Jump to content


Recommended Posts

What type of fuel is recommended for a '78 620 with a stock carb.

I was running rough at idle, I put some sea foam in one tank and in about 20 miles it totally went back to normal.

Then 2 tanks of chevron supreme it back...not as bad. but is really making me think it's just the quality of the gas these days.


I was considering paying the extra for non-ethenol, but it's a big pain. They will only fill cans where I go.


any advise would be helpful    thanks.

Link to comment
  • Replies 19
  • Created
  • Last Reply

Top Posters In This Topic

Top Posters In This Topic

Guest Rick-rat

Maybe a small piece of dirt or something in the carb, do you keep a good fuel filter on it? is it idling to low rpm, mine likes to idle at aboot 850 rpm, lower than that it is not smooth. I threw the stock carb away and put on a weber

Link to comment

I have not changed the fuel filter yet. but I should thanks. and the weber is what I was thinking too.

I have depleted my resources on this truck to the point where I am truing to wait on that one.. what should that cost me?


The report today was that it ran fine, with no rough idle.  

no tach on it either, so I would have to guess and 800- 900 sounds about like what it doing. might be a little lower, maybe just bump up the idle speed would be a good option.


it was her 2nd day driving today, day one ended with a dead batterie..  left the lights on.    I am probably just being a little overcautious, I was just curious if anybody has found a benefit to some specific fuel.  brand or octane level.  I told her to put regular in it next time to see if there was any change.

Link to comment
Guest Rick-rat

I don't put any additive in my gas, just always change fuel filter when they look dirty and keep air filter clean. I think mine was aboot 260.00 new and it is a 32/36 with manual choke. I use gas from what is available when I need gas, no favorites

Link to comment
  • 2 weeks later...

Don't run the 87 octane low grade junk - it actually has the 10% ethanol in it.


Actually, you should NEVER run this fuel because they are cheating you in cost per BTU content, not to mention that any small engine repair guy will emphatically tell you to never use it either. 


The 89 octane Mid Grade so far has little or no ethanol although EPA, etc. is ramping that up.


High Test has no ethanol.


My friend buys fleet gas for his taxis and the 87 is called BLEND, 89 is UNLEADED, and 92 is PREMIUM.


You can tell the difference in power and fuel economy upgrading from 87 to 89 and that usually only costs 10 cents of about 2.5% more in cost yet you can see over 5% increase in mpg.

Link to comment

So then do you have some possible reasons for the not so perfect idle.


Other than fuel.  Stock carb...

Small vacuum leak. Loose carb bolts, cracked vacuum hose to brake booster or air snorkel.

EGR dirty and not sealing properly (off) at idle

Idle mixture not set properly.

Valve lash too tight.

Timing chain worn causing retarded valve timing

Link to comment

I don't think fuel grade is your issue, but I've overwhelmingly found schell to give my wagon the best performance. I thought I was crazy for a while, but enough times with the same result has led me to believe it is not in my head. Chevron has been the worst option. Though most convenient, so I am often reminded that it is terrible. I buy non ethanol often, but not most of the time. Though you should never buy ethanol gas for your chainsaws, weed whackers, or small mowers. Unless you have a crush on your small engine mechanic.

Link to comment

Leaving the ethanol and other stuff out for a bit, here is a short thing with fuel and octane. You want to run as low of octane as your engine will stand, this is where it will run the best and make the most power, period. I know that's the opposite of most everything you hear, but the fact is, running too high of octane will make you lose power and efficiency of the burn. The higher the octane, the slower the burn rate. This is really most evident in drag racing and guys trying to pull everything they can out of an engine. On a newer race engine, I start off with a really high octane race fuel and start slowly diluting it. It's a really fine balancing act, because if you go too far (too low of octane) you're going to get detonation. But. until that point, you will get faster, because the fuel burn is getting closer to matching your compression ratio (so to speak). On a street driven, engine, do a similar thing, if it pings on regular, up it to plus. If it does not ping on regular, you're about as good as you're going to get.

Link to comment

Regular, Premium and Mid Grade all have the same Ethanol content.  There are only 2 gasoline "grade" storage tanks at the station.  Mid Grade just mixes the Regular and Premium 50%/50% at the pump.  Watch the little meters on the face of the pump at your next fill up.

Link to comment

I live in Oregon, and we have had E-10, for a long time.  This is may experience with it.

My Datsun runs fine on it.  I have been running Ratsun since August, no fuel issues.  When I was doing work on Ratsun, I did get the gas tank cleaned out, at a radiator shop.

I run E-10 in my Ski Nautique.  I have since it was new, in November of 1996.  My boat has 2,509 hours on it.  A boat does have a large water separating fuel filter, with a drain on it.  Running E-10, I have found NO water in the gas.


If you have NOT been running E-10, switching to it can cause problems.  The alcohol will dissolve water in the tank.  if there is a very little amount of water, the alcohol dissolves the water, and the alcohol remains dissolved in the gas.  All three liquids got through the carb, and engine, and two are burnt.  No problem.  If there is a large amount of water in the tank, the water and alcohol separate from the gasoline, go to the bottom of the tank, and the fuel pump sucks up water with dissolved alcohol, and this creates problems, water does not burn.

Another issue with switching to E-10 is the alcohol will dissolve some gunk in the gas tank, and run that gunk into the fuel pump, and engine.  This can create some problems, most commonly a clogged fuel filter.


With a carburetor, switching to E-10 will make the engine run slightly leaner.  You can also expect a slight fuel mileage drop, because alcohol has less energy content per gallon, than gasoline.

Link to comment
  • 3 weeks later...

It does vary by state and I'm in PA.  And there is a move, worldwide, to use more and more ethanol.  So time is running out.


You can measure the amount of ethanol in your gas by doing a test where you fill a test tube, cylinder, graduate, etc. about 1/4 water and 3/4 gasoline and then shake it up.  The water will absorb the ethanol and after it settles, the water level will be higher.


Since ethanol content is something that is basically kept secret, that is probably the only way to be sure.


I know here in PA, its only in the low test - of course that was 1-2 years ago when I was researching this.  That doesn't mean things haven't changed.

Link to comment

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.
Note: Your post will require moderator approval before it will be visible.

Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

  • Create New...

Important Information

By using this site, you agree to our Terms of Use.