SuperNoob Questions - Issues found; help requested.

[Anonymous]

I spent the morning cleaning and investigating this "new to me" 1981 GS that has problems idling, and I found a few things. My service manual isn't here yet, and I'm anxious to take the bike for a ride. If it's not too much to ask, could someone please answer a few silly questions?

1. There are two 1/4" ID vacuum lines that run from between carbs 1&2 and 2&3 and currently terminate to open air in front of the rear wheel. One of these had found the exhaust and was completely melted shut. The other one had found the chain and was ground to bits. I pulled and replaced both lines, but they are still terminated to atmosphere. From my idiotic "suck and blow" test, I'd have to guess these are fuel system related; perhaps something to do with the float bowl? Can someone tell me what these are for and where they should be plumbed? The bike now idles after replacing the melted shut hose that was between 1&2.

2. Oil level. Here's a real dumb question. I pulled the oil fill cap and see no level mark anywhere nor a dipstick. How do you know if the oil level is proper? How much oil does the crankcase take? How much blowby should be present in the crankcase if the oil fill cap is removed while the engine is running. This bike has a lot; very noticable puffing coming from the oil fill cap.

3. Air box and sensitivity to idle. This bike has a custom air box with an automotive type panel filter in it. The air box is made of aluminum and is nicely fabricated. Does this have a hope of working or should I be looking for a stock replacement airbox?

4. Choke. Is it normal for these bikes to run better with a little choke applied at idle? The engine will run at idle at a steady 1000rpm no choke but runs smoother with a little choke.

5. Idle speed. What is normal? It'll idle at 1000 reliably, but likes 1200-1400 better. I don't know what normal is.

6. The petcock now turns after some WD40 and a wrench. Vacuum applied to the vacuum line on the rear moves an internal mechanism. No gasoline came out of the vacuum line. Should I not worry about the petcock now?

7. Valvetrain noise / light metallic noise. Is this normal at idle? It sounds almost like timing chain slop or perhaps a loose valvetrain. If I had to guess, I'd say it's one cylinder. How much mechanical noise is normal at idle on one of these engines?

Thanks guys, and please forgive the simplicity of these questions. I did use the search feature, and didn't find the answers.

Byron

 

[Anonymous]

Re: SuperNoob Questions - Issues found; help requested.

1. There are two 1/4" ID vacuum lines that run from between carbs 1&2 and 2&3 and currently terminate to open air in front of the rear wheel. One of these had found the exhaust and was completely melted shut. The other one had found the chain and was ground to bits. I pulled and replaced both lines, but they are still terminated to atmosphere. From my idiotic "suck and blow" test, I'd have to guess these are fuel system related; perhaps something to do with the float bowl? Can someone tell me what these are for and where they should be plumbed? The bike now idles after replacing the melted shut hose that was between 1&2.

They are fuel vent lines and can be left as they are but I'd attach new tube and route it away from where it can vent fuel onto hot casing/exhaust/tyres

2. Oil level. Here's a real dumb question. I pulled the oil fill cap and see no level mark anywhere nor a dipstick. How do you know if the oil level is proper? How much oil does the crankcase take? How much blowby should be present in the crankcase if the oil fill cap is removed while the engine is running. This bike has a lot; very noticable puffing coming from the oil fill cap.

If you look in the engine cover that the oil filler cap screws into there is a sight glass that should allow you to see what your oil level is at. Should really be halfway up the glass.

3. Air box and sensitivity to idle. This bike has a custom air box with an automotive type panel filter in it. The air box is made of aluminum and is nicely fabricated. Does this have a hope of working or should I be looking for a stock replacement airbox?

Air boxes are a black art with all kinds of things to equate for such as plenum chambers, jetting etc. All you can do is try and see. If it doesn't work then look for a replacement

4. Choke. Is it normal for these bikes to run better with a little choke applied at idle? The engine will run at idle at a steady 1000rpm no choke but runs smoother with a little choke.

you need to ask a few questions like has the bike been stood for a while amd if so chances are the carbs need cleaning.As a matter of course I'd strip them anyway!

5. Idle speed. What is normal? It'll idle at 1000 reliably, but likes 1200-1400 better. I don't know what normal is.

1,200 would be OK but you can't really set it till you've got your carbies cleaned and the air box sorted. I'd hazard a guess that if you clean the carbs it'll idle a lot smoother at around 1000 to 1,100 mark

6. The petcock now turns after some WD40 and a wrench. Vacuum applied to the vacuum line on the rear moves an internal mechanism. No gasoline came out of the vacuum line. Should I not worry about the petcock now?

