73-87chevytrucks.com
73-87 Chevy _ GMC Trucks => Performance => Topic started by: roadrage41 on September 18, 2008, 06:23:44 am
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i just acquired an 82 gmc sierra 1500, with im fairly sure a 305 and th350 (going by my luck on the motor, and the tranny pan on the tranny)
the only thing done to the motor, im guessing out of necessity, is some sort of weiand intake, and a holley 750 cfm carb (part 80508)
it runs like butt. you have to start the truck and let it run for about 5 minutes or so, or itll just die every time you step on the gas.... when it does get moving, when it hits 3rd gear, if you mash on it too much, it stumbles/sputters/coughs whatever you want to call it, as if to let you know it doesnt have a problem dying right there in the middle of the street as long as you dont mind looking like an idiot. does the same in 4th, i did get it to backfire out the carb yesterday in 4th (im familiar with that sound from my younger brothers firebird fiasco)
i read an article by mr. barry that basically says theres no such things as a carb thats too large, if you tune it right. says i can eliminate most of my problems by switching to different boosters, yadda yadda.
1. is that correct? can i tune this thing to make it run better (its not a bad running truck, just an annoying running truck.)
2. im mechanically inclined, i just dont have experience with the finer points of carbs. should i try doing this on my own right now as its my primary form of transportation, and were kind of rebounding from spending a LOT of money in the last few weeks. i.e. if its not a cheap simple fix, its a bad idea for me to do it.
3. where should i start?
4. it doesnt like going up hills - has a mechanical fuel pump, looks oem.. i know they rarely go bad, but its my truck, itll go bad just to prove a point.. havent bothered to locate the filter yet. it under the truck?
5. and just to add some more crap, my gas pedal sits on the floor, its not supposed to is it?
other than that the bodies got the normal cancer spots, but the previous owner had all new floor pans and redid the cab corners, its not a bad truck.
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1. Give it a good tuneup, mainly check timing, vacuum, compression, and fuel filter (should be one between pump and carb inlet, if not put one in).
2. Look for block casting numbers and try to figure out your displacement.
3. Check out the cfm sizing calculator... http://www.4secondsflat.com/Carb_CFM_Calculator.html (http://www.4secondsflat.com/Carb_CFM_Calculator.html) If you have a 305 at 100% volumetric efficiency and regularly run 8500rpm, you might need 750 cfm
4. The holley site has carb tuning info for that carb http://www.holley.com/0-80508S.asp (http://www.holley.com/0-80508S.asp)
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1.Yes, I believe you can make almost any carb run decent, but I'm not a carb guru. I just hear that if it's too big, it won't have the same throttle response as a smaller carb.
2. I'm not really mechanically inclined, but I've messed with my carb a few times(rebuilt it and tweaked on it a bit). The actual process of doing it isn't hard, it's just knowing what to do and when to do it.
3. One of the more experienced members could probably tell you more about where to start than me. I'd say make sure you have good fuel pressure, a small fuel pressure gauge is only a few bucks(I think I payed $14+shipping for mine).
4. Maybe the pick-up in the tank got uncovered going up the hill? Maybe the float bowls on the carb ran dry?
5. Is the throttle return spring nice and tight? My pedal used to hit the floor at an angle that would keep me from going WOT. A member on here sugguested I pull the pedal assembly out and bend the arm a little to get the pedal position I wanted. It worked good.
Well I hope you get it figured out. Good luck.
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ohh thats a good point team, wheres the pick up for the gas tank (s)? front or rear of tank, ive noticed it does the whole step on it and youve got more gas, stop and youve got less, i assumed they were in the rear. i havent been able to run with much gas in it, as previously stated were broke, waiting for that first paycheck to come in.
realize i could find most of this info in a haynes or chilton's but i cant afford one yet lol.
theres definitely something screwy going on it doesnt like hill's at all.
i think the gas pedal problem might be to do with the throttle cable, gonna see if i can rig it. i think its just too long. guessing whomever put the carb on put a longer one in as the 2bbl one propably wouldnt reach anymore. theres some slack in it, where it passes through the firewall and connects to the pedal.
once we get back to having money in the bank again, im gonna do a tuneup on it, the components for the ignition system dont look very old, but itll give me an excuse to "need" to rebuild the distributor ;D
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did you say somthing about 4th gear?
