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Make sure he knows you have a week vacuum signal, 9-10Hg. That makes a significant difference on the primary circuit and part throttle tune. The fact it pulled after the secondaries opened is encouraging.
Does John customize and install the "third screw"...power piston adjustment. Look into that. That is next level QJet tuning.
Now that its ideling OK can you adjust the timing and A/F screws to obtain anything higher that 10Hg?
1) Wideband oxygen sensor to tell you whether the carb is rich or lean at idle, part throttle & WOT. When you can see it real time on the road, it’s world of difference.
2) Progression Ignitions Bluetooth HEI distributor to get you away from less precise (and factory) springs, weights and vacuum advance cans. I tried a ton of Olds & non-olds combinations and could never quite get timing where I wanted it across the RPM bands.
My problem on my 455’s was once I had the part throttle and WOT advanced to max power but not pinging, I was too advanced at startup. I could hear the starter straining. Then when I backed off the timing for easy starting, performance suffered.
Humble suggestion to start with factory settings and go from there. Gas has alcohol now, which wasn’t on the radar in the 60’s and 70’s, you’ll need to tune for what you can buy at the pump. There’s no lead in gas anymore ( at least in my state ) so that’s a chemical change the engineers couldn’t predict either.
Anyway as an engine novice, these devices have helped me.
The Jet piece has the APT adjustment, but the 9251 (new carb) does not. The mix screws on the Jet carb are almost completely bottomed out, the APT has had some adjustment as well (don't remember how much without getting the notebook out)..but it still runs pretty rich. It also had a stumble when the air temp is up, but I never got down that path.
I agree, and have been on board with the benefits of a wideband setup for years..even before this car. I just know I could collect the data but I'd have no clue what to do beyond that. Not saying I couldn't figure it out, but being the fact that this entire time my intention is to have the professionals do it on a chassis dyno..thats kinda just been my motivation-get it close enough so they just have to do the fine tuning.
I'm encouraged that swapping the carbs out has rectified the rough running/rough idle/stalling/detonation issue..and the fact that in finally getting around to checking (and correcting) dwell and knocking the timing back down a bit has produced much better response with the Jet piece. I'm curious what the result is of the 9251..but I'm thankful that he stands behind his work and is willing to go through and verify everything checks out.
At idle, see if your screws are bent or worn. I've found that "high vacuum" grease helps with vacuum connections at least in the cabin, if not the hot caustic environment of the engine. If the idle screw passages are worn, you might also try a tiny (3/32"?) O-ring on the fat end to reduce, eliminate vacuum leaks there. If you have an old Qjet around or 2, remove the idle screws from them to see if they have a different taper than the ones you're using. That may/will lead to a different idle mixture which could help you. Or buy some different screws from one of the online vendors. Qjet parts haven't been too expensive to me. It just takes a ton of _time_ to tune these things.
Regarding the O2 sensor, believe me, I'm no guru at all. Here's the scoop: The Innovative Solutions units are set from factory to read in AFR (Air/Fuel Ratio) which is familiar to some car USA guys. If it's not familar to you the general goal is 14.1 AFR or thereabouts for best power, but you might want leaner at part throttle cruise, you do want richer on acceleration and probably want richer at WOT. The fun part is that their product will also show Lambda which is an input fuel injection systems use to enrich or lean out modern car mixtures. Lambda varies from .70 (extremely rich) to 1.50 (very lean) and is centered on 1.00 as "perfect combustion". So all you do is figure out if your car in a given condition (idle, part throttle, WOT) is different from 1.00 or what you think should be (maybe .85 for acceleration, 1.05 for part throttle cruise and .85 for WOT, if you like) and swap in the qjet parts you need to improve it - bigger rods to lean it out, smaller rods to enrich, turn the idle screws or whatever. The sensor is one of the best tools I've ever had for tuning a carb. Probably the best. With the APT, see the books that show you how to cut a slot in it so you can adjust it without removing the airhorn.
If your carb has a mix of 170-series and 70-series parts, you might want to get to a known-factory combination of airhorn (the top part), main body (where the jets go) and throttle plate to be sure that the air, vacuum and gas passages are all where they are supposed to be as a complete carb unit. Otherwise tiny, barely visible variations in gaskets, hole size and passage size can throw off metering in ways that will be hard to predict and rectify.
