nailhead9 Posted June 17, 2016 Share Posted June 17, 2016 I have been having a hesitation problem with my 19567 Buick Roadmaster. The Buick has a Rochester 4-barrel carburetor (which I had rebuilt) and when starting form a stop (with out changing my foot pressure on the gas pedal) after a short (200 feet or so) the car has a very brief hesitation and then still maintaining the same pressure it picks right up and drives find. it also happens while driving at a steady pace going down the road. I just had the vacuum advance on the distributor replace, points were check and timed. Thank you for you help solving this problem. Warren Link to comment Share on other sites More sharing options...
tripwire Posted June 17, 2016 Share Posted June 17, 2016 Warren, Shall we assume you've already checked for vacuum leaks everywhere? Shall we assume you've already checked for sticking mechanical advance weights in your distributor? Any chance this could be something with the transmission, a sluggish shift, maybe? Fuel pressure and volume up to specs? How old is the gas? Any more clues you can share? WParo in VT Link to comment Share on other sites More sharing options...
Bhigdog Posted June 17, 2016 Share Posted June 17, 2016 1 hour ago, nailhead9 said: I just had the vacuum advance on the distributor replace Put your vacuum gauge on it for starters..................Bob Link to comment Share on other sites More sharing options...
vermontboy Posted June 18, 2016 Share Posted June 18, 2016 I know it may sound silly but most old carbureted and even throttle body fi cars have their little quirks. Before I spent a lot of time and effort in locating the problem I would find someone with as similar car and ask them to drive it. Since you state it happens when you are maintaining the same light pressure on the throttle it may be you are feeling the transition between circuits in the carburetor - it would be sort of a "fluttering" or "flat spot" effect. Link to comment Share on other sites More sharing options...
padgett Posted June 18, 2016 Share Posted June 18, 2016 (edited) Is that a Rochester or a Carter ? Do you know the model number of the carb ? Edited June 18, 2016 by padgett (see edit history) Link to comment Share on other sites More sharing options...
Guest Posted June 18, 2016 Share Posted June 18, 2016 (edited) The original post says "Rochester". By the way that is a beautiful automobile. I love the colours. Edited June 18, 2016 by Guest more comment (see edit history) Link to comment Share on other sites More sharing options...
60FlatTop Posted June 18, 2016 Share Posted June 18, 2016 It's either a Rochester 4GC or a WCFB. Get a gasket kit and start snooping around inside. The accelerator well check ball is a good place to start. That's all after the vacuum advance is checked and the heat stove for the choke is gone through. That's one carb that responds well to an electric choke conversion. I have found the WCFB easier to work on. Just remember, it's only a pot of gasoline with some holes the gas sucks through. There are a bunch of other things that do a lot more work than the carb. They just aren't right on top with tempting screws on them. Bernie 2 Link to comment Share on other sites More sharing options...
JamesBulldogMiller55Buick Posted June 18, 2016 Share Posted June 18, 2016 On 6/17/2016 at 1:46 PM, tripwire said: Warren, Shall we assume you've already checked for vacuum leaks everywhere? Shall we assume you've already checked for sticking mechanical advance weights in your distributor? Any chance this could be something with the transmission, a sluggish shift, maybe? Fuel pressure and volume up to specs? How old is the gas? Any more clues you can share? WParo in VT Good things to check for. Except for shift... there's a guarantee that there is not a shifting problem in the Dynaflow 1 Link to comment Share on other sites More sharing options...
tripwire Posted June 19, 2016 Share Posted June 19, 2016 23 hours ago, JamesBulldogMiller55Buick said: Good things to check for. Except for shift... there's a guarantee that there is not a shifting problem in the Dynaflow Silly me, what was I thinking. Link to comment Share on other sites More sharing options...
padgett Posted June 19, 2016 Share Posted June 19, 2016 Interesting. I get jumped on for mentioning that Carter was supplying to GM in 1957 but no-one twigged to WCFB (hint - the AFB successor was available in GM cars in 1957). Perhaps someone who knows what carbs were available on a Buick in 1957 should chime in though I agree that if a Rochester 4bbl it would have been a 4GC. Link to comment Share on other sites More sharing options...
