Lean Spike Coming up on the Brake

General Nitrous Discussion

Moderator: John_Heard

Message
Author
User avatar
John_Heard
Site Admin
Posts: 5695
Joined: Thu May 12, 2005 11:20 am
Location: Resume Speed, Kansas
Contact:

Lean Spike Coming up on the Brake

#1 Post by John_Heard » Thu Jun 28, 2012 5:13 pm

Looking for ideas what would cause a lean spike like this when coming up on the chip, you can see where it pegs the O2's at 20:1 lean, then is richer on one side then another while on the launch RPM.

Mark Whitener ? Anyone else got an idea?

Did try larger squinter size and didn't seem to make any difference. It's lean enough it really makes it stumble, you have to tip it in somewhat slow - like it ain't getting any squirter shot, but it is so?
Attachments
leanspike.jpg
leanspike.jpg (33.35 KiB) Viewed 4332 times

User avatar
BracketNova
Posts: 618
Joined: Sat Apr 25, 2009 6:46 pm
Contact:

Re: Lean Spike Coming up on the Brake

#2 Post by BracketNova » Thu Jun 28, 2012 8:51 pm

My car was acting like that a while back. I don't have all the fancy logging stuff...yet, but it was acting just as you said. After messing around with the carb I gave up and called the carb guy. He told me to double check my timing, I assured him it was where it needed to be. He assured me it was not. I checked it and it needed 2° more. Put the timing in...stumble gone.

My .02, check the timing 8-)
"I always compare drag racing to lighting $100 bills on fire, only it's more expensive." - Craig W.

Check out my website...
http://www.findmoneyraces.com


'71 Nova E85
6.69 @ 100.2 MPH 9/6/14
1.4257 60'
1700' DA

13:1 439 BBC
3330 lbs

User avatar
supernova
Posts: 2552
Joined: Sat Feb 02, 2008 7:35 pm
Location: Ft.Worth Tx

Re: Lean Spike Coming up on the Brake

#3 Post by supernova » Thu Jun 28, 2012 9:05 pm

Hey John,
Do you think that is may be metering wrong (set up to lean) on the brake? Where it rich'ens back up is the where the t-brake is released? If so it's metered wrong. My carb is metered fat on the brake. That is how it was set up from Gary Willams. He even told me it would be fat on the brake and it is but cleans right up when the t-brake is released.........

I think it's metered way lean on the brake....... I bet it doesn't do that when just reving it up.....
Blackhoodmafia!!!! :mrgreen: :mrgreen:

1972 Nova SS
572 C.I. BBC

Best to date: 1/8
et: 5.28
mph: 134
new wt. 3340 lbs

User avatar
John_Heard
Site Admin
Posts: 5695
Joined: Thu May 12, 2005 11:20 am
Location: Resume Speed, Kansas
Contact:

Re: Lean Spike Coming up on the Brake

#4 Post by John_Heard » Fri Jun 29, 2012 6:54 am

I think it's possible it's something to do with the metering blocks. Maybe the best thing to do is to freshen it up and clean everything out, especially since it's been sitting so long and go from there. The differences between right bank/left bank make it seem more like a metering/bleed problem of some sort to me.

User avatar
supernova
Posts: 2552
Joined: Sat Feb 02, 2008 7:35 pm
Location: Ft.Worth Tx

Re: Lean Spike Coming up on the Brake

#5 Post by supernova » Fri Jun 29, 2012 9:02 am

I think you'll find that its not metering right for you engine combo and it's a easy fix. What funny is it seems to work well on your engine even not being right cause your car hauled ass before the make over.
If I can just get the weight out of my car I might have a chance to run with your's!!!! :mrgreen: :mrgreen: :mrgreen: :mrgreen: or not!!!!!!!! :shock: LOL
Blackhoodmafia!!!! :mrgreen: :mrgreen:

1972 Nova SS
572 C.I. BBC

Best to date: 1/8
et: 5.28
mph: 134
new wt. 3340 lbs

User avatar
John_Heard
Site Admin
Posts: 5695
Joined: Thu May 12, 2005 11:20 am
Location: Resume Speed, Kansas
Contact:

Re: Lean Spike Coming up on the Brake

#6 Post by John_Heard » Fri Jun 29, 2012 9:17 am

I hope it hauls ass better than that, it needs to run 4.90s to keep up with the Mako boys, but that'll probably take some testing to get things figured out.

User avatar
jmarkaudio
Posts: 278
Joined: Fri Oct 26, 2007 4:22 pm
Location: Florida
Contact:

Re: Lean Spike Coming up on the Brake

#7 Post by jmarkaudio » Fri Jun 29, 2012 10:22 am

If it's been setting a good cleaning may help. You have to also remember when an engine misfires it can show a lean spike when there may be plenty of fuel available. This may be caused because the fuel isn't prepped well by the carb/induction, plugs are not hot enough or fouled, timing not advanced enough at that point, ignition weak or crossfiring somewhere, fuel is stale... lots of things can cause it. If you run nitrous the tune is marginal for it to run well before the nitrous is activated to keep it from frying parts on the nitrous, so it doesn't take much to be wrong to cause a misfire. Put in fresh plugs, ensure all the ignition components are in good condition and check for proper rotor phase if you run a crank trigger.
Mark Whitener
Image
____________

Good work isn't cheap and cheap work can't be good.

