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Single 40 tuning issues? This is a long one...

Masdomonkey

Member
Ive got a 1776 engine that had a bugspray on it, just junked it because it leaked like crazy because of efp. So i got a idf 40 from a guy that ran it on his 1776 manx. I swapped it, it runs but at idle it runs like a tractor. So my first thought was main jet...

now after the swap i was messing with the distributor (its still in time) and ive noticed that when i pull 1 and 3 wires from the distributor while running at idle there is no change in how the engine runs. Ive driven it with them unplugged and it runs like s&it. But when i drive it with them plugged in it runs normal when i pass idle. It does bog at first but thats the jetting i need to do...

I asked around and a guy said to get a spray bottle of water and spray it on the exhaust pipes near the ports and he said if it doesn't evaporate instantly the cylinder is running cold( depending on the cylinder i sprayed). He said that it could be compression, valves, or timing. Timing is a check but heres the thing, how could it be valves or compression if it drives normally when past idle? So it i concluded it had to be the carb....or is it?

Im new to vw and i really dont want to tear into the engine so i was hoping that someone had the same problem with single carb 40 setup but figured it out... please help:(


I dont always go fast, but when I do its defiantly not in bed
 

dzrt performance

Well-Known Member
if it runs "ok" up top...it probably has good cylinders IE compression, valves and so forth.

you mentioned changing the main, yet the main does not come into play at idle.

I would check your valve lash as a matter of due diligence. this is something on ACVW's that needs constant attention.

I would also look at your spark plugs and wires, probably even replace them. if these items have mileage on them, they can look good, but cause all sorts of misfires at sporadic times. This would include looking into the cap and rotor and replacing them as well. another trick is to put a timing light on each cylinder wiring and see if each one is firing.

the trick with water on the pipes is a valid test, but seen even better wit a typical low cost laser pyrometer/thermometer. you will see a large temperature disparity between cylinders that are firing vs cylinders that aren't. cylinders that aren't firing will still absorb heat from the engine, so the water test can be misleading.

finally, the idle jets can easily be clogged. I would take them out and clean them.

if your cylinders are misfiring because of spark, typically the raw fuel goes through the cylinder and out the exhaust, producing pops at the tail pipe.

if the cylinder is misfire due to carb issue (lean) it may back fire up through the intake or at sudden acceleration.
 

green787

Well-Known Member
Valve lash and Ignition timing are critical for a VW to idle properly.... I would take the carb off and blow out the idle circuit with compressed air, check to see that the idle jet and main jet are not clogged or damaged.... Check for silicon gasket sealer plugging the ports around the butterfly....
Set the valve lash at 0.10 if you don't want to hear a bunch of noise... Make sure your distributor shaft is not worn and causing point bounce issues at idle....
Set the timing to 10 degrees advance at idle, and watch to see if your centrifugal advance and vacuum advance are working properly.... Scrape the contacts on the cap and rotor....:D
Do those things, and hit the start button and everything should work....:cool:
 

Masdomonkey

Member
Ive swapped the cap, rotor, and plugs, not the wires tho, i have electric distributor no vacuum. so if i swap idle jets would it kill the bog at acceleration?


I dont always go fast, but when I do its defiantly not in bed
 

Masdomonkey

Member
Ive actually moved the wires around but the problem stays on 1 and 3

Thank you all for your replies much love


I dont always go fast, but when I do its defiantly not in bed
 

Randog

New Member
This might sound dumb but ive seen it many time and it sounds like your problem. But check the intake boots from the end casting to the intake and make sure there's no cranks or holes in it where it could be sucking air. Or at the head where your end casting bolts down is tight and seats flat in the gasket.


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Nino Ficara

Well-Known Member
This might sound dumb but ive seen it many time and it sounds like your problem. But check the intake boots from the end casting to the intake and make sure there's no cranks or holes in it where it could be sucking air. Or at the head where your end casting bolts down is tight and seats flat in the gasket.


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Could possibly be.
 

green787

Well-Known Member
Ive actually moved the wires around but the problem stays on 1 and 3

Thank you all for your replies much love


I dont always go fast, but when I do its defiantly not in bed
Remove all spark plugs.... Check the compression on all four cylinders and report back to your fans....:D
 

5racer

Well-Known Member
idle jets ,and check float gasket not all gaskets are created equal some have holes that will give you a air leak symptom
 

Masdomonkey

Member
Remove all spark plugs.... Check the compression on all four cylinders and report back to your fans....:D
Compression test was good, swapped the idler jets too 55 and my pump jet to 00, its running normal now


I dont always go fast, but when I do its defiantly not in bed
 
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