Bike struggling to start when warm

[Dynamo_Delboy]

My 1989 ZX10 seems to be struggling to start after a ride.

If im out on it and stop for any reason and turn the engine off it wont start again for about 15-20 mins.

It tries to start but just wont kick up straight away.

Any ideas what could be causing it?

Thanks

[Tankbag]

Heat causing a kink in the fuel line ? Vapour lock on the fuel pump ? Hope you find an easy fix

[Mississippi Bullfrog]

Compression will be higher when hot so sometimes a weak battery will show as reluctance to start when hot.

But if it's spinning over fine then look at either vapour lock or fuel mix.

[Bianco2564]

Does it start better if you open the choke at all?

Usual suspects;spark plugs,airfilter all ok?

Throttle balance

Carb inlet rubbers perished/hardened causing weak mixture.

Valve clearances closing up when hot causing loss of compression.

[Dynamo_Delboy]

Makes no difference with choke open or closed.

Noticed my rubbers between airbox and carbs are hardened and have a slight gap between them and carbs.

Could this be the problem

[Dynamo_Delboy]

Plus it smells like it may be running rich

[Tankbag]

Plus it smells like it may be running rich

 

How old is your battery ? Hot starting will have higher compression & more load on your battery which will knock on to a weak spark & then you'll get your running rich smell.

[Dynamo_Delboy]

Battery is about 2 years old mate

[Tankbag]

Any joy ??

[Fozzie]

Check fuel lines - Should go downwards to carb from the tank. Any turns that make them go up, and you have a prime spot for a vapour lock to occur.

Fuel mixture - Could the hot engine be causing the fuel to more readily turn to vapour, causing a very rich running event on a hot start. Lean out the mixture if possible and see if it makes a difference.

Make sure carb float etc are all set to stock levels.

[TimR]

old kawasaki suffer with ignition switches getting hot from exhaust and engine heat .

this allows the wires/contacts in the rear of the switch to move and lose contact .

my old zzr took it one level further and the contact point was so loose it fell out and cut the power in 3rd lane m4 ...

i had been struggling with hot starts prior to this and tried everything feasible ..ie valve cleaeances , carb balance new.plugs , battery etcetc

after replacing the switch unit i had no further issues ( i had a temporary toggle switch system until i sourced a reasonable ignition switch unit ) which made me realise that i had no problems starting when hot .

only problem was i did once get so complacent with this system i just get on the bike start off and then realise i had not put the key in to disengage the steering lock ... and i had a pillion on board .we both ended up on the floor .Lesson learnt .

remove the lower section of switch( bit with wires) ( no need to undo the tamper bolts )

look at the wire to contact mounts and see if they rotate in the mouldings .

[whitedevil]

My street triple did this, a new battery fixed it. Even though the battery tested fine, it didn't have enough power to crank the starter motor fast enough to start the bike. My battery was 5 years old though. I think some triumphs have weak starter motors that get high resistance when they're hot which was causing my problem. £35 for a new battery was the first and cheapest option.

What actually happens when you press the starter?

[Dynamo_Delboy]

Pressing the starter it just tries to turn over but wont fire up. Its a strong turnover but just wont fire until its been left a while

[Dynamo_Delboy]

Any joy ??

 

Not had a chance to do anything to it yet mate

[Mississippi Bullfrog]

If it is a weak battery then higher compression when warm will draw enough amps to make the spark weak. So it could be as simple as that.

[billy sugger]

I used to have a Honda that had dodgy coils, and when they got hot with heat from the engine they would cause starting problems until they cooled down. turns out the windings of metal (aluminium?) in the coils were losing resistance or something so would not create enough oomph for a decent spark

[Kristers]

I have a KTM 525 SX 2006 while the bike can sit in the shed and then noting can be touched 2 kicks it will start but when I’m out riding it if it cuts out or I simply just turn it off it will take me 5 minutes to get it back on even with the choke for the warm engine what could the problem be I tried regulating the pin in the carb up 1 or down 1 either way it’s not making a difference really don’t get it fairly frustrating out in the field aswell

[WD-40]

You could bring a spare spark plug with you and when cuts out and won't restart disconnect a spark plug lead and plug in the spare spark plug, ground it against the engine and hit the starter button and check if you've got spark or not. Be careful not to shock yourself.

