TheSamba.com :: View topic - Need help dialing in 36mm Dells on a 1904

Sat Aug 30, 2014 7:01 am

So these Dells on my 1904 have

32 vents
135 mains
70 idles
180 air
.2 emulsion

And I've got two problems right now:

1. By everything I've read the idles and mains are too big and I can't get a smooth idle no matter what I do and the exhaust smells rich. I had some 55 idles and 125 mains on hand and when I put them in I could barely get it to idle smoothly and when I drove it spit through the carbs. I'm on the east coast around sea level so those jets should be okay but they weren't. These are the good jets from aircooled.net. Before I spend more $$ on a new round of jets is there something else I should look at?

2. One barrel won't catch up to the others. I can get 3 barrels up to 5 on my "snail" sync tool but the #3 barrel won't ever get above like 3.5 no matter what I do with the mixture screw. What can I do? These are rebuilt carbs from alfa on ebay. They were gone over again by my engine builder and he had the same problem as me but was still able to get a smooth idle. Is it time to adjust the air bypass screw?

Sat Aug 30, 2014 7:23 am

Try 60 idles and 130 mains with your 32 vents.

Sat Aug 30, 2014 7:40 am

To fix your problem you will need to do more than turn screws and change jets.

1st check your valve adjustment and do a compression test...

I everything comes out close to equal on your compression, and the engine is sound...

Pull your carbs and thoroughly clean them.. I mean clean, ultrasonic triple clean until the water runs clean.

Set you float heights. Triple check them.

Hold the carbs up and look at each barrel with the idle stop screw backed off... Look at the amount of light between the butterfly and the bore of the carb. All 4 should be equal or very close to equal.
- If they are not, then the butterflies need to be re-set, or you might possibly need the throttle shafts straightened / replaced.

Clean the entire fuel system... Empty / remove the gas tank, clean it... If its shitty, replace it. Make sure you have adequate fuel flow through the metal fuel line in the chassis.
Re-install everything with a heavy duty (metal case) fuel filter under the tank, and at least one clear fuel filter near the engine.

Make sure your air filters are doing their job... You do not want to re-infect the fuel or air systems with contamination... This is key.

Change your spark plugs... make sure your ignition has new / good parts.

Your idles are way to big.

Sat Aug 30, 2014 7:44 am

Here's a tip.

Warm up the car.

When you are going DOWN on the idle jets, change one idle jet at a time.

Change the jet on #1, then re-adjust the idle mixture on #1. The mixture screw will have to go out to get the same idle mixture you had with the larger jet.

When that one is done, turn the car off and change the idle jet on #2. Adjust idle mix on #2. Etc etc.

A common mistake is changing all 4, then the engine absolutely will not idle. So it's very difficult to get the idle mixture screws set properly.

Alternatively you can back out the idle mixture screws until they almost fall out, then adjust them one at a time by moving the screw(s) in.

Sat Aug 30, 2014 8:19 am

Thanks guys.

This is a brand new motor, already broken in and dynoed and now with maybe 100 driving miles on it. I looked at the dyno sheet and at 5000 rpm the AFR was 12.39 so the jetting is too big for real.

I have 2 new metal fuel filters between the tank and the pump but I did not clean the tank which I know I must do. I didn't consider that the throttle shafts might be bent and will look to that. Air filters are newly oiled and there are no deposits on the filter base or down by the jets but running them with the filters off for synching I guess can introduce dirt.

I do not have a ultrasonic cleaner and many of the ones I see look too small to hold Dells. Is there a brand and size that is known to be good for cleaning out carbs?

John, both of your tips sound great! When I did all 4 at once the engine wouldn't stay running long enough to dial anything in.

When I get to the idles, I will start with 60's and move from there. I have jet doctors but did not install yet because I thought I should get base jetting good first.

Sat Aug 30, 2014 8:36 am

What John said.

Dependant on cam and CR of course 0,60 idle seems to be on the large side for such a set up (at least with "our" fuel) I usually end up with 0,58 idles.

Did´nt they test part load on the dyno ?

If it is running 12,3 AFR with 135 mains and 180air it sounds like it is not overly efficient, OR the float height is off.
What CR. Wich cam, which heads. What exhaust ?
Can you post a copy of the dyno pull ?

T

Sat Aug 30, 2014 8:41 am

Alstrup wrote: What John said.

Dependant on cam and CR of course 0,60 idle seems to be on the large side for such a set up (at least with "our" fuel) I usually end up with 0,58 idles.

If it is running 12,3 AFR with 135 mains and 180air it sounds like it is not overly efficient. What CR. Wich cam, which heads. What exhaust ?
Can you post a copy of the dyno pull ?

T

The CR is 8.5:1 with Engle 110 cam, custom big valve heads (40 x 37.5) with port and polish, and 1 1/2" header with heater boxes and single quiet pack. Don't have the dyno pull handy right now to post up. Does this info help at all?

Sat Aug 30, 2014 11:37 am

I do not understand why they did not adress this when the engine was on the dyno.
Anyway, You have a couple of issues.
The intake is slightly limiting for the big valve heads. It will run and can run well, just saying. That leads to the too large exhaust valves. Those are high rev or turbo specific heads. Your set up is none of the two.
The W110 cam actually makes it worse because it is so advanced.

