partial throttle misfire
Thread Starter
Melting Slicks
Joined: Dec 2000
Posts: 2,130
Likes: 1
From: mesa,az
partial throttle misfire
Ok when I get on the highway and just cruise a few seconds after i reach about 3000 RPM the car starts hiccuping. dosent do it when i mash the pedel and accelerate fast, dosen't do it putting around town at 2500 RPM just when crusing at 3000 RPM or above. I have checked the fuel filter and it is clear, the fuel pump is not the right one but it dosen't starve under heavy acceleration. I am going to try changing the vacume can on the distributor so which one should i get. the car is a 327/300 , stock as far as i know. open to any suggestions .
PS the can is a B28 and io have set the timeing at 8 degrees advanced at idle with vacuum plugged.
[Modified by panchop, 10:58 PM 6/30/2004]
PS the can is a B28 and io have set the timeing at 8 degrees advanced at idle with vacuum plugged.
[Modified by panchop, 10:58 PM 6/30/2004]
Le Mans Master
Joined: Nov 2000
Posts: 7,246
Likes: 21
From: Going too fast over the hill. Iowa
Re: partial throttle misfire (panchop)
One of the other NCRS people can tell you about the "correct" can. I use an adjustable can to avoid this situation.
First make sure that the mechanical advance mechanism under the rotor is clean and operating freely. It (or a loose timing chain) will also cause the problem that you have.
First make sure that the mechanical advance mechanism under the rotor is clean and operating freely. It (or a loose timing chain) will also cause the problem that you have.
Instructor
Joined: Aug 2003
Posts: 112
Likes: 0
From: Fairfield CT
Re: partial throttle misfire (panchop)
The B28 can that you have should give 8° of advance with 8" of vacuum. You may want to check that this is what it is giving you. I don't know the correct can for your engine.
I had the same problem that you have described with my big block. It turn out to be the centrifical advance was not giving me enough advance causing the hicup. A change of the weights and springs solved the problem.
I had the same problem that you have described with my big block. It turn out to be the centrifical advance was not giving me enough advance causing the hicup. A change of the weights and springs solved the problem.
Burning Brakes
Joined: Aug 2000
Posts: 883
Likes: 2
From: Hilton Head SC
Re: partial throttle misfire (66BB)
Surging at cruising speed, but not a definite hiccup, can be a sign of too much advance. Why not throw a light on it and see how much advance you have at 2500 and 3000 them someone ought to be able to make a suggestion.
Team Owner
Joined: Oct 2000
Posts: 38,897
Likes: 1,926
From: Washington Michigan
Re: partial throttle misfire (JSB69)
The can with the correct specs for a 327/300 is the Echlin #VC-680 (stamped B1); starts at 8"-11" Hg., provides 16 degrees when fully deployed at 16"-18" Hg.
You need to "map" your advance curve (with the vacuum advance disconnected) to see when your centrifugal advance starts, the max advance it provides, and at what rpm that occurs. Most SB's like about 34-36 degrees, all in by 2500-3000, with 20-24 degrees of it in the distributor. Vacuum advance is in addition to that. Most old distributors have never had any maintenance, and it's not unusual to find centrifugal advance systems gummed-up and sticky.
You need to "map" your advance curve (with the vacuum advance disconnected) to see when your centrifugal advance starts, the max advance it provides, and at what rpm that occurs. Most SB's like about 34-36 degrees, all in by 2500-3000, with 20-24 degrees of it in the distributor. Vacuum advance is in addition to that. Most old distributors have never had any maintenance, and it's not unusual to find centrifugal advance systems gummed-up and sticky.
Thread Starter
Melting Slicks
Joined: Dec 2000
Posts: 2,130
Likes: 1
From: mesa,az
Re: partial throttle misfire (JohnZ)
OK changed out to a B-1 today and that seems to have cured the problem. the old B-28 unit when i take it off has hardley any spring force in it and had a rubber sleeve around it to limit movment. the new B-1 has at least 5 times the force needed to move it and i didn't put the rubber sleeve back on. seems to work OK but i wonder was the B-28 wrong or just worn out. anyway to tell? Another thing when i changed cans my idle jumped aeround 400 RPM, anyone know why.
thanks
again
greg
[Modified by panchop, 4:16 PM 7/1/2004]
thanks
again
greg
[Modified by panchop, 4:16 PM 7/1/2004]
Race Director
Joined: May 2000
Posts: 12,712
Likes: 2,270
Re: partial throttle misfire (panchop)
The "B1" can is correct for '63 to '64 300 HP engines. "B28" was only used on SHP engines that generate 14" or less manifold vacuum. It is too aggressive for medium performance engines.
Later 300 HP engines used a can with 16*@12", which is now available as NAPA/Echlin VC 1765 marked "B20".
Duke
Later 300 HP engines used a can with 16*@12", which is now available as NAPA/Echlin VC 1765 marked "B20".
Duke
