Hesitating When Warm

[lizmcl527]

I've finally got my brake problems in my '41 Dodge Kingsway D20 (Canadian Plodge) sorted out -- replacing the hard lines did it -- but now the engine's developing an issue. It runs like a champ for about thirty miles or so, and then starts to randomly hesitate going up hills -- but only those hills I start up below about 30mph or so. If I've got a good momentum, 40 or 45mph or so, I can usually make any hill without much trouble. But if there's a stoplight at the bottom of the hill, watch out.

 

This is very new -- I took a 120 mile drive over the weekend, and only really noticed it after about 45 minutes of driving thru hilly country.

 

My engine is entirely stock -- long-block 218 with a D6A2 B&B carburetor and a new rebuilt fuel pump installed last fall. The engine was rebuilt last year, and now has about 2800 miles on it. Starts fine, idles fine, runs fine until it starts in with the sputtering. I thought the problem might be the accelerator pump link being set for the wrong season -- I moved it from the "winter" to the middle hole after the trouble started -- but that doesn't seem to have made a lot of difference.

 

The fuel filter has about 2800 miles on it, but doesn't look especially gloppy. The fuel tank is new, installed at the same time as the engine rebuild. I'm running 87 octane gas from a pump which doesn't have an ethanol sticker on it.

 

Thoughts or theories?

[Don Coatney]

Is the engine miss firing or just lacking power? What brand of spark plugs are you using?

[greg g]

I would suspect the step up jet circuit. If the plunger that pulls the metering rod out of the jet does not have full motion,your engine will lwan out and suffer the consequences. The acc pump is only good for one shot of fuel as you step onthe gas. The step up circuit works to supplement and prolong an enriched mixture until manifold vacuum is restored.by releasing the gaspedal or reaching cruising speed on level road.

[TodFitch]

Any chance your coil is getting weak when it gets warm? I've seen cars with similar symptoms where after chasing a lot of fuel system things the problem turned out to be the coil.

 

The more pressure in the cylinder, the hotter the spark needs to be to ignite it. And when you are at wide open throttle you are compressing the most air/fuel mixture, so you need the strongest spark then. So sometimes a weak coil only shows up when pulling a grade.

[Lumpy]

Good point. A bad coil will often start acting up once it warms up.

 

Carbs often get flogged half to death when there is an ignition problem! Could the plugs be fouled out a bit from when the engine was breaking in, and burning a bit of oil? Also, re-check, re-gap the points...?

 

k.

[Ulu]

I too have had the coil go weak when it gets hot. Car starts fine, then eventually starts to sputter as it warms up.

 

I'd certainly look for a vacuum leak. Particularly one that opens up under heat, like a cracked carb base.

 

The cold propane test might prove useful.

 

As an aside, it's funny how engineers often look at things from different angles.

 

A Carter "step up" piston does the same thing as a Holley "economizer", but they describe it in reverse. You can think that its purpose is to lean the mix slowly as vacuum is increased, or to richen the mix whenever vacuum is reduced.

 

The classic glass half-empty/full conundrum.

Edited May 13, 2014 by Ulu

[lizmcl527]

Definitely missing and losing power. The first time it happened I thought a wire had fallen out of the distributor cap (happened to me once last summer) but all connections were tight. Plugs are Champions. Definitely not burning oil -- I haven't added any since my last oil change 2000 miles ago.

 

One thing I noticed when I got home from my trip was that the rotor was visibly pitted on one end of the contact -- it was a generic Chinese part installed at the time of the rebuild. I replaced it with a NOS Auto-Lite I had handy and noticed an immediate improvement in overall engine power, but the hesitation when warm wasn't affected. Seemed odd a rotor should wear out so fast.

 

The coil wasn't replaced at the time of the rebuild -- I have no idea how old it is, but I doubt it's original. The car was a daily driver in Nova Scotia for over twenty years, and I imagine it got a replacement coil at least once.

 

All the vacuum hoses were replaced at rebuild, and the guy who did the rebuild (Columbia Classic Cars up here in Maine) said vacuum looked okay at the time, but possibly something might have gone south since then.

 

I was driving home from work this afternoon and it started sputtering up a hill after running for five minutes, so whatever it is seems to be getting worse. Not a bad sputter, but clearly one that shouldn't be there.

