Interesting. Is that a part I can get from the other carb, assuming they are the same? If I can't swap it in, it'll save some $$ on the rebuild if I go that route (and its looking more likely that I will)

Small part that is somewhat hard to get at without a rebuild. My test for it is to plug the bowl bent line. And take if for a drive. If it pulls better and stops running rich at higher RPM's, it needs to be replaced.

The down side of plugging the vent is that the motor might be hard to start when its hot.

You could rig up an external valve that closes when powered to do the same thing.

Kevin

The rich mixture should reduce HC emissions. Not increase it. High HC is the result of excessive combustion chamber temperatures. I would check EGR operation for that. The rich mixture you describe should produce a high CO.

I could be off on this.... But you may want to double check that, CO and HC would be up. If I remember right, NOx is high from excessive combustion temp.

Conner, for once I have to disagree. NOx only forms at very high combustion temps, usually leanout conditions, where there is the excess oxy to combine with the atmo nitrogen. This will only happen at very high temps, which is why they dilute the intake charge with the egr to prevent it (which hurts max power potential)

HC and CO are due to insufficient oxy, or a rich condition (two ways of saying the same thing). The hydrocarbons are left over from unburnt fuel. The carbon monoxide only forms when you burn hydrocarbons and there is inadequate oxygen to fully oxidize the carbons to carbon dioxide (CO2).

The bowl vent valve is a common failure point in the Mikuni.

Everybody seems afraid to rebuild the carb. It is not hard, or expensive to do this. Certainly easier than doing the mods to install a Weber, and cheaper to boot. The Mik is a pretty good carb...

The stuff I've been thru with this Weber, I am definitely having second thoughts of having sold it. Having dealt with Weber IDA & IDF carbs, Their ICT duals and all kinds of DCOE side-draft applications, I thought this progressive wouldn't be a problem. That thing worked great on the MudRaider, and will work great for him once he hits the ignition switch.

I figured out part of the mystery. The Mixture Control Valve was only on carbs for manual transmissions, and the new carb came from a Raider that had an automatic. Reading up on it, it isn't required. Its just an emissions thing to lean out the mixture between shifts. I looked at the Montero manual instead of the Raider manual and it explained what it is for and how it works. Looks like I'll be bolting that carb on when I have the time. Thanks so much to everyone for their help in this, I really appreciate all the feedback and information.

Today I got the carb installed. The truck idles lower than it used to, around 600rpm which is fine with me. It had been idling really high around 1100rpm! It also does not diesel when powered off. Furthermore, its got much better throttle response. This turned out really well. Thanks everyone for the help. I had the job done in well under 2hrs and it runs great! Hopefully now I'll get better than the 12mpg I've been getting, and it'll pass smog come September.

Good on ye, son...

Always liked somebody who keeps on pluggin'...

Dude, you better get better than 12. I got 15 on trips with 35's. Glad it worked out. Well, sorta. Now I wish it was on the Shogun, the Weber is kicking my <img src="/forums/images/graemlins/butwiggle.gif" alt="" />