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251 flathead timing degree

IMP

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My J5 runs good.... but not perfect. Just after I accelerate, after say climbing a steep bank I can hear it miss a few times. And it's running a bit rich. Plugs are running a bit sooty looking and I see black smoke occasionally when I'm working the machine. It starts really good if the engine is cold but on a warm engine I have to crank the engine 5-6 revolutions before it starts. And it seems to burn 10 - 15% more gas than my buddys J5 all things running equal. The engine has good compression, all new ignition parts and rebuilt B&B carburetor and remanufactured distributor.
I set the timing as per the manual at 5 degree BTC. I talked to a guy at Vintage power wagon who said that 5 degrees BTC is meant for fixed engines like generators or a saw mill but on something you drive they set them up at about 1 degree advanced. He also said gas was much better years ago which effects the timing. My question is where do you 251 Chrysler flat head motor guys set your timing. I haven't messed with anything yet I just noticed these issues when I took the J5 hunting this fall. Just Looking for ideas before I try anything
 

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J5 Bombardier

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That's a pretty nice paint job, good to here its installed and mobile. As for timing I usually run them at around 5 degrees, trying to avoid pinging under load . You might have a carb float issue with that missing on steep grades problem. I run three flatheads , one with electronic ignition and the other two with points. I would switch them to electronic also but I see powerplant swaps in the future to diesel or a more modern gasser, as rebuilding can get pretty pricey on these old workhorses as you probably know . It seems whether playing or working, my J5's can easily use at least 5 gallons of gas each a full day.
J5 Bombardier:hammer:
 

rcc

Member
Nice looking engine.
If the engine has been rebuilt with new rings and bearing, valve job etc it will be "tight" and you will use more fuel until it is broke-in. No diff than any new vehicle. Depending on how much you use it, it will slowly break in and loosen up giving better fuel usage.
You should also check the heat riser valve to be sure it moves freely and the spring is on it. If this is stuck in a more closed position you will have more restriction in the exhaust. Something to keep in mind.
I would see how it is after 50 or so hours.
I have just rebuilt one of my 251's, and looking forward to getting in installed and started up. If didn't cost to much and I did most of the work myself except for the valve job.
Connected it to a TH350 transmission and installing a driveshaft disc brake. Should be interesting to see how it goes.. and stops!
 

IMP

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Ok Thank You for the responces. I have about 150 hours on the engine, so it should be broke in now. I'm not that concerned about the fuel evonomy, my point was that I'm using more gas than my friends J5 doing the same work. So that helps confirm that my engine is running rich. But it does not diesel when the engine is shut down. When I turn the key off the engine just stops everytime. The carburator is jetted so there is no adjustment that I know of short of changing the jet smaller. I'll try advancing the timing a bit and see how it acts. It's hard to work this machine to test it around the neighborhood. Nothing like heading into moose camp crashing brush and swamp for 25 miles to put the J5 to the test
 

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mla2ofus

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Excess fuel usage and black smoke could be from intake/ air filter restriction or float level a little too high.
Mike
 

IMP

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I checked the float level and it was right on spec. But I decreased the float travel anyway to see the effect and it was not good. So I changed it back to within spec again. The air intake is original oil bath with no modifications? Seems good. Also The heat riser on the exhaust manifold has been completely removed. I wonder if I could get a different jet for that old B & B carburator?
 

IMP

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Wow, This is a tough crowd... I thought I would at least get a comment on the photo of the northern lights over moose camp? You don't have to be a J5 owner or a hunter to appreciate the beauty of a moose rack and J5 silhouetted by that kind of Alaska night sky.
 

rcc

Member
Sorry about that, it is beautiful... and I really enjoyed the video adventure on youtube that you sent. I still need to find and post up some video of my J5's. Just no time to get it together. Tooooo focused on the situations presented on the forums.
Regarding the oil bath air filter, I would toss it and put in a good air cleaner/filter. Those old oil baths filters are not very good and with the verticals you do moose hunting you do not need the oil going down the carb....
 

IMP

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Yea your right I should adapt a paper filter to it. Do you have the parts and modification figured out now that it's on my list of things to do?
 

rcc

Member
It will make the engine breath much easier and actually clean the air going into the engine. I welded up a small diameter custom air filter on all 3 J5's I will send you some pics when I go back to the cottage next week. These 251's only run 3600 rpm max... so the CFM is so low so a small filter works great. If you want the CFM calculation I can dig it up or just go online and type in....
 

IMP

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Mr Liberty thanks for those specs! If I read it right it says "timing mark at 0" in the tune up section. If that's telling me to set the time to the 0 degree mark that's what the Vintage Power Wagon guy said to do. I'm going to try that. Maybe J5 Bombardier has all 3 of his J5's timed 5 degrees wrong?
 

IMP

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Mla2ofus. Yea I checked the choke butterfly position for full open, its adjusted good. Thanks for the input. That was the first place I looked. Would firing #1 spark plug 5 degrees early cause it to run rich?
 

mla2ofus

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Nope, usually intake air supply, float level, idle mixture and main jet setting make it run rich. Does this carb happen to have an adjustable main jet?
Mike
 

MNoutdoors RIP

Gone But Not Forgotten
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Too much advance is hard on valves. Not enough makles her a gutless gas guzzler. Hope this helps.

Great picture also
 

rcc

Member
Here is the pics of the breather assembly in put on two of the J5's, the other one is a smaller diameter. I made the base so it is offset so it does not hit on the engine side cover. One has the crankcase vent valve on the manifold the other I put inside of the breather element.
 

