Hello all trying to fine tune by 1980 242 b21 kjet here. I started working on it a few months ago. Replaced entire cooling system., exhaust, intake, valve cover and throttle body gasket. Cleaned injectors. Washed everything in solevent. New injector seals. New. Coolant sensor alternator, oil pressure sender, engine wiring harness, engine mounts, tranny mount, carrier bearing, you name it, it's. Been replaced. Oneproblem though, now it wont start worth a ****, suspected flooding and has a high yet erractic idle while in neutral / on the clutch. Drives great once it starts. Sometimes I can crank her and crank her with no success other times she fires right up. Idle steady at 1500-2000 rpms. I can adjust the knob on the throttle body, and correct the idle but after revving it bogs downnand wont restart so I have to open the valve up again to get a chance at a restart. Ive got a lot of time and money in this project and I'm going crazy with this little problem!! I'm not thinking head gasket or fuel pump cause it has plenty of power through all gears and compression is 155-170 accross all cylinders....

Does the frequency valve buzz during cranking and running every time you operate the car?

Phil

Frequency valve? I'm not familiar I guess. A little more description, in the morning it sometimes starts even if it is difficult to start, but will idle high. I adjust the knob on throttle and get idle squared away. Later that after noon I start it again. It is more difficult to start but idle is so low it dies and knob on throttle has to be relieved. Also, after I tore it apart and replacedneverything operating temp is higher than it was before, about two thirds on the temp sensor. It also fired right up before I replacedneverything and had a rough but steady idle. I looked today though and after just a couple hundred miles on the new exhaust from header on there is black soot in tail pipe. A lot. I really think its running really rich and flooding. I don't know though. Any other ideas or some clarification on that frequency valve?

One other thing to check is the cold start valve. Mine was leaking and it caused a lot of the symptoms you are describing. Not all and not exactly the same but, if it's dripping here and there it will cause the engine to run rich. Just a thought. I'm still learning about the K-jet system as well though so, deff not an expert.

The frequency valve controls mixture as Lucid has said in his reply. Lucid is the man or kingpin when it comes to K-jet knowledge IMO and I was hoping he would catch this thread.

I agree with your thoughts that the compression is to good for the engine to cause the problem. The mechanics of the engine will not vary things as you describe. You have a mixture variation going on.

I would back up and reset the throttle plate to make sure it closes and that the stop screw acts only as a stop screw and does not hold open the plate any at all. Forget the tiny turn that the manual calls for. If the screw wiggles the plate, any at all when setting it, that is enough.
The stop screw is there only to prevent the plate from jamming itself into the bore from excessive spring pressure or a quick movement to shut it especially after the throttle bore becomes smutty or grimy.

The reason I pick on the throttle plate is that it uncovers a port that bleeds air to the vacuum diaphragm that shifts timing. In addition, a switch tells the ECU to idle the engine that is somewhat sensitive to work with the airflow shift.

Another thing to check is the auxiliary air control valve and its vane “open space” adjustment that controls cold idle. On my 78, its starting point has to work in conjunction with the fuel pressure regulator. Those two units have heaters inside them to “mimic” what the engine may be doing while being held beneath the “under the hood” conditions.


As Lucid said the frequency valve follows the 0-2 sensor/ECU commands but the airflow starting points are up to you. Later on, the LH systems with the more expensive AMM and Idle Air Controls do that. Once you get these K-Jets dialed in, it has been my experience; all you have to watch for are bad vacuum hoses that plague all car systems.

Lucid can help you more than I can and the K-Jet.org site has been recommended several times in the past here on the BB.

Just keep filling us in like a doughnut and we will squirt out knowledge somewhere! (:)
Phil

"I really think its running really rich and flooding. I don't know though. Any other ideas or some clarification on that frequency valve?"

Good question by "Machine Man" Phil above. The picture below may not look exactly like your Frequency Valve, but it should be visibly connected to the Fuel Distributor. With engine running the FD should be buzzing, which can be felt and heard. [Make sure the wires are plugged into it.]

It's purpose is to "fine-tune" the mixture, as seen by the O2 sensor. Let us know if it buzzes or not. If not, it might well be your problem.




--
Bruce Young, '93 940-NA (current), 240s (one V8), 140s, 122s, since '63.

Volvo_Problem_Solver_--_Advanced_Edition(1).pdf

cut an paste this link into your browser...you should get a pop up dialoge OPEN or DOWNLOAD

https://files.me.com/dustinl.c/le9rdc

Can you clarify the conditions present when the symptoms occur? Is the problem related to how warm the engine is?

At first glance it sounds like some kind of variable vacuum leak. Have you gone through the typical vacuum leak procedures?