Q-jet inlet filter questions - The 1947 - Present Chevrolet & GMC Truck Message Board Network

CCCC · 03-31-2016, 11:09 AM

These carb inlet filters seem to come in two forms - one with a check valve and one without.

In what situations does one need the check valve? Does it merely help with cold starts by keeping fuel from draining back in the line? Is there not a check valve in the fuel pump for that purpose?

As compared to a filter without valve, does it take significantly more fuel pressue to overcome that valve at the carb inlet?

Up and/or downsides of using one filter type or the other?

Thanks for any insights.

Wrenchbender Ret · 03-31-2016, 03:55 PM

The reason the check valve was put in is to prevent fuel from leaking out on a roll over collision. I've used them both ways & can't tell the difference in the performance. I've blown through them orally & it takes quite a bit of pressure to open it.

GRX · 03-31-2016, 04:08 PM

Check valve filters can be more restrictive in high RPM situations. Many prefer the non-valve version for that reason. An old trick was to remove the valve and snip a couple coils from the spring. Partial to the sintered bronze style filter myself.

CCCC · 04-01-2016, 06:50 PM

Thanks Wrenchbender and GRX - got it - now have a plan.

03-31-2016, 11:09 AM	#1
CCCC Registered User Join Date: Mar 2007 Location: San Pedro River, SE Arizona Posts: 735	Q-jet inlet filter questions These carb inlet filters seem to come in two forms - one with a check valve and one without. In what situations does one need the check valve? Does it merely help with cold starts by keeping fuel from draining back in the line? Is there not a check valve in the fuel pump for that purpose? As compared to a filter without valve, does it take significantly more fuel pressue to overcome that valve at the carb inlet? Up and/or downsides of using one filter type or the other? Thanks for any insights. __________________ CCCC 67 Sting Ray Coupe 327 4sp; 68 K10 Suburban 327 4sp; 69 K20 Lifted 383 4sp; 69 C80 Fire Truck 478 V6 5sp/2sp; 69 C20 Longhorn 327 4sp; 70 C30 Wrecker 350 4sp; 70 C30 Flat Bed 350 4sp; 71 C20 LWB 350 4sp; 72 K5 Blazer 350 4sp; 72 C30 Flat Bed Gooseneck Hauler with sleeper 350/TH400; 72 C20 Longhorn 402 4sp; 52 Mack LTL Supercharged Cummins 5sp x 3sp; 01 Dodge 5.9 HO Cummins 6spd; 02 Safari Trek 2430 8.1 Vortec on Workhorse Chassis; 03 Silverado 2500 HD 4wd Duramax/Allison Moved but still in the family 70 C20 Custom Camper 350/TH350; 72 K5 Blazer CST Highlander 350/TH350 Recently sent to new homes 72 C30 MoHome 402 4sp; 72 K5 Blazer Conv 350 4sp; 75 GMC 6000 Aerial 350 w Allison; 72 GMC 3500 Utility 350 4sp; 70 GMC 3500, 350 4sp

03-31-2016, 03:55 PM	#2
Wrenchbender Ret Registered User Join Date: Oct 2005 Location: Overland Park, Ks. Posts: 5,229	Re: Q-jet inlet filter questions The reason the check valve was put in is to prevent fuel from leaking out on a roll over collision. I've used them both ways & can't tell the difference in the performance. I've blown through them orally & it takes quite a bit of pressure to open it.

03-31-2016, 04:08 PM	#3
GRX Registered User Join Date: Jul 2010 Location: MD Posts: 1,937	Re: Q-jet inlet filter questions Check valve filters can be more restrictive in high RPM situations. Many prefer the non-valve version for that reason. An old trick was to remove the valve and snip a couple coils from the spring. Partial to the sintered bronze style filter myself. __________________ 1969 c-10 Step Side Long Bed. I-6 250cid = = 1969 Pontiac GTO hard top. 400, 4-speed.

04-01-2016, 06:50 PM	#4
CCCC Registered User Join Date: Mar 2007 Location: San Pedro River, SE Arizona Posts: 735	Re: Q-jet inlet filter questions Thanks Wrenchbender and GRX - got it - now have a plan. __________________ CCCC 67 Sting Ray Coupe 327 4sp; 68 K10 Suburban 327 4sp; 69 K20 Lifted 383 4sp; 69 C80 Fire Truck 478 V6 5sp/2sp; 69 C20 Longhorn 327 4sp; 70 C30 Wrecker 350 4sp; 70 C30 Flat Bed 350 4sp; 71 C20 LWB 350 4sp; 72 K5 Blazer 350 4sp; 72 C30 Flat Bed Gooseneck Hauler with sleeper 350/TH400; 72 C20 Longhorn 402 4sp; 52 Mack LTL Supercharged Cummins 5sp x 3sp; 01 Dodge 5.9 HO Cummins 6spd; 02 Safari Trek 2430 8.1 Vortec on Workhorse Chassis; 03 Silverado 2500 HD 4wd Duramax/Allison Moved but still in the family 70 C20 Custom Camper 350/TH350; 72 K5 Blazer CST Highlander 350/TH350 Recently sent to new homes 72 C30 MoHome 402 4sp; 72 K5 Blazer Conv 350 4sp; 75 GMC 6000 Aerial 350 w Allison; 72 GMC 3500 Utility 350 4sp; 70 GMC 3500, 350 4sp



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