Hi all, I am having trouble with my new engine that I built, the Weber seems to be running on when I rev the engine e.g. when I rev the engine to lets say 3500rpm, when I let go of the throttle and it returns properly, the engine revs hold and then drop or they hold and then go up then drop...

Does any body know what the problem would be????

The engine specs are as follows:
1293cc
11.8:1 comp
MD296SP cam
Full race prep Head by Performance techniques then fixed up by GR
1.5:1 Swiftune rockers
3-1 Maniflow exhaust manifold
6" Inlet manifold
28deg total timing
Running on Pre-Max 102

Weber setup:
45 DCOE New....
36 Chokes
F2 Emulsion tubes
Tried 55f8 and 45 f9
195 Air Cor
180 Mains
Tried 40 and 50 pumps
35 aux's
??? pump bleed backs
GR's Ram tubes

The Weber set up was a basic setup the GR told me to use.....

There are no manifold leaks, So experts what’s the problem?????????

Air leak somewhere - have you got a booster?

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Boosters are for the week... thats a No

How about a vacuum advance dizzy? or PCV breather system?

No vac advance or Breather system.

If it is not an air leak, then it may be a blockage in one of the passages for fuel (ie it is getting too much air and not enough fuel). Likely things to check are blow out all the jets and places where fuel passes, check that the little lead balls used to block some of the serviceable parts are in place and not in the wrong place, and that it is pumping correctly (are both the little balls in place in the pump mechanism.

What effect does turning the mixture screws have?

I am far from an expert, but I recently had exactly the same trouble and it was due to incompetence from whomever serviced the "recently refurbished" weber I bought secondhand - there were a multitude of problems that took ages to diagnose and sort.

What is the history of the carbie that you know? has the mixture screw housings been resleeved?

We found
1. a ball missing in the pump mechanism
2. mixture screw had been resleeved and was missing an important hole not allowing fuel through.
3. Lead balls blocking passages they shouldn't be
KB

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