vacuum leak or dirty carb??

[70challengerdane]

so ive been trying to figure out whats going on and although im taking my carb to work tomorrow to give it a good cleaning regardless, i figured i post this not only to see what you guys think but also for future searchers of google who may expirience this.

the car will idle, and turning the idle screws all the way in doesnt change anything.

when trying to rev, its shaky and wants to hiccup,backfire, and not continue rising in rpm.

ok so when the car is in gear and the brakes are applied it wont stay running.

this sounds like a vacuum leak but when spraying water all around the intake and the bottom of the carb and master cylinder seal, nothing changes.

so i unplugged the booster line and capped it, and the idle rises when disconnected and settles back down when capped.

so i then sprayed a little starter fluid in the carb and the idle lowered and stayed down there, and revving still hiccuped a little but then revved up higher and smoother. but when blipping the throttle quickly, it tries to spit up through the car sometimes.


so at this point im gonna clean the carb for starters. but thought id tell everyone the scoop and get some feedback. this and time has been the biggest things keeping the car off the road at this point.

thanks guys!

 

[moparleo]

What type of carb are you using ? Is it mounted using an adapter ?

 

[70challengerdane]

no adapter, edelbrock performer 750cfm. a few years old. maybe 6? performer rpm intake, xe274h cam. nothing too big.

 

[burdar]

I'm not an expert by any means but if you turned the idle screws in all the way and the idle wasn't affected, that says to me that the engine is getting air from some other soarce. Are the throttle plates open a little at idle? They should be closed all the way. If they are closed AND the idle screws are all the way in, I think you have a vacuum leak. It's possible the booster has an internal leak. When you plugged the booster line, the idle went way up...because you took away the vacuum leak...and the idle screws or throttle blades are opened up to compensate for the vacuum leak.

Maybe disconnect the booster, make sure the throttle blades are closed, double check the timing and adjust the idel mix screws. That will at least take the booster out of the equation.

 

[70challengerdane]

Thanks for the replies guys! Id like to clarify the idle raised when I introduced a vacuum leak by unplugging the booster hose but then it settle down again once it was capped. so capped off and hooked up to the booster are the same idle. and I also sprayed water around the booster and couldn't get a change in rpm that way either though im not totally discounting the booster yet.

also timing is 10tdc, double checked a couple days ago thinking that may be an issue.

throttle plates is something I didn't think about. but now that I am thinking about it, I wonder if I could've put the secondary plates in upside down the last time I had the carb apart? ill check during my break here in a few minutes.

 

[Chryco Psycho]

clean the carb first , generally if the idle screws change nothing you have a problem with the idle circuit or the throttle is open to wide to have any effect so unless you have 3 " of vacuum at idle 7 the idle is turned way up to compensate I see th e carb as the problem also the accelerator pump circuit sound like it may be blocked or the diaphragm is not working , generally a backfire as the throttle is opened is a lean condition .You could have a low float level too , 7 /16 " is recommended , you could raise it to 3/8 "

 

[70challengerdane]

thanks! yeah i spent my lunch tearing it down and cleaning everything out. the floats pins or whatever youd call those were a little sticky but i got them so they dont stick and also it was just in general kinda gummy in there and i suspected the accelerator pump of some foul play as well. so probably tomorrow ill slap it back on the car and see if anything changes.

 

[70challengerdane]

ok so i put the carb back on and adjusted it and got it running fairly good. the best it has since the rebuild. there are some kinks still.

even after warmed up it idles at either 1000 rpm or choppy and trying to die. this happens if i lower the idle screw and also just turning the car on and off is one of those two.

second, it still dies but let me clarify its NOT when using the brake pedal, its just when it goes in gear. idles at 1k and then dies when in gear. occasionally fighting to stay running around 300rpm but never for long.

also hits a wall at 5k rpm in nuetral where it starts backfiring through the exhaust.

i got to thinking about how when i changed the metering springs and rods a few years back, i didnt have any jets to change to. so the jets may not match the rods. could this be my problem?

also all these symptoms are when the car is warmed up, with probably a quarter tank of clean gas in a brand new gas tank.

and still no sign of a vacuum leak spraying carb cleaner this time.

