OK, I have an 1988 Suzuki LT80 'K'. Got it in trade from a friend of mine. He couldn't/wouldn't fix it, so I now have it. It hadn't run for about two years when we brought it home. First, we took off and thoroughly cleaned the fuel tank / carb and replaced the spark plug & battery. After re-assembly and filling the tanks for fuel and 2 cycle oil, it started relatively easy, and off my son went...for a while, then it died. Probably talking about 15 minutes. Couldn't get it re-started so I pulled the plug and cleaned it with my plug sand blaster because it was very 'fuelly'. Re-installed, but it still wouldn't start...then decided to take a break and let myself, and the bike, cool down. Came back two hours later and it started right up and he rode it for several hours. The next day we had a repeat of the first, as it started and ran for a while, but then mysteriously died and would not start until letting it cool down again. Sometimes when I pull the plug after it dies, there is no fuel present on the plug, sometimes there is...

Most recently we have replaced the petcock with a standard, non-vacuum acuated unit, new reed valves, and rebuilt the carb with needle/seat and jets. No help, maybe even worse. Now it hardly will start at all.

Today I checked the compression, but my gauge doesn't seem to want to hold the presure so it can build up to an accurate, ultimate reading. The needle surges to about 35#, but then drops to zero, then the cycle repeats itself. Don't know if the 35# is an indicator of good or bad...going to replace the valve core in the guage's schraeder valve today to gain better intell on this subject...

Also, I now believe this has been a problem: the black car insulator was broken when I initially tore the bike down. I epoxied it together, but I now believe the o-ring was too flat, the insulator re-broke, or the rubber gasket on the reed block wasn't sealing properly, and I wasn't generating enough vacuum thru the carb to pull fuel. To remedy this, I fabricated two gaskets to eliminate the o-ring and the reed block seal and used a new epoxy to increase the strength and integrity of the insulator. After putting it all together this morning, I got it to start, but it took a lot of cranking (with pauses for the starter to cool) @ WOT and the choke off...after it started, I applied the choke and ceased to give it any throttle. It ran fine for 15 minutes, adequately fogging up my garage, until I shut off the fuel and it ran out of gas a few minutes later. At this point, I'm thinking I have it all figured out and am patting myself on the back...until I turn the fuel back on and try to start it again. Nothing. Couldn't get it to start, but fuel was dribbling out the front of the carb (haven't re-installed the air cleaner yet). At this point I removed the plug and found it to be covered with fuel, so I guess the vacuum problem has been solved, but I'm back to the combustion issue again. We have verified spark (and it did run for 20 minutes or so just prior to not starting the sencond time), so I'm wondering about compression again...

Sorry for being so long-winded, but I'm hoping to save time by providing an complete and accurate description of my problem. Again, any help is appreciated, and thanks for taking the time to read and respond.

Update:

When I went back out to try again, I noticed fuel still dripping from the front of the carb, so I took it off and found some debris on the needle...don't know how that got there, but stranger things have happened. Anyway, cleaned it up and re-installed carb and plug after cleaning it, too, and it started, but again it required thumbing the throttle to WOT to start, it then idled very nicely for about ten minutes. I shut it off, checked for fuel seepage and found none. Attempted to re-start and had no luck...getting very frustrated at this point. Any ideas why the thing won't start when warm?

 

have your valves been adjusted? sounds like when it gets hot the metal expands and your valves become to tight and are not letting the valves close properly which could be part of the vaccum problem. so adjust your valves out would be my guess and see where it goes from there.

 

Isent the lt80 a 2 stroke?

 

No valves on this unit! Check compression and let us know.

 

Knew it U got to the comp first. hopefully someone like lt80 will come and tell us whats wrong.

 

It may not be fuel related, you did say it would sometimes run fine for 15 min or so, then be hard/impossible to start, but would restart after sitting? Maybe a stator or coil problem, heat soak causes the resistance to go up, spark is lost, it dies until it cools and voltage is restored. Or there is a crack or break in a stator wire that when it expands under heat, it opens up and kills your motor. This is just a guess based on your symptoms, have your checked for spark as soon as it dies? that may lead you in the right direction. That compression sounds a little iffy, but it would not start at all at 35 psi, anything below 90 would be a hard starter, maybe you need a different comp. gauge?

 

Just got home from baseball games, so I'm not going to work on it tonite, but plan on borrowing a friends comp gauge tomorrow to verify adequate PSI. I think your right, though, it wouldn't start at 35, so I just need to see what it is actually pushing. I initially thought the coil might be weak, but it really throws a flame outside the cyclinder and it does start cold; however, I hadn't thought about the heat increasing the resistence, so I will check that theory tomorrow, as well. Thanks guys, and I will update my progress tomorrow.

 

Looks like compression is around 65#...should've dropped some oil in to see if that improved it any, but at 65#, I figured we're talking new piston/rings, etc, regardless. I got it started again (and incidently, it is much easier to start with a 40amp boost from my charger) and let it idle for probably 30 minutes, then shut it off and tried to start again immediately. No dice, so I pulled the plug, which looked pretty good as far as not being soaked with fuel. Then checked spark which was throwin' a great flame, which wasn't really expected. I did have a Briggs that showed good spark outside of the engine, but under compression wouldn't fire. This problem exists with the other three plugs I have, too, so I think I can rule out ignition. Not sure why the low compression would hinder starting a hot motor: seems as though a cold motor would be more difficult...Is it possible that the compression gets worse with a warm motor, and therefore the venturi effect in the carb is not sufficient to draw fuel up thru the jets? Seems like the plug was actually too dry when it wouldn't start hot, when I think about it. I think I'll give it a blast of ether when it's hot to see if I do actually have a fuel delivery issue. Looks like a top-end rebuild, though, so where's the best place to get top-end parts, and how much of a pain is removing the cylinder? Surely this can be done with the motor still mounted in the frame...Thanks again fellas for your input. It definitely helps when you have people to bounce ideas back and forth with.

 

Cylinder kit:: OEM parts source~888-672-5141
$119 for a new cylinder/piston kit/pin and clips (possibly the bearing too).
They buy 1000 of these direct from the manufacturer (not Zuki). This is why it is reasonably priced.
I get $130 for boring and parts.
If fuel comes out the cab, it's a needle problem (sounds like you fixxed that).
It won't start hot: remember, the cylinder expands too. So loose is loose hot or cold.
Yes, you can do the top end with the motor in the frame.

 

I have seen the $120 cylinder kits, but wondered about quality. Sounds like that is the way to go...I pulled the cylinder and piston the other day and can see daylight between piston/rings and the cylinder, which I take to be very bad. The curious thing is the gaps are perpendicular to the stroke (sideways to the direction the rod moves). I would have thought in line with the stroke would be the major wear area.

Thanks for the info LT80. I downloaded a shop manual last night and am considering tearing into the transmission and trying a few of the mods I've read about in the forum. Is this recommended or technically difficult/time comsuming? I would like to complete the tranny work before the engine parts arrive. Need to get this bike moving again soon, but also running as good as is possible. Thanks again everyone.