Ben Bruce aka First Born Posted June 20, 2016 Share Posted June 20, 2016 1 hour ago, tripwire said: Silly me, what was I thinking. Not? Ben Link to comment Share on other sites More sharing options...
Spinneyhill Posted June 20, 2016 Share Posted June 20, 2016 Are all the ignition contacts clean and making good electrical contact? Link to comment Share on other sites More sharing options...
nailhead9 Posted June 20, 2016 Author Share Posted June 20, 2016 (edited) Thank you to everyone who helped with your valued suggestions. I just had the distributor vacuum advanced replaced, timing, points check and car has a new fuel pump installed August 2013. Also the 1957 Buick chassis service manual list the Rochester 4-barrel as one of the 3 types of carburetors used on this car.The one I have is stamped with 4-jet on it. I put my vacuum gauge on it while idling and it showed 20" of vacuum. Edited June 25, 2016 by nailhead9 (see edit history) Link to comment Share on other sites More sharing options...
padgett Posted June 20, 2016 Share Posted June 20, 2016 That kind of hestitation often happens when a transition say from idle circuits to mid-range occurs too fast and the engine temporarily goes lean. Extreeme cases are known as bog. QuardraJets with too loose a secondary spring (simple adjustment) are particularly susceptible (had a Corvair Corsa with a QJ I used to autocross and had to be very careful about the secondary opening). I am not that familiar with a 4G (is supposed to be two 2Gs back to back) but if it happened to me I'd pull the carb and make sure all of the passages were free of grit. Could even happen to a new carb if the car had been sitting for a while, some of those passages are very small. Link to comment Share on other sites More sharing options...
rocketraider Posted June 20, 2016 Share Posted June 20, 2016 4GC can be notoriously finicky about having the correct throttle plate to fuel bowl gasket ( I know of at least three different ones and odds of you getting the right one in there are bout 30%), but it usually shows itself as hard to set a good idle. Link to comment Share on other sites More sharing options...
carbking Posted June 20, 2016 Share Posted June 20, 2016 (edited) Not certain I totally understand the symptoms. From the first post: (A) First issue - accelerating gently from stop, after approximately 200 feet with no change in footfeed position, there is a slight hesitation, and then almost immediate recovery. (B) Second issue? - This also happens while driving at a steady pace while going down the road. In issue (B), are you going at a steady pace then accelerating; or just driving at a constant speed with a hesitation and recovery? POSSIBLE causes of (A): (1) As Glenn mentioned, incorrect throttle body gasket (2) Ethanol fuel without modifying idle jets (3) Using vacuum gauge to set idle (99 times out of 100, it will be set too rich, creating a "rich" stumble (4) Non carburetor issue Please clarify issue (B). Specifying the tag number of the carburetor would help to determine the correct throttle body gasket. Without the tag, virtually impossible without actually disassembling the carburetor to determine actual circuitry. Something that gets a LOT of rebuilders, both novice AND professional (who aren't well versed on the 4 Jet): http://www.thecarburetorshop.com/Ventedgaskets.htm Jon. Edited June 20, 2016 by carbking (see edit history) Link to comment Share on other sites More sharing options...
60FlatTop Posted June 20, 2016 Share Posted June 20, 2016 After seeing the car, I recognize THAT'S the carburetor problem that can't be fixed. I'd be willing to take it off your hands but, you know, we''ll have to allow for the problem. Bernie Link to comment Share on other sites More sharing options...
nailhead9 Posted June 20, 2016 Author Share Posted June 20, 2016 Jon@carbking: (B) Second issue? - This also happens while driving at a steady pace while going down the road. In issue (B), are you going at a steady pace then accelerating; or just driving at a constant speed with a hesitation and recovery? I am driving at a constant speed when the hesitation and recovery happen. I do not have the carb tag. Link to comment Share on other sites More sharing options...
