Interesting find concernind B series TB

[carotman]

This thread it for those of you that Installed B series Intakes with a matching throttlebody.

I installed a B18B 60MM TB with an edelbrock manifold a few months ago on my Accord and always had problems setting the idle from then. Even if the Idle adjustment screw was completely removed, the engine didn't seem to get enough air to idle properly. The IACV kept compensating and I had an horrible bouncy idle.

I finally got rid of the problem by adjusting the throttle stop screw on the Throttlebody to leave the butterfly slightly open. This was kinda ghetto but it worked. I ajusted my TPS sensor accordingly but I was at the MAX adjustment and the TPS was barely on spec.

I discovered something interesting 2 days ago. Some Honda TBs have different idle screw port size.

The A20A/B20A idle screw port size is 15/64 inches. The B20B/Z has 5/32 and the B18B only has 1/8 (which is almost half the size of the A20A port).

I took my TB apart, took the idle screw out and bored both idle screw holes to 15/64. I readjusted the Throttle plate so it shuts completely and readjusted my TPS to .45V.

This solved my Idle adjust problem. I still got a lumpy idle (maybe because of the cams) but I can finally set the idle where I want.

This means that if you swap your TB with one from another car, make sure the idle hole is the same size as the one from the A20A (or bigger).

Thanks.

[b8er]

good work, im sure that'll help out at leats a few ppl

[bobafett]

thanks a lot for this thread. i have b series manifold with 68-70mm throttle body, im sure i will be fighting this problem too..

i will keep this thread in mind... :D

hopefully i will have this thing ready to go pretty soon so that i can fire it up and see how much of a bitch it WILL be to get tuned and idling...

[newaccorddriver]

hate to bring this thread up from the dead, but im assuming that after boring out the idle screw hole, you gotta tap some threads in there as well?

im having a hard time finding a 15/64 tap, so is it possible to use a different sized screw and tap?

[guaynabo89]

you dont bore out the threaded part of the hole, just the small hole at the bottom. youll se when the tb is off and the idle screw is out of the tb
its a pasageway built into the tb that bpasss the throtle plate.

if i misread your question sorry but I think this is what your talking about

[carotman]

You don't need to tap anything

Once you remove the screw, you'll notice that the hole behind it is alot smaller than the screw itself. Both A20A and B18 TBs used the same idle screw, it's just the hole behind it that's smaller or bigger.


Edit: Opps, guaynabo89 beat me to it.