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Thread: Carb question
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mwpayne
Hauling
Posts: 195
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posted October 04, 2007 05:04 PM |
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Carb question
REPU runs quite well, but a pretty rough idle. Checked everywhere for vac leak, none found. Also, won't fire when sitting overnight, fires right up with a squirt of cleaner down the carb.
Bet the 30 year old carb needs a rebuild. I've found a few kits for RX-4 (same, I hear), will the kit contain all I need to fix the accelerator pump, which is what I suspect is the issue on the no-start?
Never cracked open a carb before, tips welcome!
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Klaus44
Redlining
Posts: 365
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posted October 05, 2007 08:36 AM |
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Typically:
You will find what you need for your accelerator pump in the carb. kit. You'll also most likely find one or more gaskets it contains are brittle with age, and/or already compromised or broken... so, be extra careful with them! What it won't contain is anything related to your vacuum diaphragm's operation -- which is what controls the opening of your secondaries.
I'll wager there's rust/crud blocking various crucial passages in your carb. -- including, but not limited to the two small cylindrical screens located in the top inlet passages. Take care with these, and all other small parts -- they can be fragile. Also beware of warping any of the aluminum parts, such as the carb. top -- (like I once did while trying to remove a stuck inlet fitting...). Some things are sometimes best cleaned in place -- if they won't come off reasonably.
Berryman B-12 'chemtool' is my nasty spray cleaner of choice. (It will actually dissolve *asphalt*!)
Some folks like the 'chem-dip' can of nasty stuff, and swear by it -- but I don't. It's all a toxic mess, any way you slice it. Work in a *well ventilated* (read: set up a fan to work behind, outside) area. Protect your eyes, your lungs, and your skin. Cleanliness is next to godliness. Don't stick anything besides the end of the plastic carb cleaner spray nozzle into any jet orifices -- doing so may compromise/ruin them. Remember exactly where everything goes. Don't force anything.
First thing to do when you get the top off your carb., is to make sure your float has not been leaking. (Not that it sounds like this is the case, but it's a good general rule). Remove the float, inspect, and shake... is it dry inside?
How about your carb. body -- is it leaking fuel anywhere (generally from around the sight glasses...)? You need to inspect this before removal... What you describe could be (among other things) just this...
Beware of compromising any of the sealing surfaces during gasket scraping/removal. Beware of over (or under) tightening of the screws holding your carb. together!
Don't be afraid -- it's not too tough. Just don't lose any of the tiny parts (like the clips that hold the linkages in place), and you should be fine. ;)
PS-- Once you have a nice, clean, well-adjusted carb... Before it goes back on is the *best* time to replace each and every vacuum plug/cap on the entire intake -- even if you didn't locate any vac. leaks. I prefer the vinyl caps to the rubber ones -- they seem to last a bit longer. Also, consider adding another fuel filter in-line right before the carb. Remember to make sure the ends of your fuel/return lines are clean/intact enough to seal well... A clean air filter, and you're there!
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mwpayne
Hauling
Posts: 195
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posted October 05, 2007 08:48 AM |
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Thanks klaus, great read!
I guess the aceelerator pump is my suspect because I can't see any squirting of gas when I work the linkages and peer down the throat.. That is supposed to happen for startup, right? The rubber piece on the top part of that pump where the rod goes down into the thing is pretty much in pieces..not sure if that's supposed to make a seal of some sort...
Does that rubber gasket/piece coem with the kit?
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Klaus44
Redlining
Posts: 365
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posted October 05, 2007 10:11 AM |
Edited By: Klaus44 on 5 Oct 2007 10:15
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Yeah, it's supposed to squirt...
...but, not just on startup (!) Could be your accel pump; could be other things; could be (and most likely is) a whole bunch of age-related 'illnesses', including your accelerator pump, etc., etc., etc. ...
If that dust boot comes with your kit, great! If not -- it's only a dust boot...
The only way to be sure what comes in a given kit is to inspect it, visually. Don't buy any kits that aren't sealed in plastic -- they're likely missing pieces. Don't open the plastic on a kit you don't want to keep -- you generally cannot return/exchange 'em, once the plastic is opened...
Be prepared to track down/purchase more than one kit, if you want better odds of getting all gaskets intact and usable.
I have more tips for vacuum diaphragm function -- but for now, just keep gas and carb cleaner away from it, and don't tear it if and when you pull it out!
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sparky
Redlining
Posts: 299
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posted October 05, 2007 10:24 AM |
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I've rebuilt many of these carbs. I always thought my rough idle issues were carb related. Some were, most were not. When you are done with the carb rebuild if you still have rough idle connect a timming light and monitor both leading and trailing coils. Ignition break up will show with the light. Try the DLDFIS ignition upgrade. It has worked very well. My idle has never been better. Good luck.