nailhead9 Posted June 20, 2016 Author Share Posted June 20, 2016 Bernie, yes the Buick is for sale, however I intend to get the problem fix before I sell it. Matching numbers 1957 Buick Roadmaster Rivera 4-dr hardtop, low mileage car (62,650), that is all original except for a repaint many years ago, with great upholstery. Powered by Buick’s 364 ci./ 300hp. Nailhead V8, equipped with Dynaflow automatic transmission, power steering, power brakes, power front seat, power windows, power antenna, wide white wall tires, factory installed AC (needs charging, the only option available) for the 57 Buick Roadmaster and a Wonder Bar Radio that still works! This vehicle has always been well maintained and completely gone through for great touring including new transmission seals, brakes, battery, oil, lube and filter, everything that needed attention has been taken care of. Link to comment Share on other sites More sharing options...
John348 Posted June 20, 2016 Share Posted June 20, 2016 (edited) Everytime I had those symptoms it was the accelerator pump in the carb. If it was sitting awhile and with ethanol fuel I would bet on it. Even if it were rebuilt if an old pump was installed useing the old style materials it will be toast. I am far from a carb rebuilder but I have done enough of them and that was the problem. I am presuming that it idles fine, If you stomp on it does it really go flat? PS by the way I really like the car! I would not mind picking up a Buick myself just to go to the meet in a few weeks in Reading Edited June 20, 2016 by John348 (see edit history) Link to comment Share on other sites More sharing options...
carbking Posted June 20, 2016 Share Posted June 20, 2016 1 hour ago, nailhead9 said: Jon@carbking: (B) Second issue? - This also happens while driving at a steady pace while going down the road. In issue (B), are you going at a steady pace then accelerating; or just driving at a constant speed with a hesitation and recovery? I am driving at a constant speed when the hesitation and recovery happen. I do not have the carb tag. OK - this eliminates the accelerator pump as a culprit for condition (B), and makes it less likely a suspect for condition (A). When driving at a constant speed, the accelerator pump is doing nothing. My best guess for a hesitation for condition (B) would be something intermittant in the ignition system (loose wire or pulled wire in distributor, etc.) or even water in the gasoline. How old is the fuel in your fuel tank? It would not surprise me if, when you figure out the cause of condition (B) and fix it, that condition (A) disappears as well. Jon. Link to comment Share on other sites More sharing options...
60FlatTop Posted June 20, 2016 Share Posted June 20, 2016 That's a car shop joke, where the guy comes in with an untenable problem and the shop owner tells the car owners it can't be fixed but he will that the burden off his hands. I learned humor with an ironic twist from those old second rate lot dealers. I still practice the one where my Grandfather was adamant about never taking a person's last dollar. Every dollar up to that one was sure fair game, though. Back on topic, I had a 4GC that would squirt from the accelerator jet just fine on the bench, but on the running car it would hardly dribble. If I had that car back I would paint the accelerator pump well with some gas resistant paint. At steady throttle that could run the float bowl and a slightly low level. And those are float level sensitive carbs. Over time I have decided some porosity in the casting was draining the well by vacuum. Bernie Link to comment Share on other sites More sharing options...
John348 Posted June 21, 2016 Share Posted June 21, 2016 3 hours ago, carbking said: OK - this eliminates the accelerator pump as a culprit for condition (B), and makes it less likely a suspect for condition (A). When driving at a constant speed, the accelerator pump is doing nothing. My best guess for a hesitation for condition (B) would be something intermittant in the ignition system (loose wire or pulled wire in distributor, etc.) or even water in the gasoline. How old is the fuel in your fuel tank? It would not surprise me if, when you figure out the cause of condition (B) and fix it, that condition (A) disappears as well. Jon. Jon, I should have read it closer you are right. Link to comment Share on other sites More sharing options...
padgett Posted June 21, 2016 Share Posted June 21, 2016 (edited) Jon really knows carbs. Edited June 21, 2016 by padgett (see edit history) Link to comment Share on other sites More sharing options...
