Quick Fuel carb
Discussion
I thought before I get fuel injection for the car I would spend some time tuning up the carb that came with the American Speed 377.
I bought a couple of books on the Holley carburetor and used this site as another reference:
www.bob2000.com/carb.htm
The difference in the car is absolutely stunning and it has been fun experimenting with this carb. It is easy to take apart and reassemble as the gaskets are non-stick. Every circuit on the carb is individually adjustable either with a jet change or air bleed change, etc.
The changes thus far: idle air bleeds changed for 74's. I'm no longer killing mosquito's at idle. These air bleeds are much larger than what came with the carb. Big difference.
Main jet changes for 73's. The carb was pretty close with 74 main jets as delivered. No difference in drivability, small improvement on the O2 sensor gauge.
Power valve changed from 4.5 to 9.5 and as soon as I can get it, 10.5. This made a GIANT difference in the driveability of the car. At part throttle acceleration the O2 sensor would read lean ( and the motor would stumble)until I floored the car. After thinking about this and measuring my vacuum at idle at 15mmHg I put in the highest power valve I had. Now the car has the right now throttle response at part throttle acceleration that it had with full throttle before.
Another thing that I'm going to try is to bias the idle circuits towards the back two barrels. I've gotten almost all of the killed motor problem solved with a vent tube extension and close adjustment of the fuel level in the rear bowel. I think the rest will come from taking advantage of the rear idle circuit being covered with gas on rapid deceleration. The intake for the front idle circuit is dry in these conditions as the gas rushes to the front of the fuel bowels. This is a big shift to what I previously thought was killing the motor, but the O2 sensor is reading lean just before the motor shuts down.
The one thing that I wouldn't do again is get the quick change fuel bowels which allow easy access for main jet changes. It seems like this is overkill, once I got the size correct for the main jets they seem to be fine in multiple different conditions.
It's easy and fun to work with this carb.
ken
I bought a couple of books on the Holley carburetor and used this site as another reference:
www.bob2000.com/carb.htm
The difference in the car is absolutely stunning and it has been fun experimenting with this carb. It is easy to take apart and reassemble as the gaskets are non-stick. Every circuit on the carb is individually adjustable either with a jet change or air bleed change, etc.
The changes thus far: idle air bleeds changed for 74's. I'm no longer killing mosquito's at idle. These air bleeds are much larger than what came with the carb. Big difference.
Main jet changes for 73's. The carb was pretty close with 74 main jets as delivered. No difference in drivability, small improvement on the O2 sensor gauge.
Power valve changed from 4.5 to 9.5 and as soon as I can get it, 10.5. This made a GIANT difference in the driveability of the car. At part throttle acceleration the O2 sensor would read lean ( and the motor would stumble)until I floored the car. After thinking about this and measuring my vacuum at idle at 15mmHg I put in the highest power valve I had. Now the car has the right now throttle response at part throttle acceleration that it had with full throttle before.
Another thing that I'm going to try is to bias the idle circuits towards the back two barrels. I've gotten almost all of the killed motor problem solved with a vent tube extension and close adjustment of the fuel level in the rear bowel. I think the rest will come from taking advantage of the rear idle circuit being covered with gas on rapid deceleration. The intake for the front idle circuit is dry in these conditions as the gas rushes to the front of the fuel bowels. This is a big shift to what I previously thought was killing the motor, but the O2 sensor is reading lean just before the motor shuts down.
The one thing that I wouldn't do again is get the quick change fuel bowels which allow easy access for main jet changes. It seems like this is overkill, once I got the size correct for the main jets they seem to be fine in multiple different conditions.
It's easy and fun to work with this carb.
ken
Contgrats Ken.... you took the time to dial in that QFT carb & you now reep the fruits of your labour BIG TIME.... I like to state that 99.999% of the time any carb supplied new or supplied with your engine MUST BE DIALED / CALIBRATED to that particular engine combonation & car & driver ..i've never not had to recalibate any carb no matter who's...in 30 years.
Warning most HIGH PERF carbs such as Demon BG , Holley race ,Quick Fuel Tech ect are WAY over rich in callbration mostly on primary side of carb
WHY the answer is simple the manufactors go WAY rich to avoid lean burnt engines / burnt pistons & valves & there phones would ring off the wall & law suites would follow guaranteed.. as they are sold as HIGH PERFORMANCE CARBS & in most cases they have'nt a clue as to what engine its going on... out'a the box they would not be to far off on a all out race engine..eg tunnel ram intake , 13:1+ comp.. arc welder igintion system ect.
But in the REAL WORLD were most engines are driven most are WAY OFF in calibration as Ken found out...CHEERS! mate.
TIP do 1 change @ a time and check your results.. it simple easy and highly rewarding
Warning most HIGH PERF carbs such as Demon BG , Holley race ,Quick Fuel Tech ect are WAY over rich in callbration mostly on primary side of carb
WHY the answer is simple the manufactors go WAY rich to avoid lean burnt engines / burnt pistons & valves & there phones would ring off the wall & law suites would follow guaranteed.. as they are sold as HIGH PERFORMANCE CARBS & in most cases they have'nt a clue as to what engine its going on... out'a the box they would not be to far off on a all out race engine..eg tunnel ram intake , 13:1+ comp.. arc welder igintion system ect.
But in the REAL WORLD were most engines are driven most are WAY OFF in calibration as Ken found out...CHEERS! mate.
TIP do 1 change @ a time and check your results.. it simple easy and highly rewarding
Edited by fastco on Wednesday 22 November 22:16
ultimad said:
Just curious ... have folks here who have bought the Amerspeed package (i.e. engine set up by AS with carb) found the carb still requires calibration in the 'real world' ?
That is exactly what I wrote about. Read the link that I posted and do what is says and you will be rewarded with a much more powerful and fun to drive car.
ken
ultimad said:
Just curious ... have folks here who have bought the Amerspeed package (i.e. engine set up by AS with carb) found the carb still requires calibration in the 'real world' ?
Just curious here on A/S engine as they state there engines are dyno tested & tuned i would assume they come with computer print out of your engine with all engine data supplied including air to fuel ratios & EX temp ranges via pyro meter... and a smack on A/F ratio carb to suite engine after recalibration and 5 or more full pulls on the dyno to dial that carb in on the dyno to the engines requirements.
Anyone have such a dyno print out? Cheers! Dr.Dee
As to the question on REAL WORLD engine dial in VS dyno room calibration
for MAX BHP & torque... they are 2 differant worlds mates..why?
Exhaust system used on dyno not the same as the one your going to use in your car.
Dyno rooms are climate controlled , heated & A/C ect in the real world air temps & pressures are all over the place depending on were you live & drive your car.
When engine is dyno'd tested it is loaded with a constant resistance via the dyno system. Now in the real world we have very differant engine loads via gear box & tire grip & clutch engaugement & slip and cars weight , rear diff gear ratios.. all these change the load on the engine.
The answer is yes you will have to dial in / calibrate your carb & ignition for your engines climate & road loads & your driving style.
My 2 cents / pence Dr.Dee
Edited by fastco on Thursday 23 November 17:05
A good book:
www.amazon.com/gp/product/customer-reviews/1884089143/ref=cm_cr_dp_pt/104-7327767-8072765?ie=UTF8&n=283155&s=books
Correction: a great book. The best of over a dozen that I've read on the subject.
www.amazon.com/gp/product/customer-reviews/1884089143/ref=cm_cr_dp_pt/104-7327767-8072765?ie=UTF8&n=283155&s=books
Correction: a great book. The best of over a dozen that I've read on the subject.
Edited by k wright on Sunday 24th December 16:20
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