Carter TQ - VERY rich at WOT...how to troubleshoot?

[oldkimmer]

I'm running a Carter TQ 9801 (Aftermarket with the attached electric choke) carburetor on my 408 stroker.

Having been working with the TQ carbs for many many years now, right down to installing adjustable air bleeds, etc...I would say I am fairly proficient with these carbs...however this issue I have ran into has me stumped and it may very well be the simplest of things that I'm actually overlooking, and perhaps not even caused by the carb itself!

So here is the combiantion:
1) W2 408 Stroker: Victor W2 intake, TQ on the spreadbore to squarebore adapter plate
2) Carb itself is setup exactly as the original OEM config: 0.095 primary jet, 0.137 secondary, 2110 rods, the ONLY difference is that I drilled air bypass holes in my primary throttle blades to help with the idle situation (Comp Cams 292 hydraulic roller cam, 240/248 @0.050"), which gets me a healthy 10" vacuum signal at 900 RPM, idle mix screws are out 3.4 turns, so I'm good there
3) The Carter mechanical Strip pump (M6902) is what is feeding the carb, that passes through a Holley pressure adjuster (12-803)
4) 16" drop base air cleaner, using K&N filter, I have about 1.5" of free space above the TQ vent tubes

I tune using Innovate O2 setup (LM-1 and LMA-3 AuxBox), which does give me a nice readout of AFR throughout the throttle opening and matching RPM ranges.

...and here is my problem: at WOT (either from rolling start, or at cruise) my AFR goes to a pig-rich 9.5-10 level!!!

I went back through all my tuning logs and as best as I can tell I started to run into this issue when I built the W2 motor...but several things changed at that time, such as: intake combo, fuel pump combo, etc, etc...so I have too many pieces moving to be able to peg this down to one change that's the culprit.

In that sense I went back to 'square one' so to speak: work one thing at a time until I get to "something".

1) adjusted the secondary air door opening (went super wide) but that made no difference...LOL, heck if anything my AFR dipped into the low 9s this time...I figured the extra opening actually caused even more fuel to be pulled

2) I disconnected the secondaries and re-did the test just on primaries: I expected a nice & clean AFR here, but oh boy was I wrong: still pig rich!!!
- not sure what to make of that though b/c perhaps by design the primaries itself may very well expect the extra AIR volume through the secondaries and so it could very well be that they will show RICH on their own (heck, I've never had the need to try this before so I really do not know what the baseline is)

3) I tested the phenolic fuel body to see if I have a fuel leak under the primary jet well, but all seems to be good here, no leak

So the only thing that remains is to tune down the Holley fuel pressure adjuster, force it to about 4-5 PSI and see if that make a difference because it could be that the extra fuel pressure the Carter Strip fuel pump (rated at 6-7.5 PSI) is putting out, as compared to the previous Carter Street pump (M6270, rated at 6 PSI) I was running, is forcing the fuel inlet valve off of the seat and simply flooding the carb at WOT.

This might make sense seeing as the converter flash is about 4000-4200 RPM and at that level the Carter Strip pump should be putting out pretty much all the pressure it has.

Outside of this, the last couple of times I headed out to troubleshoot I noted that at WOT and buzzing right up to 6500 my vacuum signal never drops below 5", in fact it actually seems to climb as I've seen it go to 6.5" right as I shift when the Tach light goes off (which is set to 6200). This is unlike anything I've seen before and suggests a massive restriction somewhere...but where??? Or is this simply the result of all that extra fuel NOT getting burned and the engine effectively choking itself off???

Needless to say, when I spotted this I made sure that the Diaphgram Connector Rod is adjusted correctly and during a WOT throttle blip I see the secondary air door swing open...so that seems to be working fine as there are no mechanical obstructions.

Alright, many things here...but what else am I missing???

Thanks as always!

If the secondary air valve opened when u blipped the throttle to wide open that is definitely not supposed to happen from what I remember. Mim

 

[perfacar]

mopar race manual says to disconnect rods from the hanger let them sit down in the jet. i 've done this, it works. also remove the spring from under the piston.

 

[M_Body_Coupe]

If the secondary air valve opened when u blipped the throttle to wide open that is definitely not supposed to happen from what I remember. Mim

Let me clarify: it's not that it just instantaneously flops OPEN. You can tell that the airflow demand is actually what pulls it completely open.

