Hello, my '65 327/365 hp has a hesitation off-idle and very poor throttle response below 2500 rpm. The timing is set at 10 deg and Sunoco 94 fuel is used. The carb has been professionally rebuilt, the igntion has a Pertronix ignitor and an MSD 6al box, I'm running AC 45 spark plugs with new wires. The engine starts very easily, but will hardly take any throttle until it is warmed up to 180 deg. Oddly, with the vacuum advance plugged in, the engine idles very fast and comes down slowly. With the vacuum advance unplugged, the engine idles fine but the throttle response gets worse. Could it be the vacuum advance? Carb? Fuel? I have been dealing with this problem for two years after I put the car together, I'm stumped! Thanks, Bill.
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Re: '65 327/365 hp hesitation
I don't think this is your problem, but it is easily checked. The centrifical advance under the rotor can become rusty,dirty, and not function 100%. It is easy to take apart and clean the moving parts. I have always used ignition point rubbing block lubricant on the pivot points of the centrifical advance on my cars since 1968. Is you choke linkage working on cold start-ups? -
Re: '65 327/365 hp hesitation
William:
First thought is a large vacuum leak. Normally, when you disconnect the vac advance, the idle should drop sharply. You say that the engine idles too fast, then drops to normal when the vac is disconnected. Do you mean to say that you plug the vac hose as you should, while it is disconnected? If you plug the hose and the idle quality remains the same, then this indicates a large vac leak. The true test is to read all 8 plugs. They should all have light tan insulators, and the electrodes and ring should be dry with grey-black deposits.
When all is said and done, this engine is not exactly a stump puller at low RPM. If you have a close ratio box, and your 3.70 gear, then you've got to get a good head of steam before you notice the torque to start to come on. This engine has a very peaky torque curve, and is happiest at 4000+ RPM.
JoeComment
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Re: '65 327/365 hp hesitation
William,
Are you sure your choke isn't coming off too soon and that you are getting a good shot from the acc pump ?Comment
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Re: '65 327/365 hp hesitation
Thanks for the response Wayne. I opened the choke all the way, and the accelerator pump works great. Had a carb guy tell me to go up a couple sizes on the accelerator pump nozzle, I might try that this week.Comment
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Re: '65 327/365 hp hesitation
I had a similar problem with a '65 that I had. it turned out to be that the carb jets were too large and causing a slight flood till the engine caught. Changed the jets and it ran great...Comment
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Re: '65 327/365 hp hesitation
Joe,
Thanks for the response. What I meant to say was that with the vac advance connected, the engine seems to idle fast for a few seconds then comes down slowly to idle speed. With the vacuum advance hose disconnected and plugged, the engine comes right down to normal idle speed, but the throttle response gets worse. I advanced the ignition timing today to about 20 deg, the off- idle stumble went away and some of the low end came back. What it will do now is surge at part throttle around 3000 rpm. I don't hear any detonation. Is the advanced timing causing the surge? Thanks.
WilliamComment
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Re: '65 327/365 hp hesitation
Rex,
Was this only on the primary side? Where do you have your initial timing set? Thanks.
WilliamComment
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Re: '65 327/365 hp hesitation
I installed a new advance kit with springs, weights and bushings. Thanks.
WilliamComment
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Re: '65 327/365 hp hesitation
The part throttle surging is caused by too much advance whether it pings or not. It sounds like your vacuum advance diaphragm could have a leak. See if the timing advances as you reconnect the line and keep your light on it. If the timing drops back, it's leaking. You might also want to verify your TDC mark.Comment
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Re: '65 327/365 hp hesitation
William:
If you live at or relatively near sea level, then you should NOT have to modify your carburetor to get the engine to perform properly, providing it was rebuilt properly, and there are no vacuum leaks. Pull the plugs and tell us what they look like. Do you have the 1965 shop manual with the distributor advance specs? If not, let me know and I will email you a copy of the spec sheet. FIRST, verify the TDC mark on the timing cover. If you don't know how to do this, I will explain. Do you have a set-back timing light? If not, then you must degree your balancer to verify the timing curve. You should have an 8" diameter balancer, and a degree tape should be available at any good speed shop. After this is done, set your initial timing (vac advance disconnected and plugged)to 12* BTDC @500RPM( why such low RPM? Because centrifugal advance SHOULD start to come in at about 550. If the engine won't idle at 500, then you must tie the advance weights with rubber bands, and then you can set initial timing at 600-700.)
JoeComment
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Re: '65 327/365 hp hesitation
The vacuum advance unit is new, but it could be the wrong one. Could it be putting in too much advance? Are the stock units adjustable?Comment
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Re: '65 327/365 hp hesitation
Joe,
My repair manual tells me 12 deg initial timing and 36 deg full advance, is this right? No, I don't have a set back timing light. Yes I do have an 8" balancer and I'm going to purchase some degree tape tonight to see where I'm at. A have a new vacuum advance unit, but I don't know if it is the right one. Could it be putting in too much advance? Thanks.
WilliamComment
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Re: '65 327/365 hp hesitation
Just because it's new doesn't mean it can't leak and it takes all of a minute or two to be sure. Stock units are not adjustable.Comment
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Re: '65 327/365 hp hesitation
William:
I say again---check your spark plugs to rule out an improper fuel mixture. You should have the #236 vacuum can on your distributor. This is readily available in reproduction. It is not adjustable, and there is no reason for you to do so. There is a replacement can, available from NAPA/Eichin, with the same characteristics as the 236, but at a cheaper price. Duke and some others on this site know the part number. Check the archives, or post the question. The specs for your distributor are as follows:
CENTRIFUGAL ADVANCE: 0*@800RPM--------------24*@2350RPM
VACUUM ADVANCE: 0*@4 in-hg-------------16.5*@8.2 in-hg
Base timing: 10*BTDC (engine should tolerate 12-14* with the 30-30 cam)
I suggest that you verify #1 TDC first(make sure you are on the compression/power stroke and not the exhaust/intake stroke).Good luck.
JoeComment
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