carburetor advice

Listmates: This is slightly off-topic, but many of us are old enough to remember what a carburetor is, so I'll pose the question. I'm rebuilding the Rochester 4-Jet carb from a 1961 Chevy. I had the original shop manual so disassembly and reassembly were fairly easy. But one of the last steps is setting the float height. It's an old carb so I don't have a nice factory kit with a float height gauge to measure it. The shop manual cites a primary float height of 1-33/64" and secondary of 1-37/64". Geez, this is a device that you adjust by bending pieces of metal--and who can even SEE 1/64"??? So I rounded off to the nearest 32nd inch (they provide a little scale in 32nds). Then I kinda eyeballed it. So the question is--how exact do you have to be in setting float height in an old carb like this? When they talk about 64ths of an inch, it makes it sound like I ought to have a dial gauge deployed, but it's usually done with a cardboard gauge device. How much should I fret over this? Thanks, Chris Campbell

The carb kit didn't come with a guage? I wouldn't sweat it too much but as my fading memory recalls, the kits used to come with a cardboard guage. I remember those old 4 barrels well as kicking in the secondaries was like flushing the toilet. I inherited my grandmother's old Pontiac Grand Ville with a 455 cid in it and I could literally watch the gas gauge move when I punched it. Hell, I adjusted the float on my 2 barrel carb on my Jeep on the top of a mountain pass in Colorado once because all the bouncing around I was doing was bending the metal on the float plus the change in altitude was making it run even richer due to larger jets for lower altitude. Good luck - Paul From: Chris Campbell cc… [at] lsnm.org [Cal_Boats] <Ca… [at] yahoogroups.com> To: Cal_Boats <Ca… [at] yahoogroups.com> Sent: Mon, Jul 28, 2014 10:33 am Subject: [Cal_Boats] carburetor advice Listmates: This is slightly off-topic, but many of us are old enough to remember what a carburetor is, so I'll pose the question. I'm rebuilding the Rochester 4-Jet carb from a 1961 Chevy. I had the original shop manual so disassembly and reassembly were fairly easy. But one of the last steps is setting the float height. It's an old carb so I don't have a nice factory kit with a float height gauge to measure it. The shop manual cites a primary float height of 1-33/64" and secondary of 1-37/64". Geez, this is a device that you adjust by bending pieces of metal--and who can even SEE 1/64"??? So I rounded off to the nearest 32nd inch (they provide a little scale in 32nds). Then I kinda eyeballed it. So the question is--how exact do you have to be in setting float height in an old carb like this? When they talk about 64ths of an inch, it makes it sound like I ought to have a dial gauge deployed, but it's usually done with a cardboard gauge device. How much should I fret over this? Thanks, Chris Campbell

I wouldn't worry at all. Remember that a long as the float closes the needle valve before the bowl overflows you won't have a real problem. A small difference in fuel level in the bowl will have a very small effect on the fuel drawn by the suction in the venturie. The difference in fuel supply pressure will be tiny. Ted CAL 33 Celebration Newport, RI From: Ca… [at] yahoogroups.com [mailto:Ca… [at] yahoogroups.com] Sent: Monday, July 28, 2014 10:34 AM To: Ca… [at] yahoogroups.com Subject: [Cal_Boats] carburetor advice Listmates: This is slightly off-topic, but many of us are old enough to remember what a carburetor is, so I'll pose the question. I'm rebuilding the Rochester 4-Jet carb from a 1961 Chevy. I had the original shop manual so disassembly and reassembly were fairly easy. But one of the last steps is setting the float height. It's an old carb so I don't have a nice factory kit with a float height gauge to measure it. The shop manual cites a primary float height of 1-33/64" and secondary of 1-37/64". Geez, this is a device that you adjust by bending pieces of metal--and who can even SEE 1/64"??? So I rounded off to the nearest 32nd inch (they provide a little scale in 32nds). Then I kinda eyeballed it. So the question is--how exact do you have to be in setting float height in an old carb like this? When they talk about 64ths of an inch, it makes it sound like I ought to have a dial gauge deployed, but it's usually done with a cardboard gauge device. How much should I fret over this? Thanks, Chris Campbell

