Hello, I just got my 71 302 running and put on a new holley 600cfm Carb. It seems to be running real rich by its "symptoms" and by reading the black carbon on the plugs. I pulled out the Jets and they are 65H. How much should i lean it by?? How could i tell, could somone suggest the size of jets i should pick to lean it out more. Do i go 1 number down on the jet sizes? 2 numbers down, or try 2 down and 4 down or down by a measurement such as .002 or .004? By looking at jet #'s 65 already seems pretty low. -Jon

I tried this calc on this page:

http://www.bgsoflex.com/holley.html

It said my JET was to rich, i know that, but what should i get. Lower than 65 means smaller, and leaner, correct? And larger, mean bigger and richer. IS the number 65H indicating it has a .065 hole? because some jets dont say model number only the size of the whole

 

Smaller=leaner
Bigger=richer

Try 2 sizes smaller and see how it looks. I dropped 5 sizes total when my plugs were looking a little black, and it's still a little rich.

This is the fun of owning a classic!

 

try lowering the float levels first. Also while its running look down the venturi to see if fuel is seeping out of the boosters at idle, if it is lower the floats before changing jets

 

Thanks ... i looked down and it wasnt dripping... But it did backfire, one big ball, i had my hand on the throttle lever so now my arm is red and throbbing and no hair, not to mention my face was 6 inches above the carb staring straight down. I now have half a rigth eyebrow and a really short buzz...... I walked into the house and the first thing my mom said to me was " do you smell burnt hair".... All i remember is a big orange ball of fire. Anyways. i put on .052 jets i had laying around and it ran better, but going from 65 to 52 was to much of a drop and now its to lean. How is the choke supoposed to work? I hooked it up, and the butterfly snapped shut, its open about a 1/4-3/8 of a gap while its idling then opens as i hit the gas but after letting it sit for 5 mins it never went straight up is it supposed to open fully? -Jon

 

As you can see Jon, I removed a word from your post. We don't use that language on the classic section. Backfiring is caused by incorrect timing, not a carb related issue.

 

Sorry bout that,most forums have it automaticly taken out if they dont want it used in here. But, in reality thats a part of everyday language, im not sure if you work in your home or not, but at my house,swearing is used every hour and at work more than 2-3 times a minuite. Thats the real world for those of you who arent their yet. Lets see, 6* timing is correct, the timing is right, and ive only had it backfire 2 times, once when first getting it fired and forcefeeding gas, and now, after putting back together the carb. Why?, any reasons besides timing? It didnt happen before the jet change with that timing, and only once after leaning it out. If ur gonna post atleast help answer my Q's soaring! -Jon

 

lean pop.. yeah, that will cause a backfire.. kinda like a nitrous explosion where the mix doesnt have enough gas so its not a controlled burn.

Sorry about the eyebrows and other folicles.. its part of the dues you pay when workin on your stuff. Been there done that. now you know not to look down the carb and hit the throttle.. Fuel should come out when its into the main metering circuits, but not at idle. if it backfires when its at idle, then you have something else wrong. I knew I shoulda copied that post about carbs a while back. I could paste it in here right now.

Isnt it getting colder there yet? Cooler air is more dense, and needs more fuel. So a rich condition in the colder months would point to the choke not pulling off more than needing a jet change.

know how i learned about carbs? By messin with them, takin them apart, kitting them, rejetting, and reading about things other people did and what changes it made for them. Us guessing over the internet could confuse you more than help you. if it was in the driveway or in the shop outside, figuring it out would be simpler. What that means is you have an advantage to figuring it out fixing it..

Get a jet kit. its worth the $40. i have two of them. or three.. somewhere.
Get a book on tunning and modifying Holley carbs. then read it twice. barnes & noble, etc...
Take the time and think it over after you have learned how they work, the answer will often come to you that way.

 

eh, guess and check on the jets, i got that part, but is the choke fly supposed to open 90* straight up? -Jon

 

yep. Straight up so there is little impedance to airflow. if it isnt open completely, then you have found the rich cause...

 

Yonco, you have a new PM from me.