After the engine is warmed up and we're driving above 25 MPH, the engine seems to lose power and we hear what sounds like spitting come out of the carburetor, a Kingston NH.
No amount of spark retarding or advancing or mixture adjustment will make this stop or power restored. Full throttle, I believe, would cause the engine to lose power entirely.
This is all while driving straight and level. Going uphill makes it a little worse, and happen at a slower speed.
It's new gas, and the motometer is at summer average.
Any thoughts on what to look for?
Sounds like dirt in the fuel inlet seat.
Harold, my bad. I know it's an NH; Holley?
R.V., I was pretty sure Bailey had cleaned it out yesterday, but we'll do so again.
Next time it happens check & see if carb at manifold intake is wet / cold.
Yes, it is wet and cooler than it should be. When the spitting occurs, we can see vaporized gas (not a huge amount, but any isn't good) coming out of the intake.
What does that mean?
Several things could cause this problem. You said moving the timing rod doesn't change it.
Something is making the fuel burn when the intake valve is open. Since the spark comes at the end of the compression stroke and beginning of the combustion stroke, the intake valves would normally not be open anywhere near when the spark occurs. Two things I would suspect. One would be a sticking or burnt intake valve. Even a bad exhaust valve could cause exhaust from one cylinder to come into the intake manifold of another cylinder when the intake valve is open The other would be spark coming at the wrong time. The timing should be in this order 1243. If any of the wires on the timer are in a different order, it would cause two coils to fire at the wrong time. Another thing which is very common with Model T's is a grounded primary winding in the coil. Usually this happens when one of the wires between the coil box and the timer is grounded. That would make that coil spark continuously. Usual place for this is at the timer when something such as a crankcase bolt or the timing rod comes in contact with the wire, but it could happen at any location between the coil box and the timer.
Try first a compression test to see if compression is even on all cylinders and around 50 lbs. If one is low, you have a problem with that cylinder.
Next test would be lay spark plugs on top of the engine still connected and ignition on batt and check that the spark comes as each piston passes the top of the compression stroke as you crank the engine over. If one or more spark continuously regardless of the position of the piston, you have a grounded coil on that cylinder.
Are you running a hot air pipe ?
No hot air pipe. I think we have one somewhere, but are not currently using it.
Give it a try - only takes a minute to install.
Sounds like the valve clearance is too tight. When the engine warms then one or more of the intake valves doesn't close all the way.
I grind the stems or adjust to .015 intake, .017 exhaust.
Hot air pipe can make a difference in fuel atomization. Did you install a new carburetor gasket set during the carb rebuild? Jim Patrick
I agree with Jim, if I had the hot air pipe on yesterday's trip, it would have been a better drive.
To quote from my other post :
"No problems with a Grosse-Jet valve on a straight-thru NH..... '26 Runabout.
Almost swore to having my first valve problem today.... turned out to be carb & intake icing due to our high humidity & mid 80's temps. Really didn't want to put the hot air pipe back on a hot engine, richened mixture & put up with the chugging till it cleared itself."
If you do check your valves, piston position valve timing is superior procedure with work tappets, valve ends and cam lobes.
Sorry, "worn" tappets.....
Jim, yes, all carburetor gaskets are new.
Royce, are your specs when the engine is warmed up or cold?
I still haven't found the hot air pipe, but will keep looking.
Norman, no grounded coil; all cylinders have 49-51 psi compression.
The carburetor at the manifold intake is cool and wet with water condensate; what could this mean?
If you live in a humid area, the gas as it goes through the carburetor will evaporate into vapor. As this happens it cools the carburetor. This will attract water from the air. If it cools beyond 32 degrees, it will ice up. This could be the problem. The air pipe will fix that, and if it improves the performance, you will have found the problem.
We installed the hot air pipe. The intake manifold, previously cool is now warm after running.
However, the spitting and power loss occurs pretty much as it did before installing the hot air pipe.
I believe that no matter what is causing this problem, it requires the engine to be fully warmed up and running under load to manifest itself.
This engine was rebuilt in '99 and has 1200 miles since then. The car's been idle for a couple of years, maybe three.
After installing the hot air pipe this afternoon, Bailey, after letting the engine warm up a good bit, slowly accelerated 'til 35. He thought we had this problem solved.
He hit a small, small bump and yep, the carburetor spat and he had power loss again.
Sorry to repeat myself, but I truly believe this problem doesn't occur until the engine is thoroughly warm and is under load.
Any thoughts are appreciated.
Most people have no idea how important that hot air pipe is to having a good running engine.
My T came with a NH Carb and without a hot air pipe installed at all. When I got it running good enough to take a tour, it would be running along fine, then backfire and stop. I would let it set awhile and it would start right up again.
Then one time when it stopped, I noticed the carb was all iced up in the low center section. It was about 65 degrees and a foggy morning at that time.
The venturi action that sucks the gas up to mix with the air produces a pressure change which produces an air temperature change.
