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383 stroker engine

8K views 84 replies 9 participants last post by  painted jester 
#1 ·
Need help on setting carb...falling on its face trying to find the right tune..flat top pistons...lunatic cam 246/515 lift...qf 750 vac sec....200cc aluminum heads PBM...64cc..feul pressure set at 6.5...need help idle all over the place..
 
#5 ·
I have wide band and sometimes when in idle it says 11.3 and then sometimes 14.7...when I get a good idle it will be at 13.2...but when Rev the engine it goes into a high Rev 1500 rpms then turn down idle it falls on its face to 500 rpms then almost stall if you don't stay on the throttle..turn the idle screw back up about a 1000rpms..it's good til you put it in gear drops to 600 to 700...put it back in gear rises to 1500 1600..then I have to turn the idle down again..idk what to do I'm stuck?
 
#20 · (Edited)
Like ericnova72 said your past your enitial IDLE transition slots!

Your initial timing is set too low !! Your going into timing advance and staying there when you throttle it at 1500 rpms and when you turn down the idle your dropping out of advance and the engine is slowing to 500 rpms or stalling ! It could be too light of advance springs and wrong wghts, or advance diaphragm has too light of spring pressure , or the vacuum that controls your vacuum advance (if you have one) is holding it at full advance till you adjust down the idle (are you hooked to ported or manifold vacuum? if you have vacuum advance?), (if you have one ) Disconnect it and plug the vacuum fitting and try to idle and then throttle it and see how it does? !! if it changes and idles back down ? you found your problem!

If not increase your initial timing and as engine speeds up back off your rpm as you go to lower the throttle plates back onto the transition slots till you reach a point that your distributor is not jumping into advance mode and staying there when you let off the throttle and it is retuning to Idle at your initial timing!! Once you get too that point you can adjust from there! If its in your mechanical advance and sticking? tighten up your advance curve with heavier springs or the bushing that came with your MSD distributor!!

Jester (Chris)
 
#7 ·
How much transfer slot is showing at the underside of the front edge of the primary throttle plates at idle?? You'll have to remove the carb to see this.

If too much slot is exposed you will have a terrible time trying to control the idle, exposed amount of slot should look like a square, just .030-.040" of slot exposed. If it is more than that it means the primary throttle plates are open too far in order to get enough airflow into the engine for it to idle.

Fix is to close down the front blades and slightly open the rears to compensate. Rear blades on most Holleys are adjusted from under the passenger side of the secondary throttle shaft, there is a small set screw in the baseplate. Some aftermarket carbs have this adjustment from above, I'm not sure which is on your QuickFuel.

This and the timing issue mentioned are the two things to look at.....common for these problems to show with cams above 235°@.050.
 
#8 ·
. DON'T expect a smooth idle or try to tune for one... it's going to lope hard with that cam...


. Common problem also for Accel and cheap generic electronic module distributors...

. May also have wrong power valve and it's still open at idle... may have a #10.5... 246 cam = ~#4...

. If vacuum secondaries, they may be opening too soon...

. Need about #72 primary jets... #82 secondary jets with that single plane intake ( or #74 if have a secondaries power valve)...
.
 
#15 ·
If the carb has glass sight plugs the fuel level should be to the center of the glass.

If it has solid removable checking plugs fuel level should be just high enough to dribble out of the sight hole when the front end car is rocked .

Didn't the QuickFuel carb come with initial set-up instructions??
 
#13 · (Edited)
The initial timing at idle needs to be on spot in order for everything else for carb tuning to work right. As far as the fuel bowl level goes if its the old holley fuel bowls with the site plug you want to have it set to where the fuel just dribbles out the side plug hole and with you having a quick fuel carb it has site glass windows and that would equate to the fuel level being in the middle of the sight glass. It can be a hair higher or lower but in most parts the middle of the sight glass window works best for me.

If your initial timing is set up good on the idle part of things you can proceed to set and adjust the idle circuit on your carb. This is the order of things on how I tune and is not etched in stone as the correct order but it works for me. After going though the list below I keep notes of everything on where the carb was set at and every thing I adjust or change I write down how the engine ran and go back to starting point setting if needed. What your looking for is the carb to go from one circuit to the next in a smooth transition.

