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 Post subject: Sidedraft woes..
PostPosted: Sun Feb 24, 2013 10:16 pm 

Joined: Sun Aug 29, 2010 10:23 am
Posts: 115
Location: WV
So my fb is finally running and driving with the mikuni 44 side draft that I bought last summer, however I have a few issues.. At WOT, near 6000 rpm the motor acts like it's starved for fuel, it gets to redline a little slower than I think is normal. I am running between 3.4 and 4 psi of fuel pressure. Also, I have the OMP hooked up and didn't think it was working, but one of the lines keeps falling off the carb and I find motor oil drops on the intake manifold, but I see no oil coming up from the OMP lines, any ideas? Does the OMP have one return and one feed line, or are they both feed? I know I have to replace the accelerator pump b/c the car bogs with a quick foot on the throttle off idle, but otherwise it revs nicely till the aforementioned 6000 rpm or so.. Does anyone have any tips to make the Mikuni get along a little better with my 12a?


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 Post subject: Re: Sidedraft woes..
PostPosted: Sun Feb 24, 2013 10:19 pm 
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Joined: Thu Oct 04, 2007 11:17 am
Posts: 69
Location: Hope, British Columbia, Canada
Your main jets maybe a tad too small. Starving it of fuel.

What size chokes are you running?

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 Post subject: Re: Sidedraft woes..
PostPosted: Mon Feb 25, 2013 2:44 pm 

Joined: Wed Jan 16, 2008 1:54 pm
Posts: 380
Location: Southeastern Massachusetts
The oil lines are both feeds.

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78 RX-7 GS Spark Yellow
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 Post subject: Re: Sidedraft woes..
PostPosted: Mon Feb 25, 2013 6:37 pm 

Joined: Sun Aug 29, 2010 10:23 am
Posts: 115
Location: WV
Drove the car again tonight, omp lines are secure but still getting oil on manifold.. Car pulls nice and strong at lower rpm but breaks up and loses power above 5000.. Carb specs will be posted as soon as I tear it apart to clean it but I think it is the original killer bee aggressor setup from rotary reliability and racing..


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 Post subject: Re: Sidedraft woes..
PostPosted: Mon Feb 25, 2013 9:40 pm 

Joined: Tue May 20, 2008 8:03 pm
Posts: 43
Location: Austin, TX
I agree with the above post, a bigger main jet might solve your problem.


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 Post subject: Re: Sidedraft woes..
PostPosted: Sat Mar 02, 2013 9:38 am 

Joined: Sun Aug 29, 2010 10:23 am
Posts: 115
Location: WV
Does anyone know where to order parts for this carb in the states? I definitely need an accelerator pump and probably jets..


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 Post subject: Re: Sidedraft woes..
PostPosted: Sat Mar 02, 2013 3:19 pm 

Joined: Mon Aug 15, 2011 4:47 pm
Posts: 58
Location: norcal
Is the motor ported ? A easy way to make omp lines that dont leak is : use high quality German vacume line with the cloth braid outer sheathing , the stock mazda omp lines are made of brittle plastic that has went through tons of heat cycling and rubber hose ends that are usually worn out.


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 Post subject: Re: Sidedraft woes..
PostPosted: Sat Mar 02, 2013 8:08 pm 

Joined: Sun Aug 29, 2010 10:23 am
Posts: 115
Location: WV
The motor is not ported, I will surely look into replacing the lines with the German stuff.. Thanks!


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 Post subject: Re: Sidedraft woes..
PostPosted: Wed Mar 06, 2013 12:51 pm 

Joined: Sat Oct 22, 2011 9:06 am
Posts: 10
Location: Bay Area
Hi oldisgold, this "Car pulls nice and strong at lower rpm but breaks up and loses power above 5000" sounds like detonation. How is your timing?
You could put your fuel pressure gauge on a hose and tape it to the outside of the windshield to see if you are losing fuel pressure above 5k. Be sure to secure the hose on your regulator and the gauge because if it pops off under pressure you will have a fire.


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 Post subject: Re: Sidedraft woes..
PostPosted: Thu Mar 07, 2013 6:01 pm 

Joined: Sun Aug 29, 2010 10:23 am
Posts: 115
Location: WV
We tuned the car a bit the other day and adjusted the timing and mixture screws.. the car runs a LOT better than before but still breaks up noticeably after 5500 to 6000 rpm and on to redline, though this is only noticeable in 1st gear pulls. For some reason, it sounds fine all the way to redline in 2nd and 3rd gears.. Does this make sense? I'm thinking it isn't getting enough fuel, so either the regulator is not allowing enough at WOT or the main jets are too small, good idea holding the fuel pressure gauge up to the windshield, I'll try that when we tune again, which will be when the weather clears. Still need to find an accelerator pump and probably a jetting kit, who knows of a good source for mikuni parts?


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 Post subject: Re: Sidedraft woes..
PostPosted: Thu Mar 07, 2013 7:06 pm 

Joined: Mon Aug 15, 2011 4:47 pm
Posts: 58
Location: norcal
I would put a wide band gauge on that think so you don't lean that motor out and blow it up , The side draft carbs are about the worst thing you can do on a rotary for power ,I don't know how many times I have told people , Racing beat will tell you the same thing . The argument is always "it has better torque " .What you gain on the bottom you lose on the top and tuning is always a problem . You would be better off using a modified nikki carb for drive ability and power on a non ported motor .


