Mysterious problem with Gilera rcr 50. Please help!

[jasper090]

Hello,

Several weeks ago a problem arose with my Gilera rcr 50. The problem consisted of it bogging down (the bike would basically cut out and then come back alive once speed reduced) at speeds in excess of 50mph, this further developed into it bogging down when ever I gave it anything over half throttle. The bike would then fail to start for several minutes and then it would need bump starting (If left for long enough I could kick it over).

My immediate thoughts were that it was a fuel problem, so I cleaned the tank, fuel tap, pipe and carb - using a air compressor. However the problem persisted so I changed the plus and cleaned everything once again. But annoyingly the problem was still evident and the bike would continue to bog down. I eventually took it to the local mechanic who was baffled; he cleaned everything and did some fiddling. However it still failed to run smoothly.

I then bought a new CDI plus ht lead and plug cap. finally I had some progress, the bike worked like a beauty this morning... Until I rode it back from school - I was going up a hill and the damn thing bogged down again. However this time the bike continued to work in first gear, its only when I went faster than 5 mph (ish) that it would bog down and splutter. After several long miles I decided to go straight to the opposite end of the spectrum and go for 6th gear (struggling like mad) but once I had it at got into sixth and I had it on full throttle it worked just fine... up until i had to slow down into <5th gear and it would bog down...

So to summarise:

First works okay at low revs

2nd, 3rd, 4th and 5th it bogs down in

6th works fine even at low revs.

It's had a new CDI + HT lead + plud cap + plus

Additional things about the bike are:

Engine has been re-built with a bored out piston kit

Its 2008 model

hmm thats about all i can think of currently.

If any one has any clue as to what this problem could be I would be tremendously greatful!

Thank you,

Jasper Mowatt

[Weebl]

Does it have an automatic choke?

[tryme]

Or..its a hairdryer that's been chaved up and ragged til the engine fu*k3d?

[mattycoops43]

Kick start! I would be looking at battery/charge problems, Those are the symptoms to me of a battery that doesn't have enough power to run the spark over certain revs. Probably charging system as it would run the bike with a flat battery if it was all working ok, unless the battery was so dead the generator couldn't keep up.

Measure the battery voltage with it not running, then measure it with it running, it should be at least 2 volts higher when running.

Also check battery, is it a gel cell? lead acid? does it have dry cells?

Matt

[jasper090]

Does the battery actually contribute to the spark? I though it was all done by the coil? and the battery was just for headlights and alike?

However what you say does make sense as the battery is near enough w**kered! I shall test the voltage across it as soon as possible and let you know the results

In response to the guy asking about the choke - no its not automatic, but I've never needed to use it...

Thanks

[jasper090]

Battery whilst its not running is 3 volts

battery whilst running 4 volts....

seems awfully low to me??

[klingelton]

is it a vacuum problem?

[eastanglianbiker]

new bettery is the first thing in my mind with those readings,i have no idea if it a 6 or 12 volt system on it but whichever the readings are far to low

[Colin the Bear]

Not familiar with this make/model

Yes readings are low. Battery may not be duff. Try taking off and charging it. You may have just a charging problem.

The coil changes the low voltage to high voltage for a spark. If there's no low voltage , nothing to convert.

There will be some sort of generator, probably an alternator and associated bits and pieces to charge the battery.

It will explain how to check in your manual.

[jasper090]

Thanks all for your input.

When you say vaccum do you mean the fuel tap?

The battery does appear to have little fluid in. A new one is only 20 quid so what ill do is buy a new one and then I can eliminate the battery as a problem.

So do you guys think the problem sounds more electric than fuel?

Colin, from what I understand the battery dosnt actually do anything other than the lights and indicators and its a magneto that supplies the low voltage which the coil converts into high which also charges the battery... However I may be wrong.

Thanks again, I am very greatful for your advice .

[Tango]

You ain't got a magneto if you have a CDI unit.....

Dunno this bike....but normally you'll have an alternator which goes into a Rectifier/Regulator which then charges the battery....or not if any of the components are duff. If the battery was dry, then it's had it....but the downside is that it could have taken the Reg/Rec and Stator with it. But first things is to replace the battery and then check the voltage again to see if the Stator and Reg/Rec are OK. A weak spark will certainly give the symptoms you describe as others have said. So sort your battery and charging circuit and you should be OK.....

[Colin the Bear]

Stop buying things till you find the problem.

You have an ignition problem. ie weak spark.

The battery has run dry.

The electrical generator, whatever we call it, alternator, dynamo,magneto is not generating. You measured it.

All the electricity on the bike comes from this source. Some is