The Stovebolt Site Forums The Shop Area Engine Shop Testing Daytona Universal Carburetor UN2

Thanks for the update Gabriel. I hope you get good help from their customer service department.

1/15/2020 Update: Had a great experience talking to Ron over the phone at the Daytona Carburetors company. Sounds like a nice small outfit. Very knowledgeable gentleman. He took his time to listen to my technical questions and answered them clearly and calmly. It sounds like he's been working with carbs and in the automotive industry for a long time. What I learned. One is that originally GM ran the Zenith carburetors on these engines, (im not sure if he was referring to the 261's or stovebolt engines in general) and that these are a direct copy of those zeniths. These had the 32mm venturi on them, which was meant for these engines. I was happy to hear that and that they were OEM equipment on these Chevy's, that makes us purist a bit happier. I mentioned that I wasn't getting the high end performance I was getting before with my Rochester, he mentioned that perhaps my air cleaner wasn't allowing enough air to enter, or I simply hadn't richened the high speed jet enough and that I should first find out how many turns I had in fact turned out, by starting from the start (turning in and bottoming out the needle, its a very fine adjustment as I was told). I found out I was 6 3/4 turns out. I went 1/2 turn out more as instructed to see if that helps and to keep going out in half turn increments to see if I notice an improvement. He also suggested I test-run my truck without the air cleaner to see if that improves it. Another thing I learned is that the carb kit comes with a plastic red adapter to accommodate for larger air-cleaner base plate openings. He mentioned the diameter I believe it was 3 1/2 in. for the earlier type but they changed in 1960 I believe he said. I didn't quite understand how its supposed to work. Another thing I learned: I mentioned that I was looking for an adapter fitting (male to male) that would go from my glass bowl fuel filter to my UN2 carb. The one I had that worked on my Rochester was 1/8th to 1/8th mpt. but the inlet for the UN2 is a metric thread. So at no extra cost, (since I had ordered the carb from them) he said they would send me the 1/8th to metric fitting to my address so I can run my glass fuel filter again. Great customer service in my book. He wants me to follow up after I try the adjustments. Very content with my experience and am looking forward to dealing with them again in the future.
p.s he also suggested I run only 87 octane fuel because it has a higher boiling or percolating point which is 180-185 degrees Fahrenheit while 93 octane is approximately 40 degrees lower around 145 degrees Fahrenheit. Good to know.

Classic - with all due respect, your last post is historically inaccurate.

Chevrolet DID use Zenith as original equipment..............................from 1912 to 1925 on a 4 cylinder 171 CID engine. These were updraft carburetors.

Chevrolet DID use Zenith as original equipment on their 6 cylinder of 299 CID......................in 1912 ONLY. This also was an updraft carburetor.

The last Chevrolet to use Zenith as O.E. was 1925.

Zenith did offer a replacement carburetor for the stovebolt 216.

Zenith did NOT offer a replacement carburetor for either the stovebolt 235 or 261

Zenith did offer a number of "universal replacement carburetors" of different venturii; and the customer was responsible for picking the correct one for his/her application.

GMC DID use Zenith as original equipment on many different size engines, and we have been recommending these GMC versions for years.

Jon.

Thanks for clearing that up Jon, I must have misunderstood Ron, as we spoke I was jotting down what he was saying. I have heard though that the Zenith carburetor is the better carb to have for our engines, and this is a pretty much direct copy. Do you know if perhaps they came as standard equipment for GMC trucks, because I did write that they came as standard equipment on GM products. That might be where the discrepancy lies.

