So I have been noticing the pickup surging lately (figured it just had a vacuum leak due to the hillbilly rigged vacuum line that I had to install while I wait for my new one to get here).... BUT here is where it starts to get strange Yesterday as we were driving to the store it randomly cutout and then went back to normal after like 1/2 a second... As I was driving home from down the street it started getting worse and worse, cutting out, then backfiring randomly... The distributor is tight, everything in the distributor is correct, nothing was loosened, the battery isn't draining.... I take a look at the clear inline fuel filter and notice that it was close to sucking air every time it was cutting out (it might have been sucking air when it happened). So I pull it, pull the stone filter thing out of the 1 bbl Rochester and clean both out... both are pretty nasty and the carb filter was half way blocked... So I fire it up again, filter is half full like it always is, it runs longer before it starts to cut in and out and randomly backfires, but not through the carb, just exhaust. I had set the timing previously to 6 BDC like it is supposed to be and it had run like this for over a month without any issues what-so-ever. Could the fuel pump be causing this? It is vexing me.. found a fuel pump locally for $20 so it is not going to break the bank if I have to replace it... I know there is a ton of crap in the tank, but don't have the time or means to be pulling the tank, cleaning it out and doing a bunch of crap like that if it is a simple fix. Generally these engines are nothing but simple fixes.
Before you do that check the carb to see if the body is loose from the base. I've seen some of those single barrels have the body to base screws back out a bit and you can twist the body back and forth on the base.
I wiggled it around to check to see if it was tight as of last night (it was), but I will check again when I get home in a bit and put a wrench on it.
Any time my Chevy inline 6 backfires, I check the intake gasket. Let it cool off, get a pitcher of water and do the old drown the intake sealing surface on cool startup. I would waiger that most of this engine family got parked after people thought the motor was tired when it was really just a bad intake gasket.
Check you oil - if it's thin and smells like fuel change the pump. The diaphragm in the pump may have been damaged by sucking crap outta the tank and pushing it into the carb. If that's the case you'll need that replacement pump and really should pull the tank and flush it. If flushing the tanks just not in the cards at this point in time try putting a disposable filter on the pumps inlet to prefilter the fuel before the pump. This would be a temporary fix at best since a filter on the inlet isn't normally done (pumps generally push fuel better than pulling it) but would help keep the crap out of the carb.
Well this carb is causing some leak back because the check ball is not seating (allowing the fuel to drain back to the pump when shut off... I had this problem before and put a new rebuild kit in it.... yet I am still having issues... I am having to wait for the filter to fill up and then I can drive it (the pump will keep up for a while). The pump maybe weak, but since the throttle shafts are leaking on the carb, fuel is leaking from the body gasket, the intake gasket and just overall a huge POS, I bought a good reman which should get here in a couple days. Since I am swapping that out I am thinking about pulling the tank and draining it. Since the pump is only $20 I am probably going to do this too. I will run some new fuel injection line (can handle this new crap in gasoline) and an inline filter before the pump. The exhaust manifold post broke for the heat riser (I troubleshot why it was taking so long to warm up). Does anyone know of a decent fix for this? I found a replacement new manifold for $145. I could weld a post onto it, but do you think this will work? I have no idea what the original post looked like. Is this a threaded post that goes in or is it welded on normally? I would assume that it is just threaded. Does anyone have a lead for one of these posts?
Another problem late '60s 250s had was the distributor housing wearing out and allowing the point dwell to randomly fluctuate. I remember replacing several distributors years ago.
The B series rochesters really are crappy carbs, fought the one on my 63 chevy 250 for a long time. Apparently the casting aren't the greatest and like to warp causing all sorts of issues. I rebuilt a Carter YF and slapped that on there, runs like a dream now.
