Rice Krispies Engine

[Galwaylotus]

My Twin Cam is like a Rice Krispies engine at the moment. It goes "snap, crackle and pop" especially on overrun but even when not in gear. I was away for a few weeks and when I started it this morning the issue is still there. Webers have been rebuilt, electronic ignition and Stealth Black Box ignition controller installed. Battery is new and it charges well on the alternator. Advance curve is very close to factory spec for my distributor. Any ideas?

[rgh0]

If you have not done anything recently to change carb jetting it is usually due to a leak somewhere in the exhaust or maybe around the carb mounts.

cheers
Rohan

[661]

Check static advance not moved and put some new 99 momentum in it......???? Won't cost much to try

[Galwaylotus]

Thanks, guys. Rohan, I thought about a possible exhaust leak. Is there a simple way of checking? I have to work in the driveway and jacking the car up to inspect underneath isn't the most desirable operation. I somehow think the soapy water method mightn't work too well on a hot exhaust system.

[ricarbo]

The usual way I check for exhaust leaks is to have an assistant block the exhaust outlet with the palm of a hand, when the engine is idling. This makes the leak more pronounced and the hiss is quite loud. When my exhaust manifold was loose, it didn;t leak noticeably until the throttle was blipped, which made the engine rock a little, so opening a gap. Then it made a lot of noise.
Couldn't your fault be consistent with a weak mixture or over advanced ignition?
What's new 99 momentum? Never heard that before.
regards
Richard

[david.g.chapman]

If I suspect the exhaust is making a funny noise, I first of all waggle the tail-pipe to see if there are any noises there. it might also show up a loose exhaust joint.

Step two is to get an old blanket and put it next to the car between the front and rear wheels. Start the car and lie down on the blanket, look under the car and try to pin-point any noises. It is not always easy!

Sharp hissing noises normally indicates a manifold leak. Your sort of noise could indicate some leak further down the exhaust. Look for black staining from the carbon being ejected.

Best of luck!

Dave Chapman.

[mbell]

What's new 99 momentum? Never heard that before.

I'd guess petrol, specifically Tesco Super unleaded...

[StressCraxx]

My Twin Cam is like a Rice Krispies engine at the moment. It goes "snap, crackle and pop" especially on overrun but even when not in gear. I was away for a few weeks and when I started it this morning the issue is still there. Webers have been rebuilt, electronic ignition and Stealth Black Box ignition controller installed. Battery is new and it charges well on the alternator. Advance curve is very close to factory spec for my distributor. Any ideas?

Hello Galway,

The method of plugging the exhaust outlet is a good one and usually gives a result. If you are still trying to pinpoint the leak, try using a 1m length of rubber hose or plastic tube to your ear and scan the suspected area with the other end of the tube.

Regards,
Dan Wise

[Elan45]

Did you start it with the choke after sitting? The choke may be sticking partly open, causing your crackle and poor running. I never use choke on any of my Weber carbbed cars and this is one reason.

You may be able to tap on the choke links and get it to return, then don't use it again.

Roger

[Galwaylotus]

Did you start it with the choke after sitting? The choke may be sticking partly open, causing your crackle and poor running. I never use choke on any of my Weber carbbed cars and this is one reason.

You may be able to tap on the choke links and get it to return, then don't use it again.

Roger

Ditto on use of the choke. I just pump the accelerator a couple of times and then start. I don't use the enrichment circuit.

[promotor]

What is the condition of the valve seats, and are all the valve clearances set correctly?

Sounds like valves not seating on the seats properly. Has the head had any attention in the recent past? When was the last time the engine ran OK?