Aquired this motorcycle recently. Runs ok needed a tune up. When I put the timing light on it I couldn't get the mark to come up till I turned the knob on the end of the light (40 degrees ) advance. So I put it up on the stand 3rd gear found the timing mark. Baseplate at points rotated clockwise to the max. Points open to .005.
I r/r the front seal never messed with the timing. I'm thinking maybe a previous owner didn't get something right.
Is it possible to fix this with motor in the bike
1975 r90 timing issue
Re: 1975 r90 timing issue
I set my points about .015. does the bike start and run bad, if its 40 deg off I wonder how it runs. just a reminder double check your timming, if you have'nt already done so paint your timming marks so you can be sure where your at, make any adjustments a little at a time.
Re: 1975 r90 timing issue
The bike ran well but I allways thought it could b better. From a standstill my wife's r75 out runs me. Starting was difficult at times. I got the t marks hi-lighted.
I'm querious if one or two teeth off the mark at the crank and cam will let it run at all
I'm querious if one or two teeth off the mark at the crank and cam will let it run at all
Re: 1975 r90 timing issue
I think 40 deg out is a "no-run" situation, too.
Flywheel wrong would make the marks show at a minimum of 72 degrees off. More depending on how wrong!
Set your points to the correct gap then measure the timing again. Difficult starting is caused by this close (0.005 inch)gap.
A worn chain is probably the problem, but set the points first. Additionally be sure the SP gap is correct at about 0.026-0.028 inch. I have found SPs with the gap as they came from the box in friend's bikes when they complained of poor operation! If your coils are original, you might want to set the SP gap at 0.024 inch.
BMW manual says points shoould be 0.014 - 0.016 inch. (0.35 - 0.40 mm if you have mm feelers)
Static timing around 6 deg BTDC (with a light) Probably up to 25-30 BTDC at max advance.
I say probably as my manual is for 1977 engines.
Flywheel wrong would make the marks show at a minimum of 72 degrees off. More depending on how wrong!
Set your points to the correct gap then measure the timing again. Difficult starting is caused by this close (0.005 inch)gap.
A worn chain is probably the problem, but set the points first. Additionally be sure the SP gap is correct at about 0.026-0.028 inch. I have found SPs with the gap as they came from the box in friend's bikes when they complained of poor operation! If your coils are original, you might want to set the SP gap at 0.024 inch.
BMW manual says points shoould be 0.014 - 0.016 inch. (0.35 - 0.40 mm if you have mm feelers)
Static timing around 6 deg BTDC (with a light) Probably up to 25-30 BTDC at max advance.
I say probably as my manual is for 1977 engines.
Clemson, SC
R100s, R75/5
R100s, R75/5
Re: 1975 r90 timing issue
I also would suggest if you haven't already, check your valve clearence, hard to start sounds like timming issuse though. Setting points, correct timming & valve adjustment might solve your problem, at least it's a place to start. I might also say my wife's 74 model R75/6 has a10-32 rear drive and my early 76 model has a 11-37, her bike is quicker off the line than mine, but she has to run a couple hundred RPM faster at our normal riding speed. Your R90 might have a higher geared final drive than her bike. What part of the world do you live in? One of the gang might live near you.
Re: 1975 r90 timing issue
Hello Jean, thank u for responding. I got the 40deg number from my new timing light, it has a dial on the back 0 to 60. The only way I can bring the timing mark down to the line is by turning dial to 40deg mark. The points were set at 40mm, the .005 in gap is what's left to close when the s timing mark is on the line. I didn't even think about the chain, it makes sense.
Richard, the valves, points, and sp gap were all set correctly. The only way this bike will run decently is with the base plate is turned clock wise to the max. I told my wife about the rear drive numbers she just smiled and said "shure". I'm in Temecula CA a nice place to have a motorcycle year round riding. Thank u both for the input. I'm going after that timing chain.
