New Member. 87 Octane gas

[Frank DuVal]

I did miss that.

I also check to make sure they do both open all the way before I stop the initial throttle linkage adjustment as listed in the shop manual. Starts on page 6-5. No use having them perfect at idle and way off at full throttle. The brackets that hold the cross shaft get bent and cause this condition.

[joelsplace]

I think he was talking about the chokes.
Vacuum never bothered my skin but the gasoline isn't good for you.
I've read 100LL has a lot more lead in it than auto gasoline ever did.

[bbodie52]

» Mon Apr 29, 2024 8:51 am

1965 110 auto.

I will look into these. Thank you. I turned the idle screws back to normal this morning. Car started right up and idled nice til it warmed up. I just let the car run. As the car was warming up (a few minutes in), it was getting rougher and rougher and idle was getting lower and lower til it stalled. I am going to look at the choke too.

» Mon Apr 29, 2024 4:12 pm

Thanks brad for all your info. Lots to go through! Yes Massachusetts is beautiful and its funny you know where Belchertown is. I am sure most Massachusetts residence don't know where we are. I hope one day I can say that I loved driving around Rt 2 and the Berkshires in our Corvair. Feeling overwhelmed now.

The vacuum lines look good and snug. The carbs are getting jets of fuel into the chamber.

I did notice that the two butterfly valves were not lined up. One was fully open and the other, maybe a 3/4 or 1/2 open. The carbs were rebuilt.

Everything points to incorrectly adjusted and synchronized idle speed and mixture screw settings. Your description of a satisfactory idle speed until the engine warms up indicates that the FAST IDLE CAM on each carburetor associated with the choke systems is helping to keep the engine idling UNTIL GRADUALLY INCREASING ENGINE HEAT OPENS THE CHOKE MECHANISM AND DISENGAGES THE FAST IDLE CAMS.

Your second quote seems to indicate that you are looking at the choke butterfly valves at the top of each carburetor intake. There are two more butterfly valves at the bottom of each carburetor throat. THESE ARE THE THROTTLE BUTTERFLY VALVES. The individual carburetor choke butterfly valves may open at a slightly different rate, due to variations in engine temperatures as each cylinder head warms up. Both sides should be fully opened when the engine is at normal operating temperatures. The two throttle butterfly valves at the bottom of each carburetor body will normally be very close to being mechanically equally synchronized from one carburetor to the other carburetor. Any slight variation is usually "dialed in" when fine tuning carburetor synchronization using a UNISYN airflow meter to measure actual airflow through each carburetor. Minor differences are corrected with small adjustments to each carburetor idle speed screw until equal airflow is achieved on each side, and the desired engine idle RPM is achieved. This is something of a "balancing act", working to achieve equal airflow through both carburetors and an acceptable idle speed with the engine.

i would recommend going through the idle synchronization procedure described in the shop manual. 1965 Corvair Chassis Shop Manual - SECTION 6 - ENGINE TUNE-UP, Page 6-5. This includes disconnecting the throttle linkage from each carburetor. Ensure that the choke mechanism and associated fast idle cams are disengaged and not affecting the idle speed settings. The you back out the idle speed screws so they are not contacting the throttles. A strip of paper is utilized to help you detect when the bottom of each idle speed screw is just in contact with each carburetor throttle. (Steps 3 - 7). When the strip of paper indicates that each screw is just in contact with the throttle linkage, each screw is adjusted in (clockwise) an additional 1½ turns. THIS WILL GIVE YOU AN INITIAL IDLE SPEED OF 500-600 RPM when the engine is at normal operating temperature had the chokes — INCLUDING THE FAST IDLE CAMS — are fully disengaged.

NOTE THAT STEP 11 HAS YOU ADJUST EACH IDLE MIXTURE SCREW IN UNTIL IT LIGHTLY BOTTOMS OUT, AND THEN YOU BACK IT OFF COUNTERCLOCKWISE 1½ TURNS. This is an initial preset for the amount of gasoline that is mixed with air at engine idle speed.




The attached DELCO ROCHESTER - Models H, HV Carburetor Service Manual is also an excellent guide and provides more-detailed descriptions on the operation and component function of the carburetor subsystems and choke systems.

