OK..I have a friend that bought a 28 P/U roadster with a Flathead V8. It came with a Edmunds 2x2 w/97s,straight linkage, headers and mild cam,(I can't tell)..He brought it over and said it is running poorly, backfiring out the exhaust, smoke out both tail pipes, one more then the other. Smoke doesn't smell like fuel.. I checked the tailpipes and the carbon buildup was thick, like a paint chip, I could chip it out. He said he changed the oil three weeks ago. We checked and it was down two qts. He has put two new sets of plugs and both were really carboned up,(Champion H10 ??). Plugs set a 25.. All cylinders have 110 compression except one at 98..I understand that heavy buildup of carbon on the piston and cylinder head can give you a false compression reading?????? He thought it was the 97s running to rich???? Put two rebuilt 97s with progressive linkage..Got it started, smoked out both pipes(did not smell like fuel), gray in color, as soon as it got a little warm it started to backfire through the exhaust..I put a piece of paper over the tailpipes and it didn't suck it in???? Going to put new Autolite 216 plugs,what gap, 25 or 35..Stock distributor I believe that he has a issue inside the engine and no matter what we do with the carburetion it won't remedy it... Help !!!!!! Duane.
Well, you seem to have discounted the carburetors already, when the symptoms point there. Rather than messing with two carbs that might be messed up, it will take a long time for a novice to figure that out, I suggest you get/borrow, or whatever a single carb intake manifold and run the motor until you have it going good, then move on to the multi carb setup.
Yes on the compression check..110 all cylinders except one at 98..Could it be false due to carbon build up on the piston and cylinder heads.. Thanks Duane
Are the plugs fouled? Are any of them wet when you take them out? I hate champion H10 plugs in flatheads -- once they foul, just throw them out. I can't say that it is a plug issue, but swap those dogs out for some Autolites or better yet NGK. See if that changes things. He could have too tight of valve lash on the exhausts - which could cause a backfire as well. Have you checked the timing?
Shoot 4-5 squirts of oil down each hole & check comp. again ... if drastic increase, it needs rings at the very least. Pull the intake & check for adjustable lifters - if it's got 'em, adjust the valves. The Ford guys will tell you the clearances.
That fact alone should point you in the right direction. It's either leaking or burning. Oil does not evaporate. Thank you. You did a good job of describing the problem. You would be suprised how many here don't. I will assume that you are working on 21 or a 59A. Is that correct? Personally, i don't think its a carb problem. Possibly a timing problem. But I would need more info. Just like that flathead needs rings.
Hey Stromberg, I just nutted out a friends 296 FH stroker with a straight linkage on 3 x 97's; he had the same problems you have and usually, this kinda problem is ignition. A compression /psi difference of 10-15psi on ONE cylinder will not create the problems that you are describing. Does it backfire and fart under load only, or does it do the same thing while revving it in neutral? If it only does it under load then follow along !! Ok so I isolated the carbs - no dice, so carb issues were out. Had to be either fuel or spark. Drained tank and added fresh fuel, adequate fuel pressure ect, still no dice, so had to be ignition. Remembered reading about having these symptoms and that more often than not the condensor is bad. So we swapped out the condensor with a fresh one, made sure all else was right, guess what, runs like a raped ape now and absolutely FRIES the bias Firestones so easily youd think we dropped in a new engine with 50 more ci !!! We then added added the NGK BP4 plugs (As B&S has said, ditch the Champion H10 and run a hotter than normal plug to burn the shit modern oxygenated fuel and to keep 'em clean on the street) and put a decent burn on them for a 30 min drive on the freeway, cut it clean and checked 'em out. Light tan. Nice. Rechecked again after driving around town/idling etc....mid chocolate color. Nice again. When in doubt ALWAYS swap plugs and then the condensor if you're running a points type ignition. Otherwise you could be looking for stuff forver that aint the real problem. Don't ask me how I learned that one !! Coils can also go bad, they are easy to swap out and remove from the list of fthings that an go bad. Its a process of elimination. Also, check all your wiring, connections, plug wires, correct firing order, dist cap, rotor etc....if no good, replace them. Hope this helps, let us know how it turns out !!
Hello..The backfiring is when it is just sitting in neutral in the driveway..Haven't had it on the road with the rebuilt 97s..
BAckfiring whlie not under load should be either timing or incorrectly laced plug wires.,,have you checked these ? Let us know how it goes !! Cheers Rat
My flattie runs 2 97s also & it was running like shit last summer, so we 1st checked to see if it was a carb or elec issue by holding it at about 2000rpm (past the need for the acc pump), you could see the fuel was flowing, & it still missed. That told us it was an elec issue. So before we rebuilt the carbs, we had to find the miss. I swapped the coil, condenser, & resister, but no luck. So I was convinced it was the distributor because I was running the old helmet dizzy (it wasn't) so I put in a new Mallory. New plugs Re-set dwell & timing Reset carb mix screws with a vacuum gauge That got it running w/out the miss, so then we rebuilt the carbs. (note- Mike from Acme Carb is adamant about ALWAYS using a high-quality in-line filter with these old carbs. He says that's the biggest reason they fail.) It can still turn the plugs black kinda quick, which I now attribute to the stock jets. I 'll swap out the stock 45 jets with some 38s or 40s.
