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

Greetings stovebolters. I recently looked up information on Stovebolt.com regarding the Daytona Universal Carbs, and it seems nobody had tried it out yet. I thought Id try it out and update everybody on this Carb.as I went along. So I decided to write to the company directly and ask them about their UN2 unit, and how it worked. The gentleman I was in contact with Mr. Ron Hewitt was very helpful and gave me allot of information regarding their carburetor. Ill put the detailed information he gave me later in this thread if anybody is interested. What stood out of what he wrote is that they've sold over 6000 units. Chevs of the 40's alone sells about 10-20 units per month. So I thought Id give their carb a try and inform everybody on my progress and results good or bad of this carb. Ill try to be as impartial as possible.
The test vehicle is my 1946 Chevy pickup. It has a 261 Chevy engine from I believe around 1958 (ill check on that later). Ive been running a Rochester Carburetor that was working great until a few months ago. The engine is nearly all stock. except for the 12v system with alternator. Its running regular points. When I first got it, It was giving me a consistent 12 M.P.G lately that's dropped to about 10 M.P.G I suppose mostly because for some reason ive been losing the fuel in the bowl (though I haven't confirmed this but will upon removal) and the need to crank the engine until fuel is delivered after it sits for a few days. I will set my points again, most likely at 18 thousandths. Ill also change the intake exhaust manifold to a nice painted one I have ready to go. Pictures of the installation coming soon. Heres what it looks like now.

Was that his name? Coincidence I guess.

Gabriel, your truck is a beauty. It looks great!. I would never remove my Carter but I'm interested in what you come up with.
Mark

Thanks Mark, yeah I love my truck, its a blast to drive. I was told that the best Carburetor to run on these engines is the Zenith Carb. Ive heard that they are very expensive though. These Daytonas are supposed to be copies of those, that's one of the main reason I was interested in trying it, besides the fact that its a brand new Carburetor. We'll see how it runs with it and keep it posted.

The Daytona has been poo pooed here since it first became available. It will be interesting to see actual documented experience with it. If folks will keep it civil and forget the snide insulting comments thus allowing you to be as unbiased as possible. Try not to go on the defensive and just report what you find. You will have to develop a thick skin as I’m sure some will not adhere to my above advise. Good luck.

Thanks for the heads up. I personally like to keep things original also, but as carbs get older and they are constantly rebuilt, they lose a bit of their drivability. I can always go back to the Rochester, but its nice to try something new and see how it works. Im curious to see how the Daytona performs. Might like it, or might hate it, never know till you try it.

It looks like my Rochester was losing fuel somehow. It looks a bit too low in the bowl. Can someone tell me where the fuel leakage usually comes from on the Rochester? Side by side comparison of the Rochester next to the Daytona. Customizations ill have to perform. The fuel cable bracket needs to be flipped over and upside down, then have the bracket bent down 90 degrees. Another thing ill need to change is the distributor vacuum line. On the Rochester its towards the front of the fuel air mixture needle, on the Daytona its towards the rear. I will connect it by rubber vacuum line. Also, wont be able to use my original heavy duty air filter. Regular air filter should be ok.

I don't think quality control is the problem, it's the idea that a few variants can be as close to the original mixture requirements as the many, many OEM carburetors. L6 engines of the same size will not require the same carb except by accident.
They may have developed the throttle disc size, venturi, jetting, vacuum setting, pump discharge, idle and transition hole sizes and locations, etc. on a specific engine, and will give good results... on that engine.
As your engine begins to differ from their model (displacement, CR, port size, cam timing, spark advance curve, valve area, overlap, rod ratio) the results will be worse - but perhaps tolerable.
Now, the 235 is an excellent model for this due to long use with very similar tune-up specs, so we certainly would like to hear results.
TIA

Looks like the Chinese Zenith knockoff I purchased. I used the carb on a test engine (GMC 248) and it performed well.

This is what Mr. Hewitt wrote in regards to that point. "The base Daytona UN2 carburetor has been in constant production in South America since 1957". I believe they are made in Argentina. They have a 1 year warranty for manufacture defects.

