1962 BMW 700 S

1962 BMW 700 S

Postby SevenhundredS » Mon Aug 26, 2013 1:00 pm

Ah, remember me: little old BMW coupe? First and only event this year was the Ascutney Hill Climb. I'd love to be up and running for the next one in September but I'm having the nagging power issue. Any tips or advise on tuning this little Bimmer (not Beamer)*

details and some specs:
http://en.wikipedia.org/wiki/BMW_700

1962 BMW 700 sports coupe
700 cc air cooled, twin cylinder (rear)
This has the "hot" cams and therefore slightly higher compression
This has twin solex carbs
This one has the sport transmission (2nd and 3rd gear are closer.)

Here's the problem. On my third run the car was sadly underpowered (as apposed to its usual underpoweredness ;-)
It felt like a dragging brake or seizing bearing but I got brakes, differential and transmission apart and back together with no major problems found.

In neutral it revs up great and sounds perfect. Under load it can't get up to speed.
Those that hear it all give a different diagnosis.
Some say here are some of the "expert opinions"
-sounds like it's flooding: check fuel pressure
-sounds like it's starving: check fuel pressure
-sounds like a weak coil: check the coils (How?)
-sounds like timing: check the centrifugal advance (Did, working fine. Timing static adjusted)

This engine is not unlike a R69 motorcycle engine, but not the same.

SOOOOOOoooo....what do you think I may find that allows it to start and rev great but not when under load?

Cheers to you if you like techi problems. The people that know this car are few and far between and the ones who tune the keep their cards close to their chest because they want to hoard these...ok, not entirely true but...


*Ok, let's get the slang out of the way first: Bimmers are BMW cars, Beamers are motorcylces.
Last edited by SevenhundredS on Sun Aug 24, 2014 6:30 pm, edited 2 times in total.
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Re: tips on tuning??? 1962 700 S

Postby Rabbit Farmer » Mon Aug 26, 2013 1:38 pm

Ok, let's get the slang out of the way first: Bimmers are BMW cars, Beamers are motorcylces.


Never knew... I see a lot of internet chat on Bimmer vs. Beamers.

As for your fix. A smart and intelligent man would sell the car and purchase something more modern that would be easy to maintain. A car enthusiast would try to fix, run, drive, and (gasp!) race an old car that no one heard of. I would go with the second.

When I had power issues with my old carb’ed cars, it seemed to always be timing; either a tooth of the cam sprocket or the distributor was not setup properly. One interesting thing (and I’m sure it is not related to your car) with the old Rabbits (I think both carb’ed and FI), you had to first setup the distributor with the correct orientation and then set everything (TDC crank, TDC cam, and TDC distributor that was driven by an intermediate shaft) before you could even start dialing in the ignition timing.

Steve
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Re: tips on tuning??? 1962 700 S

Postby sdwarf36 » Mon Aug 26, 2013 6:46 pm

1: Cams do not increase compression.
Can you do a compression test? Even better-a leakdown test?
Have the carbs ever sat longer than 3 weeks with gas in them?
Is it still points ignition?
Translating road racing to hillclimbing:
Proper tire selection== nothing hooks up on moss or wet leaves.
Staying on the racing line==anything paved is considered good.
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Re: tips on tuning??? 1962 700 S

Postby SevenhundredS » Fri Aug 30, 2013 11:28 am

1. Correct, cams don't increase compression but it does have the higher compression than the stock engine achieved by shaved heads I believe...anyhow...

2. I'll get a compression tester and see what it gets but I think compression is good based on the fact that it starts easy, doesn't blow oil, and run clean and well in neutral.

3. The points are not on an external distributor but inside the dynostart (starter generator). The plugs are in series and fire at the same time, once for ignition and once on exhaust (clean burn :idea: ) The point are adjusted by a centrifugal advance as the engine speeds up. It is fine. The basics are this ignition are: generator, regulator, condensor and coils.

4. It has two solex carbs. Although it does sit with fuel at times it lost power during the weekend and I run the engine at least once a week to turn it over. I may have goofed up by using high test and octane booster. Since the compression ratio is only about 9.5:1 that higher octane doesn't do much. Additionally I have to put in lead additive and stabilizer. That whole concoction may have stressed it out too. My next project is to take off and rebuild the carbs, drain the fuel sell, and go back to simple 87/89 octane, lead subst., and no ethanol diluted gas.