 

[Chryco Psycho]

generally the spings under the metering rods are the problem , you need light enough springs so they will stay down @ idle in gear , also depending how many inches of vacuum you make at idle you may need to drill holes in the throttle plates so the idle speed can be lowered enough to get the idle circuit to work while allowing in enough air to keep it running , I would start with a 1/15" hole in the primary plates if needed , you can always increase the size if this helps , the other trick if you have say less than 5" of vacuum is to restrict the air bleeds for the idle circuit , this is easy on a Holley & nearly impossible on a Eddy

 

[moparleo]

To eliminate the carb completely do you have a friend you can borrow a carb from for testing. Just swap the carb without adjusting anything and see what happens.

 

[70challengerdane]

leo: i was just wondering the same thing haha

cp: id like to hope/assume lighter springs would do the trick as i had this same carb running for a few years in my 383 before i rebuilt it. at the time it had a stock cam that was fully retarded. dont ask i didnt do it. same intake, ignition, and booster so really all thats changed is the cam growing a little.

 

[70challengerdane]

ok at idle its at 6 inches of vacuum. which isnt much. i got a calibration kit for it and im gonna put the orange springs designed for 5 inches in and then if that solves it ill work on adjusting the jets and rods as i go. the next step up is for 7 inches so im assuming 5 inches would be best right?

also vacuum is not totally steady it kinda bumps around when its trying to die (it was really warmed up cause i did it while my wife was drying her hair before we left for dinner haha)

do i need to let it warm all the way up before i do this test?

 

[70challengerdane]

ok this is driving me nuts. im about ready to push the car off a cliff. so right now i have the blue springs for 3in of vacuum and it helps but ist enough, i have rich rods in and likely the factory jets. at 700rpm im getting a fairly smooth correct sounding idle but only 8 inches of vacuum. i fixed my timing because i didnt realize you were suppose to set it with vacuum advance off so when i took vacuum advance off, my timing was retarded. so i set it to 10btdc with the advance off and with it back on im at probably 20btdc or so. im still hitting a wall at 5000rpm, still cannot find a single vacuum leak, and still cant keep it running in gear. i got it to stay running in gear a little earlier but after i move the car when i try to stop it dies as always. this car will never work. the last thing im gonna try is changing the jets, rods, and trying the stiff springs and just seeing what difference it makes. thats the only thing i can think to do. i dont have a good carb to swap with it so im stuck. this car will never drive. sorry to be so negative but ive been out there since 10am trying to dial everything in and trying to figure out reasons it might be doing this but no matter how much the motor has improved in idle and smoothness and all this stuff, it wont work.

 

[70challengerdane]

ok i found a chart and the original rods and put them in and tried all the springs and none of them work

 

[moparleo]

Just a question. What engine are you working with and did it ever run? We need to know exactly what we are working with. Stock engine? Rebuilt ? If so , parts that were changed? What type of ignition, Electronic or standard? I remember last year you were working on a 383 I think and it was nothing but problems. Not that engine I hope?

 

[70challengerdane]

well "same engine" except nothings the same about it anymore.

got another 65 383 steel crank complete engine, stripped it down and put bearings and rings in it
used the 452 heads off the other motor with trickflow valve springs
another new xe274 cam/lifter/tchain kit,
new pushrods
high volume oil pump,
same chrysler electronic ignition, performer rpm intake, and performer 750cfm carb, starter, and water pump fuel pump and hooker headers i drove for two years with in my coronets 383
new boucheline non ac pulleys
new alt
same ps pump
new plugs, wires, cap and rotor and coil,
carb has been gone through several times but has original jets, and now the original rods are in it again and the springs for 8in of vacuum,
new gas tank, old lines, clear gas coming out of the filter though, no crud witnessed.
new oil psi guage, tach, and im getting around 75-90 psi on throttle and about 45- 50psi at idle.
i did some pocket porting on the heads, checked them with a machined straight edge, honed the block, checked the deck with a straight edge, washed it in the parts washer, cleaned it with warm soapy water, rinsed it and dryed it with a coupe cloth rags, didnt bother painting it this time haha primed the oil pump when i put it together and used the cam lube and proper assy lubes.
oh and i should be around the stock 8.5 ish compression iirc cause i didnt use the 516 heads.
i cant think of anything else i didnt mention.

