2 random carb questions

[joedoozer]

As a "rule of thumb". Should all 4 idle mixture screws be set the same? And whats the max difference in primary and secondary jets? 4 or 5?

[andy16]

well it all depends lol like most things. to an entry level carb guy yes all 4 corners should be real close. i start by turning them all in LIGHTLY till they seat. then back them all off three full revolutions. then start engine and let it warm up. put your hand on the intake manifold and wait till its warm. then start backing them out 1/2 a turn at a time. turn all of em out 1/2 turn then check your tach. you want to keep backing them out until you have a peak rpm and it starts to fall again. then back up to the peak rpm at idle. at least this works for me i could be wrong. should be somewhere in the range of 3.5 to 5.5 turns out on my carbs and motors anyway.

jet size diff is a whole nother story and a big arguement among carb builders. if you use a power valve in BOTH primary and secondary yes a couple of jet sizes max. however if you BLOCK off the power valve in the secondaries (back barrels) you will see a large differncefrom 7 to 10 jet sizes differnt. i run the blocked powervalve setup and my jets are 9 sizes differnt.

every combo will be a little differnt. rule of thumb if its overheating for no reason (oil temp not real high) put some jet or squirter in it better to be too rich than burn your pistons up
in my humble opinion

[joedoozer]

Well the reason I asked was I have a new Holley Ultra HP. Out of the box the primaries were 1 1/2 turns and the secondaries were 3 turns. It has a power valve in the secondary, and the jets are 76 and 76. It is pig rich at idle, and burns your eyes really bad. I think I need to change the primary jets.

[stock car driver]

1.5 is correct..

[andy16]

well i made a mistake. checked my notes again. you want to achieve the lowest rpm reading not the highest. what i would do is this. back off idle speed screw to lightly touching throttle shaft on primary and secondary. turn the primary and secondary idle mix screws to same distance whichever you choose but need to be the same to start with. start the engine adjust idle speed if necesary but not much to keep it running till manifold is warm. when engine is warm and running look down at butterflies w proper face saftey stuff on and see if you can see the small transfer slots at edge of butterly if you can you need to back off the idle speed screw untill you cant see them anymore. once you are certain the butterflies aren open too far look at the boosters. no fuel should be coming out of boosters at idle. if fuel is coming out of boosters your float level is too high. when your sure that butterflies aren open too far and float level is ok then pay attention to your tach. while watching or have someone watch tach screw all 4 idle mixtures 1/2 turn in or out dont matter. after you have turned them your rpms will either rise or fall. if they rise you went wrong way. if they fall you went right way. next go 1/2 more turn if they continue to fall good. keep going till they start to rise again. when they start to rise again back up a little and your good. then re adjust idle. dont open the butterflies too far tho or you will expose transfer slots and idle terrible rich again. if you cant get high enough idle without exposing transfer slots you may need to drill a small hole in each buttrfly but should already have them, phwew hope this helps

[sj valley dave]

We have always seen that 1 1/2 to 1 3/4 turns out on all 4 corners is close to the set up...With power valves on both sides, square jetting is fairly normal. Without power valves we were at 74/80 on a 422" 15:1 roller deal at an adjusted altitude of 1,000 feet..

[DaveBauerSS6]

Well the reason I asked was I have a new Holley Ultra HP. Out of the box the primaries were 1 1/2 turns and the secondaries were 3 turns. It has a power valve in the secondary, and the jets are 76 and 76. It is pig rich at idle, and burns your eyes really bad. I think I need to change the primary jets.

Leave the jets alone.
Set the blades and the idle needles for idle as he said.
Get a vacuum gauge on the manifold and verify the idle vac is above the power valves if it still burns your eyes.
The rear butterflys have a opening adjustment also. You can slightly open the sec and close the primary to close off the primary transfer slots without drilling holes.

Keep asking questions, its cheaper than burning pistons.

[joedoozer]

Leave the jets alone.
Set the blades and the idle needles for idle as he said.
Get a vacuum gauge on the manifold and verify the idle vac is above the power valves if it still burns your eyes.
The rear butterflys have a opening adjustment also. You can slightly open the sec and close the primary to close off the primary transfer slots without drilling holes.

Keep asking questions, its cheaper than burning pistons.

That's what I did with the old 3310 I had. Propped the rears open so I could keep the primary transfer slot set correct. It always idled a little rich, but that may have been just an initial timing issue. It is running and idling better now. Still a little rich but I think my timing light took a crap on me. It says I have 70+ degrees of advance haha. Which is impossible of course. Going to get a new light tonight and check it again.

[DANNY]

We have always seen that 1 1/2 to 1 3/4 turns out on all 4 corners is close to the set up...With power valves on both sides, square jetting is fairly normal. Without power valves we were at 74/80 on a 422" 15:1 roller deal at an adjusted altitude of 1,000 feet..

I AGREE, if its burning your eyes jet it down ONE step and see then... Like most say a little smoke is better then a new motor...

On my 362's I run 73 in front and back... And I do have a little smoke as long as its not running in an enclosed area for more then 10 min it dont get too bad or burn much lol

[Hurst390]

Jets have nothing to do with the idle circuit..if your engine responds to the idle mixture screws and it's still rich at idle reduce the size of your IFR...The poor mans way is to insert a strand or 2 of electrical wire into the ifr's..bend them 90deg and let them imbed into the metering block gasket to hold them in place...that will reduce the square area of the ifr...
If your engine does not respond to the idle mixture screws most likely you have something in the needle and seat...it only takes a very small piece of contamination to keep the needle valve from closing causing rich idle..

[andy16]

i dont have a vacume guage but the rpm method is essentially doing the same thing. vacume is highest at a lower rpm. so if rpms are dropping vacume is rising. imho

i have another question. when my engine is in shop running i set my carb idle and etc. and it idles good no stumbles or nothin. but after the race or a few practice laps the idle is way up. like +500 rpms from normal. so i turned it back down. then after engine cools and i start it again idle is too low and it wont stay running. why is this happening? on a 360 sb2. has always done it str8 from engine builder?

[DaveBauerSS6]

i dont have a vacume guage but the rpm method is essentially doing the same thing. vacume is highest at a lower rpm. so if rpms are dropping vacume is rising. imho

i have another question. when my engine is in shop running i set my carb idle and etc. and it idles good no stumbles or nothin. but after the race or a few practice laps the idle is way up. like +500 rpms from normal. so i turned it back down. then after engine cools and i start it again idle is too low and it wont stay running. why is this happening? on a 360 sb2. has always done it str8 from engine builder?

The gauge suggestion was to verify the power valves are not opening.

I had a similar problem and found the advance springs were too soft and the initial timing would vary. Easy to check, get the timing when you feel it is right and when it messes up check the timing again.

[sj valley dave]

We run a 422" SB2.2 and find the same problem with both a 750 Willys and a 1000 Braswell. You have to have the idle adjustment up even when it shows some temp, but when it really gets heat in it it will pick up idle RPM...We just set it where we want it to be after we have blocked the rad and then send him out...This is both on a crank trigger and locked out distributor...Timing is not moving...We just basically ignore it and set it were on the track he will be at about 1200 rpm

[andy16]

my timing is locked also @ 30deg. thats basically what my carb guy said too that they just idle high even the bush/cup engines did the same. very glad to confirm w someone else tho thanks

[sj valley dave]

Your right at the sweet zone in the timing also...On our crank trigger we are at 30.5* and we run the 2nd ignition system at 27* to kill some torque when the track goes away...Two boxes, coils, etc.....