Carb Help Please

R&S Motorsports · 10-06-2010, 03:29 PM

I just switched to gas from Methanol I put a 1150 Dom on my 438 SBC 750HP, My problem is starts great, idles great, no stumble not under load very crisp, when I set the transbrake and mat it, it stumbles and dies. Carb has 42 squirters, 96 jets square I am no carb expert so looking for some help ran injection for the last 10 years. Thanks for any help.

TCOONLY · 10-07-2010, 10:33 AM

Bigger squirters

TERMITE S/G 2122 · 10-07-2010, 07:04 PM

First of all, what kind of fuel delevery system are you using ? What i found was it takes a lot more volume to run methanol . Pressure is not as important as volume. I needed a #10 line feeding a bolaws fuel log. Sounds like your running out on the hit. NO VOLUME. Hope this helps.

pmrphil · 10-07-2010, 09:00 PM

start with raising the float level about as high as it will take without running out of the boosters (after setting the fuel pressure to no more than 6 lbs.) and also fatten up the idle circuit. Make sure the primary blades are not exposing the transfer slots, if so, open the secondary blades to facilitate closing the primary blades a bit. Confused? Don't be. It's not that hard. Holler if you need help. Phil

voltdr · 10-11-2010, 10:22 PM

The three most important things about an off-idle stumble.
1. Big Squirters
2. Bigger Squirters
3. Even bigger squirters on alcohol.

Ron Finney · 10-12-2010, 10:30 AM

Unfortunately you probably have too big of carb for your application. A 1050 or maybe even a little smaller carb would be a much better choice. Carbs siphon fuel based on a change in atmospheric pressure. When you snap the throttle quickly, the air rushes in to equalize pressure from the low pressure inside(vacuum). Since fuel is heavier it takes longer to get there. The purpose of the accelerator pump is to mechanically squirt fuel until the siphon feed can get started. Increasing the squirter size may help, also check your pump arms and make sure they don't have excess play or need adjusting. Even with this, you may still need to downsize to increase the draw on the circuits in the carb.

I did the same thing with a 1250 on a big block in super comp. When I snap throttle it would bog or die, but if you could keep it running it would fly. Also, when I would enter the water box and just give it a hit to turn the tires slightly before doing the burnout, it wasn;t punchy. Much better with 1050 back on.

Good Luck.

kbcarbman · 10-12-2010, 05:28 PM

I would agree with the above replies,however I don't think an 1150 is too big.I run one on my 358. It's probably too lean on the idle circuit ,the jetting sounds odd(hopefully it has holes above the jets w/#96) and 42 squirters are too small. KB

THE LEGEND · 11-27-2010, 10:14 AM

Carb too big.

rod butcher · 11-29-2010, 08:08 AM

X2 on to big
I only use 4150 carb on a smallblock, bracket motor. If you were running B/ED thats a different story.

SCOTT SST2871 · 11-29-2010, 09:12 AM

He's switched from alcohol to gas,not the other way so the jets sound reasonable to me...like some others have said try larger squirters and check the throttle blade to transfer slot..thats where i would start
scott fifield

10-07-2010, 10:33 AM	#2
TCOONLY Junior Member Join Date: Aug 2009 Location: Buffalo NY Posts: 18 Likes: 0 Liked 0 Times in 0 Posts	Re: Carb Help Please Bigger squirters __________________ Tom Coonly 1211 HR

10-07-2010, 07:04 PM	#3
TERMITE S/G 2122 Junior Member Join Date: Apr 2009 Location: n.c. Posts: 86 Likes: 0 Liked 9 Times in 6 Posts	Re: Carb Help Please First of all, what kind of fuel delevery system are you using ? What i found was it takes a lot more volume to run methanol . Pressure is not as important as volume. I needed a #10 line feeding a bolaws fuel log. Sounds like your running out on the hit. NO VOLUME. Hope this helps.

