Compression problem

[B.B.]

Hey guys looking for a little help on a compression issue. First off I have had the bike running last year but it never ran right. Got it back out and went to working agian. Thought I would start with a compression test. I did not do the compression with the throttle open so I know I got some low readings. For the most part the bike has good compression. It will push ur finger off each cylander. Now the problem. On the compression test they all read about 90 except for the #1 cylander. It would just jump to 30 and 60 and the needle would fall immediatly back down. What does this mean? the other help the pressure. Also all 4 spark plugs were really black on the ends but I know when the bike was running that I kept having problems with the carbs leaking fuel so I figured it was because it was running rich. Any help is greatly appreciated. Going to try and look it over again tommorow. Thanks

[WMarshy]

... On the compression test they all read about 90 except for the #1 cylander. It would just jump to 30 and 60 and the needle would fall immediatly back down. What does this mean?...

It just means the intake or exhaust valve is open and the cylinder isnt holding any pressure... does your tester have a check valve in it?

IDK what kind of pressure tester you are using but all the normal ones I've ever used have a check valve in them to tell you what the maximum compression was and it holds it there... Make sure your battery is healthy, use WOT, and crank it over until the compression gauge stops increasing... You must have a leak or bad gauge because I dont think it will run with 60 psi compression, if it does then it would be really poor! Also, remove the other 3 spark plugs so your starter doesn't work as hard...

[ViperRon]

Remove all plugs from cylinders. First spray some carb cleaner into each cylinder and crank it over several turns to clean or clear any minor rust from cylinders. This can also fog up and clean some valve steems. Let the bike set for a bit to evaporate the carb cleaner out. Make sure the throttle is open and do the test on all cylinders and make sure it spins quick and several times. After that test make sure the bike is level and spray some light oil in each cylinder and redo the test. The light oil will fill recesses in the rings and increase compresssion if they are worn. If the compression does not go up with the oil then your issue with low compression is valves. The problem is not always damage to valves in a bike that has been setting. One valve is always open in these engines and many times after setting can develop a little rust causing the valve to stick open. If you have poor compression after the test pull the valve cover check timming and check the valve shims to make sure there is clearance (valve Adjustment). If all that looks good you will need to remove the head to see what the problem is. Hope this helps.

[TADracer]

If I might ask, why are you doing a compression check on a cold motor that has been sitting for a long time? Will the motor start and if yes, get it heated up well before you do a comppresison check and you might find your readings are right where they are supposed to be. Testing compression on a cold motor is always hit and miss at best.

If after a hot check your compression is still off on your #1 then a leak down test is in order. That can tell you if it is the intake or exhaust valve, rings or a leak at the head gasket.

[B.B.]

Thanks guys for the input. I had removed all the spark plugs and used a few drops of transmission fluid in each cylander waited a bit and blew them out, then checked compression. they spun over quickly and like I shared it would blow your finger off the hole. The bike will fire up using a little ether in the air intake but dies in a few seconds and runs rough. It ran real rough last year and seemed to miss. So this year to start I decided to check compression, I know the readings were low probably because the motor was cold and I didnt hold the throttle open, but my main concern was cylander #1 that would not hold the pressure. The gauge worked fine on the other 3 cylanders but would just bounce on the #1 cylander. What would you guys do next?

Last year I road a total of 10 miles off and on and it kept leaking fuel I would pull the carbs clean them and it would stop. then I would take it down the road and it would start agian. Just trying some different things this year. Any more suggestions would be great. Thanks guys.

[natemoen]

First off, if your carbs are leaking then you need to clean them again and inspect the float needles and seats and replace if needed. If you have late model carbs then also replace the o-ring on the seat.

Then, check your valve clearances and just if necessary.

Then, sync and adjust carbs.

Then, ride it.

[Nick7777]

i know on cars if you put a few drops of oil in the cylinder and do the compression test again and if your number jumps up to your other readings it is rings, and if no change its in the top-end

[B.B.]

got a new issue

Thanks for the help guys now I got a new issue. I went ahead and put the bike back together and pulled the carbs and cleaned them again.

The bike is running after you open up the throttle to get it to crank. Thats the good news.

Now the issues im having- And Yes I have looked at many of the other threads.

1st- The Carbs - I take them off and clean them put them on and open the petcocks and it does great (no leaks) but after I crank the bike and run it for a few minutes and then turn the bike off some times they leak so I tap with screwdriver and it helps some of the time. Ok my Q's. What else do I need to replace or should I get new carbs? Last year I replaced the jets and o-rings and releveled the floats. the floats looked good and seemed to move freely.

2nd- Blue/white smoke - the left exhaust pipe smokes bad. I know that after it has sit since last year that it would smoke but for how long? It is also smoking where the pipe goen into the #1 cylander? And its smoking from the hose that goes from the back of the oil pan up to ur breather?

3rd- the idle - you have to open the throttle all the way to get the bike to crank and then it idles right down(today is the first day to start it) after it ran for a few it seconds it wanted to die. It idled way down and I would have to tweek the throttle a little to keep it running. after about 2 or 3 minutes the bike picked up idle and started idling fast. the rpm gauge is broke but I would say it was around 2500rpms. I would rev the bike up and it would go back to that idle and stayed that way for about 5 minutes before I turned it off and posted this thread. It was smoking really bad by that time.

