Carb chuffs and hollow exhaust pops stop when engine reaches operating temp

[Tony]

Very strange.  When I first start the '93 Super Sprint engine, carbs 1 & 4 chuff and you hear hollow pops out of the exhaust.  Let it run until really hot and the symptoms disappear.  After that it runs great, but when cold it runs really rough.  Never had this problem before, wondering if the temperature rise causes something in the carbs to change or it is related to ignition.  Have over-the-winter storage gas in it now, planning on refreshing it soon.  Also waiting for recommended new B8ECS plugs (lost in transit from UK) to replace the current BPR8ES plugs which have a resistor.  The B8ECS plugs do not have the resistor and from what I understand, the Aldon Ignitor requires plugs w/o resistor.  

 

Any of this ring a bell, make sense?  Baffled as to the cause, interested in your thoughts.

 

Thanks,

Tony

[Alex-Ks1]

I had this happen once , drove me crazy , ran like crap , back firing popping out he read , then when I got warm it ran fine .

Plugs sure didn't help , not words or cap or rotor ,carburator was good , so I stated checking for vacuum leaks  .

It turned out to be the end carb on a tri power set up , the base gasket had shrunk to a point of a leak , when it got hot it swelled to seal it up . 2.50 cents fixed it .it might not be your problem , but spray carb cleaner on all the carb bases , if the RPMs speed up , that the problem ..

[MV8]

I'm not sure how well over winter storage additives work with ethanol blends. I'd drain everything and add fresh non-ethanol. You might also pour the existing fuel in a clear two liter and let it sit, looking for separation of water and fuel. Old Caterhams don't always have sealed evap systems and let the humidity in to settle under the fuel. Checking for water under the fuel in the tanks is a common, regular process with aircraft that do not have the disadvantages of ethanol blends.

[Tony]

Gentlemen,

Thought about the carb gasket leak, ie vibration damper, gave each of the nuts a 1/2 turn and it seems  to have done the trick.  Yes! No removal of carbs........ yet.

Thanks for that hint!

Will run out the gas now that it is running better and refill with fresh.

Appreciate the insights.

Thanks,

Tony

[MV8]

Hooray! I completely forgot about that crazy spring loaded gasket.

[Alex-Ks1]

Glad it worked , usually the simplest of things are the hardest to work out