73-87chevytrucks.com
73-87 Chevy _ GMC Trucks => Engine/Drivetrain => Topic started by: Johnbravado on August 02, 2017, 07:25:33 pm
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So I did a tune up, replaced cap and rotor and plugs. adjusted timing and carb. replaced fuel filter, breather, and cleaned air cleaner.
When i smash the gas though it seems like i got no go. like the system is not getting fuel. and sometimes when i am driving it feels like it cuts out for a second then gets back on it after a second even though i have not released the gas. I wish i could also explain the weird sound, like gurgling but it is air gurgle
I was thinking it may be my vacuum. Just for info on the truck. it is a 300hp crate engine from JEGS online and only has roughly 15k miles on it. I put a steel high rise manifold and 650cfm 4bbl carb on it. new fuel pump and water pump on it at install. rebuilt the TH350 tranny and new driveshaft at time of engine install. Drove from AZ to MD after the 500 mile breakin oil change towing a car and loaded. This 78 c10 is a beast.
But i saw my vacuum lines may be worn and there is something called a vacuum canister but i cant seem to figure out where it goes or what it does considering the vacuum comes from the engine block. and i think what i am calling a vacuum canister may be the charcoal canister for the fuel vapor
Any ideas on what could cause a sluggish acceleration?
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was it sluggish before the tuneup? whats your timing set at?
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timing was done at a mechanic and I just got my timing gun today in the mail, but didnt have time to verify the timing. I will verify 10*BTDC tomorrow, i am assuming the mechanic set it to standard issue 350 engine timing. so if 10*BTDC is not std issue 350 timing that could be my issue
Just reading the spec of the engine also it says the vacuum advance should be disconnected because it is internally timed and that the vacuum advance should be plugged.If the vacuum advance n the distributor is NOT plugged could that be causing the issue?
And i gave the turck a tune up because f the sluggish acceleration. I was hoping the tune up would have fixed it.
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check out our notes on the timing HERE (http://forum.73-87chevytrucks.com/smforum/index.php?topic=32085.0)
in short when doing your timing when you unplug the vacuum advance if you dont plug the carb or the hose going to the carb you will create a vacuum leak and this will raise your rpms.
i normally set mine to 16°. then once timing is set plug the vacuum advance into my manifold vacuum and reset my idle
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i am assuming
Herein lies your first problem
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I always just set the timing with a vacuum gauge to its highest idle vacuum and back off just a bit
Or by ear , making several trips running it up a steep hill advancing it a little each trip until it starts pinging / knocking , then back off just a bit , like 2 degrees
I have one truck that's set at 27 degrees idle with the advance unhooked and plugged and it runs great
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in maryland we have very few steep hills ive always just tried to power brake
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While those methods can get you in the ball park it does not optimize your performance. Consider it base-lining at best. Power braking does not adequately simulate engine lugging, ratio changes, temperature, altitude, aka normal driving conditions, not to mention it's murder on your transmission.
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its also very hard to do in a standard
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so it appears to be timed per spec and i did the i adjusted the carb for max 20 in/Hg. It started good and then when i turend around and came home if i smash the gas it just does not accelerate. What are effects of a vacuu leak or bad vacuum. I have really old hoses and am going to just replace all the vacuum lines and the PCV valve.
Is there any other system besides bad fuel input and timing that could cause a bog down to the system? that is what it feels like, like the engine is just being bogged down under load and it just wants to give up. but if I ease it a little and massage it it will move nicely.
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Is there a strong blue ignition spark? Inspect all of the fuel hoses for kinks or collapsing then check fuel pump draw, pressure and volume. Any possibility that someone installed a redundant fuel filter? If so, replace it. Fuel filters have a marked direction of flow - make sure it is (they are) installed correctly. Verify the carburetor float level is correctly adjusted. Is the 'gurgle' originating from the exhaust? Check for excessive exhaust backpressure. Temporarily disconnect the exhaust close to the engine if you need to - but don't do this at night in a "quiet" neighborhood - lol. Does the transmission downshift with rapid throttle opening below about 40 MPH? Recheck the detent cable adjustment. Is the transmission full of fluid? Verify that the transmission vacuum modulator valve is receiving full manifold vacuum and that there is no evidence of ATF dripping from the modulator valve nipple or its vacuum hose when the hose is temporarily removed from the valve for inspection.
