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Old 03-09-2013, 11:18 AM
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Black sooty spark plugs

Hello,

I know that black sooty spark plugs means you have a rich condition but I need some direction as to what may be causing that and how to fix.

I have just put in a new carb (quickfuel ss 680 as recommended by engine builder shop as my previous one was way too small for the engine) and the truck was running fine until I started to try to fine tune it. I obviously messed something up so I need some help moving forward.

I followed the instructions provided to me by the shop I bought the quickfuel from to set it up. (note that timing continues to be locked in and verified with a good gun at initial 18 degrees with mechanical advance stop at 36; vacuum is disconnected for now)
- Set idle transfer slot on primary to 0.035, secondary is closed (when running it had to up the trottle a little, 1 turn, to keep it running as the idle was too low so transfer slot will now be open more)
- Set accelerator spring to just be touching the pump arm
- set idle mixture (4 corner carb) to be 1 turn out at primaries and 3/4 on secondaries as a start
- float is set to middle of sight window as noted in the quickfuel manual where it should. (and I taked with quickfuel and they verified that is where it should be).

So what is happening:
- when I start the truck is it runs fine (idles at 1000) for about 10 seconds and then stalls; trying to keep it going is a losing battle as eventually it will stall. I even took it up to 3000 rpm but then I started hearing backfiring and then it stalled.

I'm assuming too much fuel is being delivered into the carb but not sure how to resolve? I was thinking about dialing down the idle mixture screws on the primary to 1/2 turn but right now I have all plugs out and I'm cleaning them.

Thanks for any help.

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Old 03-09-2013, 11:27 AM
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Check secondary plate adjustment for lack of volume. Check float level, needle operation for fuel starvation..Tell us more.
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Old 03-09-2013, 12:51 PM
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Idling for an extended period of time will turn the plugs black. To geta good plug reading you should run it at full throttle for a period of time, then shut it off immediately and read the plugs without idle time on them.
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Old 03-09-2013, 01:42 PM
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Idling now but stalling

Ok, thanks for that jaw22w, that makes sense. I have been pretty much idling it all the time in doing the setup with rare bursts to full power.

Spinn, float level is verified and correct. I cleaned the needles before this weekend and I have a 40 micron filter before them so I think good. How do you check secondary plate for volume? I set secondary setting as per recommended for my engine by the builder I purchased quickfuel carb from.


I do have it running consistenly now but it requires me to hold the choke plate so still an issue.

I watched it run from cold engine all the way to warmup and the truck idles fine when the choke plate is closed (i.e. cold engine), it idles better when the plate starts to open a little but then, as the plate opens more and more to full open eventually the engine stalls (it gets up to 2000 rpm).

I was able to play with the choke plate to see what would happen and if I held it about 80% closed truck ran fine, as I let it open more it would speed up the idle significantly (without moving the idle speed screw) and eventually would start to stall until I closed the choke plate back down to a smaller opening. This was repeatable.

So, couple of thoughts/questions:
1. Too much air and not enough fuel when plate is fully open?
2. Is the choke plate supposed to fully open during idle when engine is hot? I thought it only opened fully when you tromped on it.

Thanks for the continued help
Gary

Edit: Oh Yeah, I will do the hot run and then turn off to check plug status; unfortunately the truck doesn't really have windows at this time as it is still being built so road trips are out of the question for now.
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Old 03-09-2013, 03:05 PM
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Choke should be off/ fully opened when engine is hot. Do you know what the fuel pressure is at?
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Old 03-09-2013, 03:50 PM
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Have you checked for vacuum leaks?

If the mixture settings are close, and it will only run with the choke partially closed, I would be looking for a vacuum leak. Fix any leaks you find, warm the engine, choke fully open and then set the idle mixture and the idle speed at the same time. If the primary throttle plates are open to far just to keep it running, you will never be able to set the idle mixture properly. Make sure the plates are closed or nearly closed on the primary and closed completely on the secondary. Then tune it, it should idle all day if set properly, that is if you don't have a high lift cam. Adjust primary first to get it to idle, then tweak the secondary idle circuit to smooth it out.

Regards,

Andy
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Old 03-09-2013, 04:54 PM
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Plug your vacuum advance in to manifold vacuum source then Idle it down to get adjustment back on your carb.
I assume you're working in a heated garage!
What intake are you using?
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Old 03-09-2013, 05:35 PM
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Ongoing saga

Hi, I went back to baselining everything (idle transfer slot at 0.035, secondary closed, mixture screws all at 1 turn out) and now I have it idling somewhat (18 degrees initial @ 900 rpm) but I'm hearing low volume backfiring from the tailpipes when I go close to them; just audible enough when close. jeez. I also noted surging between 600 rpm and 1000 rpm but at least it seems to keep running. Also, when I put it in drive and stepped on the gas, instant stall.

To answer some of the question below:
* I verified that choke is off; took a while to get it off as I could not keep it running long enough to get it hot; managed to get it hot in the last hour as I managed to keep it running by keeping the choke plate mostly closed manually. I also took the fast idle totally out of the picture by dialing it back so much that it wasn't doing anything. I am doing any fast idling needs when cold by hand (not having windows in a truck is handy to reach out through
* Fuel pressure gauge at carb shows average of 7 psi (bounces between 6 and 8 at idle, gets more stable when you go up in RPM)
* I checked and rechecked and just now checked again for vacuum leaks; there are none that I can find but I will check yet again. I verified all connections and used propane around every part of the intake/carb/lines so I'm pretty confident no vacuum leaks but if that is what is causing it there must be one somewhere then.
* Vacuum advance has been disconnected all along and plugged at carb and vacuum pot; wasn't planning on involving that until carb is dialed in as I don't want it messing with my initial timing and rpm.
* No, I was working outside as it was 6 degrees and sunny today
* Running edelbrock performer EPS dual plane intake.

