Todays gas w/ high compression engines?

[Edward J.]

A friend with a 68 327/350hp has some driveabilty problems, Im leaning toward todays fuel related octane It performance is lagging, idle speed erractic,(370 rear axle)

Just some details on this car, timing is exact to spec.s, vaccum advance is operating, carburator is rebuild (original),carb. secondarys are working.

This is a 38k car, with T.I. ingnition system,It does have original spark plugs wires, and maybe even the spark plugs. , it seems to drive without any engine misfires at normal cruise.

My question is the gas octane of todays prem. fuel with the 10 percent ethanol will this cause the older high compresion engines problems, or maybe the old T.I. module advance curve should be replaced?

My next plan is replaced the spark plugs, but maybe I should add some octane additive to fuel?

Maybe a few of you 68 327/350 owners have seen these problems, your comments welcome.

[Duke W.]

Re: Todays gas w/ high compression engines?

Unless he is experincing detonation, octane is sufficient.

Today's ethanol laced fuel can cause percolation problems, which is often evident by hard hot starting.

If you can be more specific about the "driveability" problem(s) you might get some better responses.

One improvement would be to change the ported vacuum advance to full time, but you may also have to change the VAC. Look in the CSM and quote the specs for a recommendation on whether it will work with full time vac. advance or whether it needs to be changed. While you're at it, quote the centrifugal specs, too.

Duke

[Jim D.]

Re: Todays gas w/ high compression engines?

While today's gasoline may some problems related to being 10% ethanol remember, ethanol is added not only for a cleaner burn of the gasoline but to raise the octane as well. Ethanol is 113 octane. Regular gas without it is 84 octane but the ethanol raises it to 87.

[Timothy B.]

Re: Todays gas w/ high compression engines?

Edward,

How old is the gasoline in the tank?? What condition is the tank in.. Sometimes problems arise from rust forming in the tank and can wreak havic on carburetors..

Might not be a bad idea to make sure it's getting a good flow of clean gasoline. The sock in the tank sending unit and the filter may need attention. Start with the simple things, if the springs in the distributor snap back and the weights move freely I doubt if the distributor is the cause.

[Edward J.]

Re: Todays gas w/ high compression engines?

Duke, I will map out the centrifical advance and vaccum advance, switching vac. can to full time advance may be a opition.
and I think fuel percolation maybe also be problem,although The carb. does have a heat sheild under the carb base.

It seems that when restarted after a hot drive the idle speed tends to be high for a moment the stablizes. The car originally had a new rochester replacement some time ago, and he had the original in box, I disassembled the original and found a few problems with it and repaired and installed a carb. tune-up kit. so the problem is still prevalent with both carbs.

The seems to be lagging under full accelaration, for a small block with 350 horsepower and 370 gearing, It should have more power, I think my 72 200 horse would be alittle quicker.

One other question, is the T.I. system have anything to do with performance of car. since it has a mech. and vaccum advance system?

[Erv M.]

Re: Todays gas w/ high compression engines?

If the car has no missfire during a normal cruise and no detonation the fuel is fine; As Duke has stated.

There is a difference between octane and btu's, but that is another topic altogether.

If the car is timed correctly I would strongly suggest you start with the plugs and wires.

Remember rule number one when thinking you have a fuel/carburetor problem; leave the carburetor alone until you are sure the ignition system is operating properly.

[Jim T.]

Re: Todays gas w/ high compression engines?

My 68 original owner 68 327/350 4-speed 3:70 rear end. I have used a Holley 650 6210 650cfm double pumper carburetor since 1974. Still use the point type original distributor and have since I can remember used full time vacuum advance. Use Champion brand sparkplugs and have used Moroso BLlue Max spiral core plug wires for about 25 years. Runs very good when doing just normal driving, comes very much alive when the secondarys are used for a 42 year old engine with 95,000 miles.

[Dan M.]

Re: Todays gas w/ high compression engines?

FWIW I agree with the comment on possible old gas. I have found that today's gas doesn't seem to be able to "sit" as long as the older days fuel. I would recommend topping off the tank several times if the fuel has been sitting a more than a couple weeks.

