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73-87 Chevy _ GMC Trucks => Engine/Drivetrain => Topic started by: hondarider188 on February 15, 2013, 12:10:56 am
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I am looking to get the most out of my engine like everyone else when it comes into the fuel economy. And i dont have any idea on how to tune my engine to get good mpg. I have a 1983 chevy k10 with the 350 and a edlebrock intake manifold and carb. with the high flow triangle air box. And the main thing i need help with is that i dont know where the air/fuel mixture screws should be at and the same for the idle. The truck runs great and starts good but i would like to get more out of it. The last thing is the choke, it has been converted to manual and i do need to use it to start easier in the cold cold mornings but shouldn't the engine be able to run with the choke still on? for my doesnt but kills the engine.
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You can use a vacuum gauge plugged into a port with full or "manifold" vacuum to tune the idle mixture screws. Your goal is the highest vacuum reading. You can also check your timing, initial should be around 10-12 degrees with the vacuum tube disconnected and plugged, then reconnect after you time it.
Yes, it should run with the choke on. It may be possible you have the idle mixture screws "off" enough to cause problems.
You didn't say what carburetor you have...................I'm guessing Edlebrock?
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Have you given thought of going to a throttle body injection like the 87's have?
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Yes my carb is an edlebrock, but i dont know what size it is or how to identify it. and i havnt thought about the throttle body injection, but i would think that the conversion would cost alot.
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i dont think that converting a carburated engine into an injected engine is very feasible... by spend over a thousand dollars just to gain 2-3 mpg... a well tune carb engine can give the same results as an injected engine...
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No disrespect, but I think you're fooling yourself if you think you can get a carb to perform like injection.
About the best you can get with a carb will probably be by using what GM put on it and modifying everything else to be more efficient, like the exhaust and friction reduction measures.
The factory had many years of engineering and testing to design and tune their carbs. They usually work pretty well. Buying an edelbrock, holley, or even a quadrajet that was not calibrated for your engine will end up being a compromise.
Take a look at the Holley on a 1985 mustang GT. Very highly tweaked version of what summit racing sells.
Dan
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check out this article... http://www.chevyhiperformance.com/tech/engines_drivetrain/induction_poweradders/0510ch_carburetor_tuning_gas_mileage/viewall.html
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Interesting article, too bad it doesn't address qudrajets
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Interesting article, too bad it doesn't address qudrajets
true... but 21mpg as stated in the article is not bad for any old v8
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I have a narrow band O2 sensor now installed in my header pipe and it's of limited usefulness but I plan to get a wideband towards the end of this month.
I actually have fully adjustable air bleeds in the carb body(s), I have 6/32 brass set screws, and a tap that I used to install them into the metering block for full control over my IFR. I have a box of jets, a boatload of squirters, a downleg booster body, an annular discharge booster body, a vacuum gauge installed on my dash, quick fuel e85 metering blocks (I've run e85 for a bit) and lots of time sitting under the hood pulling changing parts (one at a time) to tune.
While I won't claim that 21mpg is impossible in a car with a cam over 250 degrees duration @.050 and a holley, I think it's probably extremely rare. I gotta say that just because a magazine says they did something like that I hesitate to take it at face value. It looks like something that sells magazines. I'm not arguing that carbs can't be tuned, but that it is very difficult and time consuming to tune them to work as well as fuel injection. The carb in the magazine article didn't even have a choke.
Dan
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No disrespect, but I think you're fooling yourself if you think you can get a carb to perform like injection.
Dan
I have to agree and say that it is not as easy as everyone says to tune your carb only to get great mpg. It is a little bit more involved.
You can use a vacuum gauge plugged into a port with full or "manifold" vacuum to tune the idle mixture screws. Your goal is the highest vacuum reading. You can also check your timing, initial should be around 10-12 degrees with the vacuum tube disconnected and plugged, then reconnect after you time it.
This is the best for you are your current level of understanding. It is admirable that you acknowledge your limited understanding. I encourage you to learn all that you can.
