soooo, it's been about 6 months since i originally installed my mikuni on my 12a, and many battles with it since then. I can honestly say that I had definately bitten off more than I could chew when I went for this swap, but I'm surely not a quiter and definately a tinkerer by nature.

I suffered from similar complaints that many sidedraft owners often complain of, poor throttle response, unstable steady cruising, poor gas mileage etc... and I have tried many remedies.... re-jetting, new fuel pump, new regulator..blah blah blah, but nothing worked. Well, last night afgter a bit more tinkering I FINALLY got this thing running right and let me tell you this thing is sooooo quick now.

For anyone thats interested I found my problem to be a combination of a few things mis-adjusted float levels, inaccurate fuel psi gauge, and thus too much fuel pressure. When I recieved the carb the float levels were horribly out of adjustment, so I set them to the recommended 12-12.5mm setting from mikuni (thanks trochoid for the mikuni tuning manual page), but it still didn't correct the problems. My fuel pressure read the recomended 4.5 psi. So, I assumed the needle/seat was bad and planned to buy a new one and rebuil kit. Well, lo and behold I stumbled upon my problem by accident. I was going to do a seafoam treatment on my engine, using their Deep Creep product and I was also going to shoot it through the carb passages to help clear out any crud. So I pulled the fuel pump fuse and started the car and began to rev it to run the fuel out of the float bowl so i could seafoam it, and I noriced the car was running imensely smoother/better. So it got me thinking......

Well I soon began messing with my fuel pessure, turning it down bit by bit, and driving the car. Each time it would get closer and closer. I also found that I had to raise the float level just a bit because i was running out of fuel in the top of third gear. So last night I got it perfectly dialed in with my Fuel Gauge reading 1.5 psi!!!!!?!?!?!? lol

So, the leason here is never trust the acuracy of your gauges.... and don't be afraid to tune your carb... and that's why fuel presure gauges suck, and my mikuni rocks!!

 

http://www.yawpower.com/fueldel.html

2nd that - never trust gauges.

I got an accurate 0-10psi industrial grade gauge from ReSpeed, and *that* thing knows what it's talking about.

Jon

 

Interesting read, I know Respeed sells a accurate low pressure fuel gauge if your looking for an alternative.

I know I had similar problems with my weber 45dcoe, but never really got the thing running just so. Instead I decided to go with fuel injection for streetability and reliability.

 

Fpgs are notorious for being inaccurate. I've gotten to the point that I use them as a range finder instead of a gauge. Does't make sense does it. Basicly, don't believe the # that the gauge shows, use it as an indexing point instead. If the fpg shows 5 psi, but it's running rich, drop the pressure down to 4 and see if it runs better. One simply uses the crappy gauges as a reference point, not as an actual reading.

Billy has one of the very few fpgs that I would trust.

Good to hear you got the Mikuni setup the way you want it. I like them personally.

 

yeah...it's unbelievably different...almost feels as smooth as the fuel injection on my buddies vert.... I'm lovin the rex again!!!

 

Rotaries usually run harder, faster and smoother when they are a little lean. That's also when they *pop*.

One of my old FB's won several street races in one night, against faster cars. She was running like a monster. She popped on the way home. When the engine was taken apart, it was obvious she was running lean.

Just a heads up. When it comes to rotary fuel, it is better to be RICH than poor (or lean).

 

yeah... i'm aware of the danger of running lean... but I'm sure it's not too lean for a couple reasons.... first off I'm using a holley 4-9 psi reg... so I'd like to think that at it's lowest setting that it wouldn't go below the 4 psi mark...also previous to the adjust ments I could smell plenty of un-burnt gas near the intake of the carb and could see fuel dripping out of the booster venturis... also at a steady cruise thecar would buck/miss/kick until I put the clutch in and revved the car... as if it was loading up with fuel and revving it cleared it out...then it would cruise fine for a couple seconds and back to flooding... also just for good measure I bumped the main fuel jet up... she still makes my eyes water if i stand behind her for too long and everyone can still smell my "rotary cologne" at work..lol but i'll keep my ears open for any detonation...

 

By the time you'd hear the detonation, most of the damage would be done. I would suggest a little time a with a wideband, or better yet: a wideband and a dyno.

 

+1 on the respeed fuel pressure gauge and dry break kit. awsome!

 

Very timely posting for me. Just finished bolting on my Mikuni 44 last night on an 83 12a streetport. Running a 41 choke and what appears to be a very free flowing header. Haven't started it yet so your experience may be helpful. Its in a Lotus Super 7 clone that weighs about 1200 lbs. Do you you have the jet and choke numbers for your carb? Any other mods? Got any HP numbers?