I wanted to let you guys know what I stumbled across on my 302 stumbling issues that I had since day one. I had ordered and was installing my new distributor and coil today. When hooking up the vacuum advance hose to the distributor, I noticed the hose was a little too loose on the distributor so I was going to cut it back a few inches to snug it up. I happened to look in the end of the hose and saw something that looked like a ball bearing jammed in there about a half an inch. The hose was completely stopped up. No vacuum at all was getting through. I'm thinking this was my bogging/stumbling issue. I wish I had found this problem before I had bought all this new stuff and installed everything including cutting and extending new wires, drilling holes and paying people for nothing. I'm waiting on some correct plug wires to arrive then I can button it all up. I do want to thank everyone for their input.
Prior owners can be idiots. I have spent hundreds correcting other's "Fixes." Spent a few correcting my own too. I'm sure people on the board have done the same. Welcome to the club. I hope you got it solved. Micah
Well that could help as you'll now have advance under light throttle, BUT at WOT vacuum advance doesn't function so isn't going to make any real difference...
What carb do you have? I have an old 1850, and am in the process of learning all about them. It had almost everything wrong with it and now it is waiting for a bigger squirter to replace the .25 one it has.
ok....I read the original thread.....probably not the carb. I would begin this by getting your #1 cylinder to top dead center and see if your timing pointer is at zero. If you have a collection of miss matched parts between your timing pointer and balancer, you need to know, and correct this stuff....if you havent already. How many bolts hold on your bottom pulley? Is your pointer on the driver side or passenger side of the balancer?
yes....but it is possible to have the pointer on wrong side of balancer if parts get mixed from '60s and 70s, which kinda messes up timing by the marks. 3 bolt balancer has marks on driver side, four bolt has marks on passenger side; must have correct pointer location for balancer....I suspect some engine rebuilders send things out with parts they didnt come in with.
Exactly right, Tom. In fact, the vac advance pot is the LAST thing to be tuned in the overall tuning process. It is purely supplemental and only aids efficiency levels(manifested as increased idle and cruise manifold vacuum) during idle and very light load situations. Unfortunately you can only dial them back/restrict them so far(to about 8-10°) and end up robbing Peter to pay Paul while compromising the rest of the ignition curve. Now don't get me wrong.. I'm not saying that implementing the vac pot into the spark curve can't remedy pig rich conditions that could also cause bogging or poor performance(because manifold vacuum levels are directly attributed to the boosters performance/mixture homogeneity and circuit transition reaction time(idle/transfer slot to main jet transitional fuel flow).. just that it(vac assisted advance) was not meant to be part of the "meat of the ignition curve" which initial and centrifugal were meant for. In a nutshell.. IF hooking up a vac pot clears up such an issue?.. the engines tune is FAAARRRR from ideal to begin with. And what many never fully realize is that when the ignition curve is far from ideal?.. the fuel curve can NEVER be dialed in even remotely close to its idealized flow. The ignition curve has to be well within the ballpark, preferably inside the diamond, before carb tuning can even begin. But as is often the case, cookie cutter carb tunes(shelf or OEM carb's) require going back and forth between the ignition and carb calibrations to avoid excessive lean out from pushing the advance curve too quickly while the fuel curve lags too far behind. So it ends up being a back and forth game to dial everything in and keep the motor safe along the way. Most novices will quit when reaching the carbs point of lean out requiring IFR and air bleed orifice size modification. Which is entirely too bad because that's where that last 5% low-rpm power gain lies hidden. PS. not to rub salt in wounds here.. but troubleshooting 101's golden rule is to check hoses for obstructions and make sure diaphragm is good in the vac pot. Literally suck on the hose or use a handheld vac pump to quickly test both at one time while connected to the vac pot.
Those are correct. If you want absolute peace of mind, pull out #1 spark plug and get your piston at top dead center. You will be on the compression stroke if your disributor rotor is pointing at the spot where your #1 wire is in the cap. If your piston is at the top, your pointer should be pointing at zero. If this is how it all behaves, then what your timing light tells you is good info. My car has two pointers, and I had to do this to know which one to use and which one to ignore. The one to use on my engine is hard to see because the alternator partially blocks the view. My alternator bracket is from a late '70s 351, and had a smog pump mount that I cut off, so it is irregular but functional. I have read your complete thread only once, and I seem to recall that you have done some stuff, and mechanics have done some stuff....I would say that getting your ignition timing set up to as close to what Groberts would recommend, and then turning focus on your carb afterwards is your best bet. I have not had a pre 1975 car for 25 years, and back then I did everything by the book. I am setting up my Comet with the timing specs that Groberts (and several others on the web) would recommend, and it is night and day difference in performance. I am learning all this stuff as I go, and since my car is not a daily driver, I am in no rush. You must be careful with what you do, and read about it until you understand it well enough. The alternative is to go back to factory spec, and ditch your 4bbl carb, use iron exhaust manifolds, and de-tune your car back to factory bliss; then you will not have a bog. OR...read and educate yourself on what to do to a motor that is departing from factory spec......If your motor departs from the factory spec sheet, wouldnt it make sense that how you tune it must also depart from the factory spec sheet?
I had a bad vacuum advance diaphragm years ago. Definitely check that. That shouldn't cause a major bog though.
Well, I did have a Holley 600 prior to the Edelbrock. I swapped those out hoping that was the stumbling issue. Was still doing the same thing.
