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[boghopper350]

Hi. As you can see I don't post a great deal! ;-) I only really use this great site for finding out stuff about bultaco's. I have found it very useful and informative. With this in mind, I thought that I would try to find out what could be wrong with a friends gas gas contact. He bought it a couple of months ago from a local bloke. He is an engineer by trade, so as you would expect, he stripped it out completely and has rebuilt it with all new bearings, chain and sprockets etc. He couldn't get it started, so asked me to help. We have stripped the carb, cleaned the jets out, put a new plug in. The spark seems a bit weak, but is blue in colour. We have checked the connections on the ignition including the kill switch (I have tried disconnecting this also). When we try to start it, it fires up really cleanly and runs for about a second- second and a half and dies instantly and wont start again for a while, after that it starts again and dies. At this point we checked the plug and it's wet. At one point we started the bike and it revved to about 5000 rpm and kept running!!(this was due to the throttle cable being snagged). I'm wondering if someone could prehaps give us an idea what could be the problem. We are wondering if it's something like the stator beaking down, when the bike revved it somehow increased the voltage and helped the problem. As you can probably tell, electrics arn't my strong point. I forgot to mention that he checked the resistance at the coil and said that it was a little bit low, but only by a couple of ohms, I'll have a word with him to find out the readings and post them later.

[coop650]

Start here:

http://www.trialspartsusa.com/diagrams/TESTING%20THE%20MOTOPLAT%20SYSTEM%201990.doc

[0007]

Quite often people move right past the simplest things and start looking for exotic problems

I have been diagnosing motorcycles (etc) for about 30 years and found the following to be one of the most usefull tools, basically, the simplest most obvious solution is usually the correct one

http://en.wikipedia.org/wiki/Occam's_razor

#1. Replace the spark plug, once a plug has fouled one time it creates a carbon track on the porcelain, you can't see it an it cannot be removed unless it is sandblasted, it can still spark but, it's life is over

#2. Leave the plug out overnight, it sounds like there is a puddle of fuel in the bottom end and when the bike fires, it pulls up liquid fuel from the cases and soaks the plug

Don't be concerned about resistance being off by a bit, every meter is different, there are a lot of variables, look for HUGE differences

Best of luck

Edited March 31, 2013 by 0007

[boghopper350]

Thanks for your help. As I have a bultaco I am used to not looking for small problems 0007 and get where you are coming from there. I am glad to hear that small a difference in the resistance re coils shouldn't be a problem ( the resistance in the blue wire to the stator is 33 ohms and the red to coil is 1.8 ohms). I have had bikes that have been flooded in the bottom of the crank, and they perhaps may just fire on one stroke (a really muffled dull pop) and then flood and have a really wet plug, dripping wet. This bike as I said fires really crisply for about 1 1/2 seconds, then stops instantly and has a wet plug that indicates fuel is present, but not overly wet, you don't have to take the plug out and it fires the same a short time after for exactly the same length of time, repeatedly.

[b40rt]

Reeds ??

[zippy]

Reeds ??

I don't see what Chad's family has to do with this?

[thats_a_five]

FYI, I have a ’94 JT25 so my bike is pretty similar to your friends.

The problem sounds like a contaminated fuel condition to me. However, I do not want to jump to conclusions without some additional information or troubleshooting.

Did the bike run before he tore it down? If not, how long had it sat before it was last run? If it had run before, then the problem occurred during the rebuild. That narrows down the search.

How old is the fuel? Water in the fuel will act exactly as you describe. When the engine stops, remove the plug and smell it. Gas or water? You can easily confirm with a small flame by the wet plug –AWAY from the bike or gas can! Another option would be to drain the fuel into a glass container, let it sit for an hour or so and you should see the water separating to the bottom of the container. If you find water, change to new fuel completely, drain and clean the carb thoroughly. Replace any fuel filters. Even tiny droplets of water can clog jets or kill a spark.

If you suspect puddled fuel in the crankcase, remove the plug, turn off or disconnect the fuel line, hold the throttle open and kick it a bunch of times. If there is a lot of fuel, you will get a geyser of fuel in your face, so tie a rag over the top of the cylinder. Once the big quantity is gone, remove the rag and kick until you don’t see fuel vapor coming from the plug hole when you kick it. Reinstall the plug and try to start – with the fuel still OFF. The remaining fuel in the carb should run the bike for a minute or so. Remember that any puddled fuel may still have water so I would advise new fuel anyway.

Let us know how you get on.

[boghopper350]

Thanks again for your help, it's much appreciated. It's all new fuel 50/1 pre mix and the tank has been flushed to make sure there's no contamination t.a.f. The bike had the same problem before the rebuild apparently. I did mention the reeds to him the other day, but I'm not sure if he has checked them yet b40rt, but wouldn't dodgy reeds give symptoms of erratic running/idle, as this bike runs very cleanly when it fires, I'm not so sure, but we will check thanks. I only mentioned that the plug was wet to explain that there was fuel present, it isn't dripping wet. I'm sure that it hasn't flooded because when it fires it is really crisp and doesn't smoke at all.(I recently had the flooding problem with a beta synt that I bought for my son). Once again thanks for your input.

[sting32]

All I can offer is 2 anecdotal incidents, on a not same bike...

1st (years ago) I had a montess (way back when) and the COIL, the part the plug wire connects to, was BAD, it would start and run for a while (longer than your describing, though) then die and not ever start, again until it cooled off. Yes I would pull plug, seem to have spark, still never start. Sold the bike for nothing, next owner changes coil, all is good, last I'd heard.

2nd: VERY RECENTLY, I bought a used 2007 250 Pro, long story short, brought it home (preparing for my buddy). It started... Throttle was routed funny, so I shut it off. It never would start again, that is until I seeminly found the problem...

I started out and checked EVERY WIRE under the tank, looking for loose grounds mainly, this also lead me to removing kill switch.... Finally decided to check behind flywheel, thinking maybe moisture in there in past, and maybe my luck I disturbed enough to lose

spark?" When I got the flywheel off, in there I found that the entire mounting plate that the lighting and ignition coils were on, had maybe vibrated loose. Anyhow, it was loose. Tightened the 3 allen-head screws tight, still runs like a champ today.

[boghopper350]

Thanks sting32, that sounds good we'll have a look. Thanks everyone for your input, I'll let you all know if we make any progress with your suggestions.

[boghopper350]

Hi, just to let you all know, we got the bike running a couple of weeks back. We cleaned the carb out for the third time! And despite the bike having a new fuel filter, fuel, and the tank having been flushed out, the pilot jet was blocked. The bike runs nice now, apart from seamingly running weak off idle. Also it seems a bit gutless, I though that this thing would really dig in, but our beta synt is far more powerful. It does suit him tough atm as he is back on a bike after a 17 year break. Thanks again everyone for your input, it's nice that people like to help us numpty's that struggle with our probs.