spark hotter" at a lower voltage. Given our feeble electrical system, anything that uses less power is good. The part number is 7803 at Advanced Auto. The plug is the DPR7EIX-9.
Worn plugs cause hard starting My spark plugs had about 13,000 miles on them and I was beginning to experience multiple tries to get the engine started, hot or cold. Figured it was time for new plugs. On Mike O's recommendation I installed new iridium spark plugs, anti-seize on the threads (steel plug into Aluminum cylinder head), and torqued to 144 inch lbs (12 ft pounds). Now starts first time every time, hot or cold. Barely have to touch the start button. Thanks Mike, they really work. NGK DPR7EIX-9. About $10.00 each, (or less) but I think they will be worth it. The bike will probably fall apart before I have to change them again. Dennis in Maryland.
 

·
FREEBIRDS MC CENTRAL NY
Joined
·
16,076 Posts

·
Registered
Joined
·
7,637 Posts
Try leaving the throttle closed for hot starts, mine backfires and fails to start every time I forget and crack the throttle. It will start in half a turn otherwise.

The AGM battery is a plus though.

You need plug wires/boots too, at least one is leaking spark. That's a common place for spark to jump.
 

·
Registered
Joined
·
13 Posts
Discussion Starter #7
Right; I've got an AGM battery, but jumping it makes it start immediately, no hesitation, so....since it needs some backpressure to start, could I fashion some sort of partial plug for the exhaust to get it started? Like put it in, start it, then yank out the plugs? I intended to make a custom pipe, but then life got in the way, and for the time being I need to keep what I got running til I can afford to take care of pipes and a dozen other issues. Right now I'm in survival mode money-wise, with keeping her running high on the list within the limits of my budget. I already carry jumper cables around all the time for when I'm out and have troubles, but I'm not always where I can rely on a good samaritan.

And may I say here, thank you so much; I've been a member of your forum for less than 24 hours and y'all have given me more to go on than I've had for months. So glad I found this site.
 

·
Registered
Joined
·
7,637 Posts
Maybe have the battery tested?

Also read battery voltage then read voltage at the ign. coils with the key on.

You might need to look into the ign. coil mod, and maybe the pickup coil mod too. I don't think the pipes are the problem.

Does it idle and run ok once it's running?
 

·
Registered
Joined
·
13 Posts
Discussion Starter #9
Brand-new battery. Once she's running, she runs great, but I pause and mutter a silent prayer everytime I turn her off, even if it's just to fill up. What should the voltage at the ignition coils read with the key on? Same as battery?
 

·
Registered
Joined
·
7,637 Posts
Volts should be the same or very near, within a few tenths.

New isn't always good, a little weak in capacity and it's going to have starting problems. The need to jump the battery, tells me voltage is dropping off somewhere, for some reason. Starter could be pulling too many amps, charging system weak, weak battery .....
 

·
..have a vulcan good day!
Joined
·
4,508 Posts
Brand-new battery. Once she's running, she runs great, but I pause and mutter a silent prayer everytime I turn her off, even if it's just to fill up. What should the voltage at the ignition coils read with the key on? Same as battery?
Where in Texas are you ?

NewRider9984 is up around Dallas area...an excellent Mechanic/troubleshooter......he always willing to assist....
(if he is not snowed/frozen in) LOL

:smiley_th
 

·
Sparky!!!
Joined
·
8,696 Posts
my 2 cents worth on the issues

Like others have said, it sounds like a low voltage issue. the biggest place for voltage drop on the starter circuit (assuming your battery is 12.5 volts or more) is the frame to engine ground located on the right side of the battery box, to the transmission. If either end is loose or corroded you will get a hard start issue.

Another thing to help out since you reduced your back pressure is the Coil Relay Mod. to give you full battery voltage to the ignition coils on start up, resulting in hotter spark.
 
1 - 12 of 12 Posts
Top