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Heiferman Samba Member

Joined: February 28, 2024 Posts: 205 Location: Georgia, USA
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Posted: Wed Dec 04, 2024 11:10 am Post subject: Re: Yet Another Kadron Backfire Tread |
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Dauz wrote: |
have you blown out the pilot jet with carb cleaner? |
Yes. When presented with the issue originally I swapped the carbs to ensure it was not a manifold or engine issue.
When it continued I tore the carb apart, cleaned everything, sprayed carb cleaner through every orifice and replaced everything that came in a rebuild kit.
I even pulled the accelerator pump tube to be sure the BB was in there. _________________ - 1973 Thing, some LandCruisers and an old Ambulance |
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Dauz Samba Member

Joined: January 05, 2010 Posts: 1858
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Posted: Wed Dec 04, 2024 2:06 pm Post subject: Re: Yet Another Kadron Backfire Tread |
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Heiferman wrote: |
Dauz wrote: |
have you blown out the pilot jet with carb cleaner? |
Yes. When presented with the issue originally I swapped the carbs to ensure it was not a manifold or engine issue.
When it continued I tore the carb apart, cleaned everything, sprayed carb cleaner through every orifice and replaced everything that came in a rebuild kit.
I even pulled the accelerator pump tube to be sure the BB was in there. |
I see. I had a bout with Kadrons a long time ago. Issues similar to yours. I threw in the towel and replaced them with 40IDFs and never looked back. I wasn't such a huge fan of a motor idling on half its' cylinders. |
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Heiferman Samba Member

Joined: February 28, 2024 Posts: 205 Location: Georgia, USA
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Posted: Wed Dec 04, 2024 3:01 pm Post subject: Re: Yet Another Kadron Backfire Tread |
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Dauz wrote: |
Heiferman wrote: |
Dauz wrote: |
have you blown out the pilot jet with carb cleaner? |
Yes. When presented with the issue originally I swapped the carbs to ensure it was not a manifold or engine issue.
When it continued I tore the carb apart, cleaned everything, sprayed carb cleaner through every orifice and replaced everything that came in a rebuild kit.
I even pulled the accelerator pump tube to be sure the BB was in there. |
I see. I had a bout with Kadrons a long time ago. Issues similar to yours. I threw in the towel and replaced them with 40IDFs and never looked back. I wasn't such a huge fan of a motor idling on half its' cylinders. |
I am getting close to doing that.
Latest:
I discovered that the other carb had a clog in the accelerator pump and the needle and seat was not properly moving. I pulled it apart and fixed all that. Now I have a seep at the strainer plug since I did not have a new washerto put in.
I swapped the carbs and, as happened before, the problem followed the same offending carb. I then swapped the idle jets. Same. Backfiring out the offending carb and visibling splashing fuel dropplets out of the throat.
Idle is for poop now too but that figures with all the tinkering.
The only things I have not pulled out of that carb is the venturi and the primary check valve.
I have a set of Empi HPMX sitting on the shelf. Condition unknown. I just ordered a set of kits for them. I am getting to the end of my rope with the Kads. I have been effing with them for over a month. I hate to let a machine beat me but thisnis keeping me from other projects. _________________ - 1973 Thing, some LandCruisers and an old Ambulance |
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Heiferman Samba Member

