Rich...Rich....Rich!!

I can not figure out why I am running so rich. Here is a little background on the bike.

It is a '82 750 Maxim with 3,300 miles. It had been sitting for quite awhile before I bought it. It was not running although I could get it to fire with starting fluid.

I read the carb rebuild thread and decided to give it a try. I used to ride a lot when I was younger but it's probably been 10 years sinve I've ridden. I've rebuilt a few car carbs but this would be the first time that I had tackled a motorcycle.

When I drained the tank, there seemed to be a lot of water in the gas. The carbs were a little dirty but not as bad as I would have thought. I tore it apart and cleaned all the parts in carb cleaner. I used spray cleaner on the carb body itself and everything seemed really clean. I set the float level to the 17mm measurement and they all needed a pretty big adjustment which seemed odd to me. The mixture screws were set to 2.5 turns out. Someone much have had the carbs apart before since the caps to the mixture screws were gone. After I put it all back together and installing them back in the bike, it started right up. It actually seemed to run pretty good and idled fine so I thought I was pretty much done. I had also installed new NGK plugs.

On the maiden voyage, it seemed to run rougher and rougher as I rode it. When I would hit the throttle, you could see a little black smoke come out the exhause. It looked like it was running a little rich. When I got home, I pulled the plugs. They were all very black and sooty.

After readying another thread on here, I thought I may have installed the floats upside down. I tore the carb apart again but the floats were installed correctly. I put them back on the bike and checked the level using the clear tubing. They were off quite a bit so I adjusted all 4 of them to the 3mm level. I also removed all 4 mixture screws to make sure the screws had all the components. They were fine. I also bench synched the carbs.

I installed every thing again and it didn't run any different. I then set the petcock to prime and removed the vacuum line just in case it was sucking fuel through the line. I cleaned up the plugs the best I could. I also turned all 4 mixture screws in a half turn. It seemed to run a little better at first and then progressively got worse and worse. It idled at about 3000 rpms but would come down eventually if allowed to idle for a little while. When I would get above 6000 rpms, it would start to buck and miss. Also when I was at a steady speed, it seemed to miss a little. When I got home, I pulled the plugs and they were just as black as before.

I probably put something together wrong but I just don't know what it could be. Anyone have any idea where I should start?

Thanks for any help anyone can provide.

 

How many turns out are the pilot screws(mixture)? I had to adjust mine alot to get them right. I spent over two hours starting, reving to 5k for 15-20 seconds, hitting kill switch, check plugs, readjust the pilots screws, then start the whole process over. I would start with turning in the pilot screws some more and do the above till you get them right. Make sure when doing this that you have a fan or two blowing fast on the engine and check it to make sure it does not overheat.

 

main jets and pilot jets reversed?? DUMB question but I did that once. Float have flat side down and float levels set with clear plastic tube at the float bowl screw or washer? Clunk Test?

 

Initially I had them set at 2.5 turns out and then I put them to 2 turns out. Since a lot of people put them at 3, is it possible that all 4 need to be less than 2 out?

Also, when they are really black and sooty, will the 5K run clean them up if I get the mixture correct?

 

Yes, I'm sure that I have the jets in the right place. The largest jet goes in the high post when the carbs are upside down. Yep, I set the levels with the clear plastic tube. No problems with the clunk test.

Thanks

 

Yes, the 5k runs should clean them up. Each run that you do will burn off more and more of the carbon build up as you get them closer and closer to the correct setting for your bike. Each time you pull the plugs you should notice that they are getting better. Not sure about your carbs but I do know that some years used a more course thread then other years so the amount of turns can be different. Somebody know the years for course vs fine thread?

 

I thought they were all fine threaded, but Chacal needs to chime in here.
How does your air filter look?
A dirty filter can cause it to run rich.

 

Yes, the early HSC32 Hitachi carbs used a coarse pitch idle mixture screw and thus would require a smaller number of turns to get the same relative mixture setting versus the later model fine-threaded screws.

