r90s Running Rich

schrader7032 · Post by **schrader7032** » Sun Jun 29, 2008 1:56 pm

Stan -

I have no experience with the Dell'Orto carbs on the R90S...others might be able to give you some hints or suggestions. If you want to read some and follow additional links on these carbs, check out this website.

http://bmwmotorcycletech.info/dell.htm

There are some R90S specific forums...you might want to consider getting involved in several forums in order to tap into a range of experience. I'm aware of this forum, but there probably are others...

http://www.bikersoracle.com/rs/forum

Kurt in S.A.

stanleyandreina · Post by **stanleyandreina** » Mon Jun 30, 2008 10:35 am

Hi again-
The bike is a 1967 r69s, with a newer engine- I think it's a 1974 r90s. It also has a sidecar. I drove it up from Boston on a very hot day (90 degrees), and got stuck in traffic for an hour on my very first ride.
I wonder: Should I be looking at the choke, the carburator, or the timing to lean out the mix?
-Stan

schrader7032 · Post by **schrader7032** » Mon Jun 30, 2008 11:39 am

Should I be looking at the choke, the carburator, or the timing to lean out the mix?

Yes! Well, I'm not too sure about adjusting the timing to lean out the mixture...seems like putting a bandaid on the problem. Most likely it is the carb. Could be the choke is stuck on. Could be the slide mechanism doesn't slide. Could be the accelerator pumps (I think these have pumps) are overactive. Could be the jets/needles inside the carb have broken or are oversized.

You got stuck in traffic...how did you get unstuck? At 18 mpg, your spark plugs must be covered in black, wet soot.

I think if you're smelling gas, my guess you'll need to look closely at the carbs, possibly tear into them and see what's wrong.

Could be you have a weak spark and the gas is not being properly ignited. That could be bad coils, plugs, or plug wires.

I would start on the carbs and work out from there. Carbs...ignition timing...valve adjustment. Sounds like the bike may need a good basic tune up.

Kurt in S.A.

stanleyandreina · Post by **stanleyandreina** » Wed Jul 02, 2008 8:50 am

Kurt-
Thank you so much for your reply. I made a small adjustment on the left side Bing carburator choke setting- it looked like the cable had slipped, and wasn't lined up the way the right side was. So I loosened the screw and moved the cable 1/8". Well, this morning, the bike started beautifully, idled a lot better, had considerably more power in the first two gears, but it started to buck and backfire in third. It seemed to struggle going up hills, and as I crested the hill and started to coast a little, I found I had to pull in the clutch and throttle down to avoid more backfiring. Argh. I was able to get to work, but the bike really doesn't like getting up to highway speed. At lunch today I think I'll pull the plugs. I bet they're soaked. My r90s has had two extra plugs put beneath the cylinders. Is this weird? I think I'll replace the plugs and air filter before I start frigging with the carb jet settings.
-Stan

schrader7032 · Post by **schrader7032** » Wed Jul 02, 2008 9:44 am

Stan -

You have a dual plugged bike. This is a mod that has been somewhat popular to help get complete combustion and to get the bike to run on a lower grade of fuel. It may help with performance of the bike at various speeds...not real sure.

Are the lower plugs hooked up with spark plug wires? You need special coils to work with this arrangement.

Sounds like your timing might not be right for a dual plugged bike. Because of the extra plug, the fuel is burned faster on each stroke. This means the timing has to be adjusted to compensate. Ideally, you want standard timing at idle, but need the full advance timing to be reduced a bit. This is somewhat difficult to do. I understand a quick way to do this is to change the timing at idle so that you see the OT mark in the timing window, or possible see the OT mark near the top of the window. What that does is pull down the full advance mark closer to what it needs to be since you spend most of your time running around at high RPMs or at full advance. It might make the bike a little harder to start but generally it works out OK on the low end.

If the bike is backfiring, it sure sounds like you have a timing issue.

Kurt in S.A.

stanleyandreina · Post by **stanleyandreina** » Thu Jul 03, 2008 1:40 pm

Well,
I thought I had it going pretty well- even dared to drive it an extra 20 miles to the Beemer shop to pick up an air filter. I would've thought a new. clean filter would HELP it to run better, but it's running like crap now. I expect to get my Clymer's manual in the mail any day, and I'll be looking at setting the timing, and perhaps re-building the carbs. I'm trying really hard to be "Zen" about this....
The Bing carbs are labelled L 64/32/11 and R 64/32/12. Is this all the info I'll need to provide to buy the re-build kit?
-Stan

schrader7032 · Post by **schrader7032** » Thu Jul 03, 2008 2:33 pm

That's all you should need to get a kit. With a number like 64/32/11-12, that sounds like a constant velocity carb??? I don't have my Bing manual with me. I thought we were talking a Dell Orto carb, but since you have a conversion bike (/2 frame, R90S engine), there's no telling what might have been used for the carbs. You can get the kits from a dealer...I would think Max BMW would be the way to go for you; they seem to know there stuff. Bing in Kansas can also provide you with kits via mail. Here's their website which you can see what type of kits are offered for the Type 64 (or CV) carbs.

