Pickup coil mod Or Ignition coil mod - Kawasaki Vulcan 750 Forum : Kawasaki VN750 Forums
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post #1 of 13 (permalink) Old 05-18-2020, 09:23 PM Thread Starter
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Pickup coil mod Or Ignition coil mod

Hello,
I have been dealing with the "hot start" issue on my 2004 Vulcan 750 (24K miles) for about 6-7 years. I have switched to iridium spark plugs and the Duracel maintenance free battery and have ran Seafoam carb cleaner and it seems like I 'm still facing the warm/hot start issue. I can usually start the bike cold with choke on and it will start with no issues, although sometimes it takes a few tires and a back fire in the morning to start. But it's bad when you try to start after refueling that it takes several tries and a backfire before it starts. Once it starts....it's smooth as silk!

I am now faced with either the pickup coil mod or the ignition coil mod. I did measure the voltage on the red wire for the front coil with ignition On and I'm getting 12.6 that matched the battery. So, in your opinion and for those that have done this, which one should I try first Pickup coil or Ignition Coil mod? I get a little nervous messing with points and timing and shaving pick up bracket, for the fear of making matters worst.

Thank you guys for sharing ....and for all the helpful information!
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post #2 of 13 (permalink) Old 05-19-2020, 03:31 AM
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while both mods can help hot starts, I can only pass on my personal experience.

I suffered from hot start problems, specifically after refueling just as you are. I did not do the ignition coil mod, but I did do the pickup coil mod. I never had an issue starting while hot after that.

I did continue to suffer from some weather related starting issues, specifically where I live we consistantly wake up to mornings where the temps are equal to the dew point, and the air is just so full of moisture that nothing starts good. my neighbors down the road had the same issues with their bikes as well (Harley and others)

2005 VN750

Sold 11-27-17
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post #3 of 13 (permalink) Old 05-19-2020, 09:38 AM
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Have you tried using the choke without touching the throttle after a gas stop?

Mine will fire right up if I do that. If I just crack the throttle and crank, it backfires with no start almost every time. Pulling the choke saves me the embarrassment at the gas pumps.

It's proven those mods help, but I haven't been forced to do that yet.

Your battery, is an AGM or just maintenance free? Cranking voltage is important on this bike, but I have an AGM and still get a backfire if I forget the choke. It's counterintuitive after stopping just a few minutes, but it's a quirky bike.

2003-21k mi
Shaved w/UniPK92+Stock Jets-TPE/MOSFET-Shinko Tires-AGM batt-bags-chrome-LEDs...more
__________________________________________________ ____________
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post #4 of 13 (permalink) Old 05-19-2020, 12:22 PM Thread Starter
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Thank you guys....I have an AGM battery. However, I have not tried the choke after refueling because I thought it would just add more fuel but when I used the throttle as you mentioned , it always backfired. So, I will try the "choke" next time and then I guess the next step is to do the Pickup coil mod.

I guess, I just need to measure the gap before I start this process, just in case I run into an issue so I can set it back if I need to. little nervous about breaking or snapping those tiny fragile pickup coil wires!

Thanks again!
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post #5 of 13 (permalink) Old 05-19-2020, 03:29 PM
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Quote:
Originally Posted by AMH View Post
Thank you guys....I have an AGM battery. However, I have not tried the choke after refueling because I thought it would just add more fuel but when I used the throttle as you mentioned , it always backfired. So, I will try the "choke" next time and then I guess the next step is to do the Pickup coil mod.

I guess, I just need to measure the gap before I start this process, just in case I run into an issue so I can set it back if I need to. little nervous about breaking or snapping those tiny fragile pickup coil wires!

Thanks again!
Yes, it's counterintuitive, and you're right it does add more fuel, but mine has never flooded. It doesn't work for every VN, but some. Now I just choke it first, and if it doesn't fire right up, I turn the choke off.

May be a combination of the engine cooling off quick, and slightly lean idle mix.

Pickup mod is good one, those coils are set a long way from the magnets. Have never seen a gap so wide!

2003-21k mi
Shaved w/UniPK92+Stock Jets-TPE/MOSFET-Shinko Tires-AGM batt-bags-chrome-LEDs...more
__________________________________________________ ____________
Repair Manual: http://www.mediafire.com/file/mj7z81..._Catalogue.pdf

Owner's Manual: http://www.mediafire.com/file/nscb5f...ers+Manual.pdf
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post #6 of 13 (permalink) Old 05-19-2020, 11:51 PM Thread Starter
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Thanks again for the help. If I decide to do the pickup coil mod, do I have to use Locktite on the Philips screws for the pick up coil and just tighten them up as normal?
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post #7 of 13 (permalink) Old 05-20-2020, 05:22 AM
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Quote:
Originally Posted by AMH View Post
Thanks again for the help. If I decide to do the pickup coil mod, do I have to use Locktite on the Philips screws for the pick up coil and just tighten them up as normal?
Don't think it's required, but if you want insurance use blue loctite, it's not as hard as red to break loose.

