Very rich at light throttle and cruising

[Overcamber]

finally had a chance to drive my truck with the new rebuilt carb.  Having a couple issues. First off wide open throttle  is crisp and clear. transition seems great!

My problem is low speed and city cruising speed.  Very light throttle , approx. 1400-1800rpm, 35 to 50 mph the mufflers are loading up and backfiring.  Even at 1/3 to 1/2 throttle. 

Can you suggest something I can try to alleviate this problem?

thanks Gary

[Overcamber]

just tried turning in the apt 1/2 + another 1/2 and it didn't improve(thought it would make it leaner).  there is a slight grade and corner on my street that you have to take at 10mph and I can barely make it up without it sounding like a machinegun...I have louder type mufflers which amplifys the whole scenario

[Overcamber]

just trying different things cause I'm off today.  turned in the apt all the way to find its original setting was at 4 3/4 turns out from bottom.

just tried 1 1/2turns out and not much difference.  its as though as soon as I squeeze the fuel its getting too much and begins to backfire??

let me know your thoughts/ this isn't my daily driver so I have some time to get it right.

[Overcamber]

Man I give up ! Adjusted the mixture screws and everything seemed happy at 2 1/2 turns out .  Go to take it for a ride and it shut off . No fuel at idle . Runs with the choke on but quits the minute I kick the choke off ?

Glad I'm working tomorrow cause I'm about to burn this truck ! Lol

[429bbf]

it seems like you have a couple of issues , first it acts like its flooding, then it sounds like your running out of fuel, vacuum leak, float sticking,filter, plugged , is the carb staying full of fuel . you say its not your daily driver ,is there crud in the tank and it ran good for a little while and now garbage has gotten into the needle and seat.did you build the carb?these may seem like dumb questions but you need to verify them one at a time before you go making a ton of adjustments. fwiw

[Overcamber]

no , I just got the carb back from Cliff.  I drive it a lot  but I meant I have a second vehicle to use at this time.

[Cliff Ruggles]

What is the carburetor number and application?

Backfiring is usually lean not rich.  May be a vacuum leak if it's acting up an idle and low speed/light engine load......Cliff

[Overcamber]

my carb number is   17086248         
                                  2315 JLH
its a 1986 gmc 1/2 shortbox 2wd   305 4bbl.

its isn't backfiring out the carb.  its backfiring in the mufflers.
thx Cliff

[77cruiser]

Sounds like a possible issue with the ignition.

[Overcamber]

although I wouldn't rule that out ,I find it very coincidental or odd its that as the carb worked fine in that area before I sent it away?. just saying? 
also it runs perfect at wide open throttle?  would an ignition problem only affect the problem area I'm having?

thanks Gary

[77cruiser]

The wires tend to break on the pickup coil in a HEI & can cause a similar deal. Not saying that's it but it might be worth looking at.

[Overcamber]

Well I've had the truck since new and I know the pickup is original . 30 years old and 230000km so perhaps that's worth a look?
Curious what cliff has to add?

Really appreciate the help guys ! Keep it coming , it's great discussion .
Thank you

[429bbf]

this might sound stupid , but I've seen a cracked cap,wet cap or sticky weights in a distributor.act similar to this. fwiw

[Cliff Ruggles]

Backfiring is almost always ignition, or the carb super lean at light part throttle, or a little of both.  Since it fattens up things at heavy/full throttle you may not have any issues there, but if trying to burn a lean mixture ignition issues show up quickly.......Cliff

[Overcamber]

Ok I'll pull the distributed and start there /. Hope I find the cure !
Thx