#4 is carboned

[KA1J]

This is an XJ700 Maxim-X with 9K miles. I've had lousy mileage since I bought it last year even though I rebuilt the carbs last fall, have Dynacoils, no resistor in line to the spark plugs. I found cyl 3 was fairly thick in carbon. Cylinder 4 was very thick in carbon. 1 & 2 were fine. Yesterday I pulled the carbs and reassessed the fuel level

I assured all the fuel levels were at 3mm and colortuned/carbtuned it. When I rode it last night I found the engine was hanging at stops like it had done last fall; hangs at 2K and then drops down to normal. Keeping the brake on & partially engaging the clutch as to stall would bring it down an it did not try to speed up. The problem had disappeared this spring and after the fuel levels were adjusted it returned.

So today I took it for a 30 mile interstate excursion and gassed up and it took .9 gallons so I'm still at the same crappy mileage as before. Decided to go for a 10 mile run at 65MPH and do a plug chop and here are the results & I apologize for the blurriness I used my cell phone in foggy conditions & it's the best I could do.






So obviously #4 is extremely carboned and 1,2,3 are too lean.

I exchanged plugs 1 & 4 and rode 6 miles home. I looked at the plug now in in cyl 1 that was carboned in #4 and it is now looking lean like the other three were. The lean plug that was in cyl 1 & now in cyl 4 is now carboned. That eliminates a bad plug as the problem.

Before I removed the carbs yesterday, plug #3 was almost as carboned as #4 is in the photos and 4 was the worst yesterday. The carboning is not wet or oily. Correcting the fuel levels and resyncing the bike fixed the issue with the carboning on #3.

So with all that, there's definitely a problem with the #4 side.

Have Dynacoils - replaced all components of the the float valve assemblies last fall with new ones - Accel 8mm ignition wire - did the zero ohm mod on the plugs - carb dipped everything overnight - replaced all the rubber in the carbs with new including throttle shaft seals - made sure the carb cleaner in a pressurized can went through the passageways in all the carbs - assured there are no air leaks around the carbs using starter fluid and propane - enrichment circuit is intact and working properly.

What would be good for me to consider doing at this point?

Gary

[Tat2demon]

You didnt happen to dip your fiber washer under the float seat did you? I did that this weekend and it turned to mush. Even after tightening fuel still poured through it.

[motoman]

Bettin' you got a hung up float, since that's what was part of what was messed with. I assume that bike has the Hitachi carbs?

[KA1J]

@ Tat; I bought brand new float valve assemblies and when I reassembled the carbs after dipping I opened the packets they came in and used them. So no dipping of the fiber seal.

@ Motoman; I had the carbs off yesterday and checked to make sure the valve was working. It shut off nicely, opened easily to let gas pass and took miniscule pressure upwards from the float to make it close.

The carbs on the XJ7700 Maxim-X are Mikuni BS33, the airhead 700 Maxim uses Hitachis.

Thanks for the thoughts, this is really bugging me, that's a lot of carbon.

[motoman]

@ Tat; I bought brand new float valve assemblies and when I reassembled the carbs after dipping I opened the packets they came in and used them. So no dipping of the fiber seal.

@ Motoman; I had the carbs off yesterday and checked to make sure the valve was working. It shut off nicely, opened easily to let gas pass and took miniscule pressure upwards from the float to make it close.

The carbs on the XJ7700 Maxim-X are Mikuni BS33, the airhead 700 Maxim uses Hitachis.

Thanks for the thoughts, this is really bugging me, that's a lot of carbon.

True. but with the bowl off U have no way of knowing whether or not the bowl gasket is getting 'squished' a bit and pused out interfering with float(just like on the 11's BS34's. Oter thing is, are they a 'pressed' in seat with an O-ring? If so, that one could be weeping extra fuel by........just throwin' out ideas.

[KA1J]

True. but with the bowl off U have no way of knowing whether or not the bowl gasket is getting 'squished' a bit and pused out interfering with float(just like on the 11's BS34's. Oter thing is, are they a 'pressed' in seat with an O-ring? If so, that one could be weeping extra fuel by........just throwin' out ideas.

To the best of my recollection, it was much like working on the carbs of my XJ11 when I rebuilt them. There was an O ring.

I checked the fuel level in the carbs and made sure there was no creep upwards of the fuel, I held it in place for around a minute on each carb just to be sure there was no leakage. Man, I thought I did such a precise job of rebuilding those carbs too...

[motoman]

To the best of my recollection, it was much like working on the carbs of my XJ11 when I rebuilt them. There was an O ring.

I checked the fuel level in the carbs and made sure there was no creep upwards of the fuel, I held it in place for around a minute on each carb just to be sure there was no leakage. Man, I thought I did such a precise job of rebuilding those carbs too...

Maybe secondary ignition. Might take that particular plug boot off and cut back the wire and re-screw it in. That plug looks like it may just not be firing a good spark all the time.....JAT.

[WMarshy]

Are you using a YICS blockoff tool to sync your carbs? Not sure if your bike has this or not just a thought... 1-3 look spot on from what I can tell, not too lean IMO.... maybe double check your main jet is the size you expect. Maybe you were given one kit with the wrong main in it?

[KA1J]

All the jets seem to be the ones called for. No, no YICS on this model, Just went through the complete #4 carb & found nothing to change. Blew out the passages again & am going to take it for a ride. I switched the plug wires at the dynacoil to see if maybe there's a problem in the dynacoil. Grabbing at straws here.

this is a 5 valve/cylinder 700CC engine with 86 HP & the Canadian version is 750CC & 90HP. They only made it two years & I've heard it called the MiniMax. Even with this carb issue it has an amazing power curve from 5K-10K. Quarter mile is supposedly 11.7 but I'll never try to prove it.

This #4 carboning problem is giving me a headache though, I'm hoping it doesn't come down to shims, to do these you have to remove the cams & it's a PITA fit to get to them & they're the diameter of a valve shaft. & fit under the lifter. 25,000 miles between shim checks though so at less than 10K miles on the engine I can't see why a shim problem would exist here.

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