Howdy folks, I've got an '03 with a 434 big bore, K&N, DMC full and CDI on it [stock carb].
When its been sitting (overnight or longer) and gets cold it takes forever to start - to the point where it will kill my previous battery. I put a new battery in it and even tried swapping out for the stock CDI to see if that was the issue. Still no luck.

It'll turn over it just wont start, however, once the engine is warm - itll start up each and every time within seconds of pushing the start button?

I've seen some threads on valves and timing (I believe both to be within spec) but am not sure this applies to me as I just had the top and bottom end (including cam chain, tensioner, etc) done last winter. Due to injury I rode it maybe 5-6 times (less than 4 hrs) after the engine work.

What could be keeping it from starting cold but allowing it to start right up when its warm?

Thanks!

- phreak

I know you said that you believe the valves to be in spec, but should still be the first thing to check. You said you have 5-6 rides I believe you said, since the head was rebuilt, your springs and cams have broken in and settled most likely, and clearances have changed I would bet. Valve clearances need to be checked again shortly after break-in.

I'll recheck the values again, but one thing I forgot to add was this has been an issue since I got the bike and seemed to persist even after the rebuild. I thought perhaps it might be related to the electrical but the fact that it starts right up once its warm makes me believe otherwise.

My wife has a stock z400 and hers starts right up within 4 tries after sitting just as long as mine. I was also thinking the petcock (because I know for a fact that it leaks) may be a contributing factor as well as the fact that I dont believe my choke cable works either?

Could those things contribute to the hard cold starts?

i would fix the choke problem while messing with it. how is the jetting? pilot jet? what has the temp been like outside when you try to start it? does it do it winter and summer?

Jetting is dead on - had it dyno jetted. It happens in summer or winter (in Arizona) despite the temp so long as its been sitting for 5 + hrs.

I know its common to have hard starts after engine mods but I figured something was out of wack. I'll fix the choke issue for sure as that feels like it might be one of the issues.

Yeah, if you are positive that your jetting is all dead on... then I would take the plastics and tank off and fix both that choke cable and check the valves while you have everything out of the way.

There is no reason that w/ mods it should be hard to start... just have to make sure everything is set up right afterwards.

Choke for sure - I've ordered a plunger replacement that moves it to the top of the carb and locks the choke place. I'll be sure while I'm in there to check the valve lash too, its not impossible for it to be out of spec.

Thanks for the replies guys.

Matt you've got me thinking now. I know the air to fuel mixture on my carb (screw and main) is dead on, but the pilot may be off. I was reading about jetting procedures and results for another problem with my pit bike and found an article that said hard starts when cold could be caused by a lean pilot. I'll have to rip my carb apart and see whats in there - does anyone know what the pilot is for a stock z400 carb?

Thanks for the post

Yeah, it could definitely be one of the two things... incorrect pilot is definitely not out of the question. Sorry, I'm not sure on the stock pilot size, I am running the edelbrock carb; just glad I don't have to worry about these issues with it.... even if a lot of people do say they are crap, I still love mine.

from the jetting database sticky in the maintenance section looks like a 22/22.5 is stock. So I'll see what a 25 and a 27 do just in case.

Between that and the choke I'm hoping it clears up the issue.

with those mods you should put a 25 i n there. that shouldn't have had anything to do with the starting though.

you may have to turn the fuel screw in some after that.

The pilot was a 22.5 so I swapped it out for the 25. It seems a little thin at the time so I threw the 27.5 in there and it was too fat for sure. So the 25 it is. I did notice that the choke isnt working at all, but I didnt have the replacement parts to fix it yet.

Hopefully with the proper jetting and a working carb/choke it should fix it. I did notice my petcock is shot and regardless of position, etc it would constantly flood the carb. Add that to the list of litte things to fix and it should be good.

btw the values were within spec, so I've ruled that out.

Let us know if all this gets it taken care of... I see yours is an '03.... I wonder if your stock valves could be starting to cup? From everything I have read, they all say that the stockers are crap. I would assume this would act the same way as if your clearances were too tight.

I was curious about that myself. The bike was half-a$$ed when I got it and I had to do a lot of rebuilding. I wasnt sure if the valves were stock or not - if these things don't fix it that'll be the next item to be replaced. Man, some brakes and new +2s and this will be a complete rebuild. FAIL!

On stock +3 valves they would only be wearing out if they got a grinding on the last rebuild.
The stockers really aren't that bad.
Just don't grind them to the seats, let them wear in.
Running Methanol, or Av gas will take the temper out after a certain operating temp.
That's what finally happened to mine.

All I do on stock valve replacement is take the polishing wheel to the backsides and the combustion side to keep them clean, and create smoother flow from the intake port.
I like CV4's but the price kills it for most people.

Quick update (I havent really been riding due to a back injury so I havent spent too much time on the solution) - the plunger mod to the carb and new petcock didnt help. [still doesnt seem as if the choke is working at all] The jetting seems to be fine once things get cranking but if the quad sits for longer than an hour or is in cold weather it'll take about 15+ minutes to start (if I'm lucky) even with the assistance of starter fluid. Once its warm it'll start every time without issue.

I'm officially stumped . I guess its time to look at the valves unless anyone else has any ideas?


- Phreak

aaaah you said they are within speck, how ever your really only going to get just so many redo's on the valves.
they do ware out , a n d , i just happen to have a new, never used, in the package ,set for sale. i would say its your lucky day.,

Got a good deal on kibblewhites - the valves were cupped as @#$@ once I got the head off. Should be back running by Wed.

We'll see (it should) if it fixes the cold start problems.

I'll keep the thread updated.

PLEASE I JUST GOT MYSELF A BIG BORE 434MM, AND MY BIKE HAD TERRIBLE COLD STARTING PROBLEMS AS WELL BEFORE I TOOK APART, CAN YOU POST BACK IF THE VALVE JOB FIX THE PROBLEM, THE DEALERSHIP SAID THAT FOR BIG BORE U HAVE TO USED A DIFFERENT SETTING FOR THE VALVES THAN STOCK,

THANKS