TheSamba.com :: View topic

Thu Mar 13, 2008 11:12 pm

I found a web site that had a comparison of running dual IDF's vs. a single center mounted IDF, but I've lost it and have not been able to find it.

If anyone out there knows what the site is, please forward the link to me.

I'm currently running dual IDF's on my wife's 2275 powered bug but am getting tired of messing with the linkage and trying to get the carbs in sync.

I guess the big question is..... Is there a performance advantage to running duals?

Since the engine is only drawing air/fuel one cylinder at a time, it doesn't seem like it should be a huge difference whether it's one carb throat per cylinder or two cylinders sharing single throat.

Also it would seem like the air /fuel velocity would be higher if one throat was feeding two cylinders thus keeping the mixture more consistant rather than starting and stopping each time an intake valve opens under each carb.

anyway....got a little longer winded than planned...

if anyone out the knows the web site or has experiance with this set up i'd appreciate the info....

Thanks,
Ralph

Fri Mar 14, 2008 12:09 am

Invest in a better linkage. Dual carbs are way better than a single center mount dual throat carb. Single center mount is going to be fun to jet. Performance wise there is a big diffrence as well.

Fri Mar 14, 2008 8:20 am

I'm currently running the CB hex bar set up which is about the best one out there from what I'm told.

You made a couple of statements about jetting and the performance but no reasoning behind them.

Do you have personal experience with both setups or just info from word of mouth?

Why would jetting a single carb be more difficult than duals?

Fri Mar 14, 2008 9:08 am

Jetting a single IDF is not a big deal as long as you start your journey with a 70 to 75 squirter nozzle in the carb.
If you decide on duals, IMHO the best linkage going, is the belcrank linkage from CSP.

Fri Mar 14, 2008 9:19 am

I have a set of the CB hexbar linakge for my IDF's. Although the quality is quiet excellent, and the filter bases are super thick, on the left carb that throttle arm stand off they have sucks! because the right carb is bolted directly to the linakge, while the left has to go through that stand off, the right one opens first while the left one lags and the arm flexes. I switched to the SCAT centerpull linkage I originally had on my Kads, and have not looked back. You can pretty much set it and forget it.

Fri Mar 14, 2008 9:27 am

There is a HUGE difference between a single center mount and dual carbs. I wouldn't put a single center mount carb on my carb if it was free and someone paid me. Think about how far the fuel has to travel on one vs the other. I've always found the throttle response to suck on center mounts. They are great if you are blasting off-road with the throttle wide open. I don't have any numbers to prove this just 16 years experience building engines for customers and myself.

Fri Mar 14, 2008 9:31 am

Center pull sounds like a good option!

I redid the arms so that both are the same length and I am not using standoffs at all. The opening seems to be pretty even but getting them to work together and syncing them is a whole different story.

It's easy to get the carbs in sync using the idle adjust screws, but as soon as the throtle comes off idle everything changes. I've tried holding the linkage off of the idle adjust screws and it seems to be a little better but still not perfect.

Fri Mar 14, 2008 9:32 am

66Primer wrote:

Why would jetting a single carb be more difficult than duals?

If he's having a hard time keeping duals sync'd, and asking if a single is better than duals he most likely will have a hard time jetting :shock: .

Fri Mar 14, 2008 9:36 am

Roy,

The web site I had looked at a while back had back to back numbers done on a dyno and from what I can remember they were pretty darn close.

When I originally found the info I didn't much pay attention because like everyone else thought 2 was better than 1 etc.

The stock carb set up in the original VW design is a center carb and it seems to work and respond quite well. How does the length of the intake runner affect the throttle responce?

Fri Mar 14, 2008 9:42 am

sammyphsyco wrote: 66Primer wrote:

Why would jetting a single carb be more difficult than duals?

If he's having a hard time keeping duals sync'd, and asking if a single is better than duals he most likely will have a hard time jetting :shock: .

Hey Sammy,

If you're going to take the time to write something, be constructive don't ASSume things or just throw out comments to take up space. If you're going to give advice have something to back it up, like personal experiance or some level of logic to what you say.

Try to help out, not just comment on what you think I can't do. :oops:

Fri Mar 14, 2008 11:10 am

If your mind is made up to put a single center mount carb on motor just do it. Each combination has its own unique set of problems, you will learn as you go....

My experience is if you don't have correct arms on carb shafts with a dual setup, the most expensive or best quality linkage is not going to work well....

Years ago WEBER made left and right carbs for VW/Porsche applications. EMPI and some others still make the special arms.... These arm sets are available from several web dealers.... Also a 1 inch spacer on left hand carb does wonders to get linkage alignment to help get carbs to sync. Also use return springs from carb linkage to carb body. Do not depend on 'linkage" to close carbs. Also it takes patience to get it right.... If you get in a hurry its never going to work for you....

If you decide to go single in the center, thats ok, its not going to change the way the sun rises and sets.......

Dale

Fri Mar 14, 2008 11:23 am

66Primer wrote: I've tried holding the linkage off of the idle adjust screws and it seems to be a little better but still not perfect.

Sync carbs with throttle linkage disconnected..... Connect linkage (adjust rod lengths) to match carbs....

Dale

Fri Mar 14, 2008 11:39 am

66Primer wrote: sammyphsyco wrote: 66Primer wrote:

Why would jetting a single carb be more difficult than duals?

If he's having a hard time keeping duals sync'd, and asking if a single is better than duals he most likely will have a hard time jetting :shock: .

Hey Sammy,

If you're going to take the time to write something, be constructive don't ASSume things or just throw out comments to take up space. If you're going to give advice have something to back it up, like personal experiance or some level of logic to what you say.

