Stumped

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gumper said:
One thing I didn't mention is it slowed the car to a 9 second 1/8 time, over a second off what I run with the air-gap. It's a very significant stutter. When I launch it's off the two step at 3000 with the carb already wide open, and it flashes to 4000. I pulled the plugs just now and they are all black all the way down into the base of the porcelain. The tips of 1/2/8 are tan in color, and 3/4/6 are all black. This was just after idling for a few minutes, so that throws things off a bit. The burn on the strap is right on the bend.
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The highlighted in black is exactly the issues with to much intake. This is your proof. Not that it can't be worked out. I just really do not think you'll like the way it gets worked out.


gumper said:
I can't believe that this swap would kill everything so bad.
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gumper said:
..
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Oh yea! It sure can. IMO, if you wanted a single plane intake up top, I would have suggested a M1 single. But then again, it may not have paid off ether.
Sorry to say, I think you need to change the intake again.
 
If you roll out of it when it occurs and it picks up, then as you roll back into the throttle to WOT and it happens again, I'll guess it's likely real rich.

I'd try jetting down to 90 or 92 square and see if it cleans up.
 
No I cleaned them up. Very thin layer of carbon. With the air-gap they were tan on the porcelain. It sounds incredibly unrealistic, but could it be too rich since now each cylinder is getting the full carb instead of half due to the air-gap being divided? I wouldn't think it'd stutter under WOT with too much fuel, but at this point I have no other ideas. Can richen it up a few sizes first then try the other direction.
 
rumblefish360 said:
The highlighted in black is exactly the issues with to much intake. This is your proof. Not that it can't be worked out. I just really do not think you'll like the way it gets worked out.
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How can it get worked out?
 
My two cents and this happened to my engine before it went to level ten. My car runs great then when try to tune the most power out I could I took out the Power Valves and blocked, then added the extra jets size to compensate. Every time I shifted I would get a huge stumble then power would come back on as RPM came up. I put the power valve back in the primary side and the problem went away. At this point it could be worth a shot. Just my two cents. Make sure power valve is half of the idle vacuum.
 
Flyfish worked it out earlier on his ride. He would be the one to ask how he over came the same issue your having now. He described it some in his post.
 
I had a 6.5 power valve in Friday and it ran way worse than now with it plugged. Maybe it's pointing toward too rich?
 
flyfish said:
Be careful with assuming...I know, at least for me, a lot of times when I'm working on my car something totally unrelated to what I'm working on breaks while I'm working.
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I can't help but thinking that way myself, as I've been there many times also. I've thought about things "outside the box", but the statement below is hard to argue with anything outside the intake swap/carb tune?

gumper said:
I rule out anything unrelated to the intake since the same problem was happening Friday with the super victor, and when I put the air-gap back on Saturday the car ran just fine. Put the SV on again yesterday, and the problem came back.
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That's what makes this so tough. It's hard to go against the A-B-A testing you've done.



Just a comment: Stuttering issue aside.....I wouldn't be surprised if the car slowed a hair with the SV in the 1/8th mile. With a shift point at 5500, the time you spend in the sweet spot for that intake is really short.....Unless you're geared for the 1/8th, it's only the top of 1st/2nd gear. I personally think it would really shine in the 1/4 mile where you can leg out 3rd gear running some rpm for a decent amount of time.


I haven't given up trying to help, I just don't know where to go at this point.
 
I put 88/89 jets on to see if it helps, but I have to try it tomorrow. The 95 jet is .118 and the 89 is .105, quite a jump.

I'm running 4.30 gears with 28" tires. It is wound out about 6000 in the 1/4. It may not speed me up, and if not I'll swap back. I have read of several people picking up 2 tenths in the 1/4 over the AG. Main reason why I bought the SV was I want to run it with a new set of heads and a bigger cam next year, and my gift certificate to edelbrock expired 8/14. Nothing else they sell appeals to me.
 
Tried the smaller jets, it made it better as in it doesn't stumble much. A little bit as soon as I get on it but then it goes like hell. Pull two plugs; one is brown and the other still black. Going to drop 10 more hole sizes and try again (I dropped 15 last time).

