I had a vacuum leak for (apparently) some time with the 292 in my coupe. I didn't know for about 3 years. When I initially bought the car I put on a brand new Holley 600 (1850-?) and was KIND of surprised that I had to jet up a couple of sizes (from 66 to 68) from out of the box. it would also backfire when I "blipped" the throttle to downshift so I upsized the accelerator pump nozzles. It ran well enough. Late season last year I realized it was leaking where one of the runners went into the head. I replaced the intake with one I opened up a little and put it all back together. When I started driving it again a month ago, I would go to pull away from a stop light it bucked. If I give it a lot more throttle it eventually catches up takes off. I was thinking it was rich because I could smell gasoline even under soft acceleration. I went down to 66 jets and put the .031 acc. pump discharge nozzle back in (I used the ones with the tubes). It was definitely better...seemed like the stumble was lower in the RPM range- maybe 2200ish RPM when I "stabbed" the accelerator. I put 64 jets in, and still seems better...the bog seems largely to be down under 2000 RPMs. When I "blip" the throttle to down shift, it almost "hiccups." There's no hiccup when you just sit at a stoplight and rev it. If not for that odd "hiccup" on the downshift blip, I'd say I would put in the next size down acc. pump nozzle. COULD it be a problem with my coil? I replaced the coil around the same time. My tach needle was jumping around a bit and I thought maybe a new coil would help. It has a Pertronix Ignitor 1 and a flame thrower (the 1.5 ohm model, like the Ignitor 1 is supposed to use). Any thoughts?
Have you checked the clearances on the accelerator pump arm to make sure there's no gap? I think the 64 jet size is what the 600cfm Holleys had originally, but not sure about what size nozzles they were? I want to say they were 28's, but would need to check for sure.
Acc. Pump arm is good. I got those numbers for jets and nozzle from the Holley List, so assuming I followed the correct line across, it should have been 66 and .031. I was surprised to see that 66 was the jet size…like you, I had 64 in my head. To confirm, i had extra 66 and .031 in my spare kit.
Is it rich at idle? The .31 discharge nozzle is stock and should be good. Is the backfire through the carb or exhaust? They say that the majority of carburetor issues are actually ignition problems, so it could be the coil, or timing. Rich at idle could be float adjustments, popping out the exhaust could be lean idle adjustment.
I don't know what's going on! I got the car 4 years ago and from reading plugs I jetted up to 68s. I still had that backfire (I think it was a carb backfire) when blipping the throttle to downshift. I went up to .035 nozzle and it was good. Late in the season last year I realized that the vacuum leak was bad enough for me to hear a whistle while driving...Not wanting deal with it during cruising season, I gooped some Right Stuff on there and put it on the back burner. Early spring I took the intake off and replaced gaskets and put on a different intake that I did a half-hearted port job on...smoothed the bottom edges around the carb ports to straighten out the air a bit...nothing crazy. I put it all back together and I don't even remember if I drove it right away or not. An unrelated issue, the tachometer needle would dance around so I figured I'd throw a new Flame Thrower coil on it, since the signal comes from the coil. I don't know if THAT has anything to do with it and I don't know if I did that before the problem started. A few weeks ago I took a short ride to run an errand and don't remember anything wrong. I got back in and drove a couple miles to grab a bite and it was difficult pulling away from lights. To the point where I was afraid someone would rear-end me because it was bucking. It always initially feels better but once it's hot the stumble SEEMS to get worse...Can there be a problem with this coil when it heats up? The problem is THERE when it's cool, but feels worse when the engine is at operating temp...I THINK.
I started down the bad coil rabbit hole and I'm going to try a new one tomorrow. Wouldn't that be funny? I'll post back. Thanks.
