Marvel not fully cycling

During a match last Sunday one of my Marvel conversions would not cock the hammer after firing a bullet. I have successfully shot the unit since April until Sunday. I had the problem with 4 diffferent mags. I am thinking that the Marvel spring needs to b e changed. Do I need a stronger or weaker spring? Or am I thinking of the problelm incorrectly? Thanks in advance for the help.
John
Minnesota

John..If you are shooting SV ammo get a ISMI 8lb recoil spring and keep the slide rails wet with oil..Also make sure the top of the slide is not rubbing the bottom of the sight rail..If it is rubbing slightly put some oil on the top of slide where it rubs the sight rail..If you are using HV ammo I'd use a 9lb ISMI recoil spring..I use an 8lb ISMI spring with Federal 711b ammo and keep the slide rails oily and have shot several bricks of 711b thru mine and have had 100% sucess..My Marvel has a slight rub of sight rail so I keep it oiled as well..These conversions work extremely well after a bit of trial and error..

Mark. Thanks. I have been using mine for at least six years. I was unsure if I need stronger or weaker spring to increase the travel of the slide to insure locking back the hammer. The 8 pound spring sounds like the ticket.John

John,
Check the screw that holds the steel chamber face to the aluminum slide. If it comes loose it will drag on the frame and slow down the action.
-Mike

I had asimilar situation and it corrected itsself when I loosened the front rod and subsequently re-tightened it. Apparently the unit was installed slightly cockeyed and rubbing on the frame.

One other issue may be gunk/powder residue on the sear and disconnector. I have a old GI frame with a 2 lb trigger which I use with my Marvel. I also use this sanme frame with a Jarvis unit and Remington Golden Bullet ammo for plinking and steel challenge matches. HWen I tried using the Marvel last week I had hammer follow through and finally discovered a huge amount of dirt in the sear & disconnector sich that the disconnector was not free to move in the frame. Cleaned it up and problem was resolved.