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carburetor stumbles when I stab throttle need help.
I have a lq4 with a ms3 cam work 806 heads victor jr intake holley xp 950. My issue is when I stab the throttle my air/fuel mixture leans out for a split second as this happens there is a stumble in the carb then clears up when rpms wrap up. I have to roll the throttle to get the best performance. The carb has the pink pump cams in the 1st hole 6.5 power valve in the front with 95s and rear blocked off with 98s. Front squirter is a 32 and rear is a 37. With the carb setup now the stumble is not as bad when i first stared tunning. Any info is greatly appreciated and if i forgot any info that would help please ask.
Make sure there is no slop in the accel pump linkage. Even the slightest throttle movement should cause a strong shot down the carb.
Going to a 50 cc pump without upgrading to the larger brown cam won't help your problem.
I assume you have a wideband. What do your AFR's look like with slow throttle movement? Getting that mixture right first will mean you need less accel pump shot.
i have found that LS motors tend to like the blue cam. This obviously doesn't mean all motors will but its usually what I end up with. It really shouldn't need 50cc pumps but you never know unless you try. Try some different cams, use this chart and use cams that have more displacement lower in the curve. Once the stumble goes away, back down the ssquirter size until the stumble comes back and then go back up a size or two.
[QUOTE=Pop N Wood;19257782]Make sure there is no slop in the accel pump linkage. Even the slightest throttle movement should cause a strong shot down the carb.
Going to a 50 cc pump without upgrading to the larger brown cam won't help your problem.
I assume you have a wideband. What do your AFR's look like with slow throttle movement? Getting that mixture right first will mean you need less accel pump
When i get a chance today ill check to see where the A/F mixture when i slowly roll the throttle. If i remember correctly its running fat around 12 something for A/F mixture.
i have found that LS motors tend to like the blue cam. This obviously doesn't mean all motors will but its usually what I end up with. It really shouldn't need 50cc pumps but you never know unless you try. Try some different cams, use this chart and use cams that have more displacement lower in the curve. Once the stumble goes away, back down the ssquirter size until the stumble comes back and then go back up a size or two.
Ima switch the position of the pink cam first and see what happens if i see no change ill swap the blue cam to see what happens. Thanks for the advice
I have a lq4 with a ms3 cam work 806 heads victor jr intake holley xp 950. My issue is when I stab the throttle my air/fuel mixture leans out for a split second as this happens there is a stumble in the carb then clears up when rpms wrap up. I have to roll the throttle to get the best performance. The carb has the pink pump cams in the 1st hole 6.5 power valve in the front with 95s and rear blocked off with 98s. Front squirter is a 32 and rear is a 37. With the carb setup now the stumble is not as bad when i first stared tunning. Any info is greatly appreciated and if i forgot any info that would help please ask.
Go to .040" accelerator pumps front and rear. Put a 50cc pump on the front and make sure you have the big pump cam made for the 50cc pump. Problem will be fixed.
Then you can start optimizing your WOT A/F ratio. You will likely find it runs best at about 12.5:1.
I have a lq4 with a ms3 cam work 806 heads victor jr intake holley xp 950. My issue is when I stab the throttle my air/fuel mixture leans out for a split second as this happens there is a stumble in the carb then clears up when rpms wrap up. I have to roll the throttle to get the best performance. The carb has the pink pump cams in the 1st hole 6.5 power valve in the front with 95s and rear blocked off with 98s. Front squirter is a 32 and rear is a 37. With the carb setup now the stumble is not as bad when i first stared tunning. Any info is greatly appreciated and if i forgot any info that would help please ask.
That seems like a big carb for your setup. I have an LQ4 with a custom cam that is almost identical to the MS3, and I have 799 heads. I have a Demon 750, with pink cams in slot 1 front and back, 40 squirters front and back, without a 50cc pump and my car launches very hard with no stumble.
Adding more fuel can cure the stumble, but I am curious if maybe the 950 is adding too much air to begin with?
i have found that LS motors tend to like the blue cam. This obviously doesn't mean all motors will but its usually what I end up with. It really shouldn't need 50cc pumps but you never know unless you try. Try some different cams, use this chart and use cams that have more displacement lower in the curve. Once the stumble goes away, back down the ssquirter size until the stumble comes back and then go back up a size or two.
Weird. My q850 came w 50cc pumps. The holley i had before that needed 50cc pumps before it would work right.
I jacked w cams and felt like i was pissing in the wind.
Ok been busy for the last two weeks but had a chance to mess with carb last weekend. I used the information I got from here and reading online. So heres what ive done. I kept the everything the same on the primary side then I changed the squirter on the secondary side up a size until I reached the #52 squirter. After that it still wanted fuel on the initial stab of the throttle so I went to a 50cc accelerator pump and changed pump cam to yellow. Once I did this there was no more stumble upon stabbing the throttle. Im stocked now just to dial in the Air/Fuel alittle more then on to the timing. I really appreciate everyone's information it definitely help with solving the problem.
You will need to revisit that big squirter once you get the rest of the carb and timing set right. You want the smallest shot needed to get rid of the bog. Accel pump should always be the last thing adjusted on the carb.
Get the main jets set right so your WOT is where it needs to be. Than see what your AF ratios are like with light throttle driving. My guess is you will be slightly lean. Once you get those set right by adjusting bleeds and idle feed restrictors you will be able to take the 50 cc pump back off.
You will need to revisit that big squirter once you get the rest of the carb and timing set right. You want the smallest shot needed to get rid of the bog. Accel pump should always be the last thing adjusted on the carb.
Get the main jets set right so your WOT is where it needs to be. Than see what your AF ratios are like with light throttle driving. My guess is you will be slightly lean. Once you get those set right by adjusting bleeds and idle feed restrictors you will be able to take the 50 cc pump back off.
Im gunna go back over the carburetor and was thinking that I may have to make some further changes. I have the new holley xp after readjusting idle air screws if the idle AF ratio doesn't lean out I just have to adjust the center screw instead of the air bleed jets correct?
Im gunna go back over the carburetor and was thinking that I may have to make some further changes. I have the new holley xp after readjusting idle air screws if the idle AF ratio doesn't lean out I just have to adjust the center screw instead of the air bleed jets correct?
I'm not familiar with the XP carbs. From what I have read the idle bypass is similar to the idle stop on the butterflies. That doesn't sound like the same thing as an air bleed. What the bypass will do is adjust the idle RPM while keeping the butterflies set so 20 thousands of the transfer slot is showing. Keeping the right amount of transfer slot uncovered is very important to light throttle driveability.
This link has a pretty good side box on how to adjust the idle bypass
05-11-2016, 03:20 PM
carburetor stumbles when I stab throttle need help. 
