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Index > Engine/Drivetrain > Thread: My first carb rebuild, first question?
Thread: My first carb rebuild, first question? [' This thread is 2 pages long: (1) 2 ']
mwpayne


Hauling
Posts: 195
posted February 01, 2008 06:16 PM

My first carb rebuild, first question?

Well, I removed the carb with no problems, replaced the secondary diaphragm, pretty easy so far.
I saw a corroded hunk of metal on one side, and according to the rebuild kit paper, it's an 'idle switch'.
It's obviously not working, how important is it, and how does it affect idle?
Bear with me guys, I'm a carb NOOB, I'm sure I'll have more questions as I go along.
Thanks in advance!

       
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Klaus44


Redlining
Posts: 365
posted February 02, 2008 11:14 AM

Where did you find...

...a functional NOS vacuum secondary diaphragm? Are you positive you're not referring to some other part? Those don't come in the carb. kit...

Is your REPU 100% stock, in terms of intake, exhaust, distributor, and emissions? If so, that idle switch might matter; if not... I doubt it -- but, since nothing I have is 100% stock, I'm not the guy with your definitive answer...

       
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mwpayne


Hauling
Posts: 195
posted February 02, 2008 01:09 PM
Edited By: mwpayne on 2 Feb 2008 13:10

Nah, emissions gone, 85 RX-7 distributor, I'll probably chuck it.
Honest and for TRUE, the diaphragm is orderable from NAPA. Wasn't in the kit, but I gots one!
Go to NAPA online, do a search for Mazda RX-7 pickup (yeah, I know), the kit and diaphragm are listed.

Thanks again Klaus!

       
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Klaus44


Redlining
Posts: 365
posted February 02, 2008 01:49 PM
Edited By: Klaus44 on 2 Feb 2008 13:54

Nice!

Is it still soft and pliable? (That's gotta be the best news for Hitachi's since I don't know when!)

Just remember to make sure *anything and everything* that's superfluous that you remove gets capped/plugged securely. Sometimes, it's better to leave an unneeded fitting in place, simply because it's the best thing to cap an otherwise hole...

The function of your secondaries may still be improved, if need be, by soldering shut the 'air bleed' jet that controls the amount of vacuum reaching the diaphragm. The other mod to consider, if needed, is cutting down the return spring a bit... (if your secondaries still need yet more 'encouragement' to snap open fully when they ought to.)

Vacuum leaks --actual, and potential-- are the enemy!

To that end, be *extra* careful not to warp any carb components while attempting removal of any stuck bits... (don't ask me how I know!)

;)

       
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mwpayne


Hauling
Posts: 195
posted February 02, 2008 05:12 PM
Edited By: mwpayne on 2 Feb 2008 17:15

Yep, still soft. In fact it felt/looked like a brand new part. I can highly recommend you getting one, if you need it.
The carb is in surprising good shape, not really gummy like I expected. I suspect it had been rebuilt before I bought the truck. Only really crappy part was the accel pump. The plunger part was hard as a brick. Floats not leaking. One thing I noticed was that practically every screw/bolt was WAY too easy to break loose, some barely finger tight.
I'll reassemble tomorrow..any bets on whether it'll start?

       
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Klaus44


Redlining
Posts: 365
posted February 02, 2008 06:34 PM

Too loose isn't good...

...but too tight is far worse for many of the carb. fasteners!

I'll guess you'll be careful and conscientious, and it'll fire right up for you, no problem.


       
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dhood


Hauling
Posts: 134
posted February 02, 2008 07:35 PM

Check the wiring diagram. Idle sw controls the coasting valve so if you have removed the valve (called coasting valve in manual) you won't need the idle sw either. If its shorted out the valve will leak and engine will run lean, maybe not idle at all without pulling on the choke. You can just connect or disconnect the wires to keep the valve shut or open all the time but then it'll either backfire when decelerating or not idle, your choice. You can control the backfire by not backing off the agas too fast. But if the valve is gone, you dont need the sw anyway. Sw are obsolete, can't be found except at wrecking yards, maybe, or on someone elses spare hitachi carb.

       
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mwpayne


Hauling
Posts: 195
posted February 03, 2008 06:58 AM

Thanks, I'll check the wiring diagram and see where that coasting valve is, don't think I have one.

"The function of your secondaries may still be improved, if need be, by soldering shut the 'air bleed' jet that controls the amount of vacuum reaching the diaphragm. The other mod to consider, if needed, is cutting down the return spring a bit... (if your secondaries still need yet more 'encouragement' to snap open fully when they ought to.)"

Klaus, where is that bleed jet? Is it the hole on the diphragm housing?

       
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Klaus44


Redlining
Posts: 365
posted February 03, 2008 01:00 PM

'Jet' does not = 'hole' in housing!