Joined: February 28, 2024 Posts: 205 Location: Georgia, USA
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Posted: Wed Dec 04, 2024 3:34 pm Post subject: Re: Yet Another Kadron Backfire Tread |
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I will bet that the PO bought these on Ebay from someone who was having the same issues, thought he got a deal but never ran them.
They were not fully installed on the car and he said he had not run them. They clearly have had fuel through them and considerable tinkering based on what I have discovered but they were super clean. So when dude said new he meant new to him.
I will lay money they were jacked up for whom ever ripped off the PO of this engine. He just never realized it since he gave up on the car. _________________ - 1973 Thing, some LandCruisers and an old Ambulance |
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Alstrup Samba Member
Joined: July 12, 2007 Posts: 7646 Location: Videbaek Denmark
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Posted: Wed Dec 04, 2024 3:38 pm Post subject: Re: Yet Another Kadron Backfire Tread |
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Heiferman wrote: |
Latest:
I discovered that the other carb had a clog in the accelerator pump and the needle and seat was not properly moving. I pulled it apart and fixed all that. Now I have a seep at the strainer plug since I did not have a new washerto put in.
I swapped the carbs and, as happened before, the problem followed the same offending carb. I then swapped the idle jets. Same. Backfiring out the offending carb and visibling splashing fuel dropplets out of the throat.
Idle is for poop now too but that figures with all the tinkering.
. |
OK.
No offense, but 50% of the time its the person behind the wrench which is the problem.
Now.
Did you check if the inlet valves actually close, and do not have some sort of dirt in them? A piece of fuel hose in there is very common.
Did you check that the acc pump check ball is in place in both carbs?
Are you 100% sure that the linkage isnt fluffy, so that one side can vibrate so the acc pump membrane siphons fuel into the system?
Once in a blue moon there is a Kadron carb that just doesnt want to work, but it is very very rare. In my time (30 years by now) I have come across 2. That´s it. _________________ https://www.thesamba.com/vw/forum/viewtopic.php?t=435993 |
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oprn Samba Member

Joined: November 13, 2016 Posts: 14209 Location: Western Canada
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Posted: Wed Dec 04, 2024 4:04 pm Post subject: Re: Yet Another Kadron Backfire Tread |
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Dauz wrote: |
Heiferman wrote: |
Dauz wrote: |
have you blown out the pilot jet with carb cleaner? |
Yes. When presented with the issue originally I swapped the carbs to ensure it was not a manifold or engine issue.
When it continued I tore the carb apart, cleaned everything, sprayed carb cleaner through every orifice and replaced everything that came in a rebuild kit.
I even pulled the accelerator pump tube to be sure the BB was in there. |
I see. I had a bout with Kadrons a long time ago. Issues similar to yours. I threw in the towel and replaced them with 40IDFs and never looked back. I wasn't such a huge fan of a motor idling on half its' cylinders. |
^^^This was my experience too!^^^
I must confess that I only spent 2 summers tinkering with them... then gave up. I am one of the 50%! The used 40mm IDF Webers ran nearly perfect right from the first start up. _________________ Our cars get old, we get old but driving an old VW never gets old! |
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Heiferman Samba Member

Joined: February 28, 2024 Posts: 205 Location: Georgia, USA
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Posted: Wed Dec 04, 2024 4:44 pm Post subject: Re: Yet Another Kadron Backfire Tread |
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Alstrup wrote: |
Heiferman wrote: |
Latest:
I discovered that the other carb had a clog in the accelerator pump and the needle and seat was not properly moving. I pulled it apart and fixed all that. Now I have a seep at the strainer plug since I did not have a new washerto put in.
I swapped the carbs and, as happened before, the problem followed the same offending carb. I then swapped the idle jets. Same. Backfiring out the offending carb and visibling splashing fuel dropplets out of the throat.
Idle is for poop now too but that figures with all the tinkering.
. |
OK.
No offense, but 50% of the time its the person behind the wrench which is the problem.
Now.
Did you check if the inlet valves actually close, and do not have some sort of dirt in them? A piece of fuel hose in there is very common.
Did you check that the acc pump check ball is in place in both carbs?
Are you 100% sure that the linkage isnt fluffy, so that one side can vibrate so the acc pump membrane siphons fuel into the system?
Once in a blue moon there is a Kadron carb that just doesnt want to work, but it is very very rare. In my time (30 years by now) I have come across 2. That´s it. |
Given my past luck with carbs, me being the problem certainly is in the equation.
All the things you listed have been checked. Both balls are in place and I have been unable to identify any other clog or obstruction.
I have messed quite a bit with the linkage since I have started from zero multiple times. When I have gotten a decent idle I have disconnected the linkage and got a decent sync before reconnecting but linkage or not, the same carb spits gas and backfires when given gas. Timing also does not effect it much. Advanced or retarded I still get backfiring through the carb along with other issues you will experience with a poorly timed engine.
Given that the problem follows the carb to either side I am certain this is a carb centric issue. I did not swap the main jets to see if they are somehow to blame and I have not swapped the throttle bodies or top ends to see of I can isolate it to one of the three main parts. _________________ - 1973 Thing, some LandCruisers and an old Ambulance |
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AlteWagen Troll

