Author Topic: Dual Carb Troubleshooting  (Read 9257 times)

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Offline LUFTVOLKS

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Dual Carb Troubleshooting
« on: July 19, 2010, 03:12:48 PM »
i have a  SP 1600...   just last week, a couple of us grease monkeys installed dual 34ict's and an exhaust.  (i know duals on a SP 1600?)  i just wanted to make this a bada$$ SP 1600.  now, she isn't running right.  we didn't have the right adapter to sync the carbs.  so that's the problem (maybe?).  it can be the dizzy or vaccum leaks as well?  running a 009, but i think that's fine?  to much forum reading and advices from other VW heads just gave me a headache.
Anyways, sorry for ranting but i love this bug and i can't even enjoy her cause she's a little sick.  having one of the guys come over this wednesday to help me sync them.  like the saying goes, "if it's not broken...  don't fix it"


-rich (scratchyratchy)
(o\!/o)

Offline LUFTVOLKS

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Re: Dual Carb Troubleshooting
« Reply #1 on: July 19, 2010, 03:13:01 PM »
A SP with dual singles kicks ass and is a torque monster!! One thing you have to do is make sure that the tune up stuff is done first, dual carbs make the engine run more efficiently and if not tuned will run like crap. So do your valve adjustment, replace points, condenser, cap, rotor, wires and make sure to time it using a timing light. With the 009 time it to 28* total advance at 3000 rpm.

After all that then you can start tuning the carbs. Were they new or used? Are you running a cross over tube between the manifolds? What type of linkage do you have? What fuel pump?

Remember if it aint broke dont fix it, but you can ALWAYS make it better!!

Offline LUFTVOLKS

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Re: Dual Carb Troubleshooting
« Reply #2 on: July 19, 2010, 03:13:41 PM »
carbs were purchased used, but in excellent condition.  we did open them up and cleaned them.  yes, i am running a balanced tube between each manifold.  have a steel hex linkage.  running stock fuel pump.  i believe that's enough flow or even more?  need to get a fuel pressure gauge.

Offline LUFTVOLKS

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Re: Dual Carb Troubleshooting
« Reply #3 on: July 19, 2010, 03:20:42 PM »
To bench sync the carbs without the sync tool, just set the butterfly to the very bottom edge of the progression port. You can only do this with the carbs off looking from the bottom. Once you bolt them on they are synchronized. Do not hook up the linkage until the very end after the fine tuning of the idle circuit. Base line is 2 1/2 turns out. Turn the mixture screw in until the engine rpm drops then back out until you get the highest rpm then 1/4 turn out. The balance tube will smooth out the idle quite a bit, if you run without it the engine will only fire on 2 cylinders at idle.

To find any vacuum leaks shoot some carb cleaner at the base of the manifold and the base of the carb, if there are any leaks the rpm will rise or drop. Make sure your vacuum ports have good block offs, not the rubber ones but the colored plastic. They will last much longer. Also make sure to use the thick paper gaskets not the original steel ones as they are one use only and will leak with aftermarket manifolds.

Offline scratchyratchy

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Re: Dual Carb Troubleshooting
« Reply #4 on: July 19, 2010, 04:19:50 PM »
thanks again for the info...  i'll let you know the outcome on wednesday.

Offline slammed66

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Re: Dual Carb Troubleshooting
« Reply #5 on: July 19, 2010, 10:09:54 PM »
i had a set of 34 icts on a 1641 SP that was a real torquey machine. timing and sync

Offline LUFTVOLKS

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Re: Dual Carb Troubleshooting
« Reply #6 on: July 21, 2010, 10:34:45 AM »
You can make an adapter for most sync tools from a 20oz coke bottle if desperate.  You can also sync using a vacuum gauge hooked up to the vacuum port on the carb. If you have two gauges you can sync even faster and more accurate than the snail or flow gauge.

Let us know how it goes.