I have four books on holley tuning and is very helpful to understand how each circuit works with the others. Go to amazon and type in Holley tuning and the first three books are very good to give you good knowledge on how to tune each circuit on a holley style carb.

http://www.bob2000.com/carb.htm

1 Set up the distributor for proper timing curve.
2 Set up carb with base line settings.
3 Set initial timing for what the engine will need.
4 Get engine running and up to operating temperature then set the idle rpm and the idle mixture screws and check fuel pressure.
5. Take vehicle out and test drive and see how it performs off idle and how the throttle action is off idle and with along with low speed cruising.
6 Tune the transition circuit along with the pump shot circuit as needed.
7. Test drive and tune the main circuit.
8. After main circuit is tuned then proceed to wide open throttle and secondary tuning.
9. Recheck timing curve and make adjustments if necessary.
10. Make any adjustments needed to the carb.
 
#18 ·
They likely were, but as soon as you turned the idle speed screw you changed that setting, as the throttle plates are opened they expose more of the slot.
They also were not likely set for use on an engine with a large 246°@.050 cam. They figure once you get into cams that big you are going to buy a more race series carb, usually a Double Pumper. What you have will work, you just need to custom tune it rather than it just being right out of the box.

The carb will like 5 psi a lot better, the float won't have to work so hard to keep the fuel level stable. Increasing the pressure doesn't help things, if it runs out of fuel in the carb while under power you need more volume(bigger pump), not more pressure.

And meaning closing throttle plate in the front and compensate meaning opening the sec plate from how much you close the front plate...I'm new to the carb situation so don't think I'm a stupid person...meaning I'm slow on things sorry...
If you look at the picture that was linked, remove the carb from the manifold and view the underside to see the transfer slots.... close down the front blades until the slot shows just a square of opening, then open the rear blades so they show about a square opening....then place carb back on the car and adjust the idle speed screw to your desired idle speed....hopefully you won't need to turn the speed screw more than 1/2 a turn in either direction to achieve the idle speed you want.
 
#19 ·
. That carb. should be able to handle 6.5 psi... the Eddy carb.s usually only go 5 psi...


. Yeah close primaries as opening secondaries... I think your carb. may also be able to do the same by adjusting air bleeds instead of secondaries...


. Base timing around 16-20 BTDC (before vacuum hooked back up) should work for idling...


. Shoot us any other questions that pop up... we prefer ask us before throwing $$$$$ at a problem...
.
 
#21 ·
So close the front blades to square opening gs and open the rear blades to a square opening? Where should the idle screw be when I'm doing this? All the way unscrewed or half way or all the way screwed in?..my jet in the front are 72 and rears are 82 with one power valve in front that is 4.5...don't really know about air bleeds either or where they are located? Thx for all this help to everyone that has posted to me...awesome people you are..
 
#23 · (Edited)
Its your build every build is different and timeing can very a lot from one to another! No one on here can tell you exactly what your timing should be ! We can only suggest from experience! A good Idle and timing will have the greatest manifold vacuum readings on a Vacuum gauge at Idle with valves properly lashed ,so you can set your timeing and idle with a vacuum gauge and then check and remember it with a light! And then tune to what satisfies you! (Not saying for you to do that if you have never done it before!)

Your vacuum advance comes into play when driving off idle into the lower cruise area and advances the curve before your Centrifugal comes into play It is designed to aid the transition to Centrifugal advance in lower acceleration cruising !

What is your initial timing now ?

You could START FROM THE BEGINNING Try setting your initial timeing without the car running !! Close the primarys and the secondarys completly it will not start, crank it and set with a timeing light at about 8 to10 degrees before TDC with Vacuum advance disconnected and plugged !! once you have set the timeing, then open the primarys a little by turning the Idle screw and start it then set your Idle and mixture metering screws! Now you can tune from there by increasing your timeing or your idle as you wish!! Or cracking the secondarys if needed!

I say this because you sound confused at some of the suggestions:confused: If you do too many changes at once you will have a real can of worms trying to get back to a good starting point !!! Just do one change at a time if it does not work put it back were it was and then do another test !

Right now you need to know your initial timing before the engine starts to run at idle!!! and then tell us if it changes when started and idling and what it changes to, then plug in the vacuum advance to ported vacuum and see if it changes at Idle ! and tell us your findings and once these basics are done we can go from there and lead you the rest of the way!!!

