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post #1 of 11 (permalink) Old 05-25-2013, 11:51 AM Thread Starter
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Another jet question

My bike is a 1996 VN750 . I recently added slip on mufflers and now I need to rejet to get rid of the backfire when I get off the throttle. Does anyone know what the stock jet sizes are ? Also, should I change both the main and pilot jets ?
Thanks for your help
Kevin
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post #2 of 11 (permalink) Old 05-25-2013, 12:01 PM
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Jets alone won't correct the decel pop (backfire is thru the intake). You will need to block the reed valves on each jug and eliminate the emissions system before it's completely gone. The decel pop was always there, just hidden by the stock baffling.

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post #3 of 11 (permalink) Old 05-25-2013, 12:16 PM
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for doing slip on exhaust no re-jet is needed, as Blaz said, you just need to cap off the reed valves... search "marbeling" and "coastering"
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post #4 of 11 (permalink) Old 05-25-2013, 12:20 PM
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Quote:
Originally Posted by 69 El Camino View Post
My bike is a 1996 VN750 . I recently added slip on mufflers and now I need to rejet to get rid of the backfire when I get off the throttle. Does anyone know what the stock jet sizes are ? Also, should I change both the main and pilot jets ?
Thanks for your help
Kevin
If the 750 is anything like the 800, what I did was ran a piece of radiator hose from front jug to back juck, to the reed valves, no marble inbetween - marbles can break. I also got rid of the whole epa nonsense and the breather fro the crank case now goes to an open element type with a bottle underneath to collect vapor buildup.

good luck

kenny

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2000 Vulcan Drifter 800
Roadhouse classic 2 > 1 exhaust
Okie Smokie intake config
Changed jets
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post #5 of 11 (permalink) Old 05-25-2013, 12:24 PM Thread Starter
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I failed to put in my post, that the emissions system was removed.( trying to do too many things at once) The pipes come straight off the heads and go into the mufflers.
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post #6 of 11 (permalink) Old 05-25-2013, 12:31 PM
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Quote:
Originally Posted by Mercury View Post
If the 750 is anything like the 800, what I did was ran a piece of radiator hose from front jug to back juck, to the reed valves, no marble inbetween - marbles can break. I also got rid of the whole epa nonsense and the breather fro the crank case now goes to an open element type with a bottle underneath to collect vapor buildup.

good luck

kenny
Not sure what connecting the reed valves does. Never read a report of a marble breaking in this application either. Keep in mind the term "marbling" does not always refer to using an actual marble, but just something to block the hose.

To me if your going to block off the system so it doesn't work, you might as well just remove it then as its now useless added weight. But that's me...


Did the 800 also suffer from deceleration popping? The "EPA" stuff has nothing to do with the issue BTW.

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post #7 of 11 (permalink) Old 05-25-2013, 01:26 PM
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Quote:
Originally Posted by Knifemaker View Post
Not sure what connecting the reed valves does. Never read a report of a marble breaking in this application either. Keep in mind the term "marbling" does not always refer to using an actual marble, but just something to block the hose.

To me if your going to block off the system so it doesn't work, you might as well just remove it then as its now useless added weight. But that's me...


Did the 800 also suffer from deceleration popping? The "EPA" stuff has nothing to do with the issue BTW.
http://www.angelfire.com/ak5/russwolf/mods.html

800 professional website.... good links there... I did most of my stuff based off the 800 guy there.

The two jugs have a nipple on each valve cover which used to go to some kid of vacuum switch, allowed hot gasses from the engine back into the intake from what i recall, hence the 'popping' on decel, any unburned gasses would hit the hot exhaust pipes and pop.

On my bike, yes it was epa crap. Every 800 I know of, mine, my fathers all popped on decel, it is the nature of the beast, but without the epa stuff / after burner, it does not.

With the 'afterburner' removed i no longer have pops.

According to russian wolf there was at least once occurance of somebody using a marble and it did break allowing glass into the reed valves.

If you tie the two reeds together without blocking off it seemed to work ok for me, again i have an 800 not a 750, do not know how much different they are.

I still have all my old epa crap too, in a box in the attic.

Now on decel, it just slows down and never pops.

here is a direct link, again for the 800....

http://www.angelfire.com/ak5/russwolf/afterburner.html

Sorry i do not know the 750, I can only offer links to the 800 stuff...

kenny

Merc
2000 Vulcan Drifter 800
Roadhouse classic 2 > 1 exhaust
Okie Smokie intake config
Changed jets
52K miles or so, always going up
Corbin Seat
Painted flat black winter '12
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post #8 of 11 (permalink) Old 05-25-2013, 01:29 PM
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Wanted to mention.... the reed valves do get gunked up with carbon, seems like no matter what, I had it blocked off, they got carboned up, i had them tied together and same thing... There is a way to make a block off plate but a waste of time i figure, just tie um together and that makes um useless from what i can tell.

I have my engine apart if anybody wants me to look close at where this 'stuff' goes internally.

Again, this is an 800 but i would be happy to look

kenny

Merc
2000 Vulcan Drifter 800
Roadhouse classic 2 > 1 exhaust
Okie Smokie intake config
Changed jets
52K miles or so, always going up
Corbin Seat
Painted flat black winter '12
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post #9 of 11 (permalink) Old 05-25-2013, 01:33 PM
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Or, instead of having an ugly hose, you could get a pair of 1/2 inch copper pipe caps, paint them black (or other matching color) and seal them on to the reed valve housing. I used make a gasket to perma-seal them on. Just gotta paint them now. I figure it's cheaper this way.

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post #10 of 11 (permalink) Old 05-25-2013, 04:07 PM
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Stock Jet size

On my '03 the stock jets were 138 main jets with 38 pilot (also known as slow) jets. After tinkering with these carbs I've found that the pilot jets seem to affect the fuel air mixture when cruising (less than 1/3 rd throttle) and the main jets have more to do with higher throttle settings.

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Last edited by Spencer1; 05-25-2013 at 04:15 PM.
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