# 16V on Webers, First Carbs, First Time.



## White_Rabbit_GTI (Apr 27, 2007)

Well over the winter I put my 16V mk1 on dual 45 webers, bought them brand new with these specs:
f960 idle jets, .050 accelerator pump jets, 155 mains, 170 air corrector jets and f16 emulsion tubes.
My engine work consists of a flowed head with HD valve springs and 276* cams, its running about 2* advance on the cam sprocket and its running a good amount of spark advance (don't have the necessary equipment to measure spark advance) and its running about 2.8Psi fuel pressure and MSD 6AL.
car was fully running and functioning on the CIS-M just dumping retarded fuel. So today was my first run on the carbs the idle was pretty smooth @ 1100Rpm and under no load it rev'd clean and had no stumbles or faults, when we took it out to the road however its started stumbling and misfiring like crazy but only certain times in certain gears:
1st: made good power up to 5,000Rpm before its started stumbling and cutting.
2nd: made good power up to 3,200 before its started stumbling and cutting.
3rd: made good power up to 3,000Rpm before its started stumbling and cutting.
4th:made good power up to 2,600Rpm before its started stumbling and cutting.
5th: (diesel 5th): made good power up to 2,300Rpm before its started stumbling and cutting.
I notice that in 3rd gear when it began cutting if I held it at 3,000Rpm for a few seconds and then rev'd it it would give me anther 800Rpm then flat spot and began cutting again, it would do it in every gear just more noticeable in 3rd.
I figured it may have been leaning out so I turned the mixture screws out to about 6-ish turns (I will have to measure how many turns actually in the morning) trying to get it to run really rich to stop it from leaning out, that did not help, so I returned the screws and thought that I may have needed more advance so I advance the spark timing a bit more still with no results.
I am reading through some weber tuning books I've purchased but cant find anything in the trouble shooting that quite fits this.


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## DOHC15 (Feb 28, 2007)

you shouldn't really be messing with the timing if you dont have a timing light just some advice from experience...and try retarding the timing bit by bit and see if you get a change


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## antichristonwheels (Jun 14, 2001)

*Re: 16V on Webers, First Carbs, First Time. (White_Rabbit_GTI)*

http://www.amazon.com/Weber-Ca...r=8-1


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## B4S (Apr 16, 2003)

*FV-QR*

The mixture screws only control the idle mixture. The minute you start to roll, they basically stop working.
It's really important to do some research before you try to tune it, because without a wideband it's going to be very difficult to tune for a novice.


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## White_Rabbit_GTI (Apr 27, 2007)

A few things I should have mentioned, I have a wideband but, have no place for it in this exhaust, wont be able to install it till my new exhaust comes in, second they are 45's which I forgot to mention. I have been doing alot of research over a years worth before my purchase and am constantly flipping through my weber books, I am just looking to see if anyone has gone through something similar.


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## B4S (Apr 16, 2003)

*FV-QR*

Have you checked the floats? How big are the needle valves? What fuel pump are you using? What regulator? What chokes? What auxiliary venturis? How many turns out on the mixture screws at idle? What emulsion tubes?
I'm not trying to be a dick, just trying to point out that now pretty much everything is a variable. Your idles seem REALLY rich, and your pump jets are huge, but it seems ok-ish. I'd start off with 180-200 air correctors myself, but 170s will move the main jet engagement up a bit, and keep the fueling good at high RPMs. Your problem sounds like a fuel delivery issue to me, since you've definitely got more than enough jet to fuel it. I had the same issue with my Dells last year, and it turned out to be a clogged fuel filter.


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## White_Rabbit_GTI (Apr 27, 2007)

Well, I have done some checking and it seems that all my internals are big enough, I reset my idle mixture screws to 2 3/4 turns out and turned my fuel pressure up to about 3.1psi is was around 2.4Psi before and Thursday I am getting a timing light that will allow me to correctly set my spark advance. the fuel system is not obstructed everything is brand new parts and lines.
Also I re-attached my 4 port syncrometer and attempted to even our my air flow by the little screws on the side, I forgot what the book called them but they are used to balance the vacuum, doing this I was able to get the 1st and 2nd carbs tuned to about 26cmHG but the 3rd is about 16cmHG and the 4th is 20cmHG, I know my compression is not perfect but its still within an acceptable range could this lower vacuum because by my rad sitting in front of carbs 3 and 4?
I will continue to research, I wont have any new info until my next road test Thursday, B4S I thank you for the help and all the previous help you've given me in previous times over the years, I don't have answers to your questions but I am going to try my damnedest to find them.


