Fuel or "Gas"

Create a thread to track the progress of you MB/GPW restoration progress. Previously a General Discussion board.
Mark Jesic
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Fuel or "Gas"

Post by Mark Jesic » Mon Apr 24, 2017 5:45 am

Guys ,scanning through some of these pages, the subject of fuel seems to come up quite often. In England we have 95 Octane unleaded. The jeep runs fine on this, but i have started to use a Zero Lead substitute. You use one capful for every full tank of fuel, and the jeep seems to run slightly better on this. I was warned though, only to use the same brand, which is Morris superclean zero lead. Sales gimmick maybe, opinions welcome. 8)


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Re: Fuel or "Gas"

Post by Wolfman » Tue Apr 25, 2017 4:37 am

Don't know if you are using the same octane rating system in your AO as we are in the States.
Here 95 octane would be over kill.
The low compression L-134 would lose power because of the slower burn rate of the higher octane "gas". You would have to "up" the compression the get high octane gas to burn at the rate it needs to.
We have things like "Lead Plus" here. Suppose to save the unhardened valve seats in older engines. Might help the intake valves but the EPA won't allow anything on the shelf that makes it out the exhaust, so I doubt it does much for the exhaust seats.
As for octane ? Lead additive won't lower that. Only a different blend of fuel, gas or petrol will do that.
Mike Wolford
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Re: Fuel or "Gas"

Post by Mark Jesic » Tue Apr 25, 2017 6:39 am

Mike, 95 Octane is standard over here, hence, i use the addative, a lot of jeep owners over here swear by it.

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Re: Fuel or "Gas"

Post by Wolfman » Wed Apr 26, 2017 6:03 am

We live on the same planet but in different AOs. 9/16 and 14 mm are the same for you and I. Just different was of expressing it.
Why I don't know if your 95 octane and my 89 octane are the same. Maybe. Maybe not.
At any rate, both will work. Putting 95 octane in an engine that is made for 89 octane. OK
Putting 89 octane in an engine made for 95 octane. Not OK. ( what is that pinging noise ?? )
We do have octane booster additives, here, that are suppose to increase fuel octane ratings.
Don't know of any additive that will lower octane ratings.
Back to lead additive. Has nothing to do with octane. Won't change a thing octane wise, unless there is more in the can than " lead additive".
The lead additive is intended to protect the soft valve seats in engines that do not have hard valve seat inserts.
That includes older L-134s that have not been upgraded.
Mike Wolford
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Re: Fuel or "Gas"

Post by Mark Jesic » Thu Apr 27, 2017 3:42 am

Hi Mike, apparently the additive does protect the valve seats, we dont seem to have the choice of fuels that we had in the 70s and 80s. then it was leaded coming in at 2star, 3star, and 4star, 4star being for the flash guy in the sports car, with the sexy young chick in the passenger seat. :mrgreen:

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Re: Fuel or "Gas"

Post by Wolfman » Thu Apr 27, 2017 5:17 am

:D Ahh The Memories !! :D
Back in the day ( like that one ? ), we didn't have star ratings. Just octane ratings.
It was the guys driving the cars that required Sunoco 260 that had the good looking young ladies.
I had a car and a Harley that both needed Sunoco 260. Field goal for my side !!
I liked it back then !
Mike Wolford
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Re: Fuel or "Gas"

Post by Mark Jesic » Thu Apr 27, 2017 9:53 am

I would love to go back to the 70s, but then it occurred to me, i didnt have a jeep back then. :D You are a field goal up as i only had a saloon car in the 70s, and the chick i had at the time always wore jeans, no short skirts in my car. :x

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Re: Fuel or "Gas"

Post by Seff » Tue May 09, 2017 8:25 am

Unless you do a lot of hauling (high load driving for sustained amounts of time), your engine does not need lead substitute. Your engine, if the stock compression ratio is maintained, has 6.48:1 compression - this is an engine designed to run on 68 Octane fuel. 95 won't hurt it, neither will 75 for that matter.

As is mentioned above, higher octane will burn slower, albeit only a slight amount. If this is really what is causing your engine to run poor, then you can advance the ignition timing a few degrees to make sure you ignite your fuel and air charge at the optimum time. Beware that advancing too much will cause engine knock, which is very harmful.

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Re: Fuel or "Gas"

Post by Mark Jesic » Wed May 10, 2017 12:06 am

Interesting point Seff, at the moment my jeep is running fine, so if it aint broke, dont fix it, mine had an engine rebuild in 2010 so i hope to have many years out of it. I also never push it, 35mph max speed, unless im going down a steep hill.

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Re: Fuel or "Gas"

Post by artificer » Wed May 10, 2017 2:12 am

Seff raises important issues but running retarded [or advanced] is not desireable.
So hook in a vacuum gauge & let's know the readings you get.
John GIBBINS Member Institute of Automotive Mechanical Engineers [Ret], ASE Master Medium/Heavy Truck & Auto Technician USA -2002 Licensed Motor Mech NSW MVIC 49593 Current 2015
TO DIAGNOSE, TROUBLESHOOT OR FAULT FIND ANY AUTO SYSTEM....
Understand how system parts interact with one another. GOOD parts can then be established & the NOT GOOD problem/s part/s isolated for repair or replacement.

