Thermoquad....how lean can I go ?

[brasil]

Hello folks...

just installed my "new " Thermoquad today.... First of all... Idles fine@ 14ish AFR... but crusing AFR is way to lean ( in my opinion)...@ 15.5-16.4 AFR If I accelerate HARD..my AFR goes to 12.8-13 ...
If I say "cruising" ..I mean I just keep the car rollin...coasting.... @ 40-50 mph.... not under load...

I change the main jet...was 0.098 and I went up to a 0.101 main jet.. the Rods are 2086( 0.069/ 0.061/0.040 ) but as I wrote...the carbs still runs a little lean ( in my opinion )

My Distributor ( MSD ) runs @ 15 ° BDTC at Idle and all in is@ 36 deg. at 3000 rpm...

My question is.. Does the carb run way to lean..?? What´s your opinion...? Should I go up with the jets ...??

The carb is a "leanburner" afaik... but there is a ported vacuum on the driver side of the carb ..?? The idle mixture screws are working perfect ( btw)

Thank you for opinions

Greetings Juergen

 

[Photon440]

I wouldn't really worry about that. Your WOT levels seem fine, and for light throttle cruising you're in the right ballpark for optimal fuel economy. You're probably only making 30-35 hp. at that setting and won't run into overheat problems.

From 'AutoSpeed' :
Bosch state that most spark ignition engines develop their maximum power at air/fuel ratios of 12.5:1 - 14:1, maximum fuel economy at 16.2:1 - 17.6:1, and good load transitions from about 11:1 - 12.5:1.

However, in practical applications, engine air/fuel ratios at maximum power are often richer than the quoted 12.5:1, especially in forced induction engines where the excess fuel is used to cool combustion and so prevent detonation.

 

[brasil]

Thank you Photon440 !

...so you think it´s o.k like this? I was thinking that the lean AFR will hurt the engine...running hot , burning holes in the pistons. etc...

If the engine would be a "newer" one.... with catalyic converter..and Lambda sensor... I wouldn´t be so fearfull..

Greetings Juergen

 

[Photon440]

It won't run hot at low throttle openings. If you want to re-assure yourself, pull the plugs after a cruise and check for signs of overheating.

 

[brasil]

...that sounds like a good idea

 

[bigblock]

At wide open throttle,running lean is your enemy! A light throttle cruise is fine,provided that your combustion chambers are efficient. If you notice pinging or miss firing then fatten the mix.

 

[brasil]

Thank you bigblock

The car drives normal ( I would say..) Didn´t hear pinging.... also miss firing wasn´t present.. I bought a 10-203 Strip Kit from a Forum member here... hope this kit will arrive in the near future. Because the kit includes some other needles/rods that can help to make the cruise /economy mod a little richer.

Greetings Juergen

BTW is there an INTERNAL Difference in the so called LEAN BURN Carbs.? Besides the jetting and the ported vacuum port ...

 

[bigblock]

I thought the lean burn carbs were feedback computer controlled.

 

[miller]

Yeah, me too.

 

[brasil]

... the "computer " only deals with the Ignition.. ( as far as I know... ) the carb would be jetted on the lean side.... But perhaps some here can jump in to explain the difference between a "normal " and a" lean burn" carb When I orderd the carb I looked for a 73 carb..... but unfortunatly Rockauto shipped a 76 carb... BUT this carb has a ported Vacuum port.... Greetings Juergen

 

[bigblock]

My 73 was not lean burn. Just a regular old TQ. Has ported vacuum too. It runs great. Dont know about the 76 tho. All the lean burn cars and truck I messed with got a regular carb and distributor. Problem solved! Your AFR's are good,leave it alone.

 

[sleepar]

Adjust you're accelerator pump linkage to give a bigger shot leave the rest alone

 

[Meep-Meep]

The best way to tune a carb is to go lean until you have drivability problems then start progressing to the rich side. It's much easier to find the line from rich to lean than lean to rich.

 

[brasil]

..ok. guys I understand. But there are still three things that make me a little confused...

