OK I just cleaned (not rebuilt) my new Mikuni 44 and installed it with 1 piece intake. Car idles and runs like a champ. Engine bay looks MUCH cleaner. Took it for its first ride a few minutes ago and it was not as much of a difference from my Nikki... actually hardly any difference other than the sound and eveness of power.

My 12A is stock port and I have always had an RB header and exhaust but just switching from my nikki (with mech secondaries) to the mikuni really didnt make that much of a difference (unless there is that much more in the fine tunning of the mixture or something else I may be missing).

Always have had a holley red fuel pump, and bumped my fpr up to 4.5. Using the stock return fuel line from the nikki on the Mikuni instead of dead heading the "T" connector. Timing is set to stock.

At a loss... maybe I expected too much...

Any ideas?

 

I think the real difference will be noticeable with a full exhaust system, and more tuning. Did you play with the jets or anything?

 

No I did not change the jets other than cleaning them. I do have the full rb exhaust though... sorry for not being clear on that... I just was reading in another thread that performance could be impacted by using the tee for the fuel line on the mikuni and connecting (as i did) the fuel pump to 1 end and the stock fuel return line to the other. It makes sense that the pressure would not really build properly by doing that as it would flow freely down the return line. I'm going to try closing off the return completely (I think that was called dead heading it) and test driving it again.

 

Which fpr are you running? One can, and imho, should run a return style fpr with the Holley Blue simply because of it's gph. At 110 gph, the pump will last longer with a return line. The 72 gph pump is more than sufficient for a stock, sp even a 1/2 bp engine.

Did you remove the stock barrel fpr from the return line? If not, that may throw off your fuel pressure.

The Mikuni should show a marked performance increase over the stock Nikki. If not, you may have other issues to deal with. Fuel flow, ignition, timing, etc., not to mention tuning the Mikuni.

 

should be a significant improvement probably jetting issue

http://www.wolfcreekracing.com/

these guys can help

 

I know I'm lining myself up for some real bad comments but I prolly need to be schooled on this so I'll just take em...

I know its a crappy dial regulator. Heres a few pics showing how I have the return line right now as well. There was never anything in the return line that I had ever seen so I just hooked it up extactle as the nikki was hooked up. Can I just cap off the return... or will that cause a world of hurt?

I added a couple extra shots of the jets (prior to cleaning)....

 

Post the jetting that the carb has along with the venturi size. That will give a baseline from which to start.

 

Didnt realize it 11pm. will do in the a.m. and post back.

 

I capped off the T in my OER, just make sure you are running the correct fuel pressure!

 

That FPR is junk. I would recommend a Holley unit, they're cheap and work much better than any dial type (this is per Yaw). Do you have a fuel pressure gauge installed?

 

I know... the FPR is junk.... it was what I could afford at the time... I will find a holley fpr today.

I didn't have an FPG installed because... from what I read... FPGs should be used as a point of reference due to the inacuracy in many. I read that if you need to run x amount of pressure... you cant just read it off the FPG and say that because the FPG says x... all is done... rather you use it as a point of reference adjusting up and down from that point checking performance along the way.

I then ask.... If you use the FPG solely as a point of reference... why not just use the settings on the FPR as the point of reference and save a few bucks (I know it doesn't look as cool though)?

I'll still buy 1 while I'm at the store anyway.

TROCHOID... I think you might have thought I had the Holley blue, but I have the holley red. Would you still recommend a return style FPR?

 

if you get a fuel psi gauge DO NOT GET A liquid filled gauge they are very wronggave me fuel problems for almost a year

 

+1

 

pilot jet = 62.5
main jet = 200
main air jet = 240
venturi = 39mm
Type S5 carb 44mm carb

I dead headed the return line and set my cheapo dial at 3.5 ran it out on the road however after some hard fast running... fuel was comming out of the air horns on top of my nice hot engine!

What could have been the cause of that? That did not happen when I had the return line hooked up?

 

When all this stuff was new, the Mikuni setup did not make as much advertised horsepower as Dellorto or the twin Weber setups.

 

Get your gauge from www.re-speed.com

They have what seems to be the most accurate gauge (extremely accurate) and at a very nice price...

