My 318 w/850 Thermoquad never idles well in gear, and stumbles off the line

[8v-of-fury]

It would seem that no amount of fiddling with the idle jets and throttle screw ever get it so I get a good Start/idle/off-line acceleration. Also I might note that it does seem mostly inconsistent, sometimes it will sit and stumble at an in-gear-idle where the oil pressure light comes on and other times it doesn't. Sometimes it stumbles to get off the line, other times its got as much power as it's ever had.

This is a bone stock 1988 318, with the addition of an edelbrock 4v intake and 850cfm Thermoquad up top. I also switched to a performance mechanical ignition system to do away with the ELB/ESA system that hung off of the air cleaner.

I do not think I have a vacuum leak, as the engine at idle pulls about 22in/hg. I do fear as though my junkyard thermoquad might be junk ;) lol. It has been on the engine for about 1.5 years now and generally starts properly, unless it stalls out (from said shitty idle) then getting it restarted is 20-30 seconds of cranking....

What causes that? is this the carburetor running out of fuel? Perhaps my fuel pump is weak?wouldn't that make itself more noticeable at higher rpm's though? If you leave the trans in 1st gear, it will pull and pull till the exhaust system chokes it out and you have no power left.. So I do not think that is it either.

I am having a friend put together a spare spreadbore carb for me tonight and I will try that out, if the same symptoms prevail then I guess we need to look deeper! eh?!

 

[zombywoof]

850 is kinda big for a stock 318... might wanna try something in the 500 - 600 cfm range

 

[fratzog lover]

Why did you need an 850 for your stock 318? There are better choices, I am guessing it was off a bigger v8 truck. Did this unit ever run well since you did the transplant?

 

[Dragonbat13]

Personally I would disable the secondaries to get the primary side tuned then go from there.

BUT, I havent had a chance to mess with a TQ either. I want to give advice, but I dont have enough knowledge to give it regarding a TQ.

I can tell you that there is alot more to it than just messing with idle jets and screw setting. If you couldn't get it to idle at all then that would be your source, but what your saying is it is bogging off the line, correct?

 

[fratzog lover]

Assuming your ignition is functioning correctly and not needing attention. Lots of "carb problems" have their roots at the distributor. Dont overlook that.

 

[Dragonbat13]

assuming your ignition is functioning correctly and not needing attention. Lots of "carb problems" have their roots at the distributor. Dont overlook that.

+1

 

[Triple J]

I had a bone stock 318 a couple of years ago, I ran a holley 600 with vacuum secondaries, it was really quick and got decent mileage ( around 20 mpg on the highway) I think it was a perfect match for the 318

 

[daredevil]

Whats the plugs look like. My guess black. 850 probably has too big a pump shot for a teen.

 

[rumblefish360]

Sorry, I'm not trying to be insulting, but your entire post reads "No experience" at all. The TQ is to large, the pump shot needs adjusting for less, the rods and jets at there smallest are what your looking for from a 318.

What is the carb number. Goggle "TQ guide by Vannth" for a very good listing of jets rods etc... From other TQ's.

IMO, try and find a TQ with an electric choke. 9800 series.

 

[straightlinespeed]

Here is that guide.

http://www.carbkitsource.com/carbs/tech/Carter/pages/tqguide-Vaanth.html

 

[8v-of-fury]

No offence taken, I do not have much carburetor experience or I wouldn't have needed to have written this post now would I have? ;)

The 850 is a vacuum secondary carburetor and very rarely (if ever) dips in to the secondary sides. The secondaries only open if you leave the gear selector in 1 or 2 and hold WOT intentionally well in to higher RPM's. You can hear the gushing whoosh of the secondaries opening, so them giving the engine too much isn't really too much of a concern. The carburetor is never really allowing the 850cfm to be taken ;) However! when you do hold the throttle open and allow the secondaries to come on line it handles it well and does not bog down or do anything odd. It gains speed, and you can feel the power come on.

I have seen other people run the 800/850 TQ's on their 273 or 318, as well as some low power 360's. To say the Thermoquad is too big for a 318 seems a little ignorant to me no? They came on some 318's and I have seen them used on super sixes even! lolol. *do not take my light heartedness as disrespect* I chose the 850 because it was what was available to me at the time, and this car was not running anywhere near right with its stock 2bbl and ELB/ESA system. This system has gotten the car back on the road, so far it is a win-win.

My TQ is a 1975 400 federal application, 9046S is the build number or what have you.

