Well, failed the first try...didnt have alot of hope. After fixing idle problems by cleaning out the venturi tubes (thnx Forum), Jeep runs great until you stick your foot in it too far. Then it bogs down really bad. Failed on "High HC" (unburned fuel) and "High CO" (air/fuel mix too rich). Stock Carter BBD and air cleaner. It does have a whistle that is consistent with engine RPM, which I assume is a vacuum leak. Is that where I start to just get it through emissions?
What is the altitude at your test site? There is a high altitude jumper for YJs based above 4,000 ft msl (or close, cna't remember the exact figure). You will be out os spec on the rich side if you do not use the jumper.
It is mentioned in the factory maint manual, and has been written up here several times.
418 miles on 19 gallons of gas. Can't beat the BBD !
I disagree completely with the above post. I went through all this about 8 months ago. Ripped off the carb and put howell FI on. Best $ I've spent on the Heep. The vacuum system is 100x simpler with the howell and it passed emissions cleaner than the stock vehicle brand new. Its not a waste of $$. I say do it and save yourself a ton of headaches with the POS stock carb. It also allows you to tear out about 60 feet of redundant wiring and really clean everything up.
If you want the upgrade to simplify the setup and get better performance, then do the Howell. But be careful thinking that the Howell will solve all problems. Double check your intake manifold - retorque all the bolts to spec and do the carb spray trick to check for vacuum leaks. The Howell will not fix a bad intake/exhaust manifold gasket, nor will it fix a crack in the exhaust manifold and both can cause a fail. So, if you are set on doing the Howell, I highly recommend you track down that vacuum leak whistle, before doing the kit. And for good measure make sure the exhaust manifold doesn't have any cracks. That'll cause a rich condition too by messing with the O2 sensor.
With that said, I found the Howell to be a vast improvement in simplicity and increased performance over the OEM setup. I used to spend entire weekends under the hood f-ing with the OEM setup trying to diagnose and track down a simple problem. A TBI setup like the Howell is what Jeep should have put on the 4.2L YJ in the first place, but I suppose it was easier and cheaper to just keep using the CJ components.
While it's true the Howell can't solve all the problems, it gets rid of a lot of the vacuum lines and controls and meters the fuel more accurately. Assuming your engine is decent it should work. I'm quite pleased with mine
Keep in mind that there are two Howell versions, only one is actually EPA approved. Both may well pass the sniffer test but in a lot of places you need the approved one.
'89 Wrangler YJ
97 Grand Cherokee (ZJ)
87 MB 560SL roadster