Joined: February 23, 2007 Posts: 8635 Location: PNW
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Posted: Fri Dec 06, 2024 2:59 pm Post subject: Re: Yet Another Kadron Backfire Tread |
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If its shooting gas out of the top of the carb Id look at fuel pressure and make sure the needle valve is clean. Go for 1.5 psi for fuel pressure and make sure the valve opens and closes all the way.
The mods on the carbs look like kaddie shack style, is there a KS stamped on the front of the carb?
The pic of the emulsion tube shows evidence of water in the circuit. The main is pretty simple, jet in the bowl, emulsion tube, air bleed. They all connect and must be cleaned with a stiff pipe cleaner from the jet side then the e tube side. Run a wire through the air bleed and make sure its clear as well.
Make sure the area where the booster connects is clear and the booster itself as Ive seen them clogged with black shit that blocks or narrows the outlet significantly.
If the backfire is at part throttle make sure to clear the idle circuit and most important the progression holes in the throttle body. More black shit there will cause lean back fire as well. There are several gaskets at the TB including the plastic isolator, they can get blown out if the back fire is big causing a vacuum leak. _________________ Grapes of Wrath $200 Engine Rebuild
Official Dual Carb Thread
Cylinder Head Quick Reference Sheet |
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Heiferman Samba Member

Joined: February 28, 2024 Posts: 205 Location: Georgia, USA
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Posted: Fri Dec 06, 2024 3:21 pm Post subject: Re: Yet Another Kadron Backfire Tread |
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Thanks for the input. I just at 1.5 psi running a Holley regulator. I need to check the hose end pressure to ensure it is truly at 1.5.
I have not noticed the KS anywhere. Will look again. _________________ - 1973 Thing, some LandCruisers and an old Ambulance |
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Heiferman Samba Member

Joined: February 28, 2024 Posts: 205 Location: Georgia, USA
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Posted: Sun Dec 15, 2024 2:52 pm Post subject: Re: Yet Another Kadron Backfire Tread |
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I am back. I hate when a thread gets abandoned.
I waited for a new jet guage and a new kit for the second carb.
Here is waht I found.
Yes, these carbs have been to Kaddieshack
I pulled both carbs down again and put all new parts in the one I had not previously rebuilt that had the sticky needle and seat.
I ran brushed and wires in every orifice I could and sprayed everything with carb cleaner again. I have found no clogs. I did not pull the venturis or primary check valves.
The carbs have:
40-32 venturis
.55 idle jets
1.50 main jets (my guage only goes to 1.50. It felt loose but the back of a 1/16 drill bit which is 1.55 would not go in) so I am going with 1.50.
1.47mm washers at the needle and seat. The offending carb had 1.96mm but the other one was 1.47 so I swapped them out to be the same.
.70 marked accelerator pump spray tubes. I did not replace them since they were clear and marked and already bent.
Check ball is installed on both. Gaskets are new.
I awapped the uppwr carb body carb to carb.
I do not have a great way to measure the accelertor pump delivery amount. Next I am going to go back to the thread someplace here that is about aiming the nozzle of the pump tube. _________________ - 1973 Thing, some LandCruisers and an old Ambulance |
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Heiferman Samba Member

