Recently rebuilt my 47 Ford flathead. Did not change a thing except valves, guides ,springs,lapped them ih ,had a good seat. Also installed new pistons and rings.Honed cylinders. Compression now is at 115# the highest and 105 the lowest. Engine will not idle.Put vaccum gauge on and it tells me to chech timming or adjuct carb.Did both and still no change.Only 14 inches of vaccum.If I open the throttle quickly and let it go ,then vaccum will rise to about 21 inches then drop back to 14 inches. I have rechecked timming on crank and dist.Checked vaccum lines,all good.Checked manifold for leaks. Is it possible that I have not run the engine enough to really seat everything?Put about 3 miles on car since rebuild.Everything seems fine except for the vaccum problem that appears to be the reason why it won,t idel. Engine ran better before overhaul. Thanks for your interest.Ron
Your vacuum readings are pretty consistent with what I read on mine and it runs great. Might want to go over on the Fordbarn where a lot of f/h knowledge resides and post your inquiries. If you do, you may want to say what carb, what distributor and what the condition of your coil is.
Ron, give it a little time and break it in some. engine is prolly a little tight still. be sure that the carb and timing is as it was before your overhaul until it breaks in some . run it 500 miles at low load and vary the speed, change oil and then fine tune it you might just find it will be ok
The vacuum reading (when the carb is opened quickly and released) should drop suddenly to around 5psi+/-, then up quickly to 18-20+. What's your ignition setup? Are you using a vac advance? My guess is a carb issue.
I've got very limited experience with flatheads, but here goes... How much idle vacuum did it pull before the overhaul? Did you only lap the valves and seats or did you also grind them prior to lapping them in? This got my attention only because you mentioned installing new guides. Maybe the flatheads are more forgiving, but on newer engines replacing guides usually requires grinding the seats because with the new guide the centerline of the valve stem tends to move slightly. Grinding the seat after the new guide is fitted will put everything back on center. Lapping alone won't remove enough material to do this. Assuming solid lifters, did you use the same valve lash settings as before? Changing valve lash will slightly change the valve timing which will effect manifold vacuum. Decreasing lash will open valves sooner and close them later. Increasing lash will open valves later and close them sooner. Changes to the intake closing in particular will affect manifold vacuum. As already mentioned, the increased drag of a tight, fresh rebuild could pull the vacuum down a bit too. If it's running well otherwise, not smoking or overheating, give it a couple hundred miles to get all the new parts run-in and then maybe look a little closer at your tume-up.
I'm no expert either. But assuming all was installed right and lash was set correctly you should be able to get 18psi at idle. Although from what I gather from the description is that it will not idle or stay running at idle. Low compression readings would show any leak through piston/valves (although 115 to 105 is a bit of variance, but not catastrophic). Also a fluttering vacuum reading would suggest a valve issue.
LOL! I'm figuring he's already half way to getting thngs sorted out just because he's diagnosing it with a vacuum gauge! Just found this page with some nice animations explaining how to interpret vacuum gauge readings... http://www.secondchancegarage.com/public/186.cfm
Same here. And he might already have it fixed and is driving around while everyone makes comments!!! :] I have a couple of printable ones. I can't find the higher-rez one at the moment.
When you diagnois "timing" that means, cam to crank, mechancial, vacuum and initial timing along with dwell (point) gap. Is it running rich? The vacuum gauge readings should indicate an area of concern possible vacuum leak, leaking guides, leaking valves, lapped or ground? Did you check the cam lobes? Check your muffler bearings....
Should be lots more friction with new rings on new cross hatch. Turn it over by hand, see if it feels tighter than before.
This is a stock engine with a stock cam, right? A high performance cam throws "normal" idle vacuum readings out the window.
Hmmmm...I suspect you need to look at the non-idle as a tuning problem, not a problem inside engine. Just a guess from afar. You don't have greatly excess friction, probably, or you'd be asking us why the starter won't turn it... Good compression suggests valves are at least functional... You may have something real simple like plugged idle passages or such. A vac leak is a possibility, but manifold and carb mounting on a flathead are simple and flat, hard to mess up...do be sure the fittings are in and tight. If stock '47 you have a compound fitting below carb on driver side, and SOME have a plug behind carb where atruck engine would have gotten a brake booster line. Again assuming stocker, timing should be close to center of scale on distributor. Have you tried simply pulling out the choke as you let engine speed down towards idle?? Result of that might explain something.
A stock distributor for that engine can only go in one way when it goes onto the cam. If you set the timing slide in the middle of the mark it should run and idle. I think what you have is a carburetor problem. Is the gas old, are the carburetor to manifold bolts tight, was this carburetor messed with while it was off the engine? Check all the small dumb things, you'll be surprised how many of us over look some thing small. Set the idle high let it run for a while then bring the idle down. If it idles then adjust the carburetor.
Not to offend you , but did you check your firing order? Crossed wires will allow the engine to run at higher speeds and run rough at lower speeds. Part of the " timing" they refer to. If you didn't change valve timing and the lash is correct , I would say your problem is not inside the engine. Try a can of carb cleaner with a nozzle to check for vacuum leak as Bruce referred to.
Just wanted to thank you guys for your input. I think that I will put some more miles on it,as suggested,and try and tune it from their. One thing that I forgot to mention was that I put in a set of adjustable lifters and set the gap to stock specs. Might have to change that as suggested also. Thanks again,Ron
On the lifters...there are a number of suppliers, and some are apparently garbage that will not hold adjustment and might actually be severely worn as well after very little mileage... on valve timing, the Ford bolt pattern makes only way to mess up assembling the gears themselves with wrong teeth engaged I would disassemble carb first, clean out every part of the idle passages and the vent holes in nozzle bars.
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