Carter Thermoquads ~ 'More General Information'
4bbl,
Thanks for the links.
Further comments.
- some good info in those links but a lot of nonsense as well.
- I have been tuning TQs for decades. Have never had a problem getting good & adjustable idle quality with the mixture screws. I have never touched the idle or pri ABs, no need to. Since Grant brought out his adj AB Holleys, now everybody is a carby engineer! I noticed on the Ford TQs that they had tiny sec jets. So I investigated. Reason was small sec AB 029, not the normal 040. All TQs that leave here have 040 sec ABs & perform great. No other ABs are touched.
- the idle cct is separate from the main cct, but of course the idle cct has to 'hold the fort' until the main cct starts. This function is controlled by the ABs carefully sized by Carter to get the overlap correct. Rich/lean can be controlled by the fuel jet size.
- some of the idle setting info in those links showed some folks didn't follow [ or didn't know ] the basic rule for setting up the idle cct. A small amount of T slot must be showing at idle, in gear, if auto. Most common problem is too much T slot, from low vac, which then upsets the delicate idle to main transition. The fix is to add bypass air, one method is drilling the t/blades. I do not drill pri blades on TQs or QJs because of the risk of nozzle drip. I drill the sec blades for bypass air; if the carb has a hot idle compensator over the secs, I remove that & use the orifice for bypass air. The engine doesn't care where the air comes from, as long as it gets it.
- a popular misconception is that the IFR in the above scenario needs to be increased for idle purposes. It does NOT. There is always enough fuel available for idling; some very late QJs have small idle port discharge holes, actually become the restriction, & give the perception that the idle jet needs to be bigger, when all that is needed is the holes enlarged.
- increasing the IFR is done for transition, not idle. Low vac cams need more fuel in the mix to prevent lean surge etc.
- I mentioned earlier in this thread soldering closed the holes in the sec discharge tubes & cutting off the the tube ends at angle like the CSTQ. I do that on every TQ that I build for a performance engine. Always perform great, no bogs. We dynoed an 850 on a Pontiac LeMans with a 455. A/F ratio was spot on. Alum heads, 3900 lb without driver, T400, 3.31 axle street driven & registered, street radials, driven by an inexperienced driver. No tuning was done on the carb or ign timing at the track; best time was 11.47; best mph was 118.