Given that fuel injection systems installed are north of $2500, I don't have a problem giving SMI (Sean Murphy Induction) $600 or so for a rebuilt performance carb. I've found that he jets 'em a little rich for my street cars, but that's exactly the right way to err on the side of caution for performance cars.
I'm not affiliated with any of these vendors, just passing along what's worked for me.
My problem on my 455’s was once I had the part throttle and WOT advanced to max power but not pinging, I was too advanced at startup. I could hear the starter straining. Then when I backed off the timing for easy starting, performance suffered.
I've red that some folks with high compression and advanced initial timing install a toggle switch to control power to the distributor. Turn the switch off so the engine turns easily while cranking, then turn the switch on once the engine is spinning to fire it up.
Not sure if it was mentioned. Some after market rotors have ribs on the bottom that have been known to hang up/bind the advance. I have seen it on HEI's, not sure if I have on points. Might be worth checking. Easy fix with a dremel or even a sharp knife.
It sounds like something like a progression ignition is something worth trying, you can completely customize your timing curve in seconds on the fly. As said, manifold vacuum on the vacuum advance should alow a lower base setting quite a bit for cranking but add part throttle timing where you need it. Get a wideband, one of the tools the dyno uses to optimize your motor. Aftermarket EFI isn't the magic bullet either, plenty of issues with it as well. Good luck.
Carburetor was sent back to John, who took it straight out of the box and bolted it up to a car. It was primed, then fired right up. He said the curb idle screw was turned in a bit too much, resulting it high idle and more than likely its got too much of the transfer slot exposed.
I had to turn the curb idle screw in to get the car to even idle.
It fired off well on a different engine, and my engine fired off well with a carb change. So while I'm really confused at this point, he's going to go ahead and tear it down to ensure nothing fishy is going on internally. Meanwhile, I'm back to the idea that maybe I have some sort of issue that's being masked by the fact the Jet carb is dumping more fuel at idle and through the band.
... Meanwhile, I'm back to the idea that maybe I have some sort of issue that's being masked by the fact the Jet carb is dumping more fuel at idle and through the band.
I'm willing to make a large bet that when you find out what that issue is, it'll have something to do with the insanely low vacuum reading you're getting.
It fired off well on a different engine, and my engine fired off well with a carb change. . . . . . . . maybe I have some sort of issue
I said it before but .........
With the camshaft you have in the engine you are almost certainly going to need a carburetor that is built to work with that camshaft along with an appropriate ignition advance setup.
Until you accept that fact you are simply going to continue beating your head against the wall
With the camshaft you have in the engine you are almost certainly going to need a carburetor that is built to work with that camshaft along with an appropriate ignition advance setup.
Until you accept that fact you are simply going to continue beating your head against the wall
Right, which is why it runs better with the Jet unit. Hes going to tear it down to ensure nothing is wrong, since it's there, but neither of us are confident there is a problem with that carb.
My goal is, and has been, to get it to run well enough to take it to the dyno for professional tuning. I know my limitations on the fine tuning, but this is the first time I've struggled THIS bad.. lol.
I cant imagine the difference being in rod/jet combo..but Ive also never had that much of a variation to where its a conversation.
The low vacuum may be causing the power jet spring to hold the power jet needles high in the jets causing mixture en-richment. That is why the carb works good on the test engine but not yours. The Jet carburetor may have been set up for a high overlap cam explaining why it runs better. My explanation backs off of BillK's explanation. Perhaps you can discuss this with John. Maybe he can supply you with lighter power jet springs so you can tune the carb on your engine.
Not sure I'd the power jet system that you're referencing is the same as the ATP adjustment, but the Jet Qjet has a hole that allows for ATP adjustment. The new carb does not.
Coincidentally, i did some digging and found how to check the vacuum advance canister via hand pump. It obviously didn't tell me how much it's set to, but it did tell me the diaphragm isn't busted as it held vacuum.
How do I verify how much advance the vacuum advance is producing? I cant trust the spec sheet for the distributor unfortunately.
Hook up your vac pump to the advance unit. Hook up your timing light to number one. Start the engine and at idle using your dial back timing light, dial your timing mark on the damper to tdc and note the degrees on your timing light. Then apply vacuum to the advance unit and dial the mark back to tdc and note the degrees on your light. Subtract the lower number from the higher number and you have the degrees of advance the vac advance unit is capable of.
