stumble at 2000rpm
02-02-2001, 02:29 PM
#1
Supreme Member
Thread Starter
Join Date: Oct 2000
Location: New Orleans
Posts: 1,158
Likes: 0
Received 0 Likes
on
0 Posts
stumble at 2000rpm
Any ideas what could cause a stumble right around 2000rpms? My car has a non computer controlled setup with a carter carb and vacuum advance distributor. I figure I'll ask here first because for some reason I figure it is a carb thing. I guess it could be timing or spark related though, but I don't know. Just put in fresh spark plugs and richened up the mixture a bit, as the plugs seemed to indicate lean to me. Thanks.
02-03-2001, 07:28 AM
#2
Banned
Join Date: Jan 2001
Location: Belleville, IL USA
Posts: 1,429
Likes: 0
Received 0 Likes
on
0 Posts
when the rubber seal on the acellerator pump plunger wears down, it can cause a stumble when opening the throttle under load (driving). It can also be caused by dirt and moisture in the air-bleed tubes or acell-pump squirters.
good luck
------------------
White 1986 Irocz, 305/383 with Edlebrock Performer-RPM intake and Performer #1407 carburetor, +110hp shot of crack, 700R-4 tranny, 3.25:1 rear, Mcreary Road-Stars, single 3" Borla exhaust, Linginfelter-TPI camshaft pulls 17" vacuum solid. N/A runs 10.9 @124, Crack-runs 10.3 @135... haven't run at track since Oct-99
good luck
------------------
White 1986 Irocz, 305/383 with Edlebrock Performer-RPM intake and Performer #1407 carburetor, +110hp shot of crack, 700R-4 tranny, 3.25:1 rear, Mcreary Road-Stars, single 3" Borla exhaust, Linginfelter-TPI camshaft pulls 17" vacuum solid. N/A runs 10.9 @124, Crack-runs 10.3 @135... haven't run at track since Oct-99
02-05-2001, 09:17 AM
#3
Supreme Member
Thread Starter
Join Date: Oct 2000
Location: New Orleans
Posts: 1,158
Likes: 0
Received 0 Likes
on
0 Posts
Thanks for the reply,
I doubt that it is caused by anything wearing down because i bought my carb new about a hear and a half ago. Dirt and/or moisture could be a problem I guess, but they seem rather unlikely too (at least dirt does). I forgot to say before that this stumble seems to occur more (or with more severity) with low load on the engine. It does it in neutral, and seems to do it even worse when I am getting back on the gas at the bottom of a hill. I don't know, maybe I just need to continue tuning the thing and hope it goes away.
Thanks,
Mike
I doubt that it is caused by anything wearing down because i bought my carb new about a hear and a half ago. Dirt and/or moisture could be a problem I guess, but they seem rather unlikely too (at least dirt does). I forgot to say before that this stumble seems to occur more (or with more severity) with low load on the engine. It does it in neutral, and seems to do it even worse when I am getting back on the gas at the bottom of a hill. I don't know, maybe I just need to continue tuning the thing and hope it goes away.
Thanks,
Mike
02-05-2001, 10:08 AM
#4
Banned
Join Date: Jan 2001
Location: Belleville, IL USA
Posts: 1,429
Likes: 0
Received 0 Likes
on
0 Posts
[QUOTE]Originally posted by MikeS:
[B]Thanks for the reply,
I doubt that it is caused by anything wearing down because i bought my carb new about a hear and a half ago. Dirt and/or moisture could be a problem I guess, but they seem rather unlikely too (at least dirt does). I forgot to say before that this stumble seems to occur more (or with more severity) with low load on the engine. It does it in neutral, and seems to do it even worse when I am getting back on the gas at the bottom of a hill. I don't know, maybe I just need to continue tuning the thing and hope it goes away.
Mike,
I have family in Atlanta, so next time I go visit I can bring some stuff with me including a carb or two of mine to let you try. I also have a vercom, so if you have a 1/4 mile strip of road to run it you can make a pretty detailed comparison between the carbs.
As far as your carb problem, this new info changes things considerably. I have seen acellerator pump plungers wear in only a years time because of fuel additives (like alcohol & MTBE), but you're right it is unlikely.
It will help my diagnosis greatly for you to describe every detail about this drivability problem. For instance what happens when you hit your brakes at the bottom of a hill or turn a corner at the bottom of a hill?
I ask this because those symptoms point towards a float being set too high... and sometimes fuel pressure being just slightly too high can do that too.