We shall see. Thankfully, I'm currently unemployed so I have time and no money. Why can't I ever have both? (here goes another lecture on not trying to run an antique :lol: )
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Re: tips on tuning??? 1962 700 S

Postby sdwarf36 » Fri Aug 30, 2013 11:53 am

Better gas won't hurt anything.
When it died in front of me at Ascutney, it sounded like 1 cylinder had gone away-and the other 350cc couldn't pull the hill. It would be nice to found out which one was dead to help troubleshooting.
Translating road racing to hillclimbing:
Proper tire selection== nothing hooks up on moss or wet leaves.
Staying on the racing line==anything paved is considered good.
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Get you some AVGAS

Postby Mopar 151w2 » Sun Sep 01, 2013 2:43 am

Ethanol is not the devil incarnate, but it's a pain in the ass, and better understood than cursed. Avoiding it has a price, and restrictions. So, after the magic 8 ball circles the campfire and factors in price: Fuel RFG/E10 is $3.75 + Sta-Bil (must be for Ethanol) + lead sub + octane boost, blended by taste and eye, true carachteristics unknown, will not pass SCCA fuel check

Fuel AVGAS "100LL"(?) $6.60/gal. , LL plenty leaded, with real tetraethyl lead, storage stable (not RFG, E0), 100 octane conservativly rated. Blended by pros, for a criticaal audience. . The more your engine is like a piston -engine aircraft, the more it will like AvGas. Availablity good at airports. NOT LEGAL FOR ROAD USE - but only the guy who sells it cares. For the BeyMmVey, ideal if you can get it.

!st runner-up: VP/Cam2/Sunoco Standard /Rockett "108 leaded stock car gas, in bulk, from the track or close by" $8- $10, a little more in 5# cans, plenty lead, ties with Av Gas for most consistent, reliable, safe lead source (high concentrations stone lethal), Cuts well with 92 E10 , but loses advantages of storage stability and no ethanol.
blending non-critical, as effectives falls off at higher concetrations, so a simple estimated average will always have a safety margin. The more your car is like a race car or bike, the better it will like it. Way much octane hurts power, best power is made when octane is a little over just enough, ethanol helos power because it is an oxygenate - it results in a leaner mizture by substituting more oxygen for a little fuel in the chamber, check your jetting if you use it.
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Re: tips on tuning??? 1962 700 S

Postby SevenhundredS » Mon Sep 02, 2013 2:07 pm

Yikes, I'm not trying to win. I'm just trying to get the little motor running again. :o
cheers,
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Re: tips on tuning??? 1962 700 S

Postby walterclark » Mon Sep 02, 2013 4:41 pm

Thsi is what i know about "avgas". Take it for what its worth.

100LL avgas has an automotive equivalent octane (RON/MON) of around 95-96. It contains about 1.5-2 grams of TEL per gallon. Your engine was probably designed with much lower TEL content assumptions if used straight so you need to be vigilant to lead fouling. It should have excellent storage characteristics compared to pump gas and as it contains no Ethanol, corrosion and moisture contamination issues are avoided. All avgas fuels are designed for a relatively slow burn because aviation engines are designed not only to be stable at low pressure but to run around 3500RPM. You may have unburnt fuel in the exhaust running at much higher RPM.

91/96UL avgas is basically 100LL without any TEL. Its not clear to me how widely available it is in the US but it might be a good way to dilute 100LL to reduce the TEL concentration without adding in any unknowns such as additive interactions. It would lower the 100LL octane but with a 9:1 CR you dont need anything over a real 90 ROM/MON). Still has the slow burn issue.

I think the biggest issue for your car is the introduction of Ethanol in fuels. Your car was built WAY before it was used commercially and I would expect the corrosion issues that it precipitates in fuel systems before about 1980 model year cars (I cant remember exactly what year our Gov't said all parts had to be Ethanol compatible) would affect your 700. Everything from dislodging previous bits of contamination in the fuel lines to etching metals and causing galvanic corrosion are risks...not to mention phase separation, wherein thanks to Ethanol's hygroscopic character, water in the tank beyond what it can absorb will cause the water/Ethanol solution to separate out from the fuel and drop to the bottom of wherever it is sitting.

Personally I would try my best to buy Ethanol free fuel for this car. I cant speak to the accuracy of this but there is a site: http://pure-gas.org/ where members track availability of Ethanol free fuel. Since you probably dont use that much, it seems like a reasonable precaution to try to buy it for the 700.
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Re: tips on tuning??? 1962 700 S

Postby Mopar 151w2 » Mon Sep 02, 2013 5:12 pm

A bit more on the ethanol-free fuel - a few years ago, VP Race Fuel introduced Small Engine Fuel, which is store-stable, ethanol-free, 94 (R&M/2) octane gasoline, formulated for small engined equipment which HAS to work - their target market includes fire and rescue equipment (rescue saws, pumps, generators0, home backup generators...
SEF (tm) is unleaded, around $9 a gallon - the hustle comes when you buy a quart can with 50-1 oil premix, for $8/quart.....
So, if you gotta have the lead, mixing this and 100LL should rock!
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Re: tips on tuning??? 1962 700 S

Postby Challenger392 » Mon Sep 02, 2013 8:51 pm

Completely different application but for what its worth, my engine runs either avgas or VP C12 interchangeably up to its 6500rpm redline. But again about the only thing our engines have in common is that their carburated and have pistons. :D it would be interesting to see the high rpm hp rating with both fuels, if only I had a dyno....
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