Got a bit of an update from John this morning. Though he is swamped, he is working on getting my carburetor addressed. He said he stuck it on a friends car and noticed it wouldn't idle. I told him that helped me feel a little better knowing he was able to replicate the idle issue onsite (well, somewhat onsite) and that it 'should' mean the issue isn't something directly with my car. At this point I'm still more curious than anything. Hopefully he'll have the time to get it squared away and I can put it on there before the weather gets too bad. If not, my father-in-law's enclosed trailer is ready to go..so I'll just trailer it down to the dyno and go from there.
But your other carb idled fine right?
John’s a good rebuilder, but he’s really not a tuner. He’ll tell you that as well.
You’re going to need some dyno time to truly figure out what the real issue or issues are.
Last edited by cutlassefi; Sep 23, 2024 at 11:45 AM.
But your other carb idled fine right?
John’s a good rebuilder, but he’s really not a tuner. He’ll tell you that as well.
You’re going to need some dyno time to truly figure out what the real issue or issues are.
No. the idle screw was way far in to get a decent idle, but even then it would randomly increase 3-500 RPM and not drop down until I backed the screw down.
My car idles fine with the Jet carb, not with the rebuilt one. John unpacked the rebuilt one after I sent it back and it idled fine on one engine for him, but not on another.
The detonation problem we're thinking is due in large part to the fact that at some point it was damaged. Assuming over shipping, but the result was a secondary pick up tube had fallen into the secondary well. That has been rectified, and a few changes to the idle circuit as well. I put the carburetor on last night and am hoping to get a chance to fire it off when I get home. If this allows me to idle as it should, and drive like it should to the point where minute A/F adjustments are what's left, I'm happy. At that point, we'll load it up and send it to the dyno so people who really know what they're doing can turn some screws.
Well, it fired right up for me, fast idled well, and we were off to a great start. I pulled it out of the garage and it ran for about 15 minutes or so, then I burped the throttle a bit and everything just kinda went to crap. It wouldn't stay running for nothing..but after turning the idle screw in a ways and turning the mix screws out a ton..it was idling pretty decent around 900RPM. I was fluctuating around 8-9 hg of vacuum, so I got it, out it in gear and it dropped hard. Back into park I went and it was then doing the same thing it had been..barely idling with next to no vacuum, engine stuttering, vacuum all over. Tried to chase it back and got it to where it'd be okay, and as soon as you give it throttle it gets out of whack.
in talking with John, he threw out another couple of suggestions that I'm going to try tomorrow after work. Hopefully that'll make some headway.
A vac signal that low isn't enough for the carb to pull fuel through the venturis. Thats why only high idle works ok, like 1500rpm. No vac signal points to a mechanical problem or one hell of a large cam, very late valve timing or an intake leak.
Did you check the port match between the intake and heads?
A vac signal that low isn't enough for the carb to pull fuel through the venturis. Thats why only high idle works ok, like 1500rpm. No vac signal points to a mechanical problem or one hell of a large cam, very late valve timing or an intake leak.
Did you check the port match between the intake and heads?
Well, it's been narrowed down to a carb issue based on the fact it'll idle with the other 2 carburetors that have been on it. The valve timing was corrected over the winter, intake has been pulled and reinstalled a couple times now, and the cam is a 228/235 with. 504 lift.
I have a couple questions. If you put your hand over the primaries, like above the choke, and cover it up, does the car die? Another test, if you turn the idle screws in a lot, even on just one side, does the car die? If you spray carb cleaner around common leak areas like the throttle shaft and the gasket flange, does it do anything to the idle? You have atrociously low vacuum. I have an uggah uggah cam in a 455, and even it gets 16 in.
I've read this thread numerous times. It is absolutely critical without any question of doubt you must be able to perform the test in the upper LH corner of this illustration. If you cannot pass this test, evaluate very specifically why you cannot pass the first test. NOTE: It is critical the vacuum gauge remains "steady" - no bouncing, no jittering about, no loosey goosey, it needs to be rock steady.