10-07-2010, 09:00 PM	#4
pmrphil Member Join Date: Aug 2010 Location: CT Posts: 451 Likes: 1,722 Liked 342 Times in 148 Posts	Re: Carb Help Please start with raising the float level about as high as it will take without running out of the boosters (after setting the fuel pressure to no more than 6 lbs.) and also fatten up the idle circuit. Make sure the primary blades are not exposing the transfer slots, if so, open the secondary blades to facilitate closing the primary blades a bit. Confused? Don't be. It's not that hard. Holler if you need help. Phil __________________ Phil Molski PMR Performance S/C 1623

10-11-2010, 10:22 PM	#5
voltdr Senior Member Join Date: Jan 2008 Location: Texas Posts: 705 Likes: 77 Liked 97 Times in 50 Posts	Re: Carb Help Please The three most important things about an off-idle stumble. 1. Big Squirters 2. Bigger Squirters 3. Even bigger squirters on alcohol.

10-12-2010, 10:30 AM	#6
Ron Finney Member Join Date: Jul 2008 Location: Greenwood, IN Posts: 168 Likes: 0 Liked 0 Times in 0 Posts	Re: Carb Help Please Unfortunately you probably have too big of carb for your application. A 1050 or maybe even a little smaller carb would be a much better choice. Carbs siphon fuel based on a change in atmospheric pressure. When you snap the throttle quickly, the air rushes in to equalize pressure from the low pressure inside(vacuum). Since fuel is heavier it takes longer to get there. The purpose of the accelerator pump is to mechanically squirt fuel until the siphon feed can get started. Increasing the squirter size may help, also check your pump arms and make sure they don't have excess play or need adjusting. Even with this, you may still need to downsize to increase the draw on the circuits in the carb. I did the same thing with a 1250 on a big block in super comp. When I snap throttle it would bog or die, but if you could keep it running it would fly. Also, when I would enter the water box and just give it a hit to turn the tires slightly before doing the burnout, it wasn;t punchy. Much better with 1050 back on. Good Luck. __________________ Ron Finney 396V S/C

10-06-2010, 03:29 PM	#1
R&S Motorsports Junior Member Join Date: Oct 2008 Location: Wind Lake, WI Posts: 54 Likes: 0 Liked 0 Times in 0 Posts	Carb Help Please I just switched to gas from Methanol I put a 1150 Dom on my 438 SBC 750HP, My problem is starts great, idles great, no stumble not under load very crisp, when I set the transbrake and mat it, it stumbles and dies. Carb has 42 squirters, 96 jets square I am no carb expert so looking for some help ran injection for the last 10 years. Thanks for any help.

10-12-2010, 05:28 PM	#7
kbcarbman Junior Member Join Date: Jan 2008 Location: maumee,ohio Posts: 3 Likes: 0 Liked 0 Times in 0 Posts	Re: Carb Help Please I would agree with the above replies,however I don't think an 1150 is too big.I run one on my 358. It's probably too lean on the idle circuit ,the jetting sounds odd(hopefully it has holes above the jets w/#96) and 42 squirters are too small. KB

11-27-2010, 10:14 AM	#8
THE LEGEND VIP Member Join Date: Aug 2002 Location: Fayetteville, n.c. Posts: 1,411 Likes: 0 Liked 1 Time in 1 Post	Re: Carb Help Please Carb too big.

11-29-2010, 08:08 AM	#9
rod butcher Member Join Date: Dec 2005 Posts: 252 Likes: 297 Liked 132 Times in 27 Posts	Re: Carb Help Please X2 on to big I only use 4150 carb on a smallblock, bracket motor. If you were running B/ED thats a different story.

11-29-2010, 09:12 AM	#10
SCOTT SST2871 Member Join Date: Oct 2008 Location: PORT ST JOHN FLORIDA Posts: 226 Likes: 0 Liked 0 Times in 0 Posts	Re: Carb Help Please He's switched from alcohol to gas,not the other way so the jets sound reasonable to me...like some others have said try larger squirters and check the throttle blade to transfer slot..thats where i would start scott fifield