dies when hot - HELP

[dwem]

Hi,

I took my 1991 kat (600) out for an MOT today, first time I've properly ridden it, and it started fine, after about a mile it started to run a bit rough, and stall.
bit further on it totally died, and wouldn't restart.
If i did with full throttle it would get to about 1k rpm and die.

I pushed to MOT station, had test (failed on back break pads)
the engine had cooled down, it started up great, and i started to ride home, after about 2 miles it did the same thing.

I let it cool down again, and it would start up, and i got about another mile.

got it home in the end.

The MOT mechanic, biker mate, and biker uncle reckon it's not the fuel, as the problem only start when the engine is hot.
They are thinking about the lines of coil or rectifier.

Any thoughts????

please help, i want to have this running and back down to the MOT station in less than 2 weeks.
am gonna go grab my haynes manual now as well

[The CyberPoet]

(A) Do you have any idea of how hot it ran? There's a difference between hot enough the fuel was vaporizing better and so hot that the oil was overheating.

(B) Given today's weather in Southampton (about 64 degrees F as the high), and the fact that the issue cleared after cooling down again, I'd guess it's probably jetted too richly. As the bike warms up, the fuel vaporizes better. This can take a cold bike that is marginally OK and let it act like it's getting way too much fuel when hot. Also check for a stuck/binding choke cable...

(C) It is also conceivably possible that you have a bad charging system, and the battery is carrying the bike. When the bike quits, the battery is depleted past it's limits, then over time it builds a charge back up (chemically). This is very simple to test, but I doubt it's the case.

You can test the coils simply enough using an ohm-meter and a hair dryer -- check the resistance against what the manual says it should be, then hit the coil with the hair dryer for 5 minutes and recheck -- the values shouldn't have changed more than a few percentage points.

Cheers,
=-= The CyberPoet

[KickItJP]

I would guess too lean if it ran poorly AFTER reaching riding temps...

I screw mine rich, and it only starts running well after it warms up....

[md86]

(B) Given today's weather in Southampton (about 64 degrees F as the high), and the fact that the issue cleared after cooling down again, I'd guess it's probably jetted too richly.

I have a few things to say about rich jetting .
If it was so rich it stalled , letting it cool ain't gonna help . Plugs'd be fouled , so restarting ain't gonna happen unless the plugs are seen to .
I've heard about this , and seems to point to the ignition shutting down when getting hot . Don't remember what part that WAS exactly , but here's what I'd do .....
Get a hair drier and extension cord . Point it at the coils for a couple minutes until they get good and hot , then try to start . Move on to the pc (on the battery box) and do same . Should give you a clue .

[dwem]

cheers md86.

I know it's not a problem with the fuel, so i will be stripping all the plastics off, and tank to see if i can spot the problem

[gaillarry]

Could be a plugged vacum line? Try and start the bike with the gas cap open.

[TRH1]

I had the same problem with my bike, it is due to it running rich when it gets up to operating temperature due to worn needle jets. They wear oval due to the steel needle going in and out of the brass needle jet. You can replace all needle jets, or what I did was lower all the carburettor floats to 1mm above standard, this has the effect of leaning out the mixture. This method worked for me and I was glad I did not have to buy any over priced Suzuki spare parts!

[mq1kael]

I had a similar problem with my gsxr, one of the connections in the main harness had corrosion so when I ran for a while it created heat and the plastic stopped holdin them together. But when cool it wasn't a problem, Just a thought for you

[dwem]

it's not a problem with the engine running rich/lean, that we're sure of (have spoken to mechanics here)

On the weekend i'm going to measure the ohm's of the coils cold, and then hot to compair if they are the problem.

What is the best way to test the vacum advance??

[The CyberPoet]

There is NO VACUUM ADVANCE.

Bikes are generally much simpler than cars, and don't use it.

You can check for vacuum leaks by getting the engine running, then spraying WD-40 (or starter fluid) around all the areas that should be sealed -- if there's a vac leak, it'll suck in the flammable spray and the RPM's will suddenly change as a result.

Cheers,
=-= The CyberPoet

[md86]

I had the same problem with my bike, it is due to it running rich when it gets up to operating temperature due to worn needle jets. They wear oval due to the steel needle going in and out of the brass needle jet. You can replace all needle jets, or what I did was lower all the carburettor floats to 1mm above standard, this has the effect of leaning out the mixture. This method worked for me and I was glad I did not have to buy any over priced Suzuki spare parts!

Sure , MAYBE if the parts aren't worn too badly . Mine were , and I tried EVERYTHING as far as jetting is concerned . Had it running ok , but was still way rich . Ended up buying new parts .