It's located inside the top of the carb. It's an actual 'jet' fitting... (Brass screw-in orifice of specific size).

Seems the 'techlit' (carb kit) instruction sheet (# 50-511) fails to depict it...(or at least I'm not finding it on the one I have on file).

From page 17 of the Mazda REPU Parts Catalogue ('carburettor' schematic/blow-up view), I think to have ID'd it as being labelled part 16 -- Mazda Part # 0268 23 394; Bleed, Air-190.

There's only one of these in the carb., and you may not need to mod it at all, since you've got that nice, new, pliable diaphragm...


       
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mwpayne


Hauling
Posts: 195
posted February 05, 2008 12:58 PM

Well, she fired up!

Once I set the idle, very smooth, definite improvement. There is one issue, seems it wants to bog upon quick accel. I've fooled around with the idle/air adjustments, no effect.
What'd I screw up?

       
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Klaus44


Redlining
Posts: 365
posted February 05, 2008 01:27 PM

Fully warmed up?

What RPM's prior to pedal-to-the-metal? If it's any less than 3.5 to 4K... could it be that your secondaries are *snapping* open so well, that this is the cause of the bogging?

How's your timing/the rest of your ignition system? How's your fuel pump/delivery pressure/volume? Fuel pump electrical/ground connects? Anything possibly clogging the flow, anywhere in the system? You were *scrupulous*, uncompromising, and *complete* in your disassembly and cleaning of *each and every* passage, component, and orifice, right?

NO chance of any vacuum leaks, *anywhere*?

Which hole in the lever did you use for your accellerator pump linkage?

Could be as simple as that...

       
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mwpayne


Hauling
Posts: 195
posted February 05, 2008 02:59 PM
Edited By: mwpayne on 5 Feb 2008 15:01

Stupid me...

I had the air mixture and idle adjustments mixed up,,,turning air to adjust idle and visey versey...
Once I followed the book and adjusted it s l o w l y.., that fixed it.
Right after that, the fitting cracked on the oil sending connection, glad I had a bag of cat litter handy.
Thanks Klaus..and your opinions DO matter!
Oh, and there's only one hole that I can see for the accel pump linkage?

       
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mwpayne


Hauling
Posts: 195
posted February 08, 2008 01:32 PM
Edited By: mwpayne on 8 Feb 2008 13:34

Accel pump question

Well, cold starting has much improved since the rebuild, but I wonder if I have the accel pump adjusted correctly.
Working the plunger up and down gives a dribble of gas out of the ports (I was expecting a squirt). Is it possible for a carb to have an enlarged prostate? :)

Seriously, I can pull up the plunger farther than the linkage allows it to go when I stomp the pedal, maybe I can adjust the 'throw'? Right now, I must continuously stomp the pedal over and over while cranking before it'll start, which is at least better than before.

       
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Klaus44


Redlining
Posts: 365
posted February 08, 2008 04:05 PM
Edited By: Klaus44 on 8 Feb 2008 16:09

RE: Adjustable 'throw', etc.:

(Apparently only) *some* versions of the Hitachi had/have accel. pump linkage 'arms' featuring a choice of three hole positions, equating to three different 'throw' lengths of the accel. pump. -- on these models, I believe the middle position would have been the 'normal', stock spec. ...

If the squirt/spray is more of a dribble... how thoroughly did how much B-12 chemtool make it through all those passages/orifices, and what about about the function of your idle circuits, for that matter?

*Any* seepage of fuel from the float bowls, anywhere? How does it sound (and for how long) when you go to the first click on the key, and listen for your fuel pump working to build pressure, after it's sat overnight?

Cold starts involve much more than just the volume your accelerator pump put out per squirt. How 'dialed' is your choke's operation, as well as adjustment? Retaining any carb. 'pre heating' warmup conventions? How *superb* is your ignition electrical? Enough juice to crank relatively *fast*?

(Beware the aging (and possibly failing) ignition switch; had a truck that could be cranked, or run -- but the 'in between' those two positions developing in the switch made it damn near impossible to fire up.)

If everything else is basically OK, but your choke no longer functions in the factory stock manner (i.e., manual setting and auto release), you may want to manually wedge the choke (knob in cab) at certain functional positions via the use of a folded-up matchbook cover, or cutting a little piece of the plastic from an old credit card to suit... (I know, it's "ghetto", but it's a trick that can be useful!)

Consider also that you may simply need to revise your 'standard' starting procedure from whatever 'used to' be required. (Provided, of course, that all else is basically OK, and *especially* that there are NO hidden vacuum leaks, or fuel delivery/cleanliness issues!)

