Viterbo Posted March 3, 2016 Report Share Posted March 3, 2016 I'm having a carburettor issue that is unusal as hell. WIth a 3K carb from a KE20 the engine works well but it can't idle (it stalls)) unless chocke is pulled so it makes 2500rpms. With a 4K carb (original one) it idles perfectly, doesn't stall but shakes a lot and one cilinder isn't working. The 4K carb worked for a year with no stress until it started to give problems. The 3K carb worked well (the engine never worked so well, very smooth idle) for about 1 week. So, one carb idles but isn't working properly, the other one can't idle but works. What the hell is going on here? Quote Link to comment Share on other sites More sharing options...
Banjo Posted March 3, 2016 Report Share Posted March 3, 2016 Possible air leak somewhere on the inlet manifold ? Second stage, take 4K carby & dismantle, & give it a good clean with carby cleaner aerosol. Third stage, give ignition system a complete check overall, & replace anything defective. Forth stage, do a compression test to see how your valves are. One of those scenarios will most likely reveal the cause of your woes. Cheers Banjo 1 Quote Link to comment Share on other sites More sharing options...
altezzaclub Posted March 3, 2016 Report Share Posted March 3, 2016 Probably the idle jet is blocked, or a blockage anywhere in the idle circuit. As Banjo says, pull it off and clean the whole carb thoroughly. I use a small syringe without a needle on to hose petrol through alll the drillings and passages. 1 Quote Link to comment Share on other sites More sharing options...
Viterbo Posted March 3, 2016 Author Report Share Posted March 3, 2016 Above 12 bar in all cylinders. Rotor, cap, points and condenser are new. No problems with the wires. Quote Link to comment Share on other sites More sharing options...
rebuilder86 Posted March 4, 2016 Report Share Posted March 4, 2016 Viterbo; after countless rebuilds of this type of carb, and witnessing every problem it can give, I consider myself the utmost expert with this particular carb now. Can you show me a picture of your carb, there are a few different types, I want to know exactly which one you have before I start analysing. Does it get any better when the car is hot? If so it most likely a fuel atomisation problem. Fuel atomises better when the intake is hot, so large droplets of fuel don't burn when the car is cold. An excessively rich mixture can cause this, but its most likely caused by a vacuum leak elsewhere which results in the user upping the idle speed and mixture screws to compensate. Again, this makes the droplets bigger and exaggerates the problem. First thing to do, is disconnect the choke to throttle connector so you can isolate the choke and see if it will idle with the choke engaged, without the corresponding overkill of 2500 RPM from the throttle actuator. This will test if there is really a blockage in the idle circuit by forcing vacuum into it to suck more fuel. If it does idle better in this setup, you cal ALMOST eliminate a downstream vacuum leak. and suspect a partial blockage of the idle fuel circuit. Areas in the idle circuit which are prone to issues: Idle circuit above solenoid but after idle (slow) jet. Some of these carbs had a bolt in place of the fuel cut solenoid, take this bolt out or the solenoid if equipped, take the fuel bowl cover off and locate the little brass tube close to the accelerator pump bore. Undo the mixture screw completely and heavily spray carb cleaner or degreaser into the idle screw hole and check that it bubbles out of the 'fuel solenoid or bolt hole' or the little brass tube. If not, its likely that there is a blockage, Its easier for the pressure to exit out the top of the carb than out through the idle port, making this is a good way to backflush the idle circuit. The bolt or the solenoid itself are also good places for crummy deposits to settle and make a new home, they sit in very tight spaces. Float level. The float level on these carbs are so incredibly touchy. On mine, if it is out by 1mm fuel level either way, the damn thing wont idle properly. To set it, have the car on perfect level ground, run the engine for a second of 2 at as low an RPM as possible, then cut it by leaving the shifter in 4th and letting the clutch stall the engine, to ensure the float is as full as it wants to be. If you just turn off with the key, you might pull a bit of fuel through as the engine winds down. You want it to stop very suddenly. Undo the fuel supply line to the carb first before undoing the fuel bowl cover and let all the fuel drip off the float into the bowl, and check the level. It should be sitting at exactly the line of the step on the secondary venturi side of the carb, the big step which is about 1.5 by 1 cm. If it is not at this level, make it at this level by adjusting the float tab with trial and error. You don't need to do up all the screws on the cover to do this trial and error adjustment. just 3. Jet The slow jet as Toyota call it (also refereed to as idle jet) , is incredibly small, one piece of gummy deposits or carbon or anything, will completely block it. And finally, and very unlikely, the power piston vacuum bleed. One more thing to check is the vacuum bleed hole for the power piston. This is a small hole in the fuel bowl cover which vents the vacuum which gets past the power piston, to stop the vacuum reaching the fuel bowl and altering the characteristics of the idle circuit. If this hole is blocked, plus the 2 vent tubes leaning out over the venturis, it will cause the fuel bowl to de pressurise, mostly at idle when there is high vacuum acting on it through the leaking power piston. All power pistons leak, it is this little vent hole which stops the leak reaching the fuel bowl. Start there and leme know how you go. 1 Quote Link to comment Share on other sites More sharing options...