Any suggestions on what to do next?

I even took a short 30 sec. video of what it was doing and sounded like but not sure how to post it. Its really loud since the bike was idling so high.

Sorry for the long post and thanks for taking the time to read. this is my first bike and bought it last year as it was suppose to just need a throttle cable. I don't mind doing the work just not that up on mechanics.

[natemoen]

We gotta get a baseline here before we really get going.

What carbs do you have (early, late, in-between hybrid carbs)? What jets do you have in the carbs? What did you set the floats to? Are the floats brass or plastic? Exhaust (stock, aftermarket (what kind))? Have you synced the carbs? What work all have you done to the bike?

[B.B.]

What carbs do you have (early, late, in-between hybrid carbs)? What jets do you have in the carbs? What did you set the floats to? Are the floats brass or plastic? Exhaust (stock, aftermarket (what kind))? Have you synced the carbs? What work all have you done to the bike?

Ok so I bought the bike last year from a guy who said it was his dads that got it new in 80. He had not ridden the bike in about a year since the throttle cable broke. To your q's.
-the carbs seem to be old; I did not replace the jets(sorry I know I said I did) but I cleaned them; I replaced the O-rings. I guess the jets are the same as well. The floats are plastic and set them to the hieght stated on the forum just the way the forum said to do it. Exhaust is factory as well.

The work I did last year.
-put starter button in, it was missing
-put new throttle cable
-cleaned the carbs about 20 times - replacing the o-rings, adjusting the hieght of the floats and fixing float arm on #4, adjusted mixture screw to 1 3/4 turns. synched the carbs.
-re-built the petcocks.
-removed rust from tank
-put new spark plugs in
-put new fuel lines in with fuel filters
-new oil filter and oil change
-new gear oil
-rebuilt front brake master cylander
-bought fuse box that was suggested on here and replaced the fuse box and fuses
-put in new K&N air filter
-put new battery on

Not sure what else but that was a pretty good start. I rode the bike about 10miles all of last year and it kept running rough and leaking fuel.

But I am back at it this year and hopefully with all of your help I will have it up and running.

[natemoen]

Ok, first we are going to focus on your carbs and get through that.

You are going to have to pull them again. Verify for sure what carbs you have, cause if you have the hybrid carbs you NEED the rubber plug in the pilot jet tunnel. Good pictures will help. Since you have the plastic floats you need to use the float height of 23mm +/-1mm.

There is something wring with your float and/or float needle/seats. You probably need new needles at least, the viton tip often gets a groove in it and won't seal well.

[WSL91]

It just means the intake or exhaust valve is open and the cylinder isnt holding any pressure... does your tester have a check valve in it?

IDK what kind of pressure tester you are using but all the normal ones I've ever used have a check valve in them to tell you what the maximum compression was and it holds it there... Make sure your battery is healthy, use WOT, and crank it over until the compression gauge stops increasing... You must have a leak or bad gauge because I dont think it will run with 60 psi compression, if it does then it would be really poor! Also, remove the other 3 spark plugs so your starter doesn't work as hard...

It might run on 60 but a motor would not start on 60 without additional help. With Flathead tractor motors 60psi means pull starting with something else. These overhead valve motors should be 125-160 I would think. The other rule of thumb is no more than 10% difference between cylinders. Like the others said check it warmed up, with all plugs removed, and WOT If the motor has run recently then I'd skip the carb cleaner in the cylinder. I'd probably not spend much $$ on it until the source of poor compression is identified since there is smoke involved as well. Could be stuck rings, maybe.

[natemoen]

Rings can clean up and reseat. He can get it to run right now, let's focus on that! We will redo the compression later.

[Rasputin]

Rings can clean up and reseat. He can get it to run right now, let's focus on that! We will redo the compression later.

I agree. Older carbs and newer (plastic) floats means there is something that has been changed that we do not yet know. We need to know what he is working with before any solid advice can be given. Appears to be older carbs does not quite cut it. Do a search on the carb differences and maybe take some pictures of what you have so we can respond appropriately.

[DGXSER]

I think he is just saying the carbs are original to the bike, not new. Reality is they do not sell them new anyway (not at a price less than two bikes anyway). You keep telling us you cleaned the carbs, and the floats are leaking. You replaced the o-ring, but did you replace the float needle valve and seat? Those are the parts that cause the leaks. When I work on a set of carbs I always replace the float valves and seats.

The blue white smoke may well be a result of your leaking float valves. If your getting raw fuel into the cylinder and it i s getting pushed through the cylinder into the exhaust, that fuel will burn off and smoke int he exhaust even after you turn the bike off. If a cylinder or two is getting way to rich you will get that smoke.

As to the idle (You do know about the choke/enrichment, yes? You did clean out the enrichment jets in the bowls, yes? These bikes need the extra fuel to start and run right till warmed up even in 90 degree weather when first started. FI your not getting the proper feed from the enrichment circuit, will need fuel to start and try to run. If your saying the idel goes low and then climbs after the bike is running and warmed up, that will be solved by a good carb synch when you have the other issues corrected.