Got a Q-Jet E4MC on my 86 buick 307 small block. When rebuilding the carb I accidentially screwed out the M/C selenoid plungers adjustment screw without paying any attention to how many turns it took to settle the srew. Now I don't have no measure at which point the plunger is set correctly. Haynes rochester carb manual doesn't really help... Who can give me a hint??? greets Matt
Matt, I have a EMC 4 Q-Jet laying around here, maybe I can check for you ? Just tell me what you want me to do.
Hi! Well, there must be something like a factory set adjustment - don't know if that's the same adjustment to all E4MC carbs. Anyway, if you remove the airhorn you can see the m/c selenoid plunger in the float bowl. It's helt in place by a screw with a D-shaped head. If you could turn this screw clockwise for me counting the number of turns until it gets settled - that might help. I know that there is a special gauging tool to adjust the m/c selenoid plunger hight. But I got no clue how to use it... By the way - thought that the m/c selenoid is controlled by the ecm which reacts on the oxygen sensor's voltage output. If that's the case, why is it so important that the plunger is correctly set? I mean it's a feedback system so if the mixture gets too lean (or rich) due to an incorrectly set plunger the system should be able to compensate for that mistake, shouldnt it? Matt
Matt, Rochester Carburetors, by Doug Roe has several pages devoted to adjusting the MCS. They mention a gauge. I can probably photocopy the pages for you, but if your into working on these carbs, the book is a worthwhile purchase.
If you have noticed, the metering rods are different for this carb; it is stepped rather than tapered. The purpose of these adjustments is to allow the correct adjustment to allow the computer correct ranging. Here's a tip. Using a six cylinder dwell meter, connect the meter between ground and the dwell control. It will either be correct, or make the dwell meter act screwey. If correct, the engine will run well, but, if in closed loop, the dwell will vary, according to the mixture. If lean, the meter will go high, if rich, it will go low. Adjust for about 20 deg in both idle and 3000 rpm mode. I have some 30 years experience with this set up, but it has been a while. I'll check my literature, but I can answer any questions you may have. Note, if any codes are set, the check engine light wioll be on, and the dwell will be fixedx the cause of the light before attempting to adjust the mixture control dwell. Ray
Matt - I have all the tools for adjusting the electronic carbs. I think it was called the Thexton 2500 (on the cover of the case). Got it from Snap-On years ago. Still like new condition (mostly from not being used). ou: I'd take $200 plus shipping.
All, thanks for your numerous replies :Comp: I'm currently on holiday (just gettin out of munich whilst the "beerfest" is helt :beer: ;-) ) As soon as I get back home i'll go into this matter again. Let's see what I can do... so long Matt
