700 Maxim X Too Rich at Idle

I have a 700 MAxim X I purchased not running. I'm under the belief it ran before it was set up too long and had dirty carbs.

I'm not new to carbs, I have rebuilt and recalibrated lots of auto and a few motorcycle carbs but his one has me stumped. It runs too rich at idle. I can close the idle mixture screws all the way shut and it is close to correct but still too rich. The float level is good and the pilot jet as well as the pilot ait jet is correct. The main circuit seems OK the main jet is 107.5 and the jet needle is stock.

If I shut off the fuel the idle stays rich even when the bowl level gets down to half full. At that point the main circuit goes lean as you would expect.

The starter circuit seems OK and even if it was leaking it shouldn't be that significent (normally an engine will run with the choke on).

What is interesting is the problem is with all the carbs. It has to be something in common.

Any ides?

Ron

 

If you closed the idle mixture screw and it is still rich the only two things that will keep fuel going to the engine is float level too high or starter circuit leaking by. Seems like are confident in the float levels, check the starters. I have had that problem before. Even if it leaks a little that is too much. It is more common to have it happen on one or two carbs and not all 4.

 

Thanks for the reply mlew. I can't find anything wrong with the starters, I think I will try to find a way to disable them; possibly tap a set of threads where they dump into the carb barrel and plug with a set screw. That is a bit of work but I'm running out of ideas.

 

I *am* 'new' to carbs, but working from just the knowledge (and lack of experience) that I have--is there a chance it was incorrectly jetted up? I dunno, maybe someone put pods, got bigger jets, and then put the airbox back on to sell it to someone?

 

Stay away from that idea, once you do there is no going back.
Have you checked the size of the pilot jet? Might be too big or someone modified it.
I test my starter circuits by putting a piece of 1/8 silicone tube(at hobby shop for model airplanes) on the brass pickup tube and sucking through it. It should hold vacuum , then open the starter and see if it closed again.

 

1) Are all the jets marked with the original correct stock sizes?

1a) Are you sure that even if they are marked with the original stock sizes, that they are in fact the original correct stock sizes?

Does it run rich on the main circuit as well, or are you hunting an idle only problem?

 

Mlew, I guess I wasn't clear when I said I would disable them. It would be temperary. The plugs would go where the starter circuit dumps the fuel/air mix at the engine side of the carb. The threads won't change the calibration of the starter circuit. Your method of checking the starter with the tubing is good. I'm working from memory here but I think the starter can also pull air from the roof of the float bowl. If clearances are loose on the brass barrel it could draw some air even when the starter is closed. Still this air would have to have fuel with it.

It is possible the pilot jet has been opened up. That may be hard to detect, that jet is so small.

I guess I'm not convinced the extra fuel is coming through the pilot circuit and looking out side the box.

I'm not in the mood to pull the carbs off the bike again but I think it is my next step.

Thanks for the help.

 

Another thought'
Mikuni has two different types of pilot jets that are not interchangable. I can't remember what type of carbs the 700 has. I have been cought by this one one time and it drove me nuts.
Look at this page from MikesXS.com, it shows the difference in the two.
http://www.mikesxs.net/products-39.html#products

The air holes in the jet make a difference, If the wrong one is installed it will let too much fuel in the idle circuit.

 

I fought with my carbs for months. I have a 4 into 1 Jardine pipe. Ended keeping all stock jets. Set my float at 1 MM lower than spec. Opened up fuel air mixture screws 3 turns and its blistering fast. So be patient with them.

 

Thanks guys, I will check out that link. I'm going to New Orleans for a week and when I come back I'll have some new vigor and get this thing figured out. Until then it's time to eat crawfish.

 

Also, the air pilot jets are sort of backwards in their sizes compared to fuel jets.

The idle pilot air jet is the BIG HOLED one.

The main air jet is the SMALL HOLED one.

If you have them backwards you'll get a stupid rich idle.

 

I found the problem. The pilot jets were modified. I put new jets in it and that corrected the problem. When tuning it now looks like two and a half turns on the pilot screws are about right so as a system I thank that is good. One odd thing is when I let off on the throttle it drops to about 2000 rpms and stays there for fifteen seconds and then drops to 1000. I'm not sure what is causing that.
As for high speed circuit; I took it through the gears to readline and the accelleration was strong and smooth all the way up. I didn't feel a powerband at the top like some bikes have but I think that may be the characteristic of the five valve. It was very strong from 3k on up.
Now I need to fix a petcock leak and get a speedometer cable and it is go time.

 

Ron, I am having this same 'hanging idle' issue with my 700x....seems like the hotter the engine gets the longer it will hang. Others have posted this is normally caused by a vacuum leak but I have done several tests and find no sign of a leak.

If you figure this out please pass it on....

 

Don't forget the o-rings on the intakes. I attached a picture of what I started with (a prime cause of vacuum leaks). All could be equally deteriorated and need replacement.

By the way, your valve clearances are correct right?

 

Bad intake o-rings should show up on one of my vacuum leak tests, right?

Yeah, valves in spec <500 miles ago, carbs rebuild & floats to spec, A/F out 2 1/2 each + a smidgen, runs strong except for the hanging idle and a slight roughness at idle.

 

Yes, an intake o-ring should show up on a leak test. I wanted to provide an example of how awful mine looked. My bike was not running when I got it and when going through it and checking everything, I discovered how bad they were.

Needless to say, like my "old school mechanic" that was my mentor would ask, do you know for sure if they're good?

Back to the hanging idle, make sure the sync is done as well and each individual carb return spring is working as it should. Also, make sure the throttle cable is not hanging up and upon release of the throttle, it snaps the carbs back to the idle position.

Basically, it's a process of elimination and I hope that I've helped.

 

Pretty much covered all those bases but appreciate your replies.

Not much left to do now but pull the carbs again and go back over everything....I missed something.... :?:

 

Another place to look would be the vacuum port caps. They harden with age, and do not always show up on a leak test.

Ghost

 

Thanks Ghost....I'll give them a look.

 

I need to fix the fuel leak at the petcock and then I will check for vacuum leaks.

FYI- A good way to check for leaks is to wave an unlit propane torch around suspected leak areas. If the leak is there you will see a change in rpm.

 

+1
The positive side is that the propane is much more stable than starting fluid, and will not dry out your rubber parts.

Ghost

 

Yeah, propane is always my choice too.....didn't show anything, neither did carb cleaner.....but it's still classic vacuum leak signature....maybe I'll try it again.