Hardly runs when HOT!!!!!

[peteremsley]

Guys – I really need your help!

I have a 75 R60/6 that is misbehaving terribly when it gets hot. It drops to 1 cylinder above about 3.5k revs and is not really safe to ride – It runs, but I can hardly keep up in traffic.

So far… general consensus was that it was a coil, so I bought 2 and replaced them. I thought the problem was gone until the temps got back up to the seventies, and it happened again. Next was wires… new wires and NGK plug caps – went out for a ride last night (80 or so miles) and everything was great (I was happy with myself, and the bike,,,) Yippee I thought – finally cured for $5. Since it was cured, I braved a Denver commute today. I guess I asked for it… the problem came back this afternoon. Air temps were in the top 70s. Rode about 20 mins and started loosing power, down to 1 cyl. Stopped at a light and could get it above 4k rpm. I managed to limp home, but only just.

What should I try next – parts or dealer????


Thanks.

[James.A]

If your problem is consistently side specific, you might try getting the motor warmed up and taking compresion readings. That doesn't cost anything if you have a compression tester. Did you change the spark plugs too? Do the old plugs look the same from the good side to the afflicted side. Also, a vacuum leak could cause the motor to heat up from running lean on one side and manifest as a loss of performance. One cylinder running lean would show on the spark plugs. Your R60/6 has mechanical carbs that seal to the intake spigots with hardened paper tubes. These are prone to vacuum leaks.

[peteremsley]

You know, I can't really tell if its side specific. It just runs at 50%. I've tried to identify a 'side' in the garage, but both heads and pipes burn and remove skin with equal ferocity. I have put new plugs in (NGK), checked the timing, point gap, advance and all seem to be OK. Plugs look better than you could expect... both perfect Haynes 'tan'.

Could I be barking up the wrong tree? I'm wondering if I have fuel issues induced by heat - float level, perculation, etc??? Doesn't really gel with my tan plugs, but I'm struggling...

Thanks for your time!

p.

[bprigge]

Peteremsely,

Many years ago I rebuilt a Honda 90 motor for a friend. It had the same symptoms that you have after the rebuild, turned out to be the condenser.

just a thought, Bruce

[peteremsley]

Thanks Bruce.

Someone else (airheads) said the same thing. I snuck over to the dealer at lunch and they lightened my wallet by thrirty-something dollars for a new condenser and points. I will install tonight and see what happens!

[flash412]

Have you MEASURED anything? If you simply threw used coils at it, they might not be good either.

[bmwmick]

Someone else (airheads) said the same thing. I snuck over to the dealer at lunch and they lightened my wallet by thrirty-something dollars for a new condenser and points. I will install tonight and see what happens!

Peter,
Have you checked the valve clearances? If they close up to 0 clearance, you will have very similar symptoms.

[pmdave]

I remember similar symptoms when the points screw loosened itself and the points almost closed.

When replacing points (we'd have to explain that to owners of todays bikes, eh?) look carefully at the point gap and note whether the contacts are barely worn, or there is deep pitting. If the contacts are deeply burned or pitted, the condensor is bad. If the points aren't burned, but are simply worn out, re-use that old condensor.

One other item to check: the fuel cap. The screw-in fuel caps were designed to vent through the keyhole, but crud and corrosion can block off the vent, and the tank draws a vacuum--so fuel flow is restricted. The bike will start and run at idle, but won't run at higher power settings. The test is to get the bike stalling and then unscrew the cap. If there is a "hisss" and the engine immediately picks up, the cap needs a vent hole drilled in it. I've forgotten the location, but will make a diagram if needed.

pmdave

[peteremsley]

put new points and condenser on, cleaned a bunch of ingition connectors and the problem seems to be gone. My guess is the condenser cured it.
Ran great on a 1 1/2 hr ride in the 90s yesterday.

Thanks to all that offered help and suggestions.