the old motors death was first ruining the cam upon breakin after a 3 month rebuild at school cause i didnt put thread sealer in the cam bolt and it backed out, so i replaced the cam and lifters with a new cam lifter and tchain kit and pushrods. then when i finally had it all back together i put some water in it at like 1130 at night on friday cause schucks was closed started it up and it was running good. turned it off cause i had open headers and felt bad for my neighbors, woke up the next morning to continue and it had somehow snowed and cracked the cylinder walls cause i couldnt wait till the next morning to get antifreeze. totally my fault. so i yanked it again and bought a new complete 65 motor and reused the heads and top end stuff i mentioned from the cracked motor and did the bearings and rings and put it together again and during the rebuild the carb was covered in a doorless shed for several months and had never been cleaned again since the motor froze. so i just cleaned it the other day and thats where this thread started.

this cam does not seem big enough to be this much of a problem heres the specs at the bottom of the page http://www.atlanticspeed.com/productcart/pc/viewPrd.asp?idproduct=8216

carb is the eddy 1411 which is the "2% leaner" of the 2 750s which i assumed was ok because had already driven for 2 years with it in my old 383 before the rebuild and my motor always ran pig rich and 750 should be plenty for a mild street 383 right?

also, i found that mopar muscle magazine did a very similar build and had decent results so i felt i did my homework fairly well as i found this after i put my motor together. although i believe they used a demon carb and eddy heads but still, http://www.moparmusclemagazine.com/...opp_0112_rebuilt_resto_stock_383/viewall.html

so anyway im stumped. ive cooled off and am not so discouraged but im still kinda bummed this kind of stuff has been plauging me for too long. good learning expiriences i guess :/

 

[70challengerdane]

me and the wife are gonna go buy a cheap not so classy cigar and rig up a smoke test

 

[70challengerdane]

well, blew through the booster line, and the manifold advance line and even with a shirt over the carb wadded and pressed tightly, blowing hard, the only smoke was coming up through the primaries and out through little folds in the shirt. so im gonna say its actually not a vacuum leak. not too surprising considering how hard i worked making sure i sealed things well.

 

[moparleo]

OK So lets do this. I know you replaced everything but it doesn't run right so we go back to the beginning. Pull your spark plugs and recheck the gap and check for cracked porcelain. Use the original equipment Champions, about a buck apiece. Closely inspect the wires again,checking for bad connections, if possible use a volt/ohm tester to check for continuity, resistance in the wires. Use dielectric grease on all ignition connections eg, spark plug tops, ignition wire boots on the plugs and cap. This gives you a waterproof connection and makes it easier to remove the wires without damaging them by pulling too hard on the boots. Modern plug wires are not solid wire so they are damaged easily inside the insulation. Recheck the cap and rotor for cracks or any other damage. I know this sounds like a PITA but we need to verify everything is ok so we know where else to look. Do a wet compression test to make sure we have even compression. Set the initial timing with the timing mark on the harmonic balancer. Also your connections to the coil, ballast . This will give us a baseline to work with so you don't go in circles.

 

[70challengerdane]

ok. and for the timing, what should the initial, non vacuum advance timing be set to? ive been researching that all morning and it seems it should be in the 10 to 15btdc range. its currently at 10 with the advance off though i realized when researching that i didnt plug the manifold vacuum line when i set it. not sure why i didnt think about that but i didnt so it should be reset anyhow. also ill have to wait until tomorrow before i can borrow a compression tester from work so for today i may do the other things and see what changes i get first.