G5 100 Issues

Hey everyone!


First post on the forums here, and it's mostly because I'm stuck big time.


I have a '73 G5 100 that I just turned over 3000 miles on. I've been having issues about every other year I've had it. The bike is pretty much identical to the KE100.


Last year, the bike was getting so hot that the fuel was vaporizing before it could reach the carburetor, often bubbling up in the line. Threw in the next step colder plug (BR9HS) and the next step larger main jet. The bike ran okay for a while.


Most recently, the bike was running terrible/intermittent. Found the points were corroded and the condenser was only making 2V AC. So threw in the new parts and timed the bike with a timing light (when a guy at work helped me initially time it, it was actually about 10 degrees retarded). Also happening right as we speak, the tank is rusting and sending sediment down to the carb. Luckily I installed a fuel filter off a snowmobile that a buddy gave me. I would like a plastic tank if possible.


Fast forward to today. I threw new fuel line in (had some Tygon line that expanded and was pinching itself) and ran the bike around my subdivision. Ran okay until it started getting hotter. When I'd get hard on the throttle and up in rpm's, the bike would sometimes pop, and I knew I'd have to try to get home (just in case). Some instances it seemed it wasn't getting any fuel for a second or two. I dropped the bowl before I threw in that fuel filter and there was (and I say was) a large flake that I could bet the main jet would suck up and block off anything else. I would like to think that with this filter that nothing should be getting down to the carb.


Crank seals? More ignition issues? Any ideas? This bike is a 50/50 learning experience and pain in the rear :lol:


Thanks guys!

You can use a Kreem liner kit on your rusty tank. My 1982 KE100 used to run hot with a 75 main jet. It would start right away and be peppy but after about 20 minutes it would get hot and lose power and feel like someone was shutting off the gas valve. I installed a 80 jet and now I have to warm it up for a while because it will be sluggish when cold but is OK after it warms up and it doesn't overheat anymore.

Before you ruin that tank with creem, try a rust remover first.  I was able to remove a poor creem job (lol) from my KD, then cleaned up residual rust spots.  


You need to correct what's obviously wrong (tank debris) first, then see what's going on, if anything, with the bike.  No sense trying to jet an engine with a dirty carb.

The Kreem kit is 3 bottles that includes rust remover.

Unless there's pin holes or a leaky seam, I would just use evapo-rust or something like that.  I used mineral spirits with a length of chain and just shloshed it around. I did a Z1 tank with an oxylic acid bath too, but still needed a little of the chain treatment after.

So I guess I'll attack the first issue: the fuel tank.


From your guys' responses, I can assume that a plastic tank may be out of the question? My uncle told me about an Eastwood product that would seal up the tank, said he's fixed many a rusty tank with that.


I forgot what jet size is in the bike right now.



I actually sold the bike to my dad, but I'll still be working with it to get it right.


I ran the bike today and tried out a bunch of things. Stock BR8HS is back in, there's an in-line fuel filter (removed the one in the petcock) so that should be ok. Still need to bump down to stock main jet.


The bike runs awful. Very hard start, and doesn't like a lot of throttle as it cuts out, backfires, spits and sputters, etc. It has new points and condenser but I will have to check the timing with the light again. 


I thought about the exhaust maybe being plugged up (just bouncing around ideas) and upon pulling the pipe off I found a bit of piston scoring. Not the worst I've seen by far, but certainly there. Pulled off the baffle, and the packing was all kinds of jacked up. It was pulled every which way and there was good carbon buildup throughout. Maybe the bike will run better without that possibly plugged baffle? Answer: NO. Just sounds bad and doesn't like to idle now.


I'm not sure yet. Any tips, this thing is an absolute mess to wrap my head around.  :banghead:

It sounds like your carb is still dirty or lacking fuel.  Make sure you can blow brake clean through all the passages in the carb ESPECIALLY the passages in the float bowl. If those are dirty it will be hard to start and have symptoms similar to what you describe.


You should not have removed the screen from the petcock, but since you already did, make sure the sediment bowl is clean on the bottom of the petcock. Pull the fuel line from the carb side and check for good fuel flow.

You should not have removed the screen from the petcock, but since you already did, make sure the sediment bowl is clean on the bottom of the petcock. Pull the fuel line from the carb side and check for good fuel flow.

For what it's worth, that screen that was in there wasn't doing it's job when I got rid of it. I think the tank is coming back off and the petcock will be checked again.


I installed the stock 102.5 main jet in the carb. No difference since the bike still runs awful. Baffle is back in.


After all the fuel came out of the filter and out the needle valve when I took it out, fuel did not continue to flow. In fact, when I turn the fuel on there is but a few drips going into the in-line filter. Maybe the petcock is crammed full of rust shavings again. Before, when I had this same problem, I got the system to flow by removing the fuel line at the petcock SLIGHTLY and letting air in. That got fuel flowing.


Oh, another thing: when I removed the carburetor (fuel is still in the filter and carb) fuel came pouring out of the 2 little vents at the bottom of the float bowl, they have a rubber piece that vents them out to the atmosphere from the cover.


I think I'll check the petcock next, no real progress tonight.

You need the baffle installed for it to run good.

I'd really like to get a spark tester for this bike to see running spark. I have a B&S spark tester but it has the rounded cap, rather than open threads like what the NGK plug boot is made for. I have to unthread the little cap on top of the plug to use them.


What is the best way to know if the miss is ignition or fuel related?

My dad went ahead and tinkered with the bike while I was at work yesterday, and he saw that once AGAIN, the points are not opening up. He readjusted them so that they would, but what is the long-term fix to this issue?


He said the fuel filter takes forever to fill up, and wonders if there's issues with the vents in the carb (not letting air purge out, not letting gasoline in the system). The silly thing still dumps a bit of fuel when the bike is stood up straight (out the 2 little nipples on the bottom of the float bowl).

Do you have a service manual?


For the fuel, disconnect the fuel line from the carb, turn the3 gas on and see how well it flows.  Your tank needs to be vented too.

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