I am unaware if my ignition system is functioning properly, it is entirely new last year (time of 4v upgrade) with less than 5k kms on it all. (plugs, wires, cap, rotor, coil, wiring, spark box, distributor and carb rebuild). Now that you mention it, and I had a friend ride with me tonight, we may be thinking it is an ignition miss at idle.. it goes away once the RPM is brought up at all though, which is a weird one to diagnose. He thinks it is ignition related because of how quick the miss is, 1 cylinder ever so often seems to miss.. and then maybe it will be 3 cylinders in a row where it really brings the idle down. I am at a loss on how to test that one exactly.

He suggested to get it to do the stumbling, and then get the timing light on every plug wire to see if and what cylinder is misfiring.

This engine, one day, will have some aluminum heads, a superb cam and some headers added to its repertoire of awesome LOL.

 

[RustyRatRod]

How do you have the primary piston adjusted? An offline stumble usually indicates too lean of a mixture right off the bat.

The 850 TQ will not be too big. The last thing I would do is swap metering rods or jets YET. You "should" by all accounts be able to get what you have running very acceptably by simple adjustments.

I recommend this:

http://www.ebay.com/itm/Carter-Ther...ual-/181768176540?hash=item2a523a439c&vxp=mtr

Get it. Read it. Adjust yours accordingly and I just "bet" you will see a huge improvement.

As a starting point for your primary piston adjustment.

Push the primary piston tower and bottom it in its travel lightly with your finger and hold it there.

With a small flat blade screwdriver, turn the adjusting screw in the center counter clockwise and watch the tower and metering rods drop.

Continue slowly turning counter clockwise until you see the tower and rods stop dropping.

Now, adjust the screw clockwise until you see the tower and rods begin to rise, then go one more full turn clockwise. This is your baseline starting point.

From there you can adjust the primary piston screw clockwise to raise the rods (richen the mixture) or counter clockwise to lower the rods (lean the mixture).

I would no more than one half a turn at the time, recording the adjustments so that you can easily return it to its original position if you need to.

Every adjustment on that carburetor has a baseline starting point and until you get all the adjustments there, you will be shooting in the dark.

That manual will help.

 

[340fourspeedDuster]

Most 318s that had Carter Thermoquads as stock units were the 800 CFM. The 800 CFM has slightly smaller primaries than the 850 CFM. All secondaries have 2.25" diameter butterflies.
Was the J/Y Tquad rebuilt before installation? check the Thermoquad phenolic section, inspect to see if it is leaking fuel at the epoxied sections of the bowl. This will require disassembly of the air horn/phenolic/butterfly base. Are the round seals that go inside the phenolic section in good condition(item # 49 in pic)? These are a specially designed seal that is flat on the top and bottom to prevent gas leaking in the main well. These are critical components. The bottom of the wells are the epoxied part that tends to leak gas. If either the seals or the epoxied parts are not in good shape, additional fuel will be going into your engine. This will cause rough idle/dying/poor initial acceleration. See item #49 (seals) and check the bottom of the phenolic bowl (item #50).
Good luck. I would suggest finding an 800 CFM TQ or 600 Carter/Eddy carb for your application.

 

[AJ/FormS]

I have an 800 equipped LC teener, circa 1973, that runs absoutely great. That carb can be made to run gangbusters on just about anything. The primary side is just a small 2bbl and can be tuned as such.The secondary air door can be adjusted to satisfy various cfm requirements. That's part of what made this such a great carb, back in the day.
The difference between the 800 and the 850 is just the primary bores. Most oem 2bbls are bigger than the 800 primary(1.375, IIRC). The 850 primary was 1.5 IIRC, which is about the same as a lot of Carter 2bbls. I love that TQ.
I would check the bushings inthe baseplate where the throttle blades pass through. If the blades don't park in the same place every time, relative to the transition ports, this is what you get; intermittent idle and tip-in problems. A stiff return spring will aggravate the condition. So check that first.If its sloppy, you'll have to fix that.

Well-used TQs also have problems with the accelerator pump circuit. It seems the pump checks don't last forever, and that short plastic connector pipe looses it's grip over time as well.So if your baseplate is useable, then a re-kit is probably in your carbs future. There is a test for the pump circuit.

 

[8v-of-fury]

Tonight I adjusted the carburetor with a vacuum guage, a tach and a timing light.

I took probably 3 full turns out of my idle speed screw after adjusting the idle mixtures for best vacuum (19-20in/hg). As can be seen the choke was fully open, the timing is set to 8* BTDC, and the idle speed is roughly 825. This helped IMMENSELY with my issues.

 

[8v-of-fury]

Yes, the carb was rebuilt before installation. Also all baselines regarding secondary air-door and the primaries metering rods were set-up prior to installation as well.

It is not so much a stumble coming in to the primaries, it is a stumble because of the idle circuit I do believe. I am sorry I cannot include every detail in my first post so that you all know what level of troubleshooting/settings I am at.. as I simply do not remember them at the time ;).