@Deyomatic ,asking 292 straight 6 ? 600 ,cfm 2 barrel ? 4 Barrel Vac sec? 4 barrel mech ? Really does not mater , each carb you would tune a little different But function the same way. Just throwing Ideals out their, To start with , Looking @ plugs on pump gas with Ethanol is not like gas blends of over 20 or so years ago . Just to give a ideal what I mean , look @ Modern new vehicles tailpipes, Computer control tail pipes black, so going to up jetting Not because plugs looked Lean , More likely Jetting up was because of air Leak . Are you aware of functions of carburetor, as in Transfer slot Power Vale Emulsion tubes Accelerator pump, Accelerator pump cam Air bleeds Squirter's Enrichment screws Idle ,cruise , wot Just asking to help you diagnose your problem. Your static Timing , & Total Your typical engine is going to like 15 degs of initial or even up to 22 ish Over stock Shop spec , Total 30- 45 , Rpms , 500-1,000 ish Not set in stone the Rpm @ idle Heat range & gap's . Use A Vac gauge will help , tune tool A wide band O2 will get you there faster & tell you more what going on with Fuel & afr , Jetting , and a different circuit of the carburetor. it's a tool that can be removed, tune tool . Plug gap Intake temps , to base of carb, hot or boiling of gas , Quality of tach , for bouncing, slow or ect ,
Must all areas have been discussed , one that I always try is turn the mixture screws in and out , change or no change . No change I usually look into a new power valve . The transfer slot is a big issue as stated . A large cam normally causes the blades to be above the slot . Only way I have had any luck fixing this issue is drill a super small hole in the primary blades it will allow them to closed to where they need to be below the slot . Just my 2 cents
Probably a ridiculous question but just in case…….. is the (-) terminal of the coil going to the distributor?
I slapped a new coil in there and it behaves the same. I think the 64 jets are good but now I don’t know about going down to 28 with the pump nozzles. That is probably my next step. I had my young assistant, take a video of my foot, my tachometer, and a vacuum gauge today. I just have no way of hosting that video anywhere. The vacuum drops immediately to near zero when I stab the throttle It seems to be under 2000 RPMs. Maybe a little higher. But above that, there’s no stumble.
This time of year is the worst for boiling fuel, you still have winter blend at the pumps but spring time temps are here and the butane in the winter blend fuel will allow it to boil like mad just barely warm. A phenolic carb spacer makes a big difference, Summit has one at 1/4" thick and it works great. Take a vacuum reading at idle, and divide by 2 to get the proper power valve value needed, for example you get 13 hg at idle, you install a 6.5hg power valve. Set the floats so you have to nudge the fenders to get fuel to trickle out of the sight plug.
Update… I have a 1 inch final spacer in there, and it’s had one on there for years. My idle vacuum is 15, I’ve got a 6.5 power valve in there now. Could it be a bad power valve? That one would have been original, and with the vacuum leak I changed it and put a different one in there. I’m wondering if it ever backfired before even though it’s a new carburetor, it is supposed to be protected from that. Maybe the 6.5 is no good anymore. Even still, 7.5 to 6.5 doesn’t seem like it would be this much Of a difference to make it stumble. Anyway, the update. I put the .028 nozzle in and it still stumbles. Leaning it out in whatever way, has definitely helped. It’s totally drivable unless I stab the throttle pedal. When the problem first happened, it would stumble and stutter just getting going. I shot around the intake and carburetor today with some brake clean and there are no leaks. A local guru suggested I check the timing. I haven’t touched that in forever. It should be still set to 37 total. It’s an older Mallory distributor with a first series pertronix igniter. I’m starting to wonder if maybe that igniter is the culprit. There is no vacuum advance. I will check the timing again.
Your combo is not OEM now , Total Timing is Total , 34-39 ish whats the Static @ Idle , ? Timing curve ? 15-20 deg @ idle needed . Yes power valve could be blown from back fire , to test suck on it . Did you check transfer slot ? If No miss under load , more likely no problem with Distributor , just needs to be tuned /adjusted correct , Air / Fuel & Timing
I last set the total timing to 37 a couple years ago. I never loosened anything but I will reverify that. I never checked the static timing at idle…until whatever is wrong now, it always ran great. I will look into the transfer slot.
292 FORD...right ?! Give that distributor a good yank and put more timing in it ! 37* means NOTHING anymore with this horrible fuel we are forced to burn. Put hi-test gas in it....keep advancing the timing until it rattles when going up a hill (in top gear) at a low speed. Sorta lugging the engine down........ Then back off the timing a couple degrees and see if the rattle goes away ! Make sure your battery can spin it over good when the engine is hot and you try to crank it. (BEST to use a piston stop and find/verify TDC and mark it on your balancer..to begin with.) Use a timing tape (on the balancer) so you can read what the timing advance curve is doing... Let us know what happens 6sally6 PS IF it still bucks and pops...THEN go back to playing with your carb....
It sure sounds like a misfire check your wires and plugs do you have points or electronic if points check them for ware or adjustment if electronic check the pickup.
