vapor lock

[jensen]

Hi

At the moment it's very hot (and very humid) in the Netherlands (around 90 deg F). It's very unusual for this region to be this hot. I was driving my CB72 and was waiting for a traffic light (rather long), as the bike started to run irregularly, and when the light went green, and I opened the throttle, the bike stalled.

After some cooling down, the bike ran, and while driving on the highway, the bike ran without problems. I encountered this issue before with my C50 step thru, some 25 years ago, and found out it was due to vapor lock.

Does anyone, especially in the warm area's in the world encountered similar problems ?

Jensen

[e3steve]

Nope. Idle is rock-steady-Eddie, even at 43ºC (that's 109ºF in old money). Doesn't miss a beat.

[davomoto]

Jensen, I had a Chevy pick-up that would vapor lock on hot days, 100 degrees, while towing my boat. Arghh, almost to the lake, and crap! BTW, got the book, and it's truly awsome. i've only looked at the pics so far, can't wait to dive in to reading it!

[teazer]

Vapor lock is fuel boiling and changing state from liquid to gaseous. As a gas, fuel pumps have a problem delivering fuel.

Our old bikes are gravity fed and vapor lock is extremely rare. It's possible that heat soak caused the fuel in the float chambers to vaporize leaving insufficient liquid fuel to burn.

It's also possible that one or both condensers are heat soaking and breaking down at elevated temperatures. But you have an electronic ignition, so that shouldn't be an issue, unless some other component is breaking down at elevated temperatures.

That happens to Dyna S units form time to time and probably to others.

[jensen]

Hi,

Thanks everyone for the input. Teaser, it seems to be that the fuel in the float chambers is getting to hot and starts to vaporize. I have had the problem several times now, with one specific traffic light only.

When I come from the highway for about 25 miles, there is a traffic light were I have to wait for a while. I drive this piece of highway pretty fast so the engine is really hot.

I did put a little ventilator on my CDI, but had the same problem on the same place, so it's not the electronics.

The last time it happened I closed the choke just before accelerating, and the engine didn't stall.

The remedy for me is killing the engine just before stopping for the traffic light, and start her up when the light turns green.

For the time being I run original carbs on my CB72, the early type and with power jets. Main jet is 125, idle jet is 38, needle is on the second clip (from below), power jet is fully functional, it has the old style air cleaner (but with foam) with the extra tubes. The bike has the early stainless mufflers.

The temperatures are much cooler now, the problem is gone.

Jensen