Have a 680 quick fuel ss carb. I am wondering beings how these carbs have power valve blow out protection is it possiable for it to still happen? I had a back fire a few days ago while I was messing around and every since then my plugs foul really quick. I looked on summit and they are'nt very exspensive an i will probably change it just in case as it's cheaper then a set of plugs every 10 miles. I've driven the car a bit in the past an had'nt come across fouled plugs till the backfire. I think it ran a little rich before though. And the exhaust smelled alot like gas. But had'nt fouled the plugs till the backfire. I installed smaller jets in the front per quick fuel, for the altitude in Colorado, but with it fouling the plugs so quick It's hard to tell if it helped or not. When I installed the new jets in the front I was reseting the 4 corner screw in the same and I noticed that when I screwed in the drivers side all the way in while the car was running it did'nt stall at all. I did'nt try screwing them all in to see if it would die. But in the past if I screwed in the adjustment screws to far the engine would try and die. This is why I am leaning towards the power valve being out. I am hopeing I am on the right track, third set of plugs.
power valve
- Thread starter slowdown
- Start date
-
I forgot to ad that when I install a new set of plugs it runs strong at first, maybe 10 miles or so then starts to have popping through the exhaust when I step on it. What caused the backfire, I reinstalled the distributor 180 out and tried to start it sount like a gun shot. I messed up I know...
805moparkid
Slant and AFX Guy
well to advanced of timing will cause it or to tight of lash...
as for the PV how old is the carb? i thought all the newer carbs have PV blowout protection
as for the PV how old is the carb? i thought all the newer carbs have PV blowout protection
Carb is pretty new I got it last year I think but it's only got about 100 miles on it. I've been working on my car for awhile. I get it running and then end up doing something else that has it sitting for awhile. The timing is set at 34 degrees. I was reading up on the symptoms of a blown out power valve and it just seemed to fit my problem because the car ran fine before. Maybe a little rich but not fouling plugs. And before if i screwed the 4 corner screws in to far the car would start to idle rough. But like I said, now when I screwed one in the engine did'nt stumble like before. I don't know much about carbs, to speak of so I'm shooting in the dark. I installed new plugs and reset the timing, I idled it up to about 2500 and put the mark on 34 and adjusted the idle. It ran great till the plugs fouled.
Snake
Mopar Nut
yep I would say the power valve is gone,the clue is turning those mixture screws and getting no response bingo.What protects the power valve from a back fire is a small ball it can pass a tad and screw that valve been there.
motorpirate
serial mopar owner
If you pull the metering block and there is fuel behind the power valve.. It's blown...
805moparkid
Slant and AFX Guy
i agree it sounds like PV but i thought all carbs made after like 2000 has PV protection
Thanks guys I will give it a try and hope for the best. 805moparkid luv the hemi scoop I have one on my 68 dart as well.
The total timing monster strikes again!
Still does not make the PV immune. Ever heard of ethanol?
So I installeding the new power valve hoping that was my problem, turns out it may have been part of the problem but it didnt cure the fouling plugs. I have 65 primarys 69secondarys and it still fouled the plugs in no time.. Quick fiel says they use 6.5 fuel pressure an fuel in the middle of the sight glass. Just in case I thought maybe this is to much pressure an maybe to much fuel in the bowls so I turned pressure down to 5.5 and put the fuel just a hair above the sight glass just to see if this may help. I havent driven it since this adjustment. I just put in a fresh set of plugs in an thought I would ask a few more questions before I foul another set. Now when I try to adjust the fuel mixture screw with a vacuum guage the best I get is 14 an it idles nice an thats with the screws 3/4out but I cant drive it with it set there because it dies when I put it in gear an let out the clutch. So I just turned it out 1 1/2 turns an it runs but if I stomp on it stumbles an sputters.
What engine is this carburetor on? What is your initial timing? What is your total timing? Where is your vaccum advance? Is it on ported or full vaccum? And how much timing is your vaccum advance adding?
I have the exact same carburetor on a (300hp) crate 360 magnum. And I have been tuning it for the last couple months and have gotten pretty familiar with how it works and what adjustments do what. Tell me what engine it is, what your initial timing is and your total timing is and where your vaccum advance is and how much timing it's adding. And let me know.
Thanks for sharing. But I've come into another problem. Turns out I have a dead cylinder, number 1. I will have to deal with the carb later. But I think I am on the right track. I've been told to turn it back to initial 18degrees when warm. I live in Colorado so the air is thinner here right now it has 65 primary's and 69 secondary's. I would appreciate any input you have.
I did a compression test and bleed down test and confirmed dead cylinder. I have a camera that fits down the spark plug hole and found the piston is letting oil past the rings. The top of the piston looks good, but I won't know about the rest until I get it out. The carb is on a 318 stroked to a 392 with rhs heads. Vacuum is plugged into the side of the metering block in the middle of the carb. I think the mp distributor ads 15 degrees vacuum advance but I am just quoting what I've read.
Are you sure you have a dead cylinder and it wasn't just the carburetor fouling the plug on that cylinder from being extremely rich? My quick fuel right out of the box foued 3 plugs on my engine, I live in Idaho, 4000 feet above sea level and I had to lean my carburetor down quite a bit.
I'd get a new set of plugs and get some larger idle air bleeds and some smaller idle feed restrictors installed into the carburetor and see if it will run without fouling plugs then. I would also put your vaccum advance on a manifold vaccum source on the carburetor to give you more timing at idle to burn the mixture , that will help keep the plugs a lot cleaner too. That stroker of yours will like a lot of timimg at idle, probly 28-30 degrees.
I'd get a new set of plugs and get some larger idle air bleeds and some smaller idle feed restrictors installed into the carburetor and see if it will run without fouling plugs then. I would also put your vaccum advance on a manifold vaccum source on the carburetor to give you more timing at idle to burn the mixture , that will help keep the plugs a lot cleaner too. That stroker of yours will like a lot of timimg at idle, probly 28-30 degrees.
Unfortunately there is a dead cylinder. At one time it was firing but this engine has been through several build changes with very few miles on it. I know it was firing at one point but here lately with the fouling plugs I've been pulling plugs out left and right and noticed the clean number one plug. I was hoping for the best, but with the camera down the hole I had my son turn the engine over with a large ratchet while I watched the screen and as the piston went up and down with the oil pressure oil would pool up at the bottom of the piston. I don't know if it's from all the gas washing down the cylinders but I am pretty sure oil isn't supposed to be on top of the piston. I am afraid I will have to take it apart again.
-
