I took my newly purchased 79 bronco for safety and emissions, and it failed on the emission side of things. It is running way to rich, i adjusted the mixtures, but the guy who tested it said that i would have to put smaller jets in to get it to pass.

The guy who built the engine, said you can change the rods? metering rods? cant remember, and sometimes it will pass without having to jet down.

The state max is something like 2.9in the CO% area, mine was 4.9.

Will changing the rods pass emissions? Or should i just rejet the carb? Its an edelbrock 600cfm, and, where are the jets on these things?

Thanks for your advice.

 

Get a calibration kit for your carb from Edelbrock, Summit, Jegs etc. The kit will have instructions.

 

Thanks for the info, will get on it.

 

I have a 1980 F-350 4x4 400 auto in Salt Lake City - altitude approximately 4,500 feet, but I do regularly drive up Parleys Canyon to Strawberry and to the ski areas at a maximum of 9,000 feet. My truck is basically stock other than 2 1/4" dual exhaust, no smog anything, double roller chain and recently an Edelbrock 2171 intake and 1411 4 barrel carb. Out of the box, the carb is set for sea level so I initially rejetted the carb moving the 107 secondary jets to replace the 110 primaries and installed 104 jets for the secondary. I did not change the stock metering rods or springs. I then tuned the engine and carb and there was noticable improvement climbing the mountain canyons. Two weeks ago, I drove the truck in for the emissions test and failed badly with that setup. CO was 8.47% at idle and 4.26% at 2,500 rpm. Maximum CO for 1980 is 4.00%. I rejetted again leaving the 104 jets in the secondary and installed 104 jets in the primary as well. I also replaced the 075 x 047 metering rods with 070 x 042 rods keeping the original orange springs. I then tuned and went back for another test. Rejetting and changing the metering rods made an huge difference in the emissions test with little loss in performance. The results were 0.38 at idle and 0.26 at 2,500 rpm. CO2 did increase the second time at idle from 9.3 to 12.7, but HC was reduced from 415 ppm at idle to 138 and from 124 at 2,500 to 62. Granted, after the test I enriched the mixture a bit for additional performance, but that was to be expected...

 

You can get the Edelbrock calibration info on-line at www.edelbrock.com. You may not need the whole kit, just one set of metering rods to get you one stage leaner.

A lighter spring will keep it in cruise mode longer. If you need to pass smog at a higher RPM than idle, you might want the lightest springs or no springs at all.

 

timing is just as important as the carb /jetting. if the distributor is advancing a lot, either by vacuum, mechanical, initial, or the whole combination, the engine will fail. you have to make sure your timing is set and the distributor is operating in a manner that will pass the test. basically this means stock settings. minimal initial, and the vacuum connected to either ported vacuum or disconnected for the test. going too lean on the carb is worse than too rich, btw.