I have rebuilt many carburetors over the years and have never changed the float height. I think that is something you do when you are installing a new float. Once it is set, just leave it. If I had to do it, I would use a caliper or make a cardboard gauge and measure it with a caliper. Not that it is necessary, but why not? Allen On Mon, Jul 28, 2014 at 8:13 AM, 'Ted Wrobel' tw… [at] tacticaltech.com [Cal_Boats] <Ca… [at] yahoogroups.com> wrote: > > > I wouldn’t worry at all. Remember that a long as the float closes the > needle valve before the bowl overflows you won’t have a real problem. > > > > A small difference in fuel level in the bowl will have a very small effect > on the fuel drawn by the suction in the venturie. The difference in fuel > supply pressure will be tiny. > > > > Ted > > CAL 33 Celebration > > Newport, RI > > > > *From:* Ca… [at] yahoogroups.com [mailto:Ca… [at] yahoogroups.com] > *Sent:* Monday, July 28, 2014 10:34 AM > *To:* Ca… [at] yahoogroups.com > *Subject:* [Cal_Boats] carburetor advice > > > > > > Listmates: > > This is slightly off-topic, but many of us are old enough to remember > what a carburetor is, so I'll pose the question. > > I'm rebuilding the Rochester 4-Jet carb from a 1961 Chevy. I had the > original shop manual so disassembly and reassembly were fairly easy. > But one of the last steps is setting the float height. It's an old carb > so I don't have a nice factory kit with a float height gauge to measure > it. The shop manual cites a primary float height of 1-33/64" and > secondary of 1-37/64". Geez, this is a device that you adjust by > bending pieces of metal--and who can even SEE 1/64"??? > > So I rounded off to the nearest 32nd inch (they provide a little scale > in 32nds). Then I kinda eyeballed it. > > So the question is--how exact do you have to be in setting float height > in an old carb like this? When they talk about 64ths of an inch, it > makes it sound like I ought to have a dial gauge deployed, but it's > usually done with a cardboard gauge device. How much should I fret over > this? > > Thanks, > > Chris Campbell > > >

On 7/28/2014 11:44 AM, Allen Edwards al… [at] gmail.com [Cal_Boats] wrote: > > > I have rebuilt many carburetors over the years and have never changed > the float height. I think that is something you do when you are > installing a new float. The inlet valve and seat in the kit are a different design than the original, so it changes the float height when installed. Thanks for the replies so far. I think I'll open up the carb one more time and verify that I've got the float height reasonably close. That will allow me to stop worrying about it. It's easier to recheck it now, off the car, than to have a lingering doubt later when I finally try to start the thing. I don't think I'll worry about whether the 1-37/64" height is really set at 1-36/64 or 1-38/64. Chris Campbell

I'm 55, so yes I have seen my fair share of carbs and rebuilt plenty. Regarding adjusting the float....I just went through that this past weekend during a carb rebuild. I am lucky in that my 1977 Toyota FJ40 Land Cruiser carb has a sight window on the bowl, with a nice dot in the center, so after you have adjusted the float and put everything back and the truck is running (hopefull), you can visually see if you got it right. But, regarding adjustment, as others said, each time you rebuild, you do need to adjust the float due to variances in the needle and such. What I do is measure and cut out a gauge from a nice stiff piece of construction paper. Something that will go all the way across so as like a straight edge I can slip under the float. You always take the measurement with the top of the carb inverted, and no gasket. Slip the gauge between carb face and bottom of float. Adjust until it just slips under without raising the float. Done. On Mon, Jul 28, 2014 at 11:51 AM, Chris Campbell cc… [at] lsnm.org [Cal_Boats] <Ca… [at] yahoogroups.com> wrote: > > > On 7/28/2014 11:44 AM, Allen Edwards al… [at] gmail.com > [Cal_Boats] wrote: > > I have rebuilt many carburetors over the years and have never changed the > float height. I think that is something you do when you are installing a > new float. > > > The inlet valve and seat in the kit are a different design than the > original, so it changes the float height when installed. > > Thanks for the replies so far. I think I'll open up the carb one more > time and verify that I've got the float height reasonably close. That will > allow me to stop worrying about it. It's easier to recheck it now, off the > car, than to have a lingering doubt later when I finally try to start the > thing. I don't think I'll worry about whether the 1-37/64" height is > really set at 1-36/64 or 1-38/64. > > Chris Campbell > > >