Its not hard but your choice if you choose too do it.

Just a suggestion!:thumbup: Others on here may be against this :nono:/ I don't know LOL?:mwink:

Jester (Chris)
 
#25 ·
8 to 10 is a good starting point you can change it later to what it needs!! After you get the Idle circuit straightened out ! My cam in a 302 is 612 lift and 312 duration and it can idle good at 10 degrees to 20 degrees and advances to 46 Degrees at 8500 rpm up !! So duration has nothing to do with initial settings ! you are just looking for a good starting point once you get that you can move on and dial it in !!!

Jester (Chris)
 
#26 ·
Ok I set the front and rear throttle plate with trasition slot like you said..I also turn the motor over to set timing to 10 degree advanced...I also took off distributor cap off and took rotor off to see what springs I had put on and they are the 2 blue light springs...also the stop bushing is also the blue one...advance timing is all in at 2600..from what distributor box says on the side from the graph pics...but I will unplug the vac adv for know... Can I compensate turning the timing up instead of turning the idle screw up to get idle that I want trying to keep the trasition slot at a square...? Thx
 
#30 · (Edited)
Right now what are you idling at 10 degree initial timeing ? if its around 750 to 1000 with the egine loaded thats good for now, and you should be able to increase it with the idle screw no problem! your initial timing can be increased to increase idle speed ! but it takes actual driving and testing or a dyno to dial in the timeing you need! Take it out and nail it in a safe area LOL and increase your initial timing a few degrees at a time marking each time on the distributor base corresponding with a single reference line on the intake next to the dist. base! test it again and add another mark etc, etc, (as you advance the timeing you will have to lower your idle down a little) you keep doing that till your power feels like its dropping off or you hear spark knock or get starter kick back (engine cranks over hard or won't crank) and then move the distributor back to the mark it ran best at and idles good at and you will be very close to your initial timeing for your build! You can use a timing light instead of a mark and write each timing setting down and return to the setting that feels best after your test! your curve can be set by High rpm full throttle acceleration runs by changing springs and bushings till you feel in the seat of your pants what was the best run and setting without early advance knock!! I do these tests with 110 octane at first to avoid knock and when you get close to what you want, move to lower octane pump gas, and tune your timeing curve for that!!

The drag strip is the best place to do these tests and settings !! Even a dyno will not get you as good a result as the strip! do not forget to read your plugs and set jetting as you do these tests (Better to run rich then lean till you get her dialed in right.

Jester (Chris)

I just read ericnova72s post #29 and he is dead on !!:thumbup:
 
#28 ·
. It might run at 6.5 psi, but 'dead head' at 9 psi... so may have to set it lower to keep dead head pressure from over whelming the float valve at idle and shutoff... sounds like you have a pressure regulator... which possibly introduces other new problems, as well... like is it big enough to flow enough fuel for this power of engine?


. Don't want ignition to advance so quickly that it causes pinging... maybe all in by 2000... maybe stretch it out till 3500... maybe somewhere's in between... also need to see how many degrees of advance it can add...
.
 
#29 ·
Idle mixture screws basic starting setting is 1-1/2 turns out from lightly seated closed, you'll need to adjust them as you tune but that is the basic beginning point.

You will very likely need the BLACK 18° stop bushing installed in the distributor.

You can mix and match spring colors if necessary to get proper control of the weights, both springs don't have to be the same color/rate. I'd try 1 blue and 1 silver(I think silver is the next heaviest IIRC?) whatever the next heavier than blue is.

Yes, you can use timing to control idle speed somewhat, try to find a balance between timing setting and only moving idle speed screw + or - 1/2 turn from square slot setting to achieve a good idle. I would also figure that either 14-16-18° initial will be the sweet spot, but you'll have to let the engine "tell" you what it likes best...

Cam duration will likely not let you idle below 1000-1100 rpm in Park/Neutral.

Hang in there, we'll get you sorted out....
 
#31 ·
You guys are the best pit crew out there...if wasn't for you guys giving me help I don't know what helI i would have done...you guys are the best...can't wait to fire this thing up again...I ordered new feul pressure gauge to dial in pressure..so crossing my toes and fingers...lol..I will change advance bushing stop to black one and change springs like you said...I will give feed back when I've done all the above...thx again for all your guys help...
 
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