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Jeff20B
Moderator
Posts: 661
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posted October 05, 2007 11:44 AM |
Edited By: Jeff20B on 5 Oct 2007 12:41
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I like working on Hitachi carbs. I just cleaned out a chunk of trash from the primary jet of one yesterday. It now idles and runs fine on primaries. However the secondaries cause a misfire. I don't know why.
The funny part is the first engine I tried this on, when the piece of trash clogged the jet, had ok secondary operation.
This carb sat for an unknown number of years partially disassembled. I had enough parts here to get it back together and working. Now all I've got to do is solve the secondary problem and it will be ready for use. Perhaps I should try it on a different engine before I open it back up?
This carb will find itself on a rotary baja project with an engine built to the Rotary Parkway 26 (26 passenger bus in Japan) specs for excellent torque and low RPM driveability.
Jetting for the Parkway Rotary 26 carb:
90 primary fuel jet
140 secondary fuel jet
90 primary air bleed
160 secondary air bleed
Jetting and air bleeds of the carb that sat forever:
92 primary fuel jet
150 secondary fuel jet
80 primary air bleed
160 secondary air bleed
My custom jets for increased performance on Parkway Rotary 26 port timing using the carb that sat forever:
92 primary fuel jet
145 secondary fuel jet
80 primary air bleed
117 secondary air bleed (soldered and redrilled to a smaller size)
As you can see, the old bus carb had very small jets and very large air bleeds for low RPM operation. It had almost no power above about 4500 RPM. I want more performance at higher RPM for the baja so I'm starting with the primary jets in the other carb of 92 and air bleeds of 80, compared to the bus 90 and 90. Downgrading the secondaries from 150 to 145 and reducing the air bleeds from 160 to 117 aprox (that's the smallest drill bit I had handy which measured out to around 1.17mm) is still an upgrade from the bus carb's 140 secondaries. I suppose I could go with 150 secondary fuel jets just because the bus carb had 140, and they'd provide more fuel, but I felt 145 would be a good middle of the road to start with. I also have some larger primary fuel jets to help with tuning; 93 and 94. We could also buy a set of 95 from Mazdatrix.
What do you guys think is causing the stumbling/missing problem when the secondaries open? This is on my REPU with a fresh rebuild running stock '74 spec ports and somewhat larger exhaust ports than the dinky little US-spec. Again this carb didn't seem to have a problem on a friend's streetported 13B... until something clogged one of the primary fuel jets and I cleaned it and tried it on the REPU.
More testing is required.
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2wankel
Hauling
Posts: 133
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posted October 05, 2007 06:53 PM |
Edited By: 2wankel on 5 Oct 2007 18:54
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Hello,
I'm having the same problem. Idle is lumpy, but when I press the accelerator its smooth without hesitation.
I would also like to make sure what carb I have...
I have a 1975 picup its supposed to be hitachi. I just want ot make sure...
I also found this place for rebuild kits. Has anyone bought one from them?
http://216.171.221.114/catalog/pr/c2/
thanks
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VMRC Website
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Jeff20B
Moderator
Posts: 661
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posted October 06, 2007 12:22 AM |
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That is a Hitachi. I have a '74. The key differences are your fuel inlet looks different, and might even be upside down or adjusted strange. Also your throttle bracket looks to be stamped steel with a strengething rib. The '74 spec is relatively weak there and flexes when you actuate the throttle. Also the '74 fuel inlet/outlet is a funny aluminum tube thing. I like the '76 and later steel tube inlet/outlets.
I may add a gusset to my throttle bracket if it flexes too much. I also removed the emergency return spring. Was it a good idea? Maybe. The '76 and later carbs had two springs or one strong one with no emergency one.
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Rotary_Pickup
Hauling
Posts: 117
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posted October 09, 2007 05:32 PM |
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I just ordered a carb rebuild kit for my 1975. It was around $16 after tax from Auto Zone (also at www.autozone.com). It wasn't in stock but will be at the store tomorrow. I’ve never rebuilt one but for $16 I can’t go wrong.
Here's the info
Gp-Sorensen / Carburetor Kit
Price: $14.99
Part Number: 96-286
Note: Hitachi 4 barrel O.E.M. #390013200A, 390213200A, 390413200
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KansasCityREPU on RX-7Club.com
85 GSL
77 REPU (1/1/2004)
75 REPU (7/10/2004)
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mwpayne
Hauling
Posts: 195
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posted October 13, 2007 07:38 PM |
Edited By: mwpayne on 13 Oct 2007 19:39
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Hey, post up how that rebuild kit worked out. Did it include what you needed for the accelerator pump?