Information is good..."stock distributor" is utterly meaningless without a year, remember! And the missing oil...?? Look under valve heads, for one thing.
OK..Update, ran the Flathead again for about 5 min. pulled the plugs and wet with oil, passenger side..OUCH !!!! He wants to get it running and drive it awhile??? I told him all it will do is damage the engine more.. Take it apart and fix it.. Thanks for all the info and direction.. Duane..
Long shot for symptom. Bad intake gasket sucking oil into the intake ports. 110 pounds compression doesn't sound like bad rings. Passenger side only tells you that it may , indeed, be a bad intake gasket on that side. But, who knows. TeaderJack
Popping in exhaust may be symtom of big cam in the flathead. Too much fuel, goes into pipes , and then lights off from exhaust flame. TraderJack
Another look... I've seen an exhaust pop at idle taken care of by eliminating a vacuum leak. Check the intake and carb mount areas.
O/T kinda. You guys know this is interesting reading for the files in my head to refer to in the future, but it seems to me that someone out there aught to rewrite the repair book again for inherent Flathead diagnosis and repair. could be a good book deal there unless I missed that one too.
This one needs more thought, starting with basics of tuneing...the missing oil seems contrary to the goodish compression. Could be bad rings sealing nicely at crank due to inundation from oil going past them... or maybe good rings. I'd eyeball undersides of valves suspiciously...and it does sound like the engine has tuning issues as well. But whereinhell is the oil going with seemingly decent compression?
Now... Runs badly. Lean (???) backfire. OIl vanishes from pan, appeard in tailpipe. Compression decent. Have you looked over your intake gasket lately??
Just my 2 cents: If you're sucking down oil at that rate- it wouldn't be because of a cam or a condensor or anything ignition/fuel/timing related. Also, if your compression readings are accurate, one or more valves/and or valve guides may be shot. I would just bite the bullet and pull the heads. As the gang has said, oil is coming from somewhere- and you'll keep guessing until you see it for yourself. I strongly do not recommend that you try to drive it out- the last thing you want is a trashed motor. Good luck- hope you find the issue.
More on vanishing oil in an engine that may well have good rings: Intake area...loose bolts, bad gasket, cracks or warping in manifold can give direct access from ports to valley. In the valley, do inventory: You MUST have the little snap-in baffles along the middle, the vertical breather pipe in front area of valley, and on pre-49 engines the tube below fuel pump stand. If these are gone, the valley gets a lot of extra oil splash, and the guides are overwhemed by the oil...oil travels up guides into ports. Oil burns, undersides of valve heads will look like slag heaps.
Sucking oil with good compression usually means worn valve guides and/or degraded valve guide seals. Old timers recommend using the rubber seals on the exaust guides as well as the intakes. pigpen
Many of the factory engines did not have the grooves for the seals in the exhausts. They were solid/smooth down the side -- to help the heat trasfer from the guide to the block. The carbon coming out of the exhaust will seal the guide anyway - plus it is under pressure, not vacume.
If the engine has any real running time on it, the outer guide surface is now totally sealed with high-grade baked crud anyhow...and there are no seals at all on guide itself, which is why those baffles in the chamber are critical! Missing windage parts overwhelm the valvetrain with oil... If you sent the block to machinest with those parts in place, they are probably gone.
There's only one way to find out for sure why the motor is using oil. Pull the heads and the intake manifold and take a look. Crud buildup from the cause should be obvious. I don't know why the old timers recommend using seals on the exaust valve guides but I used them there on my engines anyway. I learned one thing during my 20 years in the USN. "Always listen to the old guys!" This motor was using oil and smoking a nice white cloud out of the tailpipes, after a fresh rebuild. The problem turned out to be soft rings that wore down after only a few miles. pigpen
I agree too- I have only used seals on the intakes (you can always use a second set of intake guides on the exhaust, I guess). If you ever tried to tear apart an old flathead, the exhaust guides are always a bitch as they are generally caked with carbon deposits. So it could possibly be leaking from the outside of one of the intake valve guides, but the last motor that I tore apart a couple months ago had two valves that had distorted stems and actually ovalized their respective guides! SO it may be coming from the ID of the valve guide?? Also, score another vote for keeping the windage trays (or valve galley baffles, or whatever you want to call 'em)- Henry put them there for a reason, and I have always used them.
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