Back in the early 1950's, Dad used a big Zenith 2-barrel carb designed for a gasoline engine Mack truck on a flathead Ford dirt track engine. That carb had removable venturis, which he put in a lathe and bored out until the restriction was barely there, just enough to develop a little vacuum to pull the fuel from the float bowl. Then he drilled out the main jets to the point they would break off if they were tightened too much. Why all this modifying? He was running a mixture of alcohol and Hydrogen Peroxide as fuel, and the engine needed a LOT of it to run right. 8 laps per gallon on a 1/4 mile track was about average, running a 300 cubic inch engine. That single carb routinely outran competitors running three Stromberg 97 2 barrels. All the mixture tuning was done on a chassis dyno owned by one of his sponsors, one that was normally used for road tractors. Mixture adjustments were done by changing the high speed air bleeds, meaning that to get a richer mixture, a smaller air bleed was used.
Jerry

1/17/2020 Update: Took my truck out on another 30 mile round trip stint. Runs beautifully with the UN2 Carb. I tried the two things that were suggested to me, one, run the engine without the air cleaner to see if it was too restricted, two, I also backed of the fast idle screw a bit more. I was originally at 6 3/4 ill say 7 to keep it rounded. so I went back in whole turns to notice the difference I kept going to about 11 turns out and then notices a bit of fuel coming from the adjuster screw, I guess I went too far, so I backed it back in. I can say now with confidence that this carb has the same or just about near the same power as my Rochester in the top end. The idle is better for sure, and the low end torque feels as good or better. That coupled with the fact that its a new carb gives gives me confidence in my purchase. Now just to wait and see how it keeps up as time passes. Also, we'll see how much gas mileage it gives me, the same, less, or more. So far so good.

There's too many mistakes and unscientific "tests" here to list. If you're happy with it, I guess the rest of us should quit commenting.
Jerry

Hi Jerry, Ive been honest since the beginning, im not a scientist or a professional mechanic. Just your weekend home mechanic that loves classic Chevys'. Nobody had tried this carburetor, so I thought I would check it out and document my experience, like anybody else would do at home. If you get something good out of it, then that's great. Im not recommending anybody buy this carb or not, just an unbiased test from a regular guy.

Interesting thread, thank you.

Looking forward to future updates.

Yes, thanks for posting. Your experience and reporting will help others who are curious and want to read how it worked for a real purchaser and not some fabricated online review written by a company employee.

Thanks Tom. Thanks Gord.

Your every day man testing will be of benefit to the thousands of hobbyists that don’t have access to machine shops with dynos and hundreds of thousands of dollars in test equipment. Or, for that matter, the knowledge to use them. Keep good records and post frequently to keep interest up. The more miles you put on the more relevant your “test” will be. Don’t hesitate to post the bad (if any) along with the good. You’ve got a good start. Thanks

Gabriel, another "Thanks" for taking the time to test and report. I bought a nos Zenith O-10355 (originally sold as a replacement for a 1937 ~ 1942 Chevrolet 216) from carbking to run on my 1951, 216 powered 3600. I have only praise for this carb. All that said, I recently added a 261 engine to the flock that will likely replace the 216 currently in the '51. It has the factory Rochester and I've been on the lookout for better carburetor. Your review could cause another Daytona carb to be installed when/if the 261 hits the road.

Added in edit: just been rereading earlier post and thought I'd add a test suggestion. As you're tuning for power it's easy to rely on the "seat of the pants" dyno. Most of us do. To add another test try this. Find a quite stretch of road, either make marks on the road or just identify a stop/start point with available landmarks that allow for precise identification within a foot or so. Then set your smart phone (or stop watch) to timer function. Drive at a steady (not accelerating at all) speed of say 40 mph and when you hit your first mark, put the accelerator to the floor and start the timer. Hold it there till you hit your second mark and stop the timer. Record the time and make notes on speed, wind, temp and humidity.

You now have a baseline to compare to when making adjustments that affect power. Although not likely to be worth the trouble with our truck and power levels you can find charts to adjust weather factors back to your baseline figures so you'er doing apple to apples comparisons.

Now make one change (only), go test and time, record all results, then repeat and report

If you really want to be thorough put the Rochester back on and do a test run, then one with the Daytona.

