I have a 383 that I rebuilt last year it has flat top pistons and a 268 cam topped with a weiand dual plane and an edelbrock 1407 and a set of hooker fenderwell headers. Before the rebuild it was a stock 2 barrel 68 short block with the stock heads and mentions bolt-ons and would run great all the way up to 5,500. Now after the rebuild it loses power and bogs above 3,500 rpm and seems like it misses too. I have the base timing set at 13 degrees and the dizzy is stock with a pertronix electronic ignition. I pulled two plugs and they look good and the cylinder pressure in those cylinders is 130 psi. This car starts right up and idles good and drives good around town but when the hammer is down or above 3,500 it misses and stumbles. I can't hear or feel any pinging.
check your distributor- could be frozen advance weights, and or a bad vacuum advanceunit, or source .
The advance works properly I know that much. I even tried changing the heavy spring to a lighter one to see if it would do anything but not much changed. Truthfully these days I am leaning towards the secondary jets but I am seriously looking to do a homemade megasquirt efi swap this summer not only for the aforementioned issues but also because I see the real benefits of efi. I can either build an efi kit for $600 or a new carb for $350...
Did you remove the resistor from the harness for the points? if not your electronic ignition is running with lower voltage, I changes a older SBC to a HEI and it did the same thing
If you roll into it gradually to 3500, you shouldn't even be in the secondaries. Maybe something screwy on the primary side or fuel pressure is right on the verge of being too high and overwhelming the needle and seats with the added RPM? Had that happen once and you should see unatomised fuel dripping from the boosters at higher engine speeds. Maybe even a fuel supply issue? Also, which Pertronix do you have? Does it by chance have a built in rev limiter?
If yes is the answer to Sunbeam then the distributor needs a rework perhaps. A B series (or RB) needs only 34 to 36 degees TOTAL advance at 3500. Advance cureve needs to be shortened and do NOT run vacuum advance. These engines wont ping up here. (3500RPM) Once a cam is installed the mopars need less total advance then most other engines. Shorten one advance slot by 1/3 (Dont do both because it will bounce sometimes.) then run the light spring and set total timing at 34 degrees at 3500. If you dont have a dialiable light or timing tape it is 2.21 inches on the pulley from TDC mark. (Make a piece of paper 2.21 inches long then wrap it on the pulley from TDC and mark the far end with white out. ) Don D
Yes the valve springs were replaced with the matching comp ones to the cam and I have a pertronix 1 so no rev limiter and I can take the engine above 3500 rpm easy and have even taken the car to 100. The fuel pump is a stock replacement though it is sucking fuel through a nascar style ATL fuel cell. I will try to run without vacuum advance but everything I have ever read says vacuum advance is good. The thing is that this engine is so mild that it is close to the factory 335 horsepower 383 specs though the intake and headers may let it breathe a tad more.
I had the same problem with a mild 327. I thought it was valve float. I ended up changing my newish stock replacement mech fuel pump for s loud holley blue and it fixed my problem. I didn't have a fuel pressure gauge prior to the swap so I don't know what my before was. Good luck with the fix
I went through this exact same thing with a SBC. I changed the ignition, fuel pump and carb jets(numerous times). One day as I was about to give the car away a buddy noticed that it was getting about 1/3 throttle. I threw away my hand made throttle and put one on that I had stashed, instantly, it would rev and make great power. Depress the foot throttle and someone look down the carb, you might be surprised. Tool Roomer
Check the exhaust system for blockage. A friend once bought a used Olds Cutlass, and while it idled well and ran great at low rpm, anytime you opened it up a little it would bog down and miss until you let up on it and then it went back to running great. Put it up on a lift and notice one of the exhaust pipes was crushed almost completely closed. Replaced the exhaust system and it ran like a top all the way through the rpm range. Scott
ever read says vacuum advance is good. Then perhaps you havent read Old Reliable and the chapter Mission Ignition . All you ever read is for Chev small blocks and does not apply to Mopars in General and especially BB Mopars. I wrote the articles for Chrysler Power and at his urging did the book. The reason I wrote them was because so much of the information we were getting was bogus or did not apply. Have built many many B Mopars including the 400 cu in in NASCAR RETURNS TO LEMANS project of Christopher Schwartz. I am trying to help you here. Don Dulmage(Dolmetsch)
Is this a new pump or the one used before the rebuild? Same line from pump to carb as before? What size? .
You all brought up really good points but I have narrowed the problem down to the distributor. I disconnected the vacuum advance which made an improvement and plan to recurve the distributor.
I would check the spark using a spark tester or hold a wire above a ground & see how strong the spark is. It should jump 1/4-1/2". I would also try a new set of plugs. Just standard AC , Motorcraft or Champion.
I didn't know that, it goes to show that you learn something every day. Its just a little harder at my age, and sometimes I have to learn it a couple times
this might work.. I have done it several times over the years.. It happens more than you think it would.. Check the bolts on the intake manifold. I bet they are not tight. this one is e z to check. best if done with engine at operating temp.. One other thing MOPARS are bad for the shaft on the dist bending.. This will cause the dwell to vary. EZ to check take off dist cap and watch the reluctor. the gap will differ.. I hope that these things may help you..Bobby
You should keep the ballast resistor but the Pertronix power comes off the power side of the resistor. Pertronix uses a full 12V
Had the same problem on a 360. Edelbrock carb. Hooked up the distributor to the wrong vacuum port. Try switching ports. Might work. Matt
No need to toss the Pertronix their stuff works great just like the Mopar ignition conversion. If your using Champion spark plugs that may be the problem. Their made in mexico found out the hard way my motors would not pull using Champion plugs. Tried Autolite plugs the motor would pull a little better than Champions. Next I went to NGK plugs and now the motor revs perfectly and I'm using a Pertronix conversion. Maybe this will help.
I never heard of a distributor curve causing that kind of problem or fixing one either. Especially since it was working before the engine rebuild. I would take a close look at the distributor function. The power for the Pertronix should not go through the ballast resistor. That is likely the problem if it's wired that way. The higher the rpm the more current/power is needed by the ignition. A ballast resistors only function is to limit current through the coil to keep it from getting too hot.
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