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 Post subject: Re: Sidedraft woes..
PostPosted: Thu Mar 07, 2013 8:14 pm 

Joined: Sun Jun 10, 2012 5:37 am
Posts: 8
Location: Richmond, Virginia USA
It's winding out the higher gears that would show fuel starvation more so than 1st, which goes by so quickly. Still, It sounds like fuel filter. Ignition? If you're stock the easy cheap upgrade is to 2nd gen leading coil direct fire. Takes 5 minutes, makes more better. Wolfcreekracing.com has Mikuni parts. Long ago (25 yrs) I wanted that Killer Bee intake. That was pre-internet. The Nikki is as good as one can do on a stock port motor. Strip her down, mechanical secondaries.

Edit: What exhaust are you running?

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 Post subject: Re: Sidedraft woes..
PostPosted: Thu Mar 07, 2013 9:13 pm 

Joined: Sun Aug 29, 2010 10:23 am
Posts: 115
Location: WV
Mattallac, I bought this setup assuming it was as good as a Weber downdraft configuration, apparently I was wrong. I have a great exhaust system: racing beat header, no cat 2 borla mufflers and 2.5 stainless all the way back, I'm not opposed to buying the 48 IDA weber and intake from racing beat if it will really help.. I won't go back to the nikki as I have plans to port the motor later..


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 Post subject: Re: Sidedraft woes..
PostPosted: Thu Mar 07, 2013 9:41 pm 

Joined: Mon Aug 15, 2011 4:47 pm
Posts: 58
Location: norcal
ya that sucks about your set up . I am a down draft weber fan myself , and on some of the other forums I'm known as a holly hater , they use a lot of gas and they starve for fuel around corners . But one of the guys I trade parts with in Chicago says you can get rid of the cornering problem with main jet extensions.The only problem with a weber is there is a flat spot , but tuning is easy and the carb is simple . You can't have it all , unless its injected .


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 Post subject: Re: Sidedraft woes..
PostPosted: Thu Mar 07, 2013 9:46 pm 

Joined: Sun Aug 29, 2010 10:23 am
Posts: 115
Location: WV
So should I take off the 44 and sidedraft setup and set it next to the two 6 port motors I have in the garage and label it all "boat anchors"? Is there any real performance gain to be had with this setup? If not, I'll sell it to help fund an IDA..


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 Post subject: Re: Sidedraft woes..
PostPosted: Thu Mar 07, 2013 10:11 pm 

Joined: Sat Oct 22, 2011 9:06 am
Posts: 10
Location: Bay Area
Isn't this carb supposed to run 4.5 psi of fuel pressure?
Definitely fix the accelerator pump. When you open the throttle the fuel drops out of the air in the intake and it leans the mixture. So the accelerator pump is there to enrich it back up. It's probably not what's wrong but it's hard to tune up a carb that isn't in good condition to start with.
Also be careful changing things all at once. If you change timing and jetting you won't know what fixed it (or made it worse).


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 Post subject: Re: Sidedraft woes..
PostPosted: Thu Mar 07, 2013 11:04 pm 

Joined: Mon Aug 15, 2011 4:47 pm
Posts: 58
Location: norcal
Hey Skip ,he should just change the carb , name another carb manifold that does a 180 degree turn . LOL


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 Post subject: Re: Sidedraft woes..
PostPosted: Thu Mar 07, 2013 11:28 pm 

Joined: Sat Oct 22, 2011 9:06 am
Posts: 10
Location: Bay Area
Hey Matt! I checked out your GL. I love the paint. 70's overload graphics!
I'm all involved with this carb now so I want to get it runnin' right!
These wrap around intakes don't make the most power but I loved mine. The car felt so crisp with it.
Don't all the 2nd, 3rd gen Rx7 and the Rx8 go 180 around the top of the engine?


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 Post subject: Re: Sidedraft woes..
PostPosted: Fri Mar 08, 2013 12:09 am 

Joined: Mon Aug 15, 2011 4:47 pm
Posts: 58
Location: norcal
they do, but they are injected


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 Post subject: Re: Sidedraft woes..
PostPosted: Sat Mar 09, 2013 8:26 am 

Joined: Tue May 20, 2008 8:03 pm
Posts: 43
Location: Austin, TX
oldisgold wrote:
Mattallac, I bought this setup assuming it was as good as a Weber downdraft configuration, apparently I was wrong. I have a great exhaust system: racing beat header, no cat 2 borla mufflers and 2.5 stainless all the way back, I'm not opposed to buying the 48 IDA weber and intake from racing beat if it will really help.. I won't go back to the nikki as I have plans to port the motor later..


The longer intake track gives should give better low end response than a down draft setup, but it will limit your top end flow. If you have plans to port the engine, a down draft will be better for it. A 44 PHH is good enough for a stock engine, but porting will require bigger barrels to flow enough air. You could keep your same intake manifold and use a Weber 48 DCO.

Datsun guys use http://www.wolfcreekracing.com for Mikuni parts.


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