Carb stumble
10-17-2010, 03:02 PM
#21
Banned
iTrader: (5)
Join Date: Jul 2007
Location: Wylie,Tx 75098
Posts: 649
Likes: 0
Received 0 Likes
on
0 Posts
Carb Stumble ='s not enough fuel on initial hit.
i would say bigger squirter up front and as far as a 50.. acc. pump i would say no for his application.
may also need to go to bigger jets and square them up.
78-78
also do 1 change at a time,so you know the end result
i would say bigger squirter up front and as far as a 50.. acc. pump i would say no for his application.
may also need to go to bigger jets and square them up.
78-78
also do 1 change at a time,so you know the end result
10-17-2010, 03:20 PM
#22
You don't recommend to square up jets on a street car, this isn't the 1970s, all he'll get is fouled plugs for his time wasted. Keep the power valve, keep the jetting reasonably spaced and try it out. After a 35-ish squirter you won't get much more flow out of them at tip-in with a 30cc pump shot according to the quick fuel techs. Mine still had a stumble that showed up on the wideband and was barely noticeable with 37s up front and 30cc pump shot kit. Now with 40s all around and 50cc front the issue has resolved itself.
10-17-2010, 07:42 PM
#23
Banned
iTrader: (5)
Join Date: Jul 2007
Location: Wylie,Tx 75098
Posts: 649
Likes: 0
Received 0 Likes
on
0 Posts
You don't recommend to square up jets on a street car, this isn't the 1970s, all he'll get is fouled plugs for his time wasted. Keep the power valve, keep the jetting reasonably spaced and try it out. After a 35-ish squirter you won't get much more flow out of them at tip-in with a 30cc pump shot according to the quick fuel techs. Mine still had a stumble that showed up on the wideband and was barely noticeable with 37s up front and 30cc pump shot kit. Now with 40s all around and 50cc front the issue has resolved itself.
mine never fouled,because i squared them up.
as far as fouling plugs,yes you will foul the plugs because you have used a plug where power valve goes.
YES,then will you start fouling out plugs at idle or street use.
i never understood the point of spacing out the jets.
unless your coming out of the corners,in a dirt track car.
Last edited by mred; 10-17-2010 at 07:53 PM.
10-17-2010, 07:58 PM
#24
First off leaving the power valve in the carb and running squared jets will make the primary much richer than the secondaries by 6-8 jet sizes. So how would you drive it on the street dumping all that fuel on the primaries again?
Furthermore, your link is for an ALCOHOL carb.....not a gasoline carb that 99.9% of people use. Of course you need more fuel volume for one of those but not what this discussion is about.
Furthermore, your link is for an ALCOHOL carb.....not a gasoline carb that 99.9% of people use. Of course you need more fuel volume for one of those but not what this discussion is about.
10-17-2010, 08:39 PM
#25
Banned
iTrader: (5)
Join Date: Jul 2007
Location: Wylie,Tx 75098
Posts: 649
Likes: 0
Received 0 Likes
on
0 Posts
your statement was any "4150"
like i said mine never did foul the plugs and i went 7.20s and typically there will be a plug in the rear metering block so,no its not going to typically run richer on the primaries.
so therefore you could still drive it on the street and get great fuel mileage.
like i said mine never did foul the plugs and i went 7.20s and typically there will be a plug in the rear metering block so,no its not going to typically run richer on the primaries.
so therefore you could still drive it on the street and get great fuel mileage.
10-17-2010, 08:47 PM
#26
no squaring the jets would be 80/80 primary/secondary for instance
your primary is also dumping fuel from the power valve which is usually worth 6-8 jets by itself....so your 80/80 would be more like 88/80 for jetting sizes. Therefore a large amount of fuel would be delivered while driving it around town on the primaries only and foul out plugs. Yes any 4150 gas carb, which is what we're discussing doesn't come with dual 50cc pump shots. You're just trying to start a pissing match and including wrong info about the jetting. Either way blocking all power valve and squaring the jetting or running a primary power valve with square jets is going to run super rich and take out plugs.
your primary is also dumping fuel from the power valve which is usually worth 6-8 jets by itself....so your 80/80 would be more like 88/80 for jetting sizes. Therefore a large amount of fuel would be delivered while driving it around town on the primaries only and foul out plugs. Yes any 4150 gas carb, which is what we're discussing doesn't come with dual 50cc pump shots. You're just trying to start a pissing match and including wrong info about the jetting. Either way blocking all power valve and squaring the jetting or running a primary power valve with square jets is going to run super rich and take out plugs.
10-18-2010, 07:00 PM
#27
Banned
iTrader: (5)
Join Date: Jul 2007
Location: Wylie,Tx 75098
Posts: 649
Likes: 0
Received 0 Likes
on
0 Posts
sounds like to me your the one thats getting the feathers all in a ruffle..
have you done it?
obviously not.
i have and no it didnt foul my plugs.
stumble on intial=s no fuel out of the hole, so give it more fuel
have you done it?
obviously not.
i have and no it didnt foul my plugs.
stumble on intial=s no fuel out of the hole, so give it more fuel
10-18-2010, 07:18 PM
#28
Different tuning works for different engines fellas, we cannot sit here and compare two different setups guys. We do not need a pissing match. What each of you have done and have experience with has evidently worked well and are just needing to be logged as a adjustment for the books for others to try.
10-23-2010, 05:49 PM
#30
i just installed a 50cc pump kit changed nothing else and my stumble is gone. turbo seems to spool a little better to. didn't have much time to mess with hopefully tomorrow ill have more time.
10-23-2010, 08:03 PM
#32
not sure if that has to much to do with it , the one stumble i was having it was at low rpms and just slowly touching the throttle, just cruising and trying to get up to speed. less then probably 1/4 throttle. and now the w/b shows rich instead of the off lean spike.
and whats kind of weird is with the D1SC i never had the stumble
and whats kind of weird is with the D1SC i never had the stumble
Last edited by overhere; 10-23-2010 at 08:16 PM.
06-07-2011, 09:35 AM
#34
The 50 CC pump is about twice as tall as the 30 cc pump. It drops down below the carb a good bit more. The pump arm is also quite a bit more beefy than the 30 cc unit.
If you really want I can probably measure the size of 50 CC unit. I had one on my car for awhile, but was able to switch back to the 30 CC unit after I adjusted the primary idle air bleeds. I'm convinced that adjusting the air bleeds is the correct way to fix the low RPM stumble on LS motors running an open plenum manifold.
My guess is very few carbs will have a 50 cc unit on them. So unless you put one on it will be a 30 cc unit.
If you really want I can probably measure the size of 50 CC unit. I had one on my car for awhile, but was able to switch back to the 30 CC unit after I adjusted the primary idle air bleeds. I'm convinced that adjusting the air bleeds is the correct way to fix the low RPM stumble on LS motors running an open plenum manifold.
My guess is very few carbs will have a 50 cc unit on them. So unless you put one on it will be a 30 cc unit.
