Removing Idle Tube From An 8896 (from some guy named Ray on Speedtalk com)

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Removing Idle Tube From An 8896

(from some guy named Ray on

Remove the idle tube. To remove the tube, drill the top of the idle tube dead centre in a drill press. I use a 3mm x .5 tap to thread down enough so that a 3 mm bolt with a nut can be screwed into it. Make up a spacer, so that you can extract the idle tube by winding the nut down. If you go too deep into the idle tube, you will go through. Don’t stress. You can put a bit of lead shot in to seal it up

. ... drill the main well with a 3/16 drill to the bottom...shorten the idle tube so that the tube is 1.900 inches over all.... when u remove the swaged end that is the idle feeed restrictor in earlier bloacks you will have to put a 6-32 restrictor back in the idle circcuit with what ever size idle feed for your engine ...38 thou is a good ball park....on 3 circuit blocks its best to place the restroctor at the top placing it low if u go too deep u will block off the little 50 thou feed that the idle mixture screw seats against.... and your deal wont idle .....

if u want to eliminate your intermediate circuit then the easiest an most reversable is to put a 8-32 restrictor in the intermediate feed hole and dont drill
8896 2 Circuit Conversion

(From “tuner”,

I agree with the post above by maxracesoftware in the context of all carbs in an out of the box calibration or near it. The 9375 has the smallest MAB, .034” for the 9375-1 and .025” if you’re lucky enough to have an old one with the pressed in bleed that hasn’t been molested. The 8896 has a .040” and 8082 has a .037” MAB. The reason for their poorer performance is the larger MAB makes them both leaner at WOT and richer at the beginning of main flow. The newer 4500’s are all victim of the “air bleeds gone wild” syndrome, in my opinion. The newer HP blocks have 4 E-holes per main well instead of 2 like the old school blocks and that just makes the rich low-speed, lean high-speed situation even worse.

Mark, your early version 9375 should have .025 MAB’s but even so I’ll bet if you’ve ever logged the AFR in a pass it gets leaner as the RPM increases and it’s much richer than it needs to be in the burn-out box. The major difference between the 9375 and 8896 is jets and bleeds, the boosters are the same.

badbug3, the 8082 is the best choice for the Marine engine because it’s a two-circuit carb to start with and doesn’t have the idle tube restricting the main well. For it to work well it will need the following modifications.

In my not very humble opinion, all the above carbs will benefit from the following calibration. Early style 2 E-hole 2-circuit blocks, angle channel .160”, booster pin at least .160”, MAB .025”, IJ 040”, T-slot jet .052”, IAB .076”, main jet as necessary but usually in the mid 80’s for 1050’s and PVCR as necessary but usually .076” to .093”, depends on the size of the main jet. High-flow PV required. No PV in the secondary and SMJ in the mid 90’s, as required. The only difference between pri. and sec. is PV in the pri. You will still have to tune on this a little but if you’re already doing so with a 3-circuit you may as well spend your time on a carb that won’t foul your plugs on the return road or put an oil slick on the water.

All of the recently manufactured 4500’s (35+ years) have a T-slot that’s too long. The R4575 2-circuit 1050 carbs that were made before the first R6214 3-circuit had T-slots only 3/16” long, the R6214 and later carbs are all 5/16”. In the last decade particularly, the vertical location of the T-slot has become a crapshoot. Because slot above the butterfly is air bleed until it gets below the throttle and becomes fuel feed, the idle air bleed on top has to be smaller to compensate for the large amount of air from the slot so the lower end of the slot will be rich enough. Once the throttle is above the slot the effect is to have a larger than necessary fuel feed with too small an air bleed, it is too rich. (This is why they need the small jet in the T-slot.) On top of that, at the throttle position just above the T-slot the intermediate nozzle adds to the already over-rich situation. Because that much throttle opening is associated with a high enough engine speed the richness just causes farting and smoke and most people think racing engines are supposed to be rough anyway, the undesirable richness is ignored by most people.

Transfer slot jet location


2 circuit metering block modification areas



Use 10x32x3/16 long brass allen head cup point set screws for the MAB (if needed), IAB and the TSJ.  

You’ll need some 8x32x3/16 long brass allen head cup point set screws for the emulsion holes to either block or resize.  

Use a 6x32x3/16 long allen head cup point brass set screw for the IJ.  

You'll need a couple of #21 drills for the 10x32 holes, a couple of #29 drills for the 8x32 holes (E holes) and a couple of #36 drills for the 6x32 holes.  If you don't have a small "T" handle tap holder then you need one of those also along with a pin vise to hold those small drills

by Tuner » Sat Jan 10, 2009 5:29 pm

The transfer slot has progressively less effect as the throttle is opened until very large throttle openings near and at WOT, where it becomes insignificant.  The Main Jet and PVCR are the metering elements at WOT.  At WOT, on the transbrake or any other WOT condition, the Main Jet is in control of the AFR.  Tune the T-slot for its range of operation and the Main Jet for its range of operation.

In your case, I would change to .052” in the T-Slot, in light of what you have described so far.  SlowPoke and several others are using .052” in the T-slot and they are still a little rich in that area but they haven’t yet followed the procedure of trying larger Idle Air Bleeds to find the upper limit of the IAB’s effect or it turns stupid, whichever comes first.

The general idea of this Dominator rehabilitation & remedial tuning program is to find the lean limit of useful operation in the light load throttle positions where the low speed circuit tuning elements, Idle Jet, Idle Air Bleed and T-Slot Restrictor, are in control.  The WOT tuning is done in the traditional fashion, change the Main Jet.

Because the IAB has such a significant effect and it is external, therefore easily changed, it has the role of being the first and last calibration factor to alter when other metering orifices have been changed. A good procedure is to run through a range of Idle Air Bleeds from too big to too small just to see what the effect is, to find the boundaries and form an opinion of whether the T-slot jet or idle jet may need to be changed.  With each change of any other low speed circuit calibration, change the IAB’s back and forth.  If you haven’t already, try several sizes of IAB’s larger than you have so far.  

One of SlowPoke’s Texas neighbors (only lives over yonder about 300 miles) is tuning his 1050 on a 427.  As an experiment, he removed the IAB entirely and it’s still too rich just above a level road load with a .055” TSR and only .035” IJ.  No two engines are alike.  No two of these 4500 carbs we’re dealing with are alike.  The T-Slots are not located in the same position relative to the throttles, some times not even in the same carb (like this one, regalracer described it a few posts back).  If these were all mass-produced engines and reasonably identical, all 1967 L-88’s for example, we could find a calibration everyone could use and call it good.  

Because it responded favorably to reducing the accelerator pump shot you have determined it is too rich as you open the throttle from idle.  The easiest calibration change that will affect the low speed circuit is the Idle Air Bleed.  In your case, change to a much larger IAB in steps of +.010”+.020”+.030”- etc. just to find the lean limit and exactly what the effect is going to be on your specific engine.  If the TSR is too big (and I think it is in this case), throttle openings near the upper end of the T-Slot (very light acceleration) may still be too rich even though the very small throttle openings immediately above idle are acceptable.

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