XJ650LJ (Turbo) Will not rev over 4000 RPM

Greetings all,

I’ve a XJ650LJ that I have put a XJ900RK motor in. I did this 15 years ago with wonderful results.

Basically rejetting the Pilot I size larger (aided by an EGA machine) and (I believe) 1 size larger main.

Results were just fantastic. Great driveability and all around a very nice ride.

The bike sat for 10 years and one cylinder got stuck. Replaced that set of rings, cleaned the carbs, and it fired right up.

Would not rev over 4k rpm when taken on a test ride. Just sitting there all seemed just fine.

Ended up putting a fuel filter between the fuel pump and the fuel pressure regulator, checked the pump output (60lbs’sq in).

Tried all 3 TCI ignition boxes that I have, rechecked all vacuum \ pressure lines. Checked the advance with a timing light (no marks, but it advances as I would think it should.

This bike runs so nicely from start up right up to 4k that It is hard to think there is anything major wrong, but it is not right.



Might anyone out there have any clue (no matter how farfetched) that may point me in a positive direction?



Thank you..



Stephen Bailey

 

clogged emulsion tubes under the main jet

 

no timing mark?


look into waste gate 4000 rpm it should open

 

How about when it’s in neutral without load does it still stay below 4,000?

since the boost senser feeds into the TCI I would bench test it to make sure it’s doing what it is supposed to

really curious to know more about your bike, did you keep the Turbo head and carbs? What compression ratio did you run?

 

Simmy,
I just dropped the XJ900RK motor in without any real modification. (there are several things that do need attention, but relatively minor)
Yes people, I do know turbo motors are supposed to have a reduced compression ratio, but I defy anyone to run this combination at
WFO for long enough to hurt something. I know it is possible, but it's not my style. It is just a real nice ride.
With no load, the throttle response seems fine, but if you free rev it and hold it open, it sorta seems ok, but I can not do that to
something I care about for long!
I have done all the checks the service manual suggests for ignition (as that what I and others of my circle thought) and I do have 3 total bikes.
All 3 TCI boxes act the same.


Steve

XJ650LJ
QT50g,h 4 total
750GT Ducati 1974 x2
900SS 1977 Ducati
900SD 1978 Ducati
XV920RJ w dellorto and 1100 cylinders

 

Simmy,
There is a timing mark for idle but not for full advance, but with a timing light, it does appear to advance quite close to what looks to be in line with the specs for the ignition curve.

Steve

 

Interesting - did you use the original carbs rejetted?
Anyway, if it won't go past 4000 it's either no air or no fuel.
Is the turbo spinning? Is there boost showing?
The blocked main jets or emulsion tubes are worth a look.
The wastegate should be closed unless you have boost, so its not that its not opening youwant to check for - it's if it's stuck open.

 

As another who is reviving a long dormant Turbo it might be worth inspecting the turbo itself to make sure it is spinning.
When I pulled mine apart mice had packed the exhaust with carpet fibres and used the turbo outlet vanes as a latrine.




still curious about your 900, I assume you used the 650Turbo head and carbs, if so did you measure the resulting combustion chamber volume?

 

You were spot on. Cleaned the pilot jets and all is well.

Steve

 

A final report.
XJ550h was spot on. The needle jets, which I had NOT removed during any of my efforts turn out to be the culprit. I am not used to these carbs and had not realized there are 4 rows of small holes (emulsification) down the sides of said needle jets.
Of the 36 holes per needle jet, only ~5 were sorta clogged. After cleaning, test ride shows the bike works well once more.
Thank you to all who suggested remedies.

Steve