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Tue Sep 30, 2014 11:47 am

I finally got the engine fully in and running, working through the final tuneup settings. Driving around town, and when accelerating, I get a 'cough' through the carbs. It's not a real backfire, more of a cough or 'phhhhooootttt' noise.

74mm crank, 92 mm p&c, L5 heads from ACN/DRD, w110 crank, stock rockers, weber 40's , and a SVDA distributor. Tuned the carbs with a snail I borrowed from another member, and ACN did the initial carb setup/cleaning. Runs well, lots of power, slight hesitation off idle, no other issues. I pulled the plugs, before final carb setup, although I had the balance flow correct. 1,3,4 looked a 'touch' rich, and 2 looked a bit lean. Adjusted the carbs, waiting to drive it now right after I finish some paperwork for the job.

Any thoughts?

Tue Sep 30, 2014 12:51 pm

Typically it's the idle jets clogged or running lean on deceleration/off idle. I just purchased a car with dual 40 Dellortos that has developed the same problem. Dells are a little different but tune the same. The weber manual woud be a great reference as I just received the Dellorto manual last night.

Tue Sep 30, 2014 1:34 pm

I just drove it, and I came back and checked timing. It was retarded , not really a lot, but maybe 15 degrees later than it should be. I guess I was a bit 'gun shy' on my initial setup due to having burned a piston on the last engine. That is why I had to build an engine to start with. Drove it again, much quicker, no coughing, less hesitation. I just need to make sure it doesn't ping on me, and it will be difficult to hear with the dual 40's. The muffler is plenty quiet, but the dual carbs more than make up for it.

Tue Sep 30, 2014 1:56 pm

Axitech wrote: I just drove it, and I came back and checked timing. It was retarded , not really a lot, but maybe 15 degrees later than it should be. I guess I was a bit 'gun shy' on my initial setup due to having burned a piston on the last engine. That is why I had to build an engine to start with. Drove it again, much quicker, no coughing, less hesitation. I just need to make sure it doesn't ping on me, and it will be difficult to hear with the dual 40's. The muffler is plenty quiet, but the dual carbs more than make up for it.
So where was it at? 15-17*

Tue Sep 30, 2014 1:58 pm

If you readjusted the timing then you should readjust the idle mixture screws.

Get the engine up to operating temp then do the lean best idle procedure for each cylinder and repeat it two to three times for each cylinder so you are sure you have adjusted them correctly. Then make sure the carbs are in synch and you should be good to go.

Buy a synch meter. You will need it.

Tue Sep 30, 2014 2:03 pm

Will readjust now. Yeah. Timing was about 15 btdc