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Veteran
Posts: 142
 
Location: Alabama | Freshly built 318 in my 58 Plymouth with dual quads. if you try to floor it, it stumbles and hesitates. any ideas of what is wrong? even just running 1 carb.
Thanks |
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Expert
Posts: 2003
Location: Branson, MO | Timing advance? Camshaft?
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Veteran
Posts: 142
Location: Alabama | I don't have the vacuum advance hooked up, could that be it? |
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Expert
Posts: 1740
 
Location: Alaska | It could be the vacumn advance but most likely not as it would be mostly retarded as soon as the throttle is wide open, just like being disconnected. Does it also backfire through the carb. (too lean)? Make sure your accelerator pump is adjusted correctly. |
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Veteran
Posts: 142
Location: Alabama | It does not backfire at all. it runs great until you floor it. I disconnected the front carb, and just ran on the rear one, and as long as you are in high RPM's it will eventually clear up and go, but not with both carbs hooked up. I thought maybe it needed smaller jets, like it was choking out, but I do not know enough about these carbs, to determine that. As far as the acc. pump goes, it has 3 different holes to put the little linkage into, and I have it in the middle one, but not sure that is right either. |
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Expert
Posts: 2003
Location: Branson, MO | OK, from experience here - I had a 1969 Dodge Charger with a 383 engine. The factory engine had a 2 barrel carburetor. I put an Edelbrock 4 barrel carb with a factory intake on the car and the engine ran fine but bogged under hard acceleration and when some engine RPMs worked up, it performed somewhat better but still didn't seem to have the "pull" I thought it should.
I learned the stock 2 barrel camshaft did not have the performance lift, overlap, etc. required for a higher performance engine. I put in a Sig Erson hydraulic street cam in and advanced the spark as high as I could until spark knock was just starting to come in under load and full throttle acceleration. This was roughly 10 degrees advance. The 4 barrel carb was a 650cfm if I remember right and I played with it based on recommended carb settings until I got the best performance I could manage which turned out to be fantastic. Pulled RPMs quick from a standing start and continued to pull like a banshee all the way to redline in all gears (Torqueflite) with 3.23:1 rear end ratio. I was running through the mufflers with "shorty" headers.
I'm not sure what you have other than a 318 with 2 fours but take the above info and try it if it's in the cards.
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Veteran
Posts: 142
Location: Alabama | I had Racer Brown make a camshaft for this car, based on the Fury specs. 318 with 2 fours, for a 1958 Plymouth. |
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Expert
Posts: 2003
Location: Branson, MO | 58Ply - 2016-07-21 12:18 PM
I had Racer Brown make a camshaft for this car, based on the Fury specs. 318 with 2 fours, for a 1958 Plymouth.
Cam should be OK then. Timing? What ignition system are you using? I was still using a single point stock distributor in my Charger but an electronic would be better.
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Veteran
Posts: 142
Location: Alabama | Yes, I am using single point distr., but had plans to put a Pertronixs module in it. Think that might be the problem? |
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Elite Veteran
Posts: 782
Location: Edmonton, Alberta | Out of curiosity, did you replace the accelerator pumps in both carbs? The electronic ignition isn't a bad idea, but remember these cars came with points ignition, so I wouldn't change to electronic solely to address thus issue
. IIRC, the position you have the accelerator pump is correct, but for fun, I'd try it on the bottom hole just to see what happens.
What your describing is a very similar problem to my buddy Jeff's DeSoto, but he has a single 4bbl. We're pretty sure its accelerator pump issues. They aren't that costly and are available through Mikes Carburetor Parts. Just Bing that name and you'll find his site.
Oh...almost forgot. Check your points gap. Check the manual....I think it should be be 18 thousandth, but verify that. That may help as well. If you have a dwell meter, hook that up. Again, verify with the manual, but I think you need to be somewhere between 26 to 32 degrees.
Edited by sconut1 2016-07-21 4:55 PM
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Expert
Posts: 2003
Location: Branson, MO | 58Ply - 2016-07-21 3:19 PM
Yes, I am using single point distr., but had plans to put a Pertronixs module in it. Think that might be the problem?
