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Engine Wont Catch After Maintenance

  • Thread starter Thread starter MNGATOR
  • Start date Start date
M

MNGATOR

Guest
Hi,

I'm new to this forum (although I have read info here for some time) because I now have my own sob story and need help.

My motorcycle is a 1979 GS850N which I recently purchased. It had a leaky head gasket and was running rough. Did my usual- bought a Clymer's manual for maintenance info and put it to use to work on the above issues.

Took the engine apart down to the head gasket, replaced the gaskets there and worked my way back up. Reassembled the cams as instructed in Clymer's (engine to TDC, exhaust cam arrow 1 pointing correctly, got the correct number of chain links from exhaust cam arrow 2 to intake cam arrow 3 and the tensioners right) so don't think my problem is there.

For the bikes poor running I tore apart the carbs, cleaned them and reassembled with new gaskets and float valves.

After all of this the bike does less than it did before- now it won't even start!

I've done the troubleshooting to find that the plugs are sparking and that the fuel petcock is operating correctly.

What I have found to be odd (especially after cleaning the carbs) is the plugs are dry even though the engine isn't popping. Can the engine possibly not be getting fuel after this work was done? Don't know how this could be but it also seems to be the only answer.

I am getting very frustrated at this and am considering finding a mechanic to get the bike running for me even though I don't want to spend that much more money. Plus, even though I am a novice at this, I have good mechanical skills and my pride wants me to see this project through.

Does anyone out there have some advice? I would appreciate it VERY MUCH!
 
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Plugs dry means that SOMEWHERE its not getting fuel. You've cleaned and rebuilt the carbs, setting everything to spec as per the cleaning tutorial? Check your petcock for flow. WOuld help to have a clear fuel line, but if you unhook the fuel line from the carbs, and turn the petcock on PRIME, fuel should flow freely from it. If its not, replace it, dont rebuild it. The rebuild kits are crap, and you'll only have to replace the petcock once every 15 years or so...oppps see youve already checked the petcock. Hrmm...set the float levels correctly? Install your vaccum line to the petcock? Pull one of the float bowl drain screws. Fuel in the bowls?
 
Have you tried a little fuel in the plugholes before trying to start? If you open the float bowl drain screw on each carb does a lot of fuel come out?
 
I did all of the carb work per the manual. Nothing was complicated because touching the adjustable jets and valves was said to be a big no-no.

As for the petcock- fuel does flow freely when set to prime and it also flows/responds correctly when it receives vacuum.
 
Matchless said:
Have you tried a little fuel in the plugholes before trying to start? If you open the float bowl drain screw on each carb does a lot of fuel come out?
Click to expand...

Haven't tried these yet but definitely will- they sound like good ways to check for fuel flow.

Forgot to mention earlier that I also tried getting it to fire using starter fluid. The engine didn't respond at all. Now doesn't that really take the cake!
 
MNGATOR said:
For the bikes poor running I tore apart the carbs, cleaned them and reassembled with new gaskets and float valves.
Click to expand...

MNGATOR said:
I did all of the carb work per the manual. Nothing was complicated because touching the adjustable jets and valves was said to be a big no-no.
Click to expand...

OK, I am a little confused here. You tore them apart and cleaned them, but did not touch the adjustable jets? The adjustable jets are probably the most critical parts to clean, and they have o-rings behind them that might have gotten damaged by carb cleaner.

Cleaning process: how did you do it? Did you just spray some cleaner at what you could see, or did you dip the carbs? Dipping is far better, especially for cleaning lots of gunk, but it really destroys o-rings.

Adjustable jets: where are they set? Part of every carb refreshing is setting them up to run correctly. With new o-rings, try setting the fuel screw (on the bottom) 1 turn out from lightly seated, and the air screw (on the side) about 1 3/4 turns out from lightly seated. This should get you close enough to be able to start the bike. After it warms up, you can do the fine-tuning.

Valves: I know you said you just went through the top end, but did not specifically mention a valve check/adjustment. Did you just put the shims back where you found them or did you actually check them and make necessary adjustments?