Gutentite (good and tight) should be ok, 🙂

2003-21k mi
Shaved w/UniPK92+Stock Jets-TPE/MOSFET-Shinko Tires-AGM batt-bags-chrome-LEDs...more
__________________________________________________ ____________
Repair Manual: http://www.mediafire.com/file/mj7z81..._Catalogue.pdf

Owner's Manual: http://www.mediafire.com/file/nscb5f...ers+Manual.pdf
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post #8 of 13 (permalink) Old 05-20-2020, 06:41 AM
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Quote:
Originally Posted by Spockster View Post
Have you tried using the choke without touching the throttle after a gas stop?

Mine will fire right up if I do that. If I just crack the throttle and crank, it backfires with no start almost every time. Pulling the choke saves me the embarrassment at the gas pumps.

It's proven those mods help, but I haven't been forced to do that yet.

Your battery, is an AGM or just maintenance free? Cranking voltage is important on this bike, but I have an AGM and still get a backfire if I forget the choke. It's counterintuitive after stopping just a few minutes, but it's a quirky bike.
I'm with you, Spockster - As you have learned, I have always had the hot start issue, especially when it gets damn HOT out! I have put in a new Deka AGM battery, new NGK plug resistor boots(were shot) just to start the season. Just these two things seem to have reduced the exhaust popping upon deceleration for some reason. Not totally, but noticeably. I have not switched over to iridium plugs at this point. Lately, although it's not "summertime" hot out, I have been shutting off, and when turning back on after gassing up, I am using the choke. This is certainly not a normal habit for me, but it has been working so far. It still cranks over a few cycles and then starts right up. I immediately shut off the choke and away I go, un-embarassed, lol. I will at some point, just to rule it out, check voltage with key on at battery and both coils, just to make sure the voltage is close to the same at coils. If not, I think I will do the ignition coil mod 1st. Seems pretty darn easy. If I must do the pickup coil mod, I will. Seems a dremel and a set of feeler gauges will be all I'd need, and I have both. However, I am sticking with the advice of pulling the choke, cranking a few revolutions, and hoping that even when the temps climb into the summer highs, this still does the trick. Mods are cool, and all, but not as fun as just riding. This all on a stock 86 VN750.

1986 VN750 26,000 miles
Deka AGM Battery 4-2020
All else stock, more to come thanks to VN750.com members!
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post #9 of 13 (permalink) Old 05-20-2020, 10:56 AM
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With my bike, I bought it with an AGM battery. It was a little hesitant to hot start, but never terrible. I found a slight bump of the throttle would help it. I did the pick-up mod, but I didn't notice much improvement with hot-starts. It did seem slightly more responsive off-idle. Many have suggested this mod advances the ignition, but no one has measured it to my knowledge.

I will agree with Spockster that this bike is very sensitive to voltage. I had a corroded stator connection such that my idle voltage was 11.5 V and higher rev voltage was 12.5 V.
Whenever I pulled away from a stop at a decent rate, it would mis-fire. Backing off the throttle fixed it. From 3k-7k it ran great at all throttle positions.
>7K it would mis-fire at heavy throttle again, and backing off it would run just fine up to 8.5k.
When I fixed the charging issues, all the mis-fires went away.

The point is, it takes a higher voltage to ignite a more full cylinder (more open throttle). At low RPM, there wasn't enough voltage to consistently spark when I had heavy throttle.
Mid RPM, the charging system provided just enough to work at all throttle positions.
At higher RPM, there were more sparks per second, putting more demand on the failing charging system. It was able to ignite the light throttle mixture, but not heavy throttle mixtures.

When starting, the battery voltage drops and it drops to be insufficient to spark.
Changing to the AGM battery reduces the voltage drop when starting.

Direct coil mod reduces the voltage drop between the battery and the coil.
(To check your voltage drop, it's best to check while running at high RPM when the load is greatest).

I'm not sure how the pick up mod would help with the hot-start issue.
I don't think the hot-start issues are related to this, but anecdotal evidence suggests that it helps.

Reducing plug gap, new plugs, or fine tipped plugs (iridium) should also reduce the required sparking voltage.

Spockster, I think I found out why the choke helps your bike!!!
https://dsportmag.com/the-tech/ignit...performance/2/
The first chart shows that it requires more voltage to ignite a lean mixture vs a rich mixture!
The 2nd chart shows the issue I had (full throttle mis-firing), whereby a greater air charge requires more ignition voltage.


'89 VN750 Bought stock 4/12/18 @ 17805.9 miles $800. Wrecked once. 27454.5+ miles

Completed modifications:
Removed mufflers, straight pipes out of GB. 110/90 Front Tire. Pick-up coil mod. Shindengen MOSFET FH020AA r/r. USB Outlet + Voltmeter. Repainted Metallic Blue w/ new tank bages. Ear Shave (wo/ coasters) 40/140 NO shims 45MPG. MCCT conversion.

Planned modifications:
Custom LED turn signals. Windshield. Highway Pegs. (Possible) ignition adv. Tuxedo Mod. Ignition coil mod.
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post #10 of 13 (permalink) Old 05-20-2020, 12:22 PM Thread Starter
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Wow....learning so much on this forum!! Thanks. I will start using the choke as the weather is starting to warm up and see if that gets me around the backfire and hot start issue, specially after refueling because that's the shortest time for restarting the bike. If reducing the "Spark plug " gap will reduce sparking voltage , I will try that too! Maybe I should try the "Ignition" coil mod and get power directly from battery and see if it makes a difference.

Last edited by AMH; 05-20-2020 at 12:27 PM.
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