"advance" ghost?
02-24-10, 10:46 PM
#1
"advance" ghost?
my 12a keeps advancing on it's own, then back to slow, then back advanced etc, etc. I have tried changing the idle etc. it advances about 1,000 rpm no matter if I'm idfling at 500 or 2000. I have a weber sidesraft, so no vac advance hooked up. When my efan kicks on, it sort of smoothes out temporarliy. I'm lost! my first project and all these weid issues. 
It's giving me a complex. LOL Wife thinks I'm cursed.
It's giving me a complex. LOL Wife thinks I'm cursed.
02-25-10, 07:59 AM
#7
Nobody has any ideas? Taco7 is tomorrow and I'd like to take my 7. But I'd like to be able to be reasonably certain it's going to make it too.
BTW- fuel pressure doesn't fluctuate, it's rock solid at a hair over 3 psi. My jetting is as follows
250 needle and seat
f11 e-tubes
55 pump jets
175 mains
60 f8 idle
160 a/c
Also put the timing light on it when it was at "slow" idle and it's dead on the timing marks on both leading and trailing.
Ignition is stock, new plugs and wires, only vac lines are one from booster to intake and from crank case to intake.
BTW- fuel pressure doesn't fluctuate, it's rock solid at a hair over 3 psi. My jetting is as follows
250 needle and seat
f11 e-tubes
55 pump jets
175 mains
60 f8 idle
160 a/c
Also put the timing light on it when it was at "slow" idle and it's dead on the timing marks on both leading and trailing.
Ignition is stock, new plugs and wires, only vac lines are one from booster to intake and from crank case to intake.
Last edited by installer67; 02-25-10 at 08:03 AM.
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02-25-10, 08:36 AM
#9
thought that was a possibility, but if so, not sure where it is or why it comes and goes. intake bolts are all very tight. only vac is booster and crankcase, and it doesn't seem to be coming from there either. I may pull the intake today and put some rtv on the new gasket and re install, it's just about the only thing I can think of that I haven't done.
02-25-10, 10:08 AM
#10
Assuming it's a "real" RPM fluctuation (and not a tach issue).
Is your ignition stock?
Does it only happen at idle, or will it do this under load, too?
About how long is the 'cycle' time? In other words, how quickly does it repeat?
Is it random in length, or does it have a pattern?
Just thinking out loud with you. Vacuum leak is the more obvious thought because mix plus throttle opening equals idle speed, but fluctuation in the fuel feed could do the same thing.
Sticky float pivot that lets the bowl level drop or rise too much before moving, maybe?
Is your ignition stock?
Does it only happen at idle, or will it do this under load, too?
About how long is the 'cycle' time? In other words, how quickly does it repeat?
Is it random in length, or does it have a pattern?
Just thinking out loud with you. Vacuum leak is the more obvious thought because mix plus throttle opening equals idle speed, but fluctuation in the fuel feed could do the same thing.
Sticky float pivot that lets the bowl level drop or rise too much before moving, maybe?
02-25-10, 10:55 AM
#11
It's definately real rpm fluctuation, the engine idle starts out ok, then increases, had to look at the tach to see how much, but it's noticeable. idle changes for 30 to 45 seconds or so, back and forth. Ignition is stock. only happens at idle. acceleration seems even. I pulled the carbs hat and checked the float when I replaced the needle and seat, nice and smooth, no sticking. Also pulled the little filter in the carb just to check, all clear there to. Still considering vac leak, but can't make sense of the "cycle" if that's what it is. I've checked the booster line and the crank vent line, no leaks. stumped.
02-25-10, 12:27 PM
#12
I don't know a thing about webers, but Percent does. But anyway my unlearned opinion is the carb has been going between idle circuit and main circuit. If you trust it enough to take it to Taco7, Percent could probably swap in a jet or air bleed or two from his weber to see if the idle will settle down.