I played around a bit today… Total timing is right around 37. It was weird- I had a neighbor hold it at 3500 and the scale wasn’t there so I had to retard the timing to get it to show up. Then it started hard and drove like garbage…I had wifey hold it at 3000 and advanced it to 37 and it feels great…except for this one specific stumble. I checked resistance on all my plug wires and they’re all the same- 0.6 or .06 on the 200 scale. Whatever that means. Point being they’re all the same, so they can’t ALL be bad. Is there a test for the Pertronix Ignitor? The last one I had just died completely, so I don’t think it’s that. I really think it’s carburetor related. Should I start messing with accelerator pump cams? I have a video but I don’t think I can post it here, and I don’t have anywhere else to post it.
@Deyomatic , Total is one part of timing What is your timing BTC @ idle , If to low it can cause a stumble , OEM spec are outdated for Modern Pump gas blends,, Most every gas engine from early teens to 1991 will like 15 - 20 degs of initial timing BTC , Wants you find what your engine likes , Then you dial in your TOTAL usually starting around 3,000 rpms . Its called a "Timing Curve " If your engine isn't good shape the problems you are describing are more likely timing and fuel related that needs to be " Tuned"" There is cases that can get the internals of the distributor out of phase Relationship to distributor cap poles , the rotor button and also the rector Wheel, that triggers the spark / firing of Points , Electronic ignition . There is other parts inside Any distributors that most do not know of or how to time these components /parts . More in death than then most typical people realize,
Just a high level recap… Unless something inside the distributor broke, the only logical conclusion for me to come to and focus on is that the air or fuel part of this equation is messed up. I now have brand new plugs, and the wires seem to check out good… I changed the intake with one that has been opened up a little bit…in the process, I sealed up the vacuum leaks… Now this stumble shows up and as I jet down and lean out accelerator pump nozzle it drives better.
Deyo, you are not alone. 40 year old carb build of various bits and peices, some adjusting and was fine till two years ago when power valve got tired. General rebuild, not changing anything but new pwr valve & gaskets and the running good did not come back. In the course of mucking around I did new points, condenser and wires/coil. Following thread.
Going back & reading your post , Starting after intake replaced Low RPM buck/ backfire / miss , hesitation , Is from Idle to Cruse , Causes to look @ Timing from Idle to 2,500 ish or So BTC , Accelerator pump , & adjustment Accelerator circuit fuel from Bowl to Squirter, Squirter Transfer slot A/F adjustment PV circuit From Idle to cruse No matter if lite on throttle , Still goes from Idle , cruse to WOT all 3 circuits .
I can drive this “normally” now (not trying to win a race) - it only happens when I stab the throttle pedal at or under 2000 rpms. if I stab it at say…2500 there’s no stumble. I don’t know if this means anything but that’s mostly in second gear now. Today I was testing it in 3rd gear. Much less noticeable…if at all. Should I drop down to 0.025 nozzle? I’m getting really tired of taking this off to mess with nozzles!
Timing Tape would solve this ^^^^^^ and remove the guess-work . OP never said what kind of stuff he had in the engine.... After market heads usually need LESS total timing as the stockers..... "That thang gotta cam in it ?!" ALL important issues I think 6sally6
I have one of those timing lights that you set the advance on and then you line up the 0 mark. Engine wise- nothing special. Late 50s Fairlane 292 with the coveted “ECZ-G” heads…I think the cam is stock. It’s not a powerhouse!
I’m going to chime in. You have a good timing light apparently. Watch your timing curve. You mentioned you have no vacuum advance, so you don’t have to worry about timing drop back. You mention 37 degrees total, which sounds in the ball park, if your marks are correct. Different engines can require a little more or a little less timing . Watch how your timing moves , where it starts and how smooth it moves up to 37 degrees total. It could be sticking and jumping around eradicably. Also confirm that your timing mark are correct. Bones
I had to do a rebuild on my Demon 750 (glorified Holley double pumper before Holley bought the company) and I thought I would downsize the jets to save at the pump (right). I put 74's up front and 81's in the back (no rear PV so a big spread), 7.5 PV up front and 35 nozzles and 30cc pumps. Ran...ok. Stumble like you are talking about even after adjusting both accelerator pumps to .010 and down significantly on power! No fun! . I took it back off and put the 81's back in the front and the 88's back in the back, no other changes, runs like it is possessed by the devil "herself". 8 MPG but those are a fun 8 miles. I added a 1/4" phenolic spacer, turned the four corner metering screws out one and 3/4's. Holds a nice 750 idle. I am not a tuner but sometimes they just need more juice.
I just chanced over this . If I’m thinking correctly and it’s a 292 or 312 only advance is by vacuum . Sorry to jump into this in the middle . My back is screamin and it’s late . Just thinkin aloud
Nobody has mentioned that a 600 is kind of a big carb for a 292? That 292 would scream with a high flowing 2bbl...
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