Engine Struggle

[Johnbravado]

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?

[Irish_Alley]

was it sluggish before the tuneup? whats your timing set at?

[Johnbravado]

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.

[Irish_Alley]

check out our notes on the timing HERE
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

[VileZambonie]

i am assuming

Herein lies your first problem

[roundhouse]

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


Sent from my iPhone using Tapatalk

[Irish_Alley]

in maryland we have very few steep hills ive always just tried to power brake

[VileZambonie]

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.

[Irish_Alley]

its also very hard to do in a standard

[Johnbravado]

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.

[bd]

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.

[VileZambonie]

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?

[Johnbravado]

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.

[zieg85]

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...

[Irish_Alley]

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)