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Re: Fuel or "Gas"

Post by Wolfman » Wed May 10, 2017 5:14 am

I just went through trying to get an M-38 to run better.
The owner and I have been fighting what he thinks is bad performance for a while.
After two hours of timing lights. Vacuum gauges and anything else we could think of, I did a race car set up.
Set everything manually.
Located TDC on #1 with a crooked wire down the spark plug hole. Set the distributor so the points were ready to open.
Then went to work with a " Degree Wheel".
Rotated the distributor 5 degrees advanced by the wheel. ( That is 10 degrees on the crankshaft ).
Checked the distributor advance with the "wheel ". Came in at 22 degrees by manually rotating the rotor and checking the rotation against the " Wheel".
Went for a test drive and the jeep ran better than I had seen up to this point.
I thought it ran OK. The owner thought it was better but still a little "doggy". ???
Last resort. What fuel are you using ? 92 octane!
My last suggestion. Run out the tank full of fuel he had just bought and fill the fuel tank back up with the lowest octane he could find.
I think I did make the comment, " your driving a jeep. not a Porsche ! "
Stay tuned. He has not got back with me so far.
Mike Wolford
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AOPA ( 50 yrs)
EAA ( 49 yrs)
4th Inf. Div. - 5th Inf. Div. - 2nd Armor Div. - CIB

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Re: Fuel or "Gas"

Post by Seff » Wed May 10, 2017 5:59 am

That was 10 degrees initial on the crank - was it 22 degrees total on the crank, 22 degrees on the distributor, or was it 22 degrees of advance for a total of 32 degrees on the crank or the distributor?

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Re: Fuel or "Gas"

Post by Wolfman » Thu May 11, 2017 12:03 pm

The cam shaft and distributor shaft rotates at half the speed of the crankshaft, so, each one degree of distributor housing rotation or rotor advance rotation equals two degrees advance on the crankshaft. Multiply the distributor rotation by 2 to get the results at the crankshaft.
Starting with the #1 cylinder on top dead center of the compression stroke, set the points so they are just ready to open.
Now with the cap, rotor and point cover off, lay the degree wheel over the distributor shaft. I used one of the cap clamps as a pointer. Locate the degree wheel so the edge of the clamp is at TDC on the degree wheel. Holding the degree wheel in place, If you want 10 degrees advance on the crankshaft, rotate the distributor housing 5 degrees advance on the degree wheel. Tighten the clamp. This will give you 10 degree crankshaft advance.
To check centrifugal advance, lay the degree wheel over the distributor shaft. Hold the rotor in the retarded position. Locate the degree wheel so the rotor is at zero. Then, while holding the degree wheel in place, advance the rotor to the full advance position and read the degree wheel. If it is at 11 degrees, the timing at the crankshaft will be double. 22 degrees advance. Not going to etch this in stone but I think the centrifugal advance for an L-134 is 22 degrees crankshaft rotation.
I am using 10 degrees static crankshaft advance because with 2017, 89 octane fuel, that is what I have had the best performance results using. In 194x and 68 octane fuel, 5 degrees may have been the setting that works best. I like 10, now.
One more thought, I think in 194x, a different formula for determining octane was used. So, using the 2017 formula, who knows what the old 68 octane would be today. ??? Probably not 68.
Mike Wolford
CJ-2A
VEP GPW
Comm./Inst. SEL
AOPA ( 50 yrs)
EAA ( 49 yrs)
4th Inf. Div. - 5th Inf. Div. - 2nd Armor Div. - CIB

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Re: Fuel or "Gas"

Post by Seff » Thu May 11, 2017 12:23 pm

Roger, that's how I'd check distributor advance as well. I was just confused by your numbers.

My jeep is bumped to 7.84:1 compression, so I run 7 initial. I tested it at 10 on a dyno, but it ran worse than at 7.

The 22 degrees of advance sounds right, total timing was (from my Googling) 27 and initial was set at 5 degrees from the factory. That means 22 degrees of mechanical advance. Beware that your advance springs can get old and thus sloppy, either setting initial too high or total too low.

RON (research octane number), MON (motor octane number) are just two of the ways of determining octane rating. The US uses AKI (anti-knock index) method, which is (RON+MON)/2. Europe uses RON, which means that the 99 octane I can pump over here is only as good as the 94 octane in the US.

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Re: Fuel or "Gas"

Post by Wolfman » Thu May 11, 2017 12:38 pm

How did you get the compression up ??
I can see how, at the higher compression and current octane, backing off to 7 degrees would be better.
Are you the one working on casting aluminum heads a while back ??
Mike Wolford
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4th Inf. Div. - 5th Inf. Div. - 2nd Armor Div. - CIB


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