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MG MGA - Altering carbs for Ethanol

I found this on the internet and would be interested in the board mebers opinion on the validity of this conversion. Are there any parts or points of this text that could be applied to MGA's in order to aliviate "vapour lock". IE: float level adjustment....increased jet sizing.....etc.



Carburetor Conversion
1


Acquire a spare carburetor. Converting a second carburetor to ethanol has a couple advantages. It keeps the vehicle in service while the work is being done and gives the car owner the ability to revert back to gasoline, by re-installing the original carburetor, if necessary. Check salvage yards for a used carburetor.

2


Install a carburetor kit. Carburetor kits are prepackaged parts kits containing valves, gaskets and any other parts particular to that carburetor model that can wear or deteriorate. Installing a carburetor kit overhauls the carburetor.

3


Find and measure the jets, the openings where fuel is forced under pressure into the mixing chamber. Because ethanol contains less energy than gasoline the amount of the fuel introduced to the engine must be increased. Measure the opening, which will be small, very accurately. Use a micrometer, if available, or take the jets to a machine shop for measurement.

4


Increase the size of the jets by 40 percent. Calculate the new size based on the measurements of the original jets. Determine the proper size of drill bit and use it to enlarge the jet. Home mechanics without access to a full set of drill bits and a drill press can have this work done at a machine shop. Another option is to purchase new jets of the appropriate size, if available, from an auto parts retailer.

5


Alter the carburetor float. Ethanol is denser than gasoline which would result in the float riding too high and stopping the flow of fuel into the carburetor. The float arm can be bent but that is a trial and error process and can be difficult to accomplish accurately. Another option is to add 10 percent to the weight of the float. Remove the float and weigh it. Calculate 10 percent of the float's weight and solder an equivalent lead weight to the float.



Gordon Harrison

I think it might depend on how much ethanol is being used in the gas. Here in the Chicago area 10% is typical, and other than using teflon hoses and carb seals (where available), I don't think any other changes are needed. E85, also available here, is probably another story, but why use that if there's another option. Not an expert on this, I'm sure there will be more informed opinions.
G Goeppner

I believe Gordon is talking about converting to pure Alcohol, not gasoline with the alcohol added from the pump. I raced go-karts for many years using Briggs and Stratton engines modified for Alcohol. Enlarge the jet, advance the timing were the only two mods needed. Thought about doing this for my lawn equipment but not my MG!
GTF
G T Foster

GT
I am trying to get a view of what the future will bring.It seems that as we progress,ethanol/alcohol will become more prevelant in our fuels. Therefore in preparation for this I am discussing, how we can adjust to this and what can we do to help our cars run. It mentions a simple jet change to combat the presence of alchol. Does anybody think this would work on an MGA? I am also interested, in an effort to sort out a present minor 'vapour lock". Also to find adjustments that could possibly be made, to our carbs, to combat gas additives.

I have no intention of running my MGA Coupe as a full blown alcohol fuelly, daily driver......althought ????
Gordon Harrison

The affore mentioned 40% increase in jet size applys to regular carbs, not SU's. According to "SU Carburetters Tuning Tips & Techniques" The methanol needs are 2x the petrol needs. This 40% is a start. They mention that for best power, the jet must be increased further since Methanol likes to run richer still. Therefore the carb bowl needle must be capable of this new flow rate. They suggest possibly needing a larger bowl. 2nd, the "Effective" jet size can easily be increased using the methods as outlined in the book. Both jet and needle must be custom made.

This is covered in about 2 pages of the book mentioned. There may be some concern about the Methanol/carb body compatibility for long term use.

I think I'd go straight to fuel injection & electronic ignition if that time ever came. That is if I had an MG and still had the original engine/carb setup. Just think about hiding a pair of injectors under the vacuum chambers and going stealth.......
Chuck Schaefer

If you think vapor lock is a problem with 10% alcohol, you might multiply the problem by 10X for 100% alcohol. The stuff just boils at a lower temperature than straight gasoline. For 100% alcohol fuel in the MGA you would definitely need to blow cool air on the carburetors in hot weather.

Ethanol alcohol has about 40% less energy per unit volume than gasoline. As such, 10% alcohol in gasoline reduces fuel economy by about 4%. The difference in fuel/air mixture is relatively small, so the carburetors usually get on okay with a simple mixture adjustment.

