cold starting

[gazza]

hi , can anyone help?, have a gpz1100 unitrack motor i have fitted to my z1000a2 project , when the bike was fitted with efi , it was running ok, but i converted to carbs, and have a set of z1000j carbs from which i have cleaned and cleaned but the bike will not start from cold , but once started the bike runs ok, i have calibrated and fitted corrector kit for filters i am using the rubbers of the fuel injection system as these seem to fit , any help please , i also have a set of 28 mm slide carbs from the original engine can you buy inlet rubbers so suit , this was of a u.s spec bike running on open belmouths they need a good internal clean , has anyone fitted these to a later engine if so are there any advantages over c.v carbs , thanks gary.

[PAULJAC47]

Had A similar prob to this with GS Cvs few things to check one is the choke fuel pickup tube that goes down into the float chamber two have you checked valve clearances tight ones will cause cold starting probs and lastly i know is might be obvious but if left for a while without running, have you a pri position on fuel tap? if so use it to prime carbs when started go onto main and keep throttle closed when cranking engine,one trick with cv's is to blow gently down the carb air breather tube and try without choke this forces fuel/air into engine and is a good trick with reluctant to start engines

[gazza]

i have not looked at the valve's yet that will be my next call, plus another look at my carbs , thanks for your advice gary

[Al]

gazza what have you tried so far?
New plugs and fuel is a given but what about balance and mixture settings?

How many turns out are the pilot screws and what happens when youre winding it over?
Does it spin fast and try to fire or is it laboured and stuttering occasionally. ie. respectively weak or rich. Can you smell fuel from the exhaust before it eventually goes or does it seem like it will spin all day and never catch?

If youve cleaned them out did you notice the size of the jets already fitted? In particular the pilot jet.

If winding and winding has been a feature then even new plugs may now be shot because they dont appear to like having the central insulator soaked in fuel! It can lead to the plugs shorting to earth rather than producing a useful spark.

Are you anywhere nearby?

Some people dont seem to like CV's but i cant fault mine and once set up are smooth and flexible with little loss of power over slide carbs and thats if you could even tell the difference.

I would guess that 28's on an 1100 GPZ top end would be working pretty hard but i've not tried so couldnt say for sure.

AL

[AndyZ1R]

It wouldn`t be something simple like using or not using the throttle when starting? Some bikes often just need the choke on to start using no throttle at all, and as soon as you touch the throttle you`ve buggered it.
My 350LC was a nightmare to start from cold, the previous owner had told me 'give it plenty of throttle from cold', it took around 80 kicks to start. I then tried it without touching the throttle, it started first time!

[Alexander]

gazza what have you tried so far?
New plugs and fuel is a given but what about balance and mixture settings?

How many turns out are the pilot screws and what happens when youre winding it over?
Does it spin fast and try to fire or is it laboured and stuttering occasionally. ie. respectively weak or rich. Can you smell fuel from the exhaust before it eventually goes or does it seem like it will spin all day and never catch?

If youve cleaned them out did you notice the size of the jets already fitted? In particular the pilot jet.

If winding and winding has been a feature then even new plugs may now be shot because they dont appear to like having the central insulator soaked in fuel! It can lead to the plugs shorting to earth rather than producing a useful spark.

Are you anywhere nearby?

Some people dont seem to like CV's but i cant fault mine and once set up are smooth and flexible with little loss of power over slide carbs and thats if you could even tell the difference.

I would guess that 28's on an 1100 GPZ top end would be working pretty hard but i've not tried so couldnt say for sure.

AL

Would agree with all above, sounds like weak mix on pilot or air leak. Once engine is warmed try closing off air screws while ticking over, if cylinder keeps running (or even runs better) suspect air leak. I would recommend new rubbers if this shown to be the case, I have tried sealing what appear to be good rubbers (no cracks) without sucess, I think they just go a bit hard.
If you do have to increase pilot jet you have to down size main jet but would leave as to see if cold start is sorted, would confirm step in the right direction. Opening throtle on weak fuel start up would not help starting as others have said so try and avoid this. Good luck, Alex.

[Pigford]

If you do have to increase pilot jet you have to down size main jet but would leave as to see if cold start is sorted, would confirm step in the right direction. Opening throtle on weak fuel start up would not help starting as others have said so try and avoid this. Good luck, Alex.

Don't want to pick holes, but if the bike runs OK when warm - do NOT reduce main jets. The pilot & main systems are seperate, and when over 1/4 throttle, the pilot doesn't have much say in the mixture. If you reduce the main, it could run too lean = holed pistons

[gazza]

thanks for all your resp-once's i haven't tried new spark plug as yet and i not sure that the efi intake rubbers are ok to use on carbs , or should i change them?i have a gs1000 and although the top end cams on one side are worn after a few turns she always starts with no problems , don't think its valves , the bike when turning over wants to start like its missing a stroke but unless i put my hands over one or to carbs while cranking it' will not fire enough to get it going , when i change the pilot setting on screwing in to the stop this does alter the bikes running from which it will not run , also the choke seems to stop it from firing at all , to the person asking were i live , i am 5 miles from oxford, thanks gazza.

[PAULJAC47]

Gazza ,have you tried as i suggested blowing gently into one of the carb air breathers and see if it starts with no choke? ensure fuel is on pri when you do this and keep throttle shut....Paul J...