As far as the dirt goes, better not to assume that out of the picture even if you have great filters.
More info on how it acts should help me narrow the problem down.
------------------
*I do custom performance mods on Edlebrock Performer carburetors (dualplane intake mods in the works),
White 1986 Irocz, 305/383 with Edlebrock Performer-RPM intake and Performer #1407 carburetor, +110hp shot of crack, 700R-4 tranny, 3.25:1 rear, Mcreary Road-Stars, SLP-stainless 1.75" shortie headers & Y-pipe, single 3" Borla exhaust, Linginfelter-TPI camshaft part number 74216 pulls 17" vacuum solid. Cam specs 213/219 @.050 114-LSA, .462/.470 lift @1.5:1 ratio. MSD-6AL, billet distributor, multi-retard, blaster-3 coil, and RPM switch.
N/A runs 10.9 @124,
Crack-runs 10.3 @135
haven't run at track since Oct-99
[This message has been edited by The ODB (edited February 05, 2001).]
[B]Thanks for the reply,
I doubt that it is caused by anything wearing down because i bought my carb new about a hear and a half ago. Dirt and/or moisture could be a problem I guess, but they seem rather unlikely too (at least dirt does). I forgot to say before that this stumble seems to occur more (or with more severity) with low load on the engine. It does it in neutral, and seems to do it even worse when I am getting back on the gas at the bottom of a hill. I don't know, maybe I just need to continue tuning the thing and hope it goes away.
Mike,
I have family in Atlanta, so next time I go visit I can bring some stuff with me including a carb or two of mine to let you try. I also have a vercom, so if you have a 1/4 mile strip of road to run it you can make a pretty detailed comparison between the carbs.
As far as your carb problem, this new info changes things considerably. I have seen acellerator pump plungers wear in only a years time because of fuel additives (like alcohol & MTBE), but you're right it is unlikely.
It will help my diagnosis greatly for you to describe every detail about this drivability problem. For instance what happens when you hit your brakes at the bottom of a hill or turn a corner at the bottom of a hill?
I ask this because those symptoms point towards a float being set too high... and sometimes fuel pressure being just slightly too high can do that too.
As far as the dirt goes, better not to assume that out of the picture even if you have great filters.
More info on how it acts should help me narrow the problem down.
------------------
*I do custom performance mods on Edlebrock Performer carburetors (dualplane intake mods in the works),
White 1986 Irocz, 305/383 with Edlebrock Performer-RPM intake and Performer #1407 carburetor, +110hp shot of crack, 700R-4 tranny, 3.25:1 rear, Mcreary Road-Stars, SLP-stainless 1.75" shortie headers & Y-pipe, single 3" Borla exhaust, Linginfelter-TPI camshaft part number 74216 pulls 17" vacuum solid. Cam specs 213/219 @.050 114-LSA, .462/.470 lift @1.5:1 ratio. MSD-6AL, billet distributor, multi-retard, blaster-3 coil, and RPM switch.
N/A runs 10.9 @124,
Crack-runs 10.3 @135
haven't run at track since Oct-99
[This message has been edited by The ODB (edited February 05, 2001).]
02-05-2001, 03:07 PM
#5
Supreme Member
Thread Starter
Join Date: Oct 2000
Location: New Orleans
Posts: 1,158
Likes: 0
Received 0 Likes
on
0 Posts
Thanks again. This is starting to be all kinds of helpful. I think I know what kind of answer you are looking for as far as braking and turning....my idle drops significantly under hard braking and turning (lefthand more than righthand from what I can tell). Of course, this is noticable only when the clutch is disengaged. Anyways, I have followed the float adjustment procedure that was in the thin Carter manual that came with the carb because everything seemed to point to a bad float adjustment. Do you think I should look first at the maximum float drop, or the maximum float lift? Thanks again for all of the help.
02-05-2001, 05:35 PM
#6
Banned
Join Date: Jan 2001
Location: Belleville, IL USA
Posts: 1,429
Likes: 0
Received 0 Likes
on
0 Posts
Yep,
make sure the fuel pressure at the carb is 6psi or less. Then reset your float level a little bit lower. Clean out your needle & seats while you're at it.
make sure the fuel pressure at the carb is 6psi or less. Then reset your float level a little bit lower. Clean out your needle & seats while you're at it.
