It idles fun but when I drop it into gear it runs rough. I tried messing with timing but it doesnt make a difference. any Ideas? I have done all the usual tune up stuff.
Have you checked for a vacum leak? What kind of a dizzy are you running? The old Ford electronic from the 70's is a very easy too install and it will help the performance. What kind of carb are you running?
I havent found a vacuum leak yet. IT has one of those electronic conversions for a points dizzy in it. Its an edelbrock carb. Not sure what cfm. Its probably a little to big but its not really bogging its just idleing rough.
Pull a plug, my 351 does not like all of this humid air, you may have to monkey with your jetting. Lean it out a size or so. Edit, same problem with the Brock, It seems that they want the choke adjusted as well, if you're oversize that jet gig is it, once you foul the plug she runs like junk, clean the plugs she will run better for a while and then fuel foul again and have no power. Been waiting for a jet kit for 3 weeks back ordered.
My 302 had exactly those symptoms. Vacuum leak. Your results may vary, but that's where I would look first.
How many miles on the engine? If around 100K check your timing chain. These sbf's eat chains around that mileage.
Hose down the motor with brake cleaner. Around the intake base, carb base, any & all fittings on the intake/carb. You'll know when you found a leak. Put a vacuum gauge on the motor and see what it tells you. The vacuum gauge is probably the single most useful diagnostic tool on the planet. It can tell you so much.
Take the air cleaner off, block off any open vacuum lines. With it running, place a hand over the carb air horn, if the idle picks up and it smooths out, you have a vacuum leak. If it tends to die out, you don't. Bob
I have this thing printed up poster size in my shop wall...life saver. http://www.earlycuda.org/tech/vacuum2.htm
As a former service manager and a pro mech for over 40 years there is a lot of guessing going on here. You need to know. First is the motor any good. Pull the plugs and do a compession check. Next do the vaccum leak check. I use a propane torch not lit of course but turned up high to find vacuum leaks. . The brake cleaner thing is not a bad idea either. If that is good pull the valve covers and look for a wiped cam .You said timing makes no difference so for the time being we will belive that. A bum plug wire could be an issue. An oscilloscope would show that up but where would one find someone with one nowadays. Carb would be the next place to look. Try setting it up . Adjust idle air screws in gear for best idle. Air cleaner on. Jetting shoud not change just because the carb is big. And what is too big? i have a 750 Eddy on a 225 and it runs like a dream. A carb overhaul will often make a huge difference if you determine for sure that is what is wrong. (Idle adjustment is non responsive would be clue.) Plugged idle jets and air bleeds can cause strange idle problems and the engine will still run. If it came to my shop I would do the comp check and look at the plugs first thing. Some engine dont like some plugs annd willl act up. AC in a Ford or Dodge will sometimes do this. What did you change just before this problem reared ts ugly head is another important question. first though with any tune up problem is verify the condition of the engine. #1. Don
sprayed around the base of the carb and intake and nothing happened. If I put my hand over the front half of the carb idle does pick up. Here is a pick of the vacuum gauge with it running. It stays steady righ there. Watcha think? I borrowed the vacuum guage from a buddy and I looked at the chart posted above but Im not sure if I am reading it correctly.
is this a problem that started suddenly or did you do some work and this problem started after changing anything on the engine? how about some more details about the engine, cam, carb, fuel system, ignition system. has the car been sitting or is it driven regularly? just trying to get an idea of what you are working with.
289 not sure on the year or what its out of 60's, edelbrock carb(no idea on the cfm). it doesnt get driven a whole lot. I just put a new fuel pump in it which didnt seem to solve anything. It has one of those petronix ignitions in it. I just dont get why its smooth at idle than when I put it into gear the idle drops way off and it runs crappy Plugs are new cap is new wires are new. does that picture of the vacuum gauge tell you anything??
A weak ignition coil could cause this problem. When the engine is put under a load, the increased cylinder pressure can blow out the spark. A friend had this same problem a while back.
if your checking vacum, why does your gauge read 7 psi of pressure? and a picture of a vacum gauge on a running engine isnt really helpful. if you have an internal engine problem like valve train or compression loss, the needle will be bouncing, if the problem is affecting all cylinders or the timing is way off, the reading will be well below 18-20 inces of vacum. i'm assuming this has adustable valves, did you pull the valve covers to see if a rocker arm has come loose or backed off, maybe a push rod or lifter has failed. could have a wiped a cam lobe. the valve for the affected cylinders may be opening enough to run smooth at idle but miss under load. do you have a pair of insulated spark plug wire plyers, raise the rpm until the misfire occurs and 1 cylinder at a time remove the wire from the cap and see if you find a cylinder that has no change in rpm or running condition, that will be your culprit.
Guys, if I may post even though I haven't introduced myself, my mid 70's 302 acted very near like this. I also replaced everything from the coil to the carb with no results. Finally another hamber and I was about to pull our hair out when we noticed the pickup in the dist. was cracked. A very small hairline crack that was almost impossible to see. He gave me a used distributor and I haven't had any more problems in about a year. Hope this helps. p.s. I've been on here for awhile, mostly lurking, gleaning info from all of you. Thanks
where did have your vacuum gauge taped in?, its reading psi not vacuum. If you cover the front half of the carb and the engine picks up or smooths out, its lean for one reason or another. I would first check the idle air bleeds located in the top of the carb, and spray them out with carb cleaner, do you run an air filter?
The Jalopy Journal
