hello fellow buggy folks,Im new to the site and have been seeing alot of really good info.I have a problem that i hope someone could help me out on,I have 1835 that i was running dual 40 idf's on and have swapped it to a single center mount and it idles fine but if you bring the rpms up quickly it goes flat and smothers,bring the rpms up gradually and it's ok.having run the idle mixture screws 2 plus turns out and the idle speed screw more than it really needs to be.Have set the valves and set the time.Any help would be highly appreciated.I had read where someone said something about drilling out accel pump squirter.Thanks BMR

IDF's usually all have 55 accel pump squirters in them. This is fine when used as duals. When you switch to a single, you are not squirting enough fuel for all 4 cylinders. You need to drill out the accel pump squirters to 70 at least. This will cure your stumble. You can purchase them all ready drilled if you do not have the tools to do it.

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thats your idle jets,yes u do need to drill ur squirters to about 70,but if u have a flat spot in it,u need to go up on ur idle jets,if its got 55 idles,drill them to 60,then try that,u should be good

I agree. After reading the post again and he stated his mixture screws were out 2+ turns, that's a sign of undersized idle jets for sure. Try some 60's in there and see how it does.

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HEY, thanks men for ur replys,Ive had some problems getting logged back in for some reason its probably something im doing. But anyway Roy when you say to drill the squirter are meaning the brass jet part of the squirter or the squirter housing itself,THis is the first time ive been into a IDf.You mentioned drilling to 70,the smallest drill bit I have goes down to 60 in my index.Also it was mentioned that you can buy them already drilled,do you know where because i may screw this up before i get it right,also go up to 60 on the idle jet.Once again thanks guy's for all of your info.BMR

Drill the squirter housing itself. You can buy them from CB Performance or Aircooled.net.

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It's been a while.... But isn't there a pump squirter bypass valve on the IDF's? I believe it forces the extra fuel back into the bowl?? I think you can get a "0" bypass which will force all the fuel thru the squirter instead of sending some of it back to the bowl. When using a "0" bypass with a 55 pump jet, you get a longer duration "squirt" instead of a "dump" of fuel into the cylinders. Should be located in the bottom of the bowl. Might be something to think about...

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yea there is a pump bypass ,its is in the bottom,but when u run single carb and a bigger motor u do need to drill the squiters and put the 0 bypass in,it gives u alot more throttle response,u do this after u get the correct ides and mains in it,sometimes that could be really hard

Good info fellers! I think I'd try the "0" bypass before I drilled out the pump jets. I'm trying to remember, but when I tuned my single 40 idf a few years ago, I bought a 70 pump jet but ended up going back to the 50 (maybe 55?) after I installed the 0 bypass. The car was driven on the street so fine tuning was really important. Seems like I remember the 70 pump jet dumping to much fuel and causing it's own stumble. Not to mention the extra gas washing the cylinder walls down. Took me a long time and several miles to figure it out. What I thought was a lean stumble was actually a fat stumble. Then again, it was only a 1600 so maybe that's why the 50 worked better. Either way, get your idles and mains right, get your best lean idle, go with the 0 bypass and then take it from there. Another good place I've found to get jets is http://www.vwparts.net

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The jet sizes of 50, 55, 60, and 70 that people are talking about are in milimeters. A 55 is actually .55mm. If you are looking for drill bits, most hardware stores have tiny drill bit indexes with bits in thousandth's of an inch. You can convert the mm size into american by dividing the mm size by 25.4, which is how many mm are in an inch.

.55 / 25.4 = 0.0216

So you would need around a .022 size drill bit to make a 55 size jet.