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'79 GS425 carb rebuild - help needed!

  • Thread starter Thread starter MidWestCoast442
  • Start date Start date
M

MidWestCoast442

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Hi, everyone. First post on here. First of many, I'm sure.

I have a '79 GS425 that I love. Great bike.....until the carbs decided to give me problems.

The bike ran great for several years. Now it spits and sputters and surges and backfires. It isn't rideable. I concluded that the carbs are finally due for a rebuild. Tried running Seafoam through it. No luck. They need to come off of the bike.

First question: What carbs are on my bike? I think they are Mikuni BS34SS. Right?

Second: Is there a rebuild guide for my carbs? Seems like the 750 guys have lots of support in that department. Not so much for my oddball 425.

Third: Is there a rebuild kit that I can/should buy?? What about o-rings? Cycleorings.com has kits for several carbs. But I'm not sure if they cover the carbs that are on my 425.

Fourth: Should I just buy replacement carbs for my bike? If so, then what? It looks like DimeCity sells Mikuni's that will (supposedly) fit my bike. But you know how those things go...

Future projects for the bike include: 2-into-1 exhaust, possible cam upgrade & head porting, and possible pods/stacks

Thank you!

-Ryan
 
I replied to your inquiry (to the website). Perhaps you could check your spam filter.

RB
 
Robert: I disabled email from other forum members. I will enable it. Or could you send the reply via PM? Thank you!

Tom: Thank you for the link. That helps.

So are Mikuni VM carbs more desirable than the CV's? Are they a direct fit for my bike/motor?
 
Your bike will use the same O-ring kit (on my site) as the 80-82 450's. Same 40mm intakes. Your intakes also use a gasket, which I don't carry.
 
Your conclusion on the carbs going bad- how did you reach this?

Sounds more like bad points and condensors - when were they last changed?
 
No idea when the points/condensers were last changed...possibly never. I'll take a look and see what I find...
 
Yeah i am X2 on this being ignition.

Got my carb rebuild pdf on the newbie thread and it was very easy. CycleOrings and Parts Outlaw (thank steve) for the bowl gaskets.
 
For a carb rebuild - aside from the necessary o-rings, which gaskets and other parts would I need to order? Where should I order them from?

So it seems that it wouldn't hurt to just go ahead and replace the points, condensers, and plug wires. Are there any other electrical parts that you can recommend replacing? This stuff is all old. Might as well put fresh parts in and see if the problem persists.
 
I also responded at your other thread. The oring kit from Robert and the intake boot orings and the rubber pilot jet plugs are all you should need to rebuild the carbs. Little tip...DO NOT EVER grip the float seats with pliers to remove them from the bodies. This eggs out the hole the float needles go into. Use thin blade and get it between the rim of the seat and the carb body and pry them up slowly and carefully.


http://www.mtsac.edu/~cliff/storage/gs/mc_maint/GS_CV_Carb_Cleaning_Series.pdf
 
Thanks.

So I checked the points. They look great. Gap is about .014

What now? Install a new regulator? What about plug wires? Any other potential electrical gremlins that I should tend to while I'm doing this?

Then, if these electrical/ignition improvements don't help the situation, I'll rebuild the carbs.
 
Where should I get a new regulator? Parts Outlaw? What else should I change? Coils? Plug wires? The plugs are relatively new Iridiums that are in good condition.

If the carbs DO, in fact, need to be rebuilt...then order the o-ring kit from Robert and the gaskets from Parts Outlaw? Is that it?
 
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