RonR

I'm glad to do it. The gentlemen on this site have helped me countless times when I've needed advice, with their years of experience. I'm happy to give back in this small way. That 261 is a great engine, I lucked out when I bough my 46 chevy, I thought I had a 235, but upon closer inspection found out I had a 261. I was very happy and am more than content with its performance. The Rochester B is an excellent carb, with its faults of course, but still gives stellar performance. When other stovebolters spoke of the Zeniths superiority, I wanted to look more into it. I've been told they fetch a handsome price, so of course when I learned of this near exact copy, and manufactured new, I knew I had to give it a try. I'm glad I did. It is brand new and working great, we'll see with time how it holds up. Ill try to keep everyone posted.

1/31/2020 Update: Just finished filling up my tank after putting 108 freeway miles on my pickup. It's been running great. I ended up putting 9 gallons of gas to the brim which averages out to 12 mpg's. This was driving at a pretty constant 50 mph with some average grade changes. I also did many full throttle pulls to test the high end power. I'm quite content with its power output. I still feel that perhaps the Rochester was a little almost unnoticeably better on the high end power, but the overall performance of the UN2 with its great idle, and low end performance more than make up for that. I also enjoy its performance right after cold startups, I don't have to warm up the engine as long to get smooth drive offs even when cold. Will update when I do a reasonable amount of city driving to average out its gas consumption.

Gabriel, if you are willing to weld in a 18mm bung in your exhaust down pipe, I will send you my hand held wide band to monitor air fuels.
Steve

Hi Steve, thanks for the offer. I would have no problem welding the adapter, but do you think it would make such a big difference in the outcome? It might be worth it even if I got one more mile per gallon, but from what I've heard, 12 Mpg's is pretty much the accepted fuel economy of these engines. Did it help you on your 261? What's your average mpgs?

I didn't bother welding in the bung because it runs so nice. I will do a mileage test when I bring it out in the spring and report back.
If you dont have drivability problems I wouldn't bother either. But if you have a problem you cant figure out, I have a wideband you can use in the future.

I would expect 15 MPG for a stock 216 or a 235 whether it has a ton in the bed or empty. I have verified this with each engine. The 216 has a Rochester model B, and the 235 has a Carter YF2100.

I have a recently rebuilt 235 with a Rochester B on it, im still averaging out its consumption. But my 261 seems to give me 12 mpgs no matter what.

Tidbits off the Internet for the Zenith 28 clone made in Argentina:

1.) 200 to 300 C.I. engines.
2.) 38 mm (1.5") throttle bore. Unlike Carter and Rochester, this carburetor has a removable venturi sleeve similar to the Zenith 28/228. I wish Daytona would share the sleeve diameter. This carburetor mounted on a 261 intake manifold will be 1.5" opening up to 1-11/16?". (My first thought, flow turbulence?)
3.) On a Jeep forum, a member contacted Daytonparts.com and a salesman made the statement that, "Our Daytona Universal replacement 1bbl carburetor will flow up to 195 cfm." Unfortunately it wasn't stated if that spec was @ 1.5" or 3.0" Hg. Note: At 1.5" Hg., a previous old posting here (May 55 Hot Rod) says 182 cfm was measured on the Rochester B made for the 261.
4.) There are options, that only a retail business can purchase, but these were not described.
5.) The manual says the adjustable main jet is preset for most engines for a correct fuel/air ratio. (My thought, yeah and bullfrogs have wings). For altitudes above 3500ft, follow the adjustment procedure (as described). Some owners have reported, at lower altitudes, they had to drive a distance, stop, re-tweak one revolution then repeat until it ran best. Last step was readjust idle speed to OEM spec.

Personally I would avoid buying any Chinese made carburetors (automobile, string weeder, chainsaw etc.) especially off of ebay. There is no quality control.
Buy from a USA company (even if they import) that will provide timely replacement parts and have good technical support. A business that will take it when stuff hits the fan.

Excellent, thanks for all the added information Buoymaker. Im sure it will be helpful to those interested in these carbs. As stated before, im still very happy with its performance. I would be hard pressed to tell the difference between the UN2 and the Rochester B. Its good to have another option, and if you want to go for a dual carb or triple carb setup and don't want to hassle with older carbs, this is a good way to go also.

