Thermoquad Problems - & 1/4 mi times I replaced the 750 Holley carburetor on my 430 engine (stock except GS113 cam) with a Thermoquad that I had sent off for a rebuild. The Holley ran great on the engine right out of the box, the rebuilt TQ runs terrible. First, I had to turn the idle speed screw way in to get it to idle. At 800-850rpm idle it was pulling about 11 inches of vacuum and running very rough. It had about 13 inches with the Holley, so I started tuning the fuel mixture screws. I know something is wrong because I got the best idle with the screws all the way seated and it was pulling almost 15 inches. There was also a hesitation at throttle tip in, I took the carb back off and (if it's like a Holley) there was about .090" of the transfer slot showing under the throttle blade and I'm assuming it is running on the main circuit. If this is the problem I could drill the primary throttle blades, but I don't see why it would have this problem in the first place, the Holley ran fine and has ok vacuum. Maybe something plugging the idle circuit?? Also I did take it for a drive and when I floored it, you could hear the secondaries but the engine was surging and I saw smoke in the mirror. I loosened up the spring for the air door and tried it again it was a lot better and pulling pretty good to the normal shift point. I made one more run to see what would happen if I stayed in the throttle longer (I thought it may pull a few more rpms since the carb is bigger), well I stayed in it and just a little higher rpm than when I shifted previously the thing really hit hard almost like a small nitrous shot and pulled even more rpms. With the Holley I shifted about 5000rpm (guessing no tach) or a little less, now just above 5000rpm I get the power hit and it pulls real hard to about 5500. Anyone have an idea what the heck is going on here? Thanks, Brian
Brian I would say when you swapped carbs something got in one of the needle and seats. I always flush the fuel line when swapping carbs just to be safe. If you don't want to take it apart pinch off or shutoff the fuel line to run it out of gas and it might clear it. Could also be the rubber well plugs leaking or missing. (pretty common on TQs) Also be sure you cut or put a lighter spring in the power piston or it will run like crap at idle with that 113 cam. Bruce
Here's what I've discovered so far with the carb problems. First, the metering rods were set too rich, so any fuel from the air/fuel mixture screws was too much. I lowered the metering rods enough to open the air/fuel mixture screws about 1 turn. It is idling good with 15 inches of vacuum. Second, the air valve diaphram was not operating. I found no vacuum out of the port that it was hooked to. The port must be plugged with carbon, so I just switched the hose to the other port on the rear of the base plate. That took care of the "extra hit" on the top end. Only thing now is a little hesitation when I tip in the throttle, I think a little more experimenting with the metering rod position vs. air/fuel screw adjustment might eleviate that - any other suggestions? Brian
This is what I was told from the carb guy: 144 secondary 102 primary .035 nozzle I went to the drag strip tonight and ran 13.83 @ 99.41, 2.13 60' 13.73 @ 99.94, 2.11 60' I checked the timing and it was at 17 initial and 41 total. I backed it down to 10 initial and 34 total, then ran 13.78 @ 99.42, 2.05 60'. My previous best with the 750 Holley was 13.58 at 100. From all the good I've heard on this board about Thermoquads, there's got to be something wrong with this carb. Brian
Brian: You need to take the weather conditions when comparing best runs. Also, see where the TQ is off compared to the Holley (mph, 60 ft). BE SURE to check full throttle also! BTW I usually run 149 sec jets on anything that has headers and or intake. Bruce
Stage Zero Brian, get ahold of me, I have e-mailed you, your add must have changed????, want to talk about parts, Bud. twokidsandadog@attbi.com H-425-820-8909
I just wanted to post a quick follow up if anyone is interested. I went to the strip again last Friday. Before I ran, I checked my timing and it was at 40* total, I checked it with a different light and it was at 31* total. I put the timing at 33* total with the second light and my first pass was a 13.60 If you guys have access to a second timing light, it might not hurt to double check. I guess I need a new light (although the one I have is only a couple years old), does anyone have a suggestion for a quality light? The second light I used, that I think was accurate, was a Craftsman. Brian PS These runs were with the 750 Holley back on. I will try the TQ again in a couple weeks.
Be careful....I've found the Craftsman ones to be 4 deg or so off (retarded) so we had more advance that we thought. Returned 2 of them to Sears. I double checked with a $400 Snapon and an Equis unit. Bruce
I thought the Craftsman/Sears timing lights were some of the most accurate especially at higher RPM's. I'd be interested in hearing other opinions and actual experiences on this.
I have two of the 80's units that are chrome, one plain and one that I can adjust to check total advance, they seem to be fine and I have not had them calibrated, you have me wondering now, but I set the timing around 8 up to 12 with good fuel and the motors seem fine??? and yes they have hit the ground at least once over the years, not good I agree but they tend to want jump from the fender when you are not looking.ou: Bud.
