The Stovebolt Site Forums The Shop Area Engine Shop Why I won’t journey far from home!

Posted pictures of distributor rebuild, what would the logic be behind changing to another distributor??? This one is completely rebuilt, no slop in the shaft.
Oh we'll get it Woody, one way or another we'll get it, you know how bull headed I can be, maybe it's the dang gray paint I shot it with last year, might not be the right shade after all!
Hey Jimmie D, no problems with this one starting first time over, been that way ever since I brought her home and tuned it up two years ago. And it really is a sweet running engine when it's not acting finicky. Like yesterday we took a nice long ride and other than the hesitation I couldn't ask for a nicer running engine. Needs the short block rebuilt because she rattles a little after she’s warmed up and burns some oil, but the compression is still 130 across the board.
Dint have the time to work in the garage, to busy with learning what causes C, Cmaj7, and C7 on me Gitfiddle. And besides, I need something to keep me busy tomorrow.
Denny Graham
Sandwich, IL

I see pictures of a nice clean distributer, but I see no pictures of the centrifugal advance. Did you have the breaker plate out to check it?
Also if it uses a little oil, It wouldn't hurt to put in one number hotter plugs.

I have not had the pump problem on a 6 but some time ago I had a rochester on a 283 that acted up or hesitated. Back then I simply bent the little rod to set the pump further down in the hole and it worked much better ....for a while.

Denny, well, at least this is good reading and Educational I can hardly wait till you find the problem....or the fix!!

Denny,
As far as the vacuum advance goes, you have it a little wrong on the operation. The mechanical advance starts at a given rpm and quits at a given rpm with no input from the vacuum unit, Chevrolet set these points for optimal performance. The vacuum advance is pulled all the way on at idle and backs off as the vacuum drops. So with your timing set at say 10 degrees, the vacuum will pull it in to 20 degrees or how ever much it pulls. You could have as much as 35 or 40 degrees of timing going down the level road. All this is factory set for a reason.

You have stated, that one system takes over for the other at a given rpm, this is false, they both work together, all ways changing and adapting. You want the maximum timing the engine can handle for the best fuel milage and emissions. All new cars with computors run the timing right at the point of detenation, this is the optimum point for economy.
Under a load, the vacuum drops and the timing backs off, for maximum power even if the mechanical is all the way advanced.

Depending on the model, the vacuum might be hooked above the throttle shaft or below it. Below the shaft is full time vacuum, which helps the engine idle better with more timing. Above the throttle is ported vacuum, which pulls the advance in as your open the throttle. Either way both systems work together.

As far as your hesitation, a vacuum leak will cause a lean condition which will cause a hesitation. A really bad vacuum advance unit just might be enough of a leak if you are on the edge of running lean already. Check around the intake ports for a leak or the base gasket. Something is changing with heat. One of your backfires could have blown out a gasket that was good not long ago.

Joe

Well I read through this whole thing and it just stops like 10 months ago with not solution listed?

Ever get it fixed?

What was it?

I see he is still posting just not to this one.

Yep he’s still posting Wilber, so where you been hiding all this time??? This is a discussion forum, not Auto Repair 101, there aren't alway answers to the questions. I posted this to your PM this morning also!
The reason I never came back with a solution was that there never was a definitive solution so I saw no need to just blow hot air. After rebuilding and replacing about everything on the engine the last thing that I changed was the coil, even though the engine was running fine with the original coil. I never have been and am not now an advocate of off the shelf additives but about this same time I started adding Marvel Mystery Oil to every tank of gas. That was last year and I haven't had the backfiring occur since then.
I've always had a problem with the engine burning oil, because the oil scrapers are shot. It's not enough to see smoke out the tail pipe in the daylight but it is a significant amount and it does show up in a street light when you take of at night. By significant I mean a quart every 100-150 miles.
My only explanation for the back firing would be that the oil was forming deposits in the combustion chamber and every once in a while some would build up enough that it would cause a hot spot in the cylinder and pre-ignite the incoming mixture. This would blow out the bit of carbon until a little more built up. The MMO states that “when added to your fuel regularly, it keeps spark plugs and fuel injectors free of carbon deposits.” Now like I said, this stuff has always been snake oil in my opinion, but something is not happening that was before for a while on a regular basis. Then again, it might have just been the coil, but I have no explanation why this would cause this to happen when the engine was running normal other wise.
So, sorry I wasn’t of much help, nine times out of ten it’s a timing problem. About all I could possibly add to this thread is to make sure your timing i.e., valve and ignition are all set and operating properly, that you don’t have any burnt, bent or sticking valves, that the timing chain isn’t slack, that the distributor gear is not loose, no cracked cap or loose rotor, etc., then go from there.
Denny Graham
Sandwich, IL

sometimes it is a wire inside the distr that pulls apart upon throttle response( vacuum advance movement)and then settles back in place and runs fine, this is usually at the crimp are under the insulator. Had this happen once and it just about drives one nuts trying to figure it about. noticed early in the thread where it was stated that it backfired on throttle response. just one of those little mysteries that come along once in a while
ron

Thanks for the updates. Interesting theories. I do not have backfires with mine like you did. Mine runs exceptionally great cold for about 10 minutes. Revs to redline smooth and fast. Faster than I want to go in a 53 year old truck with warn steering box and manual brakes and warn shocks! But after that 10 minutes or so it will stumble badly with even just a small acceleration. Tried regarding and advancing timing no real effect on it. It still drives ok when not accelerating. Under load 1 or 2 cylinders seems to go out. Let it cool down a couple hours and it runs great again for 10 minutes. Got to work on it soon. Got new parts but no time.

Thank you Denny for the complete rundown! Old post with a lot of good trouble shooting and information, concluding that MMO snake oil could possibly help. I found that it does under certain conditions. Rather than adding MMO to the gasoline at each fill up, I installed an Ampco upper cylinder oiler. This apparatus has a glass container with a few filters and a regulator to automatically feed MMO through the intake manifold vacuum port. Set the regulator at 1/8 to 1/4 turn and go. Fill the container each time you change the oil. MMO in the Ampco oiler when full will last 3000 miles, if set properly. Engine is less noisy on the top end.

Tim

I had a similar experience last summer. I hopped in my 49' to take it to the Sycamore car show. I made it a mile down the road and it went to hell on me. Spitting and sputtering, backfiring. It would die but start right up and idle rough. As soon as I touched the gas it was stumble and backfire and usually die. I barely limped the mile back home. I noticed air bubbles in the fuel bowl and thought ah ha that's it! replaced the rubber line and clamps from the tank to the steel line. Started up and ran great for a minute or two and went to hell again. Did all of the usual checks, vacuum leaks, timing, ignition, opened up the distributor and reworked the lead inside in case it was the problem. Every time I started it it would run great for a minute or two.
So I changed the points. Ran great, took it down the road and barely made it mile and it started all over again. Barely made it back again. Culprit was the condensor.

Denny, I don't have any advise for you but I have really enjoyed this post. Learned a whole lot. I hope you get the problem fixed and tell us what it was. I have a problem with my 49 truck 235 it hesitates at low speed but runs fine once you get going. I'll figure it out one day. Just got the brakes fixed and new tires on the back so I'm ready to start driving it now. Good luck on your problem and again thanks for the very wonderful post.

When I got my first everyday car (actual first car was
a 1935 Buick bought in 1970) and second car, my dad
put in the glove boxes a new set of points and condenser
and the few tools needed to change them.

"In case you get stuck" He also said never change the
points or a condenser without changing the other one.
Jeffrey