Your choke is there to help cut off air flow (basically) until the carb has warmed up enough to atomize the fuel properly. With a manual choke it could be you do not have your mixture screws set properly, or your manual choke is not adjusted right, so when you pull it and think it's closed off it really is not, or both.
Also as DanInMichigan stated, you could spend months resetting, retuning and messing around and never match what EFI can give you. Just got to take it as it is and shoot for the best outcome you can get.
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thanks for the help guys, what is am still wondering though is that are their any base line settings that i can start out from besided where the carb is set at now. and the other thing i wonder is what are the screws that i need to be adjusting and tuning in. also does changing the jets to a different size make a difference.
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If it is a basic Edelbrock 1406 start here:
http://www.edelbrock.com/automotive_new/misc/tech_center/install/1000/1406_manual.pdf
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thank you capt. i think that the manual is exactly what i needed.
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so one question i had when reading the manuel is that when i adjust the A/F mixture screws do they need to be turned in a sequence and adjusted the same amount. and the manual didnt talk really talk about how to adjust a manual choke. thanks
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Yes,they should be turned the same amount.........for highest vacuum.
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the way i adjust the choke is in the morning try to start your engine it should stay idling a little higher than normal... if its too fast lean the mixture.. if it stalls enrich the mixture... adjust it, once you think its not too fast nor too slow that it stalls... let the engine warm up and the rpms should come back down... always make sure that when the engine is warm the choke is fully open... a choke that doesn´t open all the way will cause bad mpg...
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thanks gildardo that helps alot, do you know what type of rpms i should be looking at? and how do i tell if the choke is open all the way? it is a manual choke and i shut it off once it starts(if i needed it). and also the engine wont run with the choke on at all. And for you fairlane i thank you also looking at my A/F screw right now they are not even judging off of the direction the flathead slot it facing.
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well for a stock engine your rpms once warm should be about 700 but if you have a larger camshaft or an automatic tranny then the rpms are a bit higher... sometimes up to 900-1000... just try to keep it as low as possible to save gas while idling such as red lights and stuff... and a choke fully open is completely vertical.. if you have a manual choke then you can shut it off once the engine warms up to the point where it can sustain idle rpm with out stalling.. on cold morning this may be longer that during the middle of the day... if the engine wont run with the choke on then you may be having too rich of a mixture... for the record both screw will never be equal at the direction of the flathead slot.. you measure the them by turns.. start by closing the two screws.. then turn them two turns out.... for example one screw may be like this / and the other slot will be like this -- but they are equal in how much fuel is being metered.. makes sense.. to tune your carb start with the screw being out 2 turns each... the engine should start..turn the idle screw to adjust your rpms to about 800-900.. turn the mixture screws clockwise until the engine wants to stall turn counterclockwise half a turn and you should be in the ball park for a good tune... all this is with a warm engine... if you have a vacuum gauge use it and go for the least amount of fuel going to the engine and getting the best reading from the gauge.. another tip for a healthy engine and good mpg... a clean air filter...
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alright i see what your saying now. and i was looking at my rpms after my drive home from work since the engine was warm and i was running about 750 so i think i am a touch high. And just to verify to start out turn hte mixture screws in all the way then out 2 turns as a base measurement. then continue counter clockwise until i hit 800-900 then in until the engine begins to stall then back out 1/2 a turn. and play with it from within that half turn until best vacuum. Then a couple more questions does the A/F mixture screws also adjust the choke? so what i mean by that is when i have the engine tuned in according to the instructions above my choke should also be set right. and yes i did check the valve for the choke and it appears to open all the way when shut off. Then the last question, if i remember right isnt their 2 idles screws? so what is the situation their or do you think i even need to mess with it? i have a vacuum gauge on its way so hopefully i will be able to get it done this week once its here. and thank you so much this helps a ton.