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I'm not sure where the pick-up is in the tank. I took my tanks out a while back, but I don't remember where the line was.
Sorry to hear about your hard times. Things will fall into place. My wife and I were in a pretty bad jam when I got into an accident a while back. We didn't have jobs at the time, and I had just wrecked our only transportation. It wasn't long before God blessed us with several vehicles and enough money to live comfortable and still play with my projects. Good luck with it bro.
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did you say somthing about 4th gear?
maybe it's a th350c.
For your application a haynes may not help you much on tuning the carb. We have some very knowledgeable guys on here that I'm sure can guide you on the carb. As stated, if it's a stock 305, a 750cfm carb is a bit too much.
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yeah i was thinking the 350c.. but isnt that just a lockup in 3rd gear?(either way not too important )
i agree with camden 750 is way to big for a 305. it sounds like its over carbed for sure..
have you checked the timing?
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havent been able to check timing, dont have access to a light at the moment. i just came off the road, making the transition from working wherever i get sent to working at the same place, putting a large chunk of change down on a new place, and buying this truck. i got a little "hey we forgot to pay you this" check from my last employer today, filled the drivers side tank, tried 3 different hills, no dice, still loses power.
got in the zone on the way to work, bought some homey chrome wire looms and some lock knobs. noticed when i got there - popped the hood to insure my coolant leak was gone, that 3 of the passenger side plug wires were resting on the exhaust manifold...... atleast my coolant leak is gone.
if i wake up on time tomorrow, im gonna pull the plugs and look for fouling, other than that im just going to "play it safe" and start replacing stuff. other than the gear, i can rebuild the top end without pulling it cant i?
the carb is too big as far as i know, and i dont know enough about replacing parts in them to warrant the attempt, probably needs rebuilt anyway, so ill keep my eyes peeled on ebay and local swap meets for something a little less ginormous.
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i would start with replacing the plugs, wires, cap, coil, and rotor ...you should be able to find someone with a timing light you could use just a quick check could do wonders .... i would be suprised if you couldnt find someone to trade with you for a smaller carb im sure theres plenty of people in the same situation noone has money to drop 500 on a new carb right it seems :-\ i have a 660 holley on my 454 right now and im looking for a 750 mechanical secondary carb but i think this 660 is still too big for your motor
check out craigslist for local used carbs alot of time people will let you hear the motor with carb still on it so you know its good before you buy it
Erik
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checked plugs, could use new ones, but theyre not fouled. ill do that on sunday probably, thinking about buying a remanned edelbrock from summit.
is 600 cfm still going to be too large?
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did you ever find out if it's really a 305? if so, then 600cfm is still to much but it will do ok. Try the calculator I linked above.
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i think a 600 edelbrock would be a world of improvment from what you have
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is there supposed to be a rubber gasket underneath the cover to the brake fluid reservoir? i seem to be leaking brake fluid, looks like its sloshing when i go up/down hills and pouring out from under the cover.
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my electric choke appears to be screwed as well, its wide open no matter what. tried giving the vaccum advance on the distributor its own vacuum connection (it shares a connection with two other things right now.) wouldnt run like that, so we went back to sharing.
is there an easier way to get the casting number? the one by the passenger cylinder head isnt visible.
theres some sort of vaccum powered something between the passenger side exhaust manifold and the the exhaust, looks like part of the emission system, could that be hurting it? all the rest of the emission stuff is gone.
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There is supposed to be a gasket under the reservior lid.
750cfm is way to big for a stock 305 or 350 for that matter. Yes you can change all the squirter etc, but that is basically making it a smaller carb.
The thing on the manifold isn't hurting your engine, they should run fine with a complete set of emmissions.
What do the float levels look like on the current carb?
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thanks capt, ill try to get out to the boneyard before work and see if i can snag one.
that thing in the manifold is all thats left of the emission system, and the vacuum line isnt attached to it anymore (assuming it was vacuum and not a line from the charcoal canister....)
cant tell on the bowl levels yet, been doing this after i get off work (work 12 hours shifts on grave) and before i pass out, hopefully ill have time to look tomorrow since i dont work sunday nights. the whole things covered in fuel goo and dirt at the moment.