User avatar
John_Heard
Site Admin
Posts: 5695
Joined: Thu May 12, 2005 11:20 am
Location: Resume Speed, Kansas
Contact:

Re: Lean Spike Coming up on the Brake

#8 Post by John_Heard » Fri Jun 29, 2012 10:56 am

jmarkaudio wrote:If it's been setting a good cleaning may help. You have to also remember when an engine misfires it can show a lean spike when there may be plenty of fuel available. This may be caused because the fuel isn't prepped well by the carb/induction, plugs are not hot enough or fouled, timing not advanced enough at that point, ignition weak or crossfiring somewhere, fuel is stale... lots of things can cause it. If you run nitrous the tune is marginal for it to run well before the nitrous is activated to keep it from frying parts on the nitrous, so it doesn't take much to be wrong to cause a misfire. Put in fresh plugs, ensure all the ignition components are in good condition and check for proper rotor phase if you run a crank trigger.
I really don't think it's a misfire condition, the point it is lean at is when the transbrake is set and I'm bringing it up to the stage RPM chip, it's doing it before it hits the chip. With it doing this, I can't just go in, set the brake and mat it, it will cough. The lean part is when I'm trying to bring the rpm up, once it's on the chip, the carb richens back up - like a bad accelerator pump or too small of a squirter. I did put larger squirters on it but additional fuel there didn't seem to help it any.

I did switch ignition boxes this year, so this will let me stage with more timing - before with the launch retard when the brake comes on the launch retard timing would kick in too (7531 box) so it only had like 20 degrees in it at that point.

User avatar
supernova
Posts: 2552
Joined: Sat Feb 02, 2008 7:35 pm
Location: Ft.Worth Tx

Re: Lean Spike Coming up on the Brake

#9 Post by supernova » Fri Jun 29, 2012 11:06 am

I use a K&R delay box to control the timing retard in the 7531 box so no activate the retard on the brake. The delay box controls the nitrous and timing retard. I would think that 20* would cause a rich condition. Or would it? Hmmmm I have to think about that one.
Blackhoodmafia!!!! :mrgreen: :mrgreen:

1972 Nova SS
572 C.I. BBC

Best to date: 1/8
et: 5.28
mph: 134
new wt. 3340 lbs

User avatar
supernova
Posts: 2552
Joined: Sat Feb 02, 2008 7:35 pm
Location: Ft.Worth Tx

Re: Lean Spike Coming up on the Brake

#10 Post by supernova » Fri Jun 29, 2012 11:34 am

Hey John,
I called a buddy over at Reher Morisson's and I told him what was going on, he said most likely it's a metering issue. He said the air bleeds may not be allowing enough fuel at the point of decking the paddle. Not getting enough fuel at that point.
Something to look at for sure.

He also asked how my car was doing since I got must of my engine stuff for them. I told how much my car weighed, he laughed and called it a lard ass. LOL
Blackhoodmafia!!!! :mrgreen: :mrgreen:

1972 Nova SS
572 C.I. BBC

Best to date: 1/8
et: 5.28
mph: 134
new wt. 3340 lbs

User avatar
John_Heard
Site Admin
Posts: 5695
Joined: Thu May 12, 2005 11:20 am
Location: Resume Speed, Kansas
Contact:

Re: Lean Spike Coming up on the Brake

#11 Post by John_Heard » Fri Jun 29, 2012 12:34 pm

haha ... well it is kinda heavy set.

User avatar
jmarkaudio
Posts: 278
Joined: Fri Oct 26, 2007 4:22 pm
Location: Florida
Contact:

Re: Lean Spike Coming up on the Brake

#12 Post by jmarkaudio » Fri Jun 29, 2012 1:22 pm

You have to have sufficient VAPORIZED fuel to start and maintain the ignition in the cylinder, if not enough is vaporized it will not start or not complete the combustion process, and essentially misfire. Too much liquid fuel can cause the same issue, not allowing the initial flame kernel to grow enough to sustain the burn on that cycle. I would still give everything a once over, make sure your fuel is fresh, and give the carb a good cleaning.
Mark Whitener
Image
____________

Good work isn't cheap and cheap work can't be good.

User avatar
jmarkaudio
Posts: 278
Joined: Fri Oct 26, 2007 4:22 pm
Location: Florida
Contact:

Re: Lean Spike Coming up on the Brake

#13 Post by jmarkaudio » Fri Jun 29, 2012 1:31 pm

Some good reading on the combustion process by Shrinker/Bruce Robertson here.

http://motorsportsvillage.com/forum/vie ... f=6&t=8245
Mark Whitener
Image
____________

Good work isn't cheap and cheap work can't be good.

User avatar
John_Heard
Site Admin
Posts: 5695
Joined: Thu May 12, 2005 11:20 am
Location: Resume Speed, Kansas
Contact:

Re: Lean Spike Coming up on the Brake

#14 Post by John_Heard » Fri Jun 29, 2012 2:09 pm

Thanks Mark I'll read through that, looks interesting.

I'm going to guess it's not because it's dirty as this carb has always done this (fresh fuel), but it certainly won't hurt anything to go through it and make sure it isn't plugged up somewhere.

While you're here, let's say just for the sake of discussion that the carb still does this after it's giving a good cleaning, fresh gaskets,etc. I do think it's lean at that point vs a errant O2 reading, just in the way it acts.

User avatar
supernova
Posts: 2552
Joined: Sat Feb 02, 2008 7:35 pm
Location: Ft.Worth Tx

Re: Lean Spike Coming up on the Brake

#15 Post by supernova » Fri Jun 29, 2012 2:35 pm

Mark has some good points. I gonna check the info and learn something. Lord knows I need to learn all I can about this stuf! :mrgreen:

Thanks for the info Mark.
Blackhoodmafia!!!! :mrgreen: :mrgreen:

1972 Nova SS
572 C.I. BBC

Best to date: 1/8
et: 5.28
mph: 134
new wt. 3340 lbs

Post Reply

Who is online

Users browsing this forum: No registered users and 1 guest