New (to me) Royal Star with low compression

[Piston]

I just picked up a '96 Royal Star with only 19k on it, bike is in great shape except for one thing... I have a pop through the exhaust. I suspected a lean cylinder and was right (on part of it) so off with the carbs for a thurough cleaning. I installed them back on yesterday and dialed everything in, huge difference in performance... but still had the pop. At idle its a rythmic; Pop.... Pop.... Pop.... Pop.... but goes away when revved and comes back again if the rpm is held constant.

 

So today I checked that cylinders carb for any leaks or possible cause for this issue, nothing found. Plenty of fuel there. I went ahead and did a compression test on both right side cylinders and they seem low to me, or at least what the manual says they should be.

 

Cylinder compression test shows 110psi on the front right and 125 on the rear right.

Spark plug was wet on the front so I dried the cylinder out and cleaned the plug... same pop and same compression reading. After this I ran a leakdown test and im just a bit over 20% loss coming out of the exhaust valves!

 

This afternoon I'll pop the valve cover and check the valve clearance but im afraid the damage has been done and the adjustment won't help.

 

My question is, what is a normal compression reading for these engines?

And can the heads come off without pulling the engine?

 

 

Thanks for any help,

[flb_78]

It wouldn't surprise me to find a bit of carbon on the valve or on the valve seat. I don't know how many miles you have put on it yourself, but you may want to run some Seafoam through the gas and take the bike out for a spirited ride.

Edited March 6, 2011 by flb_78

[Piston]

The only ride I've had on it was after the carb rebuild yesterday. When I was cranking it to fill the carbs with fuel I could hear one cylinder not contributing like it should (cranking compression test without gauge).

[Squeeze]

Put some Sea-Foam in the Fuel and ride it for 200 mls like you stole it. Rev it up and hit teh Limiter every now and then after the Motor has fully warmed up

 

 

Check again after you get back.

 

 

I'm quite sure, most of the Problem will be gone when you're back.

[dingy]

To answer your question about what is standard compression for this motor, below is a cut from Royal Star 1996 service manual.

 

Manual says 216 psi. This is base upon 175 rpm cranking speed by starter.

 

Pull all plugs, and crank with throttle held wide open.

 

Gary

 

http://i1007.photobucket.com/albums/af193/gdingy101/RoyalStarSpecs.jpg

[wes0778]

Carb Sync???????

[MikeWa]

Check to see if the plug is wet again. If it is make sure you are getting spark at that cylinder.

Mike

[Piston]

I checked the other 2 cylinders and they are both 125ish as well... so compression isn't the main problem here. Perhaps it will come up once the rings loosen up and valves settle a bit.

 

I decided just to run the ever-loving-piss out of the thing and see if it starts to behave lol. I'll seafoam it and start riding it in the next few weeks to see if there's any change.

 

It does have good spark, fuel and compression and after running for a bit today I did start feeling some heat from that pipe.

Although while doing the testing I emptied the carbs as to not foul the plugs when doing the leakdown/compression test, now I have one that the needle/seat is hung on and floods out.

 

Tomorrow I'll pull the tank/carbs/filter and clean everything again and install a new filter and gas, then see where she's at.

 

Thanks for all the replies!

[TearlessTom]

Not sure about your model but should be the same as my 07.

 

The compression is to be tested with the throttle wide open.

 

It does make a difference. Mine runs like yours around 120 with the throttle closed and 210 with it open.

 

I learned this when I thought I had a bad cylinder too.

 

Fortunately I did not.

[tazmocycle]

the 96-01 was worse about carboning up because of not being ran hot enough. over on the delphi forum we use to do a techron flush, you put 12 oz bottle of techron in gas tank, fill it up with gas, get out on open road and run the piss out of it . keeping the rpm's up high all the time till you are almost out of gas. take it home and change oil and you'll see a lot ofcarbon in it. one guy's 96 with about 31k on it, was b lowing out carbon and sparks out the exhaust after about 45-50 miles, but it was running a lot better after he ran the whole 125 mile trip with us.tew(gene wier on the forum had trouble with he's 98, where a chunk of carbon was holding the valve open. his friend's son looked into the cylinder with a scope camera and seen it. they put some kind of foam in it to desolve it.papa dan's 97 was always blowing out a lot of black smoke when he really got on it. did you spray oil into the cylinder when doing the pressure test? when we use to work on small engines back in high school we always did to get a proper test because of bypass around the ring gaps.

[Piston]

Yep I did a dry test and wet test and both were very close, im confident the rings are ok. I didnt open the throttle though, that would account for the low numbers.

 

This weekend I plan on going through the carbs and tank to clean them out (stupid needle/seat is stuck right now) then take it out for a "Spirited" ride hehe. I talked to the previous owner the other day about it and he mention how he put 2cycle oil in the gas to help coat things while it sat, so im sure there's massive amounts of carbon buildup as a result of that.

 

I too have used Techron for years, GREAT stuff! Everytime I have a car come in with drivability issues as a result of carbon or bad fuel, they get a can of this. Works great on dirty injectors and intake deposits.

 

Can't wait to give a positive post about the weekend ride!

[Piston]

This drama queen just keeps on going and going. I ran 3 tanks through the bike with no real change in performance or the popping so I decided to dive into this thing and find out just what the heck is going on. But before doing that I get a call from my Bro-In-Law (the previous owner) about how the title for the bike is a complete mess and the deal may not happen after all!

 

3 weeks later we now have the title sorted out, its signed and in my hand! So, now I feel alot more comfortable about spending some real diagnostic time on this thing.

 

Long story short, the carbs are the cause of all the issues. I have a set of used ones on the way and will rebuild those and get this girl on the road. After many conversations with bro in law, I found out that these carbs have been an issue for many many years and its never run right.. Funny how that didnt come up when I was BUYING it eh? lol. After further inspection I found that one diaphram/slider was causing a very lean cylinder and an incorrect air bleed jet and "buggered" passage was causing another lean cylinder.

 

I'm ready to get this thing on the road and put some miles behind me (and the problems)! I've already received the new tires for it and have some radio gear on the way.... Time to RIDE

[RandyR]

glad you found the source of the problems and are on your way to being ready for riding season.

[Piston]

Received the carbs from pinwall the other day, opened them up and lightly cleaned them (I knew they worked from the video provided by them) but low and behold... as I went to pull the A/F plugs out, there it sat... nothing but corrosion, the Air/Fuel adjusting needles were seized in the housings and it ran like crap.

 

I was so fed up with messing with this bike I shoved it in the corner and swore to let it rot! Then the wife starts mentioning how my sister and her husband just bought 2 new Harleys and that maybe we should think about doing the same just to get on the road. So, with that in mind I started working on the Star again LOL! Tore every one of the carbs apart (8) and assembled a good set, went over every passage, jet, nook and cranny then bolted them on last night. Its never run so good. Purs like a kitten, its DONE

[Reddog170]

Now there is some motivation for you. Threaten you with a HD (Huge Disappointment) bike and boom off to work you go. Glad to hear you got her going. Shaun