I have a couple questions. If you put your hand over the primaries, like above the choke, and cover it up, does the car die? Another test, if you turn the idle screws in a lot, even on just one side, does the car die? If you spray carb cleaner around common leak areas like the throttle shaft and the gasket flange, does it do anything to the idle? You have atrociously low vacuum. I have an uggah uggah cam in a 455, and even it gets 16 in.
Yes, if I cover the primaries, it will die. One of the suggestions made was to introduce a leak to see if it changes anything, to which I unplugged the PCV and it died immediately. The other suggestion made, and I didn't get a chance to try was that I simply hadn't introduced enough fuel into it yet. He had everything set for his 350, and while I turned the mix screws out a bunch to get it to idle as well as it did..he's suggesting maybe it simply isn't enough yet. As far as the low vacuum, i have beat my head against a wall trying to find a leak that simply isn't there. At this point, I have resigned to the hope that I can get it to run like it should, have brake when I need it, and the vacuum will end up where it does. If I can have 9hg, and it checks all those boxes..ill be happy.
I've read this thread numerous times. It is absolutely critical without any question of doubt you must be able to perform the test in the upper LH corner of this illustration. If you cannot pass this test, evaluate very specifically why you cannot pass the first test. NOTE: It is critical the vacuum gauge remains "steady" - no bouncing, no jittering about, no loosey goosey, it needs to be rock steady.
Regardless of carburetor, I can give it a quick throttle whack and it will jump about 10hg, bottom out, then return to where it had been (i may have the order backwards, but I know I have verified that before and it checks out..just my numbers are low from the start)
Regardless of carburetor, I can give it a quick throttle whack and it will jump about 10hg, bottom out, then return to where it had been (i may have the order backwards, but I know I have verified that before and it checks out..just my numbers are low from the start)
OK. Yes, I provided you the diagram twice in two previous threads. You have so many threads it becomes difficult to ascertain exactly what's happening - it requires researching your threads in hopes to gain some insight. I noted last year in August 2023 you were going to install the wide band. That hasn't happened because evidently you're going to have the shop performing the Dyno install the wide band. I guess that's why it isn't installed yet?
OK. Yes, I provided you the diagram twice in two previous threads. You have so many threads it becomes difficult to ascertain exactly what's happening - it requires researching your threads in hopes to gain some insight. I noted last year in August 2023 you were going to install the wide band. That hasn't happened because evidently you're going to have the shop performing the Dyno install the wide band. I guess that's why it isn't installed yet?
Yeah, it seems like no matter which way I go about it, I end up with the same problem/troubleshooting/etc..ha!
Correct, the idea was when the exhaust was installed, they would be putting the bung in and at that point I'd run it straight from there to the dyno. Between that time, and when the exhaust was put on, I'd switched exhaust shops, committed to buying this new carburetor, and a few other things..followed shortly thereafter by the ball joint failure which took my attention from how it ran to how to ensure it can go down the road safely.
That brings me back to the current goal of, I just want the thing to idle/run like it should, so I can confidently send it to the dyno and know we wont be an unnecessary amount of hours of labor into it on the simple stuff like trying to get it to run.
The wife and I had the conversation last night about all this..and I think my biggest frustration in it all is I've gone through this before and been able to tune it out..but for some reason this is beating me. Whether thats because I'm not allowing myself to go "too far" since it is the numbers matching engine on a car that they made less than 2500 of (and not a run of the mill 318 on a $500 car) or what..but its really wearing on me. I told her she was lucky she and the kid liked it, because I've about hit my limit..ha!
i've read this thread numerous times. It is absolutely critical without any question of doubt you must be able to perform the test in the upper lh corner of this illustration. If you cannot pass this test, evaluate very specifically why you cannot pass the first test. Note: It is critical the vacuum gauge remains "steady" - no bouncing, no jittering about, no loosey goosey, it needs to be rock steady.
Did the intake to head angle get checked after machining (port matched)?
The angle should be even as in parallel or 0°.
As the heads and block get machined the intake to head interface changes.
The heads and deck height go down toward the block. The intake will now sit higher between the heads.
Whatever amount was shaved off the deck & heads needs to be shaved off the intake to (port) match the new head height & angle.
This can affect performance and in extreme cases cause a major leak as the gasket is no longer effective.
Snap some pictures of the head to intake interface.
Is the low to no vacuum signal steady or does it bounce several inches? Fluctuating as in 5" is a valve(s) not sealing. Steady 1-2" is a leak.
