Larger Jets?

My Impala (6-cyl, Single barreled rochester) has had a bit of a "kick" at constant speed since I got her. I cured the issue with a little bit of retarded timing (I think I'm currently at 4-btdc static) but I can still feel it from time to time.

Acceleration is fine. Even the slightest bit of tip in on the throttle will cure the "kick".

I was thinking of going up a size or two on the main jet, but thought I'd check with ya'll to see if I was on the right track, or if this issue is indicative of something else.

Compression is 140-145 on all cylinders. Plugs look mostly light brown with a little grey on em.

Thanks ya'll

Kick as in it gets jerky? With that plug color I'd suspect ignition. Most fuel problems are electrical after all. If you haven't done so lately, a set of points, cap, rotor, wires and plugs wont hurt. Perhaps test the coil too.

A wise man once told me (who also said a wise man once told him) 90% of carb issues are ignition issues.

but yeah, it gets "jerky". I haven't changed points since in about 2-years, but I did adjust them recently. I'll swing by the O-vancedzone after work and do some shopping.

Thanks!

Oh, that kind of jets. I thought you meant this.

jstein77 wrote: Oh, that kind of jets. I thought you meant this.

Right!

If a little throttle cures the kick (accelerator pump adds squirt of fuel) you may have something w/ the mains there. And what others said... cap, rotor, wires, plugs etc.

Also check the vacuum advance, advance weights and springs in the dizzy while it's open to see if they're operating properly.

If retarding the timing helped, something is definitely wrong.

But isn't 4 degree near the spec ?

6deg btdc was the spec I was able to find, but it jerks a bit more at that setting so I retarded it a bit.

Looks like for a cap, condenser, rotor, and points I'll be out just a little over $20. Dang it all anyways

I'll probably do plug wires as well, I currently have an Accel universal set installed.

jstein77 wrote: Oh, that kind of jets. I thought you meant this.

Ah yes, the Scarebus A-Douglas Ripoff

Their A-400m project (AKA Le-petit prop C-17), I hear, isn't going so well either.

(Sorry, I may or may not work in the industry for another manufacturer )

Good times.

First off - POINTS?? Switching to an HEI would be my first move. It's usually a pretty simple job with basic tools. The engine will start easier and run better. Something else noone has mentioned is that the harmonic balancer, being as old as it is, may have spun which will make getting the timing right impossible. I'd just go ahead and rebuild the carburetor. It probably needs it. If the float level is too low, it may be part of the problem.

How is the dwell ? this affects actual timing.

In reply to iceracer:

Excellent point, throw a dwell meter on it.

ncjay wrote: First off - POINTS?? Switching to an HEI would be my first move. It's usually a pretty simple job with basic tools. The engine will start easier and run better. Something else noone has mentioned is that the harmonic balancer, being as old as it is, may have spun which will make getting the timing right impossible. I'd just go ahead and rebuild the carburetor. It probably needs it. If the float level is too low, it may be part of the problem.

I'd much rather deal with points than the time bomb that is old or lowest bidder Chinese semiconductors. One fails gracefully, the other just kinda E36 M3s out on you at the worst possible second.

Did this engine even have a balancer? Worth checking that TDC is actually the TDC mark.

Sounds like the carb is working fine, though a check of the float level wouldn't hurt, I wouldn't prioritize it.

Nah. There's nothing wrong with points ignition. She's made it half a century with that setup.

Besides HEI conversion would mean getting rid of the resistance wiring to the coil. Which would also mean getting rid of the solid state voltage regulator. Which would mean getting rid of the current alternator in favor of an internally regulated unit. Which would mean cutting my current harness to run the new distributor and alternator. Which would mean.... Which would mean...

The carb's been rebuilt. That's not to say I didn't screw it up, but I can double check the float level. I have a K&N filter (I forgot to mention that) which is what had me thinking about increasing the main jet size, but the problem's been there longer than the filter has.

Points were set recently (which should control the dwell, right?) to the MFR's spec, but I ordered a new set yesterday. I don't have a dwell meter, but I'll see what I can do about getting my hands on one.