[Frank DuVal]

OK, those .01% of Corvair people that can get 100LL from an airport, be careful. Wear gloves. For the other 99.99% of people working on Corvairs running on pump gas, use normal fuel safety.

Oh, and those running 100LL, if the lead is greater concentration than old pump leaded gas, be sure to drop the oil pan now and then to clean out the lead and of course replace the spark plugs every 12K miles like we did in the old days! Corvairs already have steel valve seats, so no issue there with unleaded....

[66vairguy]

OK, those .01% of Corvair people that can get 100LL from an airport, be careful. Wear gloves. For the other 99.99% of people working on Corvairs running on pump gas, use normal fuel safety.

Oh, and those running 100LL, if the lead is greater concentration than old pump leaded gas, be sure to drop the oil pan now and then to clean out the lead and of course replace the spark plugs every 12K miles like we did in the old days! Corvairs already have steel valve seats, so no issue there with unleaded....

Waste of money to use 100LL avgas in a Corvair as it is NOT the same as 100 octane automotive fuel. Octane calculation varies depending on the type of engine test.

If you are racing then you are better off buying "racing" fuel designed for automotive engines.

You'll notice at U.S.A. pumps we use an averaged R+M/2 octane. In fact R+M/2 with a 91 octane is about the same as 96 octane for the old method used in the 1960's

It will be a moot point as the FAA is finally getting ready to ban all lead from aviation fuels.

[joelsplace]

So what octane measurement method does 100LL use?

[joelsplace]

I found this on the Aviation Pros site:
"The (MON) number is typically 8 to 10 octane numbers lower than the (RON) number.

The autogas (MON) octane number is similar to the aviation rating of octane up to 100 octane, according to ASTM D 2700. When you purchase autogas, the octane rating is the average of the RON and MON, (R+M)/2 and the formula is posted on the gasoline dispenser."

This tells me that 100LL would be higher octane than pump gas numbers.

[66vairguy]

I found this on the Aviation Pros site:
"The (MON) number is typically 8 to 10 octane numbers lower than the (RON) number.

The autogas (MON) octane number is similar to the aviation rating of octane up to 100 octane, according to ASTM D 2700. When you purchase autogas, the octane rating is the average of the RON and MON, (R+M)/2 and the formula is posted on the gasoline dispenser."

This tells me that 100LL would be higher octane than pump gas numbers.

You are probably correct, but hard to say as avgas is tested using low RPM full load with both rich and lean mixtures (most older small aircraft engines have manual mixture control due to different air pressures at different altitudes). It is complicated (as most stuff in aviation is). How this translated into octane performance in a higher revving automobile engine is difficult to say. The Corvair distributor timing advance was designed to work with premium fuel of the era. If the fuel flame rate is too slow (excess octane) you do avoid detonation, but you also develop less power - complicated.

Since today's 91octane R+M/2 equals the old 96 octane RON that worked in the Corvair, I use it in my 140HP cars and have not had a detonation issue. Just me.

With a turbo engine it's a different story, but with proper ignition/fuel management folks make it work.

[joelsplace]

It said 100 at full lean and 130 at full rich.

[Frank DuVal]

Since today's 91octane R+M/2 equals the old 96 octane RON that worked in the Corvair, I use it in my 140HP cars and have not had a detonation issue. Just me.

What altitude are you running your Corvairs? Down here at sea level we run 93 to eliminate ping.

[66vairguy]

Since today's 91octane R+M/2 equals the old 96 octane RON that worked in the Corvair, I use it in my 140HP cars and have not had a detonation issue. Just me.

What altitude are you running your Corvairs? Down here at sea level we run 93 to eliminate ping.

Sea level give or take a few hundred feet. No 93 octane in our area. About 1/3 of states only go up to 91 octane. Alaska is lowest with 90 octane premium based on last data I saw.

