85 gs450 running on one cylinder

[dan0688]

I have Spark and compression on that cylinder(about 120psi) anything i should check? how would i confirm im geting fuel from that carb?

[dan0688]

I think i have fuel.... the plug is geting damp.... kinda confused.... the timing cant be off if its running on one right?? ( I can see that the valves are opening and closing, tryed swaping coil, plugs it did not follow, any ideas would be much apreciated

[Ghostgs1]

Sounds like carbs may need cleaning, does it fire on that dead cylinder if using the dreaded starting fluid? Ray

[dan0688]

I just had the carbs apart and cleaned up.... i figured out that it runs on both when not choked... but when choked it only runs on one, so i assume there is something wrong with the choke circuit in the left carb, I did not disasemble the choke when i cleaned the other jets.

[Jman750e]

I've just run into the exact same problem as Dan. I just rebuilt my carbs and got it fired up today. At first it was only running on one cylinder, and very rich. I took the filter out to help lean up the mixture and the left cylinder started firing. After it warmed up it ran real smooth. I think its a strange coincidence that both of our bikes are having trouble with the left cylinder.

[nikuk]

It is kinda odd that its seeming always the left one. I don't remember which cylinder synchs to the carb, but I'd guess (based on this thread) that the left synchs to the right. If your butterfly is a ways off thats an easy fix. Pull the carbs and use a feeler gauge or piece of paper and hold them up to a light. Adjust till the crescent of light coming through the bottom of the blade is the same.

If that doesnt do it, here is my fix.

For what its worth - This is gonna sound really stupid, but cold start it, once it settles down to idle on the right cyl, cover the Pilot Air Jet hole (intake side of carb) of left cyl with your finger. If the left cyl comes to life, you should take a look at your Pilot screw (top of carb, engine side, may have emission cap / plug over it) as its letting way too much air in.


I had the same problem on an 82 450GA, fire right up from a cold start on only the right cylinder. Once warm and off the choke the left cyl would come to life.

Mikuni BS34
Stock motor & exhaust
120# Left & 145# Right compression
new plugs, rest of ignition in good order

Tore down the carbs thrice - On the third effort I drilled & pulled the emissions caps from the pilot screw, cleaned the ports & put fresh rings in em. Snugged em, then backed em off on the bike till she idled nicely - which was about 1 1/2 turns LESS then what it was at when I took it out. Took a 3 TRUE COLD starts over two days, and no problems since.

-Nick

[dan0688]

i bench synched the carbs before reinstall, and with a vac gauge the carb synch looks to be really close, it only does it under choked conditions without choke it runs normally, the mixture screw (top of carb where plugs were drilled out) would cause this? what do I replace? the screw?

[nikuk]

Just my $0.02. It worked in my case.
Ran on right side with choke open, oncewarm and off the choke it ran on two.
Thumbed pilot screw port, choke open, ran on two. Adjusted the bejezus out of the pilot screw, same story.
Pulled the mixture screw, cleaned it, new oring, started at 1 turn out, tuned it, now runs on two regardless of choke and starts up easier.

Again, specific to Mikuni BS34SS, YMMV

[dan0688]

took the carbs apart again, found the floats to be way out of adjustment cleaned all the jets again and put back together, put the carbs on the bike and my problem disapeared.... so i fixed it.. but not sure exactly how

[maparker]

A couple of people mentioned synch. There is a super easy trick for synching these twins. Set the idle about where you want it to be, then pull your plug wire, then simply adjust to bring the rpms back to target. Put the plug wire back on and verify with the other side. Much easier than synching an i4 for sure!