I do have a question: is it normal to have the vacuum gauge drop to 2 at full throttle? Cruising at street speed I see 15-20. Wide open it drops to almost no vacuum. Since that's not feasible, must be a gauge issue?

Also, does anyone have jet advice? I've run staggered and square, any pros/cons to either way? Square in my mind would be better for all out performance.
 
Ok then, it's normal. What's the reasoning behind it having so little vacuum when it's pulling so much more air?
 
Because when at WOT you have completely opened the manifold to atmospheric pressure. Like when you cover a vacuum cleaner with your hand then pull it away.
 
I think a lot of your issue here is that your carb has been tuned in to left field. You need to bring it back to out of the box specs ie jetting, power valve, nozzles, pump cams. Many problems such as yours develop when the carb gets tuned way out side of the factory configuration.
 
Other than jets and blocking the PV it's the same as it came from bigs.

I'm at 77/78 jets now, and there's zero stumble. Not only that but it has very good response and flat hauls ***. Have to get to the track to do some finer tuning, but I have high expectations. The idle vacuum is up to 10 in hg.
 
I'm going to use my 1" open wood one for now. Anyone have good luck with a specific 4 hole? I've tried them and the open seemed better.
 
Using an open spacer is like going to an intake with a bigger plenum. That's what you're trying to get away from.
 
skrews said:
Because when at WOT you have completely opened the manifold to atmospheric pressure. Like when you cover a vacuum cleaner with your hand then pull it away.
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^^^ Exactly....very little manifold vaccum at WOT; your hand over the vacuum cleaner's opening is like the throttle plate being partly closed. BTW, your driveway tests reported earlier are likley not accurate due to the lack of any sustained load, and the drop to near 0 when you snapped the throttle shut sounds like you were measuring ported vaccum, not manifold vacuum. All the power valve settings, etc. that I can recall are based on manifold vacuum.
 
nm9stheham said:
^^^ Exactly....very little manifold vaccum at WOT; your hand over the vacuum cleaner's opening is like the throttle plate being partly closed. BTW, your driveway tests reported earlier are likley not accurate due to the lack of any sustained load, and the drop to near 0 when you snapped the throttle shut sounds like you were measuring ported vaccum, not manifold vacuum. All the power valve settings, etc. that I can recall are based on manifold vacuum.
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It would drop down when I'd open the throttle quickly. I since then ran the gauge to my window and took it for a drive which is where I have taken numbers since. I was using the port off the carb base plate, there's no others. I was hoping to see if there was a manifold vacuum leak causing my stuttering. And as it turns out it was just too much fuel.
 
I have a 410 with eddies,flat tops,flat tapet solid cam.10.5 to 1 and I have found that the car leaves better and runs more mph at the track with 32 deg. timming.Your car may want more but don't be afraid to try a little less timming.Good luck
 
I'll use this Friday at the track as a tuning day. Figure out some jetting and try a little less timing. Until the manifold swap I haven't messed with any tuning other than jet changes for altitude in a few years.
 
Yeah I read that the jet changes did the trick....quite a jump. The manifold change must have moved the vacuum 'signal' up further in to the carb throat and closer to the venturis and sucked out more fuel...not shocked but it's always very interesting to see this type of thing. Any spacer may move that point again. It'll be good to hear your times now.
 
I am surprised I had to jet down for the open manifold, but I have my theories why.
 
gumper said:
Other than jets and blocking the PV it's the same as it came from bigs.

I'm at 77/78 jets now, and there's zero stumble. Not only that but it has very good response and flat hauls ***. Have to get to the track to do some finer tuning, but I have high expectations. The idle vacuum is up to 10 in hg.
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When you got the carb from Bigs, what was the jetting? The reason I ask is that is a HUGE jump in jetting...you should change jets 2 steps at a time, make a pass, change again, make another pass, etc until you reach the best MPH in the 1/4. Jumping 10 jet sizes is dangerous, you could very easily have leaned out your combo so much that it might be hurting parts.

Also, what are your IAB and HSAB? That would give a better idea as to where you should start, or better yet, call Jesse Bigs and ask the man that built the carb where you should start...he is usually spot on.
 
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