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ok the crap on the sight glasses wont come off, and theyre basically opaque. im pretty much just gonna plan on replacing the carb now.
my check hasnt cleared completely yet so i bought plugs and replaced those, truck started up without having to pump the gas, which is an improvement. got the master cylinder gasket, so the brake fluid leak is gone. the coolant leak isnt completely gone however, think its the gasket under the neck on the manifold.
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ok, timing is fine.
carbs too dang big, and my buddy says it needs rebuilt, which blatantly places it out of my realm of knowledge. im gonna pull it off and replace it with one of the remanned edelbrocks from summit. and probly rebuild it for the heck of it just to learn how to do it.
passenger side exhaust manifold is likely warped, the gaskets on them have been replaced, and id willing to bet they werent cold when they were removed. plus its got that dang part of the old emissions thing in line.
will the 90 dollar headers from summit fit correctly? and i mean spot perfect, the truck is stock ride height, i know theyre not the fanciest, but im gonna end up redoing the motor more than likely with a big block in the future.
http://store.summitracing.com/partdetail.asp?autofilter=1&part=SUM-G9006&N=700+4294925045+4294908171+4294908134+4294923429+4294839039+115&autoview=sku (http://store.summitracing.com/partdetail.asp?autofilter=1&part=SUM-G9006&N=700+4294925045+4294908171+4294908134+4294923429+4294839039+115&autoview=sku)
also my drivers side caliper is sticking, i think i read here that this is caused by the rubber lines, and that replacing them will fix it?
the master cylinder and hard lines from it are new, the rubber lines are oem as far as i can tell. need to bleed the brakes anyway, and the brake fluid is kind of a gooey brown looking color.
prob gonna run me around 500 which sucks arse at this very moment in time, but if it makes that dang thing run decent ill be happy.
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oh other little tidbits i forgot.
the oem fuel system relied on the fuel filter in the carb right? after they put the ginormous holley on it, they didnt put an inline one in....
i hadnt noticed when i did the plugs because the dang wires are so long that one of the plug wires melted through to the core.
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redid plug wires and got some wire looms today and seafoamed it on a whim...
i love seafoam.
id say a 70 percent improvement in how it runs, i actually got it to 75 mph today, previously it was near impossible.
still bogs going up a hill, but not near as bad, and if i give it too much pedal below say 40 mph it bogs a little, but nowhere near as bad.
need a longer rubber section on my fuel line to install the filter i got (mr. gasket inline) but i got one lol. the fuel line is routed really wierd, going to have to pull the alternator to change it.
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swapping the 750 for a 650 holley sunday. still large, but not as large.
;D
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650 Vacuum secondary? If so you should be fine.
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650 is on after several trips to oreillys for parts o-rings for the tube that runs to the secondarys were shot. runs a crapton better, still bogs a little bit if you mash it below 20 mph or so, but barely noticeable. also got the inline fuel filter installed (most of the part store trips were because of it.) only thing that sucks is its chokeless, i got a crashcourse in rebuilding a carb tonight tho, so im pretty sure i could install one on my own. we swapped the #68 jets from the 750 into the 650 as the 650 had #70's. ill prob knock it down to a #64 here in the next coming weeks.
it runs like the boat anchor it should ;D
confirmed it is a th350 (i was pretty sure based on the tranny pan, but i dont know that much...), but that isnt likely what came from the factory, i have D 3 2 1 on the column, but it actually only goes from D-2-1 when you shift it. buddy said it looks too clean to be the original trans. guy who swapped me the carb offered me a choice of a thirty over 454 / or a fourty over 350 for 300 bucks each if i want em, but the 350 would be without the heads (he's got darts on it, and theyre going on his 383 build for his 'maro.)
just need to fix the exhaust leak at the manifold now. it seeps into the cab which makes for an interesting drive if you dont keep the windows down.
got all new bits for the drivers side brake system, gonna get the passenger side ones next weekend and just do em in one shot, that draggin brake sound is horrendous.