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Discussion Starter · #1 ·
so before I stored my ride I noticed this problem before I stored my ride. Maybe you guys can help me get a bead on it before next season, I have some prep work to make it ready to drive regularly, anyway.

So I've noticed that when i'm driving at part throttle, acelerating slightly in the primaries (maybe 1/3-1/2 throttle, or even just 1/4 throttle cruising, come to think of it) the car feels like its ever so slightly catching and missing, catching and missing. Like pulling a little bit backing off slightly, pulling and off. Hard to explain.

Any ideas what is causing this? I have noticed that the car doesn't feel quite right under WOT either. It moves out pretty good, but it does feel a bit uneven and I do remember it pulling harder before. Any idears?

K
 

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Sounds like a possible lean condition. Lean "surging" did you notice the problem more as the weather got cooler?

Royce
 

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Discussion Starter · #3 ·
yeah, well, I did notice it just before I was going to put it away, so yeah, in the colder days. Also the plugs are reading orange like a halloween pumpkin. These are the second set, but the first ones that were driven in august and warmer weather were reading just on the lean side of normal too, same orange pumpkin color.

k
 

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Odd this post would come about. My car does the exact same thing with a road demon Jr. carb. it`s always did it since day 1, I`ve spoke with demon techies and did as they suggested and I`ve never gotten it out, I`ve richened the mixture, went to a correct size power valve, made certain the ignition was in good shape, played with different pump shots and cam pumps, and even went over the spark timing with a fine tooth comb and no matter if the advance comes in slow or fast it still does it, and now it seems to be getting worse now that cold weather is setting in, if anyone does have a answer to solve this problem I sure would be grateful also.
 

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my plugs show normal, a clean burn. I`ve checked for vacuum leaks in each line, none have been found. My modulator line is made of tubing, and I`ve checked it over and found nothing. I`ve lived with this problem as it is, even so it`s annoying at times, it`s worse at higher speeds, 70 mph on the interstate, then it only shows when you let off the pedal to slow down, it`ll have a dead spot. driving around at 45, it`s noticible but not as bad. when my car had a exhaust leak I noticed it smelled rich when it did this on the way to the exhaust shop, so since then I`ve been suspecting if the spark is getting weak at this point, but I don`t see how, since the coil and module is a flame thrower, cap, rotor, sprial core wires, ac plugs, are all almost new, I`ve did spark tests, the spark is always blue and strong.
 

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It`s always did it regardless of where the vacuum advance was connected, I even tried it with it completely removed, and added a stop device to limit it`s amount of advance, I suspected the problem was with the advance, but it`s not, no matter if the timing is set high or low still the same. that`s why I pretty much gave up fooling with it and just left it as it is. Remember just because something don`t work for someone else doesn`t mean it don`t work for another, manifold vacuum on my engine made a big difference, on engines with bigger cams, and bigger carbs such as holley`s that have always ran on the rich side don`t need a manifold vacuum advance or not as much advance, some don`t need the vacuum advance at all. My engine is close to stock, and it benefited greatly from it being connected to a manifold source. I wouldn`t lie about it, there would be nothing to gain by doing so, and I`ll let you drive my car with it on a ported then a manifold source, and let you judge the difference.
 

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DoubleVision said:
Odd this post would come about. My car does the exact same thing with a road demon Jr. carb. it`s always did it since day 1, I`ve spoke with demon techies and did as they suggested and I`ve never gotten it out, I`ve richened the mixture, went to a correct size power valve, made certain the ignition was in good shape, played with different pump shots and cam pumps, and even went over the spark timing with a fine tooth comb and no matter if the advance comes in slow or fast it still does it, and now it seems to be getting worse now that cold weather is setting in, if anyone does have a answer to solve this problem I sure would be grateful also.


Yes my Road Demon Jr does this too. I have also checked for vacuum leaks, richened, and everything. The only thing i can figure out with mine is that Demon recommends a 220* or less duration cam and the cam i am running is getting close the that. I also have to run the floats (primaries and Secondaries) half way up the sight glass or it will starve for fuel.
 

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i think you can increase the throttle sensitivity by running a higher initial timming. i run a demon750 and it likes 18deg initial. and about 34 deg total at 2800rpm. i dont know if this is exactly what your talking about. as a matter of fact, i dont like to run vac advance on the street. i believe there is some delay in its operation that could cause a detonation condition. check out 4secondsflat.com and read there write up on demon setup.

i also like to set demons up so that the idlemix screws are .75-1 turns out.

couple of ideas
 

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If his plugs are light colored, I seriously doubt it is a power valve problem. I bet with the colder air, he is just a little on the lean side. This would also explain the light plug color.

Are you thinking the PV is not opening? If that was the case I suppose that would cause a lean condition as well.

Royce
 

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Technical Support Barry Grant
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Surge @ light throttle

Normally a surge at little throttle is going to be a lean condition. Especially if the problem becomes worse as the weather gets colder.

If this is happening at a steady speed as noted, this will most likely not be in the PV sizing. It would most likely be that the main metering jets are not large enough, or that the float levels are not high enough. Raising the float levels up will start the main circuits in the carburetor a touch quicker. This may take care of your situation.

Working with carburetors is extremely simple, if you're having a problem (and we're working with the proper carburetor for the application) it is either too rich or too lean. If you're not sure what the problem is, add fuel. If you're having a rich or lean situation, adding fuel has to make the problem better or worse. It's always safer to add fuel first, then take it back out if need be.
 

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1BAD and I exchanged emails regarding this post since what he said made sense to me, I read up on the subject elsewhere and found others who found the problem to be one in the same. I swapped back to a 6.5 power valve and the dead spot is gone. All I have to do now is wait until the jets I ordered come in since it`s running slightly lean at cruise, I would have just gotten them in town, but the only parts store in town that carried them recently went under.
 
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