83 Merc 5.7 Rochester Choke Adjustment

[BuzzM]

I have a rochester carb with a "stove" bi-metal spring type choke. The when cold, the front choke plate does not close at all, making starting a matter of pumping 15 times and getting irrated. When it finally dawned on me that I was simply increasing the fuel quantity to offset too much air,I looked at the linkage and decided that the tang on the choke rod for should be in contact with thelainkage that controls the rear plate. That fixed the cold start and it fires up beautifully & idles nicely. BUT..now when the engine is warmed, that front plate does not open more than about 1/2 inch,resulting in very hard warm starts and a rich running engine ( boggy, reduced WOT r.p.m.s, smelly, etc ). When I clicked the tang back ( towwards ther rear) and it is basically not touching anything, the front plate is wide open and it runs great ( again, when warmed up ).<br />1. How do I adjust this evil thing?<br />2. Is it possible to convert this to an electric choke wihout replaceing the carb?<br />I hope this was not too confusing.

 

[markvictor]

Re: 83 Merc 5.7 Rochester Choke Adjustment

Have you replaced the bi-metal spring...they can lose temper over time... also make sore the rod from the spring is not contacting the spring housing..

 

[Bondo]

Re: 83 Merc 5.7 Rochester Choke Adjustment

I looked at the linkage and decided that the tang on the choke rod for should be in contact with thelainkage that controls the rear plate.

I Could be Wrong,....... I Don't Do Rottenchesters.........<br /><br />But,.......<br />I'm pretty certain that the Rear Plate,.. <br />Isn't,+ has Nothing to do with the Choke,.....<br /><br />That's the Secondaries,+ They Don't Do Anything till you kick it in the butt.....

 

[Fishermark]

Re: 83 Merc 5.7 Rochester Choke Adjustment

Also make sure the choke plate moves freely. It can get gummed up pretty easily. Spray it down good with some carb cleaner. I believe there should also be an adjustment on the side of the carb - turn the "dial" one way or another as needed.

 

[markvictor]

Re: 83 Merc 5.7 Rochester Choke Adjustment

The "dial" is the outer half of an electric choke body... his is mechanical...And the choke DOES interface with the secondary linkage on many 4mv quadrajets, it prevents the secondary air valve from opening during cold starts...Here's a link to the quadrajet service manual..it will help you set up your choke properly...<br /> http://www.google.com/url?sa=t&ct=r..._mOKqHGoAKFrbGgCA&sig2=HsgEXWCGmCByUST5L9LFYg

 

[BuzzM]

Re: 83 Merc 5.7 Rochester Choke Adjustment

This is very helpful, especially the link to tocmp. I do better with pictures. I will try to locate a new choke spring. This one is pretty rough looking and the coil housing is missing. The base & mounting screws are almost rusted away. It seems to have lost tension, as mentioned. I used a bit of wire to hold it closed until warm, then removed it.. ran like a banshee. But, restarting was tricky. Thanks for the info. I'll tackle this while I change the manifolds & risers.

 

[markvictor]

Re: 83 Merc 5.7 Rochester Choke Adjustment

Well,<br />now you've given the right info...That choke will not work without the housing intact, there is too much convection without it...

 

[BuzzM]

Re: 83 Merc 5.7 Rochester Choke Adjustment

I guess the devil is in the details..I never even new there was such a thing as the housing until I saw the picture, since this was gone long before I got the boat. Any idea where I would find a replacement? <br />I may have to rig some sort of manual choke cable like some older cars I've owned.<br />Thanks for the continuing help.

 

[Silvertip]

Re: 83 Merc 5.7 Rochester Choke Adjustment

Just a point of clarification, the back "choke" plate you mention is not a choke plate. It's the secondary air valve. It opens only under high load demands. Low pressure beneath it, and high pressure above it -- hence "air valve secondary". That plate cannot open until the choke is fully open. When you get the choke housing, bi-metal coil, and cover plate as well as all other missing hardware installed, adjust the choke as follows:<br /><br />1) Cold engine. 2) throttle part way open to allow choke to "set", 3) rotate choke cover until it carries the choke plate closed. Rotate no further than to the just closed position. Tighten the cover screws.<br /><br />The choke plate should stand vertically after full warm up. No amount of adjustment will help unless all parts are in place and the choke housing is being heated properly and the pull-off is working. Do choke adjustments on a stone cold engine. After engine start up, the choke pull-off should pop the plate open about 1/8 inch or so. If that doesn't happen, the pull-off is binding or inoperative.