PMO carbs

[jamesd312]

Hi, I am considering changing my CIS for carbs on a 77 911s 2.7 and would like to know if PMO carbs can handle E10 fuel (which has just been introduced to the UK) without any ill effects on the floats seals fuel lines etc ?
thanks
James

[Joe Bob]

You could try and ask the manufacturer. I'm sure if they are newer models he made allowances for alcohol. I would be worried about fuel lines.

[911 SLANT]

I was told by Richard Parr to avoid Ethanol fuel for my PMOs. I use VP or Sunoco gas. Has no Ethanol.

[Joe Bob]

I stand corrected.

Maybe the OP should consider ITBs?

[Hi_Fi_Guy]

In Arizona (and I believe Califorinia as well as several other states) all our fuel at the pump has at least 10% ethanol and is oxygenated. We used to have ethanol free race gas but even the few places with 95 octane and 100 octane race gas at the pump now show these fuels as containing ethanol as well. I am not a scientist but will relate my own experiences. That said there have been some very good papers and articles written on the subject that are worth reading and understanding.

What I have observed.

Ethanol gas tends to percolate out of fuel bowls of carbs (PMO, Weber, Zenith) which can cause backfires as well as carb/engine fires. This typically happens when the ambient temps are 85 degrees or warmer and the car is driven, then parked for a short while (20-30 mins) and not fully cooled off, then started and run again. That’s typically when the fire occurs.

When ethanol gas evaporates it can leave behind a yellow crusty residue in fuel bowls, fuel lines, etc.

Ethanol fuel seems to attack certain types of rubber/plastics used in some accelerator pumps, fuel lines, etc. and will sometimes eat through them or dissolve them.

Ethanol fuel can seep into or be absorbed into some types of plastic fuel tanks, fuel pumps causing them to swell and distort. It is advised to leave little standing fuel in these systems when not used regularly.

Before I knew what I know now I have seen this fuel destroy the injection system on one motorcycle, swell the plastic fuel tank of another, and eat through the rubber diaphragms of the carbs on a third bike. Nothing like having a bowl full of fuel dumped onto your boots at speed and then being stranded with a dead bike

Luckily by the time I got back to air cooled cars I had a bit more knowledge and experience. I’ve run with Zenith carbs and PMO carbs on the 911 and in my own experience running ethanol fuel the PMO carbs seem to be trouble free compared to the Zeniths.

Sta-Bil ethanol treatment added at every fill up can really help the car run better and help reduce the likelihood of damage to fuel lines and rubber parts. This alone has kept my motorcycles running trouble free for the past 6 years. Before I was chasing fueling issues on a regular basis. With the 911 and other air cooled cars the only times I have encountered major carb problems was when I have forgotten to add Sta-Bil ethanol treatment to the fuel. I used to think of it as something to use only when the car was not going to be driven for a while. I now add this at every fuel stop.

Read the spec sheets on the brand of fuel you use. Some fuels will remain “fresh” before breaking down longer than others.

Rotary fuel pumps tend to run cooler and allow for back flow when ethanol fuel expands due to heat. This can save you from percolating or overflowing in some instances. A friend thought it couldn’t make a difference then he changed out an old Facet “clicker style” fuel pump for a rotary pump and many of his carb issues went away completely.

You may need to re-jet your carbs and dyno tune for ethanol gas to avoid leaning out the mixture. Especially at high RPM if the fuel is oxygenated.

You may need to replace older fuel lines.

PMO offers/offered an anti-percolation mod that would dump the fuel into the intakes instead of the top of the carb. I have not had this mod performed but it may be worth looking into.

Be sure your timing is correct to ensure complete combustion of the fuel. This can really improve low rpm running and throttle response with ethanol gas.

[Gordo2]

I've had no issues running my PMO carbs with10% ethanol.

Meanwhile, if I had a local option, I would run non-ethanol fuel for all the reasons Hi-Fi-Guy mentions.

[jamesd312]

Originally Posted by 911 SLANT

I was told by Richard Parr to avoid Ethanol fuel for my PMOs. I use VP or Sunoco gas. Has no Ethanol.

Thanks, PMO are not taking any risks !

[jamesd312]

Originally Posted by Hi_Fi_Guy

In Arizona (and I believe Califorinia as well as several other states) all our fuel at the pump has at least 10% ethanol and is oxygenated. We used to have ethanol free race gas but even the few places with 95 octane and 100 octane race gas at the pump now show these fuels as containing ethanol as well. I am not a scientist but will relate my own experiences. That said there have been some very good papers and articles written on the subject that are worth reading and understanding.

What I have observed.

Ethanol gas tends to percolate out of fuel bowls of carbs (PMO, Weber, Zenith) which can cause backfires as well as carb/engine fires. This typically happens when the ambient temps are 85 degrees or warmer and the car is driven, then parked for a short while (20-30 mins) and not fully cooled off, then started and run again. That’s typically when the fire occurs.

When ethanol gas evaporates it can leave behind a yellow crusty residue in fuel bowls, fuel lines, etc.

Ethanol fuel seems to attack certain types of rubber/plastics used in some accelerator pumps, fuel lines, etc. and will sometimes eat through them or dissolve them.

Ethanol fuel can seep into or be absorbed into some types of plastic fuel tanks, fuel pumps causing them to swell and distort. It is advised to leave little standing fuel in these systems when not used regularly.

Before I knew what I know now I have seen this fuel destroy the injection system on one motorcycle, swell the plastic fuel tank of another, and eat through the rubber diaphragms of the carbs on a third bike. Nothing like having a bowl full of fuel dumped onto your boots at speed and then being stranded with a dead bike

Luckily by the time I got back to air cooled cars I had a bit more knowledge and experience. I’ve run with Zenith carbs and PMO carbs on the 911 and in my own experience running ethanol fuel the PMO carbs seem to be trouble free compared to the Zeniths.

Sta-Bil ethanol treatment added at every fill up can really help the car run better and help reduce the likelihood of damage to fuel lines and rubber parts. This alone has kept my motorcycles running trouble free for the past 6 years. Before I was chasing fueling issues on a regular basis. With the 911 and other air cooled cars the only times I have encountered major carb problems was when I have forgotten to add Sta-Bil ethanol treatment to the fuel. I used to think of it as something to use only when the car was not going to be driven for a while. I now add this at every fuel stop.

Read the spec sheets on the brand of fuel you use. Some fuels will remain “fresh” before breaking down longer than others.

Rotary fuel pumps tend to run cooler and allow for back flow when ethanol fuel expands due to heat. This can save you from percolating or overflowing in some instances. A friend thought it couldn’t make a difference then he changed out an old Facet “clicker style” fuel pump for a rotary pump and many of his carb issues went away completely.

You may need to re-jet your carbs and dyno tune for ethanol gas to avoid leaning out the mixture. Especially at high RPM if the fuel is oxygenated.

You may need to replace older fuel lines.

PMO offers/offered an anti-percolation mod that would dump the fuel into the intakes instead of the top of the carb. I have not had this mod performed but it may be worth looking into.

Be sure your timing is correct to ensure complete combustion of the fuel. This can really improve low rpm running and throttle response with ethanol gas.

Thanks, very comprehensive