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if i smash the gas it just does not accelerate.
As in it does not downshift? Is the detent cable connected and properly adjusted? Is the vacuum modulator hooked up to manifold vacuum?
What does it do if you manually downshift to second, does it still fail to accelerate?
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when i say it does not accelerate i mean it takes like 10 minutes to go from 35-40. or if i am at 10mph it just kinda doesnt want to g faster no matter how much i give it gas. i replaced the PCV valve and that did not seem to do anything. i got a strong 22in/Hg at the carb under WOT. i am replacing the brake booster tomorrow and see if that does some magic. also this is intermittent. so sometimes i can drive it and no problem with accelerating. then all of a sudden issues. I am going to do the brake booster tomorrow and readjust the timing maybe advance it to 12*@650rpm and increase idle to 950rpm. this is a JEGS crate 290hp engine so it has a little beefier cam. the mechanic who put it in said he almost would recommend a 2500 stall converter which explains the rough to get going from a dead stop and he had up the idle to 1100 rpm. also i am from AZ and just moved to maryland so atmosphere actually matters here. is a choke important here? in tucson i didn't care about a choke because it is just always hot. here though i believe it is not the same. Should i connect the battery to o the electric choke. right now it is not connected i only groun dit.
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Does it have a catalytic converter? Sounds like it is stopped up. Have you removed the air filter element to see if that makes a difference? I've seen the element fabric put in backwards and the fine filter is outside and the filter looks clean...
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do not get that stall. if it really the stall then if you manually shift it your rpms will be in that range and she should take off. you have some other sort of issue a 290 hp engine isnt real big and shouldnt require any special parts to make it go. you have either a spark issue, air flow issue or fuel.
what came on the engine (far as accessories)
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I think you should wire the choke properly or remove it. I think I would also verify the float level is correct.
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also i live in maryland. with this weather we're having choke shouldnt be an issue unless its "on"
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accessories nothing really, i believe it is referred to as short block, everything i bought new like intake, fuel filter, water pump, flex plate, carb.
I am not sure if this was the issue, but there is a manifold vacuum port coming off the rear of the intake. It is a splitter, 1 of the lines goes to the transmission, i think based on what an earlier person was saying of things to check, it goes down i 'trace it out. the other one wrapped around and would connect to my distributor if i used vacuum advance to time the engine, but engine spec says don't do that and so it was left uncapped.
truck was sounding like garbage, when I plugged the line it picked up and sounded good, released and sounded like garbage. plugged sounded good. So i redid the timing and set the carb and will see how it goes.
and i appreciate the help from everyone.
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ok, did it come with a timing cover and harmonic balancer? the vacuum lines, cap all that arnt being used. the trans and vacuum advance should be manifold vacuum and the brake booster. when you set timing unplug the vacuum advance and plug that line. ensure you have NO vacuum leaks
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I believe I had to buy a harmonic balancer for it because we were going to use the one off old engine but the guy sold it to me lies and said it was a 350 and in reality it was a 305. The only thing right now that could possibly be giving a leak now is the old fuel carbon canister but I replaced all vacuum lines.. and thanks for the info on the no need of choke.
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you said you left one of the manifold lines uncapped ("he other one wrapped around and would connect to my distributor if i used vacuum advance to time the engine, but engine spec says don't do that and so it was left uncapped. ")
theres also three locations for the timing marks
(http://www.grumpysperformance.com/stock_tab_2.jpg)
(http://grumpysperformance.com/timingchain4c.jpg)
http://www.crankshaftcoalition.com/wiki/Timing_tabs_and_damper_TDC_lines_SBC
the only way i know to tell if you have the right setup is to manually bring the piston up to TDC and see where the mark on the balancer lines up with the timing cover.
http://forum.73-87chevytrucks.com/smforum/index.php?topic=32085.msg270456#msg270456
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i am going to have to recheck my timing. i have the cleaner looking silver bracket. except it is real hard for me to see things down there but your picture cleared it up. I don't think it is timed right now. I think it is timed to 4* instead of 10*. thanks a lot for the picture. I will have to look at it again when I get home after work.