No, I don't think it's "the" problem. Again, from my experience my engine bogging was cured without changing from a single point distributor. I am just saying that electronic ignition is "all around" better.
I never had any backfiring, stumbling, stalling, or anything but a bog during hard acceleration which the different cam and timing cured after switching to a four barrel carb. I surmised that I was dumping more fuel through the larger carb than the engine could properly handle and from the results of my changes, I believe I was correct. I didn't change anything else in or on the engine like heads, pistons, valves, etc. I did install shorty headers but only after the cam and timing changes were made and the headers had no noticeable effect, but probably offered a little more exhaust flow efficiency.
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Elite Veteran
Posts: 769
Location: Oley, PA | Does the hesitation occur instantly when you floor it? Or is there a slight delay, then it bogs?
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Veteran
Posts: 142
Location: Alabama | it is at half throttle on, and I did rebuild both carbs, so everything in them is brand new
Edited by 58Ply 2016-07-22 8:51 AM
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Expert
Posts: 2003
Location: Branson, MO | 58Ply - 2016-07-22 7:49 AM
it is at half throttle on, and I did rebuild both carbs, so everything in them is brand new
If that's the case, it appears that your bog comes right at the time the secondaries are kicking in. Which gives me the idea that they are dumping more fuel than the engine can properly handle. This is what I experienced with my '69 Charger - when the secondaries opened that's what triggered the bog. Keep in mind the secondaries are larger than the primaries on four barrel carbs and theoretically much more fuel is "dumped" along with more air when opened and the engine just can't take it. New cam and timing change (spark advance) fixed that.
Here's another experience I had back in 1962. I had a factory fresh '62 Plymouth Fury convertible with a 361 4-barrel. I was beat in a drag race by a '58 Chevy 348 Impala convertible and it ticked me off. I found a 2 four barrel manifold and carb set-up and installed it without doing anything else other than timing and carb adjustments. Wow - what a difference! But then I discovered the rear carb was only opening the primaries and the secondaries remained completely closed - did not have the linkage set properly. Ah, Ha! I fixed that and thought the car would really fly - but no - engine bog. The car ran better on 6 barrels than 8. Too much fuel and air. What did I do? Went back to the single 4, never looked back, and never raced that '58 Chevy again either. Yeah, I'm still ticked off that I got beat by that Chevy - never expected that from a 348 "Heavy" (big ol' tub of dung) Chevy!
Edited by Viper Guy 2016-07-22 5:55 PM
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Expert
Posts: 1493
Location: Jamaica Plain, MA | Viper is right. Have a look into the second carb. It could be a few things. I actually expect an over lean mix like a bad accelerator pump. There is a really easy way to check. Bolt off a line, have a buddy watch your exhaust. When the secondaries kick in, black smoke will pour out, if it's too rich. It it pops and loses power, it's too lean. Also, smashing the pedal isn't always the best was to jump. Ride the joule/kilowatt/hour curve. Racing a car in a straight line isn't just jamming your foot down and not hitting anything. You gotta know your motor. SHe has a personality. |
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Expert
Posts: 3777
Location: NorCal | sconut1 - 2016-07-21 1:34 PM
Out of curiosity, did you replace the accelerator pumps in both carbs?
Not only replace but verify that they're working? |
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Veteran
Posts: 142
Location: Alabama | Could putting smaller jets in, fix the problem? |
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Expert
Posts: 2003
Location: Branson, MO | 58Ply - 2016-07-25 7:50 AM
Could putting smaller jets in, fix the problem?
Might help but all you can do is try.
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Expert
Posts: 3777
Location: NorCal |
58Ply - 2016-07-25 5:50 AM
Could putting smaller jets in, fix the problem?
