Lacking power

Hi,

I've been riding my xj600 (Divvy) for two months and she's never skipped a beat. I've known that the air filter badly needs replacing since I’ve got the bike but have been reluctant to replace it due to a seized screw in the petcock (as I’ve mentioned before). However I’ve got an impact driver, a thread extractor & some plus gas so I’m going to face my fears this weekend.
Over the last few weeks the bike has dumped oil out of what I believe is the airbox breather when I park in on the side stand. So I’ve been parking it on its main stand as a temporary solution (assuming the air filter change would solve it). However, the bike then started to dump oil out of a separate breather below the fuel tank which meant the engine got a good covering of oil (smokes like a trooper when I start her up).
The last nail in the coffin is over the last two days, performance has dropped drastically! If I open the throttle to get the revs to about 6k then she splutters & slows down (I think it’s flooding), acceleration has gone out the window & I can’t get her past 60mph. I shouldn’t ride her like this but I’ve had to in order to get to work.
As I’ve said, I’m hoping that this is due to the filter i.e it’s blocked and so the fuel/air mix is poor causing lacking power.
However, I’m concerned that it’s something more painful like the pistons are worn (would explain the oil coming out of the air breathers) as she’s my only means to work & with Christmas coming I doubt I’ll be able to afford to get any major work done so I’ll have to do what I can myself.

For the record she’s on 46k at the moment & the oil isn’t too full, I get her to the right level on the centre stand & as I’ve said before, she’s currently eating it so she’s more likely to be low than too full at any given time.

Any words of advice or guidance would be greatly appreciated
Regards,
Si

 

Check your oil for the strong smell of gas. DO NOT run it with gas in the oil.

From everything you describe it sounds like you have at least one needle valve bad and are dumping gas into your oil.

 

cheers bill, I'll give that a check in the morning.
I've had the tank off and found that the air boxhad blown off the carbs! (It backfired once a while back so I'm guessing it's that)
Anyway, I opened the box to find the filter swimming in oil! Nice! I cleaned out the breather pipes etc as they were all emulsified. I also checked the flow of all other open pipes by blowing into them. However, when I blew into one of the pipes attached to the carbs I got a face full of petrol fired back at me! let this be a warning to all who read this that even if yo think you've cleared a system of fluid, there may be some left!
I then ran the bike without the air filter in place and a funnel as a fuel tank so i could watch the carbs running. There was no sign of oil backing up into them however she struggled at 5-6k revs. I let her run low on fuel & this gave me a full rev range.
Now this has stumped me as I can't figure out why i had oil in the air box but it wasn't pumping in up when I had the box removed!
I've asked a friend and suggested that the main jets in the carbs may be blocked. I opened one carb and there was some gritty stuff in the bottom of it & the jet was blocked (although it could have been fuel). I then started running out of daylight so I'll go over the other three in the morning.

 

Ok I've checked the oil & it doesn't smell of petrol.
I've opened the bowls off the other carbs & checked the jets but none of them were blocked.
I fired her up again out of hope that I'd shifted something. She's still struggling to hit 5k. This is really bugging me as I just can't find any other leads as to what it might be. I've done forum searches & other users tend to find it's the carbs but they seemed pretty good when i opened them.
Any other guesses as to what it might be?

 

I've just had a thought. I had a major quantity of oil in the airbox.
I assumed this was being pushed up past the piston & through the carbs into the airbox. However, on inspection the carbs were clean & there was no sign of oil coming through them when I ran her.
I've just remembered that the crankcase breather runs into the airbox as well. This was lined with emulsified oil & I believe the crank case must be over-pressuring in order to pump the oil into the airbox.
The usual cause of this is too much oil but I've checked the level on the mainstand and she's well within tolerance.

What else could cause the crankcase to over-pressurise?

 

Most of the time it is gas that overfills the oil but if you have no smell of gas then I 'm not sure what could have happened.

We have another member looking at something similar. In colder weather you can get condensation in the air box. I'm wondering if you are seeing that mixed with oil left over in your air box?

 

So when the motor started to run out of fuel, run lean, you got full rev range.
This points back to the carbs or rather to much fuel.

Bad rings can cause pressure in the crank case, there is no pcv valve on these bikes I know of, just the breather in the air box.

This really sounds like to much oil in the gearbox.
Especially the won't rev past 6K.
This is exactly what my bike did when over filled.
Mistook the highbeam light for oil light, couldn't figure out why it wouldn't go off after adding half a quart.
Don't ask.... it was one really bad day.
:roll:

 

I'm certain that the oil level is within tolerance as it's in the bottom 1/4 of the viewing window when on the centre stand on level ground. The way to be sure though is I'll dump the oil out of it, measure it & compare it to the manual specs.

