1975 BMW R90/6 - Rocinante

I got the POR-15 and carefully followed the directions. Ultimately everything went smoothly and the results look very good. They recommend waiting four days or more before putting in fuel so some time next week I'll throw the thing back together and see what happens.

BMWR90233.jpeg


The pix is crappy, I was trying to light up the inside w/ a flashlight and not get it in the pictures. Oh well, you get the idea, looks pretty good.

BMWR90234.jpeg
 
Nice work, its all in the prep for those tank liners. I used that same kit on the CB360 and it held up great for the few years before I sold it.
 
It wasn't difficult... which makes me wonder when I read reviews that are less than good. If it didn't work for them they either didn't read the directions or didn't follow them. There are several of these coating systems available but I've always heard the best reports about POR-15 so that's what I got. My late father in law always used Kreem in the old Indians he restored.
 
My Triumph tank has POR-15 and no issues. I'm pretty sure most of the sour grapes reports on liners is due to operator error. When my Triumph tank was done by a previous owner some sloshed on top of the filler hole and allowed to harden. The gas cap was hard to install/remove. I used my Dremel to clean the residue and the gas cap fits fine. When I bought it the previous owner said "The gas cap is hard to remove!".
 
Almost stumped... gas tank is now pristine inside and it's still not running right. It's a little better but still weak on the left side. I'm gunna try switching the coils next. Drat!
 
ridesolo said:
Almost stumped... gas tank is now pristine inside and it's still not running right. It's a little better but still weak on the left side. I'm gunna try switching the coils next. Drat!
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BOO. Good luck. hope you get it sorted. nothing worse than this kind of hard to figure out issue. We're chasing a similar issue on Magoo's Hawk. one cylinder running crazy rich no matter what we do and the other running crazy lean no matter what we do.
 
I'm hoping it's a weak coil on that side, otherwise perhaps the left carb needs replaced. It's been disassembled, cleaned, rebuilt, disassembled, re-cleaned, float level adjusted numerous times. The petcocks are new and just to be sure I cleaned them when I coated the tank. I'm just not sure what else I can do except replace it... eBay would have one (or a pair) but who knows if I'd get a good one and then there's the cost of BMW part$, even used.
 
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ridesolo said:
I'm hoping it's a weak coil on that side, otherwise perhaps the left carb needs replaced. It's been disassembled, cleaned, rebuilt, disassembled, re-cleaned, float level adjusted numerous times. The petcocks are new and just to be sure I cleaned them when I coated the tank. I'm just not sure what else I can do except replace it... eBay would have one (or a pair) but who knows if I'd get a good one and then there's the cost of BMW part$, even used.
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fingers crossed its the coil for sure.
 
Thanx for crossed fingers...

Just replaced the coils and it's... better, at best. I checked the spark and it's now very good, stronger than before so that coil may have been weak, tired, going, whatever. It starts quickly and, once warmed a little, will sit and idle very nicely. However, the air coming out of the right muffler is fairly hot as you would expect and what's coming out of the left muffler is warm, not cold, but certainly not hot.

Fuel, air, & spark. I know there's good spark and air isn't a problem so It's gotta be fuel, right?

As a reminder, the insides of the original petcocks looked like this:

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So I suppose it's possible there's similar damage somewhere inside that carb, but I haven't seen any evidence of it in the visible places and when I put compressed air or carb cleaner through all the various orifices it only came out places where it should have. The last time I adjusted the float level I ran water through the inlet and was satisfied w/ the position and function of the float to start and stop the flow.

Rebuild kits are pretty cheap and easy to come by so I could do another rebuild; gaskets, O-rings, and diaphram.

Suggestions? Ideas? Thoughts? I'd be pretty much open to anything except gasoline and a match.
 
Sorry if you checked this already but I don’t remember seeing it in your thread - have you measured compression?
 
You can hold the diaphragms up to a light and gently stretch them to look for tears. Is the bowl filling up with fuel? Pull the plug on that side and see if its wet after running it for a short while.

You probably checked this already, but the same thing happened on the SL175 I just helped my buddy get back together, it was running like crap and one header stayed cold, we did a quick carb clean before reassembly but had forgotten to clean out the fuel barb and inlet on the carb. It was completely clogged and the bowl was bone dry.
 
doc_rot said:
Sorry if you checked this already but I don’t remember seeing it in your thread - have you measured compression?
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Good question, no, I haven't. Don't have the apparatus but I'm sure I can get hands on one. Good idea.
 
doc_rot said:
Sorry if you checked this already but I don’t remember seeing it in your thread - have you measured compression?
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Bingo! Give the man a cigar!

According to Mr Clymer normal compression should be 123-145psi

in my case right is 120psi and left is 80. Looks like a ring job is in order.
 
adventurco said:
You probably checked this already, but the same thing happened on the SL175 I just helped my buddy get back together, it was running like crap and one header stayed cold, we did a quick carb clean before reassembly but had forgotten to clean out the fuel barb and inlet on the carb. It was completely clogged and the bowl was bone dry.
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Thanx, Nick. Yeah, there's gas in float bowl. I've put both carb cleaner and compressed air through everything in the carb and it's all clear.
 
I'll grant @Hurco550 an official "I told you so" because he said a few times I should get the cylinders honed while I had it apart. I didn't mainly because I thought w/ it having such low mileage it wouldn't need it. My bad. Thank you very much @doc_rot the suggestion is greatly appreciated!
 
Ok now... having never done this before, do I order standard sized rings and run a hone in the cyllinders or do I need to order one over size and take them and the cylinders to a machinist?
 
ridesolo said:
Bingo! Give the man a cigar!

According to Mr Clymer normal compression should be 123-145psi

in my case right is 120psi and left is 80. Looks like a ring job is in order.
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or are the valves out? the CX500 I did had like 80 and it was a tight exhaust valve. Fixed that and it went to the 150 it needed to be.
 
It could also be the valves have some crud on them, have you tried the “Italian tune up”?

You really need to measure the cylinder bore to see what’s going on. If there is taper, oval, or the piston/cyl clearance is too great no hone job is going to correct that and you will need to oversize.
 
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