Try to help out, not just comment on what you think I can't do. :oops:

sammyphsyco wrote: Invest in a better linkage. Dual carbs are way better than a single center mount dual throat carb. Single center mount is going to be fun to jet. Performance wise there is a big diffrence as well.

1. What part of get a better linkage didn't you understand?

2. I apoligize for not posting my carb resume. I have had alot of difrent carb combo's. I had weber progressive, the manifold had no heat riser tubes was a pain because gas fell out of air and created drivability problems, due to fuel droplets collecting on floor of manifold. Had a center mount weber same problems. Had dual kads on dual port, thought they were pretty good till I drove a friends car with same engine I had but he had webers, then I knew the kads were marginal.

My final conclusion is that in the case of dual carbs following the herd is a good thing if you have a decent linkage.

But now I am moving onto sequential MPFI.

Hope I was able to help :lol: .

66Primer wrote: I guess the big question is..... Is there a performance advantage to running duals?

Since the engine is only drawing air/fuel one cylinder at a time, it doesn't seem like it should be a huge difference whether it's one carb throat per cylinder or two cylinders sharing single throat.

Also it would seem like the air /fuel velocity would be higher if one throat was feeding two cylinders thus keeping the mixture more consistant rather than starting and stopping each time an intake valve opens under each carb.

Based on your initial questions one could only take it that you are not that knowledgeable about carbs. If I am incorect about this I humbly apoligize. :roll:

Fri Mar 14, 2008 6:16 pm

roy@mofoco.com wrote: There is a HUGE difference between a single center mount and dual carbs. I wouldn't put a single center mount carb on my carb if it was free and someone paid me. Think about how far the fuel has to travel on one vs the other. I've always found the throttle response to suck on center mounts. They are great if you are blasting off-road with the throttle wide open. I don't have any numbers to prove this just 16 years experience building engines for customers and myself.

Granted, fuel distribution isn't as good as dual carbs would be but, Properly setup with the correct vents and jetting a single IDF engine will have great throttle response, performance and drivability until the temps drop below 35F. I have lots of dyno time in tuning Super 1650cc off road racing engines which all ran 44IDF's.

Fri Mar 14, 2008 6:27 pm

I believe that was Bernie Bergmanns website-remember that he is a great salesman-will tell you what you want to hear to sell merchandise.

Dual is better then single esp since you already have duals. Get a good linkage and a synch meter and go to aircooled.net or get a book or get some help and learn how to synch those carbs up. More power, better mileage then a single.

Fri Mar 14, 2008 8:30 pm

Ok I got a nice 48 DRLA Dell with a split plenum manifold I will trade you for your duals. I can guarentee you will go fast and get 10 MPG.
But it looks cool! :D

Fri Mar 14, 2008 9:55 pm

I have the CB Hex linkage and haven't had any problems at all. I basically set it and forgot about it. Are you sure you've set the carbs up right to begin with?
You have to have the set up right first and then you set up the linkage.

Sat Mar 15, 2008 8:25 am

I agree, I think it was bergmanns web site that had the info, I remember the engine they used was bright red with a 911 fan. That was the first place I checked when searching for the article.

Sat Mar 15, 2008 8:45 am

Maybe I should have been more clear in my initial post, but my main interest was to gain some knowledge about the different setups, not to complain about the duals. It seems more people have spent time telling me how the fix the set up I have than talk about the main topic I was after.

My wifes car runs great 99% of the time. On occassion (about every 6-8 months) the carbs go out of sync and need a little attention. Once they are re-set we have no problems with it and she drives it 3-4 times a weeks.

What I was looking for in the initial post was some information possibly backed up with personal experience or even real dyno numbers to see the advantages of one setup over the other.

At the minimum some logical theories and discussion why one would be better than the other would have been good to. I'm not one to follow the herd because "everyone" says so or " that's the way it's always been done". With that kind of thinking you never learn anything new, you just do the same thing over again and there's no fun in that.

On my last engine I thought I'd change things up and installed the Redline / Weber fuel injection kit on it, just to try something new. Now I know all about fuel injection, maybe more than I want to!

If you don't go out on a limb every now and then, you don't expand your knowledge base. You stay in a very safe place where you don't have to face failure, and what fun is that!

I'm not looking for someone to solve my problem, I'm just looking for information to learn about something new.

Sun Mar 16, 2008 8:04 pm

I would stick with your dual carbs, and get a better linkage if you are having trouble with it. I can't suggest which linkage because I have the EMPI linkage (which almost everyone on thesamba hates) on my dual 40's, and have not had any problems with it. Dual carbs will have more performance than a single carb, and duals have a greater potential for perfomance after modification. If you have a set of ported heads, the dual intakes can be match ported to flow much better than a match ported VW endcasting that's used with a single carb. The main reason the duals perform better than single's is the VW endcastings limit the flow. A single carb isn't any more difficult to jet/tune than dual carbs. Like lostinbaja mentioned, the main thing is to increase the accel pump jet size. There is a fair amount of info on setting up a single carb in the Weber Tech Manual. The main reason I have found for people running a single carb, is the off-road crowd use them because the dual carbs will get more dirt in them when they are right beside the rear wheels. Everyone I know that has a street car, and doesn't have to worry about trail mud, uses dual carbs for the better performance. If you do decide to go with a single carb, I think CB Performance is the only company that has an intake short enough that can be used in a street car, and still shut the decklid. I cant give you dyno numbers to prove performance gain/loss between the two, but any one that I've known to convert thier single carb to duals on a buggy has noticed a significant "seat of the pants" increase in power. By using an air flow gauge to sync your carbs, you shouldn't ever need to do that again unless the adjusting screws come loose. The only reason you should ever need to adjust your linkage is to compensate for wear in the linkage components.