Hey Crew, I was wondering if anyone knew what the perfect ignition curve for a flathead is? My motor is a .20 over 8ba, offy 400 heads, sharp super dual with 2x94's (49 jets and 4.5 power valves) and stock cam. The ignition is a modded Mopar electronic unit (theres 18 degrees of mech advance in the dissy, its set at 6 deg intial for a total advance of 24 deg.). At the moment and starts and idles perfectly, the it generally feels like its missing from 1000-2000 rpm and then feels fine then feels shuddery and "missy" again from 2000 onwards. I was wondering if it is advance related or does something else spring to mind with these symptoms? Danny
Not much help, but have you checked for air leaks in the intake/carbs? Grab some wd40 or rp7 and do some spraying...
The timing figures are pretty close to what I am running on my 60 over 8ba though my initial is around 4 degrees and total at about 22, I think you should be fine with what you have. I'm running a holley 390 right now, but am making a move to two 97's on a Eddie Meyer as we speak. A lot of the guys running 94's that I know are running a power valve in the primary and plugging the secondary, also the jets seem little fat to me, I recall .045's being mentioned here and there, but I dont think thats causing your problem either. Are you running the carbs sraight or progressive, if straight are they properly synced? That can make a big difference. also, at what rpm are you obtaining full advance? Vac*** leak would probably effect idle if it's a significant one. First thing I would do is take a plug reading and see if anything strange shows.
Danny, have been flat out man so hav'ent gotten back to you man. If its stumbling off the line check your accel pump shot - make sure you're getting enough. What plugs are you running and what is the heat range of the plugs? Check your plugs - they should not be fouling with the ignition setup you have. The PV should not be opening at idle with the stock cam - check the manifiold vac*** with a vac gauge at idle to ensure it doe'snt drop BELOW the vac rating of the PV with the dual 94s on it. As far as advance goes, your stock cam wont need a lot of initial advance to smooth it out - with the Offy 400 heads youll be nudging a decent CR for a flathead so keep an eye on it. Try it at 4 deg initial @ the crank for a total of 22 deg b/c of the 400 heads and see if its better. Make ONE change at a time and see if it improves. Let us know how you make out dude... Rat
Hi Guys, Thanks for the help. I rebuilt the carbs completly, new throttle shafts, gaskets, jets, PV etc. Compression is about 110 per cyclinder, not alot considering the higher comp heads but ok I guess for a tired motor. Timing is set to approx 4 degress. I'm running the carbs with a straight linkage. There isnt enough equalisation between carbs with this manifold to run progressing. Carbs are sync'd with a flow meter as best as I could get them. I'm going to swap out the plugs for new ones (about time anyway) and throw on some new leads and see how this goes. Will attack further from there. Danny
The mopar distributor has a totally adjustable advance rate without taking the unit apart. The unit has a opening that you can see thru down to the weights. Look thru the opening and turn engine by hand , you will see a small ( weak) spring and a larger (strong) one mounted on eccentric pins. The pins have a slot on top. I make a tool by cutting ( grinding) and half moon opening in a screw driver blade. ) Then you can adjust the spring tensions and curve to make work like you want. Takes longer than using a distributor machine but works very well. I would suggest tightening up both to see if that removes your miss or surge then loosen to suit.
Curve needs to START very early too...best standard curves ('41-48) started IMMEDIATELY off idle, finshed at about 1800... Ron Holleran has been flogging flathead street curves lately. Obviously each engine will be a bit different, but his current basic curve is so: 4 degrees initial, 16 mechanical, all before 2,000, 6-7 vacuum advance for full power at low throttle openings. Within these numbers, both centrifugal and vac rates of movement would need flogging...lengthy but cheap entertainment. 11A curve, generally viwed asetty good stock curve is about so: these numbers are from a nonFord source, all I have right here, and rate can be modified with vac brake... 4 static, 0 cent at 400, curve starts right at 400, 22 by 1200!! Will check better info from Ford books. This is for basic crab distrib...hard to modify curve on these, have to bend leaf springs!