Assuming your fuel inlet is at the top of the carb, there should be no way for the bowl to drain back into the pump. The fuel pump however should have a check valve that only allows fuel to pass in one direction thru the pump. ^^^ This ^^^
I had nearly all of the problems listed when getting my 292 going. Worn distributor bushings is common as stated. I just wanted to add that you should check the Rochester B for worn bushings as well. They'll often leak fuel out of the throttle blade shaft bushing if you pump the gas with engine off, but, there is no evidence of a problem with the engine running. It's yet another intermittent vacuum leak that will make you go crazy diagnosing various problems.
Personally I would start with checking for vacuum leaks, its simple and takes very little time or effort. My favorite method is to use a spray bottle full of water on various parts of the intake while its running. You may have a ton of other issues, but start with the simple/easy stuff.
Yeah the throttle shafts are leaking, the top of the bowl won't stop leaking fuel (no its not flooding) and the check valve in the carb is allowing it to suck air and let fuel run back to the tank.... along with the fuel pump. The pump was $20 and the carb is only going to cost me $100 for a fresh one that doesn't have half the problems that I am currently having (hopefully the throttle shafts are fixed as well). In the process of me fixing this I am going to through a couple inline filters in before the fuel pump to help clean it up. I am probably going to have to drain and wash out the tank too... So much crap so little time. So yes, I do have a vacuum leak there, I know for one for sure at the tranny modulator, but that still doesn't explain why it was doing what it was doing... the vacuum leaks have been present for a while, it just acted like it wasnt wanting to run at all... I will report when I have those things fixed/replaced.
Knowing this, rig up a small, clean, remote fuel tank while doing your troubleshooting. Maybe a marine tank you've got laying around. This eliminates one source of potential problems. If you're getting fuel coming up out of the vent tubes, IT IS FLOODING! Check for sunk or stuck float. Check for loose and/or dirty needle and seat. If you've added an electric fuel pump, check for excessive fuel pressure. If there's a check valve somewhere causing this problem it's in the fuel pump, not the carb. Your throttle shaft may be worn; they are on a lot of carbs when they get this old, especially manual transmission models where you're working the throttle more frequently. But it usually doesn't cause major driveability problems like this. The throttle shaft isn't routed anyplace where it runs in liquid fuel. If you're seeing fuel seeping where the throttle shaft comes out of the throttle plate, it's because liquid fuel is dripping on to the throttle blades from the main nozzles or vent tubes when it shouldn't be. It wicks and creeps down the throttle shaft to the outside of the carb. And we're back to your flooding issues.
Thanks for the response! I have actually checked out and have done a lot of these things you mentioned already. I have rigged a small tank and it helped tremendously. I just have too many things going on to clean the tank right out right now, but will definitely need to do it soon. I maybe able to pick up a tank at the Goodguys swap meet, but that still doesn't change the fact that the sock and about everything else needs to be replaced on it that is involved with the fuel pickup. Once I remove the tank, the filler neck hoses and crap like that will not be able to be reused, so that is an added expense on top of everything else. Fuel is not coming out of the top of the tubes, it isn't even close to the top of the bowl, I have set the carb float twice, the float isn't ful of liquid and was replaced the first time I took it apart (don't forget it is a reman carb too). The gasket just doesn't seal for the top of the bowl, so when fuel sloshes around when you are stopping or starting it up it starts to saturate that gasket and then leak. I have gone through two carb rebuild kits and tried to true up the top as well to no avail. Plus the previous owner stripped out one of the holes on the top and never put a fuel filter in, so the carb was full of crap when I opened it the first time. I will go ahead and install a pressure regulator to ensure that the fuel pump is not going over the 3-4.5 psi that is required for the engine. This would probably fix most of my problem as well. Good idea. There is a checkvalve in both the pump and the carb right?, You are correct though, if it is draining that means that the fuel pump one is not working. The fuel pump is also probably resulting in my surging issue as well that I experience when idling, in gear, at a stop light. There is also one in the carb that is supposed to prevent it from sucking air to go back as well correct???... that is not working either if that is the case. Since the carb is a massive POS with too many problems that is why I opted to just replace it. The shafts don't leak while running, only when the engine has been sitting a while after running and not by much, just enough to notice that the carb looks slightly wet (has collected some dirt on that part of the carb and is damp looking, but not to the touch. This, from what I understand, really is a culprit in vacuum leaks, which I have one or two. I will check all of this crap out a second time though, This is why I love the HAMB, thanks again ClayMart
