calling Mr Holley!Help - The 1947 - Present Chevrolet & GMC Truck Message Board Network

67chevemall · 12-31-2004, 12:44 PM

Alright so this carb rebuild stuff is kind of fun?

I have a 4150\60(still can't tell the difference?)
on the go!

I'm just about to put it all together again but need to know about the jets I
have??????

I have the 4 jets two say #642
and two say #65

Which ones would be primary and which ones secondary?
How does the numbering work with jets??????????????????
bigger the # the bigger the hole????????????????????????????
Cheers and thanks

Harold Shepard · 12-31-2004, 01:43 PM

I don't know about 642 I would guess they may be #64??? But that is just a WAG. If you can't tell don't use them the new ones ae cheap enough. One quick question, does the carb have a secondary metering block or metering plate? The #65 would be a good primary jet, but as a general rule the secondarys should be 2-4 steps higher in #. So the secondary should be a #69/70. Also if it is a vac. secondary carb buy a trick kit for it and play around you will be happy with the results

Hope this helps. Harold

crazy longhorn · 12-31-2004, 02:20 PM

The jets with 3 numbers are close limit jets. they will have a 1,2, or 3 added to the size, to tell you about the flow. The jets read as a #64, with the 2 added to tell you "middle of the road" on flow for that sized jet. if you had a 1 added, its to the low end of the spec for the jet.....a 3 says to the high end of the spec for the jet.

crazyL

Zeke · 12-31-2004, 02:24 PM

642 is a Close Limit Jet and would go on the primary side, the larger 65 (I think) on the secondary side. Holley uses drill size 65 would be 0.065, couldn't find anything on close limit jets but would assume 642 would be 0.0642. Looking through Holley numerical listing 642 jets were used on 600 cfm 4160 carbs but I didn't fine one matched with a 65 secondary.

If I am wrong some please chime in.

Zeke · 12-31-2004, 02:45 PM

Guess I type too slow, see CrazyL's reply.

67chevemall · 01-01-2005, 12:07 AM

Thanks for the info!
What size jets do you run?
I think I'll get a jet kit?
642 in the primary
65 in the sec.?
New animals to me!
???

Zeke · 01-01-2005, 10:47 AM

I run a 4175 which is a QJet replacement has 62 for the main and metering plate for the secondary 134-54. I am not an expert on Holley carbs but I do know you can change out the metering plate for a metering block so you can use regular jets. I found out hard way that when you tune a Holley it is best to only make one change at a time and write down what you do. If you change more than one thing at a time and it doesn't work out you won't know what needs to be changed back. I assume the carb you are rebuilding came off a running engine? If it did I would suggest you put it back together, install it and get a starting point to make further tuning adjustments. Learn how to read sparkplugs, you are looking for a light tan or brown. Bigger jets doesn't better performance. Holley has a good tech support, FAQ and tuning tips on their web site. Also I shouldn't have mentioned drill size, unless you really know what you are doing don't drill out a jet "Holley jets are broached, flowed and stamped according to flow rate". If you are going to be doing alot of carbs it would be a good idea to get a jet kit, accelerator cam kit, bowl gaskets, orings etc.

12-31-2004, 12:44 PM	#1
67chevemall Registered User Join Date: Apr 2003 Location: NB Posts: 3,367	calling Mr Holley!Help Alright so this carb rebuild stuff is kind of fun? I have a 4150\60(still can't tell the difference?) on the go! I'm just about to put it all together again but need to know about the jets I have?????? I have the 4 jets two say #642 and two say #65 Which ones would be primary and which ones secondary? How does the numbering work with jets?????????????????? bigger the # the bigger the hole???????????????????????????? Cheers and thanks __________________ 1968 Chevy C10 307 3ott fleetside 1967 Chevy C/10 V8, 3spd, fleetside lwb.Sold 1967 Chev C/10 step, 383, M21. SOLD

12-31-2004, 02:20 PM	#3
crazy longhorn Fabricate till you "puke" Join Date: Jun 2002 Location: Ill Posts: 9,402	The jets with 3 numbers are close limit jets. they will have a 1,2, or 3 added to the size, to tell you about the flow. The jets read as a #64, with the 2 added to tell you "middle of the road" on flow for that sized jet. if you had a 1 added, its to the low end of the spec for the jet.....a 3 says to the high end of the spec for the jet. crazyL __________________ 69 longhorn,4" chop,3/5 drop, 1/2 ton suspension/disc brakes,1 1/2" body drop,steel tilt clip, 5.3/Edelbrock rpm intake/600 carb, Hooker streetrod shorties,2 1/2" exhaust/ H pipe/50's Flows , 6 spd Richmond trans,12 bolt/ 3.40 gears....

