Nebu

hey,

i've got a drop base aircleaner on my 650DP and i'm wondering if removing the chokehorn and smoothen the edges will improve the power a bit? do i have to bring the jet sizes up? if yes, how much? (roughly)

i need some work until the season starts

thanks,
nebu

xpndbl3

iTrader: (5)

yup it will improve airflow, or for $100 you can buy a proform mainbody instead. i went the cheap route and just cut off the choke horn. don't cut off the center tube though, you have to cut around that, then i used a 40 grit sand roll to smooth it all out.

Nebu

did you get any noticeable difference in hp? what did you do to the main jets?

xpndbl3

iTrader: (5)

no idea what difference it made since i haven't had it at the track yet, and as for the jets--drive ten miles and pull a plug and jet accordingly every motor would be different.

Nebu

JFWI: i milled the chokehorn a few weeks ago. smoothed and polished it out with a dremel. right now, i'm running way to lean at cruise with 1/4 throttle until ~3k rpm. above that, it's ok. i would say theres a slight improvement. (maybe because i got only ~1" clearance above the chokehorn with a dropebase air cleaner). i think it will be way better if i go a bit up with the primary jets and acc. pump squirters. if anyone wants pictures, i can make some.

i'll keep you updated about the performance.

nebu

Nebu

changed the pri. jets to 71 from 67, sec. jets 75, shooters 35 pri., 31 sec. and advance to full manifold vacuum. helped a bit. but the problem is, i'm having a rich idle all the time. O2 is around 400mv when cold and goes up to ~900mv when warm. doesn't matter how i set the idle screws (but it dies if all the way in, so i assume no vacuum leak)

when cruising i get aroung 800mv. if i slightly open the throttle it goes lean (~300mv) and goes back up when the power valve opens. do you think a bigger valve would solve this problem? got an 8,5" now.

nebu.

stroker_SS

The rich idle maybe caused by a restrictive air-bleed, and the only may to fix that would be drilling a very slightly larger hole in the air-bleed.

How can you tell when the power valves open? Sounds to me that the off-idle leaness maybe cause again by too small of jetting, i would try a step larger and see if it makes a difference.

Edit: If the idle was always too rich, i would blame it on restrictive airbleeds 100%

Nebu

yes, the idle was rich since i got the (used) carb.
you think i have to drill out the outer two holes? going small and then bigger until the idle is good? never done this before.



nebu

stroker_SS

It looks as if you have replaceable idle air bleeds, so if it was a used carb the PO may have replaced them with smaller ones, IIRC the outers are high speed air bleeds, and the inners are idle(richer due to smaller diameter). I would most definitely not drill them at this point( wasn't thinking correctly).

First, spray some carb cleaner into the idle airbleeds(since your at it, go ahed and soak all of the holes you can)to verify thier isn't any blockage then start it up, try tuning the rich idle out. IF you still can't tune out the richness, and have also verified that the needle and seat are still good, and the float is set correctly(you did do that when you got the carb...right?) Your next and last resort is to do a search on summit or jegs for holley airbleeds and order a kit and tool to replace them, going from the next size up that you have.

It sounds most likely that the needle isn't seating all the way, so check for damage or blockage on that.

Your off idle leaness may be cured buy simply messing with the pump cam, but before that verify the tension on the pump lever is fully seated, but not to preload the pump to much(very small amount of preload is needed). And then after that make sure their is no bind in the pump lever at WOT, so have someone sit in the car and give it WOT(not running of course) and check for bind even though their shouldn't be any.

MOST importantly make sure all of the fuel circutry is clean, or else no matter how much tuning it will highly unlikely ever take a good tune!

Have any more questions or see something i missed let me know.

Nebu

small update: when i open up the secondary butterflies i can get the car to idle around 400-500mv which seems good to me. rpm goes up when i touch the acc. pump. problem is, the car now has an idle about 1000-1200 which is a bit high. so either lean/high idle or rich/normal idle.

nebu.

ps. the carb on the picture isn't mine. just for reference.

stroker_SS

So you've made sure the carb is spick and span?

If not that explains it, however the secondaries being open should be completely unnecessary unless you have a WICKED cam. And in that case drilling a couple of holes in the primary butterflies would suit.

You wouldn't happen to know if the inner airbleeds are replacable do you, i'm just taking a shot in the dark without knowing your carb model and it's features.

Nebu

carb is a 650 holley DP 4777-2. after i milled the chokehorn, i cleaned the whole carb and blew compressed air through every hole i could find

do the look replaceable to you? i think so




nebu.

stroker_SS

Yep those appear to be the replacable IABS.

Definitely before you spend money on the IABs make sure the needle is fully seating.

Will the car stall if you turn them all the way in?

Nebu

yep, the car will die when the needles are all the way in. btw both are only 1-1/8 turn out atm.

btw what is it about these parts? #74-76 i've never seen this check needle during the rebuild. or is it from the 4160?

nebu.