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Rotary_Pickup
Hauling
Posts: 117
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posted October 14, 2007 08:43 AM |
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quote:
Hey, post up how that rebuild kit worked out. Did it include what you needed for the accelerator pump?
I got the kit but I'm not sure it's the correct one. They put a paper instruction sheet inside but it is for a weber model 32ADFA. Not having ever taken a Hitachi apart before, I can't tell if it's the correct kit looking at the gaskets. The kit I have does not have any parts for accelerator pump (no diaphram). I'm going to take it back to confirm it's the corrct kit.
____________
KansasCityREPU on RX-7Club.com
85 GSL
77 REPU (1/1/2004)
75 REPU (7/10/2004)
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Klaus44
Redlining
Posts: 365
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posted October 14, 2007 11:19 AM |
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Don't break open the plastic wrap!
If you do, theyll not likely exchange or refund you...
The correct kit *ought* to have the paper diagram of the Hitachi. It also ought to come with a new accel. pump plunger w./ leather cup, (which is good to lube with WD, etc. prior to assembly). Check to make sure float bowl as well as base gaskets are included!
--No kit I know of will come with any diaphragm (such as the one we wish we could simply replace that operates the vacuum secondaries)... I did get as far, once, as determining that those *might* become feasible/cost effective to get remanufactured --*IF* and when we could supply the used ones (cores)by the dozens for this purpose...
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Jeff20B
Moderator
Posts: 661
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posted October 16, 2007 12:05 PM |
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I tried the Hitachi on the other engine again and the secondary weirdnesses were gone. It turned out that my carb spacer had a vacuum leak in a secondary runner. The rubber cap was old and barely staying on under its own grip. I replaced it and tried the good old '74 carb and all is well.
I should try the other carb again, just to make sure, but I don't really care. The current carb works well enough for break in. I've got a little over 300 miles on it now.
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Rotary_Pickup
Hauling
Posts: 117
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posted October 16, 2007 05:19 PM |
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I just got off the phone with AutoZone and I'm taking the kit back because it does not have the paper diagram.
Does anyone know of a good kit and where to get it?
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KansasCityREPU on RX-7Club.com
85 GSL
77 REPU (1/1/2004)
75 REPU (7/10/2004)
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Brad
Rotorhead
Posts: 1672
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posted October 16, 2007 06:38 PM |
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I used to get mine from Pep Boys.
You can get the 13b base gasket here:
http://mazdatrix.com/c-3.htm
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mwpayne
Hauling
Posts: 195
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posted October 17, 2007 03:33 PM |
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Theres a local carb rebuilding place around here with a good rep, perhaps I'll call them and see..
Otherwise, it's looking more like I should just replace it, if parts are chancy at best.
This is an area I know less than nothing..replacement carbs.
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jfaplanet
Redlining
Posts: 356
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posted October 17, 2007 07:01 PM |
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Jeff in Nashville
Mike, I think jeff is selling his stock carb and mani off the white truck that chad sold him. You might want to get it to have a spare.
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74 REPU "Red"
74 REPU "Jethro" "TII"
74 RE-Courier vert
79 SA-SE(aka deathtrap)
79 SA-SE-FC (project
turbo)
http://home.bellsouth.net
/p/PWP-crgj
TN Forum:
http://tnrotary.10.forume
r.com/
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repu510
Hauling
Posts: 141
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posted October 18, 2007 08:27 AM |
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the carb and manifold i'm selling are spares. i bought them together on ebay several months ago. i was planning to send it to paul yaw, or someone like him, to see if i could get it reworked for more performance, but scrapped that idea. its just easier to buy a dellorto or weber. so that's why its for sale now. it wasn't the one off the white truck. its still on the truck and running well.
i ordered a carb rebuild kit and diaphram off the website from napa. i dont remember if it was listed as a rx4 kit but that seems to work better on some of these parts sites i've been to lately. if you're local, you're welcome to come by and take a look.
i just got my fuel tank back from getting lined. i hope to have it back in this weekend. after that i can get to the fun stuff, audio!
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Klaus44
Redlining
Posts: 365
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posted October 18, 2007 09:58 AM |
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Recommendations:
--Have the parts places order more than one kit, if possible, and inspect 'em all closely, side by side, prior to purchase/pick up. If they're good, correct, and complete, you've got spares. Search the web -- and Ebaymotors completed auctions -- for sellers/previous sellers of the part #'s in question. There may still be different brands of kits floating around out there...
--Also a great idea to start accumulating spare/parts Hitachi's -- they're generally cheap, so no big deal -- and invaluable when you need a part! Besides, it's educational to get to see some of the variations they came out with...
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