So my idle and WOT air/fuel numbers are right where they need to be, idle may be lean but it seems to run good where it is and I’m not sure I fully trust the idle numbers due to my camshaft overlap. WOT is right around 11.8 afr. The issue I want to work on now is my higher speed cruise, I’d like to lean it out a bit. I know after this I may need to re-visit my WOT settings but I can deal with that later. It will cruise around at 0-30mph decent, around 12.8-13.4 AFR, but at higher cruise speed let’s say 45mph-65mph it wants to run around 11.5afr. My question is should I go straight for smaller main jets, or should I play with air bleeds? I can’t tell but I’m pretty sure at that cruise speed it’s on the main jets not transition circuit. It’s a th350 with a 3200 converter 3.73 gear so it’s probably around 3000 rpm or so and pulling around 10” vacuum. Right now it’s only got 66 main jets in it and 68 secondary and I have no idea about air bleed size because they aren’t marked and I’m not sure how to measure it. Thoughts? Thanks in advance.

 

If your carb has high speed air bleeds open those a little then retune the wot. If you only have low speed air bleeds reduce them a little and pull a little main jet.

Or just wait for @tbird to post, he will get you squared away

 

Thanks man, my carb has both high speed and low speed air bleeds. Should I Try opening up the high speed bleeds a couple thousandths and then opening the PVCR’s some more to get the fuel back under WOT?

 

Normally I would say pull some jetting out of it and put the fuel back with PVCR.
But 66 is already in a good range. And I dont know what CSu has for bleeds. But changing them can mess with the fuel curve as revs thru on the main circuit.

Ive been needing to try this though, as my Tbird does the same. My buddy Eric from HP innov. has suggested to me several times to put transfer slot restrictors in . He does this often on specific setups. Keeps the low speed tslot enrichment but causes it to restrict it at highway cruise speeds. I have yet to try it as my junk is apart currently. Tslot restrictor goes in the port that feeds in main body where the metering block mates. Just tap it for a brass set screw and drill it out to desired size. I think it was like .010 bigger than IFR.

Let us know what ya get

 

thanks for the reply Tbird. That is a good idea about the T-slot restrictor. So say I put in a restrictor, then I would just get my idle fuel back by adjusting mixture screws ?

I have a hard time trying to figure out what circuit my carb is on while driving it at different speeds.

Another dumb question- how do you guys drill out jets and bleeds? I feel like if I put it in a vice hard enough to hold it while I drill it would distort the jet body.. special tools for this?

 

I use a pin vise on carb parts. Just hold in your fingers and spin the bit in the other hand.

 

Cool, thanks man. Ill have to get one on the way.

 

Ive had him build carbs for me that had t-slot restrictors. When I removed them , chasing my own problems, it had no effect on idle.
They dont effect idle and low speed t-slot fueling.

I tapped and drilled a small block for the set screw sizes I use to hold them while I drill them. Tap deep enough to allow it to tighten in the block so they stay put. Same goes with anything on the carb you may tap.
If im doing restrictors that go in the metering block I use my drill press, I just put them in the metering block and hold it by hand.

My experience, idle is idle port, t slot is off idle transition to the point the boosters are at full. So t-slot is all your low speed driving .

Most of the junk Ive played with, always seems 3000 and up is all main jet. Differenty combos might not follow this exact rpm range.

But Eric swears the t-slot will help. My junk rolls 3100 at 70 on the highway and pulls .80-.81 lambda on e85. So its definitely something I have to play with.

 

awesome idea with tapping a block I didn’t even think of that. I have a couple 1” thick blocks of raw aluminum that would probably work perfect for this. As far as the transfer slots effecting idle, I wasn’t sure if it did or not, thought maybe they would have a slight effect since about .025 of it is exposed at idle. I guess there is always one way to find out though. I’m wondering about going down a couple more sizes in main jet and see what that does. I know a 66 jet is already pretty small but maybe if I went down to a 62 or 64 ? I’m pretty sure at 55+ mph with my converter and gear ratio I’m over 3000rpm so it might be 100% on main jet. Do you think 11.5afr at cruise for 20-30 minutes at a time is rich enough to the point where it would wash cylinder walls or foul plugs? Seems to run fine to me but I just feel it would be a little better if it were at least like 13.0-14.0 afr.

 

In my experience, 11.5 afr, gasoline, will dirty plugs up pretty fast. On an old Na setup, sbc, I would locally cruise friday and sat. for two weekends that rich. Go to the track the 3rd weekend and had to change to fresh plugs cuz it would missfire. This was on a ngk 9 plug. I dont feel like it gonna cylinder wash. That takes raw fuel. But the piston top and rings will build up carbon much faster than being lean and clean.

 

I drill out small metering restrictions by chucking the set screw up in a battery drill.....then holding the pin vise stationary

Double check your floats arent too high as well.

Ive usually only done transfer slot restrictors on engine with "big" cams (250* and above at 0.050" on the street). Or on engines that are cant be loaded heavy at low RPM (jet boats and stuff with lose convertors)

Also, make sure your ifr is in the lower spot.....not up high on the metering block....above float level can cause less consistent flow than below float level.

I didnt catch what size your IFR's were.

Additionally, i have changed lightish part throttle stuff greatly just by playing with the secondary idle blade adjustment vs primary idle blade adjustment. Then adjusting the idle mix screws (in gear of course).

Reading and typing on a phone sux so i apologize if ive missed or repeated stuff.

 

Brass set screws (vs steel) are a life saver when making metering restrictions with a pin vice sized bit.

I get mine a McMaster....ive never been able to find them locally