Suggestions please!

[mattjc]

Okay, the bike in question has had a lot of time and money spent on it, and I'm sure it's almost there but one problem remains. It's really hard to start from cold and when i finally does start it only fire's on three cylinders and the choke does very little, fully open will keep the bike ticking over 2000 rpm at most. once you start riding you can close the choke and all will be fine and firing on all four. this is so confusing! Leave it in the sun and the bike will be fine after a days work, then the following morning the fun starts again.

Here's a list of things done -

• new wiring loom fitted.
• plugs changed.
• new coil and ht leads (we thought it must be these).
• carbs were cleaned and balanced by a friend of mine.
• new earth cable (battery negative).
• R6 reg/rec fitted. (using Data Racer's briliant guide)
• New battery fitted.
• I've gone round the entire bike, cleaned and wd40'd all electrical connections.

After the carbs were cleaned and balanced, we thought the problem must have been electrical but now we're not so sure, fairly sure I covered all bases here (feel free to tell me otherwise), so do we go back to the carbs? if so why would it be fine once warm (this is a real head feck). please all suggestions are welcome as I have a couple of hours in a workshop on wednesday (my brother in law is a mechanic). so with your suggestions i'll make a checklist and hopefully come up with a solution.

Thanks again.

Matt

If anyone has a set of trusted carbs I can throw to check on i'd happily pay a deposit or pay for them. (although I have replaced the carbs with a cleaned and balanced set I bought from here only to find they were worse than the ones on the bike).

[avinitboys]

Morning Matt,

What bike are we talking here. NC30?
If so, I have a couple of sets of carbs that we could build up and make work (only need jetting) and as I'm only in Twickenham/Teddington it's not to far. Am I right in saying your near Putney somwhere?

Other than that, have you checked that the choke assembly is pulling evenly on all 4 bodies? I too have had problems with carbs bought off ebay and end up pulling them to bits to make them work.
I would guess that you have an issue with one or more of the choke plungers or springs. Unscrew the nut and have a look. It's a bit fiddly though so be careful!

Let me know if you want to pop over for a set and Ill get them sorted before Wednesday.
Paul

[MexicanGringo]

Maybe crank the engine cold a good couple times and check the plugs. The non - firing cylinder is possibly flooding and has a slightly different mixture to the others. As suggested the choke circuit should enrich all cylinders when activated and should allow for easy starting, although it can also lead to flooding if the cylinder doesnt fire quickly. The carbs have been cleaned, but maybe a more thorough clean is in order, involving removing parts of the choke circuit and blasting through with carb cleaner.Fuel from the choke circuit enters the intakes from under the butterflys, its the larger opening, the smaller one is the idle circuit. When you see carb cleaner pouring out this opening you know the circuit is clear

Harvd is having the sample problem in 'rvf running on 3 cylinders', and Neosophist posted this link which explains fuelling changes with temperature changes relating to mixture. http://www.factorypro.com/tech_tuning_p ... gines.html" onclick="window.open(this.href);return false;

[Harvd]

Hey Mattjc id be keen to hear how you got on here? hopefully well as you havent posted again in this thread?

[Old Painless]

If the choke isnt doing anything it has to be a carb issue.

[mattjc]

Well wednesday fell threw and is rescheduled to this wednesday, pretty much came to the same 'it's got to be the carbs' suggestion, so they'll be looked at again. Thanks Paul for the offer but with three sets knocking about I must te able to get one good working set... But who knows aye?

Any way will keep you posted with fingers crossed.

[Cammo]

Take the carbs off and check that the choke lever is actually moving the choke rod and actuators on the front and back carb banks.

Grub screws connect the choke rod to the carbs which can become loose.

[Old Painless]

If the choke isnt pulling the carb slide until its mostly open you can adjust the choke lever throw on the carb by moving the choke cable clamp on the carb further along the choke cable sheath.

You may not have the carbs balanced properly, this can only be done on the bike with a hot engine really. If one of the carbs pilot screw or balance adjuster is way out it may not fire until the bike warms up.

How was the carb balanced ?