Only if you can verify that the bog is caused by an over-rich condition. The bog could be caused by a lean condition; have you checked the operation of the accelerator pumps as advised? |
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Veteran
Posts: 142
Location: Alabama | Ok, I have strong streams of fuel squirting into the primarys on both carbs. should I be seeing something squirting into the secondarys also, because I didn't? not sure if these carbs work that way. |
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Expert
Posts: 2003
Location: Branson, MO | I don't believe you will see the gasoline squirting from the secondaries as they only open after the primaries and I believe it's all up to the jets in the secondaries. The streams you see in the primary section are from the accelerator pump and there isn't one for the secondaries.
Edited by Viper Guy 2016-07-27 10:51 AM
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Veteran
Posts: 142
Location: Alabama | So what do I do now? |
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Veteran
Posts: 174
Location: Camptown PA | Sounds like you have too much carb. Take it for a ride - kick in the 4 barrels. Take it home pull a plug - if the plug is black and wet you have a rich condition and need either smaller jets or smaller carbs. Are the carbs on it the stock carbs that were available for that engine package? Do you know their CFM rating? Did you build the engine to stock specs or did you improve the heads and cam? A stock 318 will have trouble using much more than 675 CFM total - anymore than that will cause it to run rich and bog down. |
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Expert
Posts: 2003
Location: Branson, MO | 58Ply - 2016-07-27 12:02 PM
So what do I do now?
Have you checked the timing? Is it set at 10 degrees BTC (advance)? Is the point gap at approximately .018 inch? If so and you are not getting any spark knock, advance the timing to 12 degrees BTC and see if there is any improvement - keep going until you hear spark knock or "pinging" under hard acceleration and go no farther. In fact you should back off a little to where there is little or no spark knock. Set the timing with the vacuum advance disconnected and plugged off and reconnect after the timing is set.
If none of this works and you are still getting the bog without any type of improvement, check with Racer Brown and ask if they have carburetor recommendations/size/settings, etc. to go with your cam in your engine. They may be able to suggest jet sizes in both the primaries and secondaries. Ask about any recommendation regarding advancing the cam with respect to the crank. This is done with an offset bushing in the cam sprocket. Advancing the cam gives quicker acceleration and retarding the cam gives more top end.
If anyone else has suggestions, they may be better than what I have said. I'm going strictly from my drag racing days back in the '60s in stock NHRA classes which required stock ignition systems, stock carburetors, stock cams, etc. but we were able to adjust and re-size the "innards" to whatever worked best for us.
Good luck!
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Expert
Posts: 3034
Location: N.W. Fla. | As Phatton said, You have dual quads, but what dual quads, how much total CFM?, are you set up with progressive or non-progressive linkage? Is the linkage dialed in right, and the carbs set up correctly for 2X4s? |
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Veteran
Posts: 142
Location: Alabama | It will bog, just with one carb running, unless I am into high RPM's. the carbs are 62 wcfb's |
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Expert
Posts: 1740
Location: Alaska | Here is one more thought, you are using almost 60 year old carbs. Did you have them rebuilt? Are you sure that none of the internal passages aren't plugged? |
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Veteran
Posts: 142
Location: Alabama | I rebuilt them myself |
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Veteran
Posts: 142
Location: Alabama | I think they might need smaller jets |
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Expert
Posts: 4042
Location: Connecticut | 58Ply - 2016-07-28 1:57 PM It will bog, just with one carb running, unless I am into high RPM's. the carbs are 62 wcfb's WCFBs were not used after '58. If they are from '62, they are AFBs. Ron |
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Veteran
Posts: 142
Location: Alabama | they are most definetly WCFB's. These are Chevrolet carbs, which they used, up to 1965. |
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Elite Veteran
Posts: 888
Location: Peoples Republic of Oregon | Check with these guys: http://www.thecarburetorshop.com |
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Veteran
Posts: 142
Location: Alabama | ok. talked to the man at the carb shop. he said the carbs are too big, which causes it to pull more air and less fuel, so I have a lean condition. he said these carbs are 500's, and I need 380's. wonder if I could make restrictor plates, and that would fix the carbs I have? |
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Expert
Posts: 2003
Location: Branson, MO | 58Ply - 2016-08-18 4:50 PM
ok. talked to the man at the carb shop. he said the carbs are too big, which causes it to pull more air and less fuel, so I have a lean condition. he said these carbs are 500's, and I need 380's. wonder if I could make restrictor plates, and that would fix the carbs I have?