The coarse threaded screws seem to have been used on the 1980-81 XJ650 models only. I have not seen them used on the 1981 XJ750 Seca, nor any 1982-up carbs. all of those models use the fine-threaded idle mixture screws.

For obvious reasons, even though the screws are identical in all other aspects, they do not interchange.

 

The last test ride, I didn't even have the airbox hooked to the carbs. It's too hard to get the rubber boots back on the back of the carbs if there is a possibility that I will taking the carbs out again.

 

I will take a look at the threads on the mixture screw tonight.
Thanks for the info.

 

Get a colortune. It's a great investment, and super cheap. Also using Iridium plugs helps. You also need to realize that all of the mixture screws will not all nessicarily be the same. You may have one at 1 1/2 turns, another at 3 1/4. Be sure you have no vacuum leaks at the manifold boots, all of the caps are on the vacuum outlets. If it's running rich whats stopping you from dialing it down as low as needs to be? Bottom them out (gently) and start at 1 turn or 3/4 out. If you're making adjustments without the airbox, it'll all be for nothing when you put it back in. You should be tuning the bike as it is under normal riding conditions.

 

I'll be getting a colortune in due time. I convinced my wife that I needed to buy this bike so I could save money on gas. So far, it has been everything but a money saver so I need to wait a little before I purchase one.

I didn't know if it was acceptable to turn down the screws so much from the norm setting. I just figured I had done something wrong when assembling the carbs. I can give it a try and see what happens.

I know that hooking the airbox will change the way the plugs read but since I'm not even close, I'll worry about it later. If I had to try and hook the back rubber boots on each time I put the carb back in, I wouldn't be doing this myself. It's frustrating!!

Thanks for everyone's info!!

 

Were you pulling the carbs to adjust the mixture? A small screwdriver allows you to do it in place. You need to be doing this with the airbox in, if that's how you intend on running it. There's too great of a difference between with/without airbox.

 

No, I was pulling them to adjust the float level.

I turned down the mixture screws to 1 turn out last night and it didn't seem to make a difference. It did start much harder though even when using the choke.

You're right, there would be a big difference between with/without airbox but running without an airbox would cause me to run leaner which I would love to see at this point. :wink:

The mixture screws were the fine threaded type. :?

When I road it last night with the screws out 1 turn, it would idle when I first started it up. When I took it down the road and came to the first stop sign, it was idling at around 3000 rpms. I couldn't get it to run over 6000 rpms without it popping and sputtering. At a steady throttle, it would also sputter. Got home and pulled a plug and it was really black. :?

Thanks

 

Popping and backfiring is indicative of a LEAN condition.

Be sure your coils are hooked up correctly. Irratic idiling is also a trait of vacuum leaks.

 

When you did the Carbs ... did you push-out the Emulsion Tubes and clean them?

If the series of air metering ports surrounding the Emulsion Tubes are clogged, you won't get the correct Main Fuel Jet mixture ... and, the Fuel
being drawn-up into the Intake stream won't be atomized enough for a clean burn ... often resulting in fouled plugs.

The Emulsion Tube is released by removing the Main Fuel Jet and its washer.
The bottom of the Emulsion Tube is then exposed.
The Brass bottom of the Emulsion Tube needs to be either pressed-out or tapped-out of the Carb Body ... through the top-side.

I have seen situations where the Emulsion Tube is completely fouled and
fungus growth clogged the Main AIR Jet Passages.

Emulsion Tube - Main Jet and Washer:

 

Yes, I took them out and soaked them overnight. They all looked really clean and the holes were clear.

I am going to take the carbs apart again and look things over. Maybe I put something together wrong.

Thanks for all your guy's help.

 

Is there a way to be sure that I'm getting a hot enough spark?

 

That's not your problem. Are you 100% sure your coils are going to the correct sparkplugs?

 

I'll check it out.