I have a '69 350 with a Holley 4bl vacuum secondaries, electric choke and an Edelbrock Performer intake. Earlier today I tried to start it and it caught but then when I gave it gas a pretty large flame shot back through the carb. I had the hood up and air cleaner off so it was easy to put out.
The car ran fine a couple days ago and I verified the timing at 11 degrees BTDC within the last week. Since then I've done two things:
1) I was messing around with the accelerator pump cam, mechanism and squirter to get a good constant squirt. I probably ended up dumping a bunch of fuel into it last night through my messing around and today was the first time I tried to start it. It didn't smell flooded last night though.
2) I've noticed recently that my choke hasn't been working and it's getting colder here in Michigan! I put Holley's quick change vacuum secondary housing on over the summer and hooked the ground wire to the plastic housing with a bit of a metal connection. I thought that's where the instructions said to put the ground put it seems like it's mostly plastic. I used my voltmeter and it wasn't working so I moved the ground to one of the choke housing bolts. I took the bolt out, put the ground connector over the end and attached back to the body of the carb. The voltmeter gave me a good reading - although I can't remember if it was a full 12V or more like 8-9V. That was the last thing I did before trying to start the car and the fire came out the carb.
I subsequently read that you can put the ground to the outside of the choke cover, not the main body. I've now also started it again (after cleanup) with the choke disconnected and no fire. Could the ground being to the choke housing have somehow sparked inside the carb and ignited the gas? Just dumping a bunch of gas in last night shouldn't cause any issues, should it? This is a mystery that I hope is now solved so I can drive in peace!
The power for the choke is supposed to be connected to the tab on the black bakelite plastic. If there is a ground, connect it to a carb base nut.
Also , sounds like you need to adjust your choke spring in that black plastic cover when motor is cold. Also adjust the red fast idle cam to a desired start up speed.
You can adjust that choke coil spring to barely close the air horn opening. I usually adjust it against a pencil or something with an id of about 1/4" .
If you are still confused, search the internet for instructions. Doing this is normally like making duck soup, just can't mess it up.
Yeah - I definitely need to get the choke set up properly. I'm still curious, could having the ground at the wrong spot on the carb (or some other setting with the choke) cause the flames out of the carb? If I'm getting 12V from the power source but reading only 8-9V at the positive and negative posts on the choke cap, does that mean there's some energy escaping somewhere - like inside the carb? I'd like to wrap my mind around why I got the flame in the first place so it doesn't happen again!
My thought is , this 12 v wire, is coming from a resistor wire or the wire itself ? Where are you getting power from for this choke?
As for flame out the carb, you may have something else wrong here as the flame is actually coming from and open engine valve when you were pumping the throttle, its back fire. Its ignition firing up raw fuel in the intake side cly head chamber or intake runner in the manifold.
I have even seen cross fire between plug wires. These wires need to be separated
Brad,
Attached is a photo of how I've wired my choke. The purple wire connected to the + connector on the choke housing runs to a 12v source on the fuse block that is only hot when the motor is running. The choke housing bolt connects to the metal choke housing providing a direct ground through the 4 bolts holding the carb to the manifold. You should be getting 12v to the choke. As for the fire, I doubt it's choke related. How are your float levels?
Chris - My setup was similar to this. I didn't install the choke so I'm not 100% sure where the positive is coming from but it runs from somewhere by the ignition and is definitely an ignition-controlled power source. The difference I had when I had the flame up was that I connected my ground to the actual choke housing screw, not the cover like yours is. Mine was on the left one of the two screws that go into the body of the carb above the choke setting marks. I made that change because I wasn't getting a good ground off the quick-change vacuum secondary housing I installed earlier this summer. I made that change right before the start-up where I got the flame so it seems like a big coincidence if the two aren't related.
Overall the cars been running really good all season. I've been tuning on the carb a decent amount and have had no issues - just playing around with jet size, pump size, pump cam, secondary springs, etc. I check the float level, idle mix and vacuum pretty regularly. The float is just below the inspection hole - just a little gas comes out when the vehicle is rocked. I set the idle mix pretty lean and slowly bring it back with my vacuum gauge to get it maximized. I also check the timing fairly regularly and keep it at a decent but not too aggressive advance (10-12 BTDC).
