Adjusting Rochester Quadrajet secondary--Update--

[ottawamerc]

I have a Merc 228 85 model. I have posted before about a high speed problem, it acts up as soon as the secondaries open up. Now here's what I'm wondering about--- is it possible that the butterflies are opening to fast and leaning out the motor? I was runnin it in the laneway and was checking for fuel to the secondaries thinking it was a fuel delivery problem, but there was lots of fuel going there,,cancel that one. I happened to notice that the symptoms showed up if I opened too much on the secondary choke plates. There is an adjustment on the tension spring for the butterflies. Is there a test or setting for this spring? I think this might be the problem!<br /><br />Thanks for all the help with this guys <br /><br />-----Whishing I never sold my old boat-----

 

[rbezdon]

Re: Adjusting Rochester Quadrajet secondary--Update--

I have asked the exact question before and there are postings with the answer specifically quoted out of the manual. It a simple seting. Release the tension. turn the spring just enough to touch the choke plate closed and then like 1 turn more, tighten set screw. I have messed extensively with this setting and it did not cure my (exact same) proplem. The 2 Qjet carbs I bought (1 new and 1 rebuilt as I was convinced the problem was the carb) were both set correctly. It is also unlikely the setting changed and I am sure it was correct some time in the past but possible I guess. By the way, the proceedure in the Clymers was exactly the same as someone posted for me from the manual. Do a bit of searching on this site and I am sure you will find it.

 

[rbezdon]

Re: Adjusting Rochester Quadrajet secondary--Update--

Sorry, last year I was using another forum. Here is the link to the adjustment proceedure. Switched to this forum, it is at least 10 times better.<br /><br /> http://sterndrive.com/board/show_subtopic.cfm?ID=4365&TopicID=43

 

[ottawamerc]

Re: Adjusting Rochester Quadrajet secondary--Update--

Thanks vatter for the links and help, very much appreciated!<br /><br />Scott

 

[ottawamerc]

Re: Adjusting Rochester Quadrajet secondary--Update--

I just read the link, there seems to be a common problem here.

 

[rbezdon]

Re: Adjusting Rochester Quadrajet secondary--Update--

Yup, ,told you I have had the EXACT issue you described. I have fixed, for the most part, the bogging. I can now run WOT and get to 4600 RPMs no problem. If you search this site, this year I put in a new cam (I found out the rebuilder put in a cam from a car, not even a truck) and removed the 1/2 inch space from under the carb to a flat gasket. This seals the left and right BBLs of the carb from each other on the Performer Dual Plane intake. These two changes seemed to cure the bogging. I now have a hesitation real bed if I just go from idle to WOT (like when pulling a skier out) enough to stall. If I go to 3/4 throttle and just about plane, then open it up, it will give a slight hesitation and take off like the old 305 never did. I have the rebuilt carbon it and I cant remember what the setting on the rear choke plate is. I may have decreased it trying to get the secondary metering rods up faster to get more fuel to try to cure the old bogging. I thought it interesting as last night I pulled out the other carb to reset rhe choke setting and I was just searching for the proceedure myself to remember the exact turns. That is why I found it on the other site, I needed it myself so you got the benefit too!! I am going to reset this carb and swap them this weekend and see what happens. <br /><br />Made a deal with someone, they are paying for my gas to boat this week end and I am going to pull their kids around a bit on the tube.

 

[ottawamerc]

Re: Adjusting Rochester Quadrajet secondary--Update--

Thanks vatter, I did reset the spring to 1 turn past contact I hope to try it tommorrow. Good luck and have a blast with the kids!! With the price of gas it's good their flipping the bill<br /><br /><br />Scott

 

[rbezdon]

Re: Adjusting Rochester Quadrajet secondary--Update--

OOPS!!!!! Reread the link. My memory was wrong and it is 1/2 turn clockwise after the plate contact point. That is why I posted the link. Never trust the memory of one of us old DIY guys!! Good news is it wont hurt anything if it is wrong, just wont perform right.