nailhead9 Posted June 21, 2016 Author Share Posted June 21, 2016 John348 and others, as stated the carb has just been rebuilt by Hobbs ( a carburetor expert, been in business over 30 years). They told me the accelerator pump installed at that time was made for today's gas. I have checked the accelerator pump (engine not running and get a strong steam each time. I will try it again with engine running, I am presuming that it idles fine (yes it idles very well), If you stomp on it does it really go flat? Yes! while driving if I just floor it, it dies momentarily and then takes right off. Thanks again to all who are helping solve this problem for me. Warren Link to comment Share on other sites More sharing options...
danleblanc Posted June 23, 2016 Share Posted June 23, 2016 This was a known issue on Cadillacs in 1957 also. I have a friend with a 57 Coupe de Ville who had his carburetor rebuilt 3 times and it still had the hesitation problem (his was a Rochester). He switched it out for a Carter and the problem was solved. The car now performs flawlessly. He had indicated that this was an issue known at GM as one of the Serviceman bulletins indicated that when a customer presented the hesitation issue and the car was equipped with a Rochester to check normal things first (vacuum leaks, timing, etc). If all those checked out, the carburetor was to be replaced with a Carter (not even a mention of rebuilding or adjusting the Rochester first). Perhaps this issue spilled over to Buick as well? Link to comment Share on other sites More sharing options...
John348 Posted June 23, 2016 Share Posted June 23, 2016 (edited) For my own information did the Buick's even come with Carter's? I know on the Chevrolet's the only time I ever came upon a Carter installed seemed to be with a standard transmission, as well as every Rochester was with an automatic, (61 to 58 283's , and lo perf 327's from 62-64) I never was able to find any paperwork designating it was that specific that way and had found an application number for both Rochester's and Carters for both manual and automatic transmissions, I just never had seen them installed any other way Edited June 23, 2016 by John348 (see edit history) Link to comment Share on other sites More sharing options...
nailhead9 Posted June 23, 2016 Author Share Posted June 23, 2016 John348, my 1957 Buick Chassis Service Manual list the Carter Model AFB as original equipment on these cars. Now the question is where do I find a good Crater AFB and what cfm do I need or do I just buy a new Edelbrock carburetor and what model do I buy. Thanks, also to Dan Leblanc for your input, Warren Link to comment Share on other sites More sharing options...
padgett Posted June 24, 2016 Share Posted June 24, 2016 (edited) OK "Yes! while driving if I just floor it, it dies momentarily" there are two things that can do this. The first is a weak accelerator pump but sounds like yours are OK. The second is more obscure and more common in QJs, a maladjusted air valve spring. Note figure 9 in the attached. If that is set too weak and the air valve opens too fast, you will get a bog at WOT. (Was kinda deep into carbs and FI at one point, mostly computer cars now) ps the QJ spring was externally adjustable (and many screwed it up by backing off the adjustment thinking more faster is better. Rong. The 4GC spring was not an that it even was there is not well known. If the carb was boiled out without removing the spring it could have affected it adversely. pps I think the 4GC was in the 400-500CFM range but with Carter there were small bore, large bore, and spread bore 4bbls (not going to get into the 3636) so if get a Carter need to be sure you have the right bolt pattern (back in the day most aftermarket 4bbls fit multiple bolt patterns, don't know what happened after Eidlebrock took over Carter). And that the throttle plates do not hit the manifold (see "Adapter Plates") Edited June 24, 2016 by padgett (see edit history) Link to comment Share on other sites More sharing options...
John348 Posted June 24, 2016 Share Posted June 24, 2016 3 hours ago, nailhead9 said: John348, my 1957 Buick Chassis Service Manual list the Carter Model AFB as original equipment on these cars. Now the question is where do I find a good Crater AFB and what cfm do I need or do I just buy a new Edelbrock carburetor and what model do I buy. Thanks, also to Dan Leblanc for your input, Warren I had found a guy in St Louis years ago that had a massive inventory of AFB's I have to find his contact info, I will get that for you tomorrow and forward it on. Link to comment Share on other sites More sharing options...
