The Stovebolt Site Forums The Shop Area Engine Shop 51 running rich

Hello all. I recently got my 51 on the road. It sat for many years so I had to rebuild the carb and do the usual new ignition parts, ie. cap, rotar, condenser, plugs wires etc. I put about 100 miles on it last weekend. I noticed that the new exhaust is all carboned up. I pulled the plugs and they are all carboned up too. I adjusted the 1 BBL Rochester B carb according to the manual. Adjusted the timing too according to the manual. The truck was a brush fire truck and I believe the millage to be 42,000 original miles. With this information, what could be causing the truck to run rich and build up so much carbon? What/how should I make adjustments and to what? Any help much appreciated.

You need to look at the carb again. First pull it off & make sure there is a passage in the base gasket for vacuum to get from the hole in the bottom of the carb to the manifold passage. Take the top off the carb & make sure the power valve piston goes up & down & knocks the ball off it's seat. Make sure the float level is correct. The size is stamped in the main metering jet. It should be in the .050 to .o54 range. With the engine running slowly turn the idle mixture screw in till the engine slows down. Back it up just enough to bring it back to idle speed.

On my present model B carburetor, someone had switched the main jet from a "51" to a "58". The first one is appropriate for the 216 and thge second for the 235. It ran really smoothly with the larger jet but the plugs ran rich. I am now using the smaller jet and the plugs are fine. the number is stamped on the jet.

Is there a place you can buy those there main jets?

I think Carb King could answer that one.

I checked out the carb. The vacuum ports are clear and open and the correct gasket is on. The float is not leaking and adjusted properly. The carb rebuild kit I got locally and contained only gaskets and springs and the little ball bearings. It did not come with a new power piston or main jet so I reused what was in there because it did not appear to be worn. The main metering jet has 57 written on one side of the slot on top and 75 written on the other side. So maybe this is the problem?...I have a 57 in and not a 51-54? What does the 75 mean? Metric? I guess I should get a better kit and rebuild the carb again. Any other ideas or could this little main jet be the cause for all the carbon. Thanks a lot for the help.

My knowledge of the numbers on the parts is quite limited. I assumed that 51 referred to .051" but I am not sure. The 58 made it too rich for my 216 but the 51 seems to be just right. Somebody has switched in a 58, probably to make it run better. On another note, the used head that I bought had a thick coating of carbon all over the combustion chambers. My motor would certainly not look like that. I think an overly rich situation would coat everything.

The .057 is the diameter of the hole in inches. That is your problem. I can check Monday I might have a smaller one I can send you. George

I went around town looking for a carb kit with the proper .050-.054 main metering jet. I have come up empty handed. None of the kits even have a main jet, wright or wrong. If you have one George, I'm interested in it! And if not, does anyone know of a carb kit from any of the usual vendors that would come with a main jet or a place to buy just a main jet? Thanks, Nate

Carb kits have not contained main jets for 50 years. E-mail an address & i'll send you one. [email protected]

I found a .053 & sent it to you. Here is a poor mans exhaust analyzer. With out using the choke, if you start it up with the engine cold & drive off with out hesitating it is a good indication it is running rich. If you start it up & it hesitates till the engine warms up & then responds good it is about normal. If it hesitates even after it warms up it is probably too lean. This is kind of general. There are many contributing factors.

I think that is a pretty good summary!

Thanks a bunch George! I like the poor mans exhaust analyzer, it fits my budget. Since I got it running, I had noticed that upon starting I could just go down the road with it. I never needed to let it warm up, it just ran fine with no hesitation. I figured that it was a testament to my great carb rebuild and adjustments..or so I thought. I'm interested to see how it starts and runs once I change out that main jet. I'll keep ya posted.

Hey hope you haven't given up yet . I have been fighting with the same problem . today my problem got worse, misfiring, black smoke hard to start ect. the second time I took apart the carb I noticed the piston power ( thats the brass tube with the brass barrel with the big spring in it ) wasn't traveling very much in its hole. hope you aren't having trouble following my high tec speak. anyway I rolled up a piece of 220 sandpaper like a funny jamaican cigaret and polished the port this fits in until it worked smoothly , I was surprised how bad just a little crud was affecting this part. I put it all together and now it runs like it was touched by god ! hope this helps , at least it won't cost you anything.

Thats the glory of a model B. It's so simple to take apart. If you have to do that to a Q-jet you will be busy.

I haven't given up yet. I got the main jet from George (Thanks a lot George!) but have not put it in yet. I have been a little busy with Thanksgiving and other junk. I'm not sure I will get to it too soon. There so much junk in the gas tank that it keeps plugging up my fuel filter. I have a glass filter that comes apart so I just clean it up when it blocks up. Last time it clogged up in the middle of traffic, so I want to take the tank out and clean the junk out before I go back on the road with it. I'm not sure that is going to happen soon. Seems like the truck might be in for the winter. The snow is gonna fly this weekend. When I do get it back on the road I will post my results Rick. Thanks for the help everyone.