Is this worth trying to fix? 1981 XJ 750 Seca

I bought this bike in Sept 2006 for $800. It is very clean, and I like the looks of the bike, but when I had the bike taken in for some hard starting issues, it turns out that compression is in the 55-65 range on all 4 cylinders.

Bike has now sat in garage since April '07.

I am not motorcycle repair literate by any means, but am willing to try to learn, if this bike is worth it. I cannot afford to sink alot of $$ into it, but I have the time, and the bike is just sitting there waiting.

My question: is fixing the bike worth the $$ spent to do so?

 

I think you should first try to find out what causes this compression reading.

Maybe your valves aren't closing well enough?
Piston rings wear?
head gasket?

Than determen how much time, effort and money you can/want to spend for it.

 

Take the "easy" way, buy a motor for $200, install. Now you got spare parts, something to play with, and something to rebuild, or sell.

 

A new engine......any recommendations on where to start looking? Ebay? Reputable dealers? Repair books, if I need to buy in pieces?

 

What do you mean by hard starting? Are you sure you checked the compression correctly.... if your only getting 55 psi I doubt it would start at all.

 

The hard starting was initially thought to be due to bad idle settings....previous owner had removed air filter, 'tweaked' idle, etc.. Whenever I tried to start the bike, I had to choke it a while before it would start....and then I had to keep some choke on, even when it did start because it idled rough.

SO...then I took to shop to have it fixed the right way. I took it to (Cycle Search, Int. in Delaware, OH) and they wanted to do compression check before working through the idle issues and before I invested too much money. They determined compression was in 55-65 range (not sure how they performed test). They too, were surprised the bike would even start, at all. It only sporadically started, now it wont even do that.

They mentioned that fixing might be around $1K, and that because bike so old, there may well be other issues that come up.

So, long story short, I have a bike with low compression, teasing me by sitting in the garage, and gas prices are high.

 

I'd try to run it once more before giving up! Get a can of PB Blaster or B-12 Chemtool, or something stronger than WD-40, spray it in the plug holes, roll the engine over a few times, add a spoonful of ATF and let sit overnite. Re-do compression test with battery on boost, throttle wide open, and plugs out. (ignition off, cross the solenoid)

Then run it one more time. Even if you have to push start it.

I bought a partly stripped bike with a complete motor from a salvage yard for $200, came with rims and brakes too. E-Bay is useless, unless it's in driving distance.

 

DONT EVER TRUST anyone when they talk about YOUR bike.
Test your OWN compression.
They might have told you all that info so they DID NOT HAVE TO work on your bike.
Depending on the issue(if indeed low compression) it might be worth fixing, or a used one off ebay might do the trick too.

 

Sounds like the shop NEEDS money if they are saying $1k.... that's pricey.. you could find a donor or a great running bike for that much

 

I'd go the flea-bay route. I scored a complete engine delivered for $200 in prime condition. You can also hit the wreckers or the want-ads or Craig's List.

 

Ok...bought a can of PB-Blaster

I'm a newbie, with little motorcycle mechanical knowledge, so sorry for the lame questions. but I like to measure twice, cut once.

Ok, so here's what I plan to do:

1. spray PB-Blaster in the plug holes (having removed the spark plugs)
2. roll the engine over a few times (plugs back in, ignition on)
3. add a spoonful of ATF and let sit overnite (removed plugs, ATF in all plug holes)
4. Re-do compression test with battery on boost, throttle wide open, and plugs out. (ignition off, cross the solenoid)

This may seem odd, but how do I re-do the compression test? Can I do it myself at home? How to set battery on to boost? Battery Charger? And help me with the solenoid?? Reference or picture anyone can point me towards?

I am trying to learn. Thanks for the patience.

Also, which repair manual might be the wisest investment, as it seems that there are a few choices out there for reference?

 

Sounds like a plan.
I would only suggest you use a shot of Marvel Mystery Oil in your holes. Engines love it! ATF would work just, in my opinion, not as well.
To redo your compression test, disconnect the TCI/CDI from the main harness (little black box under the left side cover) and you can push the starting button. Spin the engine over a few times to clear the excess oil (it will fling it far and wide, look out!) and then test.
ENSURE you hold the throttle full open when testing or remove the carbs completely.
Boost is fine on a battery so long as you apply it only when you are about to spin the engine and you turn it off when you're not.
Wise investments... the least expensive (and the one I cut my teeth on and still use 'till this very day) is the Haynes. The BEST is of course the factory manual ($60 or so from Chacal, cheaper than the dealer).
Got more questions, throw them out here. We'll get you moving along.

 

ok....put in some PB Blaster, tried to re-fire......I think the starter clutch/switch is going bad......any ideas on how to start without the ignition button.....tried to push start it with wife on bike, me pushing.....I'm sure neighbors had a good laugh......unfortunately, I couldnt get enough speed going to generate rpm's.......

battery seems to be losing charge quickly since trying.......

