The Stovebolt Site Forums The Shop Area Engine Shop Poor WOT power

I am still working on getting the issues on my carb swap from a Rochester to a Carter and I have found another issue I need some help with. Most of my driving is very laid back; slow speeds (about 45 tops) and easy acceleration. The other day I was going up a hill and was trying to speed up some (or at least not decelerate anymore) and I discovered that the more I opened the throttle, the worse the engine ran. As I topped the hill and backed off on the gas pedal, things smoothed back out. I did some experimenting on the rest of the drive home including really stepping on the pedal, and I had the same issues. The more you open the throttle, the worse it runs. The engine idles fine, cruises great and accelerates well when you do not ask for it too quickly. Thinking I might have a vacuum leak, I disconnected the wipers and had no change on the test drive. I read in another post about looking for vacuum leaks using carb cleaner so I gave that a try. The only thing that changed anything was when I sprayed at the area of the throttle shaft and the engine would almost die when I did that. Worse on the front side than the back.
So my question are; could the air leak at the shaft be causing this issue? Or could there be another air leak somewhere that I have not found (I checked both ends of the vacuum advance with no change)? Could the metering rod be misadjusted? I am not confident on my attempt at getting that adjusted correctly, but it seemed to be set right.

It is a Carter 2100S.
My wife asked what WOT is; wide open throttle.

Thanks for your help,
Lee.

What gear ratio are you running? Once the engine gets out of the torque band where it's able to accelerate, it will lug down. It's either time to downshift and let the engine rev, or go to a somewhat lower rear end gear. Most stovebolters get a case of the vapors anytime an engine gets much above fast idle, so we've got a bunch of lugged-down engines running around at 40 MPH in either high gear and/or overdrive with a 3-something rear end ratio. The truck doesn't have enough torque to get out of its own way like that. Drop a gear, get the engine up around 3K RPM, and watch it scoot when you push the loud pedal! Back in the late 1960's my bone-stock 58 Chevy Delray coupe with a 235, a 3 speed stick shift and a 3.55 rear axle had no problem running 75-80 MPH, and that was on fairly low profile tires on 14" wheels. The engine rarely saw less than 3K RPM.
Jerry

Read Jerry's post (above) again, spot on.

Aftermarket tachometers are dirt-cheap. Hook one up, and see what RPM you are running.

It will also be an aid in tuning.

Jon.

It has the original 3 speed and rear diff; which according to GM archives, is a 3.90. I have been unable to find any numbers or tags on the differential to confirm type. I do not have an installed tach, just one I can hook up under the hood for tuning. I will test the acceleration next time I am driving and see if it improves in a lower gear. Thanks.

They make automatic transmissions to solve that issue.

Ed

BOO!

Jon

Hmmmm- - - -that setup should be able to accelerate smoothly at any speed above 35-40 MPH unless you're on a very steep hill. You're not running extremely tall tires, are you?

Dad had a good comment about the subject - - - - -"Automatic transmissions are smarter than all drivers and most mechanics- - - -they can't be lugged down in the wrong gear!" He had a similar opinion about automatic chokes.
Jerry

check your dwell and make sure it is between 32 and 34

The tires are 15 inchers; with the Rochester, I had no problems with acceleration or hills, even in third.
I’ll check the dwell tomorrow.

The points and dwell are fine, all within specs. I did a short test drive and the hesitation is less when I am in second or first, but there still seems to be some when you really go in on the throttle. I may be chasing a non issue here; I will need to put the Rochester back on and compare to be sure. Thanks for everyone’s help.

Lee.

It's probably the carburetor, but I'm going to complicate things a bit.

I suffered the same issue with my '49 216 with Rochester carb. I often run the interstates and keep up with traffic just fine. On hills I just hold the pedal to the floor to squeeze all the power I can get. On one such trip I found I was losing power going up a gentle hill with the pedal to the floor. Not normal. I found that if I let out on the accelerator a bit I would actually gain power. She ran like a little champ, but once the accelerator went past a certain point I'd noticeably lose power.

I gave the old truck a good tune-up and now she runs like a champ again with full power all the way to the floor. I never touched the carb, though.

Check your fuel pump output volume and pressure. Might be the pump, might be the filter or maybe you didn't open the tank valve all the way when you last changed the pump.
With restricted flow, as you get toward the top of the hill, the float bowl gets lower and the mixture gets leaner and the power drops. Yet, unless it's real bad the engine doesn't missfire. It can fool you. Most re-pop pumps aren't very good. I went to an electric pump and it solved a multitude of nettlesome little problems.

I switched back to the Rochester so as to rule out anything other than the carb and the acceleration problem went away. No stumbling with large pedal input going up a hill in 3rd gear anyway. I’ll drive it the next few days and see how it does.

Yep. Like I always say, "its always the carburetor!"

Its almost never the carb.... Unless its really the carb..

The Rochester has its quirks, and it seems the Carter has its too. I’ll just have to decide which ones I can live with and use that carb. I still think that maybe I have something mal adjusted inside the Carter. I’ll open it up again and triple check the settings and then try it once more.

Lee

Either people get me, or they don't. I'm good either way. , as long as it prompts them to think for themselves before throwing wheelbarrow loads of parts at their truck.
In the case of OP of this thread, since he had a known-to-be-good carburetor laying around, a simple swap of the carburetor was the smart thing to do.

I had a similar issue back in the mid-1960's with a flathead V8 in a 47 Ford coupe. The original Holley 2-barrel for that engine had 15/16" venturis, and I found a carb for a 1955 Ford 292 engine that had 1 1/16" barrels. Since I knew my engine had been bored 80 over by a former owner, I thought the 252 cubic inch engine (up from 239) could handle the extra carburetion. Wrong! at moderate speeds in high gear, I had to modulate the gas pedal very carefully to avoid a flat spot. I could slap it into second gear and get the RPM up, and it would run like a banshee! Ditto for top end, but the midrange in top gear was just not there!