Well if it passes gas when you suck on the vacuum line and doesn't when you don't then thats OK.

7. Valvetrain noise / light metallic noise. Is this normal at idle? It sounds almost like timing chain slop or perhaps a loose valvetrain. If I had to guess, I'd say it's one cylinder. How much mechanical noise is normal at idle on one of these engines?

These bikes make some noise, I've two GS850s and they sound like a bag of spanners but go smooth as you like. However if you've only recently got the bike and don't know the history I'd have a good old look at the thing, especially the head and valves!

 

[Anonymous]

Thanks; and more info.

Thanks; and more info.

Thanks! Would it be a bad idea to put some sort of small filter on the fuel vent lines? One of the old lines had spider webs inside. I ran both lines to small plastic fuel filters, which are left open to atmosphere to prevent this.

The mechanical noise was due to low oil level! Yikes. It took a quart of oil to get the bike to register on the site glass. After seeing that, I drained the oil. It smells fine, and looks fine...looks like I might have gotten lucky. I'd say it was 2qts low. Looks like the gray I see out the tailpipe is oil consumption; which probably also explains the crankcase pressure I see when I remove the oil fill cap with the engine running. Looks like she's not as tight as she used to be.

I'll do a leakdown as soon as I find a tester I can connect to this engine. Mine has a different thread. I do know I have compression in all 4; my compression tester is reading about 180psi per cylinder during crank. Is this normal? This is about what it reads on a regular 9:1 automotive engine; so I assume it's not too far off the mark.

Anyway, I'll wait for the manual. I'm pretty sure this crankcase pressure and oil out the exhaust I'm witnessing means the engine is badly worn. Before I proceed, I'd like to hear more on that topic. Then next step I'm taking is a leakdown before I invest energy in other areas.

Thanks again for your help,


Byron

 

[redliner1973]

Make sure your checking that oil on the CENTRESTAND - NOT the sidestand!!!!!

 

[Anonymous]

Oil Level

Oil Level

Yes, on center stand an on level ground. And yes, it was really that low.

 

[gspaul]

Well 180 is very good compression,so any oil consumption may just be down to valve seals, if it's not useing to much dont worry about it.
Fuel vent lines must be vented to atmospher without restriction.
If you need a bit of choke at idle to smooth thing's out it's running a little lean,easy fix by idle circuit adjustment, but check for vacumn leak's between the carb's and head first.
Do a search on both subject's they have been well coverd here.

 

[Anonymous]

Wow, MAGIC!

Wow, MAGIC!

So, after reading a bunch on the forum today, I decided to go out and try adjusting the idle screws using the "highest idle" method.

PAYDIRT! You guys rock.

Not only does the bike idle smoothly at anything above 800rpm now, but starts easy and it's smooth off-idle. As an added bonus, the steam/vapor I noticed that was occasionally puffing out of the filter box is gone, as is most of the rattle/mechanical noise I complained about. It was probably due to misfire and general unsmooth running.

The idle screws were all over the place. #1 was 2 turns out. #2 was all the way in and tight I was fearful of breaking something trying to get it loose; but it finally came. #3 was 4 turns out. #4 was 1/2 turn out. I hit them with a little liquid wrench, pulled them out and antisiezed the threads, then set them all to 1 1/2 turns out, fired the bike, let it warm, dropped the main idle knob down to 1000rpm and started fiddling around.

I went across the carbs hunting for highest idle and readjusting the idle speed about 3 times until I was happy with it. MAN, what a difference! LOL; whomever was monkeying with these screws apparently didn't know about this forum! Holy cow, it was really screwed up.

In any event, I took the bike for a spin just now, and other than fixing the obvious cosmetic issues and giving the valvetrain a once-over (since it has 70K on the ticker, probably a good idea), I think I have a runner!

Oh, and after setting the screws using the highest idle method, the choke now acts like a choke. Before you had to have the choke on to make it idle, and there was an intermediate location it had to be in or the engine would just die.

I almost passed out when I shut it off after taking it for a spin, bumped the start button (with zero throttle and zero choke) and it roared to life and sat there purring at a steady 900 rpm. Holy moses, what a difference!

Also, I found this: http://www.mikuni.com/fs-carburetor.html

A bunch of great mikuni information from the source. This helped a lot; the exploded view diagrams here were nice to look at...since my largest problem was trying to understand what screw is where, with no manual yet.

Anyway, thanks again! I'm up and running; in ONE DAY with your guys help. Bravo!

Byron