02-06-2001, 03:06 PM
#7
Supreme Member
Join Date: Sep 1999
Location: Manassas VA
Posts: 3,197
Likes: 0
Received 6 Likes
on
5 Posts
Car: 04 GTO
Engine: LS1
Transmission: M12 T56
Just to throw in a new idea...ever hear the expression that 99% of carb problems are in the ignition...seems like it's not worth ignoring.
Why...the fact that you've noticed it worse when under low load. That makes me think of a vacuum related miss. Since Carters don't have a power valve type thing in it, the next most active piece with vacuum would be your vacuum advance. Perhaps it is adjusted wrong (if you have an adjustable can) or it's sticky under the small vacuum changes that light load would bring, etc. I'm not sure exactly how you would want to check it though.
...i'd hate to see you tearing your hair out over the carb/float and find the vacuum advance problem after all else fails...ed
Why...the fact that you've noticed it worse when under low load. That makes me think of a vacuum related miss. Since Carters don't have a power valve type thing in it, the next most active piece with vacuum would be your vacuum advance. Perhaps it is adjusted wrong (if you have an adjustable can) or it's sticky under the small vacuum changes that light load would bring, etc. I'm not sure exactly how you would want to check it though.
...i'd hate to see you tearing your hair out over the carb/float and find the vacuum advance problem after all else fails...ed
Trending Topics
02-10-2001, 11:07 AM
#9
Moderator
Join Date: Jul 1999
Location: 51°N 114°W, 3500'
Posts: 17,157
Likes: 0
Received 134 Likes
on
112 Posts
Car: 87 IROC L98
Engine: 588 Alcohol BBC
Transmission: Powerglide
Axle/Gears: Ford 9"/31 spline spool/4.86
My guess is the ignition module wires. Pull the cap and look at the entire length of the wires from the module to the magnetic pickup.
When the rpms increase the vacuum advance will pull the magnetic pickup a few degrees for more advance. The wires may be cracked and at a specific rpm they temporarily lose contact causing a stumble.
It took me 4 hours to locate that problem once.
Use a timing light to watch the spark. As you bring up the rpms, if the timing light stops as it stumbles then it's an ignition problem.
------------------
Follow my racing progress on Stephen's racing page
and check out the race car
87 IROC-Z Pro ET Bracket Race Car
383 stroker (carbed) with double hump cast iron heads and pump gas
461 Big Block installed and ready for the 2001 racing season
Best results before the 383 blew up
Best ET on a time slip: 11.857 altitude corrected to 11.163
Best MPH on a time slip: 117.87 altitude corrected to 126.10
Altitude corrected rear wheel HP based on power to weight ratio: 476.5
Best 60 foot: 1.662
Racing at 3500 feet elevation but most race days it's over 5000 feet density altitude!
Member of the Calgary Drag Racing Association
87 IROC bracket car, 91 454SS daily driver, 95 Homebuilt Harley
[This message has been edited by Stephen 87 IROC (edited February 10, 2001).]
When the rpms increase the vacuum advance will pull the magnetic pickup a few degrees for more advance. The wires may be cracked and at a specific rpm they temporarily lose contact causing a stumble.
It took me 4 hours to locate that problem once.
Use a timing light to watch the spark. As you bring up the rpms, if the timing light stops as it stumbles then it's an ignition problem.
------------------
Follow my racing progress on Stephen's racing page
and check out the race car
87 IROC-Z Pro ET Bracket Race Car
383 stroker (carbed) with double hump cast iron heads and pump gas
461 Big Block installed and ready for the 2001 racing season
Best results before the 383 blew up
Best ET on a time slip: 11.857 altitude corrected to 11.163
Best MPH on a time slip: 117.87 altitude corrected to 126.10
Altitude corrected rear wheel HP based on power to weight ratio: 476.5
Best 60 foot: 1.662
Racing at 3500 feet elevation but most race days it's over 5000 feet density altitude!
Member of the Calgary Drag Racing Association
87 IROC bracket car, 91 454SS daily driver, 95 Homebuilt Harley
[This message has been edited by Stephen 87 IROC (edited February 10, 2001).]
02-10-2001, 01:27 PM
#10
Supreme Member
Thread Starter
Join Date: Oct 2000
Location: New Orleans
Posts: 1,158
Likes: 0
Received 0 Likes
on
0 Posts
Thanks for the all the ideas guys. I'm going to head outside today and see what I can do with it (I don't get many chances to see my car while I'm at school). By the way, I have a standard vacuum advance HEI distributor (1-2 yrs old).
[This message has been edited by MikeS (edited February 10, 2001).]
