The Stovebolt Site Forums The Shop Area Engine Shop 350 with odd SMoking Problem, follow up

About a month ago I posted a query about what might cause a 350 to smoke on a warm startup. Got a lot of good ideas that I followed up on and think I have solved the problem and thought I would report back.

In talking it out most folks had agreed the smoke was more likely some form a vapor as opposed to oil based on the the quick dissapation on exiting the exhaust pipe. So first step was to do a cold and hot pressure check of the cooling system to rule out any form of a crack in the head. Great relief when she passed the leakdown test with flying colors which was a great relief as this was my third warrenty replacement of a Napa crate engine origninally purchased just about 2 years ago.

So the next step was to start monitoring the amount of moisture blowing out of the pipes on a cold start. Right side spit hardly any while the left spat out enough to leave a two foot long wet streak several inches wide. On a hot start the right emits no vapors and the left emits a good deal, but after letting it idle a minute or so you could see a water puddle forming just inside the end of the left exhaust - confirmation we were looking at water.

Then I noticed the left exhaust was smelling awfully rich. Over to the right side and no scent of unburned gas. Pull the carb and find the Qjet was drooling out its left primary - was even a gas puddle in the intake. Toss the Qjet, on goes a Edelbrock square bore I had lying around. Quickly get things dialed in and now the left side exhaust is no longer rich. The engine is idling smoother, both sides are giving off more or less the same amount of vapor on a cold start though the left is still smoking on a hot restart. But, if I'm remembering my chemistry lessons, a rich mixture provides a ready source hydrocarbons that can vaporized into H2O.

The intake manifold is one of those with a wall to create separate right and left chambers. With that and the dual exhuasts, sans any crossover, is why the problem was completely limited to the left side where the Qjet was leaking and which was why it made sense to consider a cracked head.

BTW, I think the Edelbrock basic square bore is the right carb for what I have. Its not that the Qjet is bad, but the only place I ever got into the secondaries was on a steep hill. We are talking abot a 350 in a 66 4x4 still running the stock gearing, which pretty much lets me make 3rd gear starts and makes 3rd gear rolling stops the norm, even with 30.5 tires. With the square bore I'm getting better low and mid range response which is all I need. With those tires she's still only turning around 3500-3600 at 75 mph.

Good detective work, glad you found the problem!

What'd you do with the Q-jet? I love them.

Only 3500-3600 rpms...???!?!?!

Sounds about right for a 3.55 to 3.73 ratio. Not everybody has OD, ya know....

I was thinking more about the near-oxymoronic phrase "only 3500-3600".

"Extremely high 3500-3600" would seem more fitting. 'specially if you're talking about your 235, chiphead! :p

A healthy 350 can be held at 3500. Not a good idea with a long-stroke engine like a 235, or any engine design with limited # of main bearings or poor rod/stroke ratio.

Chiphead, the QJet is sitting on the bench waiting to get boxed up and put on the shelf of future repair parts, but if you want to make an offer ... and we aren't talking about 3.x gearing in the rear pumpkins. The old 4x4s have the 4.x gearing, though with the tall profile tires my effective gearing is a bit taller. My actual rpms may be a bit lower as that is just my best guesstimate based on an old SW tach that is having accuracy problems, the speed was determined by GPS as my speedo reads about 20% low.

But the next step is to work through the tranny/rear ends. I'd like to find a nice five speed to drop in but don't want to give up the granny gear so more than likely will just change ratios in the differentials - they are just your run of the mill Dynas. Not in a big rush to sort this out 'cause, like Chiphead says, a fresh 350 with a 5,500 readline ain't going to be troubled by running around at 3000-3500 rpm.