Note the following: I had originally ran with a very light '1 turn past AV closed' setting, and with the high stall converter and 4.10 gearing I was actually quite fine doing this...heck, loved the instant power and it never bogged!!!

I slowed that down by moving to a '2 turns past AV closed' setting in the course of trying to troubleshoot my pig rich @WOT issue. Seeing as it had no impact I am probably going to go back to that '1 turn past AV closed' setting because the secondaries kick-in was literally immediate w/o any other negative (noticeable) outcomes.

 

[M_Body_Coupe]

...I would get a new AV dashpot. Originals are decades old & rubber goes hard with age...

Agreed, I will give it a go. I was going to do a test-run w/ the dashpot being totally disconnected first (just easier to do), but we've had a few rainy/wet days here and I haven't been able to take the car out.

...I use 0.110 n/seats in perf engines & reduce the float level to 1". If you increase fuel pressure or n/seat size, it raises the fuel level which should be reset. The link below is for AFB/AVS carbs, but you can see the effect. The external adj float level is one good feature of Holley carbs...

I find this very interesting. I mean consider the process of filling a car's gas tank with a slightly bigger gas pump nozzle. The carburetor float is equivalent to the pump nozzle auto shut-off. Once the gas tank fuel level approaches a certain level (albeit at a much faster pace) the nozzle shuts off the flow of the fuel from the pump. Yes, I agree I am oversimplifying how an actual gas station fuel pump works (I think it also account for some pressure build within the car's fuel tank), but the concept is the same, no?

So I wonder if the provision to set the float level differently comes about due to the nature of carburetor fuel bowl re-fill process.

After all, when the fuel is being pumped past the needle & seat assembly, the rising float will eventually cause those two (needle & seat) to meet and shut off the fuel flow...however due to the momentum the flowing fuel has (fuel pump feed pressure would certainly impact this) some fuel will still be forced past them, so is the lower level intended to account for that momentum???

...If the AV link rod has been bent, it can sometimes bind in the AV slot opening. So check that out.
The Mopar Perf book recommends the sec WOT angle of 81* for dual plane & 88* for single plane. That is how I set them...

Oh, excellent two points here.

As applicable to the choke linkage, I have that clearance confirmed. In fact even if I push the AV to it's MAX open position (that's w/o the limit cover being present) there is no binding.

As applicable to the dashpot linkage, I also have that confirmed. That 'half-moon' like linkage path that controls how the dashpot pulls on the primary choke, and how the secondary AV is opened has no binding anywhere.

The WOT angle point you raise is particularly interesting. I've attached the two pertinent MP Engine Book scans I have saved a while back as a sort of 'baseline MP configurations'. I noted that the single plane had the steeper opening, and in fact I had that configuration in place once before and it seemed to produce a stronger pull, but I wasn't timing the car at that time so this was nothing more than a 'butt meter' reading!!! LOL (too many factors come into play otherwise to positively say this was "better")

But having searched for this or some kind of background on this topic numerous times, I have never been able to find anything official.

From my perspective it seems like the 81* setup was meant to facilitate best fuel distribution for factory dual-plane intakes. In the meantime, the large open plenum of a single plane can presumably support a larger pull of the air/fuel mixture in a way that doesn't immediately disturb/destroy that fuel distribution pattern. Although, specific intakes have various fuel-dam recommendations...albeit I haven't found anything published for the Edelbrock Victor 2920 W2 intake I'm using!!!

Alright...enough of that...the weather is looking decent enough today, so hopefully after dinner I can haul butt out there and try a few of the recommendations everyone here has provided so far...more to come gents!!!

EDIT
====
Opps, forgot about the MP Engines Book Carter TQ setup attachments!

 

[Bewy]

M body.

Float level & how it affects fuel level is just high school physics. The larger 'hole' allows for area of the needle tip to be exposed to the fuel pressure. Bigger hole, more pressure acting on the needle. So it takes fractionally longer for n/s to seal the pressure off....& the fuel level will increase slightly. Hence the need to reset the float adjustment to allow for this.

One other feature of this ingenious carb.....