I understand from the writeup that it has an adjustable main metering jet. That could make a big difference I think.

Totally agree.

Additionally, I have been unable to find any specifications of the items mentioned above by Panic. But my real issue is: where does one get parts????? One bad tank of fuel, the carb idle circuit is plugged, and the carb needs to come apart for cleaning.

If you need any verification of the parts issue, just find someone with a mid-1980's or 1990's I.H.C. tractor which was imported and renamed. We finally got enough requests to tool up rebuilding kits for some of them. This (I.H.C.) is a MAJOR brand, and information was available, just no parts.

I realize many today live in a throw-away world, but I don't!

Jon

They say they stock all components replacement parts, which is another plus. Heres what Mr. Hewitt wrote regarding adaptability : "Since the carburetor manufacturers could not continue to make each factory specific carburetor model, they would make a Universal to retro-fit original applications and unlike factory carburetors with fixed jetting and fixed throttle throw, the Universal models allow the full adjustment of the throttle lever to suit different hookup's; slotted base bolts to fit the small base US standard 1bbl (2 11/16") and also the larger flange (2 15/16"). The Universal carburetors also used a external adjustable high speed main jet to allow the fine tuning of the high speed circuit so you can match up the main jet orifice size to suit your particular engine, without tearing the carb apart and guessing at a correct jet size. This is a simple process based on the manifold vacuum your cylinders produce with the throttle open and the engine running at speed (2000-2500 rpm). Same principal as adjusting a idle circuit, except on the high speed side"

Most carburetor manufacturers like Carter, Rochester, Stromberg, Zenith, etc. stopped using adjustable main jets back in the late 1930's or early 40's. Think of all the research and development money they could have saved by simply continuing to use technology that existed back when engines had 6:1 compression ratios, Babbit bearings on the crankshaft, and needed to be rebuilt every 30,000 miles! How does the power enrichment system get adjusted for such things as automatic or standard transmissions, different rear axle ratios, and other variables that aren't directly affected by either idle or main jet adjustments? The "one size fits none" approach has been tried repeatedly, and failed every time. Maybe this time it will be different. I suppose some people will be willing to accept mediocre performance from a universal carburetor because they don't know any better. Growing up eating 30% fat content hamburger is OK as long as somebody never gets served a prime quality steak, also.

I wonder if the average purchaser of one of these carburetors will have a 4-gas exhaust analyzer and a chassis dynamometer to help get those adjustments done correctly?
Jerry

Gabriel - that is an interesting answer, that really doesn't tell us much, other than you can order parts from Daytona at this time; how about elsewhere.

I have no issue with adjustable main jets, and consider them a bonus; however, they are NOT the major criteria in selecting a replacement carburetor. Internal size IS the major criteria, which is one of the issues to which Panic was referring in his post. One really great application of the adjustable main metering jet is the ability to temporarily retune an engine on a trip. As an example, if I were to leave Missouri (elevation where I live approximately 800 feet) and make a trip to Denver (elevation about 5500 feet).

When a customer asks us for a replacement carburetor; we have a list of questions.

(1) flange size (Daytona covers this)
(2) engine displacement and engine modification. These are critical in selecting the proper carburetor, as they give us information to determine internal venturi size, which is what determines the airflow characteristics of the carburetor. If it is determined that a specific engine requires a 24 mm venturi, and one installs a carburetor with a 27 mm venturi; one can adjust the adjustable main jet from all the way in to taking it out and putting in one's pocket, and the engine will always be sluggish at lower RPM. Conversely, if the engine requires a 27 mm venturi, and a carburetor is selected with a 24 mm venturi, then the engine is going to be sluggish at higher RPM, and in effect, the venturi will be a rev limiter.
(3) once the proper venturi is selected, then the adjustable main metering jet is useful to "tweak" the mixture for the volumetric efficiency of the given engine; but it will NOT compensate for using the wrong size venturi. Generally speaking, our customers never need to adjust the adjustable jet (if the carb we sell has one) more than plus/minus 1/4 turn (generally less) from the standard setting. And other tuning components are useful as well. As an example, Carter offers at least 5 different vacuum springs to help tweak the mixture for different engine vacuum profiles. This is not possible with a carburetor with an adjustable main jet UNLESS the adjustment is connected to a dial on the dash and may be adjusted "on the fly" by the driver.
(4) next question is cost versus performance. Not everyone wants to pay for good performance and reliability (one reason the Rochester B's are still somewhat popular). The Daytona carburetor certainly fits the "less expensive" criteria.
(5) we also ask about the terrain traveled by the customer, as there are some less expensive carburetors that may be used successfully if one drives in an area that is virtually flat.

But the key for you is that if you are totally happy with your purchase 5 years from now, then that becomes the ultimate criteria.

Jon.

You know allot more about carbs than I do Jon. I appreciate the information. I just thought id try it out and see how it worked. Im sure it wont be the best, but if it gives me decent performance then ill be happy. If it doesn't, then ill go back to my Rochester carb. Its just that nobody has tried it out and seen what it can do, so I thought id do that. Ill be working on it some more today, hopefully I can get it hooked up soon. It will take me a while of driving to see its response and fuel consumption. Another reason im trying it is my Rochester was starting to give me problems. It was leaking down fuel. I saw the intake manifold was wet with fuel and the carb bowl was low. So I would have to have addressed that sooner or later. Do you know what usually causes that problem?

Gabriel - much as I enjoy throwing rocks at the Rochester B's ( ); the carburetor probably is not the issue here. Rather it is the volatility of modern fuel. The Rochester B can leak down, but only if you park the truck on its roof (upside down ) Leaking down is a function of Holley carburetors, with the diaphragm type power valves, and a gravity passage direct to the intake.

Jon.

Gabriel - see my new thread.

Jon.

Gabriel, I’ve enjoyed reading this thread. I appreciate you biting the bullet and buying this new Daytona carb so we can all learn from your experience. I’m really looking forward to reading about how it performs. Please post frequently.

Thanks Chuck, I appreciate it.
Here's the latest update. I installed the Carburetor with a temporary setup. I tried to put the old school glass bowl filter as I had it before, but was not able to find the correct fittings so I went without it for the moment. I installed the fuel filter that comes with the carb right after the fuel pump. Prior to connecting the fuel line I ran the fuel pump for about ten seconds until I could see clean fuel coming out as the instructions say. This seems to be an important step as the main reason for initial failure is that the carb gets debris inside and floods the carb. The engine started right up, idles perfectly, (as my Rochester did). Only downside I see so far is that I wont be able to use my original heavy duty air cleaner, as the mount is quite a bit smaller. The regular auto air cleaner (non heavy duty) fits right on there. I just happen to have an extra and will run that one in the meantime. Response feels nice and crisp when I touch the pedal. Now to wait for some sunny weather so I can feel if it has the same power, and see how it is on fuel consumption. I don't think ill have to worry about leaking the fuel out of the carb while it sits like my Rochester was doing.

Here's a picture of my sparkplugs I was running with my Rochester. If I remember well, this light gray coloring means it was running well. Perhaps I should take them all out and clean them to see how the new carb is running. What do you guys say? On another note, I got rid of the pesky exhaust leak I had with new exhaust/intake manifold gasket and new exhaust pipe connection gasket.

Time to adjust the High Speed Main Jet. I hope its as easy as it says in the instructions. Ill get back on that. Here also is a picture of the parts you can order in case you need to rebuild your carb in the future. To those who know Zenith carbs, is this a close resemblance to those carbs?

Reading spark plugs is a futile effort since they quit putting lead in gasoline. The white / tan/chocolate brown /black colors we used to look for don't happen any more- - - -plugs go from almost white for any normal fuel mixture to black and sooty when the mixture gets overly rich. Black and greasy still indicates oil burning. You're about 40 years late with that tuning method, which is why I mentioned a 4-gas analyzer, preferably one that can be rigged to monitor mixture during a road test. I ran a test like that on a 600-mile round trip to an advanced tuneup seminar sponsored by Snap-On about 20 years ago, but the doofus assistant principal at the school where I was teaching auto mechanics decided to clean out some file cabinets over spring break one year, and discarded the files, along with documentation of hundreds of chassis dyno and engine dyno runs. He was not welcome in my shop for a long time after that!
Jerry

hahah, I guess I am late on that tuning method. I hadn't read that information you mentioned anywhere. So much for that idea. Ill have to read up on 4-gas analyzers too. Thanks for the update.

Adjusting high speed main jet: Before adjusting air/fuel mixture as per instructions, I connected my timing light for the tachometer. Revved engine and set at 2000 rpm stayed pretty steady. On the front of carb, I turned the high speed main jet adjuster in (right) and the rpms started dropping to about 1980 rpms, I started backing up, turning out slowly, rpms started raising slowly 2020 was jumping between 2010, 2020, 2030. Kept backing up and rpms kept rising jumping about a bit 2050, 2060 until I reached a maximum of about 2080 or 2090 rpms and didn't see any more changes so I left it there. Next I hooked up my vacuum gauge to adjust air/fuel mixture. Started at about 21 lbs. of vacuum I adjusted in and out and looks like it was set pretty good from factory, stayed at around 21 and idled just beautifully. I was at 600 rpms idle and backed it down to 500 rpms, and was purring like a kitten. I revved the engine and it sounded allot throatier than before the fast idle adjusting. Now to put the air cleaner on and fill the tank to see what kind of gas mileage I get. Performance will have to be by my judgment. I was very content with the Rochester's performance but am excited to see what kind of performance I get now. We'll have to see how the UN2 does.

Here's a closeup of the modification I had to make to the throttle cable bracket. I took it off the carburetor (two bolts), flipped it over, put it in the vice and bent the end part (where the cable is tightened) 90 degrees downwards. It wasn't too difficult and was content with the outcome.

Fortunately, 100+ octane racing gas still has enough lead additives in it to do plug readings after a few hot laps. I used to go to the track with 4 or 5 sets of plugs, and we might use all of them while tinkering with mixture settings during practice. A quick trip through the glass bead blaster got them ready for the next week's racing. With a good hot spark ignition system, plugs seldom "wore out"- - - -they just got dirty enough to need a cleaning if the mixture was a little off.
Jerry

Fortunately the carb on my 1950 216 with 2500 original miles on it starts, and runs like it's fuel injected so far. They have had electronic injection 4 barrel setups for years now for V8's, and I even saw someone offers a 2 barrel fuel injection now. They are missing a big market leaving out the old 1 barrel fuel injection conversion, which would be great with a few mods on many old vehicles.

What type of power enrichment system does that carburetor have- - - - -mechanical metering rods, or a vacuum controlled power valve? You're going to need a way to monitor the air/fuel ratio at light throttle cruise, and also at around 10 inches of manifold vacuum or less- - - -simulating hill climbing and/or passing. A small change in the power mixture will make a huge difference in performance and engine life- - - -too rich severely compromises power, while going lean wipes out exhaust valves, spark plugs, and possibly pistons. By the time you "hear" a lean preignition/detonation noise, you're way beyond safe power mixture limits. I prefer to monitor those parameters on a chassis dyno run instead of doing a road test. Good luck!
Jerry

You got me there Jerry, I can only imagine its mechanical. Do single barrel carbs usually have vacuum controlled valves? I think you would have been the best one to test these carbs out. My carburetor knowledge is very limited. I can only adjust the carb like any other regular guy can with the vacuum gauge. But I cant imagine its too far off its ideal. One can tell by the smell and the feeling of the vehicle if its too lean or too rich.

"Different strokes- - - - -etc." I'm a firm believer in the slogan Sun Electric Co. used to put on all its test equipment- - - - -"We Test- - -Not Guess"!
Jerry

That's a slogan I can get behind. Unfortunately, until a professional tests one of these carbs out, my guess will have to do.

How about installing a O2 sensor in exhaust and using it to monitor mixture. Then tune accordingly.

O2 sensor, vacuum gauge, tachometer, and an accurate record of fuel consumption on at least a 10 mile closed loop test course, and adjust the raw data from several test runs for temperature, atmospheric pressure, and humidity. Some of my really impressive dyno runs turned out to be a fluke of weather, not some magic we conjured up with fuel mixture and ignition timing. One of the best indicators of what's happening in the combustion chamber is an accurate record of exhaust port temperature. On the dyno, we had sets of exhaust manifolds and headers with thermal monitors for each exhaust port.
Jerry

That's a great idea, but probably a bit out of my price range. In any case, my idea is doing what a regular guy would do, getting the results a regular guy would get. The best I can offer is doing a city driving mpg's and a separate Highway mpgs. Though I imagine it wont vary all that much since I only run about 50 mph on the highway. I mentioned before, I was getting 12 mpgs (varied driving) averages with my Rochester, but later that dropped to 10-11 mpgs I attributed to losing fuel when parked for an extended period of time. As soon as the weather improves here in northern California, ill get to the testing.

Be very careful about not getting that adjustable main jet too lean. Once the fuel/air mixture gets much below that ideal 14.7:1 (stoichiometric) mixture, combustion temperatures spike into the range where engine damage happens very quickly. One night we had a MOPAR 440 tractor pull engine on the dyno, making a final torque pull at 6500 RPM. Apparently, a bolt near the middle of the intake manifold had loosened up for some reason, and one cylinder went very lean due to a vacuum leak. I heard a very slight rattle from the engine, and before I could back off the dyno load and chop the throttle, that piston got a half dollar sized hole burned into it. Of course, the RPM/Torque calculations we made after the fact on that run yielded 714 HP running one 4 barrel carb and gasoline, prior to adjustment for temperature, pressure, and humidity. At those power levels, things happen very quickly.
Jerry

Sometimes trial and error is fun. Not for everyone, but it can be fun.

I think one reason the Stovebolt-6 has lasted so long is that it is forgiving. Forgiving for dummies like me.

I've found over 40-sometning years of doing dyno runs that the "error" part of that process can get terribly expensive. Very few engines run well with an air-cooled crankcase (big hole in the block where a connecting rod used to be!)
Jerry

Jerry - on the other hand, if one installs a sleeve, then one can convert an inline "six" into a "seven"

Jon

1/15/2020 Update: The weather cleared up for a few hours and I was able to go fill up the tank. I think we might have near the most expensive gas in the nation (northern California). This was at Costco, which is usually about 20 cents cheaper than most places, $3.75 is the average for regular right now at most gasoline shops in town. My initial impressions, and I have to stress, initial impressions on a 30 mile round trip mostly highway driving are: In town, on the low end, about the same or perhaps a little bit more grunt than my Rochester. Smoother power delivery, and less jerking when I let off the gas abruptly. The UN2 helps my 261 idle beautifully at 500 rpms. Perhaps smoother that my Rochester did. I can hardly feel the engine vibrate. One thing I did notice with this carb was that when cranking the engine, I did have to tap the gas slightly to start out even when warm, something I never had to do with my Rochester. Now that might be down to the low rpm setting. I believe I was at 600 with my Rochester. High end driving: it definitely has a bit less grunt at the high end. Now this could be attributed to a few things. One, the air cleaner is noticeably smaller, with the larger heavy duty air cleaner I had on my Rochester, when I would gun it on an uphill in high gear, I would get a beautiful metallic vacuum sound that I loved, and you could hear allot more air going in, something im not noticing with this smaller air cleaner. (I have a paper air cleaner I might try to see if this will remedy the problem) Also, I adjusted the high speed jet without the air cleaner on, this might have something to do with the more sluggish power. I must note, that though it does feel less powerful on the top end, its not greatly noticeable, and there are some things I will try to remedy this. I will call the company and see what kind of customer service they give and what kind of technical advice is at hand. So far, im very content with the carb, with that small downside regarding the air cleaner. Ill definitely try to get some more miles on my truck and post anything I find that has merit announcing (weather permitting). Other than that, just see what its like living with the UN2 day to day, and what kind of gas mileage it gives me, first highway miles, then city driving miles.