Sputtering in mid range

[MXman]

Hey Guys,

My SJ is having an issue where the motor wont rev past mid range and just sputters. If I turn off the gas for about 5 seconds it clears out and runs fine until you let the RPMs drop. My first thought was carb so I pulled it apart and everything visibly looks fine. Also tried unplugging the temp sensor but still did the same thing.

Any advice where to go next?

Thanks!

 

[fastgtfairlane]

Sounds like you could have a leaking needle and seat or seat o ring. I would remove the carb and check the popoff. Also you can check to see if the tip on the needle or the o ring is leaking by spraying some wd40 or similar on the needle and seat then use a small air pump to pressurize the fuel circuit up to 10-15psi and see if it leaks down. Also want to verify your popoff is correct. If it's too low or you have a leak, you'll have extra fuel dumping through the high speed circuit into the engine when it's not ready causing an extreme rich condition that runs good when the engine clears out. Could also have a bad coil or cdi. But I'd start with the carbs.

 

[MXman]

Thanks I'll check that out. Was just talking to a buddy and he had the same thing a few years ago and it turned out to be a CDI. I does seem like it goes down to a single cylinder, like the temp circuit is cutting off.

 

[WFO Speedracer]

Thanks I'll check that out. Was just talking to a buddy and he had the same thing a few years ago and it turned out to be a CDI. I does seem like it goes down to a single cylinder, like the temp circuit is cutting off.

If it was ignition related turning off the fuel wouldn't make it any better , ignition and carb symptoms sometimes overlap but on this one I would follow Fastfairlanes lead

 

[MXman]

Thanks, I'll give it a try.