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Discussion Starter #1
I'm considering an aftermarket programmable ignition module. I'm wanting a timing increase above 3.5k (where stock timing no longer increases). More importantly, I want to add a vacuum advance to improve performance, throttle response and MPG below WOT. This will require adding a MAP sensor.

I was thinking of running a hose from both carb vacuum ports to a manifold, then running from the manifold to:
The petcock
The air bypass system (yes I left it in after the ear shave)
and the MAP sensor.
Will this sort of cross-connection cause some issues with the carbs?

The rational is this would give a more steady signal to the MAP sensor, since it's reading both carbs. I would also expect the petcock to open sooner on start up, maybe giving a quicker start to fuel flow. In any case, I plan to only use the MAP sensor from 3K-8.5K, to avoid the pulsing vacuum at lower RPMs. I would simply program in stock tuning from idle to 3K at all MAP sensor readings.

It sounds like there's little to gain below 3.5k without risking knock. The same linked thread indicates that there's some gain above 5k though. It looks like dariv is now banned, so I never found out the results of his re-tune. But his last post showed 37 at 5.5k instead of the stock 25! He seemed to be active for another 2-3 years after that, so I'm guessing he didn't blow his engine!
 

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Experiments can always be fun, but it seems like possibly quite an expense (for the aftermarket ignition) and a lot exercise for potentially very little if any gain, with the risk of catastrophic failure. Ignition timing can be really tricky. Sometimes there's no warning of going too far before pistons are turned into ashtrays. I only say this because I've done exactly that, and it only took about 60 seconds, granted the engine was one that's ultra sensitive to timing advance.

This engine is possibly right near the edge with ignition timing, since it can use regular gas with a 10.5:1 compression ratio. Lean mixture and a lot of timing combined will put you right into the ashtray business, so plan on re-jetting, it's going to need more fuel and octane to cool off the combustion.

Don't believe there would be any interference by having the carb vacuum lines linked together. The vacuum there is only made available to operate other components, independent of carb function.

Curious about what you did with the air system hose that ran into the airbox?

If you dive in, maybe you can also find out what the mystery wire to the CDI does.

Always wondered why that poster was banned, think it happened the day after I registered.
 

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Discussion Starter #3
Experiments can always be fun, but it seems like possibly quite an expense (for the aftermarket ignition) and a lot exercise for potentially very little if any gain, with the risk of catastrophic failure. Ignition timing can be really tricky. Sometimes there's no warning of going too far before pistons are turned into ashtrays. I only say this because I've done exactly that, and it only took about 60 seconds, granted the engine was one that's ultra sensitive to timing advance.
I just got a quote for the TCIP4 system with a harness for the VN750:
"We can offer programmable unit TCIP4 standard (129 USD) with connector adapter (5 USD). This is plug and play connection. You can to add pressure sensor with this unit. We can offer pressure sensor 82051 (16 USD). Unit will be pre-programmed for work on your bike. Recommended accessories is USB/COM cable for connection with PC (12 USD). Freight DHL is 36 USD."
$200 all in.

This engine is possibly right near the edge with ignition timing, since it can use regular gas with a 10.5:1 compression ratio. Lean mixture and a lot of timing combined will put you right into the ashtray business, so plan on re-jetting, it's going to need more fuel and octane to cool off the combustion.
I don't plan on messing much with the WOT timing. It's already a bit rich. I don't want to get aggressive here.
From what I understand, partial load causes partial filling of the cylinder, which burns slower than a full cylinder.
Adding vacuum advance compensates for that.
Since it's less than WOT, I don't need to be crazy with it, as I'm not trying to push max HP.
Just trying to get a bit more out of each spark.
Since it's dual plug, this engine already doesn't need a lot of advance.
Tune Your Vacuum Advance for Better Drivability

I plan to ride at 60, 70 and 80 and note the RPM and vacuum at those speeds.
Then I was going to put it on a dyno at those RPM and vacuums, and bump up the timing 1 degree at a time until torque no longer increases (or until I hear bad noises).
Then I'll back off 1-2 degrees.
For WOT tuning, I'd similarly bump timing.

Lastly, I want to retard the timing at high vacuum/high rpm, to see if I can spit fire on downshifts. :D

This unit can hold two different timing maps, switchable on the fly.
I plan to keep the factory timing on one map, so I can switch over with bad gas or if I notice issues while riding.

Curious about what you did with the air system hose that ran into the airbox?
I ran that hose up front to another EMGO Crankcase Breather Filter Kit.
The original crankcase hose goes to one on the left side of the bike.
The air system hose goes to one on the right side of the bike.

If you dive in, maybe you can also find out what the mystery wire to the CDI does.
You mean the BK/Y wire going into pin 6?
Good question. After you first mentioned it, I wanted to connect a variable power supply to it to see if it affects ignition timing.
I never got around to it.
I gotta get my bike in top shape before I mess with the ignition.