I've spoken to some of the boys at work this morning & they're threatening me with words like blown rings, pistons & re-bores!

just a thought though, this was a sudden loss in power. Tuesday it rode fine, wednesday I'm stuck on 5k revs & 50-60mph. If it was carbs i would imagine it would be a gradual loss.

 

In that case do a compression test. If it's low do a leak down - that should tell you something.

 

I should be getting hold of a compression gauge later so I'll give it a go tonight.

Something I failed to mention, when I fired her up yesterday, I flicked on the choke and gave it some throttle which managed to push things to 8k revs.

It's pointing towards something in the fuel system. It's been suggested that i should run her then block each carbs air supply one at a time & listen to see if one of them doesn't react. if it doesn't then that one has a fault somewhere...

Also, I've got to check the diaphragms for wear etc as aparrently that's a favourite.

 

ok, I've just squirted some carb cleaner about & could max out the revs while it was burning that but once it had cleared the system it was back down to the usual 5k. Blocking each carb was inconclusive, my source for the gauge has yet to provide.

While tinkering I had a thought... fuel filter!!! I whipped it out and put the funnel in it's place... no game!

This is really starting to bug me...

 

Interesting that sure sounds like a fuel issue but I'm stumped.

Back to basics - have you pulled the carbs and cleaned them? could have blockages. Also even if you have it may be wise to pull them again and check them out.

 

I've not pulled them yet. During the week I'm working on the bike under a torch outside. Pulling the carbs is fairly complicted so I'm going to either have to take another day off work to do it or wait for the weekend. Granted the carbs will be better off being pulled & cleaned thoroughly so I'll do it. They'll want tuning as well but that'll have to wait until i can source the tools for that job.

I'm tempted to replace the HT leads anyway as i know one is dodgy but does produce a good spark.

Other suggestions today have been to check the CDI & the TPS. I'll check the tps when I remove the carbs.

 

OK, I've not updated this for a while so here's the latest:

TPS was fine, carbs have been cleaned & balanced. air cleaned the fuel system, & checked fuel pump. fresh fuel used. none of this came up with anything.
I managed to get a compression gauge in the weekend & tested the engine... 4bar (58psi) on each cylinder. The manual states around 11bar (160psi)!

I spoke to a couple of engineers, bike mechanics & other bods in the know & they've all agreed it can only be one thing, scored/damaged bores! This makes sense as the p.o worked in a limestone quarry.

My options are thus:

source a new engine (there was one going free locally about a month back)
pull the engine & get it re-bored (expensive)
sell the bike and buy another (painful to do so as i like it alot)

Any thoughts on this?
Also, how hard is it to transplant an engine as this looks to be the first step for me.

Regards,
Si

 

OK, I've not updated this for a while so here's the latest:

TPS was fine, carbs have been cleaned & balanced. air cleaned the fuel system, & checked fuel pump. fresh fuel used. none of this came up with anything.
I managed to get a compression gauge in the weekend & tested the engine... 4bar (58psi) on each cylinder. The manual states around 11bar (160psi)!

I spoke to a couple of engineers, bike mechanics & other bods in the know & they've all agreed it can only be one thing, scored/damaged bores! This makes sense as the p.o worked in a limestone quarry.

My options are thus:

source a new engine (there was one going free locally about a month back)
pull the engine & get it re-bored (expensive)
sell the bike and buy another (painful to do so as i like it alot)

Any thoughts on this?
Also, how hard is it to transplant an engine as this looks to be the first step for me.

Regards,
Si

 

Ok, the engine I was banking on has gone! I'm now left with sourcing another engine or flogging it! Really, I can't see sorcing another engine as an option as they're valued at about £200 & you can't be sure of the condition. I think I'd be better off selling it & putting the money towards another bike... not what i wanted to do... bugger

 

Next question is how bad the cylinders are. If they're not too bad, then you could get away with a honing and new rings. That shouldn't be too expensive... the honing itself should be relatively cheap; the main cost should be rings and the gasket set. If you need to go oversize, though, it's not the boring that'll cost you, it's the pistons,

 

well i've spoken to some of the lads at work & they've offered to do any machining work that's required. I've just got to open it up & bring the parts into work. Time to drop the engine out then, this'll be interesting as it's the first time i've done anything like this...

 

You may be jumping to conclusions here. Check/adjust valve clearances to be sure you don't have an issue there. RE-DO the compression test; fully charged battery, full throttle, all plugs out. Then do it again "wet." If the cylinders all MATCHED I would be more inclined to think you're just getting a bad reading. Might want to get a second compression gauge and get a "second opinion." Your original description of the problem actually sounds like a carburetion issue or a vacuum leak.

 

I agree with Fitz.

I make test equipment and sell it and have thousands of customers all over the world.

Suspect your method first.
Suspect your test equipment second.
Suspect what you are testing only after you prove to yourself that your method and test equipment are flawless.

 

Ok, I'll give it a second test with a full battery & test with a different gauge. I'll let you know how things got on...