 

Ok, from the top.
What makes you think the starting clutch/switch is bad?
It is possible to start without the ignition button but that is more work than you need right now. You can try to jump the solenoid. Look up the how-to on Gamuru's How-To thread.
Another point I'll make is that a GOOD battery is a must to start these things. If your battery is on it's last legs (or none at all), you aren't going to get it started, no matter how hard you try.
Source a new battery and get it properly serviced and installed.
Then try to turn it over.

 

I'd charge the Battery.
Put a half-ounce of Marvel Mystery Oil in the Spark Plug Holes
Rotate the engine over by hand a few times.
Rotate the engine over a few times for 10 seconds on the starter motor.

Charge the Battery; again.
Do a Compression Test with WIDE OPEN Throttles.

If the Throttles weren't WIDE Open when you did the last test; the valuse are going to be very LOW ... like the ones you got.

Re-Test that Compression and get back to us with the NEW Numbers!

 

The reason that I think the starter clutch/cable may be going bad is that after a few seconds of pushing on the starer button, the battery starts to go "click, click, click, click....." then I let go of the button, and when I press it again, it may/may not actually work.....

what i have found that seems to be a slight remedy is to turn the engine switch to OFF then back to ON....this seems to somehow "reset " the starter button.....or maybe it is pure coincidence.....

Anyhow....I will try the battery route first, and the oil in the plug holes.....

I will need to figure out how to do compression testing......I dont have any tools for getting numbers, but I'll see what I can come with......

I'll keep ya posted....

 

ok....thanks for ALL of the help so far!!! This forum has been a blessing for a newbie like me!!!

ok...so here we go...i took all of the advice, and here's the following:

1) recharged the battery (had to top off with water)
2) pulled plugs out
3) injected 1/2 teaspoon Marvel Mystery Oil into each plug holes (used syringe dropper for this)
4) let sit approx 5-10 minutes
5) attached compression gauge (rented from Advanced Auto Parts) to #1
6) throttle WIDE open
7) pressed starter button for 5 seconds (used seconds hand on watch)
8) repeated steps 5-7 for the other cylinders

Here are the NEW numbers:

Cylinder #1: 90
Cylinder #2: 95
Cylinder #3: 110
Cylinder #4: 115

So, a few questions:

Any chance that a new battery would help?
Did I add enough Marvel oil?
Do I need to let it sit longer?

Help?????

 

I will assume you turned the motor over by hand as Rick suggested to get the Mystery Oil worked into the rings.
Your new numbers will most probably all even out when you run the engine through a few heat cycles. Things look promising.
A new battery would be a swell idea. If you used tap water to top your current battery off, you will need a new one. Only use distilled water in batteries. This may also be part of your starting problem.
So far, you're off to a good start. Your compression numbers aren't the greatest but offer enough compression to start the beast.
Rick will chime in shortly with further details.
Good on ya bud, you're on your way!

 

ok.....I retested the compression.

Here are the new results:

Cylinder #1: 100
Cylinder #2: 100
Cylinder #3: 100
Cylinder #4: 100

The bike doesnt want to start.....

Any recommendations as to where to go from here?

I think I need to get a new battery (I will try to do this this coming week)....I topped off the current battery with tap water....I'm such a rookie....lol

 

The bike doesnt want to start.....although I am happier that the compression is at 100....lol

Any recommendations as to where to go from here?

 

Ok,
Do you have spark?
Is there fuel in the carbs?
Pull your spark plugs after you attempt to start and check for fuel on them. If they are slightly wet, you have fuel flow.
Now check for spark. Remove all spark plugs, plug them back into the caps, lay them on the valve cover (grounding them in the process) and turn it over. Sparks?
Check for 12V at the coil connectors and verify you have 12V at the ignition fuse. Still running the OEM fuse block? Yank that sucker out and heave it in the trash. Replace it with a modern blade fuse block or water proof fuse holder assortment.
Alternator brushes the correct length? Pull the alternator cover (left side of the bike, round cover, three allen bolts). The brushes need to be at least 11mm long. There should be a wear line on them if they are stockers. Replace any that are too short. They mess up the electrical system and cause all sorts of problems.
That ought to do you for now. Let us know what you find.

 

How would one turn the engine over by hand?

 

I put my bike in 5 TH gear on center stand, and rotated the rear wheel by hand in the correct direction. It's not that hard. 1 ST gear would be hard!

 

BTW if you pull your plugs out and let them set on the valve cover to check spark make sure they do not fall by the hole where they go. I almost started myself on fire that way here a year ago. Flames shot out my cylinder about 5 ft!! Kinda cool but scared the s$%t out of me! And I was in my shed, lucky I didn't start that on fire also. Just thought I would share my close call with you all!