Inliners International Forums General Discussion Engines 235 Acceleration

Gentlemen,

When i pulled my 235 engine powered 1951 Chevy truck into the garage it would not idle below 1,800 rpm but otherwise accelerated great up through 4,000 rpm. I fixed the high idle problem ( broken front rocker shaft; not bolted down in the center post, don't ask - it was due to my stupidity.....) and installed a used 261 cam and later a new 261 cam.

With both camshafts I could not get the engine to run over 2,000 rpm, every time I shift from 1st to 2nd it's like the fuel is turned off; the engine coughs, sputters and has zero power/acceleration.

What I don't understand is the truck easily ran above 1,500 rpm even with then broken the rocker shaft and now it doesn't. the engine is set up as follows:

Fenton intake and headers

Two Rochester BC carbs, balanced with a dual carb sync tool

Original series coil, distributor, wires; plugs are three posts which center over the tip of the spark plug. (condenser a problem??????)

Dual, 2 inch exhaust pipes, with LOUD mufflers

the lifters are solid and adjusted by the book

I set the timing by using a vacuum gauge; I advanced it until the improvement in the gauge stopped and then returned to the high point.

the vacuum gauge shows 14 pounds (?) of suction, close to the end of the red reading stating "advance distributor timing" and just before the green area stating the engine is running correctly.

I need all the help I can get,

Thanks,

Did you verify cam opening and closing timing events with either camshaft. It sounds like its lazy, like its out of time. Its easy to get the timing marks off a tooth or two and not know it.

Other thoughts:

I could not get the engine to run under load; otherwise the engine responds immediately when not under load. it idles to 4,000 + rpm immediately and snaps back immediately every time. suction is identical in both carbs.

Can you put a timing light on it to verify the advance in the distributor is working? It still acts lazy from either cam timing or ignition timing. You need to see what it is actually doing when you rev the engine.

Hi CNC,

Appreciate the comment but we can at least eliminate that possibility. I've become so frustrated with how it runs I've become anal about timing; the most recent (new) cam was installed next to the crankshaft correctly. I can say that because I took a picture of it before I installed the cam/crankshaft cover.

Before installing the fan onto the water pulley I made an adapter to bolt onto the vibration damper so i could rotate the engine slowing and carefully while setting the valve lash. The settings were done with the pistons exactly on TDC.

I tend to agree with you about timing, the engine is hard to start and, initially at 1500 - 2000 rpms, does not run smoothly. Once the engine warms up (3-4 minutes) the engine runs smoothly at 1,000 rpms and is immediately responsive to the throttle.

This issue will be solved, I just don't know when.

Thanks!

CNC, I missed your comment about distributor timing, I'll check it out!

Ted

Might be too much timing when going by vacuum? Reason i bring this up is because i had mine timed with my old cam and even after installing my new cam using the vacuum gauge. I advanced it till the gauge would not show an increase in vacuum (17.5 inches of vac)then just slightly retarded it. Truck ran good at all rpms and never knocked to my knowledge but seemed to not pull that hard and would run out of power. I actually retarded the timing way down and the vac is currently 14 inches. Man what a difference in acceleration and pull. Not exactly what the timing comes out to now as i have yet to stick a light on it to confirm. Im playing with little tweaks now to see what else i can do.

I think someone mentioned that over timing just a little can hurt as bad as under timing lots.

When your vacuum gauge is connected is the needle rock solid or does it bounce around?

Wolfcub, I'll give your thoughts a try and bring the timing to about 8 degrees BTDC, thank you. The vacuum gauge needle is rock solid, no bouncing at all.

I'm also ready to go back through my two Rochester BCs, although I can't see how they would not work now when they seemed fine when I started swapping cams.

Hello,

It runs great! I took it out yesterday and from stop to over 60 mph it just keeps pulling! I've still got some minor tuning to do but nothing serious. The solution came from two comments, one to check for a strong spark and another I picked up online.

The spark getting to the sparkplug was weak; the points were 40% pitted and the point setting/dwell was out of specifications. I had spark and the truck idled okay and when not under a load the change to higher RPM wasn't a problem. Under load the spark at the plugs simply was not strong enough to make up for the necessary change in timing.

I also went back to the engine initial timing setup. I set it up at TDC, zero advance and it fired right up and runs strong. My dwell reading is just inside the required range but I will adjust the timing to see if I can maximize performance.

Thanks to all of you for thoughts and help, I really appreciate you!

Have a great day,

Ted