Backfiring on a 1600 D/P with Kadrons.

scottk · Post by **scottk** » Wed Jun 26, 2002 8:08 am

Ok, I searched the forums and couldn't find an acceptable answer... so I'm making a new post...

I have a 1600 D/P, rebuilt, with dual kadrons. I have the valves set, timing is good at 8/30. I know nothing about setting the carbs. I managed to get the idle set fine and believe equally between the two. I am backfiring and see flames coming out my exhaust. Kind of a cool effect but don't know how to stop it. I think the air/fuel mix screw on the Kadrons is in the middle facing the rear of the car, a skinny tube that has a brass screw on the inside. That screw was screwed all the way in. Am I correct in believing that I'm running really rich and the exhaust is igniting? How do you adjust the Kadrons without a unisyn? Am I looking at the right screw? If it's all the way in should it be running rich?

Dung_Beetle · Post by **Dung_Beetle** » Wed Jun 26, 2002 8:28 am

http://www.lowbugget.com/main_page.html this guy reccomends you not use a carb synch on kadrons.

Bucko · Post by **Bucko** » Wed Jun 26, 2002 9:45 am

I can't believe you did not see a post on the Kadrons (adjustment). I posted about three weeks ago with a SIMILAR problem. Here is what I had to do:
The timing; make sure your timing is at no more than 4-6 degrees advance AT IDLE, but the best is to see that you are running no more that 30 degrees advance at 3000 RPM. Second: Sync'ing of the carbs is critical! This is where I went wrong. My backfiring (through the carbs) was due to the bottom butterfly plate (idle adjustment) was off between the two carbs. My mistake was to check the "gap" of the idle screw of both carbs and set them equal this way. Boy was I wrong! You would think that the carbs would be equal this way (sync'ed), but the easiest way is to use the sync tool, and measure the first carb's pull; the tool will have you get the "ball" to float in the center by adusting the tool. Then, you move the tool to the other carb, and adjust it's idle screw (not the mixture screw) so that the "ball" floats at the same height. You now have the carbs sync'd. My measured gap between the two was about a 1/8 inch difference; may not sound like much, but when the bottom butterfly is open this much more that the other carb, it DID make the difference. I have no more backfiring through the carbs!
What Mr Kadron did help me out with was to verify that the idle mixture screws were working; you should be able to turn them in (clockwise) and get the engine to start to die. Then back them out slowly until you get maximum RPM. This is not the proceedure to used to syncronize the carbs though!

scottk · Post by **scottk** » Wed Jun 26, 2002 10:30 am

Yeah I've got the lowbugget site up. I'm going to have to see bout getting them sync'ed. I am more concerned about the air/fuel mix though. I think I can see where to adjust it. I think I was turning out one of the jets... DOH!... If I'm correct the air/fuel mix screw is on the right (passenger) side of the carb, near the base. I'm thinking I'm just running really rich which should account for the flames coming out the exhaust.

scottk · Post by **scottk** » Wed Jun 26, 2002 12:00 pm

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by captCRUNCH:
but it sure is fun hey?!?! my engine backfires way more now with the kads on than it did with the stock set up. check your plugs, they will tell you if you are running too rich. as for the idle screws...isn't it in to make the mixture leaner?? out to make it richer? and does it backfire all the time?? or is it just when you race the engine then back off the gas QUICKLY??<HR></BLOCKQUOTE>

Ok, ok... I'm going to sell my bug now... (I'm not worthy!!!!) I switched to dual carbs, didn't block off the heat riser hole on the heater boxes... would that cause an exhaust leak????? =) I also think the exhaust system is a little screwy, it's an old rusted Kadron exhaust. I did put new gaskets on it, but the way the exhaust is designed it's really hard to tighten the screws. I also think I'm running rich 'cause of the flames... personally though I like it but I want an engine that will last a long time and get decent gas mileage. I've also noticed a lot of crud in the filter, guess I need a new filter and some decent gas, tune the carb and beg my wife to buy me a new header system...

Bucko · Post by **Bucko** » Wed Jun 26, 2002 1:34 pm

Stick with it man. Once you have those Kad's dialed in, they are great! You are correct in that the idle mixture screws are on the right bottom side of the carb. Another idea is to connect a stiff piece of vacumn tube to the screws if you have the carbs off; that way it's easier to adjust the idle mixture instead of attempting a long screwdriver while the engine is running.

CPRcubed · Post by **CPRcubed** » Wed Jun 26, 2002 11:15 pm

The Kads I had years ago, came with one of the Idle mixture screw needles broken off in the carb body passage. Screw it all the way in, all the way out ... no difference! Just another thing to check. Also check for exhaust leaks, since that will cause backfiring (through the exhaust as well. Cheers!

