What could cause some cylinders to run rich, and some to run nice and clean? Carbs?(2x2 setup) Distributor?(Mallory dual point) PCV valve??? Any help is appreciated.
Sounds like one of you carbs is running richer than the other. I have a 2x2 on my flatty and it does the same.
Yep, went through this with my buddies engine. Carbs. on the 3X2 set-up supposedly "rebuilt" by an expert. We thought it was everything else but the carbs. Changed dizzy, tore out the PCV because the "expert" said it was no good. Tore the carbs down, the dip **** had all differnet sized jets in the carbs. Fooled with the jets, corrected the rich/lean condition in the motor. I'd start with the jets.
Well, I rebuilt the carbs myself, with 4.5 powervalves in each, and I put in size 50 jets, and set float heights exactly the same. Is 50 too large of a jet size?
Didn't Ford originally use 45's in the stock (1bbl) set up? I just switched over to a Mallory dual point & I'm going thru the same tuning ritual on my dual carb set up.
If the PCV valve is plugged into an intake runner, it will lean out those cylinders. Almost all PCVs are plugged into the base of the carb so that the carb can be tuned to make up for the extra air. A PCV is a controlled vacuum leak. I yoked my PCV intake to both carb bases so that one carb would not provide a leaner mixture than the other.
Any major vacuum leak, (power brake or PCV), should come from a common area, not one runner. To get the motor really right, may take a half dozen changes. My three carbs were off for jet changes a total of six times before I was happy with it. Never give up.
A vac*** leak will cause this condition.................need a couple of questions answered first. Are the back cylinders the ones giving you black (carbon) buildup or wet conditions?....if not which ones. When you rebuilt the carbs how worn were the throttle shafts............if they are not tight you've got a vacuum leak and this will certainly cause issues like you are having. Did you lap the body surfaces during the rebuild. Are you getting any seepage that you can see between the base or top gasket (can you see any discoloration of the new gaskets) because this could be a potential vacuum leak as well. Where did you plug the PCV into? The jet size sounds pretty good and if the power valves are 4.5 you should also be good.
Learned carb dudes, I got my fresh rebuild 8BA flathead running with just the center 97 mounted on a 3X2 manifold. I'm just starting to try to do some tuning. I've noticed that once I get it warmed up and it is idling, if I turn the idle mixture jet on the p***enger side all the way in, it starts missing and dies. If I do the same to the driver's side, it might slow up but it does not die even with the needle turned all the way in. Is this a sign of a vacuum leak somewhere on that side? I hooked my pcv up up to an old South Wind spacer under the carb. It is drilled where it is open evenly to both throats. Seems to be working OK. Thoughts on that idea?
The pcv valve is coming from where the road tube would be, and is connected just underneath of the rear carb, in the fitting in the intake manifold. It is not in any of the runners. Throttle shafts were not worn in the bores. And yes when the motor is not running and I pump the gas I can see some seepage coming from the throttle bases on both carbs, but it does not do it while running. It is the front cylinders that are running rich. Thanks for the help!
So you're putting the vac leak,PCV, at the rear carb which is not normally open? Maybe move that to the front carb base. I'm ***umin you idle and run on the front, progressive linkage to the back? Or even with straight linkage, the leak is at the back and Tommy has the answer for that. Try eliminating the PCV valve and see if that fixes it. Maybe you got a nice tight engine and don't need a PC valve? I don't run one on my 235 with Total Seals. No traditional cloud of smoke Frank
If I understand you right.... If you see gas seeping from the carb bases with engine off.... ...With engine running you will not see gas seepage Because It Is ****ing Air - (Vacuum Leak) which will throw off you air fuel mixture. Also, not sure if anyone has pointed out that you will need to size the PCV valve to the engine cubes. Find one from a similiar cubed engine and instal. But also consider this... If you are running a lumpy or performance cam, You will generally have less engine vacuum to run all things like advance and pcv. jmho but I would suggest downsizing the pcv when running performance cams in order not to rob to much of the limited engine vacuum that your lumpy cam produces. just some thoughts .
Guys- Motor is totally rebuilt with an isky max-1 cam. Running straight linkage also. Motor is nice and tight, so would it be a better idea to just do away with the PCV system?