To run on pure alcohol, for the same amount of power output you need
1 / 0.6 = 1.67 times as much fuel (not just 40% more). I'm not sure how the fuel to air ratio works out for pure ethanol, if 1.67x the amount of fuel might burn properly with the same amount of air. If perchance it takes only 40% more fuel (alcohol) to burn with the same amount of air, then you would get less power output.

I suppose one of the attractions for alcohol is higher octane rating, ability to tolerate higher compression ratio, more spark advance, and presumably more power for a given displacement.

I'm with Chuck on this one. If you have to run an MG on 100% alcohol, I'd be looking seriously at fuel injection to replace the carburetors. Most of the current problems we have with hot carburetors is due to 10% alcohol in the fuel. I can't imagine trying to run a hot carburetor on 100% alcohol.
Barney Gaylord

I am not trying to run on 100% alcohol. I AM trying to figure out
#1...why the internet has the topic of removing alcohol from gasoline...#2..If future gasoline is going to contain more alcohol, will we have to modify our carbs, and how would we do that...and #3..if vapour lock occurs now, with the current gasoline,what will it be like in the future.
Gordon Harrison

#1... Because it's a problem with MG carburetors. Because it reduces fuel economy without a commensurate reduction in price of the fuel. Because alcohol costs more to produce than gasoline so has to be either subsidized by the government or mandated in law (increasing cost of fuel). Because motor fuel ethanol is mostly manufactured from food grain which is a world commodity, increasing the price of food in the entire world, reflecting a larger indirect cost of motor fuel which people are supposed to ignore. I'm sure I missed a few more points of discussion, but no one seems to have anything good to say about it, and even the Green Geeks (environmentalists) don't have a leg to stand on.

#2... Yes, for higher alcohol content the carbs would have to be modified (or replaced). How you do that is a topic of wide discussion (some of it detailed above), but will always be moderately expensive. We are already spending money on heat shields and fans and Viton seals to deal with 10% alcohol content. When changes are small and gradual they sneak up on us a little at a time. To some extent we come to be "acclimatized", so to speak, either learning to deal with it or learning to live with it as it happens. There is a fair chance that the next step might be 15% alcohol in gasoline. Unfortunately some of the acclimatizing leads to some of the vintage cars being parked and not driven.

#3... Worse, depending on what we get for fuel in the future.
Barney Gaylord

#1... Because it's a problem with MG carburetors. Because it reduces fuel economy without a commensurate reduction in price of the fuel. Because alcohol costs more to produce than gasoline so has to be either subsidized by the government or mandated in law (increasing cost of fuel). Because motor fuel ethanol is mostly manufactured from food grain which is a world commodity, increasing the price of food in the entire world, reflecting a larger indirect cost of motor fuel which people are supposed to ignore. I'm sure I missed a few more points of discussion, but no one seems to have anything good to say about it, and even the Green Geeks (environmentalists) don't have a leg to stand on.

#2... Yes, for higher alcohol content the carbs would have to be modified (or replaced). How you do that is a topic of wide discussion (some of it detailed above), but will always be moderately expensive. We are already spending money on heat shields and fans and Viton seals to deal with 10% alcohol content. When changes are small and gradual they sneak up on us a little at a time. To some extent we come to be "climatized", so to speak, either learning to deal with it or learning to live with it as it happens. There is a fair chance that the next step might be 15% alcohol in gasoline. Unfortunately some of the climatizing leads to some of the vintage cars being parked and not driven.

#3... Worse, depending on what we get for fuel in the future.
Barney Gaylord

Since you adjust the carbs with the engine running, this should sort itself - as long as the ethanol % is low as Barney says.

A bit rich is better than too lean.

Maybe with Ethanol fuels, we should go from the standard GS needle to a number 6 (a wee bit richer in the middle, right?) as standard practice.

I know from experience that you need to make sure that the float bowl rubber seals are Viton - the original rubber will perish quickly.

There is a website that lists all the gas stations in the US that sell non-Ethanol gas, so if there is one near you that might be a good solution if you are worried about it.

We have 10% at a minimum here - so I have not known anything different, and my car seems to have plenty of power. Maybe if Barney drove it he could tell the difference - I can't.

