Troubleshooting engine

hesitation
chevrolet

#1

i have a marshal blueprint 355 crate engine in a 1987 monte carlo aerocoupe. i cant quite get the bugs out. when i mash the pedal she falls on her face then takes off, hesitation. if i accelerate slowly she stumbles in low rpm. and when i try to coast in gear she chugs really bad… ive complely cleaned the carb (edlebrock-600), the timing is marked from the factory but i checked it anyway, its good. feul filters are clean. everything is new and im lost. if you guys have any segestions id appreciate it.

thanks, ryan burdick


#2

I had a similar problem with a 1965 Rambler. It turned out that the timing marks were off. If the engine was timed using a strobe light, it would have the problem you are having if the timing was set on the mark. I finally found a great mechanic that set the timing by feel and it worked perfectly. The alternative is to set the timing using a vecuum gauge. This may not be your problem at all, but it’s worth checking.


#3

this could well be a timing issue, but it sounds a lot like a vacume leak too. Vacume leaks can be tricky to find when the engine wont run because of them, esp. if it is say, because of a warped intake manifold.


#4

Get a vac gauge

http://www.secondchancegarage.com/public/186.cfm


#5

Are you sure the accelerator pump is discharging gasoline from the nozzle when the pedal is depressed. Look down in the carburetor primary side and work the throttle by hand. You should see 2 streams of gas being squirted out and instantly with no delay.

If you do then it might be time to consider a rod and jet change on the carburetor. The rod change is a 5 minute deal. The jet change takes a bit longer as the carburetor top has to come off but on this carb it’s easy to do.

A falling flat often points to an acc. pump issue and a and stumble often points to a lean problem with the rods/jets. Edelbrock has a chart for changing the rods/jets so you should use this chart and not overdo the changes. It may be a trial and error to get it just right. That’s why Edelbrock offers the rod/jet assortment kit.

(Neat car. Not many aerocoupes around.)


#6

That is a very cool link. Consider it bookmarked immediately. Thank you for posting.


#7

Agreed. The Edelbrock AFB will run out of the box, but generally needs tuning (including swapping metering rods and jets) to make it work well with whatever engine it is installed on. Get the jet kit and spend some time reading about it and swapping them until you get good results.


#8

There ia an old saying that most carburator problems lay in the ignition system and you know there always is a bit of truth in old sayings.


#9

Automotive engineers spent weeks setting up carburetors, engine by engine, model by model, until they got all the drivability problems worked out. They had an engine development lab at their disposal complete with dynamometers and exhaust-gas analyzers which allowed them to get the carb jetting and settings right on the money. Tinkering around in the driveway with a box of jets and metering rods and an after-market carburetor without haveing a clue about what you are doing, well, Good Luck…

Have you considered just installing a stock QuadraJet on that engine??


#10

Yep. I was just getting ready to ask how old and in what kind of shape the distributor cap is.