This may sound daft, but you should do this:
1. Get rid of the sgl guiet muffler and install something more free flowing, like a dynomax or similar. John @ ACN has some very nice Dynomax mufflers and decently priced too.
2. Find a set of early 1200 34 hp 1-1 rockers and install these on the exhaust alone. This will reduce theoverflow that the large exhaust valves make. Then you can get your idle good again and the engine will produce more usable power. And unless your float height is off, this will most likely make the engine want more fuel. But youre running somewhat rich already, so my guess is that it will even itself out by doing this.

T

Sat Aug 30, 2014 11:57 am

unfortunately most dyno operators know how to run the dyno, but are clueless at how to properly tune. In that case the tuning is your job.

Sat Aug 30, 2014 1:13 pm

You should have 40mm carbs.
36mm is good size for stock heads.

57 idle should work fine. , remember these are fine thread; open the idle screws five turns from seated!

Sun Aug 31, 2014 7:18 pm

Dyno time is so expensive that fine tuning during a session is out of the question unless you're the dyno owner, a relative of the dyno owner, or wealthy.

I know opinions will vary all over the place but are my valve sizes really so crazy and so incompatible with a W110 cam? My builder has over 30 years of experience in performance VW engines and I can't imagine he all of a sudden got this combo all wrong. I also have video of the dyno session and the thing idled and ran beautifully on the rich jetting (in another climate though) so I don't see how it's a question of heads and valves all of a sudden.

I provided the carbs though and the 36's were all I had. I'd love to jump up to 40mm Dells. What size vents, airs, and emulsions for a 1904 though?

Sun Aug 31, 2014 11:03 pm

Even "experienced" VW engine builders keep making the same mistakes, because they do not care about emissions among other things. Building 200 identical engines may make you good at building that, but doesnt exactly make you experienced.
I do not build that many ACVW engines anymore, but I do try to learn from every single one of them, and of course also from customers engines that I trim on the chassis dyno. Then it is reasonably easy to separate the sheep from the goats so to speak.
Yes such a valve combo will run, but not optimum. Far from it to be honest, unless non standard measures are made to it, such as split duration cams or at the very least split lift as I recommended.
What good is a "revy" engine if it doesnt make power (?) This is exactly why a built 1600 engine often can keep up with an off the shelf 1914.

But make the mods I told you. Then we can discuss finetuning lateron.

T

Mon Sep 01, 2014 2:40 am

Alstrup does have a point, that the extra big exhaust valve could be causing you some tuning trouble.

A normal size to go with a 40mm intake valve would be 33-34mm exhaust. That would give 75% area.

I could talk at great length about this, but I probably shouldn't. Lets just say it's been known a lot longer than 30 years, but is re-discovered often.

Mon Sep 01, 2014 7:29 am

Can do on the muffler. But if I use 36HP rockers on the exhaust valves will I also have to redo the rocker geometry, recut pushrods, etc?

Mon Sep 01, 2014 7:36 am

Not 36 hp. I forgot that you rate the engines different. For you its 40 hp 1200 (we rate those 34 hp) And before 1968 or so.

No, you do not have to alter the push rods. You - may- need to change the geomtry a tad, like +/- 0,30 mm. But you will have to decide upon installation.

T

Sat Sep 06, 2014 12:37 pm

I got a Dynomax muffler and it's on the car now. I also went down to 60 idles. I haven't found a good set of 40HP rockers yet.

I can get a decent idle but I cannot get rid of a miss. It sounds a little like when you hear the bass in someone's sound system at a stop light but this is more erratic.

Whenever I cover ANY barrel (makes no difference which one) the miss sound goes away and the idle smooths out really nice. Does that mean the 60 idles are too small? I've repeatedly checked for vac leaks to see if excess air was getting in anywhere but I can't find any. Also, I can smooth the idle by plugging any barrel so it seems like a jet issue.

I still had a miss with 70's but not like this one.

Any thoughts?

Sat Sep 06, 2014 1:12 pm

Have you checked the sync of the carbs ? - does each barrel pull the same vacum, or at least close to ?
The reason that it goes away when you block one barrel is that then the other 3 need to work harder to maintain idle speed.
The dynomax is nice.
Maybe you should try and contact Blackline Racing in SLC and hear if they have half a set of 1200 rockers with the 1 - 1 ratio. You really should get those installed before you go nuts with the jetting.

T

Sat Sep 06, 2014 1:20 pm

Alstrup wrote: Have you checked the sync of the carbs ? - does each barrel pull the same vacum, or at least close to ?
The reason that it goes away when you block one barrel is that then the other 3 need to work harder to maintain idle speed.
The dynomax is nice.
Maybe you should try and contact Blackline Racing in SLC and hear if they have half a set of 1200 rockers with the 1 - 1 ratio. You really should get those installed before you go nuts with the jetting.

T

The #3 barrel always lags 1 to 1 and 1/2 behind the others on my sync tool so that could be the problem.

However, I have a video of the dyno session and it was idling beautiful and smooth at around 950 even though the builder had the same issue with that barrel. He said the throttle shaft was straight as could be and that since it idled so well and that the barrel evened out once over idle rpm's that he wasn't worried by it.

Sat Sep 06, 2014 6:38 pm

Ok.
3 things can be wrong. (maybe more, but this is what comes to mind) Gunk/dirt in the idle circuit. Throttle shaft IS bent, these carbs have idle air bypass screws and they are not set correct.

T