Topic: Unleaded 95 octane

[jwurbel]

Rebuilt my 1972 CB 750 including carbs.  Carburetors are stock.  However the exhaust is an HM 300.  Initially tried current ethanol gas but it ruined my intake carb boots.  Bought Sunoco 95 as it was the only unleaded available to see what would happen. After syncing, I tried to set the air mixture  screws for idle balancing. Currently at one turn out. No appreciable effect on lean or rich idle. The ground electrode is clean and not white encrusted nor sooty. I am concerned that it might be running too hot so I haven’t taken it out for an extended ride or plug chop. Idle is steady with no stumbling or hesitation on acceleration. No pinging or backfiring.  Needle clip is in the middle setting. Pilot is a 110 and main a 40.

Any thoughts?

[newday777]

"Pilot is a 110 and main a 40."
Other way around..... 40 pilot 110 main....
Plug chops are the tell all results.
I've not had the ruined carb boots from ethanol crap. Nor do I have non ethanol available at the pump unless I want to drive 60 miles one way with a bunch of gas cans to store it in my already too little area.

[Flyin900]

I switched back to ethanol gas a few years back, as the non ethanol gas was getting really pricey and harder to find. In Canada it is typically 10% or less, if you choose medium grade. As a past carb specialist and rebuilder, I did an experiment with non ethanol gas and standard 10% ethanol gas on the O rings I use in my carb rebuilds.

Low and behold they both swelled with the steeping of the O rings in the gas overnight. When removed from the gas both O rings shrank back to a normal size again. There was no breakdown of the Buna N Nitrile in the O rings that was evident, yet it was a short sample size.

I switched back the the 10% ethanol as noted 2 years ago on 3 rider bikes with no adverse effects to any of the performance and any deterioration of the rubber bits. Maybe the US has a higher ethanol content or a different gas composition.

[jwurbel]

Regarding jetting, I shouldn’t be posting at 1 am.

So you don’t think the gas is contributing to or is the problem?

[newday777]

You won't know until you do some plug chops
But the Sunoco 95 shouldn't be a problem.

[ekpent]

Were the rubber manifold intake boots stock still or questionable aftermarket items ? Think some of the aftermarket are not so good from reports. I have not had a problem running cheap lower octane in mine.

[PeWe]

The biggest problem is not the ethanol, it is all water the ethanol can absorb.
Water not good for carbs when parked.
So  the fuel can differ from different gas stations. How much condense water they have in tanks that will follow the ethanol in fuel.
Plus condense created in your tank.
Fuel stabilizer can help.

I run my bikes and car on Shell V-Power for the octane they need and minimum amount of ethanol.
Maybe that fuel is different here in Europe.

[Deltarider]

When ethanol absorbs the water, that's not a problem. It becomes a problem when it has gone so far that  phase separation starts. Ethanol containing fuel is actually safer for the bottom of your tank than conventional gas. The latter does not absorb condens/water and that water justs sinks towards the bottom of your tank...
There are a lot of horror stories, but in my environment I know nobody who had a problem with gas that contains ethanol. You may want to read the article I've translated from german into english years ago.

[jwurbel]

Carb boots replaced with OEM Honda

[PeWe]

Different with good fuel direct when new.
 Another thing when it had been stored in a gasstations tank with condense water.

I had issues with my old car wintertime many years ago.
Solution was to use ethanol in fuel to absorb water to avoid ice plugs in the carbs. Enough with not that cold, -5C. -20C or colder it needed a few liter of ethanol. Carb ethanol sold at gas stations.

Water was condense in tank. Best to keep tank full of fuel.

The opposite with ethanol in fuel from the beginning is water that will follow from gasstation.

There are youtube clips where they separate water from fuel.

All photos of totally destroyed carbs, mostly USA bikes where the aluminium-zinc alloy in carbs turn to a white powder. Jets and float towers gone. I thought that was caused by water.

My CB750 was stored in not heated nor insulatef barns for 19 years.
Very little corrotion in the stock carbs. Bike was left with fuel in carbs. Lead and ethanol free fuel September 1990. Red slimy residues in carbs.

[ekpent]

What problem did you actually have with the new intake boots ? Did they crack or swell or turn to mush or something ?  Never have seen old hard original rubber carb to head boots go bad like that before on lots of different 750 bikes, strange.

[jwurbel]

Original boots were what turned to soft mush.

Attached are photos of plugs after 20 minute ride and shut off for a chop.

Outside ones are lean, inside ones are carboned up.

Air mixture still at one turn.

Was bogging down from standing stop.

Plugs are new DENSOX24es-u

[ekpent]

All look kinda sooty but cannot really see too well, that's why I don't use premium on my stock engine. Do you have the stock air box with a good fresh and clean filter ?

[Flyin900]

Two thoughts are those plugs are rough and old looking, so a new set is in order. In your info post you noted you cleaned the carbs, yet adjustment of the fuel screws had no effect.

That indicates the pilot circuit is still plugged or partially plugged. There’s other factors too like the electrical, points, coils, plug caps, valve adjustment and timing.

Stock parts ie air box and filter?

Without verification of these other parameters your chasing issues.

[jwurbel]

Pulled carb rack. Jets were clogged with something, not sure as it was hard.  No idea where that came from as carbs were cleaned throughly prior to mounting.  Took off fuel petcock.  Nothing on the screen.
Will put everything back on after cleaning and update.

[newday777]

Pulled carb rack. Jets were clogged with something, not sure as it was hard.  No idea where that came from as carbs were cleaned throughly prior to mounting.  Took off fuel petcock.  Nothing on the screen.
Will put everything back on after cleaning and update.

Have you de-rusted the tank??

[jwurbel]

Tank was Kremed 20 years ago.  Looked for flaking or floating debris inside but found nothing.  As I said earlier, nothing found on fuel strainer.

[newday777]

Tank was Kremed 20 years ago.  Looked for flaking or floating debris inside but found nothing.  As I said earlier, nothing found on fuel strainer.

Kareem has been known for peeling off and plugged carbs. Investigate your tank.

[jwurbel]

Update:

Pulled carbs and went through them thoroughly.  Removed jets., seats etc and made sure they were clean.  Reset floats, bench synced, and then remounted. Reset valves, dwell, timing and installed new plugs.  Synced carbs while running with air mixture screws set to one turn. 

Took for thirty minute ride and plugs are the classic light brown.

The signs of error were there.  I just didn’t want to believe it.

Thanks to all for their help. This forum is just incredible.

Jim

[newday777]

Good to hear you got it hooked up Jim.