homemade87

I have been back and forth with the people I got the carb from trying to get the carb to be street friendly . I have a ls2/l92 ls motor with a comp cam I had them spec . It is a pretty healthy motor package . My wide open throttle is 12.7 to 13.1 . I have pretty good throttle response when stabbed on . If only going to the track this is great . ( This is a 4 speed car by the way ) Idles at 9.5 vacuum

I am trying to get rid of my part throttle stumble from just off zero throttle tip in and clean up my idle and cruise afr for the street . I have a lean spike when you just touch the throttle . If I adjust it to compensate it will put the cruise and idle way rich . I did open up my 35 iaf to 37 and have been playing with the iab which with no sucsess . I think I have exhausted my options with the builder to get this straight . It time to start changing the block . I am tired of the generic answers I get .

My question is should I even try to move the idle fuel bleeds to the lower position with these blocks . I dont know if I can even adjust the emulsion on these blocks .There is only 2 ports on them . Is it worth a try or should I just get some quick fuel block and not waste the time on them .

I am new to the emulsion game but not new to carbs . Have been doing some research and would like some help on my problem to a possible solution . I am bound to get this fixed what ever it takes .

Heres my build sheet and a picture of the block.

Also I have all three sizes of brass set screws coming from Mcmaster/car . And drilling my existing blocks is not a problem for me if some of you think it is worth a try .

dogsballs

I'm by no means an expert, but that looks a little lean for me at wot, which will be exaggerated on tip in. So issue is not enough fuel, I'd actually recheck fuel pressure ie 6.5 psi, fuel bowl levels and even needle and seat stuff first. Moving the bleeds in block probably won't do alot. Wonder if pv or pvcr too big as well, but thats more higher transition. Could go bigger pump squirters

speedtigger

iTrader: (16)

I would go even bigger on the idle fuel restrictor in the primary metering block. Just remember, when you increase the IFR you usually have to increase the idle air bleed proportionately not to throw off your cruise AFR.

One more thing that just came to mind: how much idle timing do you have? And, are you running a map sensor?

homemade87

Speedtiger , I have read several of you post and have learned a lot from them from your problems from your carbs . This is why I think my motor must not like the emulsion in this carb. Right now I am at 22* and I do run a map that adds 10* so I am at a 32 total at idle .

Not a problem to up the size of the ifr . Before I upped the size of the ifr to 37 from 35 the builder suggested a 86 iab . Still had the problem . Thats when I went with a 37 ifr and still had the problem . I still have the 87 iab with the 37 ifr in when last tested .

Horsepwraddict

iTrader: (12)

I had the exact same problem with my setup. Quickfuel carb had a dead lean spot on just off idle. Not a tip in stumble from accelerator pump, just partially cracked steady throttle. It would rear its ugly head when creeping forward in a parking spot or moving up at a stop light etc. I moved up to .032 idle feed restrictors and it helped a lot. I have a set of .035's I plan to throw in next. I chased it with accelerator pump nozzles and cams
For a long time. It took a very steady foot and
Good eye to see it on my wideband, it was a narrow window. You will have to go up with your idle air bleeds as well but I would absolutely keep going bigger on your ifr's.

Horsepwraddict

iTrader: (12)

Go way smaller in your iab's too, those are huge especially for these motors. I run around 70 depending on my ifr's and combination but that's what it seems to like most of the time. Make a big change and see if it makes a difference. Then work your way up.

speedtigger

iTrader: (16)

Agreed. That is a very large IAB.

homemade87

Thanks for everyone's input . I have the carb off now and I will drill the ifr .002 more and see what happens . That will put them at .039 . The large 86 iab may like the larger ifr . I will do a test today and see what the results are .

My brass set screws are not here yet but I can go back if needed . If I have to drill ifr out and tap would it be beneficial to put the bleeds in the lower location on these blocks . Seems I have read that the fuel is more stable in that location .


Horsepw , sounds like the same thing I am experiencing . With a 4 speed with just light shifting and take off it will hesitate enough to buck . At cruise just in the throttle the afr will jump into the high 15 to 20 range for just a second or two .

