Mystery Misfire.....

[Jeremy R65]

Advice please gentlemen.  I have had my low mileage 1980 R65 "Otto" for just over a year now.  Last year I gave him a thorough going through, new points, condenser, plugs, oils etc. He ran fine all summer and I did about 1000 miles.  I do not ride over winter, so I put some ethanol damage inhibitor in the fuel tank, drained the float bowls and did not run it again until April.  I did, however, rebuilt the forks put new BT45s on it and charged the battery periodically so I have made my financial sacrifices to the old bike Gods.  Got the bike out in April and gave it a wash (done this many times with no problems) and took it down the road - intermittent misfire!  Ok for a while then popping and hesitating, then cleared again for while then when I stopped it was running rough and intermittently on one cylinder then stalled.  I left it alone for a couple of weeks, but today I checked points (clean and no spark erosion damage) and plugs (OK but a bit black), float bowls (clean) and fuel flow seems OK.  I took the tank off and wiggled all the connectors around the coils and plug leads, sprayed them with contact cleaner and WD40 (the universal panacea).  Could not see any thing wrong, except that in the rear coil the plug lead can be moved in and out a couple of mm and I cannot see how it is retained in place. I took it down the road, it was OK for about half a mile then began misfiring again.  I stopped, and revved him a bit and it cleared, but it came back.  Sometimes it sits and ticks over like a watch then for no obvious reason it runs like a dog again. I am not sure what to do next.  It seems too sudden in the way it comes and goes to be fuel related, could it be sudden problems with coils or plug leads?   All suggestions gratefully received.  Thanks.  Jeremy.

[Bob_Roller]

The first generation R65's, with twin coils, had issues with the main earthing, or grounding point being on the forward coil mounting bracket .

The bracket is prone to cracking and give electrical issues with the bike .

The ignition lead is held into the coil by the rubber boot  on the ignition lead .

[Einar]

In addition to above comment i would check:
- spark plug leads
- choke cable routing
- air filter box (did something nest inside over the winter)
- carburetor "seals". Any air coming in where the plastic pipes connect to carbu intake/outlet from air box and/or into cylinder?

[tunnelrider]

If you can hire or borrow a timing light and check/ adjust the timing, this is can be a fix for some of the above symptoms, especially running rough rolling off the throttle to stay at a steady 2000-3500 rpm after accelerating.

[montmil]

The ignition lead is held into the coil by the rubber boot  on the ignition lead .

Reading the comments got me thinking... always questionable.

The ignition leads should be firmly anchored in in the coil towers. The rubber boot is for weather protection. The coil end of the plug wire should snap into the coil and be held by a dimple on the metal end of the wire.

If your ignition wire is loose or damaged at the coil connection, that might be part of your problem.

[Jeremy R65]

Thanks for the advice guys.  I have checked the coil mountings and all seems tight and well, with secure earths.  There are no birds in the air cleaner. The timing was fine when it went into storage and the points gap is as it was when timing was set 1000 miles ago. I changed the two main fuzes for new ones just in case (they were a bit corroded at the tips).  I checked that all connections to the coils were tight and tried to remove the HT leads without success (how do they come out?) and now both are a bit loose without the rubber boot cover.  The carb mounts are tight and the fuel flow seems good enough and float bowls are clean. The end result of all this fiddling was that the running was even worse and it was reluctant to start at all.  When it runs it misfires like hell and stops.  Could it be coils or HT leads? Why the degradation are sitting doing FA for 5 months though. not sure WTF to do next except start spending money on coils and leads, or passing it to my local BMW dealer (small experienced two man outfit). Life with a Velocette is easier, if it won't go it is either the mag or the carb.....or me.  Further suggestions gratefully received.  Jeremy

[montmil]

OK, so you tugged on the HT leads at the coil and now both are loose within the coil towers. There seems to be a message here.

Likely 36-year old coil/s with sloppy loose HT leads; leads that could have multiple internal breakdowns before that get to the currently misfiring spark plugs that may or may not still be fitted with the always suspect caps.

Time to go shopping for a points ignition compatible Dyna coil, new leads and fresh NGK plug caps to match the ignition system.

[Bob_W]

Do you by any chance have the famous "Crack-A-Matic" grey coil?

Bob

[Mike V]

Jeremy,

If all else fails ... try a new condenser. Just a hunch.

[Barry]

A 1980 with points should be a pair of 6 volt coils.  

I see all the focus on ignition perhaps because of the loose HT leads but I'm not so sure. HT does not need a firm connection to work it will jump a small gap and still fire the plug just fine. Think of old cars with a distributor where there is a gap designed in.   HT tracking to earth is another thing and that is more likely to be the cause of the problem if it turns out to be ignition related.  

If you remove the plugs and crank the engine with the plugs in the HT leads and earthed how do the sparks look.  Strong blue is good, yellow not so good.

The only time my engine ran like a pig and misfired with no power it felt like ignition but turned out to be blocked jets.



  

[georgesgiralt]

I second Barry. When young the neighbor car Guru told me "when you think it is ignition, it is actually carburetor related. And vice versa".
He has proved damn right in the 40+ years since.

[Tony Smith]

My money is on a dried out "o" ring in one of the carbs that has cracked and is allowing air or fuel to go where it should not. I would also give the main jets, mixing chambers, idle jets and float needle a really good clean.

I'd also check the rubbers where the carbs connect to the heads as a crack here can create some quite surprising effects.

If all of the above proved to be OK, then I would replace points and condenser (yes I know they are relatively young, but they are also cheap and capable of creating this fault being seen.

If the above didn't work, I'd next replace plugs and plug leads and if still not improvement I would find a fellow airhead owner to  loan me a coil and I'd then change it out with mine to see if the fault "moved".

After all that, prayer would seem to be the next option.

[Jeremy R65]

Thanks gentlemen.  We are away for a week now, but when I get back I will take a look at the carbs and work through the elimination route with electrics.  After reading Monte's post, I did order new coils and plug leads to see if I can buy my way out of the problem, so we will see.........