Fouled Plugs

I have a '90 3.0 that I just did the following to: installed a new carb, put on a Petronix Ignitor II and Flamethrower coil, new set of plugs, wires, cap+rotor. It was timed to 8 deg. BTC and runs great on the muffs. After a run at about 3500 RPM she starts missing when I come back on the throttle. It has a bad miss for the rest of the day below 1200 RPM or so. It doesn't stall out but it sure runs like crap. I pulled the plugs and they were wet with gas and all carboned up! I've also got the nasty black soot line on the transom. I'm not sure where to go from here? Is it a matter of dialing in the carb or could it be something else? I've read a bunch of posts on 3.0 carb issues but can't find them now! Any suggestions would be GREATLY appreciated!

Re: Fouled Plugs

How is your choke adjustment. Is it full open when warm?
Did you adjust the idle mixture after installing the Pertronix and setting the timing? If not, you should have.

Re: Fouled Plugs

The choke WAS giving me some problems. The linkage was a little stiff and wasn't closing on cold start-up. I sprayed it with a dash of WD and it's looser now but I don't have the 5/64 ths opening in it when closed like the manual calls for. I can't figure out the diagram on which ear to bend for adjustment! I also had the tamper-proof cover on the mixture screw which I recall some wise sage had trouble with previouslyd I guess I'll try re-adjusting the mixture again although I thought it would only apply to lower RPM's and not cause fouling when running 1000 RPM or higher. I'll also re-check the timing because I couldn't locate the notch on the pulley origionally and used the probe in the #1 cylinder to locate TDC. Probably screwed that up as well!!

Re: Fouled Plugs

Just a quick question about this- I finally located the correct timing mark on the crank pulley and SURPRISE I was about 6 to 8 degrees off! It was probably running about 12-16 BTDC. Other than being totally off- would this cause the miss and fouling plugs? I think it's probably the cause, but I just wanted to check.

Also the choke linkage is still pretty stiff, when I advance the throttle prior to a cold start it doesn't always close the plate. I turned the adjustment to put more pressure on the linkage but now I'm afraid it will be running to rich cause the choke won't open all the way when warm! Is there any way of loosening the linkage to free it up?

As always, thanks for any help given! This is a phenominal forum for the rookie DYI'ers (as long as they listen)

Re: Fouled Plugs

I'm guessing timing at idle should be somehwere between 6-10 deg BTDC, and the advance is mechanical. If so then by having timing over-advanced 6+ degrees can be a bad thing if you run the motor at higher rpm. That's how you can burn holes in pistons, and also melt spark plugs. If you're having soaking wet plugs then the incorrect timing isn't as critical yet, if anything the over-rich mixture is saving you. Yes the off timing can cause a miss, in most cases if it's over-advanced it would be due to pre-ignition and/or disintigrating spark plugs. Certainly get the timing set correctly, and make sure the distributor is tightened down well so it doesn't lose it's setting. Your main problem is your carb. Just because it's a new carb doesn't mean it'll work 100% right out of the box without touching it, if you're smart you can buy one that will but do know that many times you will need to do some adjusting and tuning. What kind of carb is it?

Once the engine has been running for a minute, the choke flap should be fully open. Is it an electric choke? I'm confused when you say the linkage is stiff, do you mean it has some spring action to it? If it's not opening then you probably didn't connect the electric choke wires, you need one to ground and the other +12v coming from the ignition (+ side of coil). Otherwise if it's a mechanical choke, then you'll have to figure out why it isn't opening, and get it to stay fully open once the engine is running.

Re: Fouled Plugs

can we edit our posts yet ?

forgot to say, I wouldn't look or do anything further until you do the following, in order:

1) set timing to correct value and know you have it at the correct value.

2) make sure the choke is open fully when the engine is running.

only then can you proceed to tuning the carb and finding/fixing any other problems there might be.

Re: Fouled Plugs

The timing is now set to 8 degree's BTDC as required. It is definatley running better. The choke doesn't always close fully when first attempting to start it. When I move the throttle lever the Thermo-spring-or whatever the heck it's called- doesn't have the tension required to close the choke. It does, however, fully open after warming up. I'm leary about adjusting the dial to far as I'm afraid the choke won't open fully when warm. Will the choke continue to open regardless of where the adjustment is set until it's fully open?

I apologize if I'm not being clear but I'm having a tough time trying to describe the problem! On my old carb, when you move the throttle linkage the choke flap snaps closed. On the new one, it doesn't!

Thanks for the responses and again, I apologize if I'm not being clear!

Oh yeah- It's a Mercarb 2-BBL

Re: Fouled Plugs

with an electric choke, there's a "thermo-spring" (as you called it) housing on the side of the carb. Usually it's 3 screws on the outer end of the cover housing which clamps down a metal ring around the housing. this is what secures it so it won't rotate. what you do is loosen (do not remove) the 3 screws and rotate either the housing or the cover to it by hand. You'll see the choke flap either snap open and then have lots of spring tension when you try to close it by hand.... or it'll snap closed and have lots of spring tension when you try and open it by hand. Depends on which way you rotate the choke housing, because this determines the amount of tension from the thermo-spring which then determines how closed the choke will be at a given temperature and also how fast the choke will get to full open. There are also marks molded into the housing cover for marking position for this purpose.

Is it possible to set the choke closed too much where it won't open fully... I don't know but with an electric choke you'll never want it closed that hard. So I doubt you'll ever get it to that point. if you do, all you do is readjust it like I described, it's a 30 second procedure.

When the engine is cold, you don't necessarily need the choke flap closed completely. I have a 2002 3L, and I know with mine once it's been running for 20 seconds when cold it likes the choke flap fully open. I used to manually open it by hand till the electric choke heated up enough to keep it open until I took the time (30 seconds) to adjust it.

it may take a couple adjustments over a few outtings, where the motor has cooled off completely, to find the optimum choke setting when the motor is cold. What you do is before you start the motor the first time that day, and also before you ever turn the ignition key to run, is rotate the choke housing so the flap snaps open. Then rotate the housing the other way slowly and watch the flap close. Stop rotating when the flap is maybe 20 degrees, with 90 being fully open and 0 being shut tight.
Provided the carb and motor are in good health, if it doesn't start in a reasonable amount of cranks then you may need a little more choke. Readjust it a hair tighter next time out. The purpose of having just enough tension closed by the choke spring is so that it opens as fast as possible once the motor is running and the electric choke is getting power and opening. The reason you may have poor idle, soot lines, and nasty exhaust is because your choke is staying too closed for too long, causing too rich a fuel mixture.

Re: Fouled Plugs

Thanks ron700, I appreciate the feedback. I understand the principle of the choke and will try to "tweak" it over the next few days. I 'm sure I'll get it right sooner or later I'm just relieved that I caught the timing issue b-4 something REALLY bad happened!

It's been so long since I've owned a vehicle with an adjustable choke that I needed a refresher course.

Thanks again for the help!