acceleration problems

I have acceleration problems.

It's never been great but I've swapped quite a few different progressive carbs with different jet sizes and air correctors none seem to help. After about 3k revs it seems ok again.

It shows lean when accelerating even if I set the colour tune perfectly at idle.

Just thinking, have I got an ai leak somewhere I can't see, like in the brake vacuum pipe? Or could it be something like my vacuum advance is toast?

Any ideas guys.

It's 2ltr and progressive single carb, which I can setup fine but I'm struggling with this lean on acceleration.

I have set timing using strobe.

 

Should I see if vwfish can have a look?

Can I just unplug the brake vacuum pipe and block it and see if it improves to rule out air leak on it?

 

yep, that will tell you if its that
BTW, what was your username before??

 

And you can test your vac advance with the distributer cap off and suck on the pipe and see if the rotor arm moves or 'advances'.

check your ignition timing, and plug leads a breakdown in these may cause the spark to go to earth before reaching the plug.

 

Cheers, will try that tomorrow morning....

Rich

 

Vac advance ok... although you do have to suck really hard.

Checking brake vacuum this avo

 

Ok, no vacuum leak on brake servo line, same when connected or blocked. Checked timing 4-6 btdc on idle increasing to 28-30 at about 3k revs.

Any help really appreciated

 

Compression, 130 on 1,2 and 4,
120 on 3

Not great that 3 is down but 10 PSI is ok isn't it?

 

No ideas hey.....

This might be a job for vwfish....

 

I was hoping someone who knew more than I do would jump in, but I'm sure that 10psi down on one cylinder is fine. The values look good to me.
If it behaves the same with different carbs then it might be fuel starvation or poor spark, but I'm nowhere near being an expert.

 

10 psi is fine. The guide is 28 psi difference between the highest and lowest reading, anything more and you have a problem

 

Thanks guys, that's another thing off the list then...

How can I measure spark strength, and fuel pSI accurately?

Can I put the compression tester on the end of the fuel line and crank it?

And then just measure the coil? Or is there a way to measure what gets to the end of the ht leads?

 

Ordered a fuel pressure gauge, will hopefully test coil and ht leads tomorrow

 

timing 7 deg as far as ive been told, bentley confirms for 2 litre at that...

 

Ok, ill double check it and get it up to 7 btdc

 

Haynes ( if you trust it) says for the 2000cc it's 7.5 deg btdc at idle with vacuum hose disconnected. It also says that the vacuum advance only works when in top gear, or in all gears at below 12 deg C. There should be a switch in the gearbox that operates a control valve within the vacuum hose. I suspect that when the switch isn't working the advance will not work.

 

reset timing again...


reset plugs


still no better


gonna swap back to my other carb in case there is a prob with the new one.

 

checked coil resistance

terminal 1 to terminal 15 - 3Ohms
Terminal 1 or 15 to middle - 7600 Ohms
both of these are within tollerance so it looks like this isn't the problem.

 

reading this may help: http://www.thesamba.com/vw/forum/viewtopic.php?t=217070&highlight=weber+progressive