On 7/28/2014 1:48 PM, Leslie Newman d2… [at] gmail.com [Cal_Boats] wrote: > > But, regarding adjustment, as others said, each time you rebuild, you > do need to adjust the float due to variances in the needle and such. > What I do is measure and cut out a gauge from a nice stiff piece of > construction paper. Something that will go all the way across so as > like a straight edge I can slip under the float. You always take the > measurement with the top of the carb inverted, and no gasket. Slip the > gauge between carb face and bottom of float. Adjust until it just > slips under without raising the float. Done. The Chevy float height measurement is done with the gasket in place, which makes for an additional complication, and it's to the bottom of the float.. I'm going to build a little fixture to hold the carb top plate securely so my hands are all free to fiddle. Maybe I'll try making my own gauge, trying to be accurate within +/- 1/64" !!! I guess I was just a bit alarmed when the shop manual called it out to a 64th, suggesting that unusual precision was needed. Chris Campbell > > >

Huh. Thanks for that info. Most carbs I've done typically you do the measurement without gasket, but of course follow the instructions. You made me go do some searching and I found a great site with lots of free manuals. Here is your Carb manual (and a ton other variations). http://www.newagemetal.com/pages/Chevrolet/32-62Chevy.pdf http://www.oldcarmanualproject.com/ Leslie Cal 33-2 Puffin On Mon, Jul 28, 2014 at 2:30 PM, Chris Campbell cc… [at] lsnm.org [Cal_Boats] <Ca… [at] yahoogroups.com> wrote: > > > On 7/28/2014 1:48 PM, Leslie Newman d2… [at] gmail.com [Cal_Boats] wrote: > > > But, regarding adjustment, as others said, each time you rebuild, you do > need to adjust the float due to variances in the needle and such. What I do > is measure and cut out a gauge from a nice stiff piece of construction > paper. Something that will go all the way across so as like a straight edge > I can slip under the float. You always take the measurement with the top of > the carb inverted, and no gasket. Slip the gauge between carb face and > bottom of float. Adjust until it just slips under without raising the > float. Done. > > > The Chevy float height measurement is done with the gasket in place, which > makes for an additional complication, and it's to the bottom of the > float.. I'm going to build a little fixture to hold the carb top plate > securely so my hands are all free to fiddle. > > Maybe I'll try making my own gauge, trying to be accurate within +/- > 1/64" !!! I guess I was just a bit alarmed when the shop manual called it > out to a 64th, suggesting that unusual precision was needed. > > > Chris Campbell > > > > > > >

On 7/29/2014 10:26 AM, Leslie Newman d2… [at] gmail.com [Cal_Boats] wrote: > > > Huh. Thanks for that info. Most carbs I've done typically you do the > measurement without gasket, but of course follow the instructions. The gasket is used in place because the float assemblies capture the gasket, I guess. If you were just pulling the top plate off to check the float height, you could measure with gasket in place. But then the gasket would be used and compressed, not new like mine, which makes me wonder about GM's obsession with measurements in 64ths. The first link you sent does not show the 1961 4GC carb, but does show the 1956 version--and that one shows float height measured in 8ths--1-5/8" for both sets of floats. By 1961, they were calling for 1-33/64" and 1-37/64", neither of which is really too far from 1-5/8". That may be a clue. It would be interesting to know what GM's production toelrances were back then. I'm going to try to make a gauge to make the setting process easier. Problem is, the carb is sitting 140 miles from where I am sitting, so I'll probably make two L-shaped pieces then staple them together into a U at the right width when the carb is in front of me. Thanks for sending the links. Chris Campbell

On 7/29/2014 10:26 AM, Leslie Newman d2… [at] gmail.com [Cal_Boats] wrote: > > > Huh. Thanks for that info. Most carbs I've done typically you do the > measurement without gasket, but of course follow the instructions. You > made me go do some searching and I found a great site with lots of > free manuals. Here is your Carb manual (and a ton other variations). > > http://www.newagemetal.com/pages/Chevrolet/32-62Chevy.pdf > > http://www.oldcarmanualproject.com/ > > Leslie Send me your own e-mail, please, so I can send something off-list. Chris Campbell