View Full Version : Dist Cap pressure
06-30-2003, 10:23 AM
I noticed that you have a vented dist. cap on the market? (p/n 8438) was this a result of pressure building up inside unvented caps and having them push up or be blown off the dist. from pressure buildup? I was at Heartland Park Topeka this past saturday and when I got back from each time trial the cap was pushed up approx. 1/8th inch. Even bent the hold down prongs. Third time trial the cap blew conpletly off. Dist. end play was OK, no side to side play, gear contact pattern looked OK. I've never run into this type of problem before. Using 85561 dist. (new) have always used a crank trigger up until this year. Always with good results. Car E.T. and MPH has remained consistant since start of the year, have 86 passes on dist.
07-01-2003, 10:08 AM
The vents that are placed in the cap are to allow air to flow through the cap and reduce the amount of ionized air within the cap. This is normally used on engines with very high output ignitions with high cylinder pressure. The vents reduce the chance of crossfire within the cap between cylinders. As for the cap lifting off like you described, I have only run into that on a few occasions. The usual cause is from a float in the rear carburetor bowl set to high and when the car is launch you get fuel spillage out of the carb vent tube that surrounds the distributor cap. When the fuel ignites the pressure within the cap causes it to lift off the distributor housing. This can also occur if you use carb cleaner to clean the inside of the cap. The only other cause would be if you are experiencing extreme vibration. The PN 85561 has provisions to bolt the cap down instead of using the spring clips. I would suggest looking at your float settings and also using the cap bolt-down feature.
MSD Tech 1
07-01-2003, 02:18 PM
No float problems, I'm running a toilet. The vibration problem is where I went also due to my 225" hardtail (yard-dart). slid a new cap and rotor on and used the screw option this time. I guess time will tell if the vibration was the problem. Fired up alright after the refit will know after this coming weekend. Thanks for your response. Randy Hill
Noticed the new cap has a vent on top also.
07-01-2003, 08:04 PM
Keep us posted!
07-08-2003, 12:22 PM
The screw down option seems to have solved the problem. Biggest race of the year here at W.I.R. Div. 5 and took runner up. :)
07-09-2003, 08:15 PM
Congratulations! Sounds like your getting it dialed in. I am glad the cap retaining system worked.
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