[This message has been edited by MikeS (edited February 10, 2001).]
[This message has been edited by MikeS (edited February 10, 2001).]
[This message has been edited by MikeS (edited February 10, 2001).]
02-11-2001, 03:02 AM
#12
Senior Member
Join Date: Jan 2001
Location: outerspace(maybe..pluto)?
Posts: 527
Likes: 0
Received 0 Likes
on
0 Posts
[quote]<font face="Verdana, Arial" size="2">Originally posted by The ODB:
[b] the odb please email me at
burnoutrpm@hotmail.com
i have a question or million about edle carbs!! need great advice about mine tooo... running bad and dont know where to even start!??? pleae help!
------------------
1989 firebird formula
Mods: converted from T.B.I. to a carburator 305 to a 350. Flowmater exhaust,hedman shortie hedders,202 160 (882) heads,.447/.447 lift 222@.050 duration speed pro 327/350hp cam 350 .40 over (356) Edlebrock torker2 and a 600 edlebrock manual choke (1405)
Future mods performer rpm air gap intake (polished) comp roller cam, and way better headsa 400 defintely in the works!
[b]
Originally posted by MikeS:
Thanks for the reply,
I doubt that it is caused by anything wearing down because i bought my carb new about a hear and a half ago. Dirt and/or moisture could be a problem I guess, but they seem rather unlikely too (at least dirt does). I forgot to say before that this stumble seems to occur more (or with more severity) with low load on the engine. It does it in neutral, and seems to do it even worse when I am getting back on the gas at the bottom of a hill. I don't know, maybe I just need to continue tuning the thing and hope it goes away.
Mike,
I have family in Atlanta, so next time I go visit I can bring some stuff with me including a carb or two of mine to let you try. I also have a vercom, so if you have a 1/4 mile strip of road to run it you can make a pretty detailed comparison between the carbs.
As far as your carb problem, this new info changes things considerably. I have seen acellerator pump plungers wear in only a years time because of fuel additives (like alcohol & MTBE), but you're right it is unlikely.
It will help my diagnosis greatly for you to describe every detail about this drivability problem. For instance what happens when you hit your brakes at the bottom of a hill or turn a corner at the bottom of a hill?
I ask this because those symptoms point towards a float being set too high... and sometimes fuel pressure being just slightly too high can do that too.
As far as the dirt goes, better not to assume that out of the picture even if you have great filters.
More info on how it acts should help me narrow the problem down.
</font>
Thanks for the reply,
I doubt that it is caused by anything wearing down because i bought my carb new about a hear and a half ago. Dirt and/or moisture could be a problem I guess, but they seem rather unlikely too (at least dirt does). I forgot to say before that this stumble seems to occur more (or with more severity) with low load on the engine. It does it in neutral, and seems to do it even worse when I am getting back on the gas at the bottom of a hill. I don't know, maybe I just need to continue tuning the thing and hope it goes away.
Mike,
I have family in Atlanta, so next time I go visit I can bring some stuff with me including a carb or two of mine to let you try. I also have a vercom, so if you have a 1/4 mile strip of road to run it you can make a pretty detailed comparison between the carbs.
As far as your carb problem, this new info changes things considerably. I have seen acellerator pump plungers wear in only a years time because of fuel additives (like alcohol & MTBE), but you're right it is unlikely.
It will help my diagnosis greatly for you to describe every detail about this drivability problem. For instance what happens when you hit your brakes at the bottom of a hill or turn a corner at the bottom of a hill?
I ask this because those symptoms point towards a float being set too high... and sometimes fuel pressure being just slightly too high can do that too.
As far as the dirt goes, better not to assume that out of the picture even if you have great filters.
More info on how it acts should help me narrow the problem down.
</font>
burnoutrpm@hotmail.com
i have a question or million about edle carbs!! need great advice about mine tooo... running bad and dont know where to even start!??? pleae help!
------------------
1989 firebird formula
Mods: converted from T.B.I. to a carburator 305 to a 350. Flowmater exhaust,hedman shortie hedders,202 160 (882) heads,.447/.447 lift 222@.050 duration speed pro 327/350hp cam 350 .40 over (356) Edlebrock torker2 and a 600 edlebrock manual choke (1405)
Future mods performer rpm air gap intake (polished) comp roller cam, and way better headsa 400 defintely in the works!
Thread
Thread Starter
Forum
Replies
Last Post
RedLeader289
Tech / General Engine
10
05-28-2019 01:47 PM