Joined: February 28, 2024 Posts: 205 Location: Georgia, USA
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Posted: Sun Dec 15, 2024 4:06 pm Post subject: Re: Yet Another Kadron Backfire Tread |
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Ok.
Things are a bit better.
Seem to be no more backfiring up the carb. Seems a little rich now.
Not really liking my 009 but am going to wait to mess with my svda until I get this better dialed. Running about 32 advance at 3000 rpm. I think I need to dial it back just a couple degrees.
I wish I could point to one thing that I did to improve things. I got a few jets to try but did not expect I would be starting at 150. If I am in fact rich now I may grab myself some a bit smaller (145s maybe) and try them. Although taking these out and messing with them again scares me since it really is running better.
As others have noted, KS did not leave the jet size on either the main jets or the idle jet. So sneaky. _________________ - 1973 Thing, some LandCruisers and an old Ambulance |
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Rome Samba Member
Joined: June 02, 2004 Posts: 10228 Location: Pearl River, NY
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Posted: Sun Dec 15, 2024 11:37 pm Post subject: Re: Yet Another Kadron Backfire Tread |
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150 main jet seems "huge". When Aircooled.net's website was still operational, it had a few reference articles on venturi and jet sizing. Venturi diameter was 3-5 mm smaller than your cylinder head intake valve diameter. Seeing that your engine is a 2180, it probably has larger intake valves than the stock 35.5 mm. So if you consider a first "major step" up from a stock head, the valve size could be 40 mm. So your venturi will work OK.
Next, the main jet size. Same source recommends sizing the main between 4.1 to 4.3 x the venturi diameter. In your case with the 32 vent, main jets would range between 132 to 137. So a 150, even a 145 is still very large. If you're going to test various new jets (which are still stamped for size), I'd try a 135 and 140. And remember that main jets are most active at highway speeds, not at idle/low throttle.
And idle jet- try a (marked) 55. |
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Heiferman Samba Member

Joined: February 28, 2024 Posts: 205 Location: Georgia, USA
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Posted: Mon Dec 16, 2024 7:51 am Post subject: Re: Yet Another Kadron Backfire Tread |
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Rome wrote: |
150 main jet seems "huge". When Aircooled.net's website was still operational, it had a few reference articles on venturi and jet sizing. Venturi diameter was 3-5 mm smaller than your cylinder head intake valve diameter. Seeing that your engine is a 2180, it probably has larger intake valves than the stock 35.5 mm. So if you consider a first "major step" up from a stock head, the valve size could be 40 mm. So your venturi will work OK.
Next, the main jet size. Same source recommends sizing the main between 4.1 to 4.3 x the venturi diameter. In your case with the 32 vent, main jets would range between 132 to 137. So a 150, even a 145 is still very large. If you're going to test various new jets (which are still stamped for size), I'd try a 135 and 140. And remember that main jets are most active at highway speeds, not at idle/low throttle.
And idle jet- try a (marked) 55. |
Thanks for that feedback. I felt like 150s were way too big as well based on all I have read. Unfortunately I do not have all the specs on this engine. I wish I did. That might take some guess work out of it.
I happen to have both marked 55 idles and a pair of 140s (the largest in my set). _________________ - 1973 Thing, some LandCruisers and an old Ambulance |
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Heiferman Samba Member

Joined: February 28, 2024 Posts: 205 Location: Georgia, USA
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Posted: Mon Dec 16, 2024 2:44 pm Post subject: Re: Yet Another Kadron Backfire Tread |
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Did a little more tuning.
Swapped the unmarked idle jets out as suggested. Seems to actually be running a little better. Maybe I am imagining it. I also spent a little more time on the mixture. I hooked my timing light up again since it has a tach and was able to visibly see the change in the idle when turning the screws so I think I have that pretty well dialed in.
I went ahead and ordered a set of 145 mains just to have so that when they get here I can spend some time experimenting with 135, 140 and 145 jets. They were super cheap on sale at CIP1 so I pulled the trigger on new tailights too to get rid of my funny Euro lights.
I put the laser thermometer on it after a short drive and it seems like the number 4 cylinder is running too hot. Everything else is shows very cool. I need to grab a new 9v battery before I finalize that assesment and once cooled I am going to double check the valve clearences yet again. (Running chrome moly pushrods. )
I know I need a larger exhaust (running a small 4 into 1) but want to try to get the other really bad stuff worked out before I drop $700 on a decent header.
I do appreciate everyone's input. _________________ - 1973 Thing, some LandCruisers and an old Ambulance |
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oprn Samba Member

Joined: November 13, 2016 Posts: 14209 Location: Western Canada
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Posted: Mon Dec 16, 2024 8:12 pm Post subject: Re: Yet Another Kadron Backfire Tread |
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Save yourself a pile of time and beg, borrow or steal a wide band AFR meter and quit guessing. _________________ Our cars get old, we get old but driving an old VW never gets old! |
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Heiferman Samba Member

