carb backfiring

[Mosier]

I had a similar problem with my B2, changed the accelerator pump on the carb and it was fine afterwards.

 

[lmtpop]

ok continuing saga but getting better, pulled carb again adjusted fast idle cam per book. discovered an open vacuum port on the carb that did not have the nipple on it. scavenged one off the old carb and put a plug on it for now. starts better idles slower fast idle kick down works but continues to back fire on occasion through the carb and actually had a small carb fire. have not rechecked timing with a light in a few days. any suggestions?

 

[PetesPonies]

Well as it had to be, you fixed a couple vacuum leaks. Can you get a gauge to check the vacuum level? Where is your idle adjustment now? Is your accelerator pump working? Have you checked it?

 

[kimcrwbr1]

Set the timing at 10 dbtdc with the advance unplugged and a small phillips plugging the hose. You should get 10 degrees vacuum advance and around 15 degrees mechanical advance. Run the advance ported off the carb if you use manifold vacuum you will have trouble getting it to a good idle speed. Adjust your idle air needles out for the highest possible rpm or vacuum pressure when the engine is up to operating temps. Once you get it timed and the carb dialed in then you can make the proper choke adjustments. It usually takes a couple times adjusting the choke I just wait till the next day and adjust it at first start the key being you want the choke to be fully open when the engine reaches around 135 degrees up about half on the temp guage.

 

[lmtpop]

duraspark fast idle

time has been re-set at 10 deg BTC . valves adjusted all known vacuum ports plugged. still not much better, cranks better, but idles around 1200 rpm. if you back off the curb idle screw to bring it down it just dies. i have squirted almost an entire can of starting fluid looking for vacuum leaks and none are apparent. could fuel pressure be an issue? it is the only thing not replaced during the duraspark conversion. it still back fires a little through the carb. it seems happy to run at 1200. i have not driven it yet just drive way work. thinking about pulling the intake and replacing the gasket or getting a rebuilt carb.

 

[kimcrwbr1]

I cant remember have you capped off the EGR be sure and use a good felpro egr gasket that part of the engine gets real hot. A piece of vacuum tubing about two feet long put one end up to your ear and search around with the other end. If you stick it in the carb you will hear the hissing. search around all the gaskets and vacuum fittings and hoses. I doubt the intake manifold is leaking at the heads but it is possible. I had problems with the base of the carb get spacer felpro # 60529 and make a gasket for the base of the carb. I took a nice flat piece of A/C plywood and cut it the size of a sheet of 200 grit sandpaper coated the plywood with elmers glue and placed the sandpaper on the plywood then with a couple bricks put the sandpaper down on my tablesaw and set the bricks on top. It made a nice sanding block and carefully worked the base of the carb nice and flat. The put the spacer on the egr spacer and the gasket between the carb and the spacer and in a cross pattern slowly pull the carb down snug do not overtighten the most common mistakes is reuseing a carb gasket and tightening it down too much. I allways make a new carb gasket whenever installing a carb of any kind. The vacuum hose also is good for isolating exhaust leaks instead of hissing you hear ticking the closer the louder the hissing/ticking. My exhaust guy showed me that trick he has a 4ft tubing with a soft wire taped to the end keepin the end open you can reach into those areas that would be impossible to get to any other way. Allways be aware of moving parts when the engine is running. Did you plug or use the vacuum port on the back of the EGR spacer it points straight back at the firewall it is under the brake booster hose and hard to see. It is the vacuum that originally goes to the vapor cannister. If you can get your hands on a vacuum guage you want to see 17 inches Hg or above at an idle around 700 rpm if you can achieve that you pretty much have all the vacuum leaks stopped up.