This is a 91 rxl switched over to carbs. We had it it today on the trail for the first time and about 3 hours into it it statred acting up . It would only rev up to 400 rpm and would back fire when I tried to give it more gas to try to get it moving, after about 10 minutes of this it came back to normal. When it was just barly idling I pulled each plug cap of and they all made an equal drop in rpms so I dont thinks it the coils. About another hour down the trail we stopped and idled for a few minutes and when he went to go it did it again but it only took a few minutes to get back to normal. Could it be the CDI, stator, pickup,,,,someone said maybe fuel pump but that doesnt explain the back firing. Any ideas. the previous owner said it was having a problem with the mag side not firing sometimes and he replaced the CDI and the stator.