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Joined: Sun Sep 17, 2017 4:11 pm
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Vehicle: 1991 Suzuki Sierra

Post Posted: Mon May 28, 2018 4:47 pm 
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Hi all,

Soo wondering if I can get some help. I'm quite new to the forum, yet have still gained a great amount of knowledge. However, as the title suggests i'm having carby problems. Now this is not the stock carby we're talking about. I pulled the stock carby off because it started playing up and wasn't running right. So i replaced it with a brand new toyota 4k carb from ebay.
One of these bad boys:
https://www.ebay.com.au/itm/Carburetor-for-Toyota-4K-Corolla-Starlet-Townace-Liteace-Sprinter-Carb-Carby-New/272925739762?fits=Make%3AToyota&epid=16011139102&hash=item3f8ba44af2:g:sA0AAOSwPpZaBXTO

I followed the instructions of one of the members of this forum on how to install the carb, the one by Bammo

http://auszookers.com/forum/viewtopic.php?f=5&t=54665&hilit=4k+carby+toyota

Now to the problem. I'm sure it lies somewhere within the carby but i don't know where to start. After i put the carby on, i took it for a test drive to see how much better it would be compared to the stock one. I found that I it would continously surge (or stall not sure) when i was at WOT at around 4000-5000 rpm. I was also only getting around 200 km from a tank (which works out to be about 19-20 L/100 km). So i bought a vacuum gauge to try and tune it, but the surging/stalling problem still exists and my economy is still only around 260-270 km to a tank when i was getting 350 km with the old carby. I've checked timing and changed spark plugs just to be sure and still hasn't changed. It also backfires once you've let of the accelerator

Interestingly when i take the stock carby hat off, and drive without it, it drives fine with no surging/stalling. Does this mean that the air/fuel ratio is wrong? do i need to change the jets? or do i need to fine tune it some more?
If it helps, i installed extractors with a full 2 inch exhaust system, retaining the stock Cat converter and a less restrictive muffler.
Any advice would be appreciated.

Thanks for reading.

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Joined: Sat Mar 31, 2007 12:00 am
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Post Posted: Mon May 28, 2018 9:50 pm 
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Theres a lot of things that could be wrong and its almost impossible to diagnose the problem over the internet but...
I have seen the problem where the carb hat has been pressing on the accelerator plunger before causing similar probs. Would make sense if it dissapears when hat removed.
Regards to jetting and fuel consumption its really a matter for a dyno run or a gas analyser. It will tell you if its stoich or not in various rev ranges and will give you an idea if jetting needs changing.
To be honest it would of been cheaper to get the stock carb sorted in the first place it was designed for that car and that engine.

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Joined: Sat Feb 04, 2012 7:41 pm
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Location: Oberon, NSW
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Post Posted: Tue May 29, 2018 6:48 pm 
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FWIW, I put a 4k carb on my brothers sierra and had the same WOT issue. Pulled the high speed jet to find out its size, 155. Swapped the high speed jet from the stock aisin carb and the issue disappeared (110 jet)

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Post Posted: Tue May 29, 2018 11:44 pm 
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Pretty sure the stock secondary jet is a 104.

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Joined: Wed Jun 10, 2009 12:00 am
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Location: Sydney -ish
Vehicle: 92 Suzuki Sierra

Post Posted: Tue Jun 05, 2018 5:42 pm 
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105 :)

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Joined: Sun Sep 17, 2017 4:11 pm
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Vehicle: 1991 Suzuki Sierra

Post Posted: Sat Jun 09, 2018 11:42 am 
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Thanks Blkfxx,

After reading your reply i took apart the 4k carby and removed the 155 jet. I also took apart the two stock sierra carbs i have, one from an 1996 g13ba with an autochoke and one from a 1991 g13ba with a manual choke. I couldn't get the secondary jet out of the manual choke carb so i put the one from the autochoke. It was a 141 size. After putting it in i took the car away over the long weekend and managed to drive 350 km off one tank, with no WOT issue anymore.

One thing down one to go :D

So now the only problem i have is that it idles really weird. It won't idle when cold (most likely cause i don't have the manual choke hooked up and don't use it) but when it's warm it will idle at 1500 rpm, then randomly drop down to idle at about 800-900. The reason i say 800-900 is because it fluctuates. I thought it might be a vacuum leak but i've changed the vacuum hoses and it hasn't changed. Could this be something relating to the idle solenoid or whatever it's called?

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Location: Sydney -ish
Vehicle: 92 Suzuki Sierra

Post Posted: Sun Jun 10, 2018 9:16 am 
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I had 141 in stock engine for while based on a carb taken from a 90's swift into my stock aisin. Friends reported gouts of black smoke when underload. dropped down to 120 no smoke. Since/ dropped it to 115 as i can't feel the power difference but hoping better economy. One thing i noted about the 4k carbs is they have even sized primary /secondary throats (30mm or 32? from memory) where as the aisin carb i am remembering correctly 28/32 or possibly 30/34. Whatever it was i remember that it sits inbetween the aisin carb and the aisin carb is significantly smaller than the weber.

Point being jet sizes may not be optimal. as for the erractic idle check your spark plugs and be sureall t/he ignition components are up to scratch.
Also a can of Nulon f/oaming intake cleaner through valves and cylinders may clean up yourr gunk. Do an oil change within 3 days.

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Post Posted: Sun Jun 10, 2018 10:18 am 
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FWIW there's a couple of different 4K carbs.

The KE70 ones are 28/32 (from memory) and very similar to the Sierra carb.

The eBay 4K ones are 28/28 and have a number of differences but are the same fitment.

Standard Sierra is 26/30.

My weber has a similar sort of idle problem, it's because the throttle return spring isn't strong enough. Grab a can of fly spray of whatever and spray it around with it idling, the revs will drop if there's a vacuum leak. :)

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Vehicle: Holden Drover '85 NT 1,3

Post Posted: Fri Jun 15, 2018 2:03 am 
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sideways wrote:
...it's because the throttle return spring isn't strong enough....


THIS!

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Joined: Sun Sep 17, 2017 4:11 pm
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Vehicle: 1991 Suzuki Sierra

Post Posted: Fri Jun 15, 2018 9:26 am 
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Well, I've already put another throttle return spring that is strong enough to pull it back so i don't think this is causing the issue.

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Joined: Fri Mar 01, 2019 3:44 pm
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Location: Townsville
Vehicle: 1992 Sierra sj70 Tin Top

Post Posted: Fri Apr 12, 2019 9:42 am 
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Ethanv wrote:
Well, I've already put another throttle return spring that is strong enough to pull it back so i don't think this is causing the issue.


i had the odd idle like yours mine was just the idle screw not being backed out enough lol

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Joined: Wed Apr 11, 2018 7:20 pm
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Post Posted: Sun Apr 14, 2019 8:29 am 
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just fixed my idle and it was a blocked idle jet . its the one with tiny holes around the circumference and you can get to it w.out stripping the carb . at least in the f10 aisin

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