carbking Posted June 24, 2016 Share Posted June 24, 2016 (edited) John - in 1957, Buick used Carter 2507s. This was superceded by 2982s. If you think you must change, be patient; don't settle for a clone. If your really have no patience, check this link before buying a clone: http://www.thecarburetorshop.com/Four_barrel_mounting_flanges.htm The GENUINE Carter AFB is a great carb; but so is the Rochester 4-GC. The Rochesters were pretty much misunderstood (still are) by many mechanics. Properly adjusted, they function very well. And with the garbage being sold today as fuel, the Rochesters actually can have better in-traffic manners in 90 degree plus than the AFB. Padgett - the bulletin you posted states the auxiliary air valve spring cannot be field adjusted, IT CAN BE! There was a later bulletin, but pretty much internal only, not released to the general public. The adjustment, like most of the later Q-Jets, is 1/2 turn past touching. The spring is the same spring as used on the Q-Jets. Jon Edited June 24, 2016 by carbking (see edit history) Link to comment Share on other sites More sharing options...
padgett Posted June 24, 2016 Share Posted June 24, 2016 Thank you Jon, just grabbed my 4G(C) bulletin to show it was there. Point is if the air valve spring is loose it can cause a hesitation when floored but few know it exists. Link to comment Share on other sites More sharing options...
nailhead9 Posted June 25, 2016 Author Share Posted June 25, 2016 carbking, I will try calling you on Monday. I problem has started happening more often. I could not find any tags on the carburetor body, here are photos of the numbers stamped on body. Thank for your help, Warren Link to comment Share on other sites More sharing options...
padgett Posted June 26, 2016 Share Posted June 26, 2016 Just FYI 7010070 is for an early 57 Buick. Link to comment Share on other sites More sharing options...
nailhead9 Posted June 28, 2016 Author Share Posted June 28, 2016 padgett, thank you for the information Link to comment Share on other sites More sharing options...
carbking Posted June 28, 2016 Share Posted June 28, 2016 To keep everyone up to date: Warren just called and we had a good discussion. Warren stated the hesitation is while driving at a constant speed, almost like the engine is cutting off and then restarting. This to me eliminates the carburetor, or at least virtually so. We started talking about ignition, and the possibility of a dirty ignition switch; and Warren remembered that occasionally, when he kills the engine, there will be a faint sound from the horn, even after the ignition is turned off. I suggested to Warren to remove the ground cable so there is no circuit; then work the key in the ignition from lock to off to on and back until his arm tired then replace the ground cable and see if the issue disappears. Jon. Link to comment Share on other sites More sharing options...
carbking Posted June 28, 2016 Share Posted June 28, 2016 On 6/23/2016 at 10:37 PM, padgett said: Thank you Jon, just grabbed my 4G(C) bulletin to show it was there. Point is if the air valve spring is loose it can cause a hesitation when floored but few know it exists. Absolutely, and since the spring is mild steel, they do tend to fatigue after 50 years or so. Of course, so do we When we were still restoring carbs; replacing this spring and installing the "turn" bushing in the bowl/airhorn vacuum passage were always done. Jon. Link to comment Share on other sites More sharing options...
60FlatTop Posted June 28, 2016 Share Posted June 28, 2016 I wonder if the key gets hot. You don't touch it for long when you shut the car off but I have felt some pretty warm ones. Bernie Link to comment Share on other sites More sharing options...
nailhead9 Posted June 29, 2016 Author Share Posted June 29, 2016 Thank you again Jon for taking the time to help me solve this problem, it was a very informative conversation and I will work on the ignition switch today. Bernie, thank you for your help as well. I have never noticed the the ignition key being even slightly warm when turning off the engine. There is a very soft horn sound when turning the key from on to either off or lock. Warren Link to comment Share on other sites More sharing options...
nailhead9 Posted July 3, 2016 Author Share Posted July 3, 2016 Jon, I have tried switching the ignition key on/off about 400 times (battery disconnected) with no change, the car still has a hesitation. Bernie, I have been watching the amp meter (and other gauges) to see if when I have a hesitation there is any indication of electrical failure, there is not. Link to comment Share on other sites More sharing options...
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