85rotarypower

Ok, I need some help with my Mikuni 50phh2, which is an early 50mm. I've got it on the car and its running alright, but FAR too rich all across the board and won't hold a steady idle. Anyway, here is what I currently have:

Large Ventruies - 34mm
Main air jets - 200
Main fuel jets - 195
Pilot jets - 47.5
Fuel pressure - 4.5 psi
Float may be off a little

Ok, now for the technical stuff. Starting with idle, thats not too bad. I got the mixture screws out about 3.5 turns and idle speed at 1000 rpm, higher than I would like but it won't hold too well any lower than that. Under 1500rpm while cruising and less than 10% throttle I'd say, its not bad, in the 13:1 range on my wideband. After that, it gets messy. Cruising above 1500rpm but less than 10% throttle, it runs immensly rich, under 10:1 on the wideband at times. Give it more than 10% throttle, it starts to lean out, but only as high as 12:1, and thats at 4000rpm or higher. Above 3500 rpm under light throttle, it stumbles and spits like crazy in the low 10:1 a/f range. So, basically its running rich everywhere in the range.

Now, I'm very confused here since my searching has turned up guys with the smaller 44phh are running bigger jets all around, yet even with a bigger carb and smaller jets the engine is falling on its face because its running so rich. I'm thinking my large venturies are part of the problem, but as it is right now, I'm thinking I have to drop the airs down to 160, mains to 150, and pilots to the upper 30's. Something is very screwy here. The only thing that might affect it a little bit outside of the carb is the vacuum advance on the dizzy isn't hooked up, there seems to be no timed vacuum port on this carb.

Anyway, and help or insight into the way this carb works would be greatly appreciated.

jay85gs

When I installed my Mikuni 44 it was setup of a streetport, it had #90 pump nozzles(way to big). Since I have a stockport I was told they should be #40 nozzles. Made all the difference, the car ran much better under load, almost all the bogging was gone. Running 3.6 psi on fuel pressure @ 3 turns out on the af screws.

85rotarypower

Well, I don't see what pump nozzles have to do with my cruise problems, but if anything that would make it too lean as my pump shot is a little on the small side, leans out if I hit the throttle open too fast, but not enough to worry too much about it.

I'm going to look into the float levels. I can't see that making much difference either, but its worth a try.

85rotarypower

So nobody else can give me any kind of advice at all?

85rotarypower

Well apparently this thread was a waste of forum space.

Misthael

When I had my Mikuni 44PHH installed a few years back I had the same problem. I seem to remember something about the throttle butterflies being open just enough to block the air bypass but not enough to let enough air through the barrel. I believe some people drilled a small hole in the butterfly, but I didn't want to do that. They're not very streetable on a stock port it seems. Mine only liked being closed or open, not in between. I'll try to dig up my old jetting. I also got a suggestion for jetting about a year ago I wrote down. I'll try to find that. If you don't have the manual I'd suggest getting that. You can find photocopied manuals on eBay and probably at Wolfcreek Racing. Wolfcreek is also a distributor for Mikuni. That's where I got all my jets. Great place, the website is just set up kinda odd.

Anyways. That's my 2 cents. I may be totally wrong, but that was my experience. Give me a few days to dig up some info. I have parts strewn about all over the place right now.

Misthael

Here's the jetting 81WideMariah sent me:

240 air
200 fuel
62.5 pilot
90 pump
37 mm chokes

I don't know what kind of porting he has if he has any, but I hope this helps.