If the engine is large enough it will flow 300 CFM.
A displacement range between 200 and 300" cannot be bridged by just a venturi change.

Panic, when someone has his mind made up, it's pointless to confuse him with facts.
jerry

Of course it can; just ask the folks that sell them!

Is there a sarcasm emoji?

Jon.

The intent of my last post was mainly to provide information. I'm not "fer" or "agin" the UN2.
I'm just shaking the apple tree hoping to get a ripe apple to fall.

Wouldn't the Carter YF 4371S be a better "universal carburetor", to use on a 261, than the UN2?
Disregarding issues that may require modification to the throttle linkage, vacuum advance and choke etc.
Listed application for 230, 250 and 292 engines.
Throttle bore 1 11/16"
Main venturi 1 5/16"
Metering jet 0.104"
Metering rod (3 step) 0.078", 0.052", 0.045"

If yes, why not clone the Carter YF instead of the Zenith 28/228? Difficulty in manufacturing? Patent issues?

2/16/2020 Update: Received complimentary fitting from Daytona Carburetors. I was told by Ron, one of the technicians that these fittings are exclusive to them. It is a 3/8ths to metric. The Metric side goes into the Carburetor. It doesn't bottom out, its the flared kind, so just snugged down. Now the setup looks much better with the glass bowl filter. Now just enjoy driving it. Will soon update with city MPG's.

Obviously, I have no special insight as to which was chosen, but manufacturing cost always includes the number of precise machining operations (removable venturi adds expense), toxicity of components (cadmium is poisonous), number of individual parts (separate choke horn, throttle body?), etc.

2/17/2020 Update: Today I hooked up my small trailer to take some metal to recycle (around 200 lbs.), I have to admit, to be completely honest, under load I could notice the engine did have quite a bit less power than with my Rochester B. I wont say it was a remarkable amount but still noticeable. It was a small trip I took, perhaps a 3 mile round trip, but on the up hills I did notice having to go deeper into the pedal to power uphill, where I hadn't had to do with with my Rochester in the past. I'll continue testing the UN2 with an open mind. My Rochester can go on it later if I like and I do have a 235 engine I can try it out on to see if its a better fit for it. Still content with its better drivability in town, but will have to try a heavier load next time to see how it performs.

That may just have been a later cut-in point for the power valve?
Thanks for the research.

Hello Panic, I didn't seem to understand what you meant by cut-in point for the power valve? I think to the best of my knowledge, that I have the main jet set as far out as possible, I have really good vacuum, ill have to see if the vacuum advance is working correctly on my distributor. I know for a fact my fuel is leaking back down the fuel pump. That ethanol just eats away at the rubber parts, I can see the fuel go down in the clear fuel filter. I cant imagine how it makes its way back up to the gas tank, but it has to go somewhere.

Your experimenting has pretty much proved what some of us suspected from the beginning. The carburetor in question does not supply sufficient air nor fuel to get the best performance from the engine, nor does it meter the fuel properly across the range of operation from idle to power production to light throttle cruise. The carburetor provides barely adequate performance- - - - -not optimum. It's better than a worn out, dirty carb, but not by much. Over time, it will probably deliver sub-part fuel economy as well. You might- - - -but probably won't be able to improve things by installing a bigger venturi and opening up the main metering system to flow more fuel than the wide open main jet can supply. Doing that properly will require more equipment and a more thorough understanding of carburetor theory and modification than you currently have at your disposal.
Jerry