From the sound of it you may be better off with a replacement carb that hasn't been bunged around so much. It may also be missing some sort of baffle in the float bowl that would help control fuel sloshing around too much. So do you have an electric pump or just the stock mechanical pump? The only check valves in the carb are to control the direction of fuel flow into and out of the accerator pump well. There's a whole lot of carbs out there in daily use that have enough throttle shaft wear to let a bit of liquid fuel leak past. When the wear gets bad enough you can end up with a vacuum leak. This leans things out a bit but it usually tends to just affect the idle quality. It would take a pretty big vacuum leak to affect the main or power circuits. And even then it would make the fuel mixture too lean, not too rich. I'm not trying to bust your chops here. But I know when you're chasing a problem like you're having it's way too tempting to go for the "throw money at it" approach instead of actually diagnosing and repairing it. If you've got the money to throw, though, well more power to ya'! You might pick up some useful information at this site. It's run by a fellow HAMB member whose screen name escapes me at the moment. http://www.thecarburetorshop.com/Troubleshooting.htm
You are probably on the right track with looking at the fuel system but, it also sounds like the ign. coil going bad. Do you have another you could swap in just to test it? N.N.
From the sound of it you may be better off with a replacement carb that hasn't been bunged around so much. It may also be missing some sort of baffle in the float bowl that would help control fuel sloshing around too much. Yeah, I am having a hard time getting it tuned, sometimes it will run great, purr like a kitten, the next hour it runs like absolute garbage. It will either run too rich or too lean, no inbetween. It should be here tomorrow, so that will be good. So do you have an electric pump or just the stock mechanical pump? Mechanical only that the PO installed... he may have grabbed a higher PSI one by mistake...plus the autoparts store puts these in the wrong boxes all the time. Since it is plugged with crap I have to take it off anyway, if I can't clean it up I have a replacement there. It's always good to have spare parts. If I don't need it then I can always return it. The only check valves in the carb are to control the direction of fuel flow into and out of the accerator pump well. Yeah after typing that and really thinking about it I realized that the statement and question about this was stoooopid. Brain lapse... probably from all the gas fumes There's a whole lot of carbs out there in daily use that have enough throttle shaft wear to let a bit of liquid fuel leak past. When the wear gets bad enough you can end up with a vacuum leak. This leans things out a bit but it usually tends to just affect the idle quality. It would take a pretty big vacuum leak to affect the main or power circuits. And even then it would make the fuel mixture too lean, not too rich. Good point, I think this is what is happening as far as the vacuum leak and the ability for me to tune it in. I'm not trying to bust your chops here. But I know when you're chasing a problem like you're having it's way too tempting to go for the "throw money at it" approach instead of actually diagnosing and repairing it. If you've got the money to throw, though, well more power to ya'! I was generally thanking you for your input, not being a smartass. I know you are trying to help and it would be ignorant to get like that with someone answering a question I asked. I really have been looking to replace the carb for a while after hillbilly rigging it to work since the last time it took a dump on me, this was just the icing on the cake and I finally got the go ahead from the Boss. She usually just lets me do my thing anyway, but she suggested to just replace it if I am having that many problems with it, without me saying much.... I can't argue with that!! I would like to upgrade to HEI eventually down the road, unless something else happens that I can diagnose the distributor as an issue... reliability is what I am looking for if I am driving this daily... Really I have only pre-purchased a fuel pump before diagnosing the problem just incase it is unable to be cleaned out. Everything on this truck, engine/tranny wise, is still stock, no real replacement parts or upgrades. (the hoses even crumbled in my hands when I touched them). You might pick up some useful information at this site. It's run by a fellow HAMB member whose screen name escapes me at the moment. http://www.thecarburetorshop.com/Troubleshooting.htm Thanks for the heads up on the web page, I will check it out.
