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I have a 79' with a 400sbc, TH350 and a holley 0-76650. I'm running ethanol free 89 octane, new plugs and wires. The car has a little bit of stumble when I tip into the throttle at about 40mph. At idle in park if I blip the throttle it seems fine but I have only recently installed this and have resisted getting on the gas until my confidence level is higher.
Primary nozzle is 31 and secondary is 28. If I understand the Holly documentation and Holley's video correctly it says I should go up in size but when I spoke to the holley support folks they said the 28 should be up on the primary and the 31 on the secondary. I would sincerely appreciate any wisdom you are willing to impart upon me. Thank you in advance.
Sometimes going to a different pump cam (or using the second screw hole) can solve your issue, you'll need to play with it. If you go to a larger nozzle, the duration of spray can go down if you keep the same cam. The idle throttle blip won't tell you much unfortunately, as you're describing an under load issue. I think you can find the Pump Can curve chart on the web, if not let me know and I can create a PDF. I may have a tech tip type doc. as well, feel free to PM me.
It'll also help to know if you are opening the Secondaries at all during the tip in. Generally you need longer pump shot for heavier vehicles/higher r/e ratio, tighter torque converts. I took a quick look at the specs and yes, the bigger nozzle is for secondaries (31), is that carb a square bore or spread? I didn't look that close.
Last edited by suprspooky; 03-26-2019 at 04:00 PM.
with the motor off and air cleaner removed. Look at the squirters, hand move the throttle arm and see if even the slightest movement causes them to ooze and get wet. You adjust the pump arm for next to "ZERO" clearance. Things do go bad with time and heat. I've replaced lots of squirter pump diaphragms. Lots of online tutorials of how to setup and adjust holley carbs.
It'll also help to know if you are opening the Secondaries at all during the tip in. Generally you need longer pump shot for heavier vehicles/higher r/e ratio, tighter torque converts. I took a quick look at the specs and yes, the bigger nozzle is for secondaries (31), is that carb a square bore or spread? I didn't look that close.
I appreciate the speedy replies. I will test the pump cam positioning as well. In regards to activating the secondaries I am not 100% sure but I didn't feel like I stuck my foot that far into the throttle.That said I am mindful that I don't have a good understanding how much that pedal effects the throttle as of now.
I guess I should have asked a couple more questions (thanks George), give some background on what steps you've done to get to the stumble. Did you just get the Carb, if so what was on there before and did it perform well at 40mph tip in? It'll probably make this go quicker, sometimes I assume too much when it comes to Holley questions, I go right to the HP tune part.
I guess I should have asked a couple more questions (thanks George), give some background on what steps you've done to get to the stumble. Did you just get the Carb, if so what was on there before and did it perform well at 40mph tip in? It'll probably make this go quicker, sometimes I assume too much when it comes to Holley questions, I go right to the HP tune part.
When I was a kid I drilled out my squirters to "Fix" a stumble. You need to figure out everything first before you start dorking up stuff up. I was a slow learner! dual 660 center squirters on a tunnel ram.
When I was a kid I drilled out my squirters to "Fix" a stumble. You need to figure out everything first before you start dorking up stuff up. I was a slow learner! dual 660 center squirters on a tunnel ram.
Damn kids, screwing up perfectly good blower carbs for a tunnel ram...
I have a 79' with a 400sbc, TH350 and a holley 0-76650. The car has a little bit of stumble when I tip into the throttle at about 40mph. Primary nozzle is 31 and secondary is 28.
Your squirters are reversed. Should have 28 on primary side and 31 on the secondary. Put them in the correct order and see if you still have a stumble. If you still have a stumble, assuming your accel pump lash is set correctly, install a 31 on the primary side as well and verify float levels.
with the motor off and air cleaner removed. Look at the squirters, hand move the throttle arm and see if even the slightest movement causes them to ooze and get wet. You adjust the pump arm for next to "ZERO" clearance. Things do go bad with time and heat. I've replaced lots of squirter pump diaphragms. Lots of online tutorials of how to setup and adjust holley carbs.
Timing advance can appear to be throttle problems
Borrowed a timing light from a guy my son and I have friended at autozone and plan on checking the timing this weekend. The whole squitter pump adjustment thing confuses my simple brian but I will check that again. Thanks for the tips sir.
I guess I should have asked a couple more questions (thanks George), give some background on what steps you've done to get to the stumble. Did you just get the Carb, if so what was on there before and did it perform well at 40mph tip in? It'll probably make this go quicker, sometimes I assume too much when it comes to Holley questions, I go right to the HP tune part.
I had an old worn out qjet prior to installing this. It definitely stumbled/bogged.
Your squirters are reversed. Should have 28 on primary side and 31 on the secondary. Put them in the correct order and see if you still have a stumble. If you still have a stumble, assuming your accel pump lash is set correctly, install a 31 on the primary side as well and verify float levels.
Get the Moroso Holley pump cam kit and try the "pink" cam if the squirter reversing does nothing.......
Also verify vacuum advance.....is it plugged into full manifold vacuum? Is it pulling 10-12 degrees?
Grabbed this picture this evening. It looks like the timing mark is arriving directly at the top. Ive never set timing before and assumed that the plate with the triangle tick marks was where the yellow mark would land. I would sincerely appreciate some advice from the tribal elders here 😁.
I think Lars can probably get you squared away, if you were stumbling/bogging with the Q-jet (assuming the Air Valve was adjusted properly) it'll be worse with a Double Pumper (I like Vac. Secondaries for most mild street motors) and Pump shot will be very important.
Get the Moroso Holley pump cam kit and try the "pink" cam if the squirter reversing does nothing.......
Also verify vacuum advance.....is it plugged into full manifold vacuum? Is it pulling 10-12 degrees?
Jebby
i do have it plugged into main not port vacuum on the carb. I am not sure if I know why you mean when asking if it is pulling 10 12 degrees. Do you mean advance on top of initial advance? Thank you.
i do have it plugged into main not port vacuum on the carb. I am not sure if I know why you mean when asking if it is pulling 10 12 degrees. Do you mean advance on top of initial advance? Thank you.
Yes sir....on top of the mechanical advance.....
Lars has a paper on which canisters pull what.....if you find yours is pulling way too much...which is usually the case.
03-26-2019, 03:37 PM
Holley Carb accelerator pump nozzles
dual 660 center squirters on a tunnel ram.
