engine rattle

[bigbadchev84]

My buddy just bought a truck and asked me to take a look at it for him. It is a 71 chevy 4x4 shortbox with 36" tires and 3/4ton 4.10s. Has a BUILT 350 motor-so the guy says that he bought it from, a 350/205 transmission.

He was having problems with the motor dieseling when shutting off and said it just dosent have the power it should. The guy he got it from said it has over 400hp anyways he came by and picked me up and went for a quick ride, the thing sounds nasty mean- big cam-tri y headers 3" dual exaust and flowmasters. He was manually shifting it and when going from 1st-2nd it starts rattling the valves, and dosent have a whole lot of power, just bogs down a little but still speeds up.

We took it home and i popped the hood, he has a performer intake and a 650 edelbrock thunder avs carb, smells really rich at an idle. I messed with the adjustment-backed them out 1-3/4turns and then set the base timing at 10 degrees. I have no idea what cam is in it, but its big and has a good lope to it. I stuck a vacuum gauge to it and it bounces from 14-10hg. I checked for vacuum leaks and found none and hooked the vacuum advance to the ported nipple, also tried the full vacuum and no differnce.

I suspect the carb is junk, but it looks to be almost new.

Where should i go from here? All i got done for him is stopped the dieseling and lowered his idle rpms

 

[4X4HIGH]

Sounds like the "rattle" is detonation. The dieseling is caused by either running too rich, too lean, timing being too far off, or the engine is extremely hot in the cylinders which is causing the fuel to burn after the ignition is switched off.

 

[Happyjohn]

Sounds ridiculous, but have you checked basics, plugs, wires,
firing order,cap, rotor, etc.???

 

[bigbadchev84]

Sounds ridiculous, but have you checked basics, plugs, wires,
firing order,cap, rotor, etc.???

All brand new,name brand distributor, wires, the works, engine looks like they ordered all the top dollar stuff out of summit. I was gonna throw my quadrajet on it and possibly adjust the valves. Sounds like im leaning more towards the running rich part.

 

[aychdee]

Sounds to me like a timing issue as well

 

[chulisohombre]

if its detination,he may not be running high enough octane fuel.with all that power added,what is the compression ratio?if its detination,you can back off the timing a lil to get it to burn closer to tdc.if hes not running premium fuel with a high compression,it will run like crap.i know mine does if i try runnin 87 octane.sounds like his engine has about the same things as mine.i just have a standard 1605 600 cfm edelbrock with spring needle and seats.could be carb.with that jumpy hg readings it may be because of the big cam.

 

[bigbadchev84]

Well threw my quadrajet on it, and re-adjusted the timing to 14* runs awesome now, but still had a rattle, luckily he was almost out of gas, so we filled it with super and the rattle went away.

 

[badmix]

Wow..nice truck, that is clean.

 

[chulisohombre]

im not surprised that was the problem.the 14 hg is just a baseline at idle.if the other carb was not jetted correct as it sounds like that was the major problem anyway.it sux to have to run premium fuel,but its better than continuous preignition pinging.

 

[K5dreamer]

yeah, from what ive read, and personal experience with the one on my brothers 1973 bronco, edelbrock carbs are kinda junk, or at the very least very hard to get set up right. my delemma is that im a fuel injection guy, so the last carb i ever played with was a Q-jet on my 1977 olds (first car, LOVED that thing). The bronco has a ford racing 302 in it, and the edelbrock carb, and its NEVER run right. my brother has been debating putting fuel injection on it, maybe ill just buy him a q-jet for his birthday, buy a q-jet manual, and set it up right for him. Q-jets have always been my favorite carbs, two little primarys for decent tooling around mileage, and two MASSIVE secondarys for scaring the women and children off the streets.

 

[chulisohombre]

i have never had to change anything on my edelbrock.just put in the spring needle and seats.runs the same now as it did 10 years ago when i put it on.i guess ive been lucky as both my 67 impala and 69 chevelleboth had the same carb also with no problems.if you know quadrajets and how to make them run right,there is no reason to run anything else.once they are setup right,there is no better carb.