12-31-2004, 02:24 PM	#4
Zeke Active Member Join Date: Jun 2002 Location: L.A. Lower Alabama Posts: 453	642 is a Close Limit Jet and would go on the primary side, the larger 65 (I think) on the secondary side. Holley uses drill size 65 would be 0.065, couldn't find anything on close limit jets but would assume 642 would be 0.0642. Looking through Holley numerical listing 642 jets were used on 600 cfm 4160 carbs but I didn't fine one matched with a 65 secondary. If I am wrong some please chime in. __________________ 1969 C10 350 3spd 1995 GMC 3500 XC 350 dually When Thomas Edison worked late into the night on the electric light, he had to do it by gas lamp or candle. I'm sure it made the work seem that much more urgent. George Carlin

12-31-2004, 02:45 PM	#5
Zeke Active Member Join Date: Jun 2002 Location: L.A. Lower Alabama Posts: 453	Guess I type too slow, see CrazyL's reply. __________________ 1969 C10 350 3spd 1995 GMC 3500 XC 350 dually When Thomas Edison worked late into the night on the electric light, he had to do it by gas lamp or candle. I'm sure it made the work seem that much more urgent. George Carlin

01-01-2005, 10:47 AM	#7
Zeke Active Member Join Date: Jun 2002 Location: L.A. Lower Alabama Posts: 453	I run a 4175 which is a QJet replacement has 62 for the main and metering plate for the secondary 134-54. I am not an expert on Holley carbs but I do know you can change out the metering plate for a metering block so you can use regular jets. I found out hard way that when you tune a Holley it is best to only make one change at a time and write down what you do. If you change more than one thing at a time and it doesn't work out you won't know what needs to be changed back. I assume the carb you are rebuilding came off a running engine? If it did I would suggest you put it back together, install it and get a starting point to make further tuning adjustments. Learn how to read sparkplugs, you are looking for a light tan or brown. Bigger jets doesn't better performance. Holley has a good tech support, FAQ and tuning tips on their web site. Also I shouldn't have mentioned drill size, unless you really know what you are doing don't drill out a jet "Holley jets are broached, flowed and stamped according to flow rate". If you are going to be doing alot of carbs it would be a good idea to get a jet kit, accelerator cam kit, bowl gaskets, orings etc. __________________ 1969 C10 350 3spd 1995 GMC 3500 XC 350 dually When Thomas Edison worked late into the night on the electric light, he had to do it by gas lamp or candle. I'm sure it made the work seem that much more urgent. George Carlin

12-31-2004, 01:43 PM	#2
Harold Shepard Registered User Join Date: May 2004 Location: Canton North Carolina Posts: 466	I don't know about 642 I would guess they may be #64??? But that is just a WAG. If you can't tell don't use them the new ones ae cheap enough. One quick question, does the carb have a secondary metering block or metering plate? The #65 would be a good primary jet, but as a general rule the secondarys should be 2-4 steps higher in #. So the secondary should be a #69/70. Also if it is a vac. secondary carb buy a trick kit for it and play around you will be happy with the results Hope this helps. Harold

01-01-2005, 12:07 AM	#6
67chevemall Registered User Join Date: Apr 2003 Location: NB Posts: 3,367	Thanks for the info! What size jets do you run? I think I'll get a jet kit? 642 in the primary 65 in the sec.? New animals to me! ??? __________________ 1968 Chevy C10 307 3ott fleetside 1967 Chevy C/10 V8, 3spd, fleetside lwb.Sold 1967 Chev C/10 step, 383, M21. SOLD

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