Joined: February 28, 2024 Posts: 205 Location: Georgia, USA
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Posted: Mon Dec 16, 2024 8:30 pm Post subject: Re: Yet Another Kadron Backfire Tread |
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oprn wrote: |
Save yourself a pile of time and beg, borrow or steal a wide band AFR meter and quit guessing. |
Thanks but I am guessing the number of people who have those are dwarfed by the number who don't. _________________ - 1973 Thing, some LandCruisers and an old Ambulance |
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oprn Samba Member

Joined: November 13, 2016 Posts: 14209 Location: Western Canada
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Posted: Mon Dec 16, 2024 8:55 pm Post subject: Re: Yet Another Kadron Backfire Tread |
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And how does that make not using one better?
I cannot understand how anyone can justify spending several thousand dollars on the best of everything to build the ultimate engine then baulk at spending $150 on the proper tool to make sure the mixture is right and are content to guess at something that critical. To me it completely defies logic!
Ignore me and carry on... _________________ Our cars get old, we get old but driving an old VW never gets old! |
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Heiferman Samba Member

Joined: February 28, 2024 Posts: 205 Location: Georgia, USA
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Posted: Mon Dec 16, 2024 9:47 pm Post subject: Re: Yet Another Kadron Backfire Tread |
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oprn wrote: |
And how does that make not using one better?
I cannot understand how anyone can justify spending several thousand dollars on the best of everything to build the ultimate engine then baulk at spending $150 on the proper tool to make sure the mixture is right and are content to guess at something that critical. To me it completely defies logic!
Ignore me and carry on... |
You are making some pretty broad assumptions and you know what they say about when one assumes.
I bought a project a guy gave up on and giving it a shot. I did not spend "several thousand dollars on the best of everything to build the ultimate engine." If you followed along, I have even stated I do not have full specs on the engine but wish I did.
Maybe try to be helpful and not condsending. Your post about just throwing an AFR in was pretty nonspecific and only vaguely helpful. As I figure it, buying one and wiring it and welding a bung in would be more than $150 unless you have a better and more helpful suggestion.
Sorry I hurt your feelings by not immediately agreeing with you and going right out and buying something you think I need. Cheers.
Edit: Oh wait, you posted you could not tune Kads and gave up after two years right? Guess you couldnhave taken your own advice. _________________ - 1973 Thing, some LandCruisers and an old Ambulance |
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oprn Samba Member

Joined: November 13, 2016 Posts: 14209 Location: Western Canada
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Posted: Tue Dec 17, 2024 6:32 am Post subject: Re: Yet Another Kadron Backfire Tread |
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All true! My apologies for sounding condescending. You are not hurting my feelings, I hurt yours!
I too bought someone else's project and had no idea what the internal specs were on the engine. Yes I did spend 2 summers trying to get them to run right with only limited success. I removed that engine due to excessive oil consumption and an oil pressure problem.
I bought Webers for the replacement engine and someone here convinced me to invest in a wide band to tune them. Thank you again whomever it was! The tuning and adjusting process was a pleasure! No guesswork and it was accomplished in a few short test runs with a bit of a wait between for jets to come in the mail.
On reflection, If I had used a wideband on the Kadrons the process would have been far less frustrating and perhaps they would not have been given away so quickly. _________________ Our cars get old, we get old but driving an old VW never gets old! |
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Heiferman Samba Member

Joined: February 28, 2024 Posts: 205 Location: Georgia, USA
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Posted: Tue Dec 17, 2024 6:54 am Post subject: Re: Yet Another Kadron Backfire Tread |
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Needling aside, where would an afr bung install in an air cooled vw application?
My header is pretty much garbage. I would love a nice Trimill or similar but that is down the road.
Answered my own question. Looks like right at the collector right before the muffler.
Given the length of a VW system I wonder how accruate these can be. I did a search on here and there are mixed reviews.
But I am now straying from what I am trying to achieve: Just a fun old street runner. _________________ - 1973 Thing, some LandCruisers and an old Ambulance |
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