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SU HIF4 Carbs - source of backfiring??

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mirceme

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This forum has been great for me. Each problem I've asked you for help on had gotten me quick and useful answers.

The problem of the week is backfiring.

It used to happen only when the engine was cold, but it is happening with increasing frequency. When backfiring, I get a gassy smell in the cockpit, making me think that maybe the carburator mixture is too rich. Which in turn led me to the Haynes manual.

I see that these strange little carburators have some sort of oil damper??? When I remove the carb cover I see no evidence any oil. (Based on prior experience with the clutch, it wouldn't surprise me that there was no oil) Is is possible this is the source of my backfiring?

Can anyone give me the abc's of these carbs...how much oil, what kind of oil or any other thoughts as to the source of my backfires.

As alway, your help is appreciated.

Tom /ubbthreads/images/graemlins/cheers.gif
 
The oil damper referred to is the plunger in the center of the top of the carb. Unscrew the black plastic cap and it and a piston can be pulled out. Fill the reservoir with light weight up to about 1/2 inch from the top and replace the piston. That reservoir needs to be checked regularly and kept filled with oil.

Mickey
 
I use automatic tranny fluid - check it every time you fill up w/gas
 
I've got HIF-4's on my MGB and have had them set both sides of the right mixture and haven't had them cause backfiring. The only thing in my exoerience that has caused that symptom is timing problems or leaky valves. I have had a distributor cap go bad and cause backfiring but it didn't run after it backfired. Only a new cap fixed that.
You might try a tune up and check compression on all cylinders while you are in there and then decide what to do from there. Also check spark plug wire resistance.
Bob
 
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