In a situation where a car or truck [ they were used on Inter trucks ] is heavily loaded & cruising at high speed, there is the possibility that the secs would be cracked open & a very rich mixture would ensue because vac would be sufficient to keep the AV dashpot deployed; this would prevent the AV from opening & it would act like a choke, richening the mixture.
To prevent this, Carter drilled a bleed hole in the carb base, in the throttle bore, at the back of the passengers side sec t/blade. The hole is hidden by the blade. The hole can be seen by opening the secs. This bleeds off some signal so that the dashpot can release. There is a corresponding passage in the black body that mates up with the hole. Make sure the hole, passage etc are not blocked by carbon or debris.

 

[M_Body_Coupe]

...Float level & how it affects fuel level is just high school physics. The larger 'hole' allows for area of the needle tip to be exposed to the fuel pressure. Bigger hole, more pressure acting on the needle. So it takes fractionally longer for n/s to seal the pressure off....& the fuel level will increase slightly. Hence the need to reset the float adjustment to allow for this...

I think we are saying the same thing here, the key point being: the larger orifice at the same inlet fuel pressure will take a slight longer amount of time to completely shut OFF the fuel flow. Subsequently to account for this extra fuel volume the float level must be set differently (lower in the bowl).

As to the "high school physics"...umm, I appreciate the simplification (encouragement perhaps??? LOL), but in reality the equations that actually empirically spell all of this out are fairly sophisticated ones, basically fluid dynamics. Easy to Google search this stuff, things like discharge coefficient and others come into play...happily enough this stuff is still largely summarized by our "friend" Bernoulli's principles.

I would hope that Carter, in order to produce the chart you had shared, did in fact calculate all of these in order to publish that matrix.

I do readily admit that this wasn't so obvious to me as you brought this up though! Appreciate you bringing this up.

 

[M_Body_Coupe]

OK, a brief update as I got a chance to try out a few things last night:

1) AV dashpot
- disconnected it, basically to rule out some kind of a mechanical obstruction that might perhaps impact the ability of the AV to open completely

RESULT => no change, there was a bit of a stumble actually, which I expected, but the AFR remained RICH

2) BOWL VENT
- disconnected the bowl vent in order to rule out some kind of pressure build-up in the carb bowl that causes the fuel to be 'force fed' into the discharge nozzles/passages

RESULT => no change, the AFR remained RICH

Given the above I think I will pull the carb next, disassemble and go back to the factory needle & seat assemblies just to rule out the float level being an issue. This of course will be reinforced by having the floats set to the correct 29/32 level.

 

[Bewy]

I think you are over complicating fuel level & the exactness of it:
- what is the 'level' doing when the engine is shaking from a big cam/rough idle
- just the car movement as the car is being driven
- cornering, braking, accelerating
- the fuel is not sitting still.

 

[JC71340]

I'm no expert, but as others have stated, I thought at WOT there was normally almost NO vacuum, isn't that a primary indication of something completely un-related to the carb? No?

 

[Mattax]

I'm no expert, but as others have stated, I thought at WOT there was normally almost NO vacuum, isn't that a primary indication of something completely un-related to the carb? No?

Typically 'no vacuum' can be 1/2" to 1.5" Hg, ignoring 2 bbl or restricted v-8 engine.
Running with vacuum secondaries and a somewhat slower opening spring my 340 will get to around 2"Hg. Same engine on dyno running WOT on primaries only the vac is close to 4"Hg at 5700 rpm.

 

[Alfajim]

Typically 'no vacuum' can be 1/2" to 1.5" Hg, ignoring 2 bbl or restricted v-8 engine.
Running with vacuum secondaries and a somewhat slower opening spring my 340 will get to around 2"Hg. Same engine on dyno running WOT on primaries only the vac is close to 4"Hg at 5700 rpm.
View attachment 1716461477

I think the problem is the TQ to manifold adapter it is acting as a venturi the restriction of the throttle bores from the TQ size to the smaller manifold size is speeding up the airflow and reducing the vacuum at the base of the carb. This is increasing the air flow velosity thru the carb and this may also cause the accel pump to act as a power valve and flow at the high volume air flow, check the accel pump inlet check to see if it is heavy enough to resist this pull across the discharge tubes. Many different carbs are set up this way on purpose they just don't tell you about it. Weber's are set up this way on purpose and is part of the tunning process.

Jim O

 

[Bewy]

The DCOE Webers have the acc pump nozzle half way down the throttle bore; it sits between the venturi & t/blade. Purposely designed this way to add fuel at higher rpms in conjunction with the main jet.

