Maxim-X bogs at 8,500 RPM

Checking the acceleration on the 86 XJ700 Maxim-X and discovered at around 8,500 RPM the engine bogs badly. It is almost like there is a governor on the engine that engages at 8,500 RPM. Here's the particulars:

10K miles on the bike.
Cylinder pressure between 140-150.
Carbs recently rebuilt - new seals throughout.
Synced via carbtune and adjusted via colortune.
Green Dynacoils.
Accel 8mm spark plug wire.
zero ohm mod to plug caps - resistor removed.
Iridium plugs.
Amsoil JASO-MA rated 10-40 oil.
K&N air filter.
No smoking from exhaust on acceleration/deceleration.
Acceleration very strong until around 8,5K Redline 10K.
Exchanged TCI with one for a XJ750 Maxim-X with no change in bogging.

Any ideas what I might look into to fix the bogging?

Thanks!

 

85-Hundred, ... huh!

I'd suspect "Fuel starvation" ... right off-hand.

It might even be a partially-clogged Petc0ck Tower Screen.

How fast is that baby going at 8.5K ???

 

Why the heck do you rev it so high? lol!

I'd go with Rick. This tower-filter in the tank can get badly clogged over the years. Or it could be your inline filter, you have one, don't you?

 

I can relate ... at 8,5k rpms I also experience a severe bog, possibly air starvation ... because I forget to breathe, scared shitless 8O

 

LOL!

The redline is 10K on the Maxim-X which has the Genesis engine; its different than earlier XJs. As to how fast at 8.5K RPM, lets say... zippy. To me, the salient point is it's designed to do this and its not. I want this bike restored to it's original expectations.

I do have an inline filter, one of the ones in clear plastic with the bronze aeration stone inside.

I thought it was a problem with the petcock as it seemed to be a non-issue when I ran it on prime on the interstate but on the way back home, in 1st gear it went to 10K immediately. in 2nd gear at WOT it stuck at around 9200 RPM. I can't believe Yamaha would have made such a bike with a redline of 10K and then made it difficult to reach 10K.

I don't have the answer but I did check out at the filter tower and it looks to be fine. Any other ideas? I'm willing to check out anything I can do.

 

Since you are able to get-over to the right-hand side of the Tach, ... I would surmise that you get fuel-starved at higher revs.

That Inline Filter may be a contributing factor.
Test by running on PRI for a high-speed run.

If it boggs-out, ... replace that Filter with a FRAM Inline which has a lerger and more porous Filter Element.
A Genuine FRAM.
Not a cheap knock-off.

 

Same bike similar issue for me except mine is at about 9k. I figured its just the way it is...

 

How are your float levels? Also +1 on what Rick said abotu the fuel filter

 

My maxim x regularly sees 8.5k.


Max tq is reached around there and max hp isnt till 9k.

2Nd gear puts me at 70mph 3rd around 95mph 4th and 5th Ill just plead the 5th on.

It shouldnt bog down at 8 or 9k. Mine didnt even bog the time or two its hit 10k.

Id try a different filter.

 

My X never bogged from the bottom to the red line, even though it wasn't perfectly tuned up.

I had the same kind of inline filter with the bronze element.

 

Oh... i had a similar issue once too... I had some pilot and main fuel jets reversed.... OOPS....

 

Another good one Rick, I thought it was OK after running it on prime a couple of days ago. Then I revisited the upper RPMs and my buddy was back. I have one of the clear glass filters, Mr. Gasket I think it is and I attached a couple 90 degree elbows to it with a nipple on one end and mating threads on the other. This was the kind of filter I used to use on my car with carburetors. It's running freely on the bike and out of sight thanks to using those elbows to get it to fit with Fang Sway.

Took the X out for a couple of good runs to check for issues & then did so again later and it pulls like a champ to 10K and would go further if one were foolish enough to do so. I have a petcock repair kit on the way and will rehab that anyway, won't hurt at all.

Starting to get the demons buggered out of it and this will most definitely be a fun bike. About the same HP to weight ratio compared to the XJ1100 too:

The 700X has 86HP at 511 pounds gassed up. 11.79 in the quarter mile.
The XJ1100 is 95HP at 609 pounds gassed up. 11.7 in the quarter mile.

The 700X is definitely more nimble than the XJ11 but as a full cruiser the XJ11 is much more comfortable on a long trip. The XJ11 has a more even torque curve and the X really pulls amazingly in the top 4K

 

Maybe check that the air filter is clean too, as that thing must be suckin like a hoover at that R.

 

I have a K&N on it and run a little of the liquid on each pleat every couple of thousand miles. More than is called for but I like to keep it sticky. Wash the K&N filters whenever they look dirty. Been using them for years.