Steps for troubleshooting rough running motor?

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Model T Ford Forum: Forum 2005: Steps for troubleshooting rough running motor?
Top of pagePrevious messageNext messageBottom of page Link to this message  By Chris S. Hill on Wednesday, March 19, 2008 - 10:25 pm:

Hello All,

I need to know if anyone can suggest steps in trying to narrow down the cause of a rough running motor. I think the culprit may be in the carb, but I'd like to narrow it down to that.

I recently replaced all the valves since the valve lash on most of the valves was way out of spec (averaged roughly .020, with a few a couple at .025 & over .030)

All eight valves have been replaced with the valve lash now set at roughly .014. From reading things on here some recommended .012, others .015. So I tried for a happy medium of .014.

All the coils are rebuilt ones from "Ron the Coil Man". I'm running a new Anderson timer from Frank's Timer Service. The carb is a new rebuilt carb from Ken Potter.

She ran quite rough the other night after I finally got the head on, so I pulled all the plugs today and they were pretty black. They are new (less than a year old with less than 25 miles on them) Champions (the cheaper of the two available). I was running them at .025 and regapped them to .032. She ran a tad better tonight (it was raining so I only run her up the street a bit and back) but it was still not running right.

I am sorta leaning towards the carb, as this is the second one I've put on her (exchanged the first because of a problem with the Grose Valve sticking closed -ball bearing style) This one has given me some trouble to. I had to adjust the tab on the float a bit to get the carb to fill the bowl the other day.

So my question is then, what tests can I do to narrow this down to the carb, then if need be, how do I go through the carb and adjust it correctly. Also I would like to go back to a needle valve, are the reproduction ones any good?

In hindsight, I should have left the old carb on there as I never had a problem with it besides leaking fuel a bit if I forgot to shut it off at the tank.

Thanks in advance,
Chris S. Hill


Top of pagePrevious messageNext messageBottom of page Link to this message  By Bob Frink on Wednesday, March 19, 2008 - 11:44 pm:

Does it run poorly all through the speed range?
Does adjusting the needle valve make it run any better or worse? Does it run better or worse when you choke it a little while it is running(poorly)? If the ignition is working well, you should be able to make it run better (for a moment) by playing around with the carb.
Are you running on mag or battery?
Bob


Top of pagePrevious messageNext messageBottom of page Link to this message  By Joe Calloway on Thursday, March 20, 2008 - 07:55 am:

First thing that pops into my head is a leak at the intake manifold, possibly between the engine block and the maifold or between the manifold and the carb. If that is the case, no amount of fiddling with the carb will help. I can ususally find that kind of leak by squirting a little engine oil around the manifold gasket (or copper seal rings). The oil will seal the leak momentarily. Hope thi helps.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Chris S. Hill on Thursday, March 20, 2008 - 08:29 am:

Thanks Guys,

I forgot to mention in my original post that I am running on a 12volt battery.

From what I can tell during the brief time I had it running yesterday is that after fiddling with the needle needle valve helped a tad, but I think that was just a fact of getting it back to the mix it was last time it was running.


After that the engine seemed to rev fine, but under load, as in taking off in low the power didn't seem to be there and it felt like it was going to die.

The one thing I did notice (and I cannot remember if this was before or after I fiddled with the needle valve) is that at one point under higher RPM (no load) it would kinda backfire through the carb (as in I could see air and fuel coming shooting out the intake of the carb).

Chris.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Michael F. Thomas on Thursday, March 20, 2008 - 08:30 am:

I would check the contacts in the coil box. Pull the coils out and look for evidence of arcing where the coil contacts meet the spring contacts. Remember, there are two on the side and one on the bottom. If you find some arcing evidence, clean it up, both coil box and spring contact, then bend the springs out a little and maybe wedge the coils in the box with a piece of sand paper.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Royce on Thursday, March 20, 2008 - 08:57 am:

Chris,

Make sure you have plenty of gas, and that the gas is fresh. Ts don't run good with low fuel level in the tank, or with old gas.

If you just replaced the intake glands and rings they need to be retorqued at least once to get a good seal after running.

Maybe it was not warmed up enough to run smooth? All the other suggestions are good. I find my cars like .025" plug gap better.

Royce


Top of pagePrevious messageNext messageBottom of page Link to this message  By Steve Tomaso on Thursday, March 20, 2008 - 09:38 am:

A short story about "old gas" Royce - just helped a friend move two of his T's that got unexpectedly parked (domestic issue) over a year and a half ago. I checked the fuel, oil and water, turned on the switches and viola - we have ignition and lift-off. I was really amazed myself considering they both sat in an un-heated garage, untouched for that period of time. They were both driven over ten miles away and never missed a lick !


Top of pagePrevious messageNext messageBottom of page Link to this message  By Jeff rey L. Vietzke on Thursday, March 20, 2008 - 09:45 am:

Chris: I think you may have answered your question. You stated that in hindsight it ran well with the original carb...just leaked. No use running down the electrical system, etc. when it was all ok BEFORE you replaced the carb. You need to baseline the car. Can you get the original carb, put it back on, and go from there? I think you're at too high a float level or your mixture screw is too rich. A vacuum leak at the intake manifold would cause a white, very clean plug, not four sooty plugs. You could have an ignition problem as well, since you are not running magneto. In my opinion, I would baseline the car, first, and go from there! Good Luck with it.