JIM in NH
AJ Mail

I've been running the MG on regular grade E10 for a few years now. It's all that's available at normal gas stations in New York. Also pretty much all I saw on my recent cross country trip with the MG. The engine runs just fine on it. I have made any specific changes. Even if they go to 20% (as has been rumored) I don't think it'd be a big deal. Just my opinion..
GTF
G T Foster

Barney is being way to nice (PC). Alcohol is terrible as a motor fuel. We only have it because the agriculture lobbies make money from us the taxpayer because of it.
Alcohol is not "Green" it wastes too much energy in production to ever be viable. It also steals from the production of foodstuffs keeping their costs artificially high.
We pay extra for every drop of alcohol that is used for fuel. Extra in maintenance, extra in tax subsidies, extra in food costs, extra in poor vehicle mileage.
For alcohol to be a viable motor fuel 2 things must be met.
#1 A complete revamp of the production, storage, distribution and sales infrastructure. A duplication of the existing gasoline system.
#2 a COMPLETE re engineering of all new cars. Cars engineered to use only alcohol.
This would create a dual system and would be unacceptable to the driving public.
The current mixing of fuels benefits ONLY the agricultural interests that back them and in doing so harms the environment.
R J Brown

The website that shows where you can get ethanol-free gas is:

http://www.pure-gas.org/

Judd Irland

Cute map. Useless for me. From the western suburbs of Chicago, nothing within 75 miles in any direction. In the east, nothing within 200 miles of Connecticut. In the west, almost nothing in California.

And yes, I was trying not to be too harsh on alcohol in the fuel, as some of us have no alternative to 10% gasohol. Otherwise I'm with R J Brown, and alcohol is a terrible motor fuel, should be outlawed.
Barney Gaylord

If you want "pure" gasoline, look for an area with heavy recreational users like boats, snowmobiles, atvs or other off-road vehicles.

Non-ethanol gasoline has become a volume issue and most retailers will not sell the product unless they can move enough to keep the gas fresh and make a profit.
Daniel Crothers

I had a conversation with a "qualified person" last night on this matter. He explained that the whole gas/etahnol/alcohol issue has now currently started to affect the recreational boating crowd as well. All be it that at the present moment,there still may be a better chance of obtaining non tampered gasoline at a marina than at your local gas station.
Gordon Harrison

Interseting. Round black cannister is a fuel cooling pot.

Gordon Harrison

It is from this twin cam racer. barney, is this the type of project your are working on?

Gordon Harrison

I live on the edge of the Finger Lakes region of New York. Most of my friends have boats. As of this year all the marinas are now selling E10 and have warned the boaters to put stabilizer in their tanks when they store the boats. Racing fuel is the only thing without it...at $7 or $8 per gallon.
It's a brave new world...
GTF
G T Foster

Gordon, -- The answer is no. In a race car processing a gallon of fuel every 10 minutes, cool fuel may mean 2% more power in a finely tuned engine. This has nothing to do with our current problem with hot carburetors and boiling fuel while standing still idling. In fact if you let a can of fuel sit in the hot engine bay while the car is sipping 1 or 2 ounces per minute and nearly standing still, that canister would likely be a fuel heater rather than a fuel cooler.

I have something different in mind. I haven't bothered to do it for several years because it is not a high priority for me. But with all the concern among MGA owners recently, perhaps this discussion may prod me into posting the scheme so someone else may want to try it. I'm pretty sure the cost of parts would be under $50, but it is likely to take a few hours of fiddling to put it together and a couple more hours to install it. It does not involve heat shields or fans or any added electrical parts, but it should keep the carburetors cool enough to avoid boiling fuel under any circumstances.

(Having set the bait, I will now sit back and grin while waiting to see who throws stones).
Barney Gaylord

OK, I'll throw a stone...

You have an idea of how to keep fuel circulating through the float bowl and back to the fuel tank. That way the bowl is constatnly being refilled with cool fuel rather than letting it sit there and boil.
Andy Bounsall

Hmmm, thinking...thinking...

