Good Carb for vintage .30 sized engine Help!
11-17-2019, 10:34 PM
#1
Good Carb for vintage .30 sized engine Help!
I'm looking for some specific carb recommendations for a .30 sized vintage engine (a Forster .29 to be precise) that I'm planning to convert from n/v to r/c. All out performance is not the point here. Instead, I would like a carb that will give good idle and transition and good running characteristics for a scale/sport old-timey flyer.
I already have an OS 20B carb and an OS 2A carb kicking around in my spare parts bin that I'm contemplating but.....since the 20B is a buggy carb I'm favoring the 2A instead which is for the OS .20-.25 FP engines. Since the 2A handles .20-.25 it should be perfect for an old .29. Anyone know if the 2A is a decent carb overall tuneability wise or would there be a better choice? Maybe an old Webra or an old Enya carb? Any ideas?
I already have an OS 20B carb and an OS 2A carb kicking around in my spare parts bin that I'm contemplating but.....since the 20B is a buggy carb I'm favoring the 2A instead which is for the OS .20-.25 FP engines. Since the 2A handles .20-.25 it should be perfect for an old .29. Anyone know if the 2A is a decent carb overall tuneability wise or would there be a better choice? Maybe an old Webra or an old Enya carb? Any ideas?
11-18-2019, 01:32 AM
#2
I personally would favor an Enya carb as one for an engine that size would be a metered airbleed instead of the standard non-metered airbleed of the OS FP series. BUT - the OS carb would likely work just fine. The Enya carb would work as well; just a little better. Since you’re not dealing with a monster powerhouse revver of an engine, I don’t think you need to be too picky.
11-18-2019, 04:10 PM
#3
Thanks for the response and for an appropriate answer. Typically these days the trend is towards high rpms and power and people would tend to steer you to the carb that they think will get the most rpms out of an engine, which is not what I'm looking for with this old girl. As with full size engines bigger is not always better. In my younger days I had an old Chevy Nova with a 327 and some very mild headwork, cam, headers and it ran great on a Holley 600cfm but was useless on a 750cfm. Anywho, glad you pointed out the airbleed feature. Now, what size Enya would be appropriate you think. Would a carb from one of the very common Enya .19 line of engines be sufficient or would it be a tad bit on the small side for a .29? I don't want to get something from a .35-.40 engine as that would over-carb the old engine and probably give it substandard air-flow characteristics. I think Enya made some .29 engines as well but those don't seem to be as plentiful as the Enya .19 series of engines and it might take some time before a parts engine comes my way. But if both the Enya .19 and .29 had the same carbs then that would be the ticket.
Last edited by meowy84; 11-18-2019 at 04:13 PM.
11-18-2019, 08:04 PM
#4
BTW, I just looked at the 2A carb and it does look like it does have a metered airbleed (i.e. it does have the adjustment screw to close/open the airbleed hole). Here's the OS exploded diagram.
11-18-2019, 09:37 PM
#5
Thanks for the response and for an appropriate answer. Typically these days the trend is towards high rpms and power and people would tend to steer you to the carb that they think will get the most rpms out of an engine, which is not what I'm looking for with this old girl. As with full size engines bigger is not always better. In my younger days I had an old Chevy Nova with a 327 and some very mild headwork, cam, headers and it ran great on a Holley 600cfm but was useless on a 750cfm. Anywho, glad you pointed out the airbleed feature. Now, what size Enya would be appropriate you think. Would a carb from one of the very common Enya .19 line of engines be sufficient or would it be a tad bit on the small side for a .29? I don't want to get something from a .35-.40 engine as that would over-carb the old engine and probably give it substandard air-flow characteristics. I think Enya made some .29 engines as well but those don't seem to be as plentiful as the Enya .19 series of engines and it might take some time before a parts engine comes my way. But if both the Enya .19 and .29 had the same carbs then that would be the ticket.
Funny that you would mention carburetor equipped cars. Back in the day I had a 455 powered Trans Am. For normal street driving I would use the stock Rodchester Q jet with a Edlebrock performer manifold, for autocross I would swap out to a 650 cfm Carter for smoother transition and better bottom end torque. For the drag strip I had a Holly dominator intake with a 750 double pump carb. Of course there were different sets of distributor weights and springs to dial in the timing advance for each setup.
11-19-2019, 03:44 AM
#6
The OS carburetor is NOT a metered airbleed carburetor. The difference between a metered airbleed and a standard airbleed is in the barrel. The barrel of a metered airbleed carb will have slits milled into it that feeds metered fuel at low throttle. What this does is turns the airbleed into a trim instead of a normal airbleed. Traditional airbleeds allow a set amount of fuel through based on needle setting and barrel opening and the airbleed controls idle mixture via adding more air. You can get a finer setting with a metered airbleed carb such as the Enya. Older engines aren’t timed aggressively and as such may require a finer carburetor setting to operate well - remember that this engine was designed to run WOT all the time. The Enya carb has a slight midrange adjustment as well - move the fuel inlet out further from the carb body. The OS May have this as well, but it doesn’t have a metered barrel. If you have the OS 2A, try it. It may work. If not, get an Enya. Probably one from a 25SS will have a metered barrel. The old .19s didn’t have a metered barrel, but they work o.k. I have one from a .19 on my MDS .21 Marine Diesel.
