Hard to start and won't idle....

[JShapiro]

I just bought my first bike, a '78 GS 400. Immediately loaded it up and drove it from New Hampshire to Maine for a few weeks on a tour. Now I'm in midcoast Maine and the bike is having problems.

It's hard to get started and won't hold an idle no matter how warmed up it is. The spark plugs, new a few hundred miles ago, already have a light coating on them. Once it starts moving it seems to run fine but at higher speeds the tach fluctuates wildly (possibly a different problem?).

If I turn up the idle speed screw, and then rev the bike, it will stay at high rpms after I let off the throttle. It backfires sometimes while it's stationary and I'm messing with the thottle.

At this point I'm stranded in my tour and am hoping to try and fix it myself. After reading some of the stuff on BikeCliff's website, I think I'll try to fix potential air leaks before I do anything else. Also, maybe I should try to replace the petcock?

The guy I bought it from synched and cleaned the carbs very recently and replaced the intake manifold o-rings. Could he have missed something? Should I try to clean them again?

 

[JShapiro]

First thing I was thinking to try is putting weatherstripping around the air intake but I'm not really sure about some parts of that. I looked at the photos on BikeCliff's website but am still a bit confused since it's a different setup on my 2-cylinder. Is the goal of the weatherstripping to only let in air from the cowl on top of the intake lid? Is that an exactly calibrated amount of air that comes in so any other possible infiltration point on the intake should be weather-stripped?

Also thinking about replacing carb boots, but they look really fresh and feel sorta flexy when I touch them. Is this something that I can tell w/out taking them off or should I remove them to really know what condition they're in?

Thanks for reading this very long post and for any advice!

 

[Steve]

Hard to start and won't idle....
The guy I bought it from synched and cleaned the carbs very recently and replaced the intake manifold o-rings. Could he have missed something? Should I try to clean them again?

Unless you were there to see him clean and sync the carbs, assume that it didn't happen.

Another very common cause of hard starting is VALVE ADJUSTMENT, or, rather, the lack thereof.

A hanging idle (rev the engine and it stays up there) is typical of a lean mixture, so the mixture screws might be mis-adjusted or the pilot circuit needs to be cleaned (see, we're back to carb cleaning).

.

 

[Steve]

Thanks for reading this very long post and for any advice!

Why does everyone think that anything over about 25 words is a "long post"?

You did a fine job of describing your problem, including a few other details.

That only prevents us from asking other questions for clarification.

.

 

[JShapiro]

Unless you were there to see him clean and sync the carbs, assume that it didn't happen.

I did in fact see him synch the carbs but not clean them.

He told me he had just cleaned the carbs when I bought it. I took it home and it ran ok, but quickly started running badly. His guess was that I had fouled it up by leaving the choke on too long. I brought it back to him and watched him synch the carbs and left. Picked it up the next day and he said he had cleaned the carbs again, found nothing, and put in new o-rings. He showed me the old o-rings to prove it. He also put in another set of new plugs as the first new set, installed right before I bought it, were dirty already.

It ran great again. I started out on my tour and w/in a week it had started running very badly again. Could it still be a dirty carb issue if it ran great very recently? I looked in the tank and it looks very clean so I'm assuming that nothing is dropping into the carbs from the tank.

 

[cowboyup3371]

If he did it overnight then they aren't that clean. I would bet he just sprayed cleaner in there and maybe swapped orings.

 

[BassCliff]

Hi,

All of the items on the maintenance lists in your "mega-welcome" must be addressed (by YOU, to be sure they are done correctly) in order to have a reliable and trouble-free machine. Skipping steps or taking short cuts will leave you stranded on the side of the road at best, injured or severely killed at worst. You have a 30 year old motorcycle that needs 20 years worth of maintenance. Do it all properly and both you and your bike will be insanely happy.


