New GS425 owner with no fuel in one cyl.

[jimfj]

Hello all,

I just brought my first GS home yesterday!!!!! 1979 425.

She runs but there in lies the first problem.

I have discovered through reading and riding the bike that at idle, the left cylinder does not fire.(Exhaust pipe cold). No power in first taking off from a dead stop. When the rpms hit about 2000-2500 the cylinder kicks in and she runs great.

What I know----

Spark is good. Nice and strong

No air leaks....I sprayed starting fluid everywhere that this could be a problem and no change in rpm whatsoever.

No vacum leaks....starting fluid again.

WHen I remove the vacum line that goes from the engine to the fuel petcock, and spray starting fluid in the fitting the second cylinder kicks in immediately-rpms go up and (Pipe gets hot).

I belive that the carbs very close to synched. I runs great and makes alot of power over 2000 rpm.

The only thing out of the ordinary that has happened in addition to the no go cylinder is that the rpms have stayed at 3000 after running/riding awhile. Happened twice. I have read that this is the classic sign of an air leak, but I can't find a thing.

Please help me with where to start. Proud to be a first time GS owner:-D

Jim

[Nessism]

The spraying starter fluid trick to find air leaks is unreliable. You should take the carbs apart, make sure all the passages are clear and the o-rings are sealing, and replace the large o-ring sealing the carb boots to the head. The pilot jets are killer small and all it takes is a very small piece of crud to plug it...which will distroy your idle on that cylinder.

[jimfj]

Nessism,

Thank you for the advice. I pulled the carbs and the pilot jet was clogged with crud, (side that was dead at idle).
I cleaned everything else very well, hopefully it won't plug up again for awhile.
Do you use an inline fuel filter? My bike doesn't have one and after having to pull the carbs it seems like a good idea?

Thanks again,

Jim

[Nessism]

You can run a filter but it must be the type that is intended for a gravity feed fuel system - such as for a lawn mower. Automotive filters will not work - they will act as a restriction. Better than a filter is clean your tank of any crud that can flow down into the carbs. Check the Por-15 website for tank cleaning products.

Good luck.

[brad81987]

Nessism,

Thank you for the advice. I pulled the carbs and the pilot jet was clogged with crud, (side that was dead at idle).
I cleaned everything else very well, hopefully it won't plug up again for awhile.
Do you use an inline fuel filter? My bike doesn't have one and after having to pull the carbs it seems like a good idea?

Thanks again,

Jim

I hate to be a new guy bringing up an old thread, but I'm having the exact same problem with my 425. Did cleaning the carbs take care of your problem? Mine blows smoke out of both cylinder when starting cold with the choke on, but after it warms up a little and I let it sit idle, the left pipe is barely warm to the touch. It seems to want to bog a bit when starting out but once it gets moving, there is more power. I don't have a tach cable right now so i can't comment on what RPM it seems to get going at. I have partially disassembled the carbs and cleaned them but not thoroughly.

Thanks

[spyug]

With issues of this type it usually all comes down to how clean the carbs are and how airtight ( i.e. o-rings).

If the bike is new to you or you know it has sat for a while drain the old gas and fill with fresh. Top up with half a tank of Seafoam and run it through. Repeat. That likely will get most but usually not all the varnish and gunk out of the carbs and get you going for a while. Sooner, rather than later, you should pull and dip the carbs in cleaner and replace all the o-rings.

For newbies, cleaning and rebuilding carbs is a major chore and very intimidating but it really isn't. Review the carb rebuild tutorial get your o-rings from Mr. Barr and have at it. The first time it may take a few hours but the more you do it the easier (and faster) it becomes.

Now clean em up and get ready to ride.

Cheers,
Spyug.

[Nessism]

Gas turns to varnish and plugs jets (particularly pilot jets that are so small) in less than one year in some cases. O-rings in the carbs dry out and get hard with age – figure on approximately 15-20 years of life.

If the bike is running poorly and the carbs need to be cleaned, it’s best to reset the clock regarding your O-rings to zero by replacing them. You will not have to think about them for another 20 years. If you don’t change them you might experience carbs problems again fairly soon. It's a lot easier to just to the job right the first time in my opinion.

[sark]

Sorry, which o-rings exactly are we speaking of?

[brad81987]

With issues of this type it usually all comes down to how clean the carbs are and how airtight ( i.e. o-rings).

If the bike is new to you or you know it has sat for a while drain the old gas and fill with fresh. Top up with half a tank of Seafoam and run it through. Repeat. That likely will get most but usually not all the varnish and gunk out of the carbs and get you going for a while. Sooner, rather than later, you should pull and dip the carbs in cleaner and replace all the o-rings.

For newbies, cleaning and rebuilding carbs is a major chore and very intimidating but it really isn't. Review the carb rebuild tutorial get your o-rings from Mr. Barr and have at it. The first time it may take a few hours but the more you do it the easier (and faster) it becomes.

Now clean em up and get ready to ride.

Cheers,
Spyug.

I'm assuming then the o-rings Rob Barr sells will fit a 425? I know he carries the intake boot rings but i wasn't sure if the carb kits would work. The 425 uses the same CV carbs as its big brothers, correct?

[Nessism]

Intake O-rings for sure and the ones in the carb as well. The bike might run okay, for a while, without changing all the internal carb O-rings. But then again, it might start to act up right away. Pay me now, or pay me later.

[brad81987]

So the ones he sells for the 4 cylinders will work? (Obviously with a lot of left overs)

[jimfj]

Brad,

Yes, the carb cleaning solved my problem. I replaced the O rings at the carb boots. One of the pilot jets was completely clogged so no fuel at ilde=dead cylinder=cold pipe.

My engine runs like a sewing machine now but it took a little while to get it that way. Here is a laundry list of what I did.
-New plugs
-Took tank off and cleaned as well as pulled petcock off and cleaned screen there. (no rust to speak of)
-Checked all fuel and vacum lines
-Pulled carbs and cleaned --I only removed bottom bowl and cleaned jets-everything else in the carbs looked okay.
_Checked and reset the timing-one side(cylinder) was off.
_Checked valve clearances. This took some time and a few tools. The end result was that I had almost no clearance in 3 of the 4 valves. My bike has 16K on it and I doubt it was done for a good long while.
-synched the carbs. I made my own manometer and gave it try. Its probably not perfect but much improved.

The one thing you will notice by doing all these things yourself is the feel of the engine. You will know when something is right or wrong. Running seafoam in the gas I believe helps keep things clean. I was riding/testing the bike all the while these things were being done so I had a benchmark for poor and better performance. Running the engine on a regular basis also helps to keep things working smoothly.

You have to keep in mind that these are 29 year old motorcycles and they need the "love" once in a while.

PM me if you need anything. I also have a good source on 425 parts.

Cheers,

Jim