200X DG carb, should i port the intake manifold to match?

[hawaiirider]

Hi i have a dg carb on my 200x, i ported the old intake manifold to match the size of the bigger carb, it ran good on top power but no matter what i did w the needle clip position it wouldnt run right in 1/4 thru mid range
i went and bought a new intake manifold as the old one started to weather check (dry rot real bad)
should i port the new manifold to match?
the mid range 1/4 thru mid is actually good with this unported manifold on so im scared to port it!!!
thanks for the help and long live the 200x

[manbearpig]

if it aint broke...

[christph]

You might test the manifolds back-to-back just to make sure that it is the porting that is making the difference. I have the 26mm DG carburetor and I haven't ported the manifold yet, but I can't see it making that much of a difference. In the future I was even thinking about opening up the head a bit to match the larger manifold.

[Dave8338]

Lean on the bottom 1/2 would not be a result of the porting. Sounds like it may have been an intake o-ring that was leaking after you pulled the intake to port it.

Just a thought.

[hawaiirider]

its definetley the intake manifold making the difference, i had to go down 2 sizes on the main for the new unported manifold, mid is good with the new, could dial it in with the ported.
anyone else delt with the dg carb before? the local shop said i needed a differnt needle but none were available anymore...

[El Camexican]

You mention porting the cylinder to match the manifold? How much bigger is it?

Explaining this might be way out of my typing/verbal skill range, but as simply put as I can you do not want large differences in the diameters of your three relevant holes which form a tube that delivers air and fuel to your engine, those being carb, manifold, intake port. I don’t have the exact formulas handy (had a book, lost the book) but to get an idea of what a performance based old school stock 2 valve engine looks like consider a 900cc Kawasaki. To the best of my memory the intake valve is 36mm, the port is about 28mm, the intake boot is just shy of 28mm and the carb is 28mm. Forget the valve size for now as it is measured to the O.D. and the seat is opened up to only about 30 to 32mm. There is a reason for this that has to do with the fact that valves open and close over an extended period and not on and off like a light switch.

My point is that the “tube” made up of the carb, manifold and intake port are all pretty much the same on a stock engine and with good reason. If you change anything in this “tube” it drastically effects the way air flows through the “tube” and in turn this effects the way fuel is released into the “tube”. If you have altered any of the three components that make up the “tube” it will change the way your carb reacts to the opening of the throttle. i.e a grossly oversized carb on an otherwise stock “tube” won’t experience the same amount of “venture effect” or negative pressure that allows fuel to rise up through the main jet as a smaller carb would. If you have any doubts as to how this works, take a soda straw, a funnel and if possible a used up toilet paper roll tube and duct tape one soda straw to either end and a used up toilet paper roll tube as is. Now take a strong breath of air through each of them. The straw should be the most restrictive. Now get a bucket of water and try to suck water through them one at a time. Obviously the straw is the only one that will work. Now imagine that the water is your gas.

So the long drawn out answer to your question is don’t port your manifold unless it is smaller in diameter than your intake manifold, or your carburetor and if you do port it only make it the same size as the inlet of the port or the outlet of the carb. After doing so you should see that your needle adjustments will change the way your engine runs.

If you do want maximum performance from your engine you would need to put a larger carb on, open up the manifold to match it, port the intake tract and get a performance cam and possibly larger valves. Then you would need to open the exhaust port up and get a performance exhaust to allow all that extra air and fuel out. Get a better ignition, undercut the trans get a stronger…;)

[hawaiirider]

thanks for the help, i should of said the carb is larger than the stock intake manifold thats why i ported the old one to match it.
my head has been flow ported by a professional.
i just couldnt dial midrange in with the old ported manifold, now that i slap a new stocker on mid seems better? oh well shes runnin, and thats what counts!!

[El Camexican]

If you matched the manifold to the carb and the head it should run better, that is unless this work is in excess of what your engine needs (I was going to mention this in my first post, but didn’t). In my four suction examples I mention trying to just use a toilet paper roll as a straw. It won’t work well because you can’t suck that hard. If your engine is ported beyond a cleanup and a little pocket work and you have a big carb then you need a cam with more lift and duration, a piston with a higher dome and the list goes on. You have to create a strong vacuum when the piston goes down in order to suck all the air out of the intake tract and create the negative pressure required to get fuel up and out of the bowl. Too much porting and you create the toilet paper roll instead of the straw. So, if a manifold that is more restrictive than everything else in your combination is making your engine run better it may mean that you overdid the other mods or it could be something as simple as your float height. If it is off it could play hell with your jetting. Might be that simple. Post ALL your mods if you want, something might pop up that leads to a fix.

[hawaiirider]

float height eh? dont even know how to set it...
my bike has a clamp on uni filter (no airbox just a short radiator hose %" to the filter) w a outwear on it
has a wiseco 10.25 to 1 piston
ported head
high lift webcam w titanium springs
dg full exhaust
honestly its not that fast, my buddys 200x is stock and not much slower
oh well at least shes runnin!!

[El Camexican]

float height eh? dont even know how to set it...
Google it, very easy and SUPER important! Did you check the timing on that cam?