I'm not too sure I'd trust your carb guy - sounds like hogwash to me. I may be wrong but I have never heard of a 380 four barrel carb assuming he's referring to CFM.
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Elite Veteran
Posts: 1115
Location: CA | Weren't the factory dual quad set-ups made to run 2 500 cfm carbs? |
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Expert
Posts: 3396
Location: Chestertown, NY ( near Lake George) | I believe the original Wcfb carb was 450 cfm. |
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Elite Veteran
Posts: 888
Location: Peoples Republic of Oregon | There is a lot of rumor but no real facts regarding the CFM ratings of early carbs. I do believe that Holley started the numbers game in the late 60's and Carter followed suite.
You can compare throttle and venturi size to a known sized carb and maybe be close.
Keep in mind when your using DUAL carbs with 8 venturies they effectively reduce the engine created vacuum under each carb significantly, compared to the same size single carb on the same engine, so a carb rated at 500cfm as a single carb probably flows less than 350cfm as a twin carb, if your new to dual quad set-ups your going to be thinking 2 500cfm carbs equals 1000cfm, in reality your looking at about 700cfm-750cfm , and two 600cfm carbs flow about 800-850cfm due to the reduced vacuum signal under each carb.
I've used both sizes and got good results from both. the 500cfm might be easier to tune for most applications but either will work.
Consider that 4 barrel carbs are rated at 1.5" of vacuum so doubling the available number of venturies from 4 to 8 effectively reduces the vacuum by at least 40% thus each carb will flow less air thru each venturi, while a single 500 cfm rated carb flows 500 cfm at 1.5 inches of vacuum it is only flowing about 365 cfm at a bit less than half the draw, like it would see in a dual quad setup at W.O.T.
I see no reason, assuming that everything else is working proper, for your carbs to not work if they are well adjusted on progressive linkage. I have had/seen many 1x4 setups produce a bog when the secondary's are opened at too low of rpm and adjusting timing has helped; opening too early simply creates a loss of vacuum and timing suffers. |
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Extreme Veteran
Posts: 360
| I think you have too much carb for that engine. Use this formula and you can assume 100% efficiency for the heck of it and see you have too much carb. Also accelerator pump + correctly adjusted spring should give you a nice squirt of fuel when you hit the pedal.
318 x 5500 / 3456 = 506 (you can multiple this result by what you think the volumetric efficiency is which is not likely 1. more likely between .7 and .9. It is Safe to assume 500cfm will be plenty for your engine. Race tuned engines will achieve more than 100% efficiency so a bigger carb will be used.
The formula is as follows
Cubic inches x max rpm / 3456. 3456 is a constant for 4 cycle engines. It is the number of cubic inches in a cubic foot multiplied by 2 since the crank has to spin 2 full revolutions in a 4 cycle engine to reopen the intake valve. This causes the final number
of cfm to be smaller. In a 2 cycle engine you would use 1728 since the crank is spinning 1 full rotation to reopen the intake valve and in turn causing the cfm need to be greater. 1 cubic foot = 12 x 12 x12 =1728 cubic inches (2 cycle) 12x12x12 x 2=3456(4 cycle)
We have to use 3456 in order to get from inches to feet in the final result. For you metric guys the formula will be a little different but similar approach depending on what is being converted. |
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Expert
Posts: 3777
Location: NorCal | 58Ply - 2016-08-18 5:55 AM
they are most definetly WCFB's. These are Chevrolet carbs, which they used, up to 1965.
WCFB's on a '65 Chebby? Have to be Corvette.