No I don't and it was kind of suspicious to me as well... It isn't getting hot and seems to be running correct voltage... my Dad is bringing one in a couple weeks, I may just swap it out with the freebee to rule it out. Any ideas on how to test this other than swapping it out?
Bet your intake manifolds gasket is bad. Get it warmed up and take a can of starting fluid and spray it where the intake manifold meets the head, if the engine surges then its a bad gasket and sucking air.
You're OK. That's the way I read your reply. I thought it might have sounded like I was grinding you a little bit. It's difficult enough at times to sort this stuff out when it's right in front of you. Trying to do it over the internet can get real tricky! Keep us posted. Try to do one repair at a time and let us know which repair cures which problem.
Alright, so the carb was full of silt again, fuel filter was plugged again, the fuel pump was full of silt. The fuel pump bolts were so short that they were hanging on with one thread each.. So I put in some longer ones, put an inline filter between the tank and the fuel pump, installed the replacement fuel pump. Tested it and it started pumping correctly... So that was part of the fix. It still wouldn't run more than a couple rotations of the engine. I noticed after the new pump was on that the carb was now acting funky. I pulled it and put the replacement on (it is rebushed and all around looks pretty nice). I found that the vacuum line to the distributor and tranny was almost all the way blocked off with some kind of gasket seal, so I cleaned it up and installed it on the carb.... I will need to tune the carb when I can get it running more than a couple seconds. So lesson learned.... until I get the tank cleaned out, don't run the tank dry so it sucks up all of that crap and dumps it throughout my fuel system. To solve the other portion of the issue I checked all of my voltages (battery, alt, coil, etc.). Everything checked out to be good. I pulled the cap off of the distributor and checked several other things there as well... Voltage good, no issues. I decided to check my points gap, so I rotated the fan and watched the points barely open when it came around to fire (barely open, just enough to slip a human hair through), it is supposed to be .019. So I tried to reset the points only to find the whole plate that the condenser and points mounts to bobbing around, not just moving back and forth for like the vacuum advance, but up and down as if it were a hemisphere moving around a flat surface.... bingo. So it looks like this is mounted to the distributor by pressing it on? possibly rivets?? I don't know if they screw on or not. I will have to check tomorrow. Any help would be appreciated. If I need to pull it I may just have it replaced with an HEI distributor. More to come.
I just read this one good you found a problem generally if you have a backfire problem out the exhaust it is a ignition problem.
Yeah, usually it points to timing, so I agree. I had a two fold problem so, half of it is fixed. Does anyone know if that plate screws down? I didn't take it apart yet. I had worked 3 days on several cars this weekend and saw it, found the issue, and buttoned it up because I didn't feel like dicking with it today.
looking in a motors manual it looks like the breaker plate rotates on ball bearings between the plate and the housing. Don't make sense to me. Sorry have not been in one for ever. With out one in my hand I cant help much.
I think that the point plate is spring loaded and has either an E clip or a cotter pin on a post that retains it.
Bring that distributor out to Bubbas , we will fix ya up...... Main street in Speedway.....1330 Main 317-487-9460
Well I found a new reman distributor locally for less than $40 after talking them down from a lot higher (they were sitting on it basically). I got it, installed it and it works great. It seems to be running fine, I need to use the timing light to get it in closer, tune in the carb, and make sure that the points gap is right. My neighbor has a dwell meter, so I can check that too. Everything seems to be going well, thanks again HAMB and thanks Jim for your offer to help. I will update when I have it running right.
The Jalopy Journal
