TheSamba.com :: View topic - Weber 34 ict cutting a groove in the manifolds

Sun May 12, 2024 6:37 am

Has anyone found that cutting a groove between intake ports on the Weber 34 ICT manifolds improves idle quality?

I have just fitted brand new Weber 34's to my 1776 type 1 engine. Bell crank, cb performance manifolds, new SVDA distributor, 7.5 BTC, 30 at 3000 rpm, balance pipe, vacuum to both carbs, balance air flow with snail, filter king fuel regulator at 2 psi, 160 mains, 55 idles.

The car starts and pulls fine but the idle is really bad with a lot of vibration. This is my last resort so wondered if anyone else has cut grooves in the manifold to smooth things out?

I had Weber 40 IDF's which idled fine but were always having the idle circuits clogged so fitted these instead.

Thanks!

Sun May 12, 2024 7:46 am

If you had issues with the 40 IDF idle jets getting clogged. I'm pretty sure you will have the same issue with 34 ICT's. Use a 2 good fuel filters, before and after the main tunnel metal line. Cutting the groove on manifolds should help with idle better. Good luck

Sun May 12, 2024 8:58 am

Thanks. I have never heard or seen any videos about ICT's having idle jet issues where as there are many videos on youtube about the design flaw with IDF's and idle circuits getting blocked.... oil or no oiled air filters!

I have 3 fuel filters fitted

I hope cutting grooves helps give me a smoother idle. Before I do so I might try a set of larger idle jets

Sun May 12, 2024 9:08 am

Dual single throat carbs always idle on two cylinders. it's the nature of the beast.
I can't remember which cylinder on each side. But the fuel charge gets robbed from one and is applied to the robber cylinder one each side of the engine.

Once the throttle plates are open, the carbs supply fuel equally to all the cylinders. As long as you have the carbs correctly tuned.

Gauze filters should be oiled to trap debris.
Just don't over oil them.

Sun May 12, 2024 9:09 am

The idle jet issue with the Webers is not a dirty fuel issue, its poor air cleaners that let small particles through and they are sucked into idle just circuit.... A simple set of jet doctors would had probably fixed the dirty idle jet problem, and been a lot less headaches the trying to tune new carb setup....

Sun May 12, 2024 12:44 pm

I would try lapping paste or wet sandpaper on a piece of glass/marble. Check for flatness with a truly flat metal.

I always alternate sides when torquing.

That crack doesn't look good also.

Good luck ... stay safe

jinx

Sun May 12, 2024 1:37 pm

That crack doesnt help idle quality. A larger plenum does, - along with a different ignition timing. "Stock" ICT manifolds are universal and fits under the lid on a type 3 too, - which makes them, well, not so interesting in a type 1 & 2.
ICT´s will NEVER be as smooth as a set of well trimmed idf´s.
Your Weber clogging issue is most likely due to what is already described. Dirt in the system. Sometimes it can be a b*tch to get out. but if you know your way around setting Webers up, properly, I would take idf´s over ICT´s any day of the week.

Mon May 13, 2024 4:51 am

Dale M. wrote: The idle jet issue with the Webers is not a dirty fuel issue, its poor air cleaners that let small particles through and they are sucked into idle just circuit....
Exactly right!
Dale M. wrote: A simple set of jet doctors would had probably fixed the dirty idle jet problem,
Or you could fix it right with better air cleaners. Jet doctors will not clean the air, the dirt will still be coming through those garbage air filters, wearing out your rings and scoring your cylinder walls.

Sun May 19, 2024 11:32 am

67rustavenger wrote: Dual single throat carbs always idle on two cylinders. it's the nature of the beast.
This is true, but that doesn't mean you have to live with it.
The makers of all of the manifolds are IDIOTS! They all make the manifolds wrong. Any carb that feeds more than one cylinder requires a plenum volume under the carb. The small volume under an ICT or Kadron is too small.
The solution is to take your die grinder and remove the entire wall between the runners almost all the way down to the gasket surface at the head. Leave about ½" of the wall at the bottom just to hold the gasket down. This will give you a large enough plenum volume so that one cylinder doesn't steal the mixture from the adjacent cylinder. Yes, it's possible to make Kadrons idle on 4 cylinders.

Sun May 19, 2024 4:04 pm

Bruce wrote: 67rustavenger wrote: Dual single throat carbs always idle on two cylinders. it's the nature of the beast.
This is true, but that doesn't mean you have to live with it.
The makers of all of the manifolds are IDIOTS! They all make the manifolds wrong. Any carb that feeds more than one cylinder requires a plenum volume under the carb. The small volume under an ICT or Kadron is too small.
The solution is to take your die grinder and remove the entire wall between the runners almost all the way down to the gasket surface at the head. Leave about ½" of the wall at the bottom just to hold the gasket down. This will give you a large enough plenum volume so that one cylinder doesn't steal the mixture from the adjacent cylinder. Yes, it's possible to make Kadrons idle on 4 cylinders.

I did a ton of debating on kads, 34itcs, or a single custom manifold IDF setup with heat risers. I built a isolated single IDF manifold with 1.5OD tube just the right plenum for great torq and FAT midrange it idles/drives smooth. Not a top end screamer for that you want dual IDFs for IDAs

MPG is the only down side. I spent a total of 265$ When you look at the $400 for EMPI trach ITCs or $1100 for Kaddie shack Kads the custom single IDF setup is not bad when done right. I kept the slot intact on the end castings.

Mon May 20, 2024 6:55 am

Bruce wrote:
This is true, but that doesn't mean you have to live with it.
The makers of all of the manifolds are IDIOTS! They all make the manifolds wrong. Any carb that feeds more than one cylinder requires a plenum volume under the carb. The small volume under an ICT or Kadron is too small.
The solution is to take your die grinder and remove the entire wall between the runners almost all the way down to the gasket surface at the head. Leave about ½" of the wall at the bottom just to hold the gasket down. This will give you a large enough plenum volume so that one cylinder doesn't steal the mixture from the adjacent cylinder. Yes, it's possible to make Kadrons idle on 4 cylinders.
I agree with this, - to an extent. The DOWNSIDE is that if you remove that much in say a Kadron manifold, you can make eve a W110 cammed engine idle quite well inside the normal parameters. But, it will be at the cost of around 10% torque across the rpm band. Depending on the actual engine size it will also require to set the engine up slightly rich at idle or the off idle pick up will not be good.
Lingwendil (and maybe Clatter too) did a picture tutorial on enlarging the plenum in Kadron manifolds. The amount they did is good for milder cams, but not enough for the "problematic" cams.
Also, people need to remember, that when running dual sgl carbs the ignition timing need to be increased at least 10% in the lower rpms, sometimes more, hence the fact that say the belowed cast 019 distributor can make such an engine work significantly better than a 009 or 010. Ditto with the newer Magnaspark/shockwave etc etc.
Getting back to the ICT´s. I´m not particularly fond of these carbs and the delivered manifolds, but they afre widely used because they are cheap. Now, with those you can increase the plenum volume with adding an extension between manifold and carb. (I believe it is even a part number at CB) Depending on how much room you have and how much cam etc 12 - 20 mm. Even the 12 mm spacer will make a significant difference in idle- and lower rpm behavior.