Viterbo Posted March 4, 2016 Author Report Share Posted March 4, 2016 The carb that is giving a cylinder fault (but idles) is a EU 4K one with the crappy emission lines: The one with which the cylinders work fine but doesn't idle is the simple KE20 3K one: Quote Link to comment Share on other sites More sharing options...
parrot Posted March 4, 2016 Report Share Posted March 4, 2016 Get it rebuilt! Quote Link to comment Share on other sites More sharing options...
Viterbo Posted March 4, 2016 Author Report Share Posted March 4, 2016 That's what I'll probably do! A few questions: how can a carb malfunction affect one single cylinder? Can 4K carb vacuum valves get damaged? Can they be rebuilt? Quote Link to comment Share on other sites More sharing options...
rebuilder86 Posted March 5, 2016 Report Share Posted March 5, 2016 id say your single cylinder malfunction is probably one of the cylinders where there is a vacuum line going to its intake tube. At high power there is a lot of flow (not vacuum) and a stuffed vacuum system can just throw air in through the vacuum line and blow the mixture up against the plenum wall, causing the mixture to loose its latent heat and turn into liquid fuel and air, rather than a combustible gas. Just go with the 3k carb, so simple, and follow my steps to fix the idle problem. I assure you I can get that 3k one idling perfect. Nice golf tees!! 1 Quote Link to comment Share on other sites More sharing options...
rebuilder86 Posted March 5, 2016 Report Share Posted March 5, 2016 How do i know about this issue? When i was working at a helicopter flight training school a couple of years back, i always wanted to know everything that was going on with the motors and I would constantly nag the mechanics to show me everything that was happening. We had a robinson R44 carby'd helicopter which on run-up (pre takeoff check) had a missfire when we selected either one of the 2 spark plugs in each cylinder for ignition. It turn out to be this exact issue, made worse by a weaker spark. Mechanic had to send the carburettor off to lycoming who discovered a simple crack in one of the vacuum lines. Quote Link to comment Share on other sites More sharing options...
Viterbo Posted March 5, 2016 Author Report Share Posted March 5, 2016 Great stuff there rebuilder86, thank you! Do you think a 3K carb is ok for a 5K? Quote Link to comment Share on other sites More sharing options...
rebuilder86 Posted March 5, 2016 Report Share Posted March 5, 2016 No, not for idle but it is ok for power so long as you arent looking for the most powerful 5k. I don't think you are judging on the state of your engine bay :P With relation to the idle issue, see my latest post ( for a fix for such a situation. It involves an angle grinder and lots of confidence. The 5k has more space to fill; an extra 300cc and therefore needs more fuel at idle, the 3k carb idle jet isn't big enough for the 4k let alone the 5k. It should say 4 - 5 on the slow jet sub assembly, meaning 0.45 mm diameter orifice. If you are not brave enough to take to your idle jet with an angle grinder, I don't blame you. In that case simply try unscrewing the slow jet about 2 turns from tight, this will allow a little bit of fuel to leak through the threads bypassing the jet to test the theory before taking to it with power tools. Ensure the idle speed is set such that the throttle plate is just sitting with a fraction of a mm of the transition slot showing when looking from the bottom of the carb up the throat. Also ensure the mixture is set at about 2 - 2.5 turns out from seat. Speaking of the seat, check the condition of the mixture scree needle, apparently some people ruin them when tuning by tightening them too much before turning it back the 2 turns. 1 Quote Link to comment Share on other sites More sharing options...
Viterbo Posted March 5, 2016 Author Report Share Posted March 5, 2016 Amazingly this 3K carb was able to idle my 5K like an angel, never seen my engine work like that, so smooth, so quiet... This was before it started having problems... Quote Link to comment Share on other sites More sharing options...
rebuilder86 Posted March 5, 2016 Report Share Posted March 5, 2016 Are you sure it was actually idling on the idle circuit, and not just pulling the dribble of fuel it needed through the top main jet over the throttle plate opening??? I think you will find that's how it was running. Take the filter off, and watch it try to idle, if u see fuel coming out the top into the primary venturi at anything less than 800 rpm, its idling on the main circuit. Quote Link to comment Share on other sites More sharing options...
Viterbo Posted March 5, 2016 Author Report Share Posted March 5, 2016 As far as I remember it really was dropping fuel in the shape of bubbles through the jet on top of the carb... I know almost nothing about carbs, I didn't knew that wasn't supposed to happen :hmm: Quote Link to comment Share on other sites More sharing options...
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