Did the intake to head angle get checked after machining (port matched)?
The angle should be even as in parallel or 0°.
As the heads and block get machined the intake to head interface changes.
The heads and deck height go down toward the block. The intake will now sit higher between the heads.
Whatever amount was shaved off the deck & heads needs to be shaved off the intake to (port) match the new head height & angle.
This can affect performance and in extreme cases cause a major leak as the gasket is no longer effective.
Snap some pictures of the head to intake interface.
Is the low to no vacuum signal steady or does it bounce several inches? Fluctuating as in 5" is a valve(s) not sealing. Steady 1-2" is a leak.
The shop that did the block/machining is not the shop that checked the intake and subsequently built the engine. That concern has been expressed, but the first shop did not document what was milled, so without tearing the entire engine down to measure I don't have a way to account for it. I have considered that though as a viable concern, but if it's leaking it's doing so internally. I do know though just the block was "zero decked", no milling to the heads.
The low vacuum signal has been pretty steady, however with this carburetor it does seem to have a fluctuation of 1-2hg.. but that coincides with any stuttering the engine does.
A dyno session will not fix a vacuum leak, and that's what you have. That engine with that cam should pull a minimum of 15 Hg all day long. Any engine that can only manage 8-9 Hg is not functioning properly. Having apparently performed all the tests possible to identify the source of the leak with the engine assembled, you (somebody -- probably the guy who built it if you're still confident in his abilities) may have to take the intake and heads off, measure everything and re-gasket in order to deal with its source..
A dyno session will not fix a vacuum leak, and that's what you have. That engine with that cam should pull a minimum of 15 Hg all day long. Any engine that can only manage 8-9 Hg is not functioning properly. Having apparently performed all the tests possible to identify the source of the leak with the engine assembled, you (somebody -- probably the guy who built it if you're still confident in his abilities) may have to take the intake and heads off, measure everything and re-gasket in order to deal with its source..
The only place it could be leaking is internally. I have heard some say 15hg minimum, I have heard some say 9-12 is about what I should expect. If this debacle hadn't cost me way more than it should have in the first place, I'd be in a better spot to yank it and have it gone through once more. Like I said earlier though, I'm about at my wits end with this..and the kicker is the fact that having 2 shops local who were trustworthy put their hands on this engine and it's still in the state it is..I'm not sure where to go without dumping another few thousand into it.
I'm hopeful that I can get out of work on time and test it again with the changes suggested last night. If that still doesn't seem to trend in the right direction, then it may be time to just shut down and reevaluate some things. The whole premise of this car was to get it out of the barn it was rotting in, drive it around for a couple years, and then find someone better suited to take care of it. So far, I've accomplished the first part, and the second part..maybe the "better suited" is a harsh reality I didn't actually expect to encounter.
The only place it could be leaking is internally. I have heard some say 15hg minimum, I have heard some say 9-12 is about what I should expect. If this debacle hadn't cost me way more than it should have in the first place, I'd be in a better spot to yank it and have it gone through once more. Like I said earlier though, I'm about at my wits end with this..and the kicker is the fact that having 2 shops local who were trustworthy put their hands on this engine and it's still in the state it is..I'm not sure where to go without dumping another few thousand into it.
You shouldn't have to dump further thousands into this engine. If the guy who originally built it is competent and honorable, he shouldn't want to allow one of his creations on the street running this poorly. He should be willing to investigate and get to the root of the problem at as little cost to you as possible.
Regardless, don't give up. With all the work, pain and heartache you've plowed into this thing, you deserve to be able to get it right and take some measure of joy from it before moving on.
You shouldn't have to dump further thousands into this engine. If the guy who originally built it is competent and honorable, he shouldn't want to allow one of his creations on the street running this poorly. He should be willing to investigate and get to the root of the problem at as little cost to you as possible.
Regardless, don't give up. With all the work, pain and heartache you've plowed into this thing, you deserve to be able to get it right and take some measure of joy from it before moving on.
He is adamant its a tuning problem, but he also swore up and down you shouldn't have to even degree a cam. He also wont work on it while it's in the car, and if I'm going through the headache of yanking the engine it's not going back there.
The wife won't let me get rid of it. Especially with the fact that the kid enjoys it and was on the front of a JWO with it.
