High idle and dieseling on shutoff.

[Armasey]

Hey guys. Got a stumper. First of what I am working on.
1989 dodge ram 50 g63b 5 speed. Been working on fixing up a lot of stuff the last few days. Overhauled brakes. Fixing rat nest of wiring left by po. And tune up. I noticed while working on everything that the secondary valve on the carb is not working. Put a hose on the controller and it is not holding vacume. So jumped on youtube and started searching. Found a video were a guy simply bypassed by connecting the spring to the throttle cable to put tension on it. Seemed to work... So I did it. Not wanting to fudge anything I used another spring rather then chop it. As soon as I fired the truck up it idled high. Around 2 and a half by my ears. So though maybe it was just from fuel from where I had been opening the throttle by hand so I took it down the road. Ran great! A lot more power. But still high idle. So checked all vacuum lines. Replaced on that was cracked. No change. So removed the spring that I had installed thinking maybe that was causing it. No change. Still high idle and dieseling. Any ideas? Runs fine otherwise. Could I try adjusting the idle? This cheep carb is rather confusing. Not even sure how to adjust it. Thank you all in advance.

[pennyman1]

What carb is it - stock mikuni, weber, or fake weber? We need pics to help if possible...

[Armasey]

Stock mikuni afaik. Still fiddling with it. On the back side close to the roller that the throttle cable goes on there seems to be a air leak. Maybe the gasket. If I hold my finger over it it calms down a little. Will grab some pics ASAP when wife gets home with cellphone. Thinking maybe time for a webber... So frustrating though. Just got my brakes working like new. And a lot of other work. Thanks again. Y'all are awesome groupe.

[pennyman1]

try tightening down the carb to the manifold - they can come loose. I think the carb bolts go down through the top if I remember correctly.

[geezer101]

Don't attempt to ghetto rig the secondary on the carby - it is leaving the issue of air leaking through a split diaphragm which will screw up the the carbies' tune. Swapping the secondary is an easy deal and doesn't take removal and disassembly of the carby to replace it. Takes a little brute force and some manipulation but you'll get the dead one out and the replacement in. Using a spring will cause the secondary to remain open partially - causing it to overfuel and create new faults (like high idle and dieseling you're experiencing) Replace the vac actuator can on the secondary and it should solve all of your running issues. :thumbup:

[Armasey]

Thanks pennyman and geezer. I've put everything back to stock. Tried tightening everything down. It is better but still not right. But it's an old better so I can imagine that something got messed up by me even touching it lol. Is it worth rebuilding the mikuni carb? I have read a lot of posts here and it seems to be the general opinion to get a webber. If I may ask a question unrelated to this post. My wife has a 98 eclipse that is soon to be retired. It has the 2.0 Dohc N/T auto. As I understand it is the same block as mine? Could this be a better option then fooling with my old engine? Rebuild the eclipse engine and drop it in. I'm no stranger to wiring and am sure I could get the fuel pum and computer all working. Will be out working on the truck in a bit and will take pictures for y'all. I really appreciate y'all and this site.

[geezer101]

The factory Mikuni car is not the harbinger of all evil and when running right does an amicable job. It isn't super awesome on fuel economy Vs power but there are worse carbies to mess with. They however are not noob friendly when rebuilding them - there is a lot going on inside of these wily beasts. If you have a good clean bench area to work on and a parts tray to stop anything from going AWOL (and you're not in a rush), you can pull one of these down and replace all the seals and diaphragms. Take note of what you're doing as you're doing it and the only thing you'll need to worry about once you have it all back together is setting the adjustment screws correctly. NOS/reman Mikunis come up on ebay fregularly and are normally a lot cheaper than buying a full kit and paying someone to swear at it.