Edited by 57chizler 2016-08-19 3:24 PM
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Elite Veteran
Posts: 888
Location: Peoples Republic of Oregon | Yeah, shiverlay was still using WCFB in 1965, and not just on a Corvette. Go figure. |
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Elite Veteran
Posts: 1115
Location: CA | So if the cam and and everything in the motor is right. can they be re-jetted or would finding correct 57-58 mopar dual wcfbs be the right answer? The original factory set-ups worked without bogging down... |
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Expert
Posts: 2003
Location: Branson, MO | Finsinthemirror - 2016-08-20 3:34 PM
So if the cam and and everything in the motor is right. can they be re-jetted or would finding correct 57-58 mopar dual wcfbs be the right answer? The original factory set-ups worked without bogging down...
The answer is "yes" and "yes". There has got to be a way to eliminate the bogging and should be able to be accomplished if everything else is "right".
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Expert
Posts: 1530
Location: ZH, Switzerland | Finsinthemirror - 2016-08-19 10:34 PM So if the cam and and everything in the motor is right. can they be re-jetted or would finding correct 57-58 mopar dual wcfbs be the right answer? The original factory set-ups worked without bogging down... After I read the full thread I came to the carburetor shop LLC and read the general informtion. There is a good essay about using a chebby V8 AFB on a Puntiac V8. It's because the (weighted) air valve for the secondary doesn't fit the fuel requirement curveof the Puntiac the Puntiac V8 shows hesitations and boging while he secondaries kick in. In my opinion the best is to get a pair of 1958 Plymouth WCFB. It's because some WCFB had vacuum controlled secondaries and others weighted air valves. The WCFB in e.g. my 1956 NY has vacuum controlled secondaries and is working perfect with my 354 Fire Power (original, factory set up). God luck! Dieter |
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Veteran
Posts: 142
Location: Alabama | I tried to find the original carbs, and they are stupid expensive, if you can even find them. i thought the carbs i had were so close, that they would work. really wished i could do something to make these work. |
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Extreme Veteran
Posts: 444
Location: North of the 49th | Hi
Do you have the Carb numbers? Perhaps I can do a spec comparison to see how far your carbs are away from the orig 58's WCFB's were never large carbs to begin with.... |
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Veteran
Posts: 142
Location: Alabama | is it on that little triangle aluminum tag? |
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Veteran
Posts: 142
Location: Alabama | 3697-5 3846247 B4. info on that tag |
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Veteran
Posts: 142
Location: Alabama | Any info please? |
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Expert
Posts: 3777
Location: NorCal |
Carburetor, WCFB 3697S GM 3846247 327/350 w/MT 1965
 (3846247.jpg)
Attachments
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 3846247.jpg (133KB - 175 downloads)
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Veteran
Posts: 142
Location: Alabama | What CFM are these? |
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Expert 5K+
Posts: 8443
Location: Perth Australia | Let me save your pain (or join in it)
I believe you have the same problem I have
Mine is a fully rebuilt 318, pistons are 40 up on stock, so the engines actually a bit bigger, I had a cam ground specifically for the 2x4 setup (cant remember the numbers, but its not "lumpy"), I also am running electronic ignition, advanced until its just under pinging
It has 2x 500 edelbrocks (brand new), 1 with an electric choke, 1 manual thats wired open (only need to choke 1 carb) and the throttle is set to operate both carbs the same
I have not messed around with the jetting yet, but I have tried staged linking the carbs, I have shifted the accelerator pump linkage in both carbs through all 3 holes a couple of times, tried without the air cleaner and have improved it, but not cured it by a long way, but one thing that did make a big difference was adjusting the kickdown.
Mine loves revs, once its up there, it goes fine, its just crap off the line and I am actually putting it down to loss of vacuum, but I have not tested that yet (havnt got around to it) but try putting a vacuum gauge in the car and go out and test it.