Of the parts ordered:

• Condenser

• Cap

• Rotor

• Points

• Plug wires

Only the condenser was in stock. The rest will be picked up today. I didn't order plugs as I don't think I even have 3000 miles on this set yet. I'll probably just hit them with a wire brush and call it good.

The poor kid at the counter gave me the strangest look when I asked him for "points". Eventually we found what we were looking for. I saw "breakable distributor contacts" (or something to that effect) on his "search" list. He probably asked me 100 times "are you sure that's what you need?".

I can check the TDC mark with a screwdriver down the #1 hole when I'm in there. I'll let you know if I find something funky.

Thanks ya'll. Good times

What's wrong with "leave it at 4BTDC and don't worry about it"?

Springs and/or weights for the advance mechanism could be (probably are) bad. Those are usually cheap, too. After all that, if you want a bigger jet, a drill index and the next size up drill bit (whatever that may be, numeric, alphabet, fractional) will get you a bigger jet on the cheap. Note that if you do that, you can't go back smaller if you went too big.

I still feel a bit of "jerking" at constant throttle while it's set at 4btdc. Otherwise I'd just leave it.

When I had the 70 Impala with a 350 and an Edelbrock 600 4pot I switched to a smaller set of jets thinking I might be rich on the bare-stock motor. I immediately started running lean at cruise (Which is what you're suspecting, I think.) The symptom I got was surging under steady part throttle. It wasn't strong enough to call it a kick, but take that as you will...

I kept the points on mine as well and always carried a spare. I could change them in 5 min on a roadside in the rain with a $1 screwdriver. And I did. About yearly.

One of the best things I did was put in a distributor advance recurve kit (Mr Gasket or Accel?) I set it up to get all the advance in as quickly as possible coming off idle, and to give a couple degrees ( I think) more advance at all-in. Idled smooth but got a little more pep in her step.

It sounds like a missfire to me.

If jetting was the issue, you could easily see it by running an O2 sensor stuck in the tailpipe.

But yeah, it sounds like an ignition problem.

Setting dwell via points gap is an indirect measurement, its liable to get you good enough on a lawnmower, and close enough on a car to get it running so yo can do a proper dwell adjustment. Ownership of a timing light, dwell meter/tach(properly set idle speed), and vacuum gauge are damn near mandatory for servicing points ignition carbureted cars.

For dwell, I like the old school analog units. http://www.amazon.com/Actron-CP7605-Tachometer-Voltmeter-Analyzer/dp/B00062YUUS/ref=sr_1_1?ie=UTF8&qid=1407916238&sr=8-1&keywords=dwell+meter You can find old ones used for cheap on ebay.

I would prioritize checking the float level before changing jets.

You should also check that vacuum advance is happy.

Distributor may be worn, dwell may be changing when vacuum advance moves.

Seriously look into an HEI replacement, the gains far outweigh any risk of Chinese component failure.

Heat paste on back of module and good wires are a must as an HEI will burn itself due to a bad wire or removing a wire while running.

Another ignition upgrade you could consider is to go straight to a distributorless ignition with a MegaJolt box or something similar.

Nah. No distributor conversions for me. Better or worse, I like her the way she is.

I couldn't get to O-vancedzone last night after work (kid had swim lessons I forgot about). So tonight after work I should have the goodies. I'll let you know how it goes.

Probably a good inspection of the distributor is needed. Does the shaft wobble at the top. Vacuum advance working right etc. I have always found that advancing the timing a few degrees over spec. works better.

If the shudder is just at tip in changing the main jet will not help much. Talk with Dayton over at Kinetic Performance. He's a Rochester carb guru. http://www.kineticperformanceracing.com/ A well tuned Point ign is fine.

Hungary Bill wrote:

jstein77 wrote: Oh, that kind of jets. I thought you meant this.

Ah yes, the Scarebus A-Douglas Ripoff Their A-400m project (AKA Le-petit prop C-17), I hear, isn't going so well either. (Sorry, I may or may not work in the industry for another manufacturer ) Good times.

My company supplies as much or more to yours as we do to Airbus. In fact, the weather radar I'm designing has the 737Max as its launch platform.

Dwell/Tach ordered. $12.00 off of fleabay.

Good times.