Richard, the valves, points, and sp gap were all set correctly. The only way this bike will run decently is with the base plate is turned clock wise to the max. I told my wife about the rear drive numbers she just smiled and said "shure". I'm in Temecula CA a nice place to have a motorcycle year round riding. Thank u both for the input. I'm going after that timing chain.
Re: 1975 r90 timing issue
The only time to worry about points gap is when the points are open to the greatest amount. Watch the cam and measure when the follower is right on top. Wrong points gap alters timing a LOT...
If you light tells you "things" look for a dwell angle of 78 degrees. That corresponds to the correct points gap.
MAYBE that 40 was the DWELL, not the "timing"?
I filed my points plate slot about 3/16 inch before I finally gave in and replaced my chain...I think that was about 1996. The new chains have a master link so you can install them without removing the sprockets.
Quicker "off the line" is going to be in favor of the bike with the low-gear rear end, but top speed will be greater AT THE SAME RPM with the bike (R90) with the high-gear rear end. The lower displacement bike (R75) will have3 the low-gear rear end.
What carbs do you have? Bing 32s or DelOrtos?
If you light tells you "things" look for a dwell angle of 78 degrees. That corresponds to the correct points gap.
MAYBE that 40 was the DWELL, not the "timing"?
I filed my points plate slot about 3/16 inch before I finally gave in and replaced my chain...I think that was about 1996. The new chains have a master link so you can install them without removing the sprockets.
Quicker "off the line" is going to be in favor of the bike with the low-gear rear end, but top speed will be greater AT THE SAME RPM with the bike (R90) with the high-gear rear end. The lower displacement bike (R75) will have3 the low-gear rear end.
What carbs do you have? Bing 32s or DelOrtos?
Clemson, SC
R100s, R75/5
R100s, R75/5
Re: 1975 r90 timing issue
40 on your timing light is a built in advance delay that is designed to enable timing to be checked at the TDC mark. It might be causing some confusion.
First thing I'd do on a points bike is set the timing statically at the S mark using a buzzer or ohm meter across the points. Points gap should be 0.016" - 0.018" but it's not hyper critical, neither is doing a dwell check. Doing this will eliminate any possibility of the timing light being faulty. It should run fine with this setting and you can then check full advance with the timing light. If there is still a big discrepancy then either the advance mechanism or timing light is faulty.
First thing I'd do on a points bike is set the timing statically at the S mark using a buzzer or ohm meter across the points. Points gap should be 0.016" - 0.018" but it's not hyper critical, neither is doing a dwell check. Doing this will eliminate any possibility of the timing light being faulty. It should run fine with this setting and you can then check full advance with the timing light. If there is still a big discrepancy then either the advance mechanism or timing light is faulty.
barry
Cheshire
England
Cheshire
England
Re: 1975 r90 timing issue
Jean, filing the baseplate was my thought long ago. Every indecator points to internal timing functions. Carbs are 32s I had to replace diaphragm in one. While cleaning carbs found one with the head broke off one of the jets, couldn't back it out to clean. It seems fine, I'll try an easy-out some day
Hello Barry. My clymer manual isn't real clear on static timing or more likely I'm not real clear on my clymer manual. If the buzzer is supposed to sound at the s mark or near it, then I'm way off. Thanks for info
Hello Barry. My clymer manual isn't real clear on static timing or more likely I'm not real clear on my clymer manual. If the buzzer is supposed to sound at the s mark or near it, then I'm way off. Thanks for info
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Deleted User 62
Re: 1975 r90 timing issue
Foot, ignition off, get the S mark in the window, connect your static timing light (or "buzzer" or volt meter) with one clip on the wire from condenser to points and the other to ground. Using your allen wrench in the alternator rotor, turn the motor counterclockwise slightly, just enough to get the S mark out of the timing hole. Now, ignition on, light should be off. Turn the rotor clockwise until timing light comes on, should happen when S is centered in timing hole. If not, rotate the points plate; counterclockwise to advance the timing or clockwise to retard it. Hope this helps...