How to adjust the K-151 carburetor

Adjusting the carburetor K-151 on their own hands

When experienced motorists casually drop the phrase “used to be extremely reliable technique”, they are in a sense right. Really, is it worth comparing the level of complexity of a modern car and its analog 50-60 years ago? And if the product is simple, then it is more reliable by definition. The owners of cars of the latest generations would probably agree with this: while major breakdowns at the initial stage of operation are very rare, it is only necessary to cope with minor faults.

In this aspect, products of the Leningrad carburetor plant can be considered legendary, and its flagship is rightly recognized as a carburetor K-151, better known under the alias Pekar. Its reliability is legendary, and it is not by chance that it is used on vehicles with power units ZMZ and UZAM, particularly on the famous domestic off-road vehicle UAZ. But, as it is known, this device demonstrates the greatest efficiency at correct settings. Today we will tell you how to achieve it.

Functions and structure of the carburetor

In modern engines, an electronic system, working in tandem with the injector, is responsible for the preparation of fuel oil. The predecessor of this scheme is the carburetor, which is able to prepare a quality combustible mixture without any participation of electronic brains. And since the proportions of the mixture change depending on the mode of the engine, the carburetor should be able to prepare the optimal composition at any load, from idle to maximum revolutions of the crankshaft. And, it must be said, it copes well with this task. Even today, K-151 can be found on such domestic cars as “Gazelle” with all its modifications, IZH, “Volga”, and, of course, UAZ.

Although the range of brands Pekar has a lot of models, “one hundred and fifty-first” was given an honorable place, and there are many modifications of the carburetor, different in the name of the letter after the numerical designation of the model. In particular, the cars GAZ-3302 (or simply “Gazelle”), as well as GAZ-3102 (“Volga”) are equipped with a modified carburetor K-151C. The differences between modifications consist in jets of different diameters, calculated for the preparation of fuel for specific power units.

The composition of the carburetor Pekar-151:

• body with a float chamber;
• secondary upper body with throttle valves, which are controlled by a drive cable connected to the accelerator pedal;
• PC cover, which serves as a platform for installation of the locking mechanism preventing overfilling of the chamber with combustible. This is also where the air damper is located, which is used when starting and warming up a cold engine;
• The metering system, which is responsible for the formation of the fuel-air mixture and includes channels of a certain diameter, two air jets and the same number of fuel jets;
• The idling subsystem, which is used when the power unit operates in the idle mode. It includes a bypass channel, one fuel and one air nozzle each, fuel mixture quantity/quality adjustment screws, and a diaphragm-type economizer valve;
• Gas pedal pump, responsible for a uniform engine dynamics, without slack in the case of sudden revolutions increase. It includes additional channels in the body with the float chamber, diaphragm device, ball valve and petrol atomizer;
• Econostat – a part that enriches the mixture when the engine operates at higher revs. It includes a system of additional channels designed to supply the intake manifold with an unscheduled portion of fuel when the throttle valves are fully open;
• Transient system, which is engaged at the initial stage of opening of the intake throttle, located in the secondary chamber, and serves for a smooth increase in RPM. It includes a pair of jets of both types.

Thus, K-151 belongs to the category of two-chamber carburetors, in which the choke open sequentially. In the inlet fitting integrated strainer. It also has a fuel line, designed to drain the excess gasoline back into the tank and to protect against excessive pressure in the chamber. As you can see this device is not very simple, that’s why its adjustment requires a lot of experience.

Connecting the hoses

The complex device of the K-151 also manifests itself when connecting it to the engine. Here provides for the use of a number of hoses, and only two different sizes are used, so that mixing them up is quite possible, with the engine on certain modes will work with failures. Order of connection of hoses to the carburetor:

• fuel supply through the fuel pipe is made to the connector located under the float chamber on the motor side;
• the return hose is put on the bottom connector – it looks in the side opposite to the power unit and is located below the inlet connector;
• two small section hoses are connected to the solenoid valve, the other end of one of them – to the economizer valve;
• the second end of the thin hose is put on the fitting located at the bottom of the K-151 on the back side of the throttle body (there are two next to each other, we will use the lower one);
• on the upper connector of this pair pull the hose that goes to the vacuum ignition timing advance (it is located on the trambler);
• large-diameter fitting on the intake housing is used to connect the crankcase forced ventilation pipe, a device, usually located on the valve cover;
• small-diameter nipple, located in the middle part of the K-151, is used to connect the thermal vacuum switch, but this branch pipe is used only if the engine has an exhaust gas recirculation system. If a particular modification of the engine does not provide such a system, this fitting is simply installed a plug. True, such precaution is unnecessary – there is no air suction through this connection.