http://www.bingcarburetor.com/bmw/bmw.html

Edit: Just checked the Bing book...the 64/32/11-12 CV carbs were offered on the R90/6 while the R90S got the slide carbs. So, it would appear that someone has swapped in these carbs. Not bad carbs, all the way around...some like the slides because they're more responsive to throttle input. But the CVs are forgiving carbs. End Edit:

If it is a CV carb, and it's been a while since anyone has overhauled them, you might need one of the complete kits, to include diaphragms and floats. It would be best to get this done right this time and then move on to any other problems. But to shotgun an unknown problem in the carb doesn't really pay...it's best to get everything taken care of and know you have a good working carb.

When you get around to going over the carb, there are several places that you can look at to get some help. Here are a couple:

http://bmwmotorcycletech.info/bingcv.htm
http://home.insightbb.com/~cdpumphr/the ... nicles.htm

This latter site has lots of pictures of the various steps and might help reduce the intimidation factor a bit. It's not that difficult...just work on one at a time so you have something to look at and compare. I'd suggest NOT changing the throttle/butterfly o-rings the first time around. The screws that hold the butterfly plate onto the shaft are peened to prevent them from backing out and getting injested by the engine. It takes some extra work to get them out and repeen (or possibly loctite) them back in plus getting the plate aligned properly. That's my 0.02...I've done my carbs quite a few times and haven't touched the butterfly...I guess I've dodged a bullet there. Maybe yours need new shaft o-rings...I'd still say do the easier stuff first.

Kurt in S.A.

stanleyandreina · Post by **stanleyandreina** » Tue Jul 08, 2008 2:13 pm

Okay, the r90s is running, idling, and not backfiring. Still no power. Yesterday, I discovered that the left cylinder is hot, and the right cylinder is cool. A sparkplug check reveals no ignition on the two plugs on the right jug. Hmmm. I'm surprised that it runs as well as it does on just one cylinder! I would have expected really obvious bad performance (maybe I've got to tap back into that "zen" thing:)
Tonight I hope to pull the tank, and investigate my ignition. I suspect that an owner before me has replaced the original system with electronics that include "pick-ups".
What should I be looking for? And how much will I have to spend?

Thanks!
-Stan

schrader7032 · Post by **schrader7032** » Tue Jul 08, 2008 2:31 pm

Stan -

Sorry, I don't know how these dual plug systems will be wired in detail, but there are some basics that might apply.

You should be sure you know the resistances of all components...it's possible that one set is open for which you're getting no spark. With a dual plug system, I believe you're going to have to have either 4 coils (one for each spark plug) or 2 dual output coils, each with two towers to plug in the spark plug wires. I'd try some simple measurements before you take off the tank. Use a multimeter and put one lead in the left-top spark plug cap and the other lead in the right-top spark plug cap. Read the resistance. Do the same for the lower set of plugs/wires. That might tell you something right there. Again, from my understanding of single-plugged, stock machines, the resistance should be about 20K ohms.

Another thing that you may want to consider... There's a recommended way of connecting dual plug bikes, in terms of wires, coils, etc. I think I've heard that have one set of coils operate one set of plugs (say the top ones) and the other set of coils operate the other set of plugs. That way if one of the coils fail, you still have one set of plugs working...basically the bike "self-converts" back to a single plug system. See how yours is wired and how that might contribute to the left-side only running. Maybe you can reconfigure to get the two top plugs running and deal with the lower plugs/coil later.

In situations like this, you can try swapping one thing at a time until you find where the component swap causes the problem to swap also...then you've discovered something to tell you what to fix/replace.

You may just have a wire jumper that's come off the coils...see what's going on.

Rick at Motorrad Elektrik would be a good person to run your problems by once you figure out what you have. He sells most bits and pieces and can also help you troubleshoot.

Kurt in S.A.

stanleyandreina · Post by **stanleyandreina** » Wed Jul 09, 2008 11:28 am

Kurt-
I can't thank you enough for your insight and patience. You're really helping to talk me through this problem (and, btw, keeping my marriage together!!). I was very reluctant to start moving the plug wires around, but I am considering these two scenerios:
1) Swap both the right wires with the left ones and see if my cylinder problem reverses.
2) Disconnect both the lower plug wires, and plug the lower left one into the upper right one to see if both pistons are firing.
I think I need to at least lift, if not remove, the gas tank in order to make a cursory check- loose wires, etc. I'll do the resistance check, too.
Any more thoughts?
-Stan

Vintage BMW Motorcycle Owners