[Kristers]

The bike isn’t electric start it’s kick start

[WD-40]

Well obviously you'd have to kick it then and check if it's sparking.

[WD-40]

I have a KTM 525 SX 2006 while the bike can sit in the shed and then noting can be touched 2 kicks it will start but when I’m out riding it if it cuts out or I simply just turn it off it will take me 5 minutes to get it back on even with the choke for the warm engine what could the problem be I tried regulating the pin in the carb up 1 or down 1 either way it’s not making a difference really don’t get it fairly frustrating out in the field aswell

 

Seems that bike has a hot start valve on the carb to make hot starts easier. Maybe you're not using it right. Read the owner's manual for more info

http://pdfstream.manualsonline.com/4/44632692-b866-53f4-bd3d-50b1bc5c5f57.pdf

And here's some more info on starting copied from here https://dirtrider.net/forums3/threads/hard-start-wr-400.161400/

This was originally posted on the Yamaha USA website around the time the YZ250F first came out.

To further enhance the enjoyment of these products, please follow the step-by-step instructions as explained by Doug Dubach, Four-Stroke Motocross Champion and Yamaha test rider. These helpful tips will ensure quick and easy starting of your Yamaha four-stroke motorcycle.

COLD ENGINE STARTING:

1.Make sure the bike has fuel, then turn on fuel petcock.

2.Pull out choke knob (black knob on left side of the carburetor).

3.Prime the engine by giving the throttle two full turns (only if the bike has not been started in a day or two).

4.Apply firm pressure to the kick-starter with your foot until you hit distinct resistance (this is the compression stroke/hard spot).

5.While keeping pressure on the kick-starter, pull in the compression release lever and push the kick-starter past the compression stroke/hard spot. The kick-starter needs to only move about 1 to 2 inches past the hard spot. That is all!

6.Release the compression release lever and return the kick-starter to the top

7.Now, kick to start. Do not touch the throttle, as the engine will start and idle on it's own

8.If the bike does not start, repeat steps 4 through 7 only until the engine starts.

HOT ENGINE STARTING

1.Pull out the hot start knob (red knob on the left side of the carburetor).

2.Follow steps 4 through 7 until engine starts.

3.You may have to apply some throttle after the engine starts until you get the hot start knob pushed back in because the carburetor is sending a lean mixture while the hot start knob is out.

The only difference between hot and cold starting is which knob you use, choke or hot start. There is no need to deviate from these simple steps. Remember, DO NOT touch the throttle during hot or cold starting. Also, there is no reason to prime the engine again on the same day of riding.

OTHER HELPFUL TIPS

It helps to become comfortable with steps 4 through 7. By becoming familiar with these steps you will become more efficient and will be able to perform them quicker. The faster you can get through steps 4 through 7 the quicker you will get going.

You need to give the engine what it wants! Understand that the choke will give the engine a rich mixture and the hot start will give the engine a lean mixture. If you have kicked the engine several times during a cold starting procedure and it still won't start, maybe it has too much fuel. Don't be afraid to push the choke back in and use the hot start, even though the engine is cold, this will give the engine a lean mixture and that might be just what it wants.

Again, make sure you don't go more than an inch or two past the hard spot when setting up your kick, and return the kick tarter all the way to the top, especially on the 250F. This will ensure that you get a proper kick and make your race day more enjoyable.

[Rob Taylor]

I reckon it's the small gap in the inlet rubber you mentioned, getting incorrect air mix to start hot.

I had the same issue with a cb250 years back but cannot remember at all what the problem was.