Jeff


Top of pagePrevious messageNext messageBottom of page Link to this message  By Ricks - Surf City on Thursday, March 20, 2008 - 09:51 am:

I had a strange one while teaching a guy to drive in his '20. It started running awful, but would idle ok. We finally noticed that the choke butterfly was closing when the engine revved up. The choke wire holding screw had come loose.

Sooty sparkplugs means it's running too cold/rich. If you're adjusting the idle with a leaky intake manifold, it will be too rich for power. I use a squirt bottle of water on the intake seals to find leaks while idling. It's safer than WD-40 which some others use.

rdr


Top of pagePrevious messageNext messageBottom of page Link to this message  By Joseph Wayne Rudzik on Thursday, March 20, 2008 - 10:05 am:

Steve,
About old gas, watch out for "new" gas as well. Twice, now, I have had to drain of water from Sam after a new tank of gas. One from Quick Trip, another from a station down the street.
My son-in-law, who is a mechanic, said they have had some people come in with the same problem. A little harder to rectify in a new car with no drain cocks.
I believe that there are stations who run their stock down as low as they can to get the most buck for their pocket and so what with the public and their cars.
That's my editorial for this moment.

Joe R.


Top of pagePrevious messageNext messageBottom of page Link to this message  By john curry on Thursday, March 20, 2008 - 10:16 am:

chris, in general, backfire in the intake, is caused by a lean mixture, which could be caused by a vacuum leak in the intake, or advanced timimg. could also be caused by leaky intake valve(s). john


Top of pagePrevious messageNext messageBottom of page Link to this message  By Chris S. Hill on Thursday, March 20, 2008 - 10:22 am:

Jeff,

My reference to the old carb dates back 7 to 8 years ago. My dad never had a problem with the carb. Last year though when I finally had a bit of extra cash to start working in the old girl to get her going I decided to go ahead and buy the rebuilt carb to eliminate any unknowns with getting her running right.

I figured since I was putting a new intake manifold on (aluminum- higher volume), new exhaust manifold, plugs, coils, timer, I therefore should put a new carb on it. Do wish I had my old one to swap back on, but its gone as it was traded in as my core when I bought the new one.

I'll check the gas, the fuel is about 8 months old and I did notice some water in the bowl of the carb when I first tried to start her after I got the head back on.
Maybe(hopefully) it is the gas.

As far as the float in the carb, is there a guide on how to adjust it so it closes the valve at the right position?


Chris.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Joseph Wayne Rudzik on Thursday, March 20, 2008 - 12:22 pm:

Chris,
Check in the "Model T Fordowner," by Murray Fahnestock and the "The Ford Service Bulletins,"
for float adjustments.
On the NHcarb, the top of the float should be 1/4 inch from the lip that the top of the bowl sets in and measure across the top of the float to get the 1/4 inch gap.
You can carefully bend the part that moves the float needle to obtain this adjustment.
Hope this helps ya.

Joe R.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Anthony J. Marino on Thursday, March 20, 2008 - 01:42 pm:

From "The Ford Service Manual" pages 208 and 209:


Float-1


Float-2


Top of pagePrevious messageNext messageBottom of page Link to this message  By Chris S. Hill on Friday, March 21, 2008 - 03:20 pm:

Well I finally got to work on her some more today. I drained all the old gas out. Pulled the bowl off the carb, and adjusted the float.

I'm still not sure if it is adjusted where it should be as the closest I could get the lip of the float to the bottom of the lip on the carb was still a bit over 1/4"

Did an oil change and ran her a bit. Was still not running that good, but was able to adjust the mix and she is doing better now. I think she was running a bit rich.

Also it seems as if the lack of power under load was that the low speed band wasn't engaging fully. I adjusted it a bit (am always nervous running to tight with the Kevlars) and she is doing better. Was able to get her up to about 32 mph (as indicated Garmin Nuvi 350) so we are getting somewhere.

I'm gonna let it cool down for a bit and pull the plugs, clean them and regap at .025, to see if that makes a difference.

Thanks all for your help.

Chris


Top of pagePrevious messageNext messageBottom of page Link to this message  By Chris S. Hill on Friday, March 21, 2008 - 04:18 pm:

Ok, I regapped at .025. Seems to be running as well I remember it running before. Not a whole lot to compare it to, as I've only driven it about 30 miles before, but it seems to be running as strong or better then.

Chris.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Chris S. Hill on Friday, March 21, 2008 - 10:09 pm:

One last thing, and this relates back to why I ended up taking the head off on the old girl to begin with.

She was running rough, and seemed to have no power. To me it was like it was missing on the number 4 cylinder, and shorting out that plug had no effect on how it idled.

Long story short, all the valve lashes were way off, but the #4 exhaust valve was way to short (over .030-- I don't know how much past that, b/c .030 was the largest feeler gauge I had at the time)

One thing I noticed today after running the car for a while and even letting it idle in the driveway for quite some time is that she didn't seem to get hot at all. When before after only a short time it would run warm (and the manifold would get very hot) Would that #4 exhaust valve not opening like it should be the culprit for her previously running so hot?

Chris.


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