------------------
1970 Bug (stock & rusted for now), 1994 F350 CC DRW PSD, 1971 Airstream. Life is good in Bear Valley Springs!

captCRUNCH · Post by **captCRUNCH** » Wed Jun 26, 2002 11:40 pm

but it sure is fun hey?!?!

my engine backfires way more now with the kads on than it did with the stock set up. check your plugs, they will tell you if you are running too rich. as for the idle screws...isn't it in to make the mixture leaner?? out to make it richer? and does it backfire all the time?? or is it just when you race the engine then back off the gas QUICKLY??

alcast81 · Post by **alcast81** » Tue Sep 10, 2002 7:21 pm

i know this post is old , but i have kads on my engine and its backfiring , sounds like pops. but it does it when i race it like he said and then when i let go its pops and backfires. i'm not sure what to do , i checked the vavle adjustment , timing just can't get it right , , i might have an exhaust leak. but what is it usually when this is happenening??

Bucko · Post by **Bucko** » Wed Sep 11, 2002 4:54 am

Backfire through the carbs on dexcelleration could be that your timing is too far advanced. Do a search on posts here and get your timing set correctly before attempting any further adjustments. The max amount of advance you would want is 30 degrees at about 2000 RPM.

Otherwise, a call to Mr Kadron should help you out. here's his web page:
http://lowbugget.com/main_page.html

Post by **Marc** » Wed Sep 11, 2002 7:05 am

ANY exhaust leak will cause explosions in the muffler on decel. When the throttle is shut and the engine is coming down to idle speed, manifold vacuum pulls more fuel through the idle & transition ports than there is air to burn it - you get a rich mixture that won't burn and normally goes out the t'pipe as unburned HC. An exhaust leak (or just a really-big outsized muffler) can let some outside air in to lean that rich mixture to the point where it will ignite from the heat inside the exhaust system => BANG!
Fix the exhaust leaks before chasing mixture/timing problems that may not exist.

It's quite common for the linkage on dual carbs to have slightly different leverage between the sides. They might both be at idle at the same time, but one gets to wide-open before the other one. This must be corrected first before any other attempt at idle synchronization is worthwhile. Often all that it takes is a slight tweak on the lever(s) to change the effective center-to-center distance between the link rod and the throttle shaft.
You can do a fine job of synch'ing Kadron idle adjustment with nothing more high-tech than a can with a hole in one end (about 3/8" diameter or so). Place it over each carb (if the idle changes at all when you do so, make the hole bigger) and bring your fingertip down over the hole to feel the suction. Go back and forth between the carbs a few times until it's the same; if you completely block the hole it should drop the idle speed by the same amount on both sides. Same principle as a UniSyn, just substituting your own senses for the little red ball, and it works fine for Kads for zero $. If you don't have the cork aircleaner-base seals (or they're hammered and leaking), save the O-rings from spin-on oil filters - or snag some from Speedi-Lube - some fit Kads like they were made for them.

aircooledsteve · Post by **aircooledsteve** » Wed Sep 11, 2002 8:11 am

Have you checked for vacuum leaks? My engine was running like s**t and backfiring through the exhaust and it was nothing more than a vacuum leak (real bad casting seam) at the base of one of my EMPI intake manifolds. On one hand I was relived to know that there was nothing seriously wrong with my engine, but on the other hand I was upset to have wasted two days trying to tweak and adjust my carburetors. Oh well, it is after all a learning experience! Good luck.
Steve

RoWaMe · Post by **RoWaMe** » Wed Sep 11, 2002 9:56 am

To check for an exhaust leak, look at your exhaust system with the engine off (and cold); at the leak point you should see black soot against an adjacent part of the exhaust. The soot will come as described by Marc. Most leaks that I've seen were at the joint of the heater boxes and the exhaust header, where you install those big asbestos rings/donuts from the muffler instalation kit (you did use new ones, right? and they were not broken, right?). With the engine running at idle you can hold your hand "near" that joint and may feel an air leak. You can patch up that joint by smearing a good bead of red high-temp RTV silicone around the clamp/donut (engine must be cold) and letting it dry overnight. Another leak was from a broken gasket at the connection of the header to the muffler. If your header is already drilled out for the intake pre-heat, and you do not plug up that hole using a gasket and block-off plate, that's another area for exhaust leaks/bangs.

After you've adjusted your carb throttle as described above so that each is pulling the same amount of air, you must adjust the cross-bar that connects both carbs exactly (using the balljoints and locknuts on the linkage ends) so that when you snap them on and off the carb throttle "ball" with engine running there is no difference in idle speed. A bunch of Fiddling... but as stated above, once you have that done and the mixture adjusted, they'll be fine.

You ARE running a stiff hose (like a domestic fuel line of approx. 3/8" or 1/2" I.D.) between the carbs, that connect to the fittings on the manifold? That fitting must be used for correct operation!

BTW- a loose manifold or other air leak on the "topside" of the engine will cause the engine to stall at idle when warm.

SportyBug · Post by **SportyBug** » Wed Sep 11, 2002 11:56 pm

Just stick with it! I put the very same setup on my 1600 after the FI went south and it took a little bit of tinkering with everything to make it work. In the end I think it is worth it, I still make about 20mpg with dual carbs even though I have a lot of moutian to deal with here.

scottk · Post by **scottk** » Thu Sep 12, 2002 10:23 am

Glad I stuck with it!!! Things are going great, my car is in my garage while I redo the fuel tank, should be finished by this weekend!

Scott