Hesitation/Flat spot

I've got a hesitation when I give gas to my 74 CJ5 232 engine. Happens in all 3 gears. If I am ever so gentle accelerating it does not occur.

I've rebuilt the carb and I've changed to electronic ignition; but no change in the flat spot.

Any ideas?

 

Can you confirm the accelerator pump is working?

Here's a good resource for the 74 carbs:

http://oljeep.com/gw/74_tsm/4-FuelCarburetion.pdf

 

I'll check out the link.

Top answer, Yea, the pump work fine it seems.

just changed the fuel filter and adjusted the timing. Seems a bit better. But, still there.

 

Vacuum advance distributor? Check the vacuum diaphram.

 

This is from a Corvette site but the principles apply to any engine.

http://www.corvette-restoration.com/resources/technical_papers/Timing101.pdf

 

Does the acellerator pump link have different holes? Maybe grab the next-richer hole. That would be the hole that causes the same amount of acellerator pump action with less throttle input.

 

Do you have the EGR?
I hooked mine up to pass emissions but it caused hesitation.
Unhooked it and it runs perfect

 

Vacuum advance to ported vacuum at base of carb, or actual manifold vacuum? Ported vacuum does not provide advance at idle, manifold does. As soon as you open the throttle they are equal, but if your engine isn't running well at idle it cannot be expected to gut up off it's butt and go without some hesitation.

 

OK.

I've changed the entire distributor, including the vacuum diaphragm, so I doubt it's that.

No EGR as I have no pollution crap on my car.

The Corvette article was semi-helpful...but a little over my head. Seems that the vacuum advance does not function once you get going, but operates at idle or just when you're taking off or when you reduce RPMs, likw when you switch gears....because that's when it happens...at the low part of each gear.

Have to check these accelerator holes, Chilly.

Runs fine at idle...but, still may be a vacuum problem, somehow.

Today, I'm installing a 3 ohm Pertronix coil. Doubt that it will handle the hesitation, though.

One note: I checked all the spark plug wires. When I removed one I got a shock...but i may have been too close to the coil and it arced? Anyhow, I changed that particular wire and it made no difference in the engine's performance ...at idle,anyway. So iswitched the wires back to original. But, perhaps there is a short and that could be causing the hesitation?

By the way, I can't tell you how much I appreciate the listen and the input, guys!

Peter

 

And, by the way, I pulled the vacuum hose off the advance, and it seemed to make no difference in engine performance at all...at idle or with accelerator depressed (gave it gas).

 

Vacuum advance is only "in" at idle, or when cruising with little throttle input. Having good throttle response off-idle starts with having a good idle to begin with.

When you pulled off the vacuum hose you say it made no difference. Did you plug it when you pulled it off? It should have run like a turd when you pulled it if you didn't plug it. And it should have run poorly at idle even if you did plug it. Throttle response really can't be judged unless you are going down the road, either. With engine in neutral it will seem to respond OK.

It is possible that even with a carb rebuild the acellerator pump may not be working right. On a motorcraft 2100 there is a red rubber umbrella-type check valve. If the metal surface where the check valve seats is corroded or pitted it won't work right. It might give a lazy squirt but might not be enough. There is also a steel ball bearing with a metal rod riding on top of it that acts like a backflow preventer, keeping the circuit full of gas. If the ball is rusty, or if the ball's seat is corroded, or if the weight is corroded, it may work marginally but insufficiently. There is also a tiny (I mean REALLY tiny) pin-hole air bleeder at the top of the accellerator pump chamber to allow air to escape but the hole is small enough to not cause a significant loss of gas when you squeeze the pump. If the hole is clogged you could have some air trapped in the pump chamber. This is all specific to the MC2100 but your carb may be similar.

I tried to reuse the red umbrella seal and it worked for a while. Then it had a horrible dead response. When I got a replacement check valve I found the other had come out of the hole and was floating around under the bellows.

 

OK, Chilly.

Well, I'm bringing the Jeep to my next door mechanic who has some damned machine which'll check the vacuum.

As for the carb, i did replace that ball bearing and everything that I could minus the body. If one of the "seats" is worn, well..... The air'fuel mix needle may be slightly blunted, so I'm going to try to find a good one somewhere. It's a Carter YF carb, so they may not be easy to come by.

Meanwhile, I'm going to continue to hunt for other causes.

Sounds like you know your business.

Peter

 

No, I don't know much. I just rebuild my MC2100 and I learned a lot about the different carb circuits in the process. I also have a factory full service manual that does a decent job of describing the carb function. There are some guys on this board who REALLY know their business, though.

You may consider installing an MC2100 before you spend too much effort on the Carter. By may accounts it is a very good carb for the I6 (with a 2-barrel manifold). I run one on a 304 and it runs very well since the rebuild. Make sure you get one with the 1.08" venturi diameters.