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914World.com _ 914World Garage _ Spitting back through carbs at idle

Posted by: David Stowers Apr 26 2014, 11:01 AM

I'm running twin Dellortos and have had them set up and balanced by a respected air cooled guy. The only problem is that it won't idle smoothly and pops and splutters back through the carbs once its warmed up.
He suggested valve clearances or sticky valves but it seems strange as it appears to be happening on all cylinders. His only other suggestion was the carbs could be trash.
Any thoughts before I go skinning my knuckle AGAIN checking the clearances or worse still looking for new carbs?
It didn't do this before my recent head replacement but is doing it on both sides

Posted by: r_towle Apr 26 2014, 02:21 PM

Does it hot, not cold?
Check your valves

I would check the timing when hot, see if your distributor advance plates are sticky.
Also wires and correct plugs.

Posted by: David Stowers Apr 26 2014, 04:04 PM

QUOTE(r_towle @ Apr 26 2014, 12:21 PM)

Does it hot, not cold?
Check your valves

I would check the timing when hot, see if your distributor advance plates are sticky.
Also wires and correct plugs.

Thanks
Yes, when hot. New wires and correct Bosch plugs.
I'll double check valve clearances and maybe go 0.2mm instead of 0.15

Posted by: barefoot Apr 27 2014, 12:51 PM

Sounds like timing or sticky intake valves, not carbs.

Posted by: David Stowers May 19 2014, 03:26 PM

It turned out the valve springs were on their way out, I had two springs on the same head fail, an intake on #4 and exhaust on #3. Spoilt our day somewhat.
I bought two brand new repro heads and its running like a dream.