Non Starter

Hi Folks
New to this site today. I have an '81 bike that's been standing for 5/6 years and just trying to get it fired up. Repaired the petcock and fitted new rubber inlet manifolds as others were cracked. Have good fuel at the carbs but plugs still remain dry. Next thing is to check the compression....am I right in thinking these plugs are 12mm diameter? as just about to order an adaptor for my tester.
I guess that if there is not enough "suck and puff" then the engine could be due for a rebuild.......what are the expected compression readings?

 

Sorry........the bike's an XJ550 seca!

 

We will not assume you tore the carbs down and correctly cleaned them and wet set the floats and did a bench sync. By any chance did you do all that?
You will also need to check valve clearances.
Before you ride please check your date codes on the brake hoses and tires, and look at your back brake shoes to make sure they are not coming apart. Be sure to put them on your list to replace since they are 30 years old anyway.
MN

 

Yep, cleaned the carbs but not synced and not checked the valve clearances as I don't really think these would change if the bike has been stood idle. I have no intention of riding the bike as the priority is really just to check the mechanics of the machine to establish whether it's worth restoring at the moment.

 

Correct. The 550s take a 12mm plug; NGK D8EA recommended.

Compression spec is 100psi (7.0 kg/cm2) minimum; 121psi (8.5 kg/cm2) "standard" and 135psi (9.5 kg/cm2) maximum.

Variance between cylinders 14psi (1 kg/cm2) max.

They want you to warm up the motor first; since you obviously can't then you may see slightly lower readings.

Out of spec valves can throw off your compression numbers. (The 550R has relatively hot cams.)

I usually see around 125~127psi on my '81 with 27K miles; and my '83 produced right at 130~132psi the last time I checked it which would have been at around 15K miles.

Is the bike really a "Seca" or is it an XJ550R? The "world market" 550R had dual front discs and a larger rear brake with "swirly" wheels and an oil cooler. The USA-market "550 Seca" had straight-spoked (RD?) wheels, a single front disc and smaller rear brake; and no oil cooler. We were blessed with the goofy cafe fairing for two years.

How many miles on this specimen? The reason everyone is on about valve clearances is because they were often neglected on these bikes, and need to be checked every 5000 miles after the initial check at 3K. They tend to tighten quite a bit in the early life of the motor so if neglected can easily cause problems as the miles start to stack up.

 

Thanks for your info. and advice. The bike has twin discs, oil cooler and swirly wheels so I guess it's a 550R? What is the difference between the Seca and the "R"? Over here in UK most people refer to this as a Seca and the Maxim is the customised version with rolled seat etc..
The bike is showing 55k and I bought it back in the 90s and used it quite a bit then laid it up.......but I've never had the rocker covers off to check the top end clearences as the bike used to run well.

 

Your first post states that you have gas to the carbs but yet the plugs are dry. This is an indication that the carbs are plugged with dried gas and green goo in the jets and the enrichment tubes that go down into the float bowl wells that the enrichment jet is. DRY PLUGS = PLUGGED UP CARBS.
Best advise is to pull those carbs back off and if you have access to spray carb cleaner over there would be to blow carb cleaner through every passage in those carbs. Then read chacals Church of Clean and Ricks old school carb cleaning, before putting them back togeather again.

Good Luck
MN

 

I did blow through the jets with Wynns Carb Cleaner (that's our local brew) when they were off so I think I'll have to pull them apart again. I have gone through the brilliant "The Church of Clean" a few days back........in an ideal world I would love to have the time to follow all those steps. Really appreciate your help and comments, many thanks.

 

It's a "Seca" all right, but in Europe wasn't marketed as such; ours actually had "550 Seca" badges, I don't think yours has.

You REALLY NEED to have a look at the valve clearances.

If you get back wonky compression readings, pop the cover and check the clearances.

Then after you've replaced most likely every shim, re-check your compression.

As for actually getting it running right, it will take getting the valves in spec, the carbs religiously clean, the float levels precisely "wet-set" and a good accurate running vacuum sync with YICS blocked.

Anything less will simply frustrate you to no end. You make your own luck.

Mikuni teardown: http://xjbikes.com/Forums/viewtopic/t=31061.html

Valve clearances: http://xjbikes.com/Forums/viewtopic/t=14827.html

 

Wow, a brilliant slide show on the valve clearances, you've talked me into doing them now! A great help, thanks again

 

Anytime. You might need Part Deux: http://xjbikes.com/Forums/viewtopic/t=29209.html

 

Well, compression ranges from 50psi to 150 across the 4 cylinders.....though I'm guessing that the one with 50psi has probably got a sticking compression ring.
Exhaust valve clearances are all .10 and inlets are .05 on three and .00 on the other!
Looks like this has not been touched for a long time. Just taken off the carbs again for a more thorough clean through......jets out etc.....

 

With valve clearances like that it could be just the tight clearances.

 

+1 to that assessment. The one you list at .00 is probably more like a negative clearance since you can't measure that but the tappet is always pushing it down so the valve is always slightly open=no compression pressure.

You can always do a wet test to determine if the rings are the issue, but I would start with putting those valves in spec.

 

Just removed the shims..........is it ok to re-use a couple of shims on other valve buckets? as they are the size that's required, or is it best to replace all with new?

 

Personally, I replace. But I also want and expect to be able to pull 10Krpm any time I feel like it without worry.

EVERYONE ELSE on the planet with an XJ just swaps shims. Go for it.

I'm used to being considered "eccentric."

 

Really Fitz, I never thought of you as "eccentric" just through!!

And hello from Ontario Canada BikerBill!

 

Hi Ground-Hugger thanks for the welcome and thanks again Fitz for the info.
Spent a cold winter back in the 80s in London, Ontario........plan to return in the summer one day!

 

Well...... valve clearences done, carbs cleaned, now starting on the button! I guess I need now to balance the carbs, are there any more "how to do..." sections on this forum please.