I had a similar issue about a hundred years ago with a rally car that I installed sidedraft dellorto carbs on.

 

The engine had a waaaaaay lumpy cam and sounded rough at idle and up to about 4,000 rpm and was really grumpy above that. I assumed it was the cam.

 

It never ran right consistently but from time to time would clear its lungs and absolutely haul right up to 9,000 rpm

 

Now I changed EVERYTHING electrical, stripped down the carbs, checked fuel pressure and flow, took the bonnet off and went for a night drive looking for sparks, you name it I looked for everything. I just couldn't solve the problem.

 

Anyway I sold it for a bargain price when I finally had enough and the guy who bought it called me up and said "hey I found your problem, the throttle linkage was only pulling one of the 2 sidedraft carbs open"

 

How stupid did I feel? Very. Turns out the car was set up just right except for my simple linkage stuff up. (No he wouldn't sell it back to me!)

 

When I was experiencing the car revving cleanly all the way to 9,000 rpm it was the vacuum reaching such a high level that it opened the butterflies on the carb that wasn't connected properly.

 

This probably isn't your issue but I had looked at my linkage a thousand times and never noticed and of course as I had made it I assumed it was right. Have you had a second pair of eyes go over your setup? Couldn't hurt.

 

Never assume anything.

 

Hope this helps.

That sounds nearly identical to my issue.. However my linkages are genuine solex links.... I'm taking it to the track this weekend to run it at tops.. So I'll see if I can locate the issue this weekend I wish I had mates who new what a carby was.. Bunch of s-chassis drift nuts haha thanks man!!

That sounds nearly identical to my issue.. However my linkages are genuine solex links.... I'm taking it to the track this weekend to run it at tops.. So I'll see if I can locate the issue this weekend I wish I had mates who new what a carby was.. Bunch of s-chassis drift nuts haha thanks man!!

 

Talk nicely to the other guys/racers in the pits you'll probably find someone who can help out.

 

Best of luck hope you get it sorted.