Im glad you were able to arrive to a certain conclusion with my experimenting with this Carburetor, though I do not wholly agree with your assertion. My initial goal was not to surmise if the UN2's performance was equal to or greater than that of the Rochester, but if it helped you to come to that initial conclusion, then that is a good thing, though it is still a bit too early to conclude that as of yet. There are still other avenues I can explore before we have the final word. As I mentioned from the beginning, my purpose for trying this carburetor out was to gauge its quality, and craftsmanship, and also its utility with our stovebolt engines, not necessarily its performance. Seeing as how no one on stovebolt.com had tried this carburetor out, I believe this experience has been favorable, and shines a good light on this carburetor. Also, something to consider, one does not always chose a carburetor depending only on all out performance. If that were the case, we would all be running Fuel Injection, which gives the optimum air/fuel mixture for performance, driveability and fuel economy. For many reasons we continue to run Carburetors, be it Rochesters, Carters, Zeniths, Daytonas, etc. My sole experimenting as of yet has been on my 261 c.i engine, but there are still many other engines one could try this carburetor on, for example the 216 ci or the 235 ci, maybe even the 250 ci. and the 292 ci. Also,one always has the option of running a dual carburetor setup or even a triple carburetor setup, which I think this carburetor would lend itself well to, if performance is what your after. I believe that so far the UN2 has proven to be a good alternative if one wants good performance, great drivability, and quality of craftsmanship, but everyone can decide for themselves and come to their own conclusion on that.

2/18/2020 Update: I called the Dayton Company and talked with Ron, one of their older tech guys. Very patient, went through all the troubleshooting I can do to fix my low power problem. According to him, they test these carbs on their 320 ci Hercules engine. The UN2 is good for up to 275 ci with no problems. So it seems to be a problem on my end which I hope to remedy. One of the main things that I hand not changed was the timing. I don't know why it slipped my mind, but im sure that will be a major contributing factor. Ill do what conventional knowledge says and advance as far as I can before I hear pinging. Any other tips will be appreciated.

I give up

I don't make them, that's what they told me. They're the professionals. It would be good to ask someone that has a 2 carb setup how it runs. How he tuned it and if he's content with it. I've seen it done many a time. Im not an expert, but ive seen Chevy 350's with 500 cfm 600 cfm 700 cfm up to 900 cfm carbs. It doesn't mean its specifically tailored to that specific engine, but im sure its close enough. I have a friend with a 366 Chevy engine (I had never heard of it either) with 2 progressively connected 600cfm carbs, he says he wants to go to a single carb 900+cfm Carb because though it does give him crazy performance, the in town usability suffers, that's a 300cfm difference but im sure its going to run great, I doubt anybody would criticize him on not having the exact perfect carb for his engine . 235 and a 261 engines are not precision modern machines (though in their time they were), im sure Rochesters and these UN2 units can be adjusted to give adequate smooth performance as ive seen done with mine (and im still tinkering with it). I cant come to grips with some peoples opinion that the carb has to be perfect to that engine. In that case, there would be no aftermarket carburetor dealers, Edelbrock, Holley, Demon, and who knows how many others.

I'm a little late coming into the conversation, this carb. (UN2), is produced primarily for the S. American market. A lot of old cars which the original Rochester "B" will work on are there. Cuba has them on everything! Like the song by Jackson Brown " you can see a Soviet transmission in a Chevrolet". I'm a Rochester model "B" fan(atic), the reason that ClassicsR4Me is having trouble with the gas drain is one of 3 reasons: leak in fuel bowl to air horn gaskt., fuel line leak at carb or the Throttle body shaft. These old carbs can only be rebuilt so many times and beginners have a tendency to warp the air horn. A whole big bunch of thanks to Classics R4Me, great job and very attentive to his testing and follow up.

moparguy, the 261 c.i.d. normally uses a a .065 metering jet rather than the most popular .058. Good luck. Doc.

Thank you for the information Doc. Its good to know these carbs are widely used and working in many applications. Your correct about my Rochester, it looks to have been rebuilt a few times and though it gave me very good service, I just wanted to try a new carb to see how it would perform. Im still fiddling with it, im sure I can get a little more performance from it yet.

I've been following this and have wondered "What would the original owner of my '48 do?" He'd probably slap on the UN2, if needed, and go feed the cows. Picture shows where my '48 grew up on the Rocky Mountain Front.

I love how forgiving our trucks are.