I've read about ported stock intakes. How exactly do you port the stock intake?
I can see that the ports are much smaller that the housing ports. I know that 'port matching' is a big thing on piston engines. Is that the porting we're talking about? Do you also alter the top of the intake? Is there actually a benefit to this, or is it a 'racer's trick' that doesn't really do anything?
I'm about to rebuild my stock Nikki (my 12a is also stock, BTW). Should I go up one size on the jets while I'm at it? I'm about to upgrade the exhaust, and I may port my stock intake. That done, will I need to rejet?
I'm hoping someone has done this already and can set me straight. Share your experiences.

 

I dont think you'll see that much of a diffrence port matching and/or "changing jets isnt that easy because from what I under stand, one cant just change the jets on a stock Nikki. Your much better off getting an after market carb or a "Sterling Carb".

 

Um . . . whaddya mean??
I can buy a new set for under 3 bucks. Since I'm tearing down the carb anyway, why can't I just swap in a different set of jets?
I've never rebuilt a Nikki before, but it's still just a carburetor we're talking about right? That's like saying 'you can't just swap the cam in your 5.0'
Why can't I?!?

 

It can be done but takes time so be sure to get a log book. Back in the days, Tripoint Engineering used to make bad *** RX-2 carbs (what we called "stage carbs"). Unfortunately, they switch to piston powered mazda and F/I RX only.

PS:
Its a pain the *** to change those nikki jets.

 

I appreciate your input, but still looking for a more in-depth answer to my original question. Somebody must have done this. Do tell!!

 

unfortunately, they wont tell you what it is. its a business and loyalty.

 

On a stockport engine I don't think porting the intake runners bigger helps at all, but matching the ports on the intake to the engine and getting rid of any casting marks and obstructions in the intake should help. You probably won't need bigger jets. I don't think you can buy different size jets for a nikki, so I hope you have a bunch of small drillbits if you do need bigger jets

 

coldy is referring to INDEX and NUMBER Drill bits. You can get them from Harbor Freight.

 

This is the sort of info I was looking for, THANKS!
BTW, Mazdatrix sells stock Nikki jets in over 20 sizes, from .095 to .210.

 

I picked up one of the carbs wacky is talking about. He knows a little more about it then i do but its a really really nice looking carb. working on an intake and airfilter for it.

 

I didn't know that, is that american or metric size? I run stock primaries and 255 secondaries

 

Um . . . judging by the rest of the engine, I'm leaning toward metric.

 

I've seen jets lisetd both ways, they dont sell jets big enough for me then.

 

You can port match the secondaries at the bottom of the manifold (match it to the actual runner and not the flare at the end) and clean up the runners of any big bumps, casting flash etc. Do NOT smooth the runners. They need a rough surface to help keep a boundary layer from forming for better fuel atomization. Without experience or a flowbench I wouldnt reccomend you do anymore. It will improve the flow.

You need some way of tuning the carb. EGT, dyno, A/F meter. Then youll know what YOUR engine package needs. FWIW, the Nikki is jetted rich at the top end from the factory. So you probably wont run lean if you leave it alone. Of course thats not gonna make max power, but it also probably wont hurt the engine.




Lazy old man!

 

About time you chime in Carl.

 

True that. ******* expensive though!

 

lol everytime I read the size secondaries you have, it makes me laugh. Daumn!

 

In the *stock* nikki you can change primary and secondary fuel jets (though they cost a fortune), but the air bleeds are integrated with the emulsion tubes so you can't change those. It limits your tuning possibilities.

The Sterling carb is fitted so that you can use Holley 10-32 air bleeds in place of both your fuel jets and your air bleeds, which makes it much easier to tune.

In terms of porting the manifold, port matching the manifold to the runners on the engine is a bad idea... you'll want to read this article on Paul Yaw's website:

http://www.yawpower.com/Flow%20Testing.html

But porting where the carb bolts to the manifold can significantly increase flow, which is why I had Carl port mine.

Jon

 

BAM! Exactly the info I was looking for. Thanks!
But . . . what does the port work on the top off your manifold look like? Any clue would help.

 

I got a bit more topend out of my 12a streetport with a stock carb by porting stock manifold and using bigger jets and removing the spring form the secondary actuator. I ported the primaries together and the secondaries together. I left the secondaries separate from the primaries though to help with velocity. I used a custom spacer to make a smooth transition and increase runner length a bit. The idea was to draw thrugh both barrels to feed each rotor and esentially double the cfm of the carb. I went ultra qhetto with this stock carb setup and drill junkyard jets with small drill bits until the mixture was good. I had a custom short primary header megaphoned to a 3.5" exhaust. Reved to ~7000prm before manifold vacuum gauge indicated increasing vacuum under WOT.

 

wow, awesome info in that link.