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yeah you got it figured out, remember the end result should be the lowest rpm possible about 700.. once you get it to 800-900 you adjust the idle screw once more at the end... the function of the choke is independent from the mixture screws.. if the carb is tune properly then the choke wont be a problem... the choke is only there to restrict air flow this causing more fuel to enter and raising rpms to warm up the engine faster and prevent it from stalling.. i went to look at my edelbrock and your right there seems to be two idle screws... i have only used the top one the one that can be turned using a 1/4 nut driver.... once you get the carb in the ball park.. check your timing, then recheck your carb... check your spark plugs make sure their clean, since you were running a little rich they may have darken excessively.. good luck and keep us updated
using that vacuum gauge really helps... you install it and start tweaking the carb until you see what the engine likes... simple and precise..
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alright thanks. im still a llittle confused about adjusting the idle screw. so after i take the mixture screw out 2 turns i adjust the idle screw to 800-900 rpm. and then turn in until begins to stall. and out half turn. and once at highest vacuum turn idle down to about 700.
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check out this video... https://www.youtube.com/watch?v=HwPFiGENMw8
the tuning details start about at the 4:30 time
hope this kinda helps a little...
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yeah the video does help a little, but unfortunatly for me i didnt see it until after i got done tuning the carb in. so i ended being turned in about 1/4 more than i originally was. and i was wondering what should i be pulling on a vacuum assuming that i dont have any leaks. the reason i ask is the gauge that i got is saying only about 12 inches and it is responding correctly when i give it some throttle but it didnt really increase when i was adjust the mixture screws, i think that the gauge may be faulty i got it on ebay for about $20, so it might be
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If you have a stock cam you should be in the 15-17 inches of vacuum range, or better. Its possible you have a vacuum leak, the cause should tell you that. Are there any ports unplugged on the carburetor? Do you have power brakes?
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a manual choke is exactly what it says. You make the adjustment based on how the engine behaves at that moment. An automatic choke can be adjusted for rpm at wide open throttle..with the car off obviously
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No they won't be adjusted the same.
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alright today in auto's class i pulled my truck in and tested the vacuum with a reall gauge and i was getting about 15-16 of vacuum. and i have the carb adjusted at the highes which is the 16 inches of vacuum. i ended up being about 1 1/4 turns out. so i will have to see what kind of milage i am getting on my next tank and see how much that quarter turn did for me. I think i might end up getting a new carb anyway, not sure when but sometime. so what recomendations do you guys have for a carb that gets good mileage and has plenty of power. i was think like a quadrajet or a holly? and what size do you think i would need. (1983 k10 5.7L)
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How much mileage are you expecting out of it. TOPs would be 17mpg on the highway, otherwise your looking at 12mpg average.
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What is your initial timing? Quadrajet gets pretty good mileage because of the small primaries.
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What is your initial timing? Quadrajet gets pretty good mileage because of the small primaries.
i agree... and then they have the huge secondaries... ready for when ever you need them... but to take advantage of the benefits of the quadrajet you have to drive with out stomping on the throttle at every stop sign and red light...
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I would like to get around 15mpg on average if i can(but probably not) and im also looking at switching over to the 700r4 instead of the 350 so the overdrive will also help out if i get it done. and my timing is a touch advanced but its running good and strong so i dont really feel i need to mess with it. and where do i get a good quardrajet i thought that was the brand but i've been seeing summit versions and Q-jet brand but does it matter even. and what size would you guys recommend i was thinking maybe a 600cfm, but idk im just guessing.
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quadrajets are made by Rochester, they came in 750cfm and 800cfm. They are limited further by adjustments on the carb itself such as linkage to secondaries so they work well with an engine that only needs 600cfm. Go to the junkyard and get one from a chevy truck and rebuild it. Otherwise check local speed shops or jegs has them at http://www.jegs.com/webapp/wcs/stores/servlet/KeywordSearchCmd?No=0&Nty=0&catalogId=10002&Ns=P_Price%7c0&Ntk=all&Ne=1+2+3+13+1147708+1147708+1500000&langId=-1&storeId=10001&N=4294966764&Ntt=quadrajet
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You can also ck ebay, get one close to the year of your truck, and rebuild it. They tend to have loose front primary shafts, but you can get a bushing kit and avoid a vacuum leak.
