BUCKING 67 327

[BTWEED]

ENGINE BUCKS AT EVEN SPEEDS, FEELS AS IF YOU WERE FEATHERING THE GAS PEDAL UP AND DOWN, RUNS GOOD, HAS GOOD PICK UP SPEED AND IDLE. CHANGED THE CARB-NO CHANGE, ADJUSTED TIMING- HELPED- NEW GEARS AND TIMING CHIAN IN MOTOR, VACUUM ADVANCE FLOATING, VARING VACUUM TO DIST????//

[lyndon sharpton]

Re: BUCKING 67 327

trun off your caps!

[Joe C.]

Re: BUCKING 67 327

It sounds like a lean condition. The "surging" that you describe under steady-state conditions is probably due to a vacuum leak.

Joe

[Roy B.]

Re: BUCKING 67 327

Try disconnecting the vacuum advance line , if it stops bucking then locate the vacuum leak

[Timothy B.]

Re: BUCKING 67 327

Check and make sure you have the correct vacuum advance can on the distributor that's matched for the engine idle vacuum and that it's holding vacuum. If the engine has an aftermarket camshaft there is alot of information in the archives about proper selection of vacuun advance cans. If the vacuum advance is floating because of insufficient engine vacuum I think this could be the cause of the surging but you mention the cars idle is fine so check for a vacuum leak. What is the idle vacuum and did the car do this before you changed the timing chain and gears?

[Les Jacobs]

Re: BUCKING 67 327

I had off idle roughness. Most noticeable @ 1500 rpm and below. Above that ran great. Did the normal stuff (points, plugs, timing), and the not so (intke manifold vacuum check, distributor replaced, carb replaced) etc. Sometimes it would seem better, but eventually uneveness would return..especially when it was up to temp. Finally changed out what looked like new spark plug wires, AND the ignition resistor. Voila, ran like a charm. The sp wire resistance actually was within spec, but I could not measure any breakdown voltage (saw no arcing @ night). So my theory is that the wires were breaking down under the shield.

[Rich G.]

Re: BUCKING 67 327

My 66 327/350 does this exact thing. In fact, I run with the vacuun advance disconnected, until it gets too hot outside and I have to reconnect it to keep the temp reasonable. I have checked for leaks and have none. I think I have the correct vacuum can. But I'm not 100% sure. I seem to have higher vacuum at idle than others have told me I should. I have no idea what cam is in this motor.

If the vacuum is around 18" (which I think it is and which I believe is too high) does that mean I need a different vacuum can?

I'll be watching this thread. I'd love to be able to fix this once and for all.

Rich Giannotti 38594

[Duke W.]

Re: BUCKING 67 327

Idle vacuum readings are only meaningful IF YOU ALSO STATE THE IDLE SPEED!!!

I can make an SHP cam idle at 20" if I set the idle speed high enough.

SO...?

Duke

[Rich G.]

Re: BUCKING 67 327

Sorry Duke

800 RPM

Rich G

[Duke W.]

Re: BUCKING 67 327

It sounds like someone has "detuned" the engine with a milder cam, but the OE or equivalent vacuum can would likely not cause the symptom.

More likely it is an ignition (eletrical) problem or an overly lean mixture.

I'm not sure where to start, but one has to go through each system and check that every component is functioning to spec. Electrical connectors on old cars can also be problematic.

Duke

[Rich G.]

Re: BUCKING 67 327

Thanks Duke

This car also has the "wrong" carb on it. It is a 600cfm holley with an electric choke. It was on there when I bought it and I got the correct holley and was planning to change it someday. Then the float sunk in the secondary so I tried to put the rebuilt correct carb on, but there is no provision for a choke stove in the manifold. The manifold has the correct casting number on it. I asked about this here and no one seemed to know how that could be. Anyway, I ended up with a new 600 cfm holley with an electric choke.

When I got the car it was running hot and through the help of you and others here I discovered the vacuum advance was not working. Fixing that and the proper total advance with a new radiator and it runs 180 all the time. But that's when the bucking started. If I disconnect the vacuum line and plug it, no more bucking. But it runs a little hotter.

Could it be that it is too far advanced for this cam? I was going to try to retard it a little, but I suppose the results would be the same, running hotter.

Thanks for all you help. I'll keep fooling around.

Rich Giannotti 38594

[Duke W.]

Re: BUCKING 67 327

Give me all the details of your spark advance map and I can probably give you an opinion. Dist. no and vacuum can ID numbers. Centrifugal and vacuum curves based on actual testing and the range of idle timing you have used. Also specify if vacuum advance is ported or full time. The whole enchilada!

Also, what is the lowest idle speed you can live with? If it pulls 18"@800 the idle speed can probably be reduced.

I am assuming it has a manual trans.

Duke

[Rich G.]

Re: BUCKING 67 327

Thanks Duke

I'm leaving for a few days tomorrow, so when I get back I will get that info together. Yes, it is a manual.

Rich Giannotti 38594