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rcc

Member
Regarding timing, I use the indicator to put the engine together, I don't use a timing light on these, just adjust at correct idle so the engine is running smoothest "by ear".

Once I have it set, and at operating temperature, (I use a 180 degree thermostat), I do check for vacuum leaks. Then a few quick revs and we are good for the year... usually.
 

IMP

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RCC Thank You for taking the time to show me your air filter set up. It looks great. I guess I could have figured that out too but the photo will make it easier and faster to come up with the parts n pieces.
Regarding timing, what kind of "indicator" do you use? It must be some kind of static test light your using or what? If so when you rotate the distributor, what degree retarded or advanced to you time the #1 spark plug too? Or do you set to the zero mark?
 

IMP

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I'm also curious how you check the for vacuum leaks. Is it simple? I haven't done that check yet. I put 160 degree T-stat in because that what was originally installed. But I do notice this engine always runs cool 150-160 according to my temp gauge. Cooler seems like it's better that hotter for a hard working engine??
 

rcc

Member
These engines are very simple, vac leaks can be through several areas around the carb for wear at the throttle plate and the base gasket, and crankcase vent. I use light oil sewing machine type. If you have a rebuilt carb and new engine I do not think you need concerned.
I use a 180 therm to keep the engine warm operating temp, no engine works good cold or cool and they will use more fuel.
With the timing I do not use the timing light etc, seems unnecessary for these engines, actually on all three engines I have there is no mark on the crankcase pulley, so I set up the machine using TDC port on #6 cylinder. Then adjust by the sound and feel of the engine by "ear". Just simple and they work great... fuel consumption... ? I look for power and throttle response. It is not a sports car engine... Thank Chrysler!
 

IMP

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My engine didn't have a timing reference mark either. I made my own mark by doing allot of careful measurements, I would probably be better off just timing by ear. I will give that a try and see what happens. Thanks rcc for all the comments and photos
 

MNoutdoors RIP

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I time by ear also,one thing to remember do not over rev these engines
It will pop the top of the valves right off
 

IMP

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Sometime I see my tach up to 2500 but I try to keep it 1600 to 2200. How does that sound to you Brad? So when you time by ear you rotate the distributor + or - #1 TDC and leave it where it sounds smoothest?
 

MNoutdoors RIP

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Sometime I see my tach up to 2500 but I try to keep it 1600 to 2200. How does that sound to you Brad? So when you time by ear you rotate the distributor + or - #1 TDC and leave it where it sounds smoothest?

4000 rpms is a definate no no. Anything over 3100-3200 and your pushing your luck


Like, RCC, no timing light, engine warmed up. Choke off. Rotate distributor untill
Best throttle response. Then try under load then fine tune. Just make sure plugs are good, wires good,points if used are good, and I find a lot of weak coils on these old ones. Last but not least have fun.
 

MNoutdoors RIP

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On a experience this fall I keep a old 1993 toyota pickup 4 wheel drive at hunting camp. And this fall it just seemed like it was slowly loosing power little by little and even some since last year and the year before. So I decided to try to figure it out. Compression was good, so new plugs, plug wires,cap and rotor where all put on.air cleaner also Very minimal change if any, new air flow meter for the EFI.
No change. Checked the timing it was off some. Really no change. So I thought
Fuel pressure regulator. So pinched off the vaccum line to it no change. Only when I did a fuel pressure test I noticed something just did not seem quite right
Some fluctuation in pressure but it was not the fuel pressure regulator. So off came the fuel tank. Took the pump out tested it it pumped good volume. But then. I looked close at the short piece of hose that came from the pump to the steel line above it. And I saw a pin hole, and then another and another. The fuel
Line above the pump was pushing gas back into the tank, and it was worse if the fuel level was below the pin holes. Installed a new piece of high pressure fuel injector hose, and that truck has never had that much power in all the years I've owned it. Not a timing related item but. Sometimes it takes a real deep investagation to find the real problem.
 

northhar

New member
Did you solve your over rich fuel problem, if not did you check fuel pump pressure.
I had this problem myself on my J5 with a 251 engine. Fuel pump pressure was too high causing rich condition. Should be between 2 and 5 lbs for a B&B carb.
 

1986mcd

New member
Sooty plugs..too rich, or spark issues. We found the biggest contributor to spark issues to be too much resistance. Engines had a 2 to 4 ohm coil with a 1 to 2 ohm series resistor on the primary, resistor wires, and resistor plugs. This produced at best, a weak copper colored spark. Check your spark. Pull the coil wire off the cap, hold the end 3/4" off the block, and crank a few times. Should see a bright blue spark. If not short across the points and check again. It the spark is better, file or stone the points. Points right out of the box must MUST be stoned to get the glaze off the tungsten. No series resistor on the coil if it's Between 2 to 4 ohms (between + and - terminals) . Use solid copper core plug wires if your using resistor plugs like auto lite 386. Auto lite 3116 plugs are non resistor, and can use resistor wires.
 
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IMP

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I thought I would update an old thread I started about a running too rich problem I was having with my J5. To make a long story short... It was a timing issue. I do not have a timing mark or timing port so I timed it using a vacuum gauge and it worked! I checked my plugs after running it intermittently for a few months and the plugs a nice tan color for the first time since the rebuild. Vacuum gauge timing was really quick and easy, I just adjusted the distributor to the point with the highest vacuum @ about 18. I was running it way too retarded. I also found a nice conversion away from the old oil bath air cleaner to a new K & N washable air filter. I thought that might help it breath better.
 

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