In the absence of experience, these connections should be made, referring to the instruction manual for the device.

Idling speed regulation on Pekar

Adjustment of idling on the St. Petersburg carburetor K-151 is of fundamental importance. This is a special mode of engine operation, which requires stable operation. This is exactly what is achieved by correctly adjusting the idling speed, which also helps to minimize the amount of carbon dioxide in the car’s exhaust, which is important in terms of modern environmental requirements.

Over time, as a result of clogging of the filter screen, the amount of fuel combusted in idling mode increases beyond the norm, and in this case, the situation can be corrected by appropriate adjustment.

This operation is not particularly difficult:

• First it is necessary to warm up the CA to the working temperature;
• then it is necessary to find the fuel injection quality screw located on the rotation shank and remove the limiter from it. Note that the rotation limiter function is not present on all Pequart modifications. If your car does not have it – just proceed to the next step;
• adjust the quality screw, which is looking for the position of the screw, in which the power unit will give the maximum number of revolutions during idling. This moment should be determined by ear (more precise methods require the use of special equipment);
• now go to the next next to the quantity screw, by adjusting which should increase the speed of the crankshaft by 100-120 rpm. After that, it is necessary to tighten the quality screw fully, which will lead to a drop in RPM by the same amount (within 100-120 RPM).

If when tightening the quality screw back the revolutions are not reset as a result of a slight mixture depletion, it indicates the carburettor malfunction.

Adjusting the PU of the carburetor K-151

The starting device is a node, which is the source of the signal that informs the starting of the power unit. If the elements of the starting system are faulty, or do not work properly – you will not be able to start the car. But even with a functioning starting mechanism, there may be problems that make starting difficult. For them and their correction and carried out adjustment of the carburetor K-151, and such work can be carried out as a dismantled and working and installed on the engine device.

Adjustment on the dismounted Pekar is carried out in the following order:

• open the choke a little and look for the control lever;
• turn it to its extreme position and fix it with something suitable (rope, wire);
• release the intake choke to the initial position. In this case, the gap between the chamber wall and the flap edge should be within 1.5±0.3 mm;
• unscrew the counternut that blocks rotation of the stop screw located on the flap lever;
• turn the screw in stages, each time by half a turn. At the same time we need to make sure that when you tighten the lock nut the screw is perpendicular to the cam, otherwise PU will not work;
• check the pull rod valley, by means of which the PU cam is connected to the air damper levers. With the PU lever turned to its extreme position and the intake valve completely closed, it is necessary to achieve the gap between the levers within 0.2-0.8 millimeters. If this is not the case, adjustment is carried out by releasing or tightening the rod head, which allows shortening or lengthening the rod itself.

You can adjust the PU of the carburetor K-151 without removing it, and the quality of the adjustment will not be affected.

• Remove the air filter of the car (of course, without removing the box);
• start the engine at idling speed;
• by pressing the accelerator pedal open the choke and pull out the hand wheel – the mechanism responsible for controlling the operation of the air damper;
• by means of a screwdriver with a flat tip open the induction tap, while determining the engine shaft speed (benchmark – 2600±100 revolutions/minute). If the speed is much higher, carry out a similar operation to the one performed on the removed carburetor: unscrew the locknut of the adjustment screw of the lever driving the choke;
• after loosening the locknut, screw in the crankshaft, if it rotates slower than necessary, you screw in the crankshaft;
• tighten the locknut.

After adjusting the starter mechanism, it is necessary to make a running-in of the carburetor.

Important: Before carrying out adjustment work, you should determine and record the fuel consumption during operation at different modes in order to be able to compare with the figures achieved after adjustment.

Setting the fuel level in the float chamber

Incorrectly set the level of gasoline in the PC is an unbalanced operation of the engine. If it is too high, the mixture will be enriched, and one of the most tangible consequences of such a state of affairs will be increased fuel consumption. If the level is less than the norm, the fuel will be depleted, which is even worse for the engine, as it can lead to serious damage, requiring expensive repairs.