       
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mwpayne


Hauling
Posts: 195
posted February 08, 2008 04:37 PM
Edited By: mwpayne on 8 Feb 2008 16:49

Good advise, Mr. Klaus!

I can guarantee all the ports, holes, tubes are clean as a whistle, so I'm comfy with that. Actually, I wasn't clear..if there's gas or starter fluid in the carb, it fires on just about the 2nd revolution, then smooth as can be. Just getting that initial fire to happen is the deal. Until the accel pump replacement, it wouldn't even TRY to fire..cranks all day long. One squirt of cleaner/fluid/WD40, it would immediately hit and run fine. Started fine after that, unless the truck sat for 2 hours or more. Then, no workee until primed again. Also, 85 RX-7 dizzy in with new mazda cap and new coils, plugs.
Looking again though, there's sho' nuff two holes on the linkage, it was set on the last/lower hole. I set it in the 2nd one, seems to give it deeper throw.
I'll try it tomorrow and see. The mazda parts guy wants to see what all those yellow-bagged parts are going into.
He's always gone above and beyond for me, as I'm the only one that is always needing RX-7/REPU stuff. Gives me 15% off to boot!
One another note, picked up the vent rubber today, looks like a perfect fit. It's amazing how much softer and more pliable new stuff is, I thought my old ones were fairly decent.

       
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mwpayne


Hauling
Posts: 195
posted February 08, 2008 04:44 PM
Edited By: mwpayne on 8 Feb 2008 16:48

Oh one other thing about the choke..the choke switch never, ever releases. Gotta push it in even when warm. it's not sticking per se, I unplug it and it releases, so something ain't shuttin' off the 'lectric.
Not a huge issue, but I need to fix it anyway.

Also, you know the accel pump 'boot' that doesn't come with the kit? I have a wide assortment of those rubber grommets..the ones we use for running wires thru firewalls and such. There's one size that sits over that pump shaft perfectly. Snaps right into place, gives just enough clearance for the shaft to work..I swear it looks like it is SUPPOSED to be there!
I love it when stuff works out..:)

Oh, (sorry this is getting so long!) regarding the fuel pump..should it 'hold' pressure when sitting? I tend to just let the pump run a few seconds when it's been sitting a while, it seems to need to build up, because there's very little fuel in the clear filter.

       
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sparky


Redlining
Posts: 299
posted February 08, 2008 05:22 PM

Hope this is helpful.....
I have always had starting issues.
#1 Spark plugs were grounding out due to small coolant leak into rotor housings. Solution: Treat cooling system with block sealer. Engine started better, but still wasn't right.
#2. Found problem with ignition switch cutting off electrical power to coil with key in start position. I used a voltmeter and verified loss at coil positive with starter enegaged. Solution: Installed toggle switch for starter trigger. Worked fine for about 6 mos.
#3 Stuck accelerator pump check valve. Had to vigorously pump pedel to get truck to start. Noticed same dribble out accelerator pump nozzles that you noticed. Solution: Pulled of top of carb and accessed accel pump and check valve. Removed check ball and cleaned on fine grit sand paper. Noticed corrossion in check ball seat. Used appropriate sized index drill bit to clean up hole/ball seat. Never started better.
ALSO: have modified ignition with DLDFIS. Best mod as of yet along with Torsen upgrade.
Hope this helps.

BTW If the distributer you have is from and 85 GSL-SE I think it comes stock with an extra 5 degrees of mechanical advance.
Good Luck.

       
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Klaus44


Redlining
Posts: 365
posted February 08, 2008 05:38 PM

'Holding' pressure while sitting, no -- I was just trying to get to the bottom of possible contributing factors, making sure we gave the pump, etc., due consideration--.

Sounds like you're onto something about the check valve there, Sparky! I was tempted to comment about it myself, but I've never had to/considered trying to use sandpaper, etc. to clean it...

For chokes that won't releaase, I seem to recall there's a fuse involved that's in there up under the dash (?) ... sometimes, cleaning electrical connections with el. contact cleaner, etc. is all it takes...

Good to be *certain*, too, about the timing and advance, for sure!

       
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mwpayne


Hauling
Posts: 195
posted February 08, 2008 06:52 PM
Edited By: mwpayne on 8 Feb 2008 18:54

Check valve? Never even noticed there was one there...totally missed it! The kit came with a couple extra ball bearing things, one of which is a blue plastic one. One of those must go there, I'd bet my little fat beagle on it...is that check under the plunger 'bottom out' area?
Guess I'll be taking the ol' carb apart again. All good, though, I'm learning alot, so thanks Klaus and sparky!

       
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Klaus44


Redlining
Posts: 365
posted February 08, 2008 07:23 PM

Yes, under the plunger...

...is the check valve where the little ball goes.

       
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