Hi Guys, This is the current state of play: The engine starts and idles really well. Bit of black smoke at idle but nothing serious. Straight off idle it revs up but its rough. If I hold it a part throttle at say 1500 rpm it runs but it's not smooth it - how do I explain it? Its not back firing or going pop or snap but its relativly rough. Its remains like that throughout the rev range but as the revs come up I think it masks the rough running more so then at the lower revs. The power is better then it has been but for how it has run in the past... its still not very good. I'm trying to change one thing at a time. Yesterday I swapped out all of the ignition leads for modern ones (old ones were solid core) and this helped but did not cure the rough running. I'm wondering if this is maybe a few problems rolled into one. Today I will swap out the spark plugs for new ones (needs doing anyway). From there I'm not sure where to go? Check for vac leaks? Is there a safer way to do this then spraying wd40 on my running motor? Danny
Worry about curve later...I think you have some other kind of problem here! Check basics...rotor phasing to cap, plug wire order, etc. Check all the stuff you think is right...the roughness sounds more like a basic ignition problem than mixture or minor advance issues.
Hi Bruce, Thanks for the help. I have been chasing my tail regarding this for a while. I'll re-check everything and let you know how it progresses. Danny
Dan another trick to try, get a spray bottle with water in it. Spray the headers individually. You should get instant evaporation, if not its not firing properly on that cylinder. We used this method on my daily a few years back and it showed which cylinders!! were down. Spraying wd40 is safe as all it does is bring the revs up if you have a leak or evaporate slowly.
Hey guys, NGK plugs will be ready to pick up tommorow. So I'll mess around with the WD40 and see if it does anything. I'm guessing spray at every join in the carb? ie. base to intake, base to bowel etc? One quick question - my tank is in the stock location in the cowl and is gravity fed through to the mechanical fuel pump. I'm running one of these filters inline between the tank and pump. I run it horizonatally but there only ever seems to be maybe 5mm of fuel on the bottom of the filter. Should I fun it vertically so it fills up and have the outlet on the bottom?
I would also check fuel pump pressure, those carbs con only handle 2.5 to 3 lbs. I have an almost idential setup as your and will run as you describ with to much fuel pressure. Your pv should be 3.5's. Also I would not go less on the jetting, I am running 51.s. It seems like you pv's are opening to soon.
Hi Guys, I'm beginning to narrow this down. Its at least partially caused by ignition... I put the timing light on all the leads and idle and number one and number four are missing. There is at least... 1-2 second gaps in the firing. All the other leads check out ok. At 1500 or so RPM there is noticable gaps in the firing. All the plugs are clean and this is with a spare set of leads. Stuffed plugs? I have some NGK's coming in first thing tommorow. I paid alot of attention to the car at idle and there side that is putting out the black smoke and making all the little pops in the exhaust is the same side as the 1-4 bank of cylinders. I adjusted out the idle mixture screws to make sure it wasnt runing too rich on the side but it didnt fix the problem. I'm going to run brand new plugs and leads on the motor and see where that leads too. Hey one wierd thing, I was checking out the dizzy cap, and there were little brown circles where the high voltage had come off the rotor to the ****on inside the cap. Is this supposed to be in the middle of the ****on becuase it seemed to be half on and half off, like it was firing where the rotor had only made half contact? Danny
Hi Mate, This is what I thought as well... I think I'll fix the ignition side and then move to fuel. Danny
If you rebuilt your carbs and put in new powervalves, pull the air horn off one of the carbs and look where the powervalve comes through the bottom of the float bowl. The new powervalves are slightly larger in diameter, and will often rub on the side of the float bowl, unseating the valve. If this is the case, you will need to take the carb apart and relieve the side of the float bowl with a Dremel until there is sufficient clearance for free movement of the powervalve. Good luck, Bob
I know this is a VERY old post, but was it ever figured out? I also have a flathead with an Eddie Meyer high-rise intake and dual 97's...sounds similar to your's and with the exact same symptoms and issues. I rebuilt the carbs with new genuine Stromberg rebuild kits, new floats, and .65 power valves. Posted from the TJJ App for iPhone & iPad
In post 21 The OP reports a timing light was flashing irregulary and intermittently. tain't right. I would focus on that first.
Some of the stock Mopar ignitions have a problem of the rotor being out of phase. That is the rotor is not in the proper spot when the coil fires. http://board.moparts.org/ubbthreads/showflat.php?Number=5217698
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