Thus, the fuel level in the float is a critical indicator for any carburetor, regardless of brand and model.

To accurately adjust the float in the chamber K-151 we need a ruler and a drill with a diameter of up to 2 mm.

• set the machine on an even horizontal ground (it is important, because we will work with liquid);
• dismantle the air filter housing, located on the power unit;
• start the engine, let it run at idle for about 5-7 minutes;
• unscrew and remove the top cover of the carburetor;
• Measure the float chamber in millimeters of the fuel level. This operation should be done promptly, because gasoline is characterized by a high evaporation rate, especially in the heat, which will contribute to the heating of the engine. Delaying, we risk getting distorted results;
• For K-151, measurements should give about 215 millimeters, which is considered normal for the efficient operation of the engine;
• If the level does not correspond to the normative – we perform the adjustment, which consists in changing the position of the float;
• To do this, we need to use something that allows measuring the position of the float during the adjustment work – the drill suggested at the beginning, or a piece of wire or any similar cylindrical object comes in handy. The main thing is that its diameter should not exceed two millimeters;
• turn the lid K-151 and put it on a flat horizontal surface – only in this position will measurements be accurate;
• measure with a ruler the distance from the carburetor cover (the reference point is a cardboard gasket) to the bottom edge of the float. This distance should not exceed two mm;
• if this is not the case, you should bend the float lever tongue so as to achieve the normal clearance.

The same operation can be done using a caliper, but in this case measure the distance from the cardboard gasket to the top edge of the float. The correct result is 30 millimeters. In case of a mismatch, again bend the tongue of the lever, achieving the required value.

It should be noted that there is a possibility of errors, especially if an inexperienced car owner does it. Therefore, after making adjustments, be sure to check its correctness. This is done as follows:

• Move the lid of the K-151 to the vertical position;
• Observe the tongue, which we bent (or did not touch, if the level was normal);
• if everything is done correctly, the tongue should slightly press and sink the damping ball located on the IR. The lever tongue should be at a level that runs strictly parallel to the needle valve;
• look also at the axle of the float stamping, which should be at a level that coincides with the carburetor cover.

If at least one of these conditions is not met – the procedure of adjusting the fuel level in the PC will have to be repeated. Many drivers limit themselves to two iterations, even if the situation requires otherwise. We still recommend completing the adjustment properly, regardless of the time spent – we will definitely need the experience!

Inspection and tuning of the carburetor K-151

Rode the car this week on business and did not like the fact that the floating idle – then fall to 500, then jump up to 1500, the engine at idle shakes. But at the same time it drives fine, without dips. Checking the ignition “by ear” with the well-known method – full throttle in 4th gear at 60 mph showed that the ignition is correct. So we need to look at the carburetor. And so today on Sunday morning good weather, sunny, decided to look at it. (By the way it is snowing outside now!).

For starters, I looked on the internet for a description of the carburetor, its construction, what connects where. In principle, the K-151 is very similar to the Zhigul “ozone”, it also has an autonomous idle speed system, the ECT economizer with the same control unit (similar in appearance) and the same electromagnetic valve. In general, I figured it out, nothing too complicated.

So I take off the “pot” and see … well, to put it mildly, that the carburetor needs to be removed and cleaned – overgrown with sludge and dirt, but that’s for later. And now, for preventive purposes, we need to replace the fuel hoses, which are all cracked from old age here and try to adjust.

The first thing that surprised me is that there is no vacuum tube on the economizer. Strange, because then the idle should not be at all. Or rather it is there, hangs around and is plugged with a screw inserted in the tube. Oh, that’s it – the former owner decided to simplify the system – he inserted a long stud instead of the throttle stopper plug, screwed two nuts on it and made it an idle speed regulator screw, regulating the degree of the throttle opening with it. This is where I just unscrew it with my hand.

In fact, the idle system wasn’t working at all, and the engine was idling because the throttle was not fully closed. Fan of “Solex” probably was the last owner, but the transition system of this carburetor is not designed to maintain a smooth and stable RPM, so RPM and floating. And the shaking of the engine was because the quality screw was screwed all the way in, but there was no O-ring on it, so the attempts to adjust the engine reacted poorly because of the lack of a rubber ring on the needle quantity. The ECT system was here, but eliminated – there is an electronic valve, but no microswitch on the carburetor. If desired, the system can be restored, but for now let’s assemble and adjust as necessary at least what is there. For the beginning we put a vacuum tube on the economizer (in the photo it is already on, but not the one on the foreground, but below, look closely. The one in the foreground is part of the EGR system, and then….