* Primary idle transfer slot is set to 0.035"; secondary is set to just closed. Unfortunately the engine cannot run at that setting (RPM too low) so I had to increase the idle screw one turn. My plan is as I'm dialing in the air mixture screws I would be slowly bringing the idle back down that one turn until, in the end, everything comes together and I have a properly idling engine - at least that's my thought but haven't been able to get there yet.
* Cam: 450 lift, 224 duration, 106 lobe centre

Thank You for your continued assistance.
G


Last edited by ggevaert; 03-09-2013 at 05:42 PM.
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Old 03-09-2013, 05:55 PM
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Easiest way to dial carb in is to plug in the vacuum advance. It's all part of the tuning system.
Your need for lots of choke is due to the cold air you're pulling in to your carb. Cold unheated air mixed with fuel doesn't stay a vapour when it gets in your cold intake.
Are you tuning with a open element air cleaner and did you block off the heat crossover in the intake?
Your intake is staying cold for a long time. And your motor takes longer to warm up and radiate heat up to your intake.
Trying to tune your motor at 6* is mostly a waste of time. Wait till it warms up over 15*.
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Old 03-09-2013, 08:59 PM
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By the way for reading the plugs, when I said to run the engine at full throttle for a period of time, I meant with the engine underload (with the truck running down the road not sitting in the garage!). Of course with no windows in the truck that will be hard to do.
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Old 03-09-2013, 09:46 PM
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Try closing the idle transfer slot a little and open up the secondary transfer slot so they are both open about the same. You said you opened the idle transfer slot a little and it was at .035 so now it is open more. This may be too much. Try to balance the opening between both slots as they should both be open about the same. Sometimes large cams can make this a tricky adjustment. Also you may need about 20* initial timing with a larger cam. Good luck
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Old 03-09-2013, 10:34 PM
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Ongoing work

Thanks for all the replies folks; all very helpful.

Looks like I'll have to invest in some exhaust lines as I can get the garage to 15 degrees easy enough but not without 'exhausting' the rest of us inside. Typically we shove the tail end of the truck outside and close the door on the box and then run it (so the engine would be around 15?). Anyway, lets hope it gets warmer soon so I can get this resolved.

I went over the entire engine intake systems and verified they were at the correct torque (they were) and that nothing was an open source of vacuum. I could not find anything.

RWENUTS, open air element, there is no heat riser in my setup.
jaw22w, thanks, hence my struggle. I'm thinking to get the windows finished now so I can at least go for a drive. (although then I need to put the entire front section on and the hood as well and that will make it more challenging to work on this motor ). I wish I had a private track !

cadillacdave1; Thank You, I had 24 degrees initial timing a couple of weeks ago (before I started mucking with the carb and it was working) but opted to go back down to 18 as there is a school of thought that I agree with that having more mechanical advance range allows for more flexibility during street driving.
Also, I agree it is too much transfer slot but my plan was to fix the idle mixture screws and that would allow me to lower the idle back to where it should be.

I should also note that the carb came with upgraded idle air bleeds (increased from stock 70 to 74 size). Quickfuel told me this would be needed to compensate for the came I had.

Cheers.
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Old 03-10-2013, 07:40 PM
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You are driving around without a vacuum advance? That will make your plugs sooty.

Depending on your cam you could need more advance at idle. To get a clean idle burn and cruise you would need some additional provided by a manifold source.

If you have driven modern cars with a obd scantool , you can watch how they time live. I try to copy what they do.

There is a good crankshaft coalition link , but I don't have it.
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Old 03-10-2013, 11:09 PM
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whats the fuel pressure, lower the floats maybe
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Old 04-27-2013, 07:21 AM
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resolved

Just to wrap this thread up (pet peeve of mine is when there is heavy discussion on an item but the resolution is not listed )

This is now resolved; truck is idling like a champ
Thanks for everyone's input!

Summary:
* put windows in truck so now I could do street runs and get some load on the engine.
* went 3 levels up in heat with my spark plugs to Ac Delco R45TS's (still finalizes that, looks like I may need to go down one level but more WOT runs will tell me that)
* Hooked up an A/F gauge and it showed an extreme lean condition which caused the engine to stall a the low RPM.
* properly set my idle mixture screws using both the vacuum gauge and tapping the accelerator methods to get the maximum RPM and vacuum. (they are at 0.8 turns out on all 4).
* verified float bowl level and fuel pressure are where they should be.
* final timing is 20 degrees with 16 degrees of mechanical advance maximum. Vacuum advance kicks in right away; I have 32 degrees timing at idle. (using full manifold vacuum, not ported)
* At that point she was idling and running great in all aspects except there was a momentary lean around 1500 rpm so I adjusted the T-slots for both primary and secondary (by adjusting the idle speed screws). I opened the primaries by 0.010" and closed secondaries by same (so that are now at 0.050 and 0.030) and that solved that issue.

Cheers

Last edited by ggevaert; 04-27-2013 at 07:26 AM.
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