Racer190, What MoeFuz said is correct. You do have a vacuum leak.............and that needs to be taken care of before you do anything else!!!!!!!!!!!!!! Fix this issue then see where you end up, I'm pretty sure this should take care of the too rich conditiion. If you are still showing rich cylinders, then I would try and size the PCV valve if you already haven't. Also, you said the front cylinders are loading up, which ones........are they on the same side or???????? Also, I ***ume you are running a straight linkage.
The front drivers side cylinder and the p***enger side cylinder second from the front cylinder are the ones loading up. The plugs in these two cylinders are not wet, but more of a fluffy black. Definately not a nice tan color like the rest. I bought a brand new mallory dual point distributor and I am not sure if these are troublesome or what? Engine runs ok, it just is rich on these two cylinders. Yes, this is a straight linkage 2x2 setup.
Are those 2 cylinders running off the same barrel of the front carb? If so sounds like you are getting more fuel through the side of the carb. Jets the same size? That one marked the same and maybe been drilled out?
Coupla things: This is a new setup. PCV is a good thing, but remove it until all is right, then figure out the PCV. Flog the two carbs separately on stock manifold, THEN as duals when you know both work properly. Both of these things save you from figuring out a whole bunch of simultaneous possibilities for diagnosis in intake, AND allow you to be sure ignition is OK. Your power valves will be later than stock running as singles at 4.5, so just avoid 9/10 throttle... South Wind adapter for PCV...Ford did the very same thing on some factory PCV engines during WWII. On a stocker, the other neat way is to use the big plug behind carb meant for power brake booster on trucks, found plugged on many p***enger manifolds. This is also perfect, drilled into both sides.
I agree with Bruce, you don't want to go in many different directions at once to try and solve the over rich condition. I still believe you need to fix the leaks in the carbs first as this is definately any issue that can cause issues down the road and cause problems trying to diagnose what is really going on with the motor. Do you have a vacuum gauge? This is certainly a very handy diagnostic tool and is fairly cheap.
Vacuum is 18 at idle. Throttle shafts are tight in the bore, and mating surfaces are flat. Maybe the new gaskets are junk? I got them from vintage speed. It is only the base gaskets that seep a little(the ones that are between the carb and the top of the intake) I appreciate the help!
What have you done to the motor other than Ignition and dual carbs? Do you have a cam? If you are reading 18hg at idle it sounds like you've got pretty much a stock motor, correct. If you had some type of cam I would expect it to be less than 17hg............. With that said, what happens to the vacuum gauge when you rev the throttle and then let it drop to idle. Is this a new manifold or used manifold. Obvious questions; If you bought the gaskets from CP I would ***ume they would be OK. Have you put a straight edge on the base of the manifold and on the base of the carbs. Are the nuts holding the carb tight. If all of the above questions come back positive and the vacuum gauge reads steady when you rev it up and let it return to idle................it will drop and then return to the idle reading but should do in a steady motion.........not bouncing....................then I would say take off the PCV valve, clean the plugs and go for a drive. Just thinking out loud, what is your fuel pressure at idle and when you rev it up, or do you have a fuel pressure gauge. At an idle are the throttle plates closed (you can look down the venturi with a flash light). Where are the idle screws on both carbs..............1 turn out or more.....or less.....and what happens to the motor when you lean them out. I still think if you are getting fuel leaking from the bases... air is coming with it and that is a leak, at least in my book. Let us know
A couple of things come to mind: First off, not all Stromberg idle-jets are created equal - they range from .022" to .030". Make sure you have a matched set. Then, as far as the bases, a 10-32 bottom tap comes in handy for clearing the mixture screw threads all the way to where they end. Small wire brushes through the angled p***ageways and a welder's tip cleaner can be your friends in making things right too. Hand lapping the throttleplates to the bores and new throttleshaft bushings, parallel reamed to .278" can go a long way as well. Smart move with the Southwind piece for your pcv.
This may be something as simple as having a little to much fuel pressure. 97's don't like much more than 2 or 2 1/2 fuel pressure. The needle and seats are easily over powered by to much of a fuel pump. I'd check your fuel pressure and use a good regulator to limit pressure down to under 2 1/2 lbs otherwise your carbs will run rich as the fuel will be pushed past the seat/needle. Just Curious? What are you using for a Fuel Pressure Regulator (Brand/model#?) and what are you using for an (obviously elctric) Fuel Pump????? jmho
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