One damp, foggy morning with a 38 degree temperature, a friend started a newly rebuilt engine outside on a test stand, without the hot air pipe installed. It ran about five minutes and started making a metalic pinging noise, like a valve was too loose or a piston was hitting the head. We soon noticed the carb was all iced up and the ice continued up the intake manifold. He got a hot air heat gun and removed the ice. The noise totally went away, to our surprise.
That hot air pipe also has to fit tight into the carb and it might prevent an engine fire by deflecting the flame up to the bare exhaust manifold, if the engine backfires and there is any gas or oil present on the engine.
OK so you eliminated the hot air pipe as a panacea to fix ignition problems. Perhaps we can get back to the subject at hand.
Hitting a bump and finding that it causes or fixes a problem points squarely at bad electrical connections somewhere.
I would recommend doing a compression check on all cylinders. I would guess you have a valve issue...just my two cents worth.
Bill - Unless I missed it in this thread, I didn't see what ignition system you are running,...??? Original Ford magneto/4 coils, distributor, True Fire,....??? I'm kind of a believer in the old adage,....."most carburetor troubles are ignition". And in thinking about what Royce said, a "bump" that changed things is more likely to be electrical than carburation,...FWIW...harold
Original magneto, four coils, and a clean, good condition timer (although I don't know what brand).
The problem doesn't occur with every bump, nor does it require a bump to manifest itself.
The one common denominator, for certain, is that the engine is thoroughly warmed up to summer average on the motometer.
After the problem begins, the longer we drive the more pronounced it becomes. Once we pull over and wait a minute, we can start up and drive again. The problem is still there, but less severe.
All the electrical connections are clean and secure.
The gas tank is at least half full. Today, Bailey is changing out the Grose Jet.
I agree with the adage that most carburetor troubles are ignition; this one seems difficult to find because the engine has to be warmed up first.
Air temperature drops about 70 degrees Fahrenheit while passing through a carburetor due to the compression and expansion. Warm air has more moisture than cold air contains. So on a 100 degree day the air temperature drops to 30 degrees and we all know what happens to water when it drops to 30 degrees.
Hmmmm,....frustrating, huh? Maybe a sticky valve or two that only occurs when the engine warms up? Just guessing I suppose. I'm not much for top-oil lubricant on a regular basis, but maybe a little shot of Marvel Mystery Oil or some other "top-oil" in the gasoline tank, just in case it might be a sticky valve that only occurs when the engine heats up? Of course, that would likely be an exhaust valve which would not benefit from top-oil like an intake valve would. Hmmmm,...obviously just "thinking out loud" and probably wasting space here so I'll just "shut-up". But hang in there Bud,....you'll find it yet,...and probably by accident. See it you can isolate which cylinder(s) and swap coils around in case it's a coil,....hey,....I said I'd shut up,.......harold
Just a suggestion, I would disconnect the entire gas line, : pipe, sediment bowl, carb, inlet valve & clean. A bit of scale/rust/crap may be in-line acting as a blockage at times..... it's happened.
"After the problem begins, the longer we drive the more pronounced it becomes. Once we pull over and wait a minute, we can start up and drive again. The problem is still there, but less severe"
My pickup with a vaporizer carb did that a few years ago and drove me nuts! It would totally quit. I'd pull over, raise the hood, scratch my head and look all around and under it then get back in and it would start and run a while longer. I moved the gas line further away from the exhaust pipe and the problem went away.
Try a different carb! Maybe there is a crack that when it gets warmed up expands allowing more gas to flow into it.
OK Grose Jet problem again.
Is this the same car that was doing this a few years ago when I looked at it? Remember I moved the gas line away from the exhaust line. What needed to happen is disconnect it and re-route. If it isn't clear of the exhaust pipe by at least a couple of inches it will do what you're discribing.
My e-mail address is firstname.lastname@example.org.
Please drop me a quick note so I can reply and send you a couple of pictures of the fuel line.
I can't seem to get them down to 200K so they'll fit here on the forum.
Thank you, Gary.
Just wondering are you driving on magneto power or battery? the reason i ask is that on my car the generator isn't currently putting out much of anything, and if i drive on battery power for more than a few minutes it will start to spit and lose power. luckily my mag is all rebuilt and runs great while on magneto.
Vent hole in the gas cap?
Is this a new problem or an old problem raising its head again. Blowing gas out the carburetor sound like an ignition or intake valve problem. If your intake valve clearance was too tight, you could have burned the valve in 1200 miles. I think you need to methodically approach the issue and work thru each possibility. It might be a good idea to get a good nights rest and start fresh in the morning.
Bailey rebuilt the L-4 with a new Grose Jet. We attached the hot air pipe. We re-routed the fuel line away from the exhaust pipe (Thank You Mike Black and Gary Tillstrom).
Now that the car is running a whole lot better, I'm not sure which "fix" did it! I honestly think the fuel line's being re-routed away from the exhaust pipe is what did it.
Thank you all for your input.