Maybe you could accomplish this by removing the needle valves and replacing the overflow tubes with a fuel line that leads back to the fuel tank.
Andy Bounsall

Anything that causes above atmospheric pressure in he bowl is going to upset the mixture and cause a constant fuel flow to the engine. You would need an overflow system to a collection pot and a pumped or gravity return.
Art Pearse

Here's my stone - it's a long induction pipe and mounting the carbs on the other side.
Art Pearse

taping up the exhaust headers with insulating tape?

louvers in the bonnet?

4X spacers between the carb and mainfold?

Do tell!

JIM in NH
AJ Mail

Okay, you have all been very patient, so here's the skinny. Andy was very close, but gave up too soon. Indeed it is a scheme to recirculate fuel back to the fuel tank to keep cool fuel flowing. The fuel tank will be a large radiator to keep the fuel relatively cool even if it picks up quite a lot of heat from the engine bay. This setup will not pressurize the float chamber. Done with care, this installation will require minimal modification to original parts, and should be bolt-on reversible.

See attached picture (catalog image). This is an in-line pressure relief valve, available in brass or stainless steel, 1/4-18-NPT threads, male inlet, female outlet, internal seal in Viton or Teflon to be fuel resistant.
-- Circle Seal Controls, Inc
-- L500 Series Low Pressure Relief Valve
For this application it may work as well with metal-on-metal and no seal (small internal leakage does not matter), but I haven't found one like that yet. Another brand may be available with 1/4-inch straight thread tube connectors. Have the cracking pressure set to 1.5 psi. The vehicle fuel pump must be capable of making higher than 1.5 psi at low flow rate (but not to exceed 4.5 psi, as original).

Where the original fuel line comes to the rear carburetor there is a banjo fitting with two side ports, fuel in from pump and fuel out en-route to the front carb. At the front carb there is a banjo fitting with single side port for fuel in from the rear carb. The first task here is to change the front banjo fitting to have two side ports like the rear one. It may be sufficient to drill and tap a new female thread port in the original fitting. Or install a "T" fitting in the hose immediately before the front banjo fitting. Install the in-line PR valve at that point.

Wrap several turns of 1/4-inch copper tubing around the front float chamber leaving the ends exposed. Ditto for the rear float chamber. The tubing needs to have intimate thermal contact for heat exchange with the float chamber. So wrap the tube first around a slightly smaller cylinder so the coil will be a snug spring fit on the float chamber. It would help if the tube was rolled to be somewhat flat where it contacts the float chamber (more surface area in contact), keeping it round at the ends for connectors. Secure the coil(s) in place. A smear of silicone grease may improve the thermal connection. If you don't mind modifying an original part, you could solder the tube to the float chamber (might be the easiest way to secure it).

Run an additional 1/4-inch steel or copper pipe parallel to the original fuel supply pipe, returning all the way to the fuel tank. Secure that pipe in place. Connection to the fuel tank can go anywhere on the tank. For instance, in the side of the filler pipe just below the boot floor, or anywhere on the end of the tank. If you don't want to modify the tank, then a 90-degree elbow screwed into the tank drain port could work (with consideration to possible road hazards).

Back in the engine bay, use heat and fuel resistant hose to connect the PR valve to the front coil, and to connect the front coil to rear coil, and to connect the rear coil to the return pipe. Alternate plumbing can place the PR valve on the heater shelf return pipe rather than on the front banjo fitting. Pinch clamps should suffice here, as it is a low pressure return line (can never exceed the fuel pump pressure). Switch on, pressure up, check for leaks, and take it for a drive in the hottest weather and worst slow traffic conditions you can find.

This installation will never starve the carbs for fuel, as it will maintain 1.5 psi minimum pressure at the carburetors. Under conditions of highest fuel demand (full throttle high speed), all of the fuel delivered is available for supply into the float chambers as needed, same as original. High fuel flow rate through the carburetors will help to cool the carburetors, as original. No one has ever reported fuel boiling at normal road speed.

Under conditions of lower fuel consumption, such as slow driving or standing still idling, any excess fuel supply from the fuel pump will be allowed to pass through the PR valve to return to the tank, cooling the float chambers on the way. If all goes as intended, fuel temperature inside the float chambers should be about the same as temperature of the constantly flowing fuel supply, and the fuel should never make any vapor bubbles.

