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Index > Engine/Drivetrain > Thread: Cold start issue
Thread: Cold start issue
mwpayne


Hauling
Posts: 195
posted June 10, 2007 07:43 PM

Cold start issue

Kind of suddenly, the beast is hard to start after it sits a few days. Cranks, but no fire at all. Fuel is flowing through the fuel filter (new), so no problem there. One squirt of carb cleaner down the throat and it fires up just fine. Warm starts ok too.
I'm not real sharp on carbs, but my neighbor is, and said it sounds like an accelerator pump.
My question is, do you have to pull the carb to get to that do-hickey? Is it a part I can find locally?

Or should I plan on pulling and rebuilding a carb that seems fine otherwise? My 'if it works, leave it the hell alone' alarm is going off in my head..:)

       
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Klaus44


Redlining
Posts: 365
posted June 11, 2007 11:52 AM

Could be a lot of things...:

I'd double-check the operation of the choke, first off. Then, I'd look for fuel/vacuum leaks, everywhere from carb thru intake manifolf... What about the operation of your fuel pump, and detritus-free flow from pickup tube thru to carb inlet?

Yes, you have to open up your carb. to get to the accellerator pump; the bits you'd want/need to replace come with a carb. rebuild kit.

Of course, what are the odds it's a (minor?) electrical/ignition issue -- and not fuel at all? How perfectly was/is it timed? How corroded/worn are your contacts in the cap/rotor? What about all the other crucial electrical contacts? (they all corrode/get iffy over time.)
Simply a 'worsening' ground can influence matters... as can an ignition switch that may be on it's way out: what can happen there, is that a 'position' develops *in between* cranking, and firing... (a *royal* pain!) Does it fire right up if you let off the key, "just a little" ?

Some ideas, anyway...

       
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mwpayne


Hauling
Posts: 195
posted June 11, 2007 12:51 PM

Thanks Klaus

Electrical wise, I THINK I'm ok. All new plugs, wires, dizzy cap/rotor. It used to fire right up when cold. Ignition switch doesn't seem to matter. Fires up immediately whn carb cleaner is applied.
Looks like I'm about to learn how to rebuild a carb. Where to get kits for these hitachis?

       
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repumax


Redlining
Posts: 427
posted June 11, 2007 02:44 PM

I've seen rebuild kits on ebay. That would be my first try.
____________
1974 Mazda Repu
1986 Yamaha RZ 500
1988 Yamaha YSR 50
1991 Suzuki RGV 250
1992 Yamaha TZR 250 SP
1996 Aprilia RS 250
2003 Ford F-450 6.0 Diesel
2004 Mazda RX8
2006 Yamaha Banshee
2014 18' Eclipse Toy Hauler

       
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sparky


Redlining
Posts: 299
posted June 11, 2007 08:57 PM

Checking operation of accelerator pump is fairly easy. Turn on ignition key so fuel pump turns on and bowls in carb fill. Remove air cleaner. Use a flash light to look down the carb. No matches or lighters if you value your eyebrows. This is a good time to see if float needle valves are seated, no fuel spilling into carb. In between the primary throats you'll notice a large brass flat head screw with 2 small tubes to the side pointing down into the throats. Shine the flashlight there while you rotate the throttle cable cam opening the butterfly valves of the primaries. If the accel pump is working ther will be 2 small streams of gas shooting out both tubes into the primaries. If you don't...more than likely the ball check valve is stuck at the bottom of the carb. These carbs are pretty easy to work on. Good luck.

       
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Klaus44


Redlining
Posts: 365
posted June 12, 2007 09:31 AM

Yep...

Just realize that any kit you get'll likely contain one or more hardened, brittle, (if not broken...) gaskets -- (save everything you can for possible re-use!)

The same year's rx-4 kit is likely still more readily found, and is basically identical.

I'm sure you'll find just as much crud/varnish, etc. in your carb as it's been years since it's last rebuild... don't forget to handle those two little cylindrical screens inside the top (inlets) with care! A rebuild is also your perfect opportunity to solder up the 'vacuum bleed jet' that controls the amount of vacuum to your secondary diaphragm, *if* those haven't been popping open as desired. If need be, the spring behind that diaphragm can also be shortened *a bit* to make up for the hardening of age...

Just don't make the mistake I once did: Don't try too hard to remove a seriously stuck part like the inlet fitting itself -- I bent a carb top that way once... <embarrassed>

       
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mwpayne


Hauling
Posts: 195
posted June 12, 2007 08:00 PM
Edited By: mwpayne on 12 Jun 2007 20:03

I think you nailed it, Klaus

I took off the inlet assembly and blew it out with air, then noticed a cracked vaccuum line. It's a funny setup, there's a small line coming out of a mushroom valve-looking thingy, this hose attaches to a hollow plastic elbow. The other end of the plastic elbow has another small black vac hose. This goes to ANOTHER hollow plastic elbow, then another 1/2" of black hose, then to a port on the carb. All these little pieces of hoses were cracked.

I took all this off and attached one 6" vaccuum hose. Fired right up. I think that's got it, I'll know for sure after it sits a few days.

       
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Jeff20B


Moderator
Posts: 661
posted June 12, 2007 10:44 PM

My very first rebuild was a '74 Hitachi. The secondary throttle valves were rusted to the throttle body. I freed them up. I also replaced the two rubber hoses but kept the nylon tube. I felt it looked more professional than replacing with a single rubber hose. I was right. The carb looked pretty sharp. I was proud of myself. Oh, and it ran freaking flawlessly. Must have had low miles.
____________
'74 REPU
'76 Cosmo
'77 MG Midget 13B
'81 RX-7

       
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Klaus44


Redlining
Posts: 365
posted June 13, 2007 08:00 AM

Nice!

Eliminating 'failure points' --especially with all of the used/unused vacuum hoses/ports/fittings-- is essential...

       
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mwpayne


Hauling
Posts: 195
posted June 13, 2007 04:56 PM

Agreed. Although there are a couple of ports open and seem to have no vac to them at all (emissions stuff??), I still cap 'em.
Those plastic elbows do look kinda good, but there is at least four points of potential leaks using them with short pieces of vac hose.
And..there must have been a leak, 'cause this thing wouldn't idle AT ALL after warmup since I 'fixed' it...
Had to readjust idle from having adjusted to compensate for the leak that I didn't know was there.

Also, and unrelated, the truck is at the upholstery guy right now getting carpet and a headliner.

My father's day present!!

       
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Klaus44


Redlining
Posts: 365
posted June 13, 2007 06:21 PM

Most excellent!

You're a lucky man.

       
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