• To ALL forum users - As of late I have been getting quite a few private messages with questions about build ups here on the forum, or tech questions about your personal project. While I appreciate the interest, sending me a private message about these topics distracts from, and undermines the purpose of having a forum here. During the day I wear many hats as a small business owner-operator and I work tirelessly to provide the absolute best service possible to you, our valued customer. When I created this forum I rounded up some of the best minds I knew so that any tech question you might have could be asked and answered by either myself or one of my highly experienced moderators, this way the next time this same question is asked the answer can be easily found and utilized by the next IH enthusiast having the same question. This allows me the freedom to run the day to day operations of the business and minimize the impact to shipments and shop activities that these distractions can cause. It is of the up most importance for me to complete the daily tasks in order to best take care of you our customer, all the while providing you a forum to get the level advice and input you have come to expect and deserve from the premier IH shop in the country.

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    Jeff Ismail


Alley Rat

New member
First I apologize for possibly posting an issue/problem that may have been answered earlier.

I have a 1974 Scout II, Tara with a 304 engine, auto trans. It runs great at idle, and full speed... but when I try to accelerate or start off, the engine hesitates…. sometimes it backfires.
I had installed a new distributor with EI, spark plugs, new carburetor rebuild and a new fuel pump. My next guess would be the timing chain maybe off a click/link. Do you have an other possible cure? I would appreciate some guidance on this issue.

Robert Kenney

Super Moderator
Hesitation and popping back through the carburetor upon acceleration is 99% of the time a lean condition, or retarded ignition timing.
No reason to think the cam timing is off. Also these engines use a gear driven cam and unless things are going seriously off the rails it is likely fine.

Back to the fix, some historical info. will help. Did it run like this before the carb rebuild and other work? Who did the rebuild?
The carb would have been a 2 barrel Holley I think, and they have a cam actuated accelerator pump system.

With the engine off, and the choke open, while looking down the carburetor with a flash light, advance the throttle off of the idle position and see if you get a good solid squirt from the accelerator nozzles. It should start squirting right as you begin the movement.

Alley Rat

New member
Thank you Mr. Kenny,

I had hesitation problems before the new distributor, carb rebuild, coil and fuel pump. I thought all would end the hesitation problem.

I will check out accelerator pump as you have directed. I got the rebuilt carb from Auto Line products out of Canada. Where can I buy a better one?

I am scheduled to have the water pump replaced and I thought checking the timing chain for slack would be a good time while somewhat close to water pump. Is that a good idea?

Again, thank you sir,



As Robert said above, these engines use a gear drive for the cam, no timing chain to inspect/replace. I would use a can of carb cleaner at idle to spray around the intake manifold and vacuum ports to look for a vacuum leak. If idle changes while spraying the carb cleaner, you most likely have a vacuum leak.

Alley Rat

New member
Thank you Mr. Hondo,

I am at fault not understanding all about no timing chain. Mechanic suggested to do this and I did not question him then.

I will, within the hour, check carb and for vacuum leaks.

Thank you again Sir,

Alley Rat

New member
Thank you Sir....

I have done some homework to see how the distributer works.

Obviously, I was gullible to my Mechanic's suggestion.

Thank you again,

Where are you in Canada? I'm in southern Ontario. Should have just installed a new Holley 2300 carb.

Have you gone through the carb tuning procedure as set out in the service manual?

Alley Rat

New member
I don't live in Canada....... I live in Colorado, USA.
I got the rebuilt carb from Canada.
My latest search for the hesitation problem is around high altitude adjustment. I live and travel 8,000-10,000 feet. I am installing smaller jets..... We will see....