02-25-10, 12:27 PM
#13
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so just to be clear. if you start it up, it'll idle @800, and without you touching anything the idle speed will change?
if you have it idling @ 800, then open the throttle and close it, and the RPM is different, that would be like a sticking throttle.
if its changing on its own, i'd be looking at the brake booster, throttle cable being too tight, or there might be something in the carb (dunno about the DCOE, but maybe the choke circuit? or anything with a spring?)
it might be possible to have the mechanical advance be coming in too, so that the higher it revs the higher it WANTS to rev, but this is unlikely IMO
if you have it idling @ 800, then open the throttle and close it, and the RPM is different, that would be like a sticking throttle.
if its changing on its own, i'd be looking at the brake booster, throttle cable being too tight, or there might be something in the carb (dunno about the DCOE, but maybe the choke circuit? or anything with a spring?)
it might be possible to have the mechanical advance be coming in too, so that the higher it revs the higher it WANTS to rev, but this is unlikely IMO
02-25-10, 09:04 PM
#14
Yes, it will idle at about 800 rpm, and then suddenly idle up to 12 or so then hold there a while, then go back down and so forth, throttle cable isn't tense, so it's not that. I did raise the idle up to about 1000 to 1100, because it's an early opening street port. That was recomended by the builder/previous owner. It still fluctuates though. I'll have to look at the FSM to see how to test the brake booster. Or maybe I'll just disconnect it and put a vac plug over the nipple and see if that makes it better. The dcoe does have a starter circuit, but I don't have it hooked up. It certainly acts like the mechanical advance though, but clueless as to why or what to do if it is. LOL
Jeff - It is running enough to take to Taco7, and I just got a handfull of jets tubes etc. in. I'm going to bring my kit in case someone there knows webers and can be of help. It DEFINATELY needs tuning. I'm ******* all through the low end and good up top. I hit 4000 and Ive got a raped ape, but under that and shes a chimp with the *****.
I am running the same jetting setup the PO ran, even the same carb setup. But my weber is an old style dcoe 9, I think that may have something to do with the tuning. But this is my first sidedraft too, so I'm just searching for my *** with both hands and no map. LOL
Jeff - It is running enough to take to Taco7, and I just got a handfull of jets tubes etc. in. I'm going to bring my kit in case someone there knows webers and can be of help. It DEFINATELY needs tuning. I'm ******* all through the low end and good up top. I hit 4000 and Ive got a raped ape, but under that and shes a chimp with the *****.
I am running the same jetting setup the PO ran, even the same carb setup. But my weber is an old style dcoe 9, I think that may have something to do with the tuning. But this is my first sidedraft too, so I'm just searching for my *** with both hands and no map. LOL
02-26-10, 10:59 AM
#15
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Yes, it will idle at about 800 rpm, and then suddenly idle up to 12 or so then hold there a while, then go back down and so forth, throttle cable isn't tense, so it's not that. I did raise the idle up to about 1000 to 1100, because it's an early opening street port. That was recomended by the builder/previous owner. It still fluctuates though. I'll have to look at the FSM to see how to test the brake booster. Or maybe I'll just disconnect it and put a vac plug over the nipple and see if that makes it better. The dcoe does have a starter circuit, but I don't have it hooked up. It certainly acts like the mechanical advance though, but clueless as to why or what to do if it is. LOL
Jeff - It is running enough to take to Taco7, and I just got a handfull of jets tubes etc. in. I'm going to bring my kit in case someone there knows webers and can be of help. It DEFINATELY needs tuning. I'm ******* all through the low end and good up top. I hit 4000 and Ive got a raped ape, but under that and shes a chimp with the *****. I am running the same jetting setup the PO ran, even the same carb setup. But my weber is an old style dcoe 9, I think that may have something to do with the tuning. But this is my first sidedraft too, so I'm just searching for my *** with both hands and no map. LOL
Jeff - It is running enough to take to Taco7, and I just got a handfull of jets tubes etc. in. I'm going to bring my kit in case someone there knows webers and can be of help. It DEFINATELY needs tuning. I'm ******* all through the low end and good up top. I hit 4000 and Ive got a raped ape, but under that and shes a chimp with the *****.
I am running the same jetting setup the PO ran, even the same carb setup. But my weber is an old style dcoe 9, I think that may have something to do with the tuning. But this is my first sidedraft too, so I'm just searching for my *** with both hands and no map. LOLi'd also play with the starter circuit and make sure its OFF
jeff could be right too, although the IDA doesn't really do that, so i'd put it in the unlikely column
03-01-10, 10:10 AM
#20
idle issues
New 91 alternator is on the way! Hopefully that will help, other one is grinding either way so it's time. Idle is much better after pulling crankcase vent off intake and puting a "T" between the runners to the booster. It evened out the idle considerably.
03-20-10, 01:58 AM
#21
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Check where the carb mounts to the intake and be sure those nuts are tightened down good. Also be sure the air control valves that go into the choke tubes are closed completely. I'm using the DCOE as well, have u tried the 65f9 idle jets?
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