Edited May 13, 2014 by lizmcl527

[Don Coatney]

Replace the Champions with something else and there is a great possibility your problem will disappear.

[lizmcl527]

Simple solutions are always my favorites. That's the first thing I'll try.

[Ulu]

Yeah WTH has happened to Champion plugs? They used to be the best ones in the 60's.

[navyboy]

champions suck, they even corrode badly, I would go with autolites. Sounds more like ignition issues, I would check spark plugs, points, timing, and change the fuel filter, also an oil change if you haven't done one since the rebuild as well a valve check.

[JD luxury liner]

new plugs & not champions! 

[JD luxury liner]

dont make all of the changes at once so you will know which one fixed the problem!

[_shel_ny]

Check timing?

[Lumpy]

Okay...I'm putting my money on the coil.

 

k.

[jeffsunzeri]

If you are running one, change the condenser/capacitor first. It is the least expensive of everything you will change, and is the most likely suspect.

[Ulu]

If you are running one, change the condenser/capacitor first. It is the least expensive of everything you will change, and is the most likely suspect.

 

I agree to change it, but if the car starts well, I doubt that the condenser's bad.

 

Every time I had a bad condenser, the car simply would not start.

[Niel Hoback]

I just changed my distributor condenser two days ago.  It ran like the fuel pump could not keep up,  and was also was hard to start on the battery, but would jump to life if I popped the clutch while coasting.  A weak condenser will cause a weak spark.

[JD luxury liner]

ok a little off topic. I purchased a Toyota landcruiser because the owner could not make it run properly. I checked it out at his house and soon found champion plugs installed. I had some old ngk  plugs with me. I installed the ngk plugs and the landcruiser came to life. I told him I wanted the car. he said that it needed to go the muffler/smog  shop. CALIFONIA$$  I picked my landcruiser a week later & thought it was awesome . A couple of weeks went by & I drove home one day. I got to my driveway & the vehicle could not make it up the small hill! I was shocked. The smog shop replaced my ngks with champions again . Replaced plugs NGK proplem solved.

[lizmcl527]

Well, I started the day by swapping out the Champions for Autolite 303s. The Champions were a little bit grey brown, but not choked with soot or anything -- however, they were gapped by the engine rebuilder at .030, while the original service standards call for .025. I gapped the Autolites at the latter size, which translated right off the bat into more power. I took the long way around driving to work this morning, and didn't notice any real problems. Took a couple of moderate hills from a stop without incident, but the real test will come on the next long drive, which, weather permitting, may be next Monday. But so good so far.

[W.F. Brown- III]

Well, I started the day by swapping out the Champions for Autolite 303s. The Champions were a little bit grey brown, but not choked with soot or anything -- however, they were gapped by the engine rebuilder at .030, while the original service standards call for .025. I gapped the Autolites at the latter size, which translated right off the bat into more power. I took the long way around driving to work this morning, and didn't notice any real problems. Took a couple of moderate hills from a stop without incident, but the real test will come on the next long drive, which, weather permitting, may be next Monday. But so good so far.

 

Hope this solves the problem.  Let us know how it works after a long drive.

[Lumpy]

Oh oh...shouldnt' have put my money on the coil. !!! You would think that a spark plug would either work or not. A million years ago, I had a 1952 or '53 AJS 500 single. NGK's would not last more than three days, I don't remember now which ones would. Autolites seem to work for me now.

 

k.

[lizmcl527]

Just back from a sixty mile drive, and it ran like a champ up the hills and down again. I did notice, however, when fooling around with it the other day, that the plug wires were looking ratty, and found that the cap terminal for cylinder 6 was quite visibly blued and corroded, like it had been arcing. These were the wires that came with the car when I got it three years ago, modern carbon-fiber ones, and after reading thru some of the archives here I noted that a lot of folks recommend going with copper wire, so I put on a set of those before heading out. It didn't particularly improve things from what they were after the plug replacement, but I could see that terminal going bad fairly soon, so better now than later.

 

I ran into a rainstorm about a quarter of the way along the trip, and discovered that my windshield seal leaks -- as in, my ankles are soaked. Evidently I forgot to finish tightening the garnish molding when that seal got replaced. Oops. I can assume, though, that my vacuum is just fine since the wipers worked as well as can be expected.