Initial break in with dual carbs

[olskool68]

Hello all. A quick intro, I've been working on antique vehicles most of my life. I've come to find my comfort zone with all Chevy inlines. I currently have an original 48 chevy with a 216 and a 1920 rat rod with a '76 250. While mostly a tinkerer and repair guy, I recently took on my first rebuild project of a leftover '55 235. I got a little aggressive a went with a Patrick's 3/4 cam, Williams daul exhausts and a water heated offy dual intake with Siamesed W-1's. Getting fairly close to break in and I'm wondering if I should block off one of the carbs so I'm not trying fight that fire while I'm just trying to go through the initial 30 minute break in. I know timing isn't a critical issue during break in, so what about fuel delivery? I'd hate to crank the engine up and find out I have to stop to make adjustments to the Carters.

On that same note, what happens if you have to stop in the middle of a break in? Say 10 minutes into it a leak develops prompting you to stop the break-in. How do you continue after?

Love all the info you've put out, Deve. I built a start cart similar to yours with the clipboard and printed out SEVERAL articles as a guide during my build! It's been a slow build with two toddlers wanting to join dad in the shop! Thanks for the help!

[Deve]

I have never done a dual carb setup, so I hope others chime in, but it would seem to me, blocking off one carb for the breakin makes sense. I guess I would have the screwdriver standing by to turn the mixture screw a bit more if needed. The most important thing is to have a 20 minute run without interruption if at all possible. If you have to stop, I would shoot for another 20 minutes. There are others here who know more about dual carb setups than me for sure. Be sure to let us know how it turned out!

[olskool68]

So I fired her up using both carbs. Ten minutes into the break-in, the temperature started climbing drastically and I had to shut it down. After removing the block plug, what looked like coffee and scale dribbled out of the block. I attempted to back-flush through the radiator and eventually got a good stream and clean water. Take two and this time I make it 15 minutes when I have to shut it down due to temperature again. This time I pull the radiator, water pump, plug and what a mess. Apparently the machine shop I used didn't flush my block out sufficiently!

Two days of scraping and flushing, I assemble her back up and this time I'm getting a steady 185. But after the break in, I noticed I couldn't get the RPM's below 950. Adjusting the idle mixture screws didn't help and the idle speed is backed completely off without any change. The neat (and troublesome) part about these dual Carters is the common throttle shaft to the throttle valves. I contacted the gentleman who built this setup and he's given me a few things to try.

I've posted a video on youtube of the engine after the break in but can't find how to share it here.
Question, how long do you continue to use the break-in oil? I don't have a filter set-up on my 235.

Thanks again, bud! The information on the static timing and initial lash was invaluable! She fired right up the first time!

[Deve]

I do the initial runup and then change to regular oil. 20 minutes or so. It just needs to run long enough to seat the rings properly. At 1500-2000 rpm for 20 minutes, its seated and then some. I have sent many engines to the engine shop for what I thought would be a proper cleaning and felt disappointed after. Its really hard to get those passages clean. Good luck on the dual carb setup!

[Tony B]

I will be putting dual W-1s on my 235 as well and was wondering about doing the break-in with the duals. Then I thought that maybe I would put the stock manifolds on and run a single carb for the break-in then put the dual set up back on once the break-in was done. The break-in would be done with the engine out of the truck.

[Deve]

Probably as good idea Tony. Adding the extra problems that could come up for that 20 minutes is probably a bad idea. Those are nice carbs! Let us know what you really think about the dual carb setup after a few years of running them. A person can never hear enough about this issue. If you get a performance boost from it, it would be good to know how much. Ive heard things both ways, but nothing definitive.