: holly carb tuning
May 23rd, 00, 04:53 PM
can anyone give me any input on what can be done to a holly 750 vacuum secondary carb to tweak the performance.(jetting,etc.) i have a 355, 12.1 comp. sportman 2 heads, camshaft is 256 duration 523 lift, victor junior intake. i have already changed the spring for the vacuum secondaries. any suggestions on jetting? anything would help, just looking for a all the ponies i can get. i have heard of cutting the choke horn off, can this be done and does it help. thanks
355, SUPER T10 4 SPD
May 23rd, 00, 06:46 PM
I wouldn't do anything I couldn't reverse. Try a stubstack, and a good air cleaner. Try a 68 jet in the primaries, it worked well for me in keeping the engine lean enough around town, and made good power. Usually Holley perf carbs come a little rich for safety.
On the secondary jets, I'd time the car in high or third gear from, say 60 to 80, start acceleration at 50 hit the stopwatch at 60, hit it again at 80. Or go by the tach in high or third gear from 4500 to redline. See if the jets make a difference.
Watch the plugs for little silver spots, that'l be aluminum from the pistons. You'll want to go richer if you see that. Champion makes a good booklet on plug color reading.
The older I get, the faster I was!
May 23rd, 00, 07:18 PM
If you have not already done so convert your secondaries to a metering block so it will have jets. Then go out and buy a Holley Trick Kit, this comes with a variety of tuning accesories such as shooters, springs, cams etc. Don't forget your ingition. Last but not least buy a book on tuning the carb. The best place to tune your car will be the drag strip, let the clock tell you if you are doing things correctly. You will need some accurate way to guage your work, seat of the pants is not accurate. Good luck.
May 24th, 00, 01:07 AM
Certainly examine your plugs. They'll tell you what's going on from a combustion point of view. Also, if it hasn't been done recently, do a thorough tuneup to get he best baseline. It's amazing how performance can deteriorate over time. Last, but not least, you may want to look at your timing - both initial, total and advance rate.
May 25th, 00, 11:33 PM
Rick is right. I encourage you to get a book on supertuning. there is so much stuff you can do you will be amazed. it is the little things you do that will get you the best gains. Trust me I have a daily driver chevelle that runs hi 12s at 109 mph. tune at the track and read read read,
Jun 13th, 01, 08:24 PM
i will have to agree on the replys. there is alot of things you can do to a holly to make more power but there is not just one thing that can make alot .2 or 3 poneys here and there ,will add up in the long run . one thing to remember is the air bleads and the circuts in the metering block now i now im getting into some touchy things that if you dont now what you are doing i suggest leeving it alone here is a trick to tune your fule mix to a te turn you air mix screws in til the motor starts to bog ,back it out till it smooths out now there is two air bleeds in the top inside the vintures the outer ones are for idel and the inner ones are for hi rpm put your finger over the outerones 1 by 1 starting with the driver 1 first notice the time between the finger over hole and the motor wonts to die now do the same to the pass side if the time is diffrent like longer turn in the mix screw in alittle and do it again when you get both sides to bog about instly the sec you plug idel air bleeds then the air bleads will be mached to the air volosity this is how you super tune air bleeds or inotherewords the fule mix screws me email addy is firstname.lastname@example.org haller at me if you have anymore q ill try to help :)
Jun 13th, 01, 09:35 PM
Good method nitrus. I was told to put the eraser-end of a pencil over the airbleeds of which you speak in order to determine whether or not they were functioning at all, or if they were plugged. The engine wants to die when I put the erasers over the bleeds, so I know they are working, but I never knew about the fine tweaking like you described. Thanks!