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Discussion Starter · #1 · (Edited)
guys looking for some tunning help/advice. ive become pretty good at tuning my 2276 drawthru but I have the aid of an inboard afr gauge and adjustable jets so I think I am lucky.

the dub in question is a friend of mine who has a new build we just completed not to long ago and im getting stifled while trying to tune this thing to run correctly. aside from him not having a working tach lol, I don't have the benefit of an afr gauge also in his car.

the specs of the motor are as follow:
2498cc
94 pistons
90 crank
5.7 rods
1.4 rockers
fk 8 cam
holley 850
gtr 35 turbo
scat super d head 44x37
7.5 to 1 compression
timing locked at 24*
msd ignition setup

my first question is jetting. what is a reasonable starting place for jetting on primary and secondaries (mechanical)? I don't remember where we left off with jetting at the moment but seems I have made it worse lol. valves are adjusted good (loose zero), timing triple checked, pulled plugs and don't seem to bad etc..

second question is the idle mixture screws. someone told me to only use the two on the primary side for tuning and to just bottom out the two on the secondaries as "u don't need them opened". that is how I set up my carb and is tuned pretty good but my carb is smaller (670) and my intake and runner lenth is significantly smaller also. not sure if that matters tho. is this true or do I just follow the same procedure on all 4 mixture screws?

everything else has been triple checked, jus cant seem to get this carb to cooperate with me, and don't really have any reference point to "start over" on the carb tuning.

all advice on these questions would be greatly appreciated, and if any other info needed ill try my best to reply. thanks in advance!!!
 

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With that motor he should put a gauge in it that would help so much, we just had a carb on my car that ran good down in first and second then just leaned out from there and we torched stuff, with the new afr gauge I can see each idle air screw makes a difference don't know where I would start but if it stumbles you need to lean it out on the primary where it runs clean then go from there
 

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Discussion Starter · #3 ·
I told him the cost for an afr guage is worth it..

ive leaned it out a lot on the primary mixture screws to where it almost shuts off, then inch it up a c hair of a turn, and adjust rpm as needed but even that im guessing as this dudes tach took a dump. also leaned out the jetting on primary (cant remember where im at lol) but still jus falling as sputtering.

idk I guess its a longshot as every motor is diff but jus lookin for a ball park figure on what size jetting I should start with on primaries and secondaries. and if I in fact am supposed to adjust all four mixture screws, or leave secondary ones bottom out.

thanks again
 

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Every motor is a little different, I would think 78 on the main and 80 sum thing on the secondary we are using C-16 fuel is it vacume secondary and does it have a power valve
 

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Discussion Starter · #6 ·
yes has a power valve and yes mechanical secondaries
 

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With that motor he should put a gauge in it that would help so much, we just had a carb on my car that ran good down in first and second then just leaned out from there and we torched stuff, with the new afr gauge I can see each idle air screw makes a difference don't know where I would start but if it stumbles you need to lean it out on the primary where it runs clean then go from there
Ask him to park it until he can afford some dyno time -- you can burn a lot of parts and bend a ton of pieces trying to get it close

Been there and done that -- one little lean pop and I got 3 burnt pistons and four of these

 

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Discussion Starter · #8 ·
ouch...

yeah he really wants to drive it to the vw classic this wknd. keep telling him close enuff isn't close enuff...
 
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