Went to my nearest parts store. Yes, from spare parts for Volga there is only an air filter, but fuel hoses and rubber ring of quality screw can be put from vintage cars, and clamps are universal. I bought 2 o-rings for the quality needle (one for safety), a long fuel hose, “return” hose from 2108 suits me fine for “return” and Volga, and clamps for them.

For a start I took off all old fuel hoses, took out couplers. Here they are tired:

On the Volga the fuel hose is very serious, not just on clamps, but also on metal fittings, tightened with a wrench “for 14” (hello “Volga”, in the Zhiguli everything was mostly “for 13”, I read somewhere that the fixing “for 13” in the USSR in general came exactly with the Zhiguli, before that there were no such sizes, were somehow managed with the size “for 12” and “for 14”). I tried on the long fuel hose in place and cut it in two parts, put it on the connectors, tightened the clamps and put it.

For a long time I’ve been thinking to keep this authentic “cup” – fine filter or put a regular plastic filter. Then I decided not to break the authenticity – let it be, then I will replace the filtering element, and all right. Then I installed the “return” filter. It’s a good system, the gas pump doesn’t pump “into the wall” but works all the time dumping the extra fuel back into the tank. This eliminates the possibility of gasoline pump overheating and its failure due to vapor lock, which often happened on LPGUs.

Now let’s remove the idle speed regulator with the throttle stop. Instead of this pin I put a screw with a locknut. I tighten the screw so that the throttle stop only a little under the throttle so that the throttle is completely closed by resting against this screw and in this state lock it with a locknut.

Now I put a ring on the quantity screw and screw it to the middle position and start the engine. As soon as the engine is already able to run without “sucking” (i.e. with the air flap completely open), use the quantity screw to set the position at which the engine speed is the highest. Now, on a warmed up engine with the help of the quantity screw I put about 1000 idle RPM (according to the tachometer on the control panel) and decrease them to the 700-800 RPM, tightening the quality screw. The engine should work without interruptions, smoothly. You can turn it to the beginning of these interruptions and unscrew it back a little so that they disappear and after that you can set the correct revolutions with the quantity screw.

The engine is rumbling smoothly at idle, some steam and water is coming from the pipe. In general, those who have seen “live” how a well regulated 402 engine works at idle will understand what a song it is. The impression is that the revs are low at all, the crankshaft sort of barely rotates, but the gauge is right – 700 revs (approximately). That is the tachometer arrow is just below 1000.

Now turn on the headlights, the heater on full and the rear window heating and see how the engine will work under load of the generator and how “will sag” revolutions. If they strongly decrease, then add the amount of rpm with a screw, if the engine also quivered and stopped working, then you can add the quality, not the amount. That is, in general, the whole science.

In spite of the outwardly horrible condition of the carburetor, it was fine-tuned. The engine “whispers” at idle, picks up speeds without slack. In general, it goes, I put the “pot” in its place.

Another thing that was noted in passing – the motor has a new pump, it stands out sharply for its novelty against the background of other parts. It looks like the last owner splurged on it to get from Lipetsk region to Moscow without any problems. The old one seemed to pump very bad, so there is an additional pump in front of the heater tap, the same one I used to install on the omega when I was freezing in it in winter. The truth where it is switched on here I have not found, but the heater heats well and with not working. And there is also a crane there to kick out air stoppers (a part of this business is visible on the photo, where I unscrew the throttle stop). Most likely later I will take out all this “khoz” and replace regular ceramic valve on vintage cars, which I liked on vintage cars and the air temperature in the car can be regulated by the regulator handle, and not only lowering the window.

The radiator inspires respect with its look. When repairing under the hood it is convenient to put screwdrivers on it, the fasteners are different – it won’t fall down anywhere, as the shelf is wide and with ribs. The upper connector looks like soldered, and with cooling hoses in general some kolkhoz – tubes, adapters, clamps, the hoses themselves are already oak, all cracked, one hose is severely overextended in the bend. In general, I will order new hoses and then replace them along with the coolant. The fact that the previous owner only changed the pump and attached such horrible old hoses to it also says that he drove the car for sale.