[Frank DuVal]

Veeery interesting. Well this needs some investigation. Having not been to many states west of the Misssissippi, I only noticed lower pump octane in the high elevations of certain western states, like Colorado's 85 pump octane. Everywhere else I saw 92/93. Now I need to see why "they" didn't think it was important to ship better gasoline (well, better to Corvairs and supercharged Buicks! )

[66vairguy]

Veeery interesting. Well this needs some investigation. Having not been to many states west of the Misssissippi, I only noticed lower pump octane in the high elevations of certain western states, like Colorado's 85 pump octane. Everywhere else I saw 92/93. Now I need to see why "they" didn't think it was important to ship better gasoline (well, better to Corvairs and supercharged Buicks! )

Some of the octane variation is due to how much ethanol is in the gasoline. Most like to blame the "government" for the fuel issues, but in 2013 the EPA stated that increasing ethanol to more than 10% in gasoline was NOT RECOMMENDED due to problems in older car fuel systems!!!!! In spite of this the powerful farm lobby is pushing states and Congress to increase ethanol to 15% (or more) to increase octane and reduce gasoline costs (so they claim). Even California is resisting more ethanol since studies show ethanol is not as environmentally friendly as once thought.

Many also blame the government for limiting U.S.A. crude oil production, BUT it seems the big oil producers have been colluding with OPEC to keep oil prices up. The FTC (Federal Trade Commission) has filed a claim that the head of Pioneer oil (huge in Texas) has colluded to fix oil prices. See https://fortune.com/2024/05/02/exxon-pi ... exas-opec/

[Dennis66]

Our gas prices here fluctuate between .25 and .50 per gallon depending on the day of the week "but we have no control over the price of fuel" (whoever "we" is).
Back about 1981 I had a couple of guys in my youth group who got jobs gassing up planes at the local airport. They often gassed up their personal cars as the boss sold them Avgas at cost and there were some gas shortages here and there back then. They had no problems (100 LL as the 80 octane at the time was too low) Aircraft engines do have a lot of other complicating factors. Most aircraft engines are large cylinder displacement with big bores so flame travel is an issue. For this reason they have dual ignition (not just as redundancy). One magneto fires just a few degrees before the other. You hear the magneto impulse couplings going "click-click, click-click" if the engine turns more than a few revolutions during starting. There is also the altitude compensation that was previously mentioned. Dennis

[66vairguy]

Our gas prices here fluctuate between .25 and .50 per gallon depending on the day of the week "but we have no control over the price of fuel" (whoever "we" is).
Back about 1981 I had a couple of guys in my youth group who got jobs gassing up planes at the local airport. They often gassed up their personal cars as the boss sold them Avgas at cost and there were some gas shortages here and there back then. They had no problems (100 LL as the 80 octane at the time was too low) Aircraft engines do have a lot of other complicating factors. Most aircraft engines are large cylinder displacement with big bores so flame travel is an issue. For this reason they have dual ignition (not just as redundancy). One magneto fires just a few degrees before the other. You hear the magneto impulse couplings going "click-click, click-click" if the engine turns more than a few revolutions during starting. There is also the altitude compensation that was previously mentioned. Dennis

Good comments. Before modern aircraft ignitions (still not that common on small aircraft) you had dual magnetos and the first flight of the day you'd go to the run-up area, put on the brakes and run the engine up (always under load with a fixed propeller) and you would turn off one magneto at a time and check for RPM drop. This proved both magnetos were functioning separately. That drop in RPM when only one magneto was working was noticeable. As you said, a big bore slow turning engine is different vs. an automobile engines.

[Dennis66]

We did the run up every flight. It was allowed a certain amount of drop (100 RPMs?) or it was back to the flight line. It was the same whether it was a Continental A65 or a big Pratt and Whitney R2800 (although that had a few other checks) There were a couple of ties my instructor would switch back to both mags, run the RPMs up, lean the mixture out, set everything back and repeat the mag check if one dropped just a little past the limit. Worked every time. Just a slightly fouled plug. To my knowledge, they still have dual mags and same procedures.
BTW, we had a few old Ward LaFrance gas powered fire trucks that had dual ignition because of the size of the engines (cylinder displacement). I still have a blown 0320 piston (Lycoming 320 CID / 150 H.P) I had to replace. Victim of spark knock or wrong fuel. Airboat engine. Dennis