So we purchased a relly nice 66 Fairlane GT with a 390/4 speed. the 390 is the infamous S code (335 hp/427 torque).

so far we installed:
- new cap/rotot
- crane PS-20 coil
- Crane XR-i electronic distributor conversion kit
- new autolite 45 plugs
- taylor 8mm spiro-core wires.

we set the air gap in the distributor to .030 and plug gap to around .050.

the problems we have is the car will backfire (usually though the carb) while pulling out and sometimes while just shifting into second. once and a while it'll backfire out the tail pipe but its rare. it also seems to be idling a little higher than should be. it also seems to have a miss while cruising but that may be due to the plug wires being temporarly zipped tied together (trying to get the wire seperators). and it also seems to be running rich...

we didnt get a chance to play w/ the timing but it sounds like the timing is way off. the dist. has a vacuum advance as well.

so where should we start? i figured by resetting the base timing to around 10* BTDC (iirc that is what is called for) and im lost after that. do i need to do anythign with the vacuum advance? also, any other places to look into? and it has the original holley 4160 4 bbl carb (600 cfm), should it be rebuilt?

 

Sounds like a carb problem. ditch the zip ties, you're better off without them. If it is the original carb, yea, it probably needs attention after 40 years.

 

Check your accellerator pump for proper opperation. The air gap in the dizzy
sounds a little wide, I set mine at .010 using a brass feeler gauge. At such a wide gap the magnetic pickup may not get a good signal. Try a smaller plug
gap such as .035 and work up. Mine did'nt like any more than .042 before misfireing. Check your damper for slipping ,I had to replace the one on my wrecker , it had slipped about 20 degrees. Separators are a must on plug wires

Have a good day----------- Hotwrench

 

we reset the air gap in the dist. to .010 and it did like the change. we checked for vacuum leaks and checked for play in the timing chain. we also re-arranged the plug wires and added the serperators.

what we did notice...after driving around for a few minutes it will start to pop and back fire...almost like the carb is loading up. it runs fine when cold or while cruising...but stop and go its horrible after a few minutes. i asked a few people and they all said its the carb. so we got an AED rebuild kit and na new plastic float bowl so we can overhaul the carb. (we were going to anyway)

also, when its idling in the garage u can see carbon coming out the exhaust and fuel vapors ill accumulate on the ground. it still feels like a slight miss while cruising and doesnt seem to have its full power potiential.

i was told by many the Nitrophyl was far superior to the brass... to late now, already have the Nitrophyl ones...

it does idle a little high...like around 900 rpm...during warm up its around 1100 and doesnt seem to come down as much. how can i "fix" the choke or how can i check to see if it is sticking...because if we can hold on on rebuilding the carb till we store it in the winter...that'll be great.

so how can we go about testing/checking the choke for proper operation and how can we go about adjusting/fixing it?

 

The first time the motor backfire it blew the power valve and the thing is running super rich. Along with the rebuild kit (it has a new power valve in it) get a power valve protector kit and install it during the rebuilt. Then a backfire won't blow the new power valve.

 

how do u know the power valve blew out? or is it a common thing? and can i get one of those locally?

 

In the older carbs, before Holley went to power valve protection, they blew all the time. That's why I recommend the power valve protection kit in the older carbs. Install it and the problem is solved for good. Yes, you local auto parts store should be able to get you one. I think Holley makes one as a spare part too.

 

sweet, thanx!

u happen to know how to adjust/test/check the choke?

 

Yeah, I do but the Holley site has an instructions page in their tech service area that explains it better than me.

http://www.holley.com/TechService/

 

thanx for all the help Bear!

 

I don't know about you but blown power valves are not a common problem with backfiring. Never had one do it myself, and I've have close to a hundred or more backfires over the years.

 

To really enjoy this lovely feature, you needed a truck with triple tanks and no gas gauges on the two saddle tanks. Be zippin' down the road and engine quits, reach down and switch tanks. Mind you that the engine is still rolling over at close to 2500 rpm (lots of vacuum) and when the carb first gets fuel the mixture is super lean, a nice big backfire. Not those little coughs you will expereince on start up. Even though I have lost a couple then too, but the carbs were old and the power valves were too. What really hurts is when you have just installed a nice inexpensive (I wish) two stage power valve.

 

ok we tried a few more things today, seemed to help a little but we didnt get a chance to drive it yet (dam rain!).

- checked the base timing and reset it back to 10* BTDC (seems it was set around 6* BTDC)

- tested to see if the power valve was blown, as someone on another site mentioned it. it wasnt and passed.

- we set the idle speed down a little more, it was idling around 1000-1100 and now its around 700.

- checked to see if the choke was operating and it is.

we also noticed a lot of debris in the fuel when we removed the fuel filter. it was like sediment, so we are going to run this tank of fuel down (bout 1/2 full) and clean the tank out.

to recap what the problem(s) are:
- it backfires through the carb on initial start up and backfires when pulling out from a stop (but not all the time) through the exhaust.

- it seems to be down on power a little, from what we can tell at least.

- it also seems to be breaking up or have a slight miss at cruising.

PS: i went to Holleys tech site to look for some info and came across an article about the power valve and back firing. seems around 1992 they began using the check valve because it was a problem with the pre-92 carbs. good lookin Bear!

 

are you running one of those Xri modules or similar. Mne was backfiring through the exhaust on acceleration from a stop. It turned out the wiring through the grommet was hindereing the plate from moving to advance timng with vacuum. And POW!!!! I slid some more wire through the grommet hole and looped it around the shaft/rotor so it would not bind up and walla..

 

yes we are...and good thinking...i will have to try that. if it works i will email u a beer LOL (wish i could if it does).

not that u mention it, it wasnt doing this with the points...(it did run really rough but no back firing, it starts easier now and seems to have better pick up than before)