New engine just won’t run right

[Russ85]

i bought a gm performance crate engine to replace the stock 305. It’s a newer 90s 350 with 357hp and 390tq
I bought an edelbrock duel plane intake and 650cfm carb. After I purchased the carb I noticed the paperwork with the engine stated it needed 670 or higher. I can’t seem to get this thing to run like it should. Timing is at 10 degrees adv and the carb has been adjusted every way I know how. The best I’ve gotten it to run leaves it with a little ping at high speeds ( over 40) and slight run on when it shuts off. Everything and I mean everything is new on it. Any suggestions or help is appreciated.

 

[PrairieDrifter]

Have you tried backing your timing off a tad?

 

[yevgenievich]

Check how much total timing and how much vacuum advance is adding. If vacuum advance is on manifold vacuum, try switching to ported. I am guessing base timing was checked with vacuum advance disconnected. Some vacuum advance cans are also adjustable.
Also, what fuel are you running? The rating seem to imply a need for premium fuel.

 

[1987 GMC Jimmy]

I was going to suggest a combo of backing off the timing and checking the sheet for the octane rec.

 

[shiftpro]

If all else fails inject N20.
Or get a BB...
and inject with nitrous!

Just kidding...
Hope you get your mill freed up. Sounds like timing to me too. Something simple being a bitch.

 

[Rusty Nail]

Yep. I concur...my thoughts are adjust the carb to the highest manifold vacuum possible and then set the timing.
I also think the parts in question are junk though so I may not be the best guy to ask.
Good luck with the Weber!

 

[HotRodPC]

Have you checked for vacuum leaks? How about the base of the carb? Are you sure you have matching squarebore intake and carb, or spreadbore intake and carb? Using the correct carb to intake gasket?

 

[climb-101]

did you set the base timing with the vacuum advance on the distributor unplugged?

first thing i would do is check timing just the way it is. setup your timing light, start the truck, leave in park and watch the timing indicator as you use the other hand on the carb to rev it up until the timing stops advancing (prob around 3000-3500 RPM). You can also have some one rev the motor from the drivers seat. should be around 36 degs total timing for a normal motor (if i remember right from my old days messing with small blocks).

 

[75gmck25]

Timing is a good place to start. Use a piston stop first to verify that your timing pointer is right. You should be able to run about 8-12 degrees base timing, and 18-20 degrees mechanical without any issues. And your vacuum advance will add 15-18 more.

Next step - make sure you have good gas in the tank. Did the truck sit for a while when you were working on it?


If the Edelbrock carbureter is a standard 1406, it may not be tuned well for the engine you purchased. The 1406 is an economy minded carburetor, designed to get good gas mileage, and it may be too lean for you engine.

Since you already spent the money on a good crate engine, spend a little more and buy a decent wideband AFR gauge,. I have an Innovate gauge that is similar to this one https://www.jegs.com/webapp/wcs/sto...&submodel=&engine=&Nrpp=&No=&persistYmm=false .

When I used the AFR gauge to tune my 1406 with the Edelbrock tuning kit, I found that it was very difficult to get the Edelbrock to run rich enough, even for my base crate engine. I then switched my plan and rebuilt my stock Quadrajet, and found it was much better at keeping the AFR in the right range.

I usually cruise on the highway at about 13.5-13.8 AFR with the Quadrajet, while the out-of-the-box 1406 was sometimes as low as 18.0 at lean cruise. I may burn more gas now, but it runs a lot better.

Bruce

 

[Russ85]

I haven’t checked vacuum yet but I will. When the timing is advanced to 14 degrees it runs stronger but has run on when it’s shut off. I’m running 93 octane always and the fuel filter looks clear. The only part that isn’t new is the fuel pump. Everything else is new.

 

[climb-101]

i would back it down 2 degrees and see if it stops the run on

 

[JON79C10]

Try and double check your top dead centre without reference to the timing marks. Take a plug out and use something small to literaly feel the piston is at the very top. Reason I say this is that you are assuming that when your tab and your TDC mark are aligned it is TDC. You have gone from 305 to 350. Timing marks are different for these engines. If you reused timing cover or balancer it could have a compatibility issue. I had a Corvette in the workshop that should have been a 350 that was actually a 305. It was running like a dog - reason was it had a 350 timing tab on it so was timed completly wrong. IF you refitted your 305 timing tab or cover it will be wrong. I'm running a 350 with HEi dizzy and 14 degrees with a stage 2 cam, stock heads and pistons and it runs perfect with an old Holley 600. You should never have run on with a new engine - timing is definately way out.

 

[4WDKC]

does this engine have vortec hesds?

 

[PrairieDrifter]

If you’re pinging and have run on, there’s a good chance you’ve got too much timing in it.