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Thread: Carb. Secondaries
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Uncle-Jim
Revvin Up
Posts: 64
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posted February 05, 2003 12:55 PM |
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Carb. Secondaries
I have a couple of questions for you all.
Firstly, is it possible to get the secondaries to open while revvin' the engine in the driveway? Or do you have to have more of a load on the engine than is possible this way?
I couldn't get the secondaries to open no matter how hard I revved it.
Second, if you shorten the diaphram spring, how much is appropriate?
Thanks,
Jim
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Uncle Jim
72 Rx-2 Show Car; '77 REPU (250K & goin' strong) 2 - '76 Cosmo's
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Klaus43
Rotorhead
Posts: 1259
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posted February 05, 2003 02:52 PM |
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All depends...
Generally, the vacuum secondaries won't open just by revving it in your driveway...however, we're dealing with ancient, if NOS, vacuum diaphragms at best--so there's a big question just how positive the action can be made to be, regardless. There is an associated vacuum 'jet' in the carb that can be modified (soldered shut) that otherwise bleeds off vacuum... resulting in an earlier opening of the secondaries. Or, you can simply wire 'em mechanical-like.
Spring shortening, I don't know...
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repuguru
Redlining
Posts: 319
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posted February 05, 2003 05:03 PM |
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Yeah, you might could suddenly go wide open with the throttle and maybe the secondaries would begin to open, but you'd be up around redline by the time that happend.
Under load it another story.
The air bleed off screw has numbers stamped on it. The lower the number the smaller the hole. I have seen them from 60 to about 150. I tried them all to see if it made a difference. It does, if you vacuum system it working.
I settled on a 60 with 2 coils of the vacuum pod spring clipped off.
I've not tried plugging the hole off though?
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Uncle-Jim
Revvin Up
Posts: 64
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posted February 06, 2003 09:35 AM |
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I have a Hitachi carb that I modified for manual secondaries. It works well if you want some really spectacular performance. The problem has been that you have to use a really light touch on the throttle driving around town. The engine stumbles badly if you hit it too hard. However, once you get some rpm's, it's...amazing!
Thanks for the idea's about the air bleed. I think the '77 carbs have the 150 so that means the vacuum sec. only come in under the highest load.
Anybody know where to locate different size bleeds?
Thanks
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Uncle Jim
72 Rx-2 Show Car; '77 REPU (250K & goin' strong) 2 - '76 Cosmo's
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repuguru
Redlining
Posts: 319
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posted February 08, 2003 07:06 PM |
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Yeah that bogg you feel when you stomp on the throttle with a manual linkage secondaries is what drove me to try the vac mods to try to get the carb to open as easy as possible.
The jet came in most 74-78 hitachi carbs.REPU,RX4, and Cosmo.
I think some of the 12a carbs got the air bleed screw, but haven't messed with 74-78 A motors since I sold my RX3, so I may be wrong?
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Klaus43
Rotorhead
Posts: 1259
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posted February 09, 2003 10:17 AM |
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Vacuum vs. aging rubber...
I don't know about sourceing the different bleed jets, but I'd suggest you try sealing one off--especially if you have a spare...it was the only thing that helped in my case...but even that isn't perfect. Mechanical can work bog-less--just takes care not to put one's foot down before a certain rpm is reached.... My current Hitachi/jspec 4port/RB header setup has the sealed bleed, and likes to pop open best when floored at 2500-3000 rpm in 2nd or 3rd... and lacks top-end power, but makes up for it in the fat midrange. Pretty functional for a REPU on the cheap, but you might want different for yours. I've also heard the opinion voiced that no two rotaries are exactly alike, so when it comes to tuning it all depends...
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