Thank you for your indulgence,

BassCliff

 

[tom203]

You just learned that you should have been more intimate with your new-to-you bike before venturing on trip far from home. Lots of stuff loosens up as bike returns to road. Many brand new bike owners have had breakdowns as well.If you have to ride it, best advice is to pick up 4 correct plugs and get used to swapping them out as you return home. You could block off vacuum petcock and run on prime, but lots of fixes are more difficult at side of road.

 

[Guest]

Everything you're saying absolutely reeks of everything Steve said above...

Valve adjustments, proper carb cleaning, etc.

While you probably can't do a proper carb cleaning out on the road, you maybe be able to do a valve check, if not a proper adjustment.

All you need is a big cable tie...

 

[JShapiro]

Everything you're saying absolutely reeks of everything Steve said above...

Valve adjustments, proper carb cleaning, etc.

While you probably can't do a proper carb cleaning out on the road, you maybe be able to do a valve check, if not a proper adjustment.

All you need is a big cable tie...

I am lucky that I'm staying w/a friend right now and have access to tools etc. So I can try to do a proper carb clean and valve adjust.

If done correctly, how long will it take to do these things?

 

[tom203]

I am lucky that I'm staying w/a friend right now and have access to tools etc. So I can try to do a proper carb clean and valve adjust.

If done correctly, how long will it take to do these things?

Probably longer than you'd like. Relax and read up at Basscliff's site to discover the maintenance that this bike has most likely missed waiting for you. If you check valves, you'll need very small feeler gauge, patience,and probably new cam cover gasket.

 

[JShapiro]

Could this be causing the fluctuating tach or is that a separate problem?

 

[BassCliff]

Hi,

Could this be causing the fluctuating tach or is that a separate problem?

It's a separate problem. You probably need a new cable or the gauge itself needs cleaning/lubrication. If you do a search you'll find lots of posts on the subject with pictures and disassembly instructions.


Thank you for your indulgence,

BassCliff

 

[JShapiro]

Thanks for the advice everybody, I'll be working on it this week and will update when done or stuck.

 

[78gs1000]

Let us know! I would agree valve adjustment and carb cleaning would be a good first step, check all your intakes and make sure the air intake system is functioning good, I had this problem on my bike before.

 

[JShapiro]

Okay, I've got the carbs disassembled and now I have a bunch of dumb questions:

The carbs look pretty dang clean. In fact, I'm not even sure it's worth taking the time to soak and wipe them down. Is this a bad idea to skip this step at this point? If I should clean them, what should I use?

How picky do I need to be about the condition of the surfaces? The jet needle (not needle jet) has some shiny spots on it that I imagine indicate some abrasion, although they look perfectly smooth and you can't see any indentation. The float needle has a ring on its taper from where it sits in the seat. Again, I can't see any indentation or pitting but you can see a difference in shiny-ness. Should I replace float needles and jet needles?

The o-rings on the pilot air screws are cracked. Should those get replaced?

The o-ring on one of the needle jets is in very bad shape. I am going to replace it. Could that be a main culprit in the problems the bike is having?

Can I use regular hardware store o-rings for this stuff or do I have to order special ones from a motorcycle shop?

The pilot air screws are a different shape than the ones in my Clymer manual. Below is a photo of my screw on top of the Clymer photo. Do I have the wrong screw and should replace it?

 

[cowboyup3371]

Get orings from www.cycleorings.com (Robert Barr is a member here and runs the place). There are passages you cannot see in those carbs so do it right and dip them in a can of Berryman's for 24 hours each.

 

[JShapiro]

Will Gumout carb and choke cleaner do as good a job as Berrymans? That's all they have in the small town I'm stuck in.

 

[tom203]

Let's see- you got old dried o-rings, probably shedding bits floating to little tiny orifices and likely clogging things up. Yes, clean them, no matter how "dang clean" they look. Someone will respond on where to get new o-rings for these carbs. Your carb cleaner guy saved a few bucks by not replacing them.

 

[Guest]

If they don't have Berryman's, see if there's a Yamaha dealer close by you can get some Yamalube carb cleaner from, although I'm not sure if you guys have it in the US or not.

Edit: And yes, cycleorings.com, don't skip this or you will regret it!