First : I pulled the 0.098 jets and put 0.101 jets in the carb.... this didn´t change the AFR Ratio... ( the needles /rods are still the same.. ) How can this be ? Normaly the AFR shoud be richer now...? Right ...?

Second : AFR Ratios in the 16th ratio are really lean for a 69 440 cui HP engine ( I think ) Don´t what to kill the engine...

Third : Because my carb has a ported Vacuum.... perhaps it is a so called "Frankenstein Carb " ? The carb was remanufacterd bei AUTO LINE ....in Canada... perhaps they mixed up the parts there ? i.e a Base from an earlier carb with the top of a newer one...or vice versa..?? According to the manual the 76 carb is a lean burn carb with out this ported manifold port... ( 9097S ) but my carb has this port..... ????

Thank you for your patience
Greetings Juergen

 

[RedHot67]

Your AFR's are good,leave it alone.

Thats exactly what I told him yesterday.
As long as it doesnt stumble or backfire it's fine :icon_wink:

 

[brasil]

..... Dan is a Quickfuel guy he has a QF on top of his 440..... ( running way to rich ! ):jerk:

 

[miller]

What kind of car, what motor, and what year motor are you dealing with?

Somebody correct me if I'm wrong, but on the lean-burn computer-controlled stuff, and I'm thinking the type with the computer mounted as part of the air filter housing...wasn't there one or two 'air' ports that hooked from the filter to the carb? That was some of the so-called lean-burn stuff, controlling the air-fuel mixture the carb got.

Anyway, what you want to do, is give the engine what 'it wants', as far as your fuel mixture. Every motor is different, and will run best at the right tune for it, meaning the fuel mixture, and ignition timing. Just don't run it lean, or not very long.

Get the air/fuel mixture close to where it needs to be, re-check the timing, set it right...then the final mixture adjustment.

 

[brasil]

Hello miller....

The car is a 1966 Coronet500 with a 440 cui HP Engine ( 1969 ) HP Manifolds ,EDE Performer Intake, MSD Ign. Stock Torque Converter, TF 727 and a 3.23 rear with sure grip. As I wrote... the carb runs lean even if I go bigger with the jets.. went from 0.098 to 0.101 ... the rods are the same. Idle is o.k. @ 14 AFR WOT is @ 13 AFR... but if I go steady 20, 30 40, mls...
the carb runs way to lean.... also when I accelerate smoothly... AFR goes way up.... @16 AFR...

My Ign . Set up is as follows.. MSD Ready to run Distributor with Blaster II Coil... with 12 deg BTDC @ Idle ( 700 rpm ) and 33 deg all in @ 3000 rpm ... vacuum advance is 10 Deg on top @15 inches +

I hope that when the Strip Kit arrives, I can deal with some other Rods....

Greetings Juergen

 

[miller]

..ok.
Third : Because my carb has a ported Vacuum.... perhaps it is a so called "Frankenstein Carb " ? The carb was remanufacterd bei AUTO LINE ....in Canada... perhaps they mixed up the parts there ? i.e a Base from an earlier carb with the top of a newer one...or vice versa..?? According to the manual the 76 carb is a lean burn carb with out this ported manifold port... ( 9097S ) but my carb has this port..... ????

Yeah, your motor shouldn't have a lean-burn carb on it. But anyway, almost sounds like you might have an open air/vacuum port, or leak. That might explain the full time running lean. I'm shaking my head. Are you trying to richen the mixture using the mixture screws? Are the limiter caps still on the mixture screws? Just tossing ideas out, okay.

Sure, it's possible the carb was built wrong.

You might try getting a spray can of Berrymans B-12 (carb cleaner), start the engine, let it idle, and lightly spray different areas around the outside and base of the carb. Use a tach if you can, and watch for a rise in RPM. Of course, only check the outside of the carb.

If you get any results, you'll have somewhere to look. All vacuum ports capped, or hooked-up? Maybe a leaking vacuum hose?

One last evil thought. Maybe a FUEL port inside the carb could be plugged, or blocked.

 

[WileE]

The main metering circuit and the idle circuit would be leaner; the accelerator pump circuit and power circuit richen the mixture to prevent catastrophic damage.