[gazza]

hi paul no i haven't yet , my fuel petcock is straight throw no vacuum pip fitted this is blanked of, i will try tomorrow when its still light thanks

[Pigford]

If the engines done a few miles - could be a bit down on compression

[Al]

Oxford's not far but not that near either with what i had in mind.

Are you trying to start it without the air filters on.
From what you said about hand on the atmospheric side and air corrector kits.
If youve fitted air correctors for pods then with other settings marginal or yet to be set in stone i would advise having some sort of restriction on the intake end. ie. the filters you intend to use.
CV's benefit from a greater restricton on ATM side to generate the vacuum. Albeit for the range above the pilot circuit in the main.
If you keep second guessing it you will never get to a point where it will perform predictably.


That lozenge shaped opening at the top of the inlet side is the balance port for the diaphragms to operate correctly.
Impossible to read when you have your hand over the inlet side because it cannot be determined which of the pilot air jets and which of the balance ports you are covering and to what degree.

Suggest; 2 and a half turns out on the pilot air/fuel screws. Forget the choke or possibly tweak it half of its first notch so not onto the first stop but only if it needs it. Fit the filters and dont use the throttle to start it if you can help it.

Take a look at the choke push pull bar.
When it is fully home can you either depress or open any of the choke plungers.
Youll need the tank off to see this properly.
If you can depress any of the plungers youll need to bend the forks that operate them to seat them on their butts cos if any are not seated then youll be there forever.

Hope this all make sense.

AL

[Al]

AndyZ1R
PostPosted: Sun Mar 07, 2010 11:27 pm Post subject:
It wouldn`t be something simple like using or not using the throttle when starting? Some bikes often just need the choke on to start using no throttle at all, and as soon as you touch the throttle you`ve buggered it.
My 350LC was a nightmare to start from cold, the previous owner had told me 'give it plenty of throttle from cold', it took around 80 kicks to start. I then tried it without touching the throttle, it started first time! Rolling Eyes

Yes its funny how little things can catch you out.
My bike was caned mercilessly by my friend for a whole day at a drag meet at North Weald. I then drove it home after filling it with petrol that Andy Z1R carried for me. I did the M25 on three cylinders, the M3 on 2 cylinders and the A331 on 1 cylinder and used the starter motor to get me off the A325.
Oddly it turned out the the petrol was actually water!!!

Also my bike wont start at the moment. Seemed a little odd when it was running ok before i fitted the fuel filter Andy Z1R gave me.
Turns out that it did not work on his bike cos it was choked with fluffy BS so he gave it to me.

I'm not bitter though.


AL

[Alexander]

If you do have to increase pilot jet you have to down size main jet but would leave as to see if cold start is sorted, would confirm step in the right direction. Opening throtle on weak fuel start up would not help starting as others have said so try and avoid this. Good luck, Alex.

Don't want to pick holes, but if the bike runs OK when warm - do NOT reduce main jets. The pilot & main systems are seperate, and when over 1/4 throttle, the pilot doesn't have much say in the mixture. If you reduce the main, it could run too lean = holed pistons

Have to disagree Pigford, but I can only go with my own experiences and appreciate what works for one may not work for another. The pilot jet will affect the mixture over the whole range as detailed in the graph below, just as when you change the main jet you WILL notice a difference on start up, ie requires a little less choke and warms up quicker. Small changes in the main jet have less effect across the settings, but even upping one size on the pilot makes a substantial change across the whole carburetion, even on full throttle but especially full needle/ mid range.
However I did not suggest the main jet be reduced, I simply suggested that if a larger pilot jet was fitted a smaller main jet MAY be required as it is more than possible overall things are richened up a bit, but only to be considered if it is becoming too rich!
It is a common misconception that the pilot jet only contributes to 1/4 throttle. What actually is meant by this statement is the other components (Full Needle/Main Jet) do not come into play until after 1/4 throttle and therefore only pilot jet is contributing up to this point, but the pilot jet does still contribute all the way to full throttle, albeit to a lesser degree than the other components.
However after some rethinking I would consider upping the main jet one size and if the cold starting has improved it would suggest lean fuel mixture and from there the causes can be deliberated/investigated with some focus.

[Al]

Have to disagree Pigford, but I can only go with my own experiences and appreciate what works for one may not work for another. The pilot jet will affect the mixture over the whole range as detailed in the graph below, just as when you change the main jet you WILL notice a difference on start up, ie requires a little less choke and warms up quicker. Small changes in the main jet have less effect across the settings, but even upping one size on the pilot makes a substantial change across the whole carburetion, even on full throttle but especially full needle/ mid range.
However I did not suggest the main jet be reduced, I simply suggested that if a larger pilot jet was fitted a smaller main jet MAY be required as it is more than possible overall things are richened up a bit, but only to be considered if it is becoming too rich!
It is a common misconception that the pilot jet only contributes to 1/4 throttle. What actually is meant by this statement is the other components (Full Needle/Main Jet) do not come into play until after 1/4 throttle and therefore only pilot jet is contributing up to this point, but the pilot jet does still contribute all the way to full throttle, albeit to a lesser degree than the other components.
However after some rethinking I would consider upping the main jet one size and if the cold starting has improved it would suggest lean fuel mixture and from there the causes can be deliberated/investigated with some focus.

Agree Alexander, the pilot circuit provides trim for the entire range but he wont have it.
That diagram is slightly mis-leading when you're talking about CV's because the rest position for the throttle ''''slide'''' is approx 25% open.


AL