motor still not right

[starrider1946]

I have put several post on here about my motor. It is still not right. Just to refresh. I have a 1600 stock cc motor with dual Empi 34 epc's. I have JBug buggy duals on it. I changed to the SVDA distributor. I have tried adjustments on the carbs, tried different timing from 7 to 12, put new plugs in. I ordered new idle jets a 57 and 60 and new 140 main. I put just the 57 in and it ran even worse so I put the 52 back in.

To the best of my knowledge this is how I would explain what it is doing. Oh before I forget.

On the instructions with the SVDA distributor it doesn't list the 34epc as one of the carbs it is compatible with.

Both carbs have a brass tube off the left side on both carbs.

I have a hose off there with a t running to the distributor. I guess they are pulling enough vacuum for the carb to work right.

Now this is what it is doing. When I crank it up and it is warm it idles great. If I pop the throttle in neutral it falls on its face. Not good response. Once I get going it misses and sounds like it spits back though the carbs and pipes almost like a back fire when I am on the throttle. Just at a steady speed it seems better. Especially through the pipes if I really get down on it.

I have checked for manifold leaks and I don't seem to have any. The valves are set good so I don't think it has anything to do with that.

How do I know if the vacuum advance is working like it is supposed to.

I am still trying but it is getting more aggravating. Any comments would be appreciated.

Things i am going to do today include checking the compression and make sure it is good, change plugs wire, and recheck the gap on the plugs.

[vw driver]

To test the VA; remove dist cap, remove hose from the tee and suck on it. You should be able to see the VA assembly moving inside the dist. If you plan to keep the dual carbs a sync tool would be a good investment or you could switch to a single carb, a stock Solex or a Weber 2bbl progressive. I have stock Solex carbs on both of my VWs, they won't win any races but they are reliable and easy to adjust. As for the backfire and popping, a bad dist cap can cause it as well as a too rich mixture with retarded timing among other things.

[starrider1946]

I haven't inspected the distributor cap but I will try and look close at it. It is a new distributor but that doesn't mean the cap it is good. I'll check the advance like you said. The timing is set on 10 degrees and 30 to 32 degrees advanced. I checked the compression on all cylinders today to make sure they are ok. They are all 100 plus or minus 5 lbs. I think that should be good. All the plugs were almost white so I know that's lean. I feel like everything is ok except the jetting on the carbs. I do have a sync too.

I am going to call aircooled.net tomorrow and see if they can give me any pointers.

That is where I bought my jets from.

I'll check the vacuum like you said.

Thanks for the help.

To test the VA; remove dist cap, remove hose from the tee and suck on it.

You should be able to see the VA assembly moving inside the dist. If you plan to keep the dual carbs a sync tool would be a good investment or you could switch to a single carb, a stock Solex or a Weber 2bbl progressive. I have stock Solex carbs on both of my VWs, they won't win any races but they are reliable and easy to adjust. As for the backfire and popping, a bad dist cap can cause it as well as a too rich mixture with retarded timing among other things.

[Rsw]

Throw those junk EMPI carbs over the hill and get a single Solex 34 pict3 and be done with it!! Get a good core and intake from Scudders if they have any left and put a rebuild kit in it.

http://www.scuddersperformance.com/

[vw driver]

I'd have to agree.

[starrider1946]

It sounds like I need different carbs but right now I have to work with what I have. I put the 57 idle jets back in and messed with the carbs some and I think it is running the best I have had now. I started out like most of the of tech articles said with the speed screw out two turns on each carb and the idle adjustment in 1 1/2. When I cranked the motor it would not stay running like this. I had to go in one more turn for the motor to keep running on its on. I adjusted the speed screw on each carb and ended up with 1 turn out on the right side and 1 1/4 out on the left carb. I ended up with the right side idle screw is in 3 turns and the left is 3 1/4 in to have a 700 to 800 rpm idle. Any comments or advice.
Thanks

I'd have to agree.

[jaxbobg]

Okay, I'm intrigued. Starrider, is that why you posted the question about balance tubes that nobody else answered?

Do you have a balance tube on your Empi setup?

Judging by the quick research I've done, the VW wrenchers seem to indicate that the Empi is a Chinese version of the Weber. Further search shows that the Weber dual carbs do have a balance tube in the setup.

Maybe that's the answer you're looking for.

Just my observation. Don't flame me. I've been trying to learn about various engine designs from way back.

[starrider1946]

Thanks jaxbobg for the reply. If you read my post I have dual Empi 34's. I don't have a balance tube and still not sure what it is.Or exactly what it does or if I need one. Yes from what I understand the Empi is a Chinese version of the Weber and it seems most people think they are junk. I may go to Webers later but for now it is Empi's. I just want them running the best I can and I think it will be the jetting. I have taken them apart and they are clean and not stopped up and the float is right. I have 52,57 and 60 idle jets to try. I have a 130 main in now and I have a 140 to try. I believe if I can get the right combination they will be suitable for now.

