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Engine Upgrade problems 2007 Honda Shadow Spirit

Posted on 2009-05-15
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Last Modified: 2012-05-07
I have a 2007 Honda Shadow Spirit.  The specific model is the VT750DC.

Recently I installed:
Cobra Streetrod Slashdown Exhaust for Spirit 750 DC (Chain Drive)
Cobra Jet Kit - Honda Shadow Spirit 750 DC (Chain Drive) - Stage 1

Runs great and I'm running with NO baffles.  I used the DJ106 and DJ104 jets from the stage 1 kit.  Now comes the problem, I also ordered and attempted to install:

Thunder Manufacturing Round Custom Air Kit

Basically it's an open round K&N air filter smashed between two chrome plates.  It gets LOTS of air flow.  The air filter kit came with a DJ134 and DJ138 main jets which I replaced from the DJ104/106 jets that came in the kit.

Some things to note, there is no Stage 3 kit for my bike.  BUT, the air intake is made specifically for my bike.  It also says that a jet kit (not included) must be installed.  So I'll ASSUME that the stage 1 fuel needles and springs are OK but that is probably where my problem lies.  I don't know where to adjust the air/fuel mixture screw to because I'm NOT a carb man.  I'm just following what instructions I have and they are currently set to 3 1/2 turns out which is what the cobra kit said to do.

Here's what happens and doesn't happen.
Idles great
Accelerates smooth under low throttle on flat (down my street to the main road).
The road I am testing on is completely flat.
When I "get on it" it stutters for a second but then really takes off.
When I let off to shift, the RPMs drop, but as soon as I get on it in 2nd again it stutters for a second.  This repeats all the way through fourth.

So I turn around and head to my house (up a hill) and it won't climb the hill unless I downshift to 2nd and get the RPMs and throttle up.  Normally I climb the hill in 4th.  Once on my street, it putts along as always because there's little demand on the engine.  I also tried restricting air flow by taping off the front 1/2 of the filter and it didn't make it any better.  I REALLY think I'm getting too much air.

If I put the stock air box and the stage 1 jets on, it works fine.

Here's what I am capable of doing, looking for guidance on WHAT to do.

put baffles in exhaust
adjust air/fuel ratio (?? in, out ??)
you tell me

here's what I can't do (without ordering parts)
swap out the springs or needles
swap out the jets (i don't have any bigger jets than what the air filter came with).

Let's have at it.  I'd like to solve this myself without taking it to the honda shop.
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Question by:BrandonGalderisi
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Michael-Best earned 500 total points
ID: 24401271
Here's what I am capable of doing, looking for guidance on WHAT to do.

put baffles in exhaust
adjust air/fuel ratio (?? in, out ??)
you tell me

Try adjust air/fuel ratio to richer (more fuel) by half a turn out & post back.
Baffles might be a good idea, as engines run better with a little back pressure.
Tell me your results.
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Expert Comment

by:Michael-Best
ID: 24401293
I built / raced / self tuned / self reconditioned: carts, bikes, & rally cars.
Carbs are easy for me, but carb model / specs would help.
Some info while I wait:
http://en.wikipedia.org/wiki/Carburetor
http://auto.howstuffworks.com/question3772.htm
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Author Comment

by:BrandonGalderisi
ID: 24401337
Best I Can say (at 1:30 in the morning) is that it's the stock carb on the bike.  Will look tomorrow to get more details.

Richer would be backing the screw out right?

Makes sense since when I first removed the baffles from the stock exhaust I had to back it out 1 turn.
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Assisted Solution

by:Michael-Best
Michael-Best earned 500 total points
ID: 24401387
Richer would be backing the screw out right?
Yes, try 1/4, 1/2, 3/4 till it runs smooth.
Plug color white-grey=lean / grey=good / dark-black=rich
If its too lean, your engine will overheat & may seize.
I live in Japan a different time zone & speak great Japanese: (honda, suzuki, yamaha, kawasaki ... & fuent nihongo=Japanese)
I will look to get more details while you sleep.

I still ride a 27 year old Honda & its engines perrrrfect.
Regards
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by:BrandonGalderisi
ID: 24401609
The plug method may not work since i have less than 5 miles running with the filter and the plugs are brand new.

Will let you know in the AM (for me)
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LVL 34

Assisted Solution

by:Michael-Best
Michael-Best earned 500 total points
ID: 24401625
I think I wont need carb details, as this should solve it.

Heres how to do a reliable spark plug test: Grab some heavy gloves, and a plug wrench, and head out to a flat, empty stretch of highway. Maintain 60  70 mph for at least five miles. Shut off the engine at cruising speed and pull in somewhere safe. Before the engine cools, pull your plugs and have a close look at them in good light.
Observe the round, flat surface perpendicular to the threads. This area should be mid-brown/gray. Black indicates youre running too rich in the mid range, white means too lean.
Take into consideration your altitude (higher means a richer-running engine), barometric pressure, air temperature and the conditions under which you normally ride. Its best to tune in the same conditions, and preferably on a warm, clear day when the barometer is high.
Plug photos:
http://www.honda-tech.com/showthread.php?t=2502308

If its not air/fuel ratio to richer (more fuel)
Or
Baffles might be a good idea, as engines run better with a little back pressure.
see
http://www.cycoactive.com/mc/trail_tips/tip_float_level.html
Tell me your results.
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Assisted Solution

by:Michael-Best
Michael-Best earned 500 total points
ID: 24401937
Richer would be backing the screw out right?
This is idle mix only.

You may have to buy / change jets & needles.
" I REALLY think I'm getting too much air. If I put the stock air box and the stage 1 jets on, it works fine"
You are running "too lean", for sure.
Taking away the stock air box is changing the fuel / air ratio.
Confirm by plug color test.
Increasing float level a little may help.
see:
http://www.cycoactive.com/mc/trail_tips/tip_float_level.html
Tell me your results.
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Author Comment

by:BrandonGalderisi
ID: 24402877
Well I figured I'd start with baffles only, and it runs.  I'm not saying it's SPOT on, but it's REAL close.  I can tinker from here to get it dialed in.  Thanks MB for all the help!
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Author Comment

by:BrandonGalderisi
ID: 24403310
Ok.  So it wasn't as good as I thought.  It still dogs out at 60-70mph.  But it's climbing hills like normal again.

The plugs are carbon fouled.  That means rich and I should lean it out right.

Just say the word and I'll open a new thread.  As I said, it's MUCH better.  1/2 solved I'd say.
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LVL 34

Expert Comment

by:Michael-Best
ID: 24418249
"The plugs are carbon fouled.  That means rich and I should lean it out right."
Yes
Do a reliable spark plug test: Grab some heavy gloves, and a plug wrench, and head out to a flat, empty stretch of highway. Maintain 60-70 mph for at least five miles. Shut off the engine at cruising speed and pull in somewhere safe. Before the engine cools, pull your plugs and have a close look at them in good light.
Observe the round, flat surface perpendicular to the threads. This area should be mid-brown/gray. Black indicates youre running too rich in the mid range, white means too lean.
0

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