 

use the return set up. its better to manage. what fuel pump # not just color. get the respeed gauge, no gauge no referance point. you do not know the real presure by the marks on the regulator. get a real regulator one thats accurate.

the cause of the fuel out the horns could have been you dead heading it.

the mukini power being less is not quite an accurate statement. compaired even set up with the carbs per the old rotary rocket mag; Dellorto made the most by a couple then the mukini then last was the even sized weber total spread was 9 hp over very differant power bands.

 

weber had several sizes and configurations that offered them the ability to say they made the most power. but head up with same style intake they made less power but very even on the tQ

 

I am running deadhead on my Mikuni. No probs. It sounds like you just have way too much fuel pressure. Highly recommend a gauge. May not be entirely accurate, but should tell you if your are way off. My gauge shows just about 3.5 most of the time. I am running almost the same jetting you are.

Holley Red
Holley FPR

 

If fuel is coming out of ther air horns, one of 3 things, are happening. The float level is set too high, the fuel pressure is too high, or the carb may also need fresh gaskets. As far as running a return line, even with the smaller volume pump, the pump will still last longer and have less chance of overheating. With fuel coming out of the air horns, I wouldn't expect it to run even as well as a stock Nikki.

Since this wasn't happening when the return line was hooked up, what does that tell you?

 

I purchased the holley fpr adjustable from 4.5 - 9. I pulled and cleaned the pilot jet (which I did not do originally) and adjusted the floats to spec (12.5 mm from the cover while resting against the pilot jet not compressed) the floats were misadjusted.

The gaskets appear pretty fresh. I also purchased a non-liquid filled holley FPG and just finished mounting everything.

In just using the stock return line; without anything to cause back pressure, the pressure was sitting at 2 with the holley fprs stock setting. I did not try yet to adjust it to 3.5 - 4. Not sure that it will work because the return line is just free flowing (apparently).

I read that another member still used the stock return line but used another fpr between the carb and the return so it wasnt free flowing. I was planning on using my old dial fpr post carb in the return line so that I could then adjust the holley fpr to the recommended 3.5 to 4.

 

OOOPS not pilot jet... I already cleaned the pilot jet.... I just neglected to clean the needle valve 1st time around and adjust the floats to spec... This I hope will help with the flooding (as well as the right fpr and fpg)

 

All looks good. I used the dial fpr on the return line which built enough back pressure so that I could adjust the holley fpr to exactly 3.5. Not 1 drop of fuel out of the horns, smooth idle, revs RESPONSIVE. I'm going to replace the dial fpr with something else that will cause enough back pressure because it's now obvious why dial fpr's are crap. Every time i just tap on the dial fpr... there is fluctuation in pressure! I now can see the pressure difference using my new guage (thanks for that suggestion). Auto parts stores should drop carrying garbage like that. Will test drive in the a.m. and post back with some pics. Thanks again to all. I know this info is in bits and pieces within other threads but its always nice to have something somewhat consolidated.

 

ok lets take a step back. what holley fpr did you buy? pn#, is it one made for a return setup? they have several, one made for 4.5-9psi would be the wrong one for under 4.5 lbs. one made for a non return style setup would be the wrong one for a return setup. type of fpr would tell you if it needed to be in front of the carb or behind the carb. from your post it sounds like the one you have is mounted in front of the carb. you should not have a restricion in the return line using a fpr. a fpr made for a return set up would keep the pressure before it set to your setting, one made for a non return set up would keep the pressure set to your setting after it. useing the later style in a return set up would cause pressure cycling. the 3.5psi should only be a referance point a lot of people have had good luck with it but also many have their pressure set any where between 3.5 and up. my personal experance with stock port 12a and mikuni just over 4psi worked best many find best results at 4.5 lbs as the book says. the tech manual says 3.2 lbs -6lbs is the range depending on the set up and engine. like webbers, mikunis are very touchy to pressure changes. heres a quick read for you http://www.yawpower.com/fueldel.html he is talking about his modified nikis but the laws stay the same for your carb with in the pressure range for your carb. setup and tuned right there should be a fairly big differance. carter made the one I used back when I ran a mikuni, I think it was about $60 and adjustable between 3-10 psi there is probly something similar avalable today. maybe you have gotten lucky with what you have done and do not need to make any more adjustments and are not in need of any of this help. good luck

 

In our experience, Webers produced highest Horsepower and torque. SU and Dell'Orto were close in power, and Mikuni not a great difference. All were tested for optimised intake lengths, complimentary to each.