Finally got the "new" 401 lit-off yesterday, and my brand new rebuilt Rochester promptly screwed up. After the 30 minute run-up, where the engine ran badly, I determined that it was suffering from a massive vacuum leak. I did the usual; played around with carb to manifold gaskets, but to no avail. It still wouldn't pull vacuum, and would only run well if I held my hand over the carb throat and choked the hell out of it. So I pulled off that manifold and put the original Carter back on. It worked better, but still seems to have a vacuum leak. Dumb question; - could this be part of the break in process? Or is there a trick I'm missing to line up the intake? Anything that I didn't check? Also; - is there a difference between the front or back of a rocker shaft? How much oil is supposed to be getting to the rocker arms? I wound up switching the rocker shafts so that the "notch" is pointing up, (like the book says) and that notch is visible from the front of the motor. Are all the bolt holes in the rocker shafts the same size? It sure didn't seem to get much oil up there, but the engine is quiet and building some power. I guess I shoulda stuck to 455 Buicks; - they're a lot easier to rebuild...
the rockers normally don't get too much oil on the nail.. and as far as I know there isn't a "front or rear" just the notch going on the "up" side wes
There are other places that can have vacume leaks.... the trans vac line on cars with an auto trans, the heater/ac lines and controlls.... the vac advance....the hot water controll valve....power brake booster... you can ck them by looking, feeling,,,ect and with a unlit propane torch around the carb and the intake manifold.... did you put sealer on the intake gaskets and get them in the proper place, they are directional... I seal them with permatex 300 a.k.a. ''tobbacer spit'',,,, dont use ''gorrilla snot'' , it makes the intake hard to get off...
I went out and re-checked the torque on the manifold; - and then high-tacked the tin plate to the carb. It seems to be better now. Doc, do you mean "silicone" when you refer to "gorilla snot", if so, that's what's currently on there. When we pulled of the Rochester manifold, half the gaskets came with it. We didn't use anything on the original set-upbecause it was from a cheap kit that had composite gaskets; - are the metal ones better? Because nailhead gaskets are no longer available here in Canada and that I'm looking forward to at least another two -week wait to get new ones, yes, we just siliconed the hell out of the gaskets and slapped it together, -slightly over-torqued, and the gaskets are pointing the right way. I just did an starting fluid check to the manifold, and it doesn't appear to be sucking there. Yeah, I know...wrong kind of repair, the kind of thing a backyard hack would do, shouldn't work and all, but it seems to be holding. For how long, I don't know. I just know that when that gasket is comes off it be with a chisel and a vacuum cleaner once the new ones get here. I took the car out and just cracked the 4 barrels open, and then lo and behold, the vacuum came up to about 18. So now the silly thing is running better, and getting more powerfull as it is being driven. The vacuum is now a steady 18, the engine runs quiet, it's building power, and it's not doing too bad on gas. Now there was another problem, and that was with the fuel filter. It seems that the NAPA type is wrong for a stock set-up. I put one on today, correctly lined up, and the car would start and then die of starvation. There was lots of pressure, but no volume. So I wrecked a perfectly good fuel line and yanked it too. So tomorrow I'm going out to go and get an old fashioned sediment bowl, just like my old Invicta used to run. Evidently the new filters are geared to run with fuel injected systems that operate under a lot more pressure. A sediment bowl isn't the best answer, but my old 46 hasn't suffered any from having one, and nor did the 60 Invicta I used to have. Were these engines prone to vapour lock? Has anyone ever had the problem of the back barrels sticking open in a Carter? I'll probably tear the carb down tomorrow, since it's about the only thing I haven't f@#$%^d- up yet... Thanks for all your advice and patience...I've rebuilt about a dozen Chev small blocks and about half a dozen Buick 430s and 455s, and never had as much grief as this thing has given me!
''Gorrilla snot'' is the good old 3m yellow trim cement... wonderfull stuff, just dont use it on intake manifold gaskets on a nailhead... the exhaust crossover heat bakes it on and makes it hard to get the intake off later... the permatex wont harden and cleans up with lac thinner... From what you are describing,, sounds like you might have secondary butterflies that are not closing all the way....that would give a vac leak... ck the adjustments on the sec linkage and all the rest of the carb for that matter... a lot of carbs have the linkages out of adjustment...
Looks like I found it; - it's the secondaries all right, there's a vacuum leak and the shaft was sticking. Guess I'm going to have to have this carb re-bushed and rebuilt. At least it's an original cast and not a remanufactured pile of junk. On the other hand, the Rochester seems to have failed because they gave me a '68 manifold to carb gasket, and the plate I had made up had undersize bolt holes which caused it to ride up. I guess I'll close this thread up with a thank-you to Doc who knew where to look. :beer
what is the signal for finding a vacuum leak when using the propane near carb and intake - suppen increase in engine RPM??? what about a squirt bottle of methanol? First seals the leak with small amount of liquid, so vacuum briefly improves. Next increases engine idle when the methanol is drawn through the leak and hits the cylinders?
Personally , i like atf...... it will visually suck in and then give white smoke out the exhaust.... but all of those will work.... some are just messier than others...
What is the signal for vac leak with the unlit propane torch? What vac measurement do you expect with a stock nailhead? mine produces about 13 in-Hg at idle 550 RPM.
The signal that you have found a leak is the rpm change.... and the '' normal'' vac range depends on what cam you have in the engine.... 13 in. is some what low for a stock engine.... most will be around 18 or 19 in....but inches of vacume is relative.... depends on the rpm, cam, state of tune, how it is tuned, ign timing, carb settings ect.... kind of like the meaning of ''is''...
