Still not right! 80 CB750F

[Ricebiker]

Originally had 68 pilot jets and 100 main jets. Got rid of the airbox and exhaust, (now 4-1) So, I went up to 70 on the pilot jets and 105 on the mains. There was some popping and it just wouldn't go after 1/2 throttle. So I went up in size. 80 on the pilots and 140 on the mains. Still not right around 1/2 to 3/4 throttle. Went back down. 120's on the mains. Still not right with 1/2 - 3/4 throttle. Really lost as to what I should do next. Plugs are tan and dry even with the 140's. Bike was running good when I began so I have no reason to think there's something else wrong. 150's? (VB 42's) I'd like to be able to work this out, without putting the airbox back in. A lot of people run pods and have success. Just don't have that much time to mess with it. K&N filters. VB 42(cv) carbs. 80 CB750F,

 

[amc49]

Tried to tell you about them big jets. CVs don't like jet nearly as much as direct lift carbs do. Rich makes the slide not lift then the bike misses its' butt off when it goes even richer than the jets alone make it. Plugs can look fairly good but running them rich can melt the surface to conduct to short down the sides, new plugs the only cure for that. 75-115 or so are the jets most end up around at the CB1100F site. No needle shimming. The bike misses in an instant because of weak OEM ignition. They miss as well if valves are not set and the compression must be up on all four cylinders as well. Don't know where you're located at but I've noticed that geographically more people from up north have pod issues than down south. I'm in Texas and no issues at all when I did it other than I got too big with jet at first too.

The engines must be healthy (compression, valvesealing) to lift the slides, lackluster ones pretty much don't run on pods. It's not about the leaner of pods at all, rather, going to them then has one carb only making slide vacuum for that cylinder and one carb is down some 3/4 of the time since the intake period is only that long. 4 cylinders hooked together (airbox on) allow each cylinder to help the others maintain vacuum at the slides so they pop open quick and all the way. One cylinder vacuum suck period...............suck.............................suck........................suck. Or all 4 together..suck..suck..suck..suck..suck..suck..suck. Which situation do you think will work better there??? Pods destroy that ability. The slide vacuum drops in between the wide spaced suction periods. Slide drops then rich even with lean jets. These freakin' carbs will make you batty.

 

[Ricebiker]

SF East Bay Area, at sea level. No humidity, dry, dry out here. 70, 80 degree days. Gonna try one more, combo, the 75-115. If that doesn't fly then back to box. I'm glad I left the option open this time. The XJ650 airbox was cut to get it out.

 

[amc49]

Mine was '80 750F as well and Kerker header with pods. After the work the bike ran perfectly except that it would not pull out to the full 9500 rpm (only 8000 or so) in high gear. No missing or flat spots at all. The top gear issue was more of the same, slides not opening all the way up because of what I told you. The airbox aids that.