I will report back today with the results of the larger ifr .

homemade87

To respond to the IAB size . As you can see in my build sheet it came with a 76 . The builder suggested a 86 to resolve the problem . I did have to turn the idle screws out some . Idle screws are around 1 to 3/4 turns out I will verify before adjusting again and make some notes. The smaller IAB will richen it up some also . I will try some in between and see what happens .

homemade87

Here's and update . Drilled the IFR to .038 from .037 . I wanted to go to .039 but my cheep drill bit set sizes was off ( three of the bits were close to the same size ) so no .039 bit . I did drop the IAB to .079 from the 86 the builder suggested . The carb came with a .076 so it is now .003 larger.

With the .038 IFR and the .079 IAB I could set the idle at 13 afr which is where this engine is happy . Any richer and it blows some smoke . Test drive put my cruise in the mid 13's to 14.1 . But the just off throttle lean is still there but it does not jump into lean 17 range . It jumps in the upper 15 afr now which is better .


Horsepwraddict had suggested to go smaller that the original 76 IAB . I may give it a try since I did see some improvement from the combo above . I will have to get the brass set screws in first .

speedtigger

iTrader: (16)

Your last experiment is telling you the answer. You increased the IFR and it got better. A little more and the problem will be gone.

A lot of people buy those carbs thinking that this type of tuning will not be necessary. For WOT racing, maybe not. But, for street driving, most are better off with a Quick Fuel or an AED.

homemade87

I think you are right . I think I will move to a .040 ifr and drop a few on the IAB and see what the results are . I may try a 72 ,74 IAB,s first to see the results . Then adjust the IFR if needed .

Did drive about 40 miles today(breaking in a new clutch and tranny) and did notice a few times the lean spike jumped into the 18's when luged a bit at take offs.

speedtigger

iTrader: (16)

In my experience what the problem you have will not be solved by making the IAB smaller. You have to increase the IFR. Be careful making the IAB smaller as you increase the IFR. It will make your cruise AFR too rich at higher cruise rpms.

Horsepwraddict

iTrader: (12)

I agree, I cant justify the money on a 'custom' carb when it will need tuning anyway. Im not taking away from the fact that they are awesome carbs, but for most street vehicles you can get the same/better performance tuning a less expensive carb yourself.

Horsepwraddict

iTrader: (12)

yep, I dropped my IAB's all the way down to 60 one day just to see how it helped. It did nothing, IFR's were the only thing that helped.

It will help more, like tigger said you already proved that it helped the problem. mine used to max out my wideband, I got it down to 17:1 and the stumble went away before I went bigger again. I think I ended up settling for around 15:1 before I put it away for the winter. I have a set of .035's to slap in that I expect to drop it right into the 13:1 range. Im beginning to forget a little, its been a long winter.

homemade87

I am begining to believe this and if I had to do it over I would do a quick fuel . At least I would have more adjust ability to change the blocks . But for now I am going to see what I can do with these blocks modifying them with the help of members here . If I cant get what I want I will be ordering quick fuel blocks .

Also I will be taking everyone's advise and just move up on the IFR (.040) only and get the result . I will keep you posted

Horsepwraddict

iTrader: (12)

im curious, I looked at your build sheet and it said your IAB's are 76's. How did you end up with an 87? Sorry to backtrack.

homemade87

For some reason the builder suggested to go over .010 to clear things up. So I went from 76 to 86 . So I gave it a try . I have moved it back down to 79 now with better results . I am going to a .040 IFR and not change the IAB and see the results . If the IFR improves with no other adjustment it is telling me I am moving in the right direction .

homemade87

Here's and update . Drilled the IFR to .040 with no other adjustment . It did run fine but the lean spot is still there . The over all cruise did richen up some but not that far out .

Here's something I had noticed . The t slots on both the front and rear are completely covered . When I adjusted the AFR to about 13 I did notice I was running out of adjustment to idle the rpm down . If I adjusted the AFR above 13.5 the idle would increase and I did run out off adjustment . Both the front and rear was adjusted all the way out at the point . I had checked for vacuum leaks and there is none . All 4 blades are drilled .109 . Just wonder if my cam does not like the extra air to get the T slots and blades to where they need to be . Could this be some of my problem . Should I order some new throttle blades and get it to where there is some t slot exposed . Would like to here some input . I shoot for the idle to be about 1050 .

speedtigger

iTrader: (16)

I got rid of the bleed holes in the throttle blades too. I also ended up closing my rear all the way so that I could open my front some more to expose a little of the transition slot. I do use a PCV though.