Centre Mount 40idf woes

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Centre Mount 40idf woes

Post by jamesbissland » Thu Dec 28, 2017 4:21 am

Hi All

I have just bought a Beetle with a 1641 and it doesn't seem to be running as good as it should

When it sits idling at traffic lights it gases out cars all around and exhaust starts burbling sometimes (it actually sounds pretty awesome tbh!) and has terrible fuel economy

Its a 1641cc
Running 042 40x35.5 heads
Engle W110
German 009
Centre mount 40idf with 28m Venturi

I have pulled the jets and have found

Mains 145
Emulsions F11
Air Correctors 155
Idle 55 (Cylinder 3&4) & 50 (Cylinder 1&2)

Is it common to have different idle jets ??? Im guessing someone has done this to compensate for the minor difference in runner length?

I am in New Zealand, right on sea level, and ambient temperatures range from 25F (mid winter) to 85F (mid summer) so nothing extreme

Would anyone have recommendations on changes to the about carb configuration?

I have read somewhere also about drilling a 2mm hole in each butterfly when running a single IDF.. is this still recommended??

Lastly, I have notice that it has 195/60R15 tyres, so when cruising around town it is sitting on the 2000rpm mark, which from what I understand is right on the circuit change over mark? Would this effect fuel economy? My gut feeling is yes, because currently it is terrible

Many thanks in advance!

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Re: Centre Mount 40idf woes

Post by ainokea » Thu Dec 28, 2017 5:32 pm

Does the carburetor have the recommended 2mm holes drilled in the throttle plates? I would think not and the idle jets should be the same. you might be setting the idle speed exposing the progression holes in the carburetor body. The 2mm holes might help from exposing the progression holes and help with a rich idle. Also check your float level should be about 30mm drop and 10.5mm without compressing the spring

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Re: Centre Mount 40idf woes

Post by PEPPE » Fri Dec 29, 2017 6:02 pm

little CC, big valve, 110 cam , 009 does not help a lot for good running in economy. would be better to use dual carb in an engine like that. i would check also the compression of the engine, those heads have usually big chambers

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Re: Centre Mount 40idf woes

Post by Ol'fogasaurus » Fri Dec 29, 2017 7:25 pm

Not all 009s are the same, some are good and the others are a mixed bag. The 009s are out of a bus and the timing starts to advance at somewhere around 26° First you need to have the distributor spun to check bushing and to see where and if the advance is working. There is a stamped version and a cast version with, as I remember, the cast version being a better choice. A lot of guys use the 010 but don't use the vacuum side of the advance.

Also check the cap and rotor as they can be a hidden fault. This summer my stepson's 1835 started dropping in power so the first thing I suggested was to do a capacitance check on the plug wires. They all pegged the meter but when he checked the high tension wire from the coil to the cap it didn't peg out but did go part way. He didn't notice it but I did and had him recheck it. We pulled a high tension wire off his other rail and *^#$^(&*, it didn't even move the needle. He got a new one and got his power back.

A lot of things to look at isn't there.

My opinion is worth slightly less than what you paid for it.

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