[Ronald L.]

Re: Todays gas w/ high compression engines?

I was at GM in the mid to late 70's when gasohol was introduced. It wreaked havoc on the fuel systems. They were not ready. Once you have ruled out plug wires and the like, look at the fuel sock and line to be sure you have good clean fuel flowing to the carb. With care that can be accomplished by disabling the ignition, and watching measuring fuel exiting the fuel line/pump.

[Duke W.]

Re: Todays gas w/ high compression engines?

Duke, I will map out the centrifical advance and vaccum advance, switching vac. can to full time advance may be a opition.
and I think fuel percolation maybe also be problem,although The carb. does have a heat sheild under the carb base.

It seems that when restarted after a hot drive the idle speed tends to be high for a moment the stablizes. The car originally had a new rochester replacement some time ago, and he had the original in box, I disassembled the original and found a few problems with it and repaired and installed a carb. tune-up kit. so the problem is still prevalent with both carbs.

The seems to be lagging under full accelaration, for a small block with 350 horsepower and 370 gearing, It should have more power, I think my 72 200 horse would be alittle quicker.

One other question, is the T.I. system have anything to do with performance of car. since it has a mech. and vaccum advance system?

In addition to mapping out the spark advance map on the car I'd also like to know the specs.

Can anyone with a '68 CSM contribute?

As far as the TI concerned, my experience with it (and the HEI) is that it either works perfectly or doesn't work at all.

If you are not using the original carb, it's possibly a calibration issue. Also manually open the secondary air valve, then have someone in the drivers seat floor the throttle and verify that all four butterflies are full open. If not the throttle linkage/cable needs to be properly adjusted.

Check that the heat riser valve works and wire it full open to minimize percolation.

Duke

[Edward J.]

Re: Todays gas w/ high compression engines?

Guys, thanks for your comments, Duke I will check out the butterfly that slipped by me,I will check the secondarys, maybe the spring is wound alittle to tight,

I will be looking at the car again in the weeks to come once the weather breaks.

As far as the sock in fuel tank it okay, the car does not run out of fuel under hard acceleration.the fuel filter in carb was replaced.


This car would have been bowtie car, with 38k , one owner But the car owner was was not up for this, he did restore the interior and exterior of car, it still retains all the matching numbers.

[Paul H.]

Re: Todays gas w/ high compression engines?

My 68 427/390 runs fine on pump gas. I would definitely start by changing the 42 year old spark plugs and wires.

[Mike R.]

Re: Todays gas w/ high compression engines?

I agree with others that fuel is not likely the problem. If the idle is erratic then either the fuel delivery or the spark delivery is erratic. Look for spark leakage. I had a miss at idle with the ignition shielding installed but it was ok with it off. A new set of plug terminals cured my problem. All that said, before conducting a full witch hunt, I would try filling the tank with Avgas or racing fuel. It is not just the octane that is different with todays fuels, the vapor pressure is also different. This is a problem with FI cars (not the modern electronic ones obviously), as the fuel can effectively boil in the fuel lines. This shouldn't be a big problem with a carb but it eliminates fuel as a possible source of the problem.

Mike

A friend with a 68 327/350hp has some driveabilty problems, Im leaning toward todays fuel related octane It performance is lagging, idle speed erractic,(370 rear axle)

Just some details on this car, timing is exact to spec.s, vaccum advance is operating, carburator is rebuild (original),carb. secondarys are working.

This is a 38k car, with T.I. ingnition system,It does have original spark plugs wires, and maybe even the spark plugs. , it seems to drive without any engine misfires at normal cruise.

My question is the gas octane of todays prem. fuel with the 10 percent ethanol will this cause the older high compresion engines problems, or maybe the old T.I. module advance curve should be replaced?

My next plan is replaced the spark plugs, but maybe I should add some octane additive to fuel?

Maybe a few of you 68 327/350 owners have seen these problems, your comments welcome.

[Michael M.]

Re: Todays gas w/ high compression engines?

I add 5 gallons of Cam2 to a fillup with todays high test in my org SB 68 and it runs and starts like the day it was born.