Offline scratchyratchy

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Re: Dual Carb Troubleshooting
« Reply #7 on: July 22, 2010, 12:02:13 PM »
A friend and I was tinkering with "Jun" ALL DAY yesterday.  Here was the outcome....
1)  Double checked all hoses and made sure they were all clamped.  Checked manifolds to see if thery were bolted down good.  Right manifold was slightly leaking.  As we were tightening it, we notice a crack by the bolt.  (Not GOOD :()  So, we put some JB weld and see if it holds up.
2)  Checked timing
3)  Sync carbs...  (it's ok, jb weld worked...  for now?  will be needing a set of dual SP manifolds)
4)  Couple of test runs....  STILL sputtering!!!  You can feel it wanting to go, but still hesitating.
5)  A little more idle adjusting + a little more mixture adjusting + a little more timing = STILL SPUTTERING!!!!   :(
6)  While still doing some test runs, we try to hear the carbs.  We notice the left one is sputtering.
7)  Opened up both carbs.  Both had the same amount of fuel in the bowl.  Checked the filter.  Checked the main jet.  Hmmmm, all was clear. ???
8)  A couple more test runs + adjustments = S P L U T T E R I N G!!!!!!
9)  Now, this is where i was giving up hope on "Jun".  My friend decided to check the idle jet on both carbs.  The right one was ok, but the left one was all bad.  It was clogged!!! :o  Blew it out with some dustbuster and screwed it back on.  Gave it a test run and..........
10)  It was a miracle!!!  "Jun" took off like a bat out of hell!!!  It felt so good just hearing her run so well.......

Well, with some more test drives we did still have that sputtering problem. Now we knew that it was coming from the left carb due to the idle jet being clogged.  Pulled it out and sure enough it was clogged.  We've have been doing this for about 3x.  We decided to just pull them off and give it a good clean in carb cleaner, instead of waiting for what's inside the carb to flush out. 

Until then.....  I am hunting for some dual SP manifolds...

Offline LUFTVOLKS

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Re: Dual Carb Troubleshooting
« Reply #8 on: July 22, 2010, 01:08:07 PM »
congrats on the success!! Empi does make a new SP manifold for ICTs.  Part number 43-5305

when rebuilding the carbs dont leave them in the carb cleaner too long. some cleaners will eat your carb!! do it for an hour at a time then check it. if you leave it overnight the casting will get soft then your have to get new carbs.  Also if you have any water deposits (white chalky stuff) that the carb dip doesnt remove soak the carbs in regular white vinegar. Again only do this for an hour at a time and check frequently. get a few cans of brake cleaner and use the hose to blow out any passages in the carb till they flow clean.

Offline scratchyratchy

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Re: Dual Carb Troubleshooting
« Reply #9 on: July 22, 2010, 06:17:37 PM »
I'm actually not doing the carbs.  My friend who was helping me out is doing them.  He sent me some pics of them this morning and they look SWEEEETT!!! ;D 

I'm on the budget side right now.  So, I'm trying to look for some used ones first.  If not, then new ones it is.......

Offline LUFTVOLKS

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Re: Dual Carb Troubleshooting
« Reply #10 on: July 22, 2010, 06:49:55 PM »
start doing this stuff yourself. icts are EASY to rebuild, dont let your buddy take all the credit of building your ride!!  Even if he helps you keep the stuff at your pad to keep you motivated.

Offline scratchyratchy

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Re: Dual Carb Troubleshooting
« Reply #11 on: July 23, 2010, 01:29:17 AM »
Lol...  Sorry jedi master.  it won't happen again.  he offered and i accepted. 

Offline LUFTVOLKS

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Re: Dual Carb Troubleshooting
« Reply #12 on: July 25, 2010, 11:21:05 AM »
learn much you must when driving a VW, the force is strong with those who get greasy!!  8)


How is it coming along?

Offline scratchyratchy

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Re: Dual Carb Troubleshooting
« Reply #13 on: July 25, 2010, 12:59:44 PM »
 :)

Will be working on her tomorrow... I'm going to polish the insides of the manifolds later today.  Why, you ask?...  Just to make it smoother, thought it be a nice comfortable ride for the gas & air to go down...   ;)  Or I guess I'm bored  ???

I'll post some pics when she is done.

Offline LUFTVOLKS

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Re: Dual Carb Troubleshooting
« Reply #14 on: July 25, 2010, 02:34:02 PM »
just want to make sure you didnt give up yet! hang in there young padawon.

you dont want the ports of the manifold polished, the gas will collect there and puddle up instead of staying suspended in the air. You actually want a bit of a rough surface.

A bit hard to see but you want no obstructions like casting ridges but a bit of a swirl or cross hatch








I use a 100 grit "flapper" sanding roll

Here are your replacement manifolds too

http://www.thesamba.com/vw/classifieds/detail.php?id=989012