New Jota owner - puzzling compression readings

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Hi All

I am new to Laverda Jotas. Just bought a 1982 series 2 180, very tidy but it seems to eat plugs - fouling them in a few miles - all sooty and black.  It starts ok, needs 3/4 choke, but did idle ok when warmed up.

I put my compression tester on and came up with 75-75-75 (about 100 short of expectation). I tried my T160 and the compression tester came up with 50's. This bike runs fine (although a little rich) - which also seems very low for a 9:1 compression ratio bike.

Have I bought a dud or is my compression tester u/s?

Now I seem to have a problem with the thread in the centre pot, this feels very bad- I guess a top end strip down is a really big job.

Any useful advice?

Regards
Glenn
 
Glenn, it seems that absolute values on compression testers can be misleading.
On the plus side the values are equal, but that may just mean all three are down.
What are your valve clearances? If they are really tight it may be holding valves open.

What exhaust system is on it, standard?
What brassware sizes are in the carbs?
Air filtration?

Sounds like it is running rich but may benefit from a carb strip and clean. Check sizes, wear and general condition. This is easier than pulling the head off.

You mean the thread on the spark plug? I have seen helicoils being fitted to a spark plug hole without stripping the engine but I woudn't recommend it.
What mileage is on it?
 
Glen,

If you are getting 75 on the Jota and 50 on the T160, then it sounds like your tester is shagged (and hopefully, if it is, the 75-75-75 means your Jota pistons/rings/liners are in good fettle  ;) ).

Taking the head off is not as hard as it seems and I would be inclined to take the motor out (vs trying to bend studs around the frame). It is NOT a dificult job (unless you have a gammy shoulder like me  :( )

Fixing a stripped plug hole is not an issue and quite a common problem caused by heavy handed use of a socket wrench  :(

Pete
 
It is running standard exhaust, has 38k on the clock (MOTs seem to support this being about right). I need to go investigate carbs etc.

What plugs should it be running - the seller told me B8ES, the books say B8ES (3CL) and B9ES(Jota). I tried both, but only for 30 miles (B8) and 10 miles (B9).

Glenn
 
Glenn,

It is not unusual for Laverda triples to be fitted with jets that are miles too big. Check mains (145 is too big, 120 or 118 nearer the mark). For idle jets, 65 is too big and 50 or 55 nearer the mark. Dells need a knowledgeable hand and a set of decent vacuum gauges is really important.

Bin the compression tester, gets some new jets and retune the carbs. Reckon you may be surprised by the resukts  :D

B8Es is fine.

Pete
 
And while you're at it, replace the needle jets and needles.  These wear quickly and cause the the consumption to soar!  Inspect the jets closely, you'll probably find them distinctly worn oval.

AB265 jets and K1 needles, centre notch.....

piet
 
Hi Glenn, the comp readings sound suspiciously uniform to me, it's unusual in my experience to get them all exactly matching. However, if your comp tester is OK then the low compression reading could be down to incorrect valve timing.
All these things can be resolved one way or another so keep filling in the details and I'm sure the experts on here will identify the problem for you.
 
Glenn - B8ES is fine.  The colder B9ES isn't needed unless you're caning it on a track or running in really hot climate.

An obvious question....but I assume you had the throttle wide open when checking compression?

Check air filter (if there is one) & valve clearances - 8 thou inlet; 10 thou exhaust.  Another quick check is to see if your choke plungers are sealing properly - one screw on top of the carb body holds them.  The rubber washer gets hard with age.  Apparently a quick boil in water helps as a temporary fix!  Make sure there's enough cable travel to let them seat too.

Then you're into a more detailed look at the carbs...mixture setting is critical, as is float height.  Float needle valves can cause flooding too.

Good luck
 
Thanks all, some useful information here. The compressions were not exactyl the same, I was rounding them, they were 72-75-72

I will work thruogh the list.

Regards
Glenn
 
Step away from the compression tester Sir.  Those things are evil on a stick and not to be trusted.

If the choke plunger rubbers look a bit rough, take them off and boil them in water for a few minutes to get rid of the ridges and obviously check for cable slack when you refit them.  If your plugs are oily there may be a problem in the engine, but I bet the problem is in the carbs somewhere.

Also check if the filter is OK.  The DPO may have fitted an oiled Unifilter.  If he has remove it and rinse it out in lots of white spirit cos they're nearly always over oiled and VERY restrictive.  The dry foam will catch most of the crap.

[EDIT]

Check air filter (if there is one) & valve clearances - 8 thou inlet; 10 thou exhaust.  Another quick check is to see if your choke plungers are sealing properly - one screw on top of the carb body holds them.  The rubber washer gets hard with age.  Apparently a quick boil in water helps as a temporary fix!  Make sure there's enough cable travel to let them seat too.
Click to expand...

Woops, wot he said! :D
 
Oz Laverda Black engine tested at 250 psi on each cylinder when being spun over on the remote starter which spins at 1,500 rpm
I don't trust Compression Gauges either, readings are too high


 
190psi on all three on my 180.  I'm not going anywhere near the 120...
 
Post #2
Pete, there is no need to bend studs to get the head off in situ, which I never do any way,If you are removeing a triples head with the motor in situ, the studs do have to be removed, by the normal double nut method, most of them can then be extracted, but the ones that cant do not need to be bent.remove the ignition coils (BTZ) or coils module (CDI) and lift the head with the "difficult" studs poking through it, when you have raised it a tad, and tilted it to the left a tad, the remaing studs will come out.A second pair of hands will be desirable.

Bend the studs !!!, who was the clown who first mooted that in about 1973? I even heard of a frame with holes drilled in it, for stud removal.

I realy dont get this head off in situ method, if you are going to do it, the only extra work (that is saved) for an engine out job is the engine bolts themselves, the drive chain, wireing harness and oil cooler pipes.When on the bench all is so much easier to get at.

CLEM
 
CLEMTOG said:
Post #2

I realy dont get this head off in situ method, if you are going to do it, the only extra work (that is saved) for an engine out job is the engine bolts themselves, the drive chain, wireing harness and oil cooler pipes.When on the bench all is so much easier to get at.

CLEM
Click to expand...

You forgot the chiropractor
 
I would first check the Cams are timed correctly. Very often it happens that during replacing the cam-Chain, one cam gets turned 1 tooth to much or to less. Can cause bad compression readings, too, and sooty plugs...
 
i'm with pete, the guage is off...bin it
good news that the readings are fairly close to one another
a leak down is much more accurate way to judge the condition of the engine's valves and rings

choke plungers and jetting are the likely culprits of short plug life
once that is sorted you can check cam timing marks
and if the cover is off check valve clearances

you can run a tap in the plug hole to clean up the threads in situ
smear it well with grease to hold any chips
use an antiseize compound on the steel plug threads anytime they are installed in alloi cylinder heads
 
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