High octane convert

[Mark V]

Tightfisted cynic that I am I've never put super unleaded (91 octane) in my cars. It didn't help I read something that said it wasn't necessary for some cars, it was either carb or fuel injected I couldn't remember so I never bothered.

Feeling un usually generous the other day I put it in my '69 230/8...WOW.

I never would have believed the difference was possible just by switching fuel. acceleration is smoother and it back fires less (yeah I know probably mixture setting plus a bad dashpot unit, broken accel pump nozzle and fuel enrichment diaphram etc.), it also idles faster, I'll have to dial that down a bit as I had it on the high side before to help make up for driveability problems and the gauge seems to be moving to the left much slower. OK I'm sold, even at the 15% cost premium. I almost don't notice the missing ponies of this 2.3.....wait a minute, who am I kidding, I could still use a good 50 more HP so the driving school Corollas stop dusting me off the line.

I may make room in the garage to keep the old gal yet, the car too....

[psfred]

Mark:

Let go of the money for the carb parts, get them set up right, and you will have at least the 50 horse you think you need. Driving school Corollas shouldn't beat you off the line. That 120 hp MB advertizes it AT THE REAR WHEELS, not the end of the crankshaft......

If you are getting backfires, you have a serious lean condition or misfire or both. At least fix the vac diaphrams and try to set the mixture.

The best solution, of course, is to ditch the Stromberg and get a Weber conversion kit if you can find one -- works vastly better!

Check your timing, too -- "backfires" up the carb blow the enrichment diaphram first time -- Holley makes a "backfire proof" enrichment valve for "hot" cams to prevent this, but I'm sure MB expects the engine to never pop up the carb.

Premium fuel is great stuff in these cars -- also in older American ones, too. I drive a 92 Chevy box van with 299,000 miles on it for work. With one thing and another, including little or no maintenance beyond oil changes, it will only run on premium. Knocks like crazy on regular, even midgrade will get an occasional rattle, and the check engine light, but on premium she just purrs! Probably enough oil ash in the combustion chambers to raise the compression ratio far beyond design, and most likely a stuck closed or disabled EGR, too.

Good luck, these are wonderful cars when they run properly.

Peter

[Mark V]

Lean? Iwas expecting it to be too rich.

The backfire is primarily on deceleration and more so when cold.
Its the six cyl BTW so I have the Zeniths. Would love to have the 32/36 Webers but the new kit is too much to justify and the used ones are scarce. I plan to get the parts for the carbs when I can get in to the dealer before 5. I'd also heard a faulty air pump could cause the backfire in the exhaust. Haven't been inspired to check that yet. The carbs are mostly set up, choke and balance is good, but I didn't recheck the mix after the last go and the timing was good at last check.

Mostly I'm coasting it till its time for the big redo.

[psfred]

Mark:

Hmmm, going to have to think this out, it's been a long, long time since I had carbs to deal with!

Backfire means you have unburned fuel and air in the exhaust, ignites when flame comes out of a lit cylinder. Usually a result of misfire, although it can be running too rich on the idle circuit.

A quick look at the plugs will tell you if you are rich or not -- sooty black at the base, running rich, white all the way down with only a little brown at the base of the insulator, lean. I think this setup has a vac operated throttle positioner to hold the throttle slightly open on deceleration to keep the mixture leaner, but I may be wrong, could be later models.

At the very least, I would check the vac advance, mechanical advance, and the various temperature switch/switchover valve stuff -- if you don't get the vac advance when you should, all sorts of bad stuff happens.

At least it runs better on premium -- and if you are getting pre-ignition or detonation (you won't hear the detonation at speed), you will more than make up for the higher price with better milage since you get more power for trhe fuel burned when the pre-ignition, etc stops. Won't necessarily cause noise, but does reduce power.

And check to make sure the heat riser flaps are in the cold position -- they will overheat the carbs if stuck in the heat position, and cause mixture problems.

I know what it is to not be able to get away from work -- I've been trying for three weeks to get the title notarized for my 280 SE -- the PO lives out of town, and I now work 30 miles away. PITA, since the car runs fine but I can't drive it!

Peter