People with original points type fuel pumps might be concerned about the pump constantly ticking at high flow rate. I can only recommend that you ask folks who race the cars if constant high fuel flow rate is any problem for the original type fuel pump. Otherwise I rather like the aftermarket universal electric fuel pump that looks like an in-line filter with flow capacity about double the original fuel delivery rate and constant (quiet) running. On the off chance that you think the return fuel flow rate is higher than required for the application, it is easy enough to install a restrictor valve in the return line to slow the return flow as desired. You might even install a solenoid valve in the return line connected to a switch on the dash, so you can switch on the fuel cooler only when you think it may be needed (similar to manually switching on an electric fan).

The vapor bubble problem can happen under two circumstances, when driving slow or standing still in dire heat, or for 10 minutes after shutting down a hot engine. This setup may work well any time the engine is running. For the after-shut-down issue you might install a separate power feed to the fuel pump, and a diode on the original power wire to prevent feedback to the ignition switch, and maybe a 10-minute delay shut-down timer or time delay relay or thermostatic switch. That way the fuel pump can continue to run for 10 minutes after shut down (similar to some modern electric radiator fans). It might be interesting to let the carbs get hot after shutdown with no fuel flow, then 5 or 10 minutes later switch on ignition to run the fuel cooler, and see how long it takes to cool the carbs enough for normal restart and normal running.

All comments welcome.

Barney Gaylord

Barney, would your proposed fuel recirculating work equally well without the coils of copper tubes wrapped around the float chambers?

Even without the coils the carbs would constantly be getting cooler fuel flowing through the float chambers recirculating back to the tank.

It would be a much easier installation and probably well worth trying before going the whole floatchamber cooling coils route.

Maybe fitting an in-line fuel cooler somewhere in between tank and carbs would help. ( a few coils of copper tubing ideally exposed to airflow but away from danger of damage )

This is a really interesting thread and has certainly got us all thinking.

Colyn
Colyn Firth

Colyn, the fuel going back to the tak does not enter the float chamber, if it did, how would it get out? The return to the tank is coming from the banjo before entering the float chamber, it then serves as a coolant through the coils wrapped around the float chambers. Clever idea Barney.
Lindsay Sampford

One question about the gas tank drain plug connection. With a full tank of gas, would there actually be enough pressure to push the gas back into the gas tank? Would it not be wiser to connct to some other part of the tank...IE: from the top of the tank.
Gordon Harrison

On our Triumph cars with Lucas mechanical fuel injection the electric fuel pump ran at 110 lbs/sq.in and got very hot.
Moss sold a cooling coil that fitted around the pump and fuel was passed through that coil to cool the pump.

Image attached.

Mick

M F Anderson

I dont agree Lindsay as the engine is constantly drawing fuel from the float chambers which would also be being re filled from the re-circulating fuel supply.

I would expect that the re-circulating fuel will be significantly cooler than the fuel supplied by the standard system as it would be spending much less time in the engine compartment and therefore wouldnt soak up so much heat.
The re-circulating fuel itsself may therefore act as a kind of heat exchanger.

I just wondered if this alone may be sufficient to cool the carbs without resorting to cooling coils wrapped around the float chambers.

I suppose the only way to find out is for one of us to try it.

Colyn
Colyn Firth

I see what you are getting at Colyn, but it's surely the fuel that sits and boils in the float chambers that's the problem. The amount of fuel contained in the piping is small by comparison and the piping closest to the exhaust is rubber clothed in braiding, and not so likely to get heated. I'll let you try this one, I'll stick with my noisy duct fan!
Lindsay Sampford

Where do we get Viton fittings for the SUs?
Russ Carnes

Moss Motors sells Viton grommets for the float chamber mounting. I use Teflon O-rings (from McMaster-Carr) for the main jet seals, no stick or drip for over 100,000 miles.
Barney Gaylord

Barney, I recently bought SU grommets from LBC (Jeff Zorn) and I'm not sure they are Viton. I've since heard that Moss (and Jeff's a distributor) grommets are real rubber and there was a horror story to go along with the tale with pieces breaking off and corrupting the carbs. If you are sure Moss has changed - great. I know the grommets I got were not shaped like the originals either. They did not have the indent.

I've since ordered and received Viton grommets in the proper shape from Cecilia. They are on my work bench to install as soon as possible even though I just put in the Moss ones.
D Quinn

This thread was discussed between 12/07/2011 and 05/08/2011

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