 

[Alfajim]

The DCOE Webers have the acc pump nozzle half way down the throttle bore; it sits between the venturi & t/blade. Purposely designed this way to add fuel at higher rpms in conjunction with the main jet.

I am very familiar with weber's have rebuilt and tuned dozens of them over the years, also lots of the other various models on Ferrari's and Lamborghini's and Weber conversions on english sports cars, Jags, MG's and Harley's and Honda motorcycles.
When i first went to work at Hasselgren Racing engines building the Toyota 4age Toyota formula Atlantic engines they were using Weber's so got lots of tuning experience there shifted to electronic fuel injection a bit later.
Got very experienced on regular carbs from drag racing spent a lot of time learning how they worked and why so tuning was easier.
Also got some hands on and learning how the most marvelous perfect carb worked ever invented the Bendix Stromberg pressure injection carb on aircraft engines it is most like an analog fuel injection system works on pressure differential action, fuel and air as the inputs, very neat stuff.

 

[Valman]

Do you have a picture of the carb adapter on top of the intake manifold? Might reveal some clues.
FWIW, the photo has the adapter set up I run on my stroker 360/410. 850 TQ, Edel.RPM dual plane. You can see there’s some plenum area under the carb. May not be absolutely optimal, but it runs well, no bogging or over rich condition.

 

[M_Body_Coupe]

Do you have a picture of the carb adapter on top of the intake manifold? Might reveal some clues.
FWIW, the photo has the adapter set up I run on my stroker 360/410. 850 TQ, Edel.RPM dual plane. You can see there’s some plenum area under the carb. May not be absolutely optimal, but it runs well, no bogging or over rich condition....

So I had originally thought of adapting the W2 intake to a spread-bore setup, but sort of 'chickened out' seeing as I did not know to what extent reworking that intake top would impact the 'designed-in' flow characteristics.

I've attached a couple of photos of what I'm talking about:
1) the gasket contour showing the trimming of the carb mounting pad I would have to do
2) the adapter (3/4" thick) which I am still using on this intake, but which I was previously using on my Performer RPM

But...since my last post in this thread I was finally able to figure out what the problem was. I will detail in a separate post, as embarrassing as it may be I hope it will save others some grief!!!

 

[JC71340]

 

[M_Body_Coupe]

LOL, here comes nuthin'...

Alright, so I did say earlier that this 9800 series carb is a test-bed, right?

What this means is that I have several base plates that I use, the key difference between these being the primary throttle plates have an air bypass holes drilled. I typically switch these over when:
1) I feel that my adjustable air-bleed setup might allow me to revert back to factory non-drilled plates, most often I'm screwing around with the jet and meter rod sizing here
2) I play around with the WOT angle on the secondary bore, i.e. factory 81 vs MP recommended 86-88 setup for single plane intakes (although so far I have been using the factory 81 deg setup, short of THAT ONE TIME when I ran the 86 one)

Yeah, so "THAT ONE TIME" I swapped the bottom plates.

I use the Lokar cable setup for both the throttle and transmission kick-downs, which means that I really should re-check the cable operation each and every time. To be honest nothing should have changed with just the plate switch...alas, that wasn't quite the case!!!

Turns out I somehow lost about 1/4" linear cable travel. In terms of this translating to a degree (rotation) of the throttle, well, it was enough to leave the secondary butterflies opening maybe 2/3 of the way at most.

Now I know I said earlier that this was checked to make sure the secondary plates were fully opening, and I know we did this...but somehow I missed something. My wife was helping me (not a fault of hers) but the two throttle return springs I use make for a heavy gas pedal feel and I recall her saying she "couldn't push any further" LOL, and me telling her "just floor it honey"...ha ha...oh boy! Anyways, I could have sworn we even retested with the springs removed, but I can't argue the reality here, the linkage was off.

Take a look at the attached pics:
1) MOPAR_TQ_WOT_throttle-problem - shows the problem in that the secondaries are NOT fully opening

2) MOPAR_TQ_WOT_throttle-manual - shows the FULL opening when manually forced

3) MOPAR_TQ_WOT_throttle-linkage_fix2 - shows the corrected FINAL setup

I properly adjusted the cable and reverted all the other setups back to where they started, took the car out for a test drive and was immediately rewarded with:

1) almost 0" vacuum reading at WOT
2) massive "butt meter" reading (LOL - yeah, pulled way harder this time)
3) much nicer WOT AFR reading, albeit far too lean for my liking - 13.5-14.3

AND

3) SURPRISE => I swear, "when it rain it pours", eh?

