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View Full Version : Hesitation under acceleration and at 3k?



cjsteak
06-09-2003, 01:04 PM
Hey guys, i've been having a hesitation in the throttle at just about any rpm, but it's mostly when i'm accelerating hard. I checked all six plugs and they all came out text book PERFECT. What can this be? I upgraded my ignition system to electronic ignition using the Pertronix brand stuff, I even installed the Pertronix coil. The funny thing is that once i'm done accelerating and i settle at an rpm it quits buffeting. Come to think of it if you hold it at about 3000 rpm it'll make a buffeting soft poofing sound. No smoke though.

Thanks!

[ 06-09-2003: Message edited by: cjsteak ]</p>

Dave Russell
06-09-2003, 05:52 PM
If as you say, the problem is mainly when you are accelerating hard, minor vacuum leaks, such as the throttle shafts, are not likely to be the problem. They will affect idle though.

Plug gaps that are too wide will cause a similar problem. Try gaps of .025 to .030 & see what happens. It is easy to do. When did it last run well? Was it before the ignition changes?

Other possibilities such as fuel starvation due to plugged openings in the carbs, or fuel filters, low float levels, weak fuel pump, come to mind.
D

aeronca65t
06-09-2003, 06:03 PM
...and be sure carb dampers aren't out of oil and carb diagphram isn't ripped (if it has the Z-S carbs).

....also, I usually spray WD-40 near areas that I supect are leaking. The WD is essentially non-flammable, so the engine *slows down* if it sucks in the spray.
The WD won't hurt anything (*maybe* it will foul a catlytic convertor, if used to excess)....but I have to admit, the flammable sprays are more fun! graemlins/devilgrin.gif graemlins/devilgrin.gif

Dave Russell
06-09-2003, 06:30 PM
I think that they smell better also.
D
<blockquote><font size="1" face="Verdana, Arial">quote:</font><hr>Originally posted by aeronca65t:
.but I have to admit, the flammable sprays are more fun! graemlins/devilgrin.gif graemlins/devilgrin.gif <hr></blockquote>

Bugeye58
06-09-2003, 10:00 PM
My post regarding the worn throttle shafts was based more on the "POOF" at a constant 3000 RPM,rather than the acceleration miss. I guess I should have read more carefully, huh?
However, it definitely sounds to be fuel related, rather than ignition. When you check the plugs is it after a normal shutdown, or do you run it hard, shut it off, coast to a stop, and then read them. A normal cruise back into the driveway, and a shutdown from idle can give you a false reading on the plugs. That's why many times during a practice session prior to a race, you'll see someone coasting into the pits. They've given the engine a clean break to read the plugs.
Bugeye58

MDCanaday
06-09-2003, 11:33 PM
I think Bugeye is onto something with the fuel starvation thought. I have seen a lot of old fuel lines that over time have swelled inside to choke off the flow enough to cause trouble. I say start fresh(lines are cheap!!) Go new from tank to pump, add a filter AFTER the pump(never before). Let us know what happens!!
MD(mad dog)

Dave Russell
06-10-2003, 03:17 AM
Not sure what a "soft poofing buffeting sound" is but it sounds like your engine is running lean. There could be a number of causes.
D

Bugeye58
06-10-2003, 03:57 AM
Pay particular attention to the throttle shafts where they go through the carb body. At idle, spray some flammable brake cleaner at each end of the shafts,using the little plastic tube for the nozzle, and see if you get an RPM increase. If you do, it indicates the shafts are worn, and sucking air. Your problem sounds exactly like a lean misfire. You may also want to check around the intake manifold gaskets, both at the carb, and the head. Be careful though, and make sure you have an extinguisher handy, just in case. Usually it's the shafts themselves that wear, not the carb body, and it's simple to throw a new set of shafts in.
If you don't feel comfortable with the brake cleaner, you can use a propane torch. Just open the torch valve and get it as close as you can to the area you want to check.
Bugeye58

cjsteak
06-11-2003, 03:54 AM
I'm going to tend to agree with the guys who are thinking it's running too lean. The plugs weren't really tan they looked like new (grey) eventhough i've driven it several thousand miles since I put them in. With the upgraded ignition, I gapped them at 36. I'm noticing that it's getting harder to start when the engine is cold.

I'm thinking it's a lean problem. I'm going to replace those fuel lines for peace of mind though. I had the car die on me the other day, but it was due to a clogged fuel filter. After replacing the fuel filter, it fired right up and hasn't given me any problems yet.

Question: When adjusting the carbs, which way do I turn the tool to richen it up a bit? Clockwise or counter clock wise?

Thanks for all the replies!