No Fire Revisited

[PineGreen]

On Fri I posted the thread No Fire. Well, this PM I installed new coils, plug wires and new plugs. More spark than I eversaw before. And I'm thinking how smart I was. Started bike.Same result ,Rough running , very slow acceleration, sudden throttle inputs cause it to stumble and cough, coughing at steady RPM. On Fri I suspected left cyl. not firing, but today it is , probably was Fri too. Left head pipe gets hot like right side.Never checked it the other day. Also when I disconnect left plug wire while running it made no difference in RPM,I reconnected the lead and disconnected the right plug wire and the bike shut off. I repeated this several times. Removed left carb and disassembled. Cleaned it with carb cleaner ,wiped it down , inside and out. Blew it out. Diaphram ok , all orafaces seemed clear. reinstalled carb , started her up and did the plug wire disconnect again. Still no effect in rpm on left ,but when I disconnected the right wire the bike kept running this time. Took for a ride and pretty much the same, Rough running ,a lot of shakes, slow acceleration but now she is backfiring at steady rpm. I'm suspecting a carb problem but I am at the end of my mechanical wits.. Doesn't take much to get there does it??? Help , any input would be great

PS The other day I rode the bike and all was well, Starded it up Fri and there it was. Whatever is wrong happened suddenly.

[Guenther]

A new coil eh? Just like that. Well, I think the good news is that it wasn't the coil. I even exclude an ignition problem. with the recent changes both cylinders (should) get the same spark. You checked both, right?

The bad new is it wasn't the coil. Either you missed something odd when you checked/cleaned the left carburetor or...there is a severe problem with the valves at the left cylinder. I would start with a visual check of the rocker assembly and also check the valve clearance. Do you have a chance to get the compression checked?

What is the color of the spark plug on the left side?

/Guenther

[AnnapolisAirhead]

I'd start with the valves, as Guenther mentioned and hopefully, they are assembled correctly, maybe just a tad out of spec. (.020mm exhaust, .010 intake is what I've been using.

Just for kicks and grins:


Set the valves (on a stone cold engine, like first thing in the morning) to spec
Check the timing
If this is a points bike, check points, condensor and cam lobe condition, if you don't know their age, replace them (cheap).
Verify you are getting good, blue spark from both sides
Match your carb numbers to the Bing manual, verify correct jets, etc
Set mixture to Bing settings and verify needle position on both sides (assuming these are Bing 32 or 40mm CV carbs not type 53, sliders, Dellorto<sp> pumpers, etc)
Verify floats are healthy (not saturated or deteriorated)
Fuel flowing both sides (you do still have the cross over tube, yes?)
Verify the enricher (choke) gasket is healthy, not sucked in on one side and that the choke lever/cable are functioning properly (off is off)
Verify that the choke is assembled properly (...post should have a tiny peen and can be assembled backwards)
Balance the carbs at idle and at 3-4000 RPMs


Lastly, verify the wiring at the coils and starter relay.

You probably know all of this, but when I get frustrated it sometimes helps to have a orderly list to roll down. Also, is the airhead organization doing any tech days in your area? If you aren't involved, they've been lifesavers to me, great friends and have a knack of demystifying these bikes. Several Spring tech days are happening about this time of year all over the place. Worth attending for the friendship, bikes, learning, etc. The more we know, the better we all are. Nobody is as smart as all of us and someone will know how to fix even the toughest of problems.

I hope this helps. :thumb

[tghsmith]

make very sure the small air idle jet is clean , its the one mounted on the long brass stalk type holder forward of the main fuel jet unit, a little spec in there will mess up the entire carb operation, ps pulling plug wires while running is not healthy for your ingnition system..

[108625]

Reading both threads, I understand the problem appeared before you started exchanging parts.
For it to be something that unpredictable and erratic, I would strongly suspect spark timing or control.
Go through the troubleshooting checklist as Annapolis suggested, first.
Check, observe, adjust, but don't spend money yet.
Double check your valve timing to help rule out a timing chain and sprockets issue.
While your at it, I would recommend checking that the ignition timing plate hasn't shifted or is loose. If that's not the case, check all the connections and conditions of wires on the primary (control) side of the ignition, and lastly, consider the control unit itself ($).
It helps if you write everything down as you go along, adding mileage and maintenance history. You might reread it and figure it out later, or share it with a second party who catches something you missed.

[88bmwJeff]

I've heard of some people switching carbs (left to right, right to left). If the problem switches sides, then you know it's carb related, and which carb. I don't think you can ride the bike well, while they're switched, but maybe it will help.

[PineGreen]

Thanks for replys, Just checked valve clearences, they are ok. Ihave been doing this task for over 25 years and everything looks good. No chunks fell out . When I pulled plugs the left electrode was very dark and sooty while the right plug was clean as a whistle. This bike only ran for 10 min. max since new plugs were installed. ,so the left is running very rich. I had to replace floats on a previous bike because they became saturated by gas. On that occasion fuel was pouring out of the carb. Is it possible that this is the problem here, although it is not puking fuel all over the place?? Can't do much more myself as my mech. ability and knowledge is limited. Carbs are a mystery to me

[donbmw]

When you cleaned your carbs did you take them apart and soak them in a carb cleaner. I have cleaned carbs with the spray can cleaners that did not get everythings out and still made the engine run rough.

My take on what may be happening after going through this on my 1975 R90/6 and 1982 R65.

On the R90 it was getting hard to start but would run great after it was warmed up. Check valves, cleaned carbs but made no change. Found the when cold was not running on LH cyl. Check compression found it was low compared to RH side. Found the exhaust valve on LH cyl was deformed. Had valves reworked and problem on this went away.

On the R65 was riding to work when it acted like it was running out of gas. Switched to resvoire. Still ran like it was out of gas. Started troubleshoot and found that LH Cyl was not running when it would act up. Check valves, compression. Started change one item at a time to see what would happen. No change with a coil. Went through carbs with no change. Installed carbs from another bike with no changed. I had a old set of plugs wire from a 82 R100 and tryed them and the problem went away. Ran these wire for a few miles before make and new set of wires. Since then have not had anymore problems.

Don

[PineGreen]

Well the old Beemer is up and running again. I want to thank those who replied to this thread with their advice. It turns out that the problem was with the throttle cable. Last summer I took the cover off the cam and chain that the cable is attached to. Apparently when I put it back togther it wasn't 100% in its littlel notch and properly threaded through the cover. and over time worked its way loose Don't know how it could have run all this time ,but there is a lot of FM when it comes to mechanical devices. Completly disected left carb last night. Iwas always nervous about taking out jets and other bits from these things. Cleaned everything up, put her back togather. Once cable was secured. the bike fired right up and ran better than it ever has. Super smooth. Want to thank the two fellow members of Airhead Beemer club who came to the house to help me. They knew more about Beemes than I will ever know.
Thanks again. George

[108625]

Glad it was something simple, and better still; you only had to spend time on it, not dough.