KZ650 Hard to Start When Warm

I have a 1978 KZ650 D1 that has developed a weird problem over the last few days. I've had my bike out since early May and it has really been running great. However, this past week or two it started developing problems.

The first issue that started happening is that I would start it up in the morning on the choke and then put it on its sidestand to warm up while I put on my helmet and gear. Once I was ready I would sit on the bike and sit it upright. Once upright the bike started to bog and I would have to give it some throttle to keep it going. Once on the road and moving it would be fine.

Then four days ago it started having problems starting when warm. If I ran the bike for a while and it was warmed up then shut it off for a while it would be very hard to start and when it did finally catch it would often die. I would even have to put the choke on and it would then start but wouldn't be very stable. Once going it would bog when any gas was given. Sometimes to start it I would have to prime the carbs even though it wasn't long ago it was running. Once primed it used to run fine for a little while then it would feel like it was bogging again and then it would cut out. I had to go through this process around 4 -5 times today just to get home. There is no gas coming out of the overflow tubes.

Also, cold starting is still very good. I can use electric or kick and it starts almost instantly.

I just removed the carbs from the bike and will disassemble tonight or tomorrow to see if anything looks unusual inside. I did notice a bit of dirt (maybe rust) in the gas when I drained the carbs. Is there anything else I should be checking?

Not sure if its related but I'll mention it anyway, but there seems to be a bit of oil leaking from the valve cover where the rubber cam plugs are (both sides). I've only noticed this recently.

Any help would be appreciated.

BTW - the carbs are Mikuni VM22SS, which I have upjetted to compensate for pods (110 mains and 17.5 pilot).

I would:

Drain the fuel tank and flush it with clean gas or mineral spirits.

Install inline filters.

Clean the carbs, especially the jets.

Adjust the fuel levels.

bountyhunter wrote:

I would:

Drain the fuel tank and flush it with clean gas or mineral spirits.

Install inline filters.

Clean the carbs, especially the jets.

Adjust the fuel levels.

Thanks bountyhunter. I have everything off now and plan on doing everything you listed. I already have an inline filter and you can see a bit of rust trapped there. I planned on getting the POR-15 tank sealer and doing it over the winter, but I may go ahead and do it sooner.

Also, I believe I may have found out what my issue was yesterday when I was trying to get home. I believe I was out of gas and was too stupid to realize it. I thought I had plenty and so never switched it to reserve :blush: That was why it would start and run fine once I primed the carbs but then it would eventually run out again and shut down. I've been out of the bike scene for over 25 years and this is the first time I ran out of gas (or past the primary fuel level) so the thought never came to me. I guess I learned my lesson the hard way. At least I'm hoping this was the issue. I'll clean everything and put it all back together tonight to see if it runs fine then.

However, there is still the issue of the bike starting to stumble when I sit it upright after warming up on side stand.

How long are you leaving it on the sidestand to warm up? With the #1 carb sitting lower than the others it may be getting a bit too much fuel in that carb bowl on the sidestand, then when you raise it up level it may just have too much fuel in the #1 carb and takes a moment to equalize across all the carbs. Try setting the side stand on a 2x4 or something when you're warming it up and see if the problem goes away.

anarki650 wrote:

How long are you leaving it on the sidestand to warm up? With the #1 carb sitting lower than the others it may be getting a bit too much fuel in that carb bowl on the sidestand, then when you raise it up level it may just have too much fuel in the #1 carb and takes a moment to equalize across all the carbs. Try setting the side stand on a 2x4 or something when you're warming it up and see if the problem goes away.

You're probably right anarki, makes sense. It's usually on the sidestand long enough for me to get my jacket, gloves and helmet on. At least a minute or two. I'll either try your suggestion or put on my gear first.

Thanks.

I am glad to hear that it seemed to be the fuel level.

Happened to me when I started riding again. Man I must have kicked the bike over a hundred times before I figured it out.

Just one of those things you do once and do not forget I guess. Happy riding.

I hear that the weather has been pretty good down in Newf lately.

KOOL RYDER wrote:

I am glad to hear that it seemed to be the fuel level.

Happened to me when I started riding again. Man I must have kicked the bike over a hundred times before I figured it out.

Just one of those things you do once and do not forget I guess. Happy riding.

I hear that the weather has been pretty good down in Newf lately.

Yeah, always remember the hard lessons. :laugh:

Yeah, the weather has been fantastic here lately, get to ride almost everyday.