GT125 starting issues

[GT750Battleship]

How is "the air filter" ? An often over looked item ?
Cheers,
Roger

[Coyote]

Video's don't work. Says they are private.

[yeadon_m]

This is a tricky one. If you have a lot of history of diagnosing and fixing old two strokes, it really shouldn't be too hard to work out which bit is stopping it from going at least reasonably. If you have limited experience its tough to be sure we've described the tests to run clearly enough to be sure we can all rely on the results. Trust me, many years ago I went around and around on this board, with people trying to guide me, and in the end I realised that a chunk of the issue was that I was not properly eliminating faults. I still miss things easily on occasion!

If you've done the carbs many times then (big assumption) assuming you've assembled them correctly and have clear passageways and jets, plus correct float height, and also fuel flows fine, it should not be the carbs that prevents it starting.

So I'm going to guess its electrical. You just can't have 2v at a switched live (orange) anywhere. Yep, you can lose a couple of volts from battery positive to the end of a switched live circuit if numerous connectors are corroded, but not 10v.

So a section by section checking (leave the battery on a tender / charger) should confirm battery voltage at every stage from battery positive, up the bike's spine to the ignition switch, and out the other side, to the switched live (when its in the ON position). You should be 12v (minus a bit of loss) at every section of the orange wires, including wires to and from the run/stop switch which I assume you have on the right handle switch. Each of the two coils should have this voltage as a feed. Likewise, the two wires (probably white, or black, or black with a tracer) coming from the coils to the points. When the points are open and ignition switch on, you should see that voltage at the moving point. When you close the points, then open them again, you should see a fat spark at the plugs, assuming the plug lead, plug cap and plug are good, with the plug resting in its cap on the cylinder head.

If you get all this, then check the points are (i) clean, (ii) maximum gapped correctly ~14 thou and (iii) that the timing is roughly correct (just before top dead centre on each cylinder).

When you attempt to start it, can you smell fuel in the exhausts? you should if you've been kicking over and cursing, anfd the chokes are open )

Good luck and let us know what you find.

Cheers,
Mike
ps: apologies for the above if you've 40 years of wrenching....

[fastcaprinz]

Yeadom_m,

Thanks for your input. As stated this bike is giving me hell, a lot of stuff is not making sense and when I think I have it figured it does something completely different. Like the the first video is of the bike running after I had it sitting in my garage for 2 years. This video was taken after I had flushed out the fuel tank and peacock, checked fuel rate, replaced new battery and two new spark plugs.

This is when the issues started, it started to stall, loss power and not rev.

The next two videos are of me checking spark. The next day it stopped sparking on the right bank, and then the next day left stopped. I replaced spark plugs as no matter what way around I swapped the plugs the right bank or left bank would drop out and the other side would come back alive. I then had spark again .... ??? confused I thought the fault might be somewhere else hence me checking voltage from battery along the circuit. This is when I found the massive voltage drop and why I asked could it be voltage regulator. I know it is not part of this side of the circuit but when all other reasons fail the "logic is however unlikely must the be truth" Spoke Startrek (something like that anyway)

I will have another attempt this weekend and see how I get on. I just cannot think of anything else I can try. I have spark, I have fuel, I should have a running motor.

P.S Mechanically minded, father was a motor mechanic and I restore old cars so I am usually o.k with this stuff, but this bike has me beat hence questions here seeing if anything is unusual about this bike or perhaps overlooked

[Alan H]

I had similar on the 550 with poor sparks and intermittent wiring issues.
Pull all the bullet connectors apart and clean male and female parts (of the connectors!) shiny before putting them back. Also check where the crimp is onto the wires as I had one or two that had discoloured so didn't connect too well. Just snip off the bullet or ferrule and recrimp a new one on.
I think the problem is just crappy connections.
You don't need a connection to be very bad before it causes problems.
A small amount of resistance on 12v makes a helluva difference on 20000v on the ignition side.

[fastcaprinz]

You guys are awesome! I found the issue and you would not believe what it was.

Someone had been there before me. I was kicking over the bike looking at spark cause i would call it the best colour when the battery fell on the floor!?? Yes i can hear what your saying. . . How if it is connect. Well the bloodly earth wire was just poked into the connector mounted to the chassis. I also found the positive wire going to the voltage regulator. Was just twist wound together.

So thebike now starts easy enough however living up to its name hell bike i now have another issue which is really the first one I had. I have to hold the throttle wide open to keep it running. See new video.

Http://youtu.be/CnAeG2HYz9E" onclick="window.open(this.href);return false;

Any ideas?


Mark

[yeadon_m]

Dirty pilot jets, old fuel, air leaks on intake side, bunged up air filter....whats the state of play on the fuel / air side? have you had that to bits to have a good look?

Is it running on both cylinders (if indeed it is a twin).

Hopefully the carbs are bolted on securely )

Joking aside, my first bike, a Yahama YAS1 125 twin, came to me with its carbs loosely pushed on, a spark plug finger tight and a hole in the fuel tank. Lucky, some kindly older lads saved my bacon, and embarrassment (at least until day #2, when I laid it down on a wet roundabout

Cheers,
Mike

[fastcaprinz]

Yes new fuel today. Used the old in lawnmower.

Batt 12v (checked by volt meter)
Cant see why carbs would be dirty again.

[yeadon_m]

Clearly, something pretty major isn't right. Given you can just get it to run with near wide open throttle but not otherwise, I will lay a chunky bet the issues are in the carbs, fuel supply or air filter. I doubt you have a choice than to pull all of these and dig in, if you want it to be right.
Mechanically it sounds OK when running on your video clip.
I don't own one so cannot be more specific - grab your tools and go around again, I'm afraid!
Mike

[ConnerVT]

Looks like the same type of round slide Mikuni used on the T500. Possibly the slides got switched? The cutout goes towards the rear (air box). Happens way too often...

[fastcaprinz]

The sliders can only go one way on this carb.

Next idea?

[ConnerVT]

Yes, but can the slides from the left and the right carbs have been swapped?

That's happened so many times (just do a search of this site). The slides look the same (locating pin and idle notch), but they are actually mirror image of each other.

The curved cutout at the bottom of the slide faces towards the air box.

[fastcaprinz]

turns out you were right. the slider inside the carbs were around the wrong way. the left carb had the right slider

[dgoodsy]

Thanks for following up fastcaprinz. I read through the thread and somehow feel better about trying to get my own bike started now. Good to be aware of some of the simple-but-easy-to-overlook issues that can be caused by me or by the previous owner/mechanic.

[ConnerVT]

Don't feel bad. I think nearly everyone has done it at least once.

Just as bad, I once kicked my T500 'til my leg was killing me. Only to find I had swapped my left and right spark plug leads.