From what I have read 80% of performance is on the idle circuit side.

I know if I am going along 50 or so shift 3rd and gas it it will sit you back the seat and not miss a lick.

To me that would probably mean the high speed part is good. I will keep trying.

Okay, I'm intrigued.

Starrider, is that why you posted the question about balance tubes that nobody else answered?

Do you have a balance tube on your Empi setup?

Judging by the quick research I've done, the VW wrenchers seem to indicate that the Empi is a Chinese version of the Weber. Further search shows that the Weber dual carbs do have a balance tube in the setup.

Maybe that's the answer you're looking for.

Just my observation. Don't flame me. I've been trying to learn about various engine designs from way back.

[jaxbobg]

Okay, here goes. In high school, the group I hung out with constantly tried to hot rod our old Chevys. On dual Holley carbs we played with different sized balance tubes because the Holleys are not a plenum design.

Here is an explanation from Shoptalkforums (I quote):

"Because the four cylinders of the Porsche/VW design are on opposite sides of the engine and are not all co-joined like a V6/V8 manifold, a pair of plenum-type carbs need a crossover tube between the manifolds to make the two carbs work together as a team.

The intake pulses on each side occur at 180 degrees from each other, then have to wait 540 degrees before the next impulse. The second intake valve on each side then opens to a manifold with reduced intake charge pressure. To even out manifold pressures, the fix is to connect them with a tube.

Crossover tube systems give smoother idling and midrange performance, but soften throttle response feel somewhat if not reduce actual response time. Porsche used 12mm inside diameter crossover tubes, but throttle response feel can be improved by using as small a crossover tube as possible while still getting the benefits from it.

A carb is bolted to a manifold with a large plenum area inside it from which all cylinders draw. The negative pressure inside the plenum caused by a constant draw on it from the cylinders makes it easier for the incoming air/fuel mix to enter. This plenum area also acts to contain and dampen reversion pulses, which are shock waves that travel from the intake valve port (as the valve slams closed) all the way back up to the carb throat.

Since the Weber [also Empi] design has no plenum, sometimes at high (and sometimes even at low RPM’s) the reversion waves get so fierce that an air/fuel “fog” is forced out of the carb throat in a condition called standoff. This causes trouble, preventing a proper air/fuel mix, and the opportunity for an intake backfire or spark plug crossfire to cause an exciting carb fire."

I've found other, more technical explanations but they mostly apply to high performance engines.



Also wondering what that vacuum hose in the picture posted by vw driver was used for?

If that was to be used as a crossover, I'd say forget it and get a length of metal tube with an I.D.

between 6 and 12 mm then cut to fit.

Don't have a VW engine nearby that I can look at for reference so can only go by memory and diagrams. Hope this helps.

[jaxbobg]

Starrider,

Judging by your posts in the past few months, you have been attacking your performance issue by changing a bunch of variables all at the same time. Playing with the dual carbs, the dizzy, and the basic 1600 components (and maybe the exhaust?) simultaneously would cause many good mechanics to go screaming into the night.

Let's recap a few things deduced rom your posts:

1. You state, "On the instructions with the SVDA distributor it doesn't list the 34epc as one of the carbs it is compatible with." Okay, you don't say, but let's assume you bought a 034. Instructions state it is compatible with the Weber ICT (same design as the Empi EPC).

2. You don't specify the model year of your engine, except Roadhawk 2002. So, let's assume it's a Type 3, built sometime after 1966. Since there is a subtlety of differences between engine year designs, these variables affect carburetion, ignition timing, etc.

3. Apparently you have been combing the web, looking at sites like TheSamba.com and aircooled.net for solutions. Based on the Trike Talk responses and info on these other sites, have you been able to narrow down the problem area to something specific?

Sounds to me like you've been changing jets, ignition timing, and other things at the same time, so there's no way to really know what has a positive effect and what makes it worse.

When I've had this problem in the past, I get out the old pad and pencil. I tweak just one thing (carb idle jet, dizzy advance, whatever) and write down what I did and the result, better or worse.

Then move on to another suspect item and record the change and the result.

After about five of these changes an overall pattern usually emerges that leads to the AHAH!!

moment, (usually in the middle of the night )

Good luck with your Roadhawk mods.

I'm fresh out of suggestions.

[Fowler]

When I crank it up and it is warm it idles great. If I pop the throttle in neutral it falls on its face. Not good response. Once I get going it misses and sounds like it spits back though the carbs and pipes almost like a back fire when I am on the throttle. Just at a steady speed it seems better. Especially through the pipes if I really get down on it. I have checked for manifold leaks and I don't seem to have any. The valves are set good so I don't think it has anything to do with that.

I had what sounds like the same issue on my Trike
I checked everything and finally changed the primary idle jet form a 50 to a 55 That did the trick for me.
Mine is running a lot better and even gets better gas mileage

I am running a single carb though http://www.3fowlers.com/carb.html