dialing in 7029207 q-jet

[magicrat56]

hi guys, trying to figure-out if nozzle drip/ lack of responce with idle air by-pass is do from mixture is way off. first the engine specs are this:468 chevy781 big valve ovals,238*/248* .540/.540lift 114*,hyd. ft. 9:1 comp.,2" hookers,4-speed,right now 3:73's going to drop back to 3:31's. as of now carb on adaptor sitting on edel. rpm. engine idles at about 13" in neutral@850 rpm.problem #1 is that i have to use manifold vac at idle to bring throttle plates lower on transfer slots to avoid dripping. next is that this is with .135" idle bypass holes and .093 holes in primary butterflies!! you would think that it should be able to idle with stop screw in my pocket. carb mods are basicly the second recipe in the book. idle tube set at .037,idle down channel at .058(shouldhave been .055) lower air bleed at .070,idle air bleed in air horn set at .051,air bleed in main body at .069. 71pri. jet/.041 rod, silver spring,.135 needle/seat. all the passages have been re-checked the blockage,all idle by-pass ports open and clear. HELP!!!!!!!! thanks in advance,going to wash my clothes again!!

[omaha]

 of what you said about the manifold vacuum. I agree that this may indicate a mixture that is off.  Is it possible that you have too much bypass air? (if you cup your hand over the top of the carb while running, {choke it off a bit} do things get worse or better?....how about if you pull off a vacuum line while running?)  The manifold vac source (whuch would add advance at idle) seems to indicate that the mixture is off. But which direction. (im thinking lean) (vacuum leak?) what does the exhaust look/smell like? a 468 is a big motor, you would think that it would need alot of air.( timing?)  I think around 14 to 16 initial would do it. If you  have the initial set around 14 and you got another 10 in the advance can,  24 * advance is alot at idle. your idle setup looks good though as far as the settings with basically the 2nd recipe. whats the cranking psi? (the wide lsa has me wondering) Those big cubes should handle that cam with ease. that is why I think the vac, reading is a bit low. r u sure that you have no vac.leaks. (the adaptor on the intake for instance).  Sorry for the frustration and I dont know if any of this helped but maybe it may have givin U somethings to think about. If it were me, I,d jus keep messin with it 'til it starts to act right. This is one example where an Adjustable air bypass would be great. (I've got the idea in my head, just need to do some experimenting....haha).  Good luck, most of all enjoy!!

[magicrat56]

got up at 4am this morning,headed into garage and pulled carb off.well, what did i find? all 4 wells dripping!!! jb weld never set up. must have not mixed it right. picked up marine tex today resealled it during coffee break will try again tomorrow night. still a bit confussed on idle by-pass but will pass on what i find. thanks

[magicrat56]

back up and running, improvement at idle,but still think that the idle by-pass plus the drilled plates are doing enough, at 900 idle speed i have about 1/3 of the transfer slots exposed. if i lower and idle speed, idle quality goes away plus i like a slightly higher idle speed,keeps the cam wet. Cliff,how far can you bring out the idle by-pass? i'm sure all set-ups are different but it dosn't look like there's much more room. also, how much "travel"will the metering rods have if the apt is adjusted right. i have the plug out of the base plate and have it at 3 turns out. about1/8 of travel. last is there a any problems with running thin base gaskets under carb. right now carb seems to have improved enough were i start running thru the timing curves. have 2 more quads to go thru,17059203,1979 350/4 speed,17058229,1978 400/at gmc. let the re-learning curve begin, happy holidays!!

[Cliff Ruggles]

Keep in mind that with huger amounts of idle bypass air, you have to add additional fuel to compensate.

With 13" of vacuum you should be able to get by easily with .110" to about .120" idle bypass air and solid plates.

My guess is that you need more idle fuel available.

Difficult to advise on APT setting(s) and PP height.  It really depends on what metering rods are used.  The factory "B" series metering rods were used with the early APT systems....Cliff

[magicrat56]

Keep in mind that with huger amounts of idle bypass air, you have to add additional fuel to compensate.

With 13" of vacuum you should be able to get by easily with .110" to about .120" idle bypass air and solid plates.

My guess is that you need more idle fuel available.

Difficult to advise on APT setting(s) and PP height.  It really depends on what metering rods are used.  The factory "B" series metering rods were used with the early APT systems....Cliff

what i ended up with is going to recipe #3 and bumping up my timing 4* @ idle. quite a improvement! still need some fine tuning this spring but is idling as good or better then my much tweaked holleys. great book cliff, plus this forum makes a great place for tuners. merry x-mass

[Cliff Ruggles]

Good news!  Glad to see improvements, have a great holiday!....Cliff