Dauntless hesitation and frustration

I finally got my 68 Commando running, but I have a severe hesitation problem when I give it gas when it is in Drive.
It seems to run good when it is in Park. At an idle of 800 rpm I get a vacuum gage reading of 14, and it is pretty steady. When I accelerate in Park, it revs up nice and I can see the engine timing advance using a timing light.
When I put it in Drive the idle goes down to 600 rpm and the vacuum goes down to between 11 and 12, which is not good, but it idles without stalling. If I depress the accelerator down there is a severe hesitation. If I try to take off real slow and slowly give it more gas, there is still hesitation. I can only really drive it with the accelerator pedal just a little way down.
I have the vacuum gage connected and inside the Commando when I am running and I can see the gage go almost down to 0 when I accelerate. I'm not sure how far down it should go but I suspect this is not right.
I tested the ported vacuum from the carb and it is at 0 at idle and goes up as far as 14 upon acceleration, so I believe the advance mechanism is working. I also tried many different timing settings and I cannot find a vacuum leak. I don't know what I should check next.

 

Re: Dauntless hesitation and fraustration

Did you check to see if the float is adjusted properly?

 

Re: Dauntless hesitation and fraustration

I had the carb rebuilt by a carb shop. I would hope they would have that right. If I keep rev-ing the engine in Park, it never hesitates. Would this indicate the fuel in the reservoir is adequate? I also put a new Carter
P4070 electric fuel pump in, back by the fuel tank and it keeps the clear gas filter full.

I'm not sure how to check the level of the gas in the carb reservoir.

 

Re: Dauntless hesitation and fraustration

Thank you for the suggestions.

This morning, before turning on the ignition, I disconnected the throttle linkage and got over the top of the carb with a flashlight. I pumped the throttle by hand with a full stroke 10 times and I got a full stream of gas to both barrels every time.

I then reconnected the throttle linkage and started the Jeep. Before it was warmed up, it was idling in Park at 500 rpm and the timing was 10 degrees BTDC. The vacuum was swinging between 10.5 and 12. When it warmed up the rpm was 800 and the vacuum was at 14.

I then advanced the timing until I got the highest vacuum reading with the idle speed adjusted to 800 rpm.The vacuum was now steady at 15. When I put it in drive, the idle went down to 600 and the vacuum was swinging from 12 to 13, which is not real bad. The timing is now about 20 degrees BTDC (about an inch over the top of the index marker). When I drove it, I still got the hesitation and probably a miss with the accelerator pedal down about 1/3, even if I got it down there real slow and held it steady. If I put the pedal down about 1/6, it ran fine but of course slow.

I then took the plugs out and cleaned them. I also checked the compression. 3 cylinders were at 100 lbs, 2 were at 110 lbs, and 1 was at 120 lbs. I also checked to make sure when the timing index marker was at 0 degrees, the #1 piston was at the top.

I put it back together and took it for a ride and still had the same problem. I am now thinking the problem may be the carb jets or hopefully something else with the carb.

Tomorrow I plan to check to see if my my local NAPA has a rebuilt carb. I saw a rebuilt Rochester 2G listed at Rock Auto, but it would take over a week to get it.

 

Re: Dauntless hesitation and fraustration

I agree with Steve. Vacuum sounds low across the board and so does your compression.
First thing I would check for is a vacuum leak. Either from an intake manifold gasket, or on or around the base of the carb. you can use a spray carb cleaner to check areas by spraying it at a suspected area. If the RPM changes when you spray it, you have a leak there.

The next thing I would check before going further is valve timing. With your engine off, take the dist cap off and using a ratchet, or breaker bar, rotate the crankshaft in one direction, then the other. There should be little to no hesitation from when the crank turns to when the dist turns. go both directions, as that will compound the slack in the chain.

The reving fine with no load and hesitating with a load makes me think weak engine caused by lack of compression. be systematic, and look for the simple stuff first however. and by all means, don't just throw parts at it. That will only frustrate you more and empty your pockets faster.

 

Re: Dauntless hesitation and fraustration

Thanks for the reply.

Everything but the engine is new, Points, Plugs, Condensor, Coil, Spark Plug wires, fuel pump, fuel filter, and even the wire from the distributor points to the coil. I went ahead and cleaned the plugs , because I ran it often over the last month to test the new components without being able to drive it, because the brakes and exhaust system were not done. I did disconnect and plug the vacuum advance line when I set the timing to specs, but my lastest attempt was to achieve the greatest engine vacuum and was not concerned with factory specs.

I think replacing the carburetor is now the easiest thing to do. The compression readings are low, but I don't think it is worth rebuilding this engine. The carb that is on this Jeep is a Rochester 2GC 7029140, not stock, used on some Buick 350 engines around 1970. I had it rebuilt by a local carb shop, but they were dealing with a 35 year old component and if something was overlooked I can understeand that. If another rebuilt carb does the same thing, I think I can rule out the fuel system. I think the electrical system is already ruled out.

 

Re: Dauntless hesitation and fraustration

Thanks for the relply. I really appreciate the suggestions. I am very fraustrated.

I will check again for a a vacuum leak. I did spray WD40 aound looking for a leak, but maybe that is not volatile enough to detect one. I will also do the check for the distributor slop.

 

Re: Dauntless hesitation and fraustration

Volatility isn't what makes a difference when spraying liquids around probable vacuum leaks. The fact that the liquid slows or plugs the vacuum leak for just a second is what causes the RPM change. If you are using a flammable spray, then it can combust when sucked in, but that isn't the real reason for the rpm change. Also be careful spraying flammable stuff onto hot engine parts anyway. I know, I know, just a warning.

 

Re: Dauntless hesitation and fraustration

You are right. I will not spray a volatile substance. I have headers that really get hot. What was I thinking?

 

Re: Dauntless hesitation and fraustration

I took the distributor cap off and turned the engine clockwise facing the front of the Jeep. When the rotor started to move I put a mark on the vibration damper opposite the 0 degree mark. Then, I rotated the engine counter-clockwise until the rotor moved again and noted where was mark in relation to the timing marker. There is actually 12 degrees of slop. I went back and forth several times to verify this.

Does this definitely mean the timing chain and gears are causing my problem?