I cant offer much more than that, but I am watching 
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Extreme Veteran
Posts: 494
Location: Alberta | You have to first ensure the carb jets are the same size and then calibrate the carbs by vacuum demand vs fuel demand, both carbs should read the same[balanced] assuming the carb linkages are set properly.If your running an automatic you may have reduce the torque convertor pressure to achieve vacuum vs fuel demands. Check out YOUTUBE for vacuum/fuel calibration you may find it useful. You may be experiencing some fuel supply pressure drop. Anyway that's my 2 bits worth of info I like I always say "If I can't explain the subject matter well enough for Gramma to understand then I don't know the subject" |
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Extreme Veteran
Posts: 520
Location: Colorado Springs, Colorado | 2x4's are tough, look for a local shop with a dyno and an anaylizer and come with a nice assortment of Jets/rods for the carbs. You need to spend some serious time tuning those carbs in. You would need to do this even with the plymouth carbs. I'm going to be doing the same on my 392 even with a single carb. There is no magic bullet to fix your issue, just tuning that needs to be done. |
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Extreme Veteran
Posts: 494
Location: Alberta | I'm very interested in this topic as I intend to set up my old 354 hemi with the Dual 4bbls using the original LOG intake set up I've was fortunate enough to get my hands. So much good info shared here and in my research has found similar advantages/disadvantages to dual carb set ups.I'm using 2/4bbl original WCFB 2314's I'm leaving the old Hemi as is [stock] so I was wondering what problems the Dual 4bbl setup would cause. First was matching up the carbs I had one and fortunate to find number 2. I'm assuming that 58ply you have done you're homework too. somethings I found so far were 1} factory spec timing is just that your engine is a [ 1 of ] so assuming the cam you put in according the marks on the gears are lined up correctly on install 2) TDC marks were checked to be correct [ Remove the # 1 spark plug and place a dial indicator in the cylinder in indicate the piston at TDC by turning the engine over of coarse,now check the timing marks [piston should be at maximum height in cylinder] you may find that you have 4-6 or > degrees manual advance that can be used. Now readjust your distributor vacuum advance settings if you haven't done this already. 2) Ensure your coil is providing full power at max RPM. 3) Check the operating carbs now using your vac gauge If this indicates some discrepancies you have to balance the carbs first. Now assuming this is all correct and the problem still persists You to have establish proper intake pressures vs exhaust pressures. The cam has changed the operation of your engine. Your valve dwell and overlap and valve size are in play here. Scavenging in the cylinder occurs and are asset for higher performance up to a certain point[valve overlap] then it becomes a disadvantage as in retards the ignition in the cylinder after that. Assuming that's correct. Direct your attention to your exhaust this has to meet the demands of your engine, the back pressure may be to high or not heated enough[ tune exhaust practises] can be a crap shoot. All the information shared by the other members here should have given you improved performance. One question is this an automatic or a standard tranny behind this 318, the automatic also influences vacuum demand the same as your power brake booster would. I'm learning from others experience so as stated here I'm assuming that everything I've mentioned has been done. I get the same feeling from setting on a warm toilet seat LOL I keep reading here for follow up results Thanks Guys. Last minute research from the manual.
CARTER WCFB CARBURETOR
DUAL INSTALLATION
GENERAL DESCRIPTION AND OPERATION
The Carter carburetors used on engines with dual four barrel carburetors
differ from those used on single four barrel carburetor
equipped engines. An additional set of throttle valves is incorpo -
rated in the secondary bores of each carburetor to give better
performance at lower speeds. Also, a new form of idle adjustment
Is made through the use of an idle by- pass screw which replaces
the idle speed screw.
Edited by RUSTORICHES 2017-01-20 6:34 PM
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Extreme Veteran
Posts: 409
Location: Tampa, Florida | Back in the dark ages (1976), I drove my Fury (318) 2 X 4 carbs from Tampa to Tulsa for the NSRA "Street Machine Nationals".
I rebuilt the carbs before going and I experienced similar problems to yours.
After narrowing the problem to the rear carburetor ( original WCFB), I found that the "T" shaped piece of metal that the metering rods hang on, was slightly bowed. It would stick and the metering rods would not function properly.
I straightened it and the car ran fine after that. (My hiway mileage improved from 9 mpg to 11 mpg also) |
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