Fuel: you mentioned that the petcock works properly, but after doing carb work and when the float bowls are dry, move the petcock to the PRIME position for a minute or so, then set the choke and start the bike.

Let us know if any of this helps.

.
 
The engine should fire with starting fluid. Sounds like a spark problem. Did you disconnect the coils and forget to reconnect? Are the plug wires going to the proper plugs? Have u checked for spark?
 
My guess is that you don't have the cams in correctly. To test this, have someone hit the starter button while you hold your hand over a carb opening. If it doesn't try to suck your hand in, the cams are in wrong! Ray.
 
rapidray said:
My guess is that you don't have the cams in correctly. To test this, have someone hit the starter button while you hold your hand over a carb opening. If it doesn't try to suck your hand in, the cams are in wrong! Ray.
Click to expand...

This is the one thing that I have deliberately not wanted to consider because the amount of work necessary to go back and fix it would be so great.! Don't know how I could have them in wrong because the critical step is getting the exhaust cam arrow #1 pointed correctly and am nearly certain that it is. Yeah, I know, I said nearly.

The next time that I have time to work on it I plan to check for fuel flow and will now check for cylinder vacuum through the carbs, too. Promise to post what I learn at that time.


On the side- I'd like to express how much I appreciate the advice everyone has volunteered. This is a great site, for a great series of old bikes that have a great bunch of owners!
 
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Stop in at Hoppers and tell Dan or Paul that they need to buy you a round for all the troubles that you've been having!
 
Ok, my latest update- today I unscrewed the float bowl drain screws to find that there is fuel in them. The fuel lines are doing their job.

Also, I removed the air filter box to check for suction through the carbs from cylinder action. There was suction. There was also some air pushed back out of the carbs. Is this normal? My intuition (again, I'm a novice) is that there should be no air being pushed back through the carbs.
 
Assuming that you are getting spark and you did put some fuel in the cylinders and still nothing. I would pull the tappet cover and the plugs and check that the valves are closed when piston is at top dead centre, just to confirm that nothing went wrong when you replaced the cams. Recheck the clearances just in case.
 
call a shop and verify the cam specs and reinstall steps... I've found that the Clymer's manuals are not always the most reliable.
 
Matchless said:
Assuming that you are getting spark and you did put some fuel in the cylinders and still nothing. I would pull the tappet cover and the plugs and check that the valves are closed when piston is at top dead centre, just to confirm that nothing went wrong when you replaced the cams. Recheck the clearances just in case.
Click to expand...
Would I verify that valves are fully open and closed by looking to see that cam lobes are perfectly perpendicular to the shim surfaces? When engine is at TDC of course.

This is all getting me steamed up about the Clymer's manual! Why wouldn't a manual give information on how to verify one's work?
 
I would definitely do a compression check on it as robertbarr recommended in a earlier post. If your cams are off, I would think your compression would also be very low. As a side note, does anyone know if there is interference problem with the valves/pistons if the cam timing is too far off?

I just noticed that you're from Waconia, practically neighbors. I just live up in Richfield.
 
Hee Haw Howdy!

Hee Haw Howdy!

Hi Mr. MNGATOR,

I'm sorry I'm late to the party. I just want to invite you to my little BikeCliff website where you can download a manual for your bike and pick up your mega-welcome. It's good to have another 850 shafty in the room.
icon7.gif



Thank you for your indulgence,

BassCliff
 
Two quick questions: 1) Would performing a compression test tell me what I need to know just as well as taking off the valve cover and inspecting the cams? 2) Is blowback through the carburetors definitely a bad thing or is some of it normal?
 
some backpressure through the carbs is ok....

it just feels that way until you get them synched right, then they will pull mass amounts of vacuum every revolution...

a compression check would be very helpful.. you will have an idea by those numbers if your cams are off or not. if the valves are opening or closing wrong, your numbers will be way off! you would have to be way out of wack for the valves to make piston contact... i would think
 
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