I do have a solid return spring on the throttle arm, so that the throttle is indefinitely returning to idle everytime. I cannot say whether or not it is retuning to the same spot internally though.. I seem to recall the bushings seemed ok at the time when I dismantled it.

 

[8v-of-fury]

Most 318s that had Carter Thermoquads as stock units were the 800 CFM. The 800 CFM has slightly smaller primaries than the 850 CFM. All secondaries have 2.25" diameter butterflies.
Was the J/Y Tquad rebuilt before installation? check the Thermoquad phenolic section, inspect to see if it is leaking fuel at the epoxied sections of the bowl. This will require disassembly of the air horn/phenolic/butterfly base. Are the round seals that go inside the phenolic section in good condition(item # 49 in pic)? These are a specially designed seal that is flat on the top and bottom to prevent gas leaking in the main well. These are critical components. The bottom of the wells are the epoxied part that tends to leak gas. If either the seals or the epoxied parts are not in good shape, additional fuel will be going into your engine. This will cause rough idle/dying/poor initial acceleration. See item #49 (seals) and check the bottom of the phenolic bowl (item #50).
Good luck. I would suggest finding an 800 CFM TQ or 600 Carter/Eddy carb for your application.

Phenolic section was not warped or broken anywhere, and yes the bottoms of those caps were in place and not broken off. The epoxy was still proper, and not leaking. As well, the seals at #49 were replaced when the carb was rebuilt.

When the engine is running without the stumble at idle, it has the best accleration you'd expect from a stock, full interior 'teen with 2.23 gears.. which is actually not even that slow! It still can out accel traffic and keep-up with the hustle and bustle no problems.. Unless the idle is queer, and then sometimes it stumbles to catch its foot off idle and then it is off ot the races after that.

 

[RustyRatRod]

It can stand a good bit more initial timing, but you will probably need to end up limiting total mechanical timing somehow. My stone stock 351M in my 75 F250 for example is at 20* initial and 35 total.

 

[Magiver]

The reason people are saying the carb is to big for your 318 is because the teen can only pump 460 CFM @ 5000 RPM, thru it if there were no restrictions at all. In reality it only gets about 400 CFM thru it @ 5000 RPM. The only way to get more CFM is to use a turbo charger or a blower. Using a carb that's twice as big as needed seams kind of a waste.

 

[Bad Sport]

I had an 850 TQ on my 318 and it ran great. Only reason I switched was I could not get rid of the hot start issues.

When cold it would fire right off.

 

[AJ/FormS]

The TQ secondaries are adjustable to supply the needs of almost any engine, and for sure any SBM.
The 2 primary sizes are also a fine design to adapt it to any engine.
This carb is dynomite on any high-vacuum engine, and can be adapted to any SBM that I have encountered with up to the 292/509 Purple included.
If in my lifetime, I could only have one carb, it would be a TQ; hands down.
If only they were better supported in days gone by. I bought a box full of them and inherited others, to the point that I now have a pretty good selection of tuning parts. That's great for me, now,but was a PITA before that.

 

[8v-of-fury]

It can stand a good bit more initial timing, but you will probably need to end up limiting total mechanical timing somehow. My stone stock 351M in my 75 F250 for example is at 20* initial and 35 total.

Oh I totally agree! This dizzy has a wild advance in it, so I have to run 8* or less in order for the total to remain within a reasonable area and not ping the engine to death. :burnout:

It actually started, idled and free-revved best at around 15-17*.

@Magiver, The carb is not always giving the engine 850cfm worth of fuel/air. The carb was $10, so hardly was it a waste!

 

[rumblefish360]

It can stand a good bit more initial timing, but you will probably need to end up limiting total mechanical timing somehow. My stone stock 351M in my 75 F250 for example is at 20* initial and 35 total.

This ^^^^

Unplug and cap or crimp closed the vacuum line to the distributor. Set the initial up a bit more try 15* first. Reset idle speed. Limit advance to 35* max and then reinstall the vacuum line for a max advance of 52*. The vacuum advance canister should have a Allen key to limit the total mechanical advance. I keep for getting the size, but, *I think* it a 5/32. Someone correct me here if need be! You also may like the Chrome box or a FBO box better than the orange box.

The reason people are saying the carb is to big for your 318 is because the teen can only pump 460 CFM @ 5000 RPM, thru it if there were no restrictions at all. In reality it only gets about 400 CFM thru it @ 5000 RPM. The only way to get more CFM is to use a turbo charger or a blower. Using a carb that's twice as big as needed seams kind of a waste.