I get the theory of things like stuck valves, cross ignition, timing being off, etc. I just find it odd that it happened when I made the ground change and the only other change I made since driving it was the day before and was just the pump cam. I'm probably hoping to convince myself (or be convinced) that it was the choke as I can fix that. The unknown of what would cause the fire makes me a bit nervous to get it back out on the road...
I'm pretty much convinced now that it was the choke ground that caused the flame-up, although I can't really prove out why. I started the car again today (flame-up was yesterday) still with the choke disconnected. It started up fine multiple times, idled fine and no flames even with revving. I checked the timing and I'm still right at 11 BTDC and my vacuum gauge is holding very steady right at 20. I have a mild cam and a dual plane intake so that's pretty normal. Seems to me like if it was that big of a rich / lean thing of if I had a stuck valve my vacuum would be off, right (either down or jumping around)? Plus its definitely not a timing thing since that hasn't moved. I'm going to try it again over the next couple of days and then take it out for a test drive. I'll figure out what to do with the choke later - I'll probably try moving the ground to the choke cover, directly to a carb stud or maybe just to a non carb/intake ground source to avoid all that aluminum entirely.
One observation that maybe Im not seeing... is the intake aluminum? Are Holley carbs aluminum? I dont know if Alum. is as good as steel for grounding or not. If your ground is per instructions its probably ok but are instructions assuming steel intake and steel carb? Just something to consider if it happens again. Easy to run your pigtail down to the grounding strap on the valve cover anytime you want.
Agreed. My intake is definitely aluminum - not sure about the carb. And my problem was that I wasn't following any instructions! Lesson learned for sure. Although it does puzzle me why Chris' ground above works fine attached to the choke cover but mine to the housing caused issues. Not sure if that's a sign of something else wrong in the choke setup or not. Electrical matters aware definitely not my area of expertise.
Use a relay and draw power from the field terminal of the alternator. That way the only time the choke coil is hot is when the engine is running. The power from the alternator field terminal will pull in the relay and 12 volts will be applied when the relay coil is energized.
Brad and Click, I have had my choke neg attached to manifold base for long time. I have never had issues with ground. If you suspect no ground on that ground wire, put a fluke on it. I still feel its part of the fuel that was dumped when messing with other components.
Brad,
I agree with Jerry on the raw fuel causing the flame-up. The choke only controls the angle of the butterfly and the rpm until it warms up. i ran a wire from the "IGN" spade connector on my fuse block inside the car to the + on the choke body guaranteeing a 12v source without splicing into some other wire elsewhere and it's only hot when the car is runnng. Don't use the "ACC" spade connection in the fuse block as this is hot when the key is in the ACC position and the motor is not running. Yesterday, I switched my negative connector on the choke to one of the bolts holding the choke to the carb like you've connected your as that actuallly matches the location recommended by Holley. As for the conductivity of aluminum, all high tension power transmission lines are made of aluminum; its an excellent conductor. By the way, call me paranoid, but I carry a fire extenguisher behind my driver's seat just in case something completely unexpected goes wrong, you never know with these old cars even though we spend a lot of time on them.
Just to throw something crazy out, could there be a loose connection on the choke wiring to where when the conditions were right with the fuel and air, an intermittent and/or poor connection sparked and lit things up ?.
Thanks for the input everyone. This is definitely an interesting conversation and I'll make sure I follow the proper steps when I hook the choke back up. I'm fairly new at this but I'm still with Jim wondering if the choke somehow sparked it. Can flooding your carb or intake really cause a flare up barring already having some other issue with how the engine runs? And all the other signs suggest I don't have an issue like a stuck valve or something. Plus, I was messing around with the carb about 16 hours before the flare up - wouldn't that have cleared out by then or is the gas really trapped in an intake with the throttle closed? Last piece of evidence - I'm pretty sure when I had the choke hooked up it only read 8-9V when I used the voltmeter on the positive and negative posts. But when I used it just on the positive and grounded the negative to the engine it read 12V. Does that suggest some juice was "leaking" somewhere that could have been my spark? Sorry if that's a dumb question - the electrical stuff is still a bit of a mystery to me.
The low voltage indicates a poor ground connection. Fire out the carb is most often a timing issue in my experience. If it completely stops when you disconnect and tape up the choke wires it probably is somehow related to that but sure seems unusual. I would double check the plug wires too and make sure the rotor is pointing at #1 when that cylinder is at TDC on the compression stroke.
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