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i'm thinking of replacing the K-Jetronic on my '82 ( regularity car ) , which is for the moment running "perfect" , by Weber carbs .... the more i read about K-Jetronic and his potential "problems" , the more i lust for carbs ! Once you get them dialed in "good" , you can forget them.
I also "read" that K-Jetronic is no better than a carb , only invented for better emissions... but soooooooo more complex .
Advantage is the simplicity , better reach for the spark plugs ( open valley ) , just a low pressure fuel pump and pressure regulator....no WUR, no cold start injector, no pressure valve , no inlet manifold ,etc... it cleans up the engine bay quite a lot ! Perhaps for Sunday cruising it could stay , but for rallies it is so important one can thrust the fuel delivery...i had Webers on my BMW rally car and forgot them after 5 years ! Still working perfect without a wrench on them.
Now , in contrast with my 928 rally car ,which trumpets protrude the hood , i want to keep everything under the hood..... so i calculated possibilities , and with using IDF44 carbs instead of IDA48 , i think i can do it .
52 mm high manifolds,3 mm insulation gaskets , 103 mm carb , 15 mm trumpets and 45 mm air filters.
MPG will suffer, but in the end it's only a fun car , not a daily ! and if i loose some HP/torque , no problem, that 310 HP euro 4.7l is more than enough for regularity rallies. Goal would be use for 5...10 years without problems.... Old school carbs !
Last edited by belgiumbarry; 08-25-2020 at 02:29 PM.
Shawn , 2 reasons ...
regulations, for historic rallies we may not use modern EFI , only the oem injection or carbs. We participate in the "oldtimer" class , which is for cars + 30 years old.
and i like carbs... not wires and ECU's ....
I believe i have now a mechanical sound 928 , but don't have much faith in that K-Jetronic stuff , perhaps by reading here to much how "difficult" it is to solve problems once they occur. In the end it is a rather complex system of 38 years old.....in a car that isn't driven much , so already not good for that injection system as i understood.
Also during a rally i don't see me do anything , if problems occur , on the K-Jetronic....yes, a hose, and perhaps a spare WUR... but not the FD , injectors etc....
Not sure what all the concern about K-jet/CIS problems is. What are people reading about that scares them? I've always found it to be pretty simple, and I've always liked the fact that it's mechanical, not electrical (because I suck at/hate electrical troubleshooting!)
Strosek Ultra - Nice old 6-er. I also have an 80 635 and a couple of 79 Alpina B7Turbo Coupes. Interestingly, the Alpinas are also CIS, albeit a unique Pierburg setup, but the basic principles of system/control pressure of K-jet still apply so I found them fairly easy to rebuild, troubleshoot, and setup.
I do love Webers though, and this thread. Daily drove an old 3-series with triple IDF's for 10 years. Miss that intake sound! Love to hear a 928 with them.
If you modify a CIS engine with a hotter camshaft having more overlap, you will end up having problems.
The pressure waves from the exhaust side affects the sensor plate so that the engine will run unevenly and jerky, especially at lower speeds and under low load.
Mikeb7 thank you for liking my old BMW 635CSI. I bought the BMW almost at the same time as the king of Sweden acquired the same kind of car. The king has sold his car many years ago but
I have kept mine and will not separate myself from it until my time on this planet has ended.
Åke
Ah, wasn't thinking about modified engines, just folks wrestling with stock setup.
Thanks, Ake.
The reason why Barry wants to install Webers is more power.
The air flow through the CIS system is very poor, Weber carbs have excellent air flow.
Another argument is that it will be a very clean engine compartment.
The only things that are really needed are petrol hose, gas wire and choke wire.
Åke
Last edited by Strosek Ultra; 08-28-2020 at 07:38 AM.
The reason why Barry wants to install Webers is more power.
The air flow through the CIS system is very poor, Weber carbs have excellent air flow.
Åke
Ake, on the "rally" car yes , but not so much for the "regularity" one. It's already more then powerfull enough now with the K-Jetronic.
But i like the simple clean look of Webers instead of the oem pile of parts , fuel pipes and vac hoses....and i'm no purist , i want it to be reliable and easy maintained , more important in rally than a oem "look" .
O well, begin this year we drove 1 rally and so far everything is cancelled afterwards due Covid... let's hope for a better 2021 !
Mid September there is 1 regularity which "should" happen according latest news , and we are participating... if it doesn't change by then. But without the fun factors as gatherings , start podium and pauzes on town markets , BBQ at finish etc... just drive it ... will not be the same. But i understand the extra precautions those organisations have to make to be even allowed .
so yes, it will work to keep it all under the hood..... due the bore spacing of a IDF44 ( 90 mm ) instead of 120 mm ( IDA48) , i can make the manifolds at 52 mm height instead of 90 mm , just to clear the distributor. Also of course only 15 mm trumpets and 45 mm air filters. Cannot wait to build it.... but want to keep it as a winter project .
With the IDA48's...., here i can choose trumpet height , they protrude the hood.
and now i'm only more motivated.... Friday night we were at P7 in the regularity rally , Saturday we had to abandon . Engine became worse and worse until i could only rev to 2000 rpm. So i thought fuel pressure problems.... and indeed, after filling up ( from 1/2 tank ) it was a bit better ( i assume due more static pressure to inlet pump ) .
So byebye all that old CIS "junk" and hello Webers !
08-25-2020, 02:06 PM
