can ethanol cause roughness?

'66 911

Just had the engine rebuilt. My mechanic filled the car with 93 octane/ethanol. It's running like it runs on 3 cyls, then 4 cyls. then 3 cyls. etc.


It was doing this before the rebuild. We cleaned out the jets, put new fuel filters on it (actually even added one) and then I began using pure gas (87 octane). It ran great for several thousand miles like this.

But now....it's back. I personally believe it's the gas. I believe the ethanol is clogging the jets. When the jets are cleaned out, it runs good. But only for a little while. Then it starts doing it again and the jets have to be pulled and cleaned and reinstalled. This makes the car run good again for another little while.

My mechanic insists it's not the gas. He says the shaft that runs through the carbs....the bushing that the shaft runs through is worn, causing air to enter there and run lean. The shaft does move ever so slightly.....however.....it did before and ran just fine.

He's calling for rebuilt carbs. I'm no mechanic. But it seems to me like....if the carbs needed rebuilt....blowing out the jets would not make the engine run smooth and good.

I think the car would run good again with regular, pure gasoline.

Thoughts if any...thanks..

EDIT: The reason I ask is.....I was going to drive the car to Florida tomorrow. I just filled it up with high octane/ethanol and it's running badly. I can't take off to florida hoping the car smooths out by running pure gas and blowing out the jets. I gotta know it's right before I head out. Driving it like this for 2000 miles....I'm afraid it'll hurt the engine.

Ethanol can't clog a jet, David... if the car has Solex carbs, your mechanic is probably right regarding worn throttle shafts, which would become obvious when synching. What was the extent of the engine rebuild?

87 octane seems mighty low, yet you say the car runs better with this than with a higher octane ethanol blend? Just doesn't make sense. How clean is your gas tank? Rust fragments? Where are your fuel filters relative to the fuel pump?

I’ve been running clear premium in my 73S, don’t need premium but it’s the only way to get non alcohol. Went on a tour recently and had to use standard gas with 10% alcohol. I noticed the car didn’t run as well, especially cold. Just my observation.

It’s got Webers Russ. The cylinders were bored “1 over” around 8 thousand miles ago. I do not know who did the work. What I do know is it blew a head gasket. Seeing how that happened so soon, I opted to replace both head gaskets. The engine appeared to have never been split...so...lol...I just went ahead and overhauled it. I’ve not looked at the invoice, but I’m sure that meant new bearings. Tomorrow it’s going back to him. I will ask him about the synchronization. I only know what that means in the abstract. He may not know what it means at all...but we’re sure gonna find out.

It had a lot of clutter in the fuel when I got it Jim. Several times into the shop for this. The fuel tank...just looking into it appears clean and rust free. Mechanic says it could be the lines through the tunnel. Not something he seem particularly enthusiastic about changing out.

I took the jets out tonight, cleaned them, and it still ran poorly. That leads me away from the crud thinking. (Though It May be).

I read in the search function that larger jets may be required with ethanol (don’t ask me why).

I’ll tell ya what I’m gonna probably end up doing. If he says rebuild the carbs, that’s what it’ll be. If that doesn’t do it...it’s up to him at that point to make it right. At that point it will be his baby. Everything he’s suggested, I’ve done and paid for. It’ll be his problem to fix after that.

He should know what he’s doing. He’s 70. All he’s ever worked on are 911’s. He worked on these things when they were new cars. There’s probably a hundred people in the area who take their old 911’s to him. ApHis reputation is good.

I can tell though. He’s used to having these kinds of problems with these cars. And customers end up blaming him for it. I’ve not been that kind of customer yet. But if we rebuild these carbs on his judgement...and it’s still doing it, I will lol be.

(I don’t think they need rebuilding. But I could be very wrong)

I've put bigger jets in all my cars because of todays fuel to make them run well ; idle jets and mains . Your head gasket explanation makes no sense , a 911 has 6 head gaskets and failure is a problem I've never heard of occurring . And I don't believe the carburetor shafts are too worn . There has to be considerable movement to affect the running . My 2 cents . Good luck .

Quote:

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Originally Posted by Richy

I've put bigger jets in all my cars because of todays fuel to make them run well ; idle jets and mains . Your head gasket explanation makes no sense , a 911 has 6 head gaskets and failure is a problem I've never heard of occurring . And I don't believe the carburetor shafts are too worn . There has to be considerable movement to affect the running . My 2 cents . Good luck .

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My thinking as well Richy. The left carb has no shaft movement. The right, some...and there’s some fuel discoloration there. Not enough to make a car undrivable. (One man’s opinion.).

I’m gonna bring up the bigger jets tomorrow. (I’m thinking this has been the trouble all along. And it’s why it ran so well on pure gas)

The head gasket blew because the studs had loosened (my opinion. They’d just backed off loose. This was my motivation in just redoing all of the previous work that whoever did it, did. I don’t think they knew what they were doing...or that wouldn’t have happened.

You’ve got to be careful with this guy. His ego is such that he reacts negatively to ideas that are not his own. Once I figured out how to relate with him, he’s been much more compliant. I’m gonna bring those jets up tomorrow. I believe that’s what’s wrong with this car.

Think twice about Florida, until you can approximate this state of tune ..


https://www.youtube.com/watch?v=lzP_26p-LzQ