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## White_Rabbit_GTI (Apr 27, 2007)

Well, I suppose I could not wait for Thursday, I still have to check my spark timing but I though I may as well post a new discovery. Took it for a spin today and discovery that the issue mentioned above only happens at a certain amount of throttle, for example if I go through the gears at 15%-20% throttle the problem takes another 1000Rpm-2000Rpm to happen as opposed to if I was to go through the gears at 50% throttle or more the problem is almost immediate. Could this be a problem with my mains not activating quick enough? 
Also I've attached some pictures of my instruments at idle.
Vac








FPR








Tach










_Modified by White_Rabbit_GTI at 4:33 PM 6-8-2009_


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## White_Rabbit_GTI (Apr 27, 2007)

Well, I've got the spark advance set now to 17* at idle, the fuel pressure set to 3.0 Psi and the idle screws set to 2.5 turns and still I am having the bloody engine lean out under load. Its going into a carb shop tomorrow its bloody stumped me.


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## candm (Apr 27, 2003)

*Re: (White_Rabbit_GTI)*

thats too much advance. set it at 12 at idle and your overall at about 28. then move on to your carb tuning


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## White_Rabbit_GTI (Apr 27, 2007)

*Re: (candm)*

Really, because all the weber books I've got seem to be about 16* advance as a staple advance. How would my 2* cam advance affect my spark advance?


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## White_Rabbit_GTI (Apr 27, 2007)

Ok I reset my advances and its slightly more driveable and by that I mean it can do normal road speeds but just barely and I've lost most of my low end grunt, I know I was running at least 17* all last summer on my CIS, because thats what lets me have a tad bit of fun in the low range and still seems to make good top end power for me. I've checked over everything, in terms of my engine I know its all within spec with good components I know for a fact its leaning out under load now I just dont have the knowledge to go ahead and say its this and this jet for sure so when the carb shop opens on Tuesday shes going in. I will post the results when she is out of the shop so maybe we can all learn a little something.


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## Cynical 1 (Jan 23, 2003)

*Re: (White_Rabbit_GTI)*

fuel inlet valves are too small. has the same issue with mine and several others i've helped out. not enough fuel staying in or getting to the bowls under load. 
runs fine when you're in the idle jets, but leans out when the mains come in. 
try going to bigger inlet valves and checking your float levels.


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## MkIIRoc (Feb 20, 2005)

*Re: (Cynical 1)*

That was my initial thought as well, but he said they are brand new...if they are brand new DCOE 152's, they come with 200 needle/seats. That's what I use to fuel my 200+ hp 8 valve. You had better check them though just to be sure.
Don't worry about the idle advance...set the top end advance and let the idle fall where it falls. 
What type of fuel pump/regulator are you using?


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## woodrowstar (Jun 17, 2005)

can i ask a dumb question: where is your brake booster taking vacuum from on the manifold? (all cylinders or outta one port)


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## mack73 (Jan 2, 2002)

*Re: (MkIIRoc)*


_Quote, originally posted by *MkIIRoc* »_What type of fuel pump/regulator are you using? 

I'm going with a fuel pump issue? - Might not be flowing enough volume at high rpm's or a clogged fuel filter?


_Modified by mack73 at 9:18 PM 6-19-2009_


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## Justin 123 (Apr 11, 2005)

*FV-QR*

Put a fuel pressure gauge on it if you haven't. What pump and regulator are you running?


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## SpoolinJetta18T (Jul 30, 2004)

i like to know as well because im having the same problems im running a carter 4070 fp.


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## SpoolinJetta18T (Jul 30, 2004)

anyone on the ^ Q?


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## Big CADDY (Aug 28, 2001)

*Re: (White_Rabbit_GTI)*

inlet valves are fine. carb will draw what it wants. 
do me a favor and put a piece of carboard over your grill infront of the carbs to block incoming air.


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## Super T (Jan 27, 2007)

*Re: (Big CADDY)*

This is my friends car, I helped with a lot of the work. Problem turned out to be air filters smothering the vapor cloud. He got some proper filters and the car hauls ass.


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## SpoolinJetta18T (Jul 30, 2004)

how did you hooked up the vacuum gauge?


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