The TCIP4 has a starting mode that requires a minimum amount of rotations for starting.
But given how many cranks it takes to get fuel flowing again (especially when the carb is dry), that might not be enough.
 

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Mystery wire is the red/white branching (mid harness) off the black that runs from the start button. Shows as 4th pin from the left on the CDI in the diagram. edit: Have wondered if varying voltage on the red/white would change timing, and if it retards or advances.

All black/yellow are grounds. So don't apply any power there.

Not as pricey as I thought it could be. Does this replace the CDI or piggyback onto it? If it replaces, could be the way to go for a fried CDI.

edit: :D If you want to make a big cannon shot, plumb in a valve on a vacuum line, open the valve then go into a long decel. Not responsible for muffler damage! :)

If you want the decel pop, disable the coast enrichers. Might help MPG too?
 

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just a side note about crank time needed to start the 750... one in good running condition with a good tune on the carbs will fire within 2-5 revolutions of the crank..

also, I may be wrong here, but the vacuum ports on the sides of the carbs may be venturi vacuum, not vacuum on the downstream side of the throttle plate
 

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...

also, I may be wrong here, but the vacuum ports on the sides of the carbs may be venturi vacuum, not vacuum on the downstream side of the throttle plate
Good point, and you're right. I sometimes forget things like that if I'm not looking at the engine.

Venturi vacuum should remain near constant and wouldn't be useful to sense engine load. Otherwise, the petcock would close when you hit full throttle.

You would need to tap into the carb boot between the carb and the head in order to use a MAP for the ignition control.
 

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I wouldn't mess with the timing advance. There is a good chance of seriously damaging your engine.
 

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Discussion Starter #8
Mystery wire is the red/white branching (mid harness) off the black that runs from the start button. Shows as 4th pin from the left on the CDI in the diagram. edit: Have wondered if varying voltage on the red/white would change timing, and if it retards or advances.

All black/yellow are grounds. So don't apply any power there.
I see it. Interesting!

Not as pricey as I thought it could be. Does this replace the CDI or piggyback onto it? If it replaces, could be the way to go for a fried CDI.
It's my understanding that it replaces the stock CDI. Everything wires directly to this unit.
http://www.ignitech.cz/zdroj/en/vyrobky/tcip/manual/Kawasaki VN750 TCIP4.doc

Not responsible for muffler damage! :)
No mufflers, so I'm good. >:)

If you want the decel pop, disable the coast enrichers.
I thought those cause the pop, and are the reason people remove them.

just a side note about crank time needed to start the 750... one in good running condition with a good tune on the carbs will fire within 2-5 revolutions of the crank..
It usually does when shut off, but when coming back from empty carb bowels (carb work, or running out of gas), it's quite a bit more!!!

also, I may be wrong here, but the vacuum ports on the sides of the carbs may be venturi vacuum, not vacuum on the downstream side of the throttle plate
Good point, and you're right. I sometimes forget things like that if I'm not looking at the engine.

Venturi vacuum should remain near constant and wouldn't be useful to sense engine load. Otherwise, the petcock would close when you hit full throttle.

You would need to tap into the carb boot between the carb and the head in order to use a MAP for the ignition control.
I always wondered how the petcock remained open at WOT...
Well, that changes everything! I might have to rethink this plan...

But wait, doesn't the air bypass system use downstream vacuum to enrich the air on closed throttle?
Also, when synching the carbs, the instructions are to use these vacuum ports.
If it is venturi vacuum, this might still be usable.
I read that "the venturi vacuum is approximately proportional to the total mass flow through the engine". If this is the case, I can use a MAP sensor as a mass flow sensor.
It would just work inversely, with more vacuum equaling more load.
It could still be used to create an ignition timing profile.

This sort of cross talk between the two carbs could cause some issues with running though.

I wouldn't mess with the timing advance. There is a good chance of seriously damaging your engine.
Jerry, you're no fun. :wink2:
 

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Two of my Vulcan 750s were bought new. Lots of money. Couldn't afford to risk damage. Last one cost $2700 used. And I spent over $700 on it after buying it getting it in tip top shape. A really good condition VN750 engine is valuable. Probably more than most Japanese motorcycle engines. Increase the ignition advance, and you'll likely wind up with detonation and holes in the pistons. But it's your engine.
 

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Discussion Starter #10 (Edited)
This is my first bike, and I have yet to find another bike that I enjoy more all around (though the Triumph Legend TT is more fun, but not as comfortable living with). I don't want to replace it. After all the time and money I'm investing in this bike, I have no plans to risk damage! The bike may be worth $1000 or so on the market, but it's worth a whole lot more to me!
I understand the risks, and I appreciate the concerns. I plan to proceed with great caution.