(Not busting your balls, just some sarcasm for fun)
Yes, and this is why a 600 performs better than a 500 carb. Some fellas here even use a 750 Holley. Crazy huh? There must be some madness to the method? What black magic could it be? :banghead:
(LOL on this with me)

As A/J said, since the secondary side has a spring loaded velocity valve above the mechanical secondary butterflies, the door opens as much as needed. The carb calculators will give you a conservitive cfm size for the engine size and HP. This cfm rating is good for a city/around the town driver that will see limited Hwy. useage and that is fine. Like a 500 on a stock 318. It is even better in a heavier car.

For what I would consider a better driving experience, a 600 square bore carb should be used. Even though a 500 would work great. On the TQ, or other spread bore carbs, look for the smaller primary for a better throttle response. That is the first key on a spread bore carb no matter the maker.

8v, what car is this in? What;
Rear ratio
Tire size
Transmission
And are there any upgraded parts?

 

[340fourspeedDuster]

Sounds like the adjustments really helped.
Great vacuum @19-20. Needle is rock solid, right?
Suggestions:
1) Please get some real hose clamps on that fuel line, ditch the zip ties!
2) Get a vacuum plug, trash the short hose with the sheet metal screw in it.
3) Hard to see in the pic, the two screws in the primary bore (choke horn) are there, correct? see photo.
4) Verify that all rubber hoses and plugs to the carb are in good shape, replace any with cracking.
5) Drive the heck out of it and ENJOY!

 

[8v-of-fury]

This ^^^^

Unplug and cap or crimp closed the vacuum line to the distributor. Set the initial up a bit more try 15* first. Reset idle speed. Limit advance to 35* max and then reinstall the vacuum line for a max advance of 52*. The vacuum advance canister should have a Allen key to limit the total mechanical advance. I keep for getting the size, but, *I think* it a 5/32. Someone correct me here if need be! You also may like the Chrome box or a FBO box better than the orange box.

I agree wholeheartedly that the engine requires more advance on the timing, but until I have a way to change the mechanical advance it will not take any more base timing without serious ignition ping in current condition. Yes, this is with the vacuum hose disconnected.. Connect the vacuum hose and jesus christ you cant even touch the throttle without getting SERIOUS knock under the hood. It sounds like it has a diesel under there.. ! LOL I see you mention the vacuum canisters adjustment, but then you say it limits total mechanical advance? You mean it limits total vacuum advance correct?

8v, what car is this in? What;
Rear ratio
Tire size
Transmission
And are there any upgraded parts?

This is in a 1988 Chrysler 5th Avenue, it is the original 88 engine.. may have 213k or 313k depending on how many times the odo rolled over. It is my grandmothers and shes owned it since new, her service records that were kept recorded only go up near the 100km mark.. so I mean it is even possible the engine has 113k on it. judging by the interior.. and lack of wear I could agree with that. I'll post some pics with this post.

So;

1988 Chrysler 5th
2.23 rear gear (factory)
215/70/15 tires
Factory '88 904 transmission
Only upgrades are the ELB/ESA delete, and the addition of the 4bbl eddie intake and 850cfm TQ carb.

Sounds like the adjustments really helped.
Great vacuum @19-20. Needle is rock solid, right?
Suggestions:
1) Please get some real hose clamps on that fuel line, ditch the zip ties!
2) Get a vacuum plug, trash the short hose with the sheet metal screw in it.
3) Hard to see in the pic, the two screws in the primary bore (choke horn) are there, correct? see photo.
4) Verify that all rubber hoses and plugs to the carb are in good shape, replace any with cracking.
5) Drive the heck out of it and ENJOY!

The adjustments helped a huge amount! However, today the car was back to normal.. even as soon as I started it, there was an idle stumble. I am having a friend put together one of his spare Quadrajets with appropriate jetting and what not, so I will have that to try in a few weeks. The needle doesn't move a touch at all when it was pulling the 19-20in/hg.

1)I feel you on the hose clamps, those zipties have been there over a year! LOLOL I have just never gone back and changed them.
2)Whatever it is I have plugged there has no suction or pressure at any time, I am unaware what it is even used for. It is a small tube that is in the middle of the phenolic bowl section on the primary side.. What does it do?
3)Yes, all 10(? was it ten??) assembly screws holding the three pieces together are present.
4) All plugs and hoses were new when I put the carb on 1.5 years ago, and are still within satisfactory condition.
5) I have been driving the hell out of it even though its slow and runs like poop! LOL

I actually live and work in Alberta, and fly home to Ontario every 3 weeks for a week at home. This car sits for me for the 3 weeks at my grandmothers house in Toronto, until I come pick it up the morning I fly in I give her a real good workout for 8 days while I am here, routinely racking on 6-700kms for the week... even though I have nowhere to be!









ACTUALLY THIS IS THE PORT FROM 340fourspeedDuster's POST HERE.. it goes in to the primary venturi. Ported vacuum?