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yeah i have been looking at ebay and there are alot of people/stores offering fully rebuilt done carb for about $200 which beats jegs for the same carb. and i have a friend who might be able to sell me one, but idk how much yet and theirs a guy here in town who can do a full rebuild for $90 so if i can the carb cheap enough i might do that. and i have been noticing that their is a 1 stage and a 2 stage carb, what does that mean?
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Stage 1 and 2, refers to the "performance" level of the carburetor. For street use, I'm sure the stage 1 is fine.
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ok thanks guys if found this one on ebay and its been completly rebuilt and is ready to go.http://www.ebay.com/itm/321077967971?ssPageName=STRK:MEWAX:IT&_trksid=p3984.m1438.l2649 (http://www.ebay.com/itm/321077967971?ssPageName=STRK:MEWAX:IT&_trksid=p3984.m1438.l2649) so i think that this is the one i need but if i can find one at the junk yard and get a rebuild kit and be cheaper than ebay i might do that. and when i get the new carb can the air box off of my edlebrock work for now until i get the one i want. its the high flow triangle foam type. i am a little bit nervous if i have to rebuild the new carb, i have done carbs before but just simple dirtbikes or boats not even familiar with a quardajet.
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i forgot to ask in my last post on how would i go about setting the electric choke back since mine was converted to a manual? thanks
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I wouldn't use that air filter, just get a normal 14" from advance or grab a stock one from the junk yard. Those foam ones are junk. I just bought a timing light and did a tune on my truck, I'll have to wait and see what changes in gas mileage I'll get now, but my timing was roughly 6 degrees retarded and had poor idle quality, changed the vacuum advance to ported so it isn't pulling vacuum at idle, set initial at 10 degrees advance, total is at 33. Turns out I need a new distibutor. But it idles better now, seems to run better and smoother.
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You will need a hot wire in the key 'on" position to run to the eclectic choke.
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well if you could can you explain to me how the electric choke works it will help me out alot. and what color would that hot wire you mentioned be? I found a green wire that probably about an 12 gauge or so and it runs right along the carb and then i found it just sittle behind the alternator, so could this be it? and should't my choke light come on when the electric choke is on also, because it lights up for a second when i shut off the engine. thats another thing that i would like to do also is get a new distributor cap and rotor, but i would like to get a nice air intake assembly instead of just throwing one on their for now and then having to buy another one also. so i think i will try to find one i like and order it with the carb.
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I am pretty sure the green wire you found will be the choke wire. If you have a test light (any auto parts store), turn the key to the "on" position and see if its hot. Also check with the key "off " to make sure its not hot then too.
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ok thanks fairlane. and would you agree that this is the correct carb that i need[urlhttp://www.ebay.com/itm/321077967971?ssPageName=STRK:MEWAX:IT&_trksid=p3984.m1438.l2649][/url] the only reason that i ask is that their were two carbs on their the one is in the link above and the other it said that it fit all small block chevy's and i remeber thinking that their was something different that wouldn't work with mine, but idk. i just want to make sure before i order. thanks
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That one looks fine, should bolt right on, and that wire you found may just plug into the choke.
Some of the things I don't like about rebuilt ready to go is,.......... what kind of kit did they put in it, will it survive today's gas as far as float material and accelerator pump. Did they put bushings in the primary shaft to eliminate a possible vacuum leak. Did they check the air horn for warpage......if they give a you guarantee or trial period, then you may be fine.
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im not to worried if i remember right they have a 1 year warranty and if all else fails i can takeit and rebuild it myself.
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i tested the wire that i had told you about earlier and i has ignition power so i am good to use it as the power for the choke. but it might be a while before i can order the new carb though.