The more I think about it, the more I think the vacuum ports are manifold rather than venturi.
It's a bit foggy, but during synching, I recall vacuum around 15 inHg at idle, that would fall when cracking the throttle.
This seems way to high to be venturi vacuum at idle.
The air bypass system is designed to open with vacuum (correct?), which would be strongest at throttle closed.
The external location of the port looks like it is downstream of the throttle plate.
I can verify this in person, when I get home and can look closely at the carbs.
Additionally, it sounds like a CV type carb always has a small amount of vacuum, even at WOT, due to the restriction of the butterfly itself being in the air stream.
This might be enough to keep the petcock open at WOT?!?
That's the only part I'm not sure of.

I hope in the process, that many can learn from my experiments.
 

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The coast enrichers are supposed to stop popping on decel. I haven't known anyone to modify them. They're behind the round'ish covers on the sides of the carbs, rubber diaphragm with a 'valve' and a spring. Also called Air Cutoff Valve or just Air Cut Valve, this is the quickest pic I could find: https://www.ebay.com/itm/85-VN700A-...476670?hash=item4b3cda25be:g:sFsAAOSwmOZbiK~K

Pretty sure mine were stuck or clogged when I first got it on the road, and it popped, some miles on seafoam and it quit. Have a suspicion this is the source of popping and not the air system. The repair manual says: 2-22 Fuel System 1) Check the inlet vacuum passage for the coasting enricher system, if backfiring occurs too often. 2) If the passage is clogged, blow it through with compressed air.

Tried looking at carb pics, best I could tell the vac port looks to be behind the throttle shaft. But you could check with a vac gauge or with carb removed see if the port comes out beyond the butterfly. Can blow or spray through the port also.
 

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Bike will not run without the coasting enricheners. My diaphragms were melted (ethanol) and I spent a small fortune to replace them.
 

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"This is my first bike, and I have yet to find another bike that I enjoy more all around (though the Triumph Legend TT is more fun, but not as comfortable living with). I don't want to replace it. After all the time and money I'm investing in this bike, I have no plans to risk damage! The bike may be worth $1000 or so on the market, but it's worth a whole lot more to me!
I understand the risks, and I appreciate the concerns. I plan to proceed with great caution"

Good idea. Too bad about the bike being wrecked. Glad you are ok. I have never crashed a street bike. If I did, and survived, I would not want the bike anymore. I bought one beater street bike (1980 Suzuki GS450L) that had obviously been dropped many times. Handlebars were bent, forks were bent, sidestand bracket was broke off, lots of scrapes and gouges. 36,000 miles and ran perfect. I turned it into a rat bike and rode it to work for almost 7 years. I got used to riding it with the bent bars and forks. But I never took it that seriously. I knew it was junk, and actually kind of liked that.

I spent $2700 for a low mileage 1997 Vulcan 750 several months ago to replace my bought new 2002 which finally bit the dust at 118,000 miles due to a cam chain failure.

I saw something about a tuxedo mod in your post. If there is one thing I would absolutely NOT recommend doing, that would be it, unless the engine is out, you have the left case cover off, and some distance from the bike. Doing it with the cover on the engine will fill your engine full of metal shavings, and do catastrophic damage. When I pull the cover off an engine, I go to extremes to keep dirt, even dust floating around in the air, from getting inside the engine. This is not just me. Ask ANY mechanic about the advisability of dumping ground up metal into an engine. When building/rebuilding/repairing an engine, keeping the inside spotlessly clean is probably the most important thing you can do.
 

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Sure it will, as long as the enricher circuit is closed. Might run with it left open, just richer.
If that's true, I guess there is no reason for me to spend another $150 to replace the diaphragms if I find mine melted again. That would be great.
 

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If that's true, I guess there is no reason for me to spend another $150 to replace the diaphragms if I find mine melted again. That would be great.
You can buy one for $12.
 

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Where? All the online parts places list them at $65 each.
 

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Bike will not run without the coasting enricheners.
Sure it will. Mine have been blocked the last 8k miles. The only effect is exhaust popping on decel.
Its not loud, it won't blow up the mufflers and it doesn't hurt the engine.
 

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Discussion Starter #20
I am referring to the reed valves that sit on the sides of the engine, that dump extra air into the exhaust during decel to burn off unburned fuel. I believe those operate using manifold vacuum. These are typically removed with an ear shave, and a plate is put in place where the reed valves used to sit. As I understand it, putting these plates in place stop the popping on decel.

When I did my ear shave last year, I left that system in place, because I like the popping on decel. I didn't notice any issues with the enriching diaphragms in my carb. It ran more or less the same as before the ear shave. Only more intake noise and slightly improved MPG. I did notice that running the idle screw slightly richer than optimal, got rid of the popping.



For the Tuxedo mod, I've got the cover off (needed to remove it anyways, to remove the cam chains). It will be modified off the bike, in a different building, in a different city and county :grin2:. I actually didn't realize that people try to do this mod on bike. That doesn't sound like a good plan, for the reasons you outlined.
 
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