 

[Destin]

Re: Adjusting Rochester Quadrajet secondary--Update--

Check out the Q-jet articles on this website. <br /> http://www.corvettefaq.com/engine.asp <br />From the one titled "Quadrajet Problems Lars has seen":<br /><br />Choke pulloff seized or ruptured<br /><br />Results in: Poor cold-run characteristics, flooding when cold, stalling when cold, poor fast idle control, sag or hesitation going into the secondaries.<br /><br />Comments: This is one of the most common maladies on older Q-Jets. When the pulloff fails, not only do you loose proper control over the choke, but you also loose opening rate control over the secondary airvalve. Always check the pulloff by attaching a long piece of vacuum hose to it and sucking on it. The pulloff should smoothly retract, and it should smoothly extend when the suction is released.

 

[rbezdon]

Re: Adjusting Rochester Quadrajet secondary--Update--

Thanks for the link Destin, I printed the recommended reading for later this evening. By the way, my pull off is prefect on both of the carbs I have. Was my first thought.

 

[ottawamerc]

Re: Adjusting Rochester Quadrajet secondary--Update--

I took the boat out this afternoon. After the adjustment it worked sooooo much better. Transition into the secondaries was smooth for the most part except if I pinned it from 2800rpm it would give that kick/lag then it would run up to around 3900rpm. Although it's still not the optimal WOT of 4500rpm it is a HUGE improvement!!!<br />thanks vatter for the help there is light at the end of the tunnel.<br /><br />Scott

 

[rbezdon]

Re: Adjusting Rochester Quadrajet secondary--Update--

Since it wont hit full RPM I am thinking you were running with the 1 full turn and not the 1/2 turn and the plate is not opening all the way fully lifting the secondary metering rods to get full fuel flow. I suggest readjust the carb again and double check the timing advance at 3000 rpm to make sure you're getting the full 30BTDC.

 

[ottawamerc]

Re: Adjusting Rochester Quadrajet secondary--Update--

I did readjust to the 1/2 turn vatter before I took it out. I think I do need to recheck the timing though for full advance. I brought my old inductive light with me to see if the spark was constant which it was. I'm going hunting for a better timing light soon.<br /><br />Scott

 

[rbezdon]

Re: Adjusting Rochester Quadrajet secondary--Update--

Got my advance timing light at Sears for $69, inductive couple. I was using an old one from when I was a kid, over 30 years old but it had an orange flash which was very dim and hard to see. I finally bought a new timing light and torque wrench for my head gasket job. They work well. Nice to have good tool after using the old ones for 30+ years.

 

[Mahoney]

Re: Adjusting Rochester Quadrajet secondary--Update--

I would bring the tools out needed to adjust the spring tension with you on the boat and do some runs with varying tensions.<br /><br />2 People on the boat can really help as well. If it is possible to run with the engine compartment open and the flame arrestor off. (Don't stand over the carb doing this) Have someone monitor how the plates are operating at the varying throttle positions.<br /><br />It is a relatively simple concept. The throttle position dictates the position of the lower throttle plates allowing the carb to generate more low pressure under the airvalves. This is where it gets tricky. There are basically 2 things that happen then, depending on the pressure of the springs in the airvalve, you will need more or less pressure(throttle position to open the airvalves) Since on a Quadrajet, this airvalve position is directly related by a cam to the amount of fuel let into the secondaries, having the right setting will definitely impact your performance.<br /><br />Another setting you might want to try is the hanger hight of the secondary metering rods. Only mess with one setting at a time, or else it gets needlessly frustrating and complicated to tune. Trust me I know from experience.

 

[ottawamerc]

Re: Adjusting Rochester Quadrajet secondary--Update--

Thks Mahoney, <br />My engine doesnt seem to like to run with the flame arrestor off? Makes it run leaner. I didn't realize that the rods could be adjusted, I never saw anywhere to adjust?<br /><br />Scott

 

[rbezdon]

Re: Adjusting Rochester Quadrajet secondary--Update--

ottawa, I think you have to bend the pick up arm that rides on the lift cam to change the metering rod height. I was concerned about doing this as once it is bent there is not going back to square one (exactly).