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I'm going to have to say if your timing was off enough to cause it to run that poorly you would be causing the engine to run hot.
You said sometimes it accelerates fine then it doesn't.
Sure sounds like a loose baffle in the exhaust moving around sometimes blocking the exhaust flow
Shot gunning the brake booster seems like an expensive shot in the dark unless I missed something.
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Is there a strong blue ignition spark? Inspect all of the fuel hoses for kinks or collapsing then check fuel pump draw, pressure and volume. Any possibility that someone installed a redundant fuel filter? If so, replace it. Fuel filters have a marked direction of flow - make sure it is (they are) installed correctly. Verify the carburetor float level is correctly adjusted. Is the 'gurgle' originating from the exhaust? Check for excessive exhaust backpressure. Temporarily disconnect the exhaust close to the engine if you need to - but don't do this at night in a "quiet" neighborhood - lol. Does the transmission downshift with rapid throttle opening below about 40 MPH? Recheck the detent cable adjustment. Is the transmission full of fluid? Verify that the transmission vacuum modulator valve is receiving full manifold vacuum and that there is no evidence of ATF dripping from the modulator valve nipple or its vacuum hose when the hose is temporarily removed from the valve for inspection.
How did I not see your post and then ask the same question? durdeedurr
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Trust me. It gets worse as you get older!
Besides, great minds think alike! 8)
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lol
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So I am trying not to go through the transmission problems and hoping that resetting the timing will fix it. The timing was off a lot at 4*. It always sounds good though the first run. It is that 30 minutes drive to work or home that exposes all the ailments. Today I felt the messed up action. But when I got home. I rotated carb and the engine reved up to 1100 rpm from it's previous set idle speed of 650. I had to bring it back down to 650 and finally got it 10* @ 65rpm. Maybe a little more than 10*. I just want to stick with spec recommended right now. I am hoping this is it. If not I am going through bd's post item by item
This was a giant learning experience for me. Vacuum leaks, tune up stuffs. First time timing and carb setting. I think I still need to readjust the carb since I adjusted the timing. But it was a little rainy and I had stolen someone's covered parking to do the timing real quick.
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I'm having similar issues and then I started tracking down all the vacuum leaks, and then realized that the accelerator pump discharge nozzles were plugged from the ethanol residue in the garbage gas. I ran a small piece of wire in there and cleaned them out, big difference.
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You put a pressure gauge the fuel line at the carb yet ?
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no but i just bought a new fuel pump since it is like 20 bucks and 2 bolts. i am replacing that tomorrow. I get that feeling like my gas is flooding then starving than flooding and starving while driving an dnot moving the gas pedal. it is either pump or i am rebuilding carb and something is blocked
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johnny i know with my mud truck it was a pain to get and keep her running right. think part of my issue was a bad fuel pump that allowed fuel to drain back to the tank after i shut the engine down. i installed a universal electric pump from napa, for get the psi but it was around 5. good number for a carb. i have it set up so i can flip a switch and manually turn it off or on but also have the power wired to the fuse box so it only has power with the key on. it got rid of most my issues after a good tune and the pump installed i can have the engine sit for a year. put a good battery in her flip the switch and turn it right over and she starts every time. i also have one of those plastic boat fuel tanks that i remove when im not using the truck just so the fuel doesnt sit and i use it on other engines
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This is first time I have done a fuel pump and after completing it I should have bought the electric pump at AutoZone I saw. Think it gave also 4-7 psi but that is all we need. New pump is on. If this doesn't solve it, gotta wait about an hour to test drive for the sealant to dry. But if this don't solve it. I am going to do a carb rebuild. Haven't done one of those since my VW bug in '98 how much harder could aedelbrock 1406 be.