Compression confusion

You maybe can forestall the valve recession problem by sweetening your gas with a few percent with 100LL aviation fuel. Technically according to EPA it is illegal, but I don't think a gallon of it will hurt anybody.
Use E0 premium fuel if it is available. I have low compression cylinder base gaskets installed on my '75 R90/6 which makes it run almost like a steam engine.

Update7-5-20

First: HAPPY JULY 4TH TO ALL!! God bless America!
Got the Float Needle Seat out using a 7MM tap and 'creative' extracting. Think I'll hold off on removing the left carb seat (which has not been leaking) until I get the new right seat installed, just in case I bung up the new seat and have to use the other from the rebuild kit. OK, so my rebuild confidence only goes so far... Also since the Throttle Slide seems to be working properly, I'll hold off on trying to remove the tops till I fire her up and see how things run. Time to put all the carb 'stuff' together and reinstall. Next, take off the valve covers, remove plugs and turn her over to make sure oil is circulating and oil pressure light goes out. Any suggestions on how to re-install the Float Needle Seat? Anti-Seize compound and wood dowel has been suggested. Careful, careful...

Thank you

Thank you for the update, I am glad things are going well for you so far.

I am afraid I can't say much more about carb rebuilding other than what I have done myself.

I am not familiar with a wood dowel and never seize method of installing float needle seats?

There might be something of use in Snowbum's article at https://bmwmotorcycletech.info/earlybingR75CV.htm.

Good luck with further work. cheers, St.

Moving right along... After very carefully having to easy (?) out all 8 screws in carb tops, (ALL were rusted in), cleaned carb, replaced jets, diaphrams, needle/jet, float seat, floats and float needle. Reattached to bike. Confirmed oil flow to rockers . Can't see a spark at plugs , more backtracking to determine issue. Pleasant enough working on carbs in house, slower going working in garage when it's 100+... euromotoelectrics is becoming a good friend. Re: Antique plates, Texas said no record of 1973 title or registration (pre-computer days). At least it's easy enough to talk to the local boss and are moving along nicely. Greetings to all.

Nice to read

Nice to read you are doing well. Thanks for the updated. St.

Update 7-24-20

ALL put back together !!! Replaced coils along with points/condenser, plugs/wires. Very nice, strong spark!! No leaks from carbs (or anywhere else ). Turns over nicely BUT doesn't catch. Since I did so much on carb rebuild and sparking items, think I'll take her to a local dealer to do a tuneup. Received Antique plates. So... almost there! Greetings to all and thanks again for pointers.

Before you go to the dealer, there is an airhead guru over your way (Ft. Worth I think, maybe Mansfield)

Send him an email and you might be able to convince him to stop by and take a look. He goes by Rick and I got to know him a little at the last BMW Tech Day early this year in Denton. He has Matt Parkhouse level knowledge....

frk273@gmail.com

My Experience

While would expect the 84 100RT I recently bought after being out of airheads for 30 years, to run well on 90+ octane, how important do you think running non-ethanol fuel is given that it is a solvent, but can be difficult to find at times?

Russell

Russell, in both my 84 R80RT and my 78RS, I have 9.5 to 1 pistons. As I have said, I have never had a problem running the highest octane rating gas I can get. I prefer to use 90 Octane non ethanol when I can get it but unfortunately it is hard to find outside of bigger towns. In that case, I use 89 or 93 with no more than 10% ethanol. In a pinch, I have used 86 Octane, and while running it, I was a bit more gentle on the bikes until I could run the tank down and fill it with the usual. Didn't have any problems.

Oh years ago, I installed alcohol proof floats and I have not used the cloth covered fuel line in years having switched to better hose. I can't say much about carb seals and o rings going bad, I rebuilt the carbs at 100K miles and replaced them on the RT at 200K miles due to a worn out butterfly shaft housing that was causing a vacuum leak. Oh yes, I did replace the needles and jets recently on the RT and the RS. I have put only 20K on the RS since I have owned it and it may have 100K miles on it more than the odometer says. The carbs were rebuilt after sitting for 15 years in a box the bike rebuilt in 16 after an accident in 2000. They just got new needles and jets a couple of weeks ago.

So far, the higher percentage ethanol fuels have not made their way into my areas of riding. I hear rumors the mid West states are pumping 15% blends now. I don't follow the news much so as I say that is a rumor. St.

arcx said:

While would expect the 84 100RT I recently bought after being out of airheads for 30 years, to run well on 90+ octane, how important do you think running non-ethanol fuel is given that it is a solvent, but can be difficult to find at times?

Russell

Click to expand...

This may prompt an extended fuel string, but non-ethanol fuel is not really important at all, IMHO, particularly if you're running through tanks of fuel on a regular basis. If your bike will be idle for more than 30-60 days, I would and do use a fuel stabilizer. My '84 R100RT has the 8.2 pistons, so I've run unleaded 87 octane w/10% ethanol for the 22 years I've owned it. Nothing terrible has happened to my carbs or engine.

khittner said:

This may prompt an extended fuel string, but non-ethanol fuel is not really important at all, IMHO, particularly if you're running through tanks of fuel on a regular basis. If your bike will be idle for more than 30-60 days, I would and do use a fuel stabilizer. My '84 R100RT has the 8.2 pistons, so I've run unleaded 87 octane w/10% ethanol for the 22 years I've owned it. Nothing terrible has happened to my carbs or engine.

Click to expand...

Yeah, I have to disagree. I have two Airheads - owned them both for over twenty years. I ride both regularly, so the gas doesn't sit in the tank and collect water for months. But, even though they were run often I was finding that fuel hoses and carb floats were failing often and quickly. I'm lucky that non-ethanol gas is available in my area at several stations in 87, 89 and 93 depending on the station I choose and the bike I'm riding. I have been running non-ethanol now for quite a few years (at least 10 yrs). All of the fueling components last much longer. As a plus, the MPG is a little better.

I tend to agree with khittner. I've not noticed any obvious problems that point back to running the pump ethanol in my local area. I ride the bikes in a rotation over a 3-4 week period, but sometimes it might take me 4-5 months to go through a tank of gas. The gas line on my /7 has probably been in place for 3-4 years now...maybe more.

Adding

As I have said, I try to run non ethanol when I can. Like Khittner, I notice a slight improvement in MPG with the non.

I haven't had alcohol issues with the bikes for years. Unlike me, they run better without alcohol and I do better with small amounts. LOL. St.