CA77 Dream running GREAT! ... Until it gets HOT.

[Bob750]

So the 1964 Dream 305 I restored for my wife a year ago has been running very well. But now it's behaving poorly when it gets hot.

We'll take the bikes out around town for a half hour or so and at some point, it'll start to die when we come to a light. And then it won't want to hold an idle. We have to rev it to keep it going. It starts to pop and still wants to die. If it does die, it's quite hard to get started again. If I adjust the idle screw to a higher idle it'll start to hunt and stay at an even higher idle until you blip the throttle or momentarily feather the clutch to load the engine a little.

Months ago, something similar would happen while waiting at a light, again, after about a half hour of running. I'd have to rev it to keep it from quitting. But it would behave normally after a cooling period.

So I've determined that the bike runs great until it reaches a certain temperature at which point it won't idle. Is this indicating it's too rich or too lean at hot temps at idle?

The float on this 22mm carb is adjusted to 26mm, but I'm seeing 26.5mm as the figure. Could that be part of the issue? I've not tried any "spray tests" to see if my carb insulator is allowing air to seep in and lean the mixture. Running NGK D8HA plugs and the new stock air filter and snug connecting hose.

When the bike is cold, it'll start with choke, and after it warms up a bit holds a nice idle. But then after a good half hour of riding (more if it's significantly cool out--and sometimes never if it's downright cold out) it'll want to die at or just above idle.

I thought I might have a clogged pilot jet, so I rebuilt the carb complete with an ultrasonic bath. Went together nicely and ran well and I thought I had it licked until this (rather hot) afternoon and we had to end our ride early due to the same issue.

Can anyone point me in the right direction to a solution?

Thanks,
Bob

[mike1969]

Just a shot in the dark. Simplest thing to check would be the gas cap. Vent may be clogged.

[Bob750]

Thanks for attempt Mike :-) ...but it's not that. We can ride all day at speed with out setting up a vacuum in the tank, and it's only the idle that is the problem and only when hot.

[Bob750]

Ok, so here are some videos that may help someone ascertain what is going on.

Video 1: '64 Dream 305 at warm idle. Slowest steady idle I can get. I think it sounds pretty good. We'd taken it on a 10 mile ride, when it started "acting up" at idle. It wanted to quit. Had to rev it to keep it running. Once home, I let it cool down in the garage for a few hours and then reset the carb screw adjustments. Then I shot this video. It idled like this for 15 min straight with a gentle fan blowing on it in a 85 deg F garage before I turned it off.

Video 2: This is how the same bike behaved after a ride through the 76 deg F streets of Long Beach on this beautiful Sunday morning from about 7:45 to 9:15. I wanted to see if the cooler air temp and freer traffic would allow us to ride longer before the misbehavior started in again. About twice as long. As we pulled up to the garage, I shot this video while holding the throttle open just enough to prevent the engine from quitting. Listen to the pops and coughs. As soon as I let go of the throttle, it quits. The carb in this shot has the same untouched screw settings as in the previous video the evening before. Huh?

Video 3: Here we see the bike will start right up (after switching on the ignition...) and idle just fine after only cooling off for an hour after the previous video. After I did this, I pulled the D8HA plugs to reveal black soot. I popped in a set of D6HAs and idled it for about 10 minutes, they came out looking the same as the D8s.

Spark plugs:


It's either idling really rich, or oil is seeping past a non-OEM head gasket into the combustion chamber. There is a very slight white puff coming from the exhaust you can see in the video. (Go full screen for better detail.)

What would cause high temps to make it not idle when it idles fine all the rest of the time?

[mike in idaho]

What condition are the metering jet and the needle? Any wear evident(it doesn't take much)?You might try lowering the needle a notch to see if it helps.

[Bob750]

Well, the bike has very good throttle response all across the range and in every gear (and has for the 500 miles since I restored it). And as you can see in Video 1 above, it idles well... Only after it has been run long enough (at least 30 to 90 minutes depending on the ambient temp and riding style) to reach a certain temperature does it start to misbehave and want to quit. Once it cools, it runs fine again without any adjustment. All the brass is in good condition and OEM as far as I can tell (9000 miles on bike). I just cleaned and reassembled the carb last week to see if the pilot jet was clogged. It wasn't. All the air passages are clear too. And besides, any thing that's wrong with any jet or needle would have to be explained in terms of why it works fine when cold, and even really warm, but not when HOT, and even then, only at idle.

What condition are the metering jet and the needle? Any wear evident(it doesn't take much)?You might try lowering the needle a notch to see if it helps.

[mike in idaho]

If it's not a carburetion issue, maybe it's a fuel related issue. Have you tried a different grade of gas? Maybe some ethanol free blend(if you can find it). Maybe it's electrical, do you have a way to heat up the coil/condenser(with a heat gun or a hair dryer) to see if it acts up?