Hello !

This is my first post on the forums and I will like to say hello to you guys !

I have the pleasure to ask you a few questions regarding my beloved 3TB from 1993.

There is a small problem starting when cold recently (since the weather dipped bellow 10 degrees Celsius).

The bike turns when I use the electric start it starts after 2-3 seconds and the revs don't climb and it eventually dies out on me. After 2-3 attempts like this the bike eventually starts (the revs climb slowly then a bit faster and reach the rpm it should be with the choke fully engaged) and from there on I have no problems. (I start it once in a week or two)

Things I've tried so far:

- I played with the pilot jet adjustment screw (from 2.5 turns to 4 turns out - no improvement on starting).

- If I try to adjust the pilot jet screw when the engine is warm I sense a small raise in rpm from 2.5 turns out towards 3 turns out the it flattens out (no more increase in rpm) I didn't screw it our further than 4 turns since the bike was running to rich according to my assumptions ...

- I've changed the spark-plug with a new one and charged the battery (it was bought new in summer and my charging system is in working order)

- I've used some carburetor/injector cleaner in fuel with no visible results

- The engine was rebuilt last summer including the following - cylinder honed ,new piston,new valves,new timing chain,etc. The valves were adjusted again after 500 km and they were lapped and checked for leaks when I've mounted them.

In summer I felt it was a little lean at idle and off idle (few pops on the exhaust while decelerating and when fast revving from idle). So I've enriched the idle mixture from 2.5 turns out to 3 turns out and the problems was solved... the bike returned to idle quicker with no popping.

A mechanic set the clip for the needles on middle position on both carbs and I've adjusted the transition mechanism between the carbs. (the transition is very smooth)

The spark-plug that came out soon after the issues became more prominent was black with carbon deposits. I think the bike is too rich on the needle since this guy "had to" move the clips to middle position on both needles but this doesn't explain my problems starting since the needle / main jet is not affecting starting of the bike.

What is the default (factory setting) for the needles and for the pilot jet screw ?

For pilot jet screw I've found on the forum that is 2-2.5 turns out (and Aukeboss says 4-6 turns out which I think would be too rich) and for the needle in the primary and secondary I'm not sure about clip position.

Again the bike turns over 2-3 times and starts but the rpm drops (engine dies) or it climbs very slowly to idle speed that should be with the choke engaged.

Also when the engine is at running temperature if I engage the choke it tends to die then it clears out and the rpm raise ... This sounds too rich ? but hard to start ? A lot of controversy going on in my head right now.

Please help if you have time !

Thanks,

Bernek

I can add a few pictures of the spark plug (sadly it does have some dirt on it after was taken out)



The idle screw adjustment was around 3.5-4 turns out but I would blame it on the needle. I also have a bad habit of firing up the engine once a week and don't ride the bike. I know this is not a good idea but I can't help it ...

Hi Bernek and welcome to the forum.
If you aren't already doing so, drain the carb if you are not going to use the bike for more than a week. That will make starting easier.

Bob

__________________
Remember that Assumption is the mother of all f**k-ups.

I have same model, idle screw 2,5turn out and never any problems starting or idle. I had problems with carb before cleanup, it was the small filter inside with full off dirt making it. So yes remove carb and check filter, and the boots from carb to engine.

Thank you for posting ! I was curious why the drain plug screw shows evident signs of usage over time.

I will drain it when I'm not going it to use it for more than a few days. What is the tehnical explanation for this ? Fuel degradation ?

Regarding my starting problem:

I lowered the idle speed (as much as I could) and it seems to start a little easier now.

I'm at 3.5 turns out on the pilot jet screw and the firing and idle is better ! Will have to check tonight with the engine completly cold to see if I'm 100% right about it.

The boots are like new and the rubber is really holding good (I think they were changed recently 1-2 years ago before I purchased the bike).

The small filter I cleaned it maybe 6 months ago but I will remove it completly and install an inline filter on the hose. Any recommendations on this filter ?

Thanks for trying to help me out !

Bernek

L.E. the carburetors were cleaned using carb cleaner and compressed air in summer and I also used a carb repair kit for this model to change all the bits and pieces that are user serviceable.

I will have to solder a small screw on the pilot jet screw so I can adjust it easier... just need to find a brass screw with the same proportions. I hate burning my hands each time I'm trying to adjust this one.

Any settings for needles that you might share ? as I've stated the "mechanic" had to move them to middle position and I don't really like the spark-plug coloring that I had ... the photo is from the spar-plug that I've used maybe 1-2 months and it has close to 1000 km on it (mostly off-road). Is carbon build up really fast on these big singles ? Since the bike idled some time before I took this spark-plug out ...

No i dont have any build up on the spark its normal colour, honestly i dont remember the original settings on needle. I changed to dynojet kit, did you buy original or cheap china kit for carb? What size of jets do you have? Search forum, its all in here we have talked bout same problem before so i think you will find jet setting. If you dont find let me know, i have another original i can open and check.

The kit was not made from Yamaha but from another company (I can't remember the name) but the price was similar to an original kit. No way it was dirt cheap like chinese kits.

I think I payed close to 100 EUR for the entire kit. Chinese go for 10-15 GBP on ebay.

Regarding the needle position I searched in past (on this forum) but couldn't find something stated clearly. Just when you have time would be nice if you can check the original positions (so I can have a solid start in tuning).

I will try to start the bike again tonight to see how it will fire. I also have some doubts regarding the battery ? Since it transistored (TCI) it can't work without a battery and I might get a weak spark from an old battery ? Mine has 6 months and it was bought in spring 2017.

This is the battery that I use.

And with that weak spark and cold engine it could behave like I'm experiencing ?

It seems to me like this carb doesnt have been adjustet, but cant be sure. The diaphragm was 3notch, spacer and plastic under, remember to have hole free for the breathing in it.

So secondary (vacuum type) is 3rd notch.

Primary carb ? what position for the clip ?

Also 3rd notch you count from top (blunt end) ? Needle in working position I count 1-2-3 and on the 3rd that is middle position ? I think it has 5 positions.

Thanks a lot !

Slow down man i have take it apart first yes both was the same place, center of the pin. 3rd from up or down its the same. Anything else?

No ! Thanks a lot for the information. So the middle position is the starting point.

Great news I don't have to take them apart yet.

Ok, you have align them correct for the opening?

Yes the transition is nice no problems there ...

Only the starting problem ... Engine fires after 1-2 attempts but it slowly dies ... after 2-3 more tries it fires and the revs climb and it works perfectly afterwards ...

Could this be a weak spark ? Should I change the battery ? I will measure the current when starting to see how low it drops !

Cheers,

Bernek

Why dont you charge the battery? Its normal that the bike can die after starting and then have to start again if it has been standing for some days, do you pull throttle when it starts or just waiting to see what happens?