So, during the last such pass (weather related really: I am out in the county, crappy roads - a good crown to the road surface, weather has cooled off and even after driving for some time the tires just won't hook) I buzzed the motor ever so slightly HIGH, I suspect near 7-7.5K. This happened in 1st gear as I tried to do a steady pull starting at about 2K and mashing the pedal. Well, car initially lurched forward a few feet and immediately went sideways on me, but b/c I'm on a county road (ditch on both sides) and I am just trying to stay on the road at this point in time, I am not watching my shift-light on the tach, audibly though I hear the motor scream past that normal "time to shift now" level and so I shift to 2nd and get rewarded with a LOUD tick!!!

Grrr...I immediately left off the throttle, toss my ratchet shifter into N, RPMs drop down to idle and stay there fine...but yeah, there is an audible tick but it's that "for sure it doesn't sound good" tick.

So I pop the hood open, driver side is not happy, no obvious damage though, just a tick from under the valve cover. Oil pressure reading fine, no change from previous readings...so seeing as I'm out in the middle of nowhere I limp this thing home.

I take things apart, #3 exhaust pushrod is loose. Hmm, collapsed lifter maybe? I yank the rocker arms and THERE IT IS (or not actually): the lash cap is MIA!!!

I go looking for the darn thing, not in the head though, so I fish out my snake camera, looking through driver side lifter bank, nothing there either. So it's either popped straight over to the PASS side, or made it's way past all the other moving pieces into the oil pan (I am saying a little prayer right about now).

Quickest way to find out is to drain the oil and stick a magnet into the pan hopefully finding it. I am not feeling terribly good at the moment I tell ya...worst ideas are going through my head, I mean that cap while small is pretty hard, so had it gotten stuck anywhere it would have caused some damage.

Alright, I setup to do the oil change. My oil pan is a Milodon 8 qt piece which has a magnetic drain plug, and as I pull the plug out I get a slow trickle of oil instead of the gusher I am normally rewarded with!!!

Holy crap, I think the lash cap got captured by the drain plug magnet and is now somehow blocking the oil drain hole. Yup...indeed...there she is, poke a small screwdriver through and more oil comes. Took a while to completely drain out but sure enough, the cap was there. I grabbed my other magnet wand, poked around some more, finally managed to pull that plug through the opening, but boy the "Speed Gods" must have been smiling on me (and laughing I would hope) because the oil pan opening is literally like 0.005" wider than the diameter of that lash cap...so yeah, BARELY and I mean BARELY, I was able to extract the cap out!!!

For now gents, I am in the process of re-assembling it all. Weather permitting I just want to be able to fire it up one last time before the car is put away for winter and make sure there is no other damage.

All in all, the fact that the lash cap escaped indicates I had experienced some valve float. I run the recommended Comp Cams beehive springs (26056) and it's only been a couple of seasons, but they could have gone weaker and the roller lifters themselves may have played a role. I originally set them up with 1/2 turn past zero pre-load, so this time around I am going with the full 1 turn the Comp Cams 2012 instructions recommend.

Thank You everyone for your feedback and insights in troubleshooting this issue. Turns out the problem was quite simple to correct and had I not missed a check when swapping parts I would have never gotten to this place.

 

[Illahe]

Is there a possibility that the primary power piston is being pulled open by the strong vacuum signal at WOT?

 

[Valman]

Haha, no one ever died from embarrassment don’t worry about that! Your adapter setup should work ok on that single plane.
Glad you got it sorted out.
I had secondary throttle binding issue with a TQ once. Ended up being the air cleaner stud I was using at the time, just a threaded 1/4’’ stud. With the air cleaner on & tightened slightly ( not at all over tightened ) was enough to slightly flex the baseplate of the carb and bind the secondaries.
With a factory ‘style’ stud that pushes down slightly on the top of the fuel bowl, no more flex & no more binding.

Edit; Might be worth checking your air cleaner stud as well if you’re secondaries are sticking or binding.