Pickup Coil Mod Details - Page 2 - Kawasaki Vulcan 750 Forum : Kawasaki VN750 Forums
Electrical
Where does this wire go?
Includes Electrical mods, Lights, Stator,
Rectifier, Diagrams, etc

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post #11 of 16 (permalink) Old 05-28-2018, 09:58 AM
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I've made ashtrays (burnt pistons) in as little as 45 seconds, others have taken 6 miles at full throttle to get results.

The VN750 has a moderately high compression ratio and is designed to run on low octane gas, so it's right at the edge.

What to look for:

Ping - the sound of detonation/pre-ignition, described as marbles dropped on a glass plate. The 45 second ashtray gave no warning signs.
Overheating - or just running a touch warm
Spark plugs burned white, melted or missing electrodes.
Driveability issues - bucking, surging
Starting issues - hard cranking when warmed up

Warning - Terminal Engine Damage Ahead

One major problem is the lack of precise marks to gauge the adjustments, and precise means of making adjustments. Also, it will be very easy to have one cylinder advanced more than the other.

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

Last edited by Spockster; 05-28-2018 at 10:06 AM. Reason: when warmed up
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post #12 of 16 (permalink) Old 05-29-2018, 12:22 PM
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I am seeing several polite responses suggesting that this is not a good idea.

It's so tempting to try though ...but at what cost ?

Combining what I've read hear and some of my own research on this, I see that worst case (most prone to detonation) is full throttle at low RPM on a hot engine, with a rich mixture. Part throttle means a less dense charge in the cylinder and a slower burn. Heat makes it more prone to auto-ignite. A lean mixture (I read) burns slower. I have the stock jets in my carbs. With open pipes and K&N filters, I may be a bit on the lean side. Plug color says I'm normal.

If I use a dremel to grind off the upper ear of each coil, I can precisely measure my advance by measuring the gap between the lower ear of each coil and its locating pin. Alternatively, measuring the total length of each coil with calipers would make it possible to match them. Between 0.041" and 0.045" is 1 degree of advance. It should be non-trivial to match the two cylinders to well within 1/2 a degree.

My motivation for this mod is as follows:
Most car engines use vacuum advance, and this bike doesn't have one. I can't conceive of a way to add vacuum advance, so I thought advancing static timing would help. If there is room to safely adjust, I should gain both power (at WOT) and mpg at part throttle. But I also may gain a 500lb heap of scrap metal if I go to far.

Oh...what to do?!?


'89 Vulcan 750 Bought 4/12/18 @ 17805.9 miles $800
Purchased stock. Wrecked once
21460.1 miles & counting

Completed modifications:
Removed mufflers, straight pipes out of GB
110/90 Front Tire
Pick-up coil re-gapped to .020"
Compufire 55402 r/r series regulator
USB Outlet + Voltmeter
Repainted Metallic Blue w/ new tank bages
Ear Shave (wo/ coasters) 40/143 NO shims 45MPG

Planned modifications:
Custom LED turn signals
Windshield
Highway Pegs
(Possible) ignition advance
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post #13 of 16 (permalink) Old 05-29-2018, 02:14 PM
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I've only run into burned pistons at full throttle and high rpm. But an engine can ping easier under load at lower rpm with advanced timing and/or poor tuning.

Many unmodified carbs will go lean at sustained full throttle, which contributes to burning a piston. Two-strokes are highly sensitive with respect to timing and fuel mixture.

Seems like a lot to go through for an extra few tenths of a second on the street. You might gain a little mpg, but it's easy to jump the shark too.

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 #14 of 16 (permalink) Old 11-30-2018, 04:21 PM
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I can't let this go...

I keep coming back to this, and I think I'm just going to try it.
Near as I can tell, lean burns faster than rich (I've heard some conflicting info).
I know that part throttle burns slower than WOT. This is what vacuum advance is used for in cars. Based on that, I know I can get away with more timing advance at partial throttle. I would gain some MPGs. The danger is at WOT.

I know people have stated the bike runs lean from the factory. It probably also uses conservative timing to account for bad gas. I plan to first richen up the AFR through a larger main jet. The chart shown here indicates the main jet covers 3/4 to WOT. If I can get it rich enough, it should tolerate more advanced timing at WOT as well. All in all, more MPG and more acceleration. I'm running no mufflers, and I'm doing the ear shave. I'm planning on a 138 main jet, based on that post. I'll probably buy a set of 140s too, just to try.

The chart in the service manual (page 15-7) shows a range of timings. I'm assuming that's the tolerance band. At 1100 RPM, it shows ~3.5-7 and at 3500 RPM it shows ~24-27. That tells me that without any other modifications, I should be safe to push the 1100 advance to 7 degrees. I'd use a timing light to verify the timing of each coil. With a rich WOT mixture, I MIGHT be able to push 8 or 9 degrees.


'89 Vulcan 750 Bought 4/12/18 @ 17805.9 miles $800
Purchased stock. Wrecked once
21460.1 miles & counting

Completed modifications:
Removed mufflers, straight pipes out of GB
110/90 Front Tire
Pick-up coil re-gapped to .020"
Compufire 55402 r/r series regulator
USB Outlet + Voltmeter
Repainted Metallic Blue w/ new tank bages
Ear Shave (wo/ coasters) 40/143 NO shims 45MPG

Planned modifications:
Custom LED turn signals
Windshield
Highway Pegs
(Possible) ignition advance
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post #15 of 16 (permalink) Old 11-30-2018, 04:56 PM
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There is a wire that runs from the starter switch to the ignition system. I strongly suspect it is there to change the ignition timing during starting to make it easier.

I think it retards the timing so you get a soft start, similar to the manual retard you find on some historic bikes. Others think it advances the timing.

Might be an idea to test the theory with a timing light while connecting the ignition input to 12v and leaving it open.

If it advances the timing you have a simple way to test your theory about performance without having to dremel parts.

'99 Vulcan "Victoria"
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post #16 of 16 (permalink) Old 11-30-2018, 05:40 PM
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Quote:
Originally Posted by TonyO View Post
There is a wire that runs from the starter switch to the ignition system. I strongly suspect it is there to change the ignition timing during starting to make it easier.

I think it retards the timing so you get a soft start, similar to the manual retard you find on some historic bikes. Others think it advances the timing.

Might be an idea to test the theory with a timing light while connecting the ignition input to 12v and leaving it open.

If it advances the timing you have a simple way to test your theory about performance without having to dremel parts.
Planned to do that this past summer with the wire ... never got a round tuit.

I sense a new mod, maybe, a "Push-to-Pass" mod, like F1, or is it Indycar. (only if the wire makes it advance)

Pretty sure it's the red/white on the CDi, but I didn't check the diagram.

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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