11-19-2019, 04:47 AM
#7
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Fox EZ just metered carb barrel. It's metered by more and less of the slit overlapping the matching number in the carb body.
Metered carb barrel:
Last edited by Hobbsy; 11-19-2019 at 04:49 AM.
11-21-2019, 05:40 PM
#8
Funny that you would mention carburetor equipped cars. Back in the day I had a 455 powered Trans Am. For normal street driving I would use the stock Rodchester Q jet with a Edlebrock performer manifold, for autocross I would swap out to a 650 cfm Carter for smoother transition and better bottom end torque. For the drag strip I had a Holly dominator intake with a 750 double pump carb. Of course there were different sets of distributor weights and springs to dial in the timing advance for each setup.
The OS carburetor is NOT a metered airbleed carburetor. The difference between a metered airbleed and a standard airbleed is in the barrel. The barrel of a metered airbleed carb will have slits milled into it that feeds metered fuel at low throttle. What this does is turns the airbleed into a trim instead of a normal airbleed. Traditional airbleeds allow a set amount of fuel through based on needle setting and barrel opening and the airbleed controls idle mixture via adding more air. You can get a finer setting with a metered airbleed carb such as the Enya. Older engines aren’t timed aggressively and as such may require a finer carburetor setting to operate well - remember that this engine was designed to run WOT all the time. The Enya carb has a slight midrange adjustment as well - move the fuel inlet out further from the carb body. The OS May have this as well, but it doesn’t have a metered barrel. If you have the OS 2A, try it. It may work. If not, get an Enya. Probably one from a 25SS will have a metered barrel. The old .19s didn’t have a metered barrel, but they work o.k. I have one from a .19 on my MDS .21 Marine Diesel.
As for the Forster (the 1952 F-29 that is) being designed for WOT you're right. In my defense though I picked it for 2 reasons. First it was and still is very common and so prices are low and availability is high. The other more important reason I picked it to tinker with as opposed to some of the other old engines out there (such as O&R) was that through some research there seemed to be a concensus among the 'old timers' that the Forster lends itself well to throttling (there's a couple of videos out there) and it was also actually designed for glow (as opposed to being designed primarily for spark ignition). Some of the other old engines do not handle glow very well at all. The O&R (.19, .23, .60) comes to mind as having a nasty habit of being unable to handle glow because of the method or cylinder-to-crankcase attachment and so having a tendency of popping the cylinder right off.
11-21-2019, 10:06 PM
#9
That was back in the day when these cars were actually affordable for the average guy. How times have changed. The prices for the traditional 'muscle cars' these days are ridiculous.
Aha, now I get it. So let me get this straight. When you were referring to trying an Enya carb you didn't actually mean any old Enya such as the very old Enya .19 series all the way to the Enya .19V. While "airbleed" they are not "meterer airbleed". You meant old but newer (if that makes sense) Enya .25SS correct? Now, just in case I have a hard time hunting down one of these Enya .25SS carbs, what are some other examples/engine brands with metered carbs?
As for the Forster (the 1952 F-29 that is) being designed for WOT you're right. In my defense though I picked it for 2 reasons. First it was and still is very common and so prices are low and availability is high. The other more important reason I picked it to tinker with as opposed to some of the other old engines out there (such as O&R) was that through some research there seemed to be a concensus among the 'old timers' that the Forster lends itself well to throttling (there's a couple of videos out there) and it was also actually designed for glow (as opposed to being designed primarily for spark ignition). Some of the other old engines do not handle glow very well at all. The O&R (.19, .23, .60) comes to mind as having a nasty habit of being unable to handle glow because of the method or cylinder-to-crankcase attachment and so having a tendency of popping the cylinder right off.
Thanks for the pic, worth more than a 1000 words. So Fox carbs also have this metered airbleed? All of them or just some?
As for the Fox carbs - only the “EZ Adjust” carbs are metered airbleed as far as I recall. I don’t believe they made those carburetors for the smaller engines like the .15 - which is about the size carburetor you’d want for your Forester. I had a Fox EZ Adjust carb and didn’t care for it. The midrange was too lean. I don’t like “kit” carburetors, so I used a different brand carb that didn’t need modifications to run correctly. I know not all EZ carbs were like this, but many were.
Last edited by 1QwkSport2.5r; 11-21-2019 at 10:17 PM.
11-24-2019, 03:15 PM
#11
I had a 283 in a full sized Pontiac. Got the smallest Carter AFB I could find maybe 500cfm. That worked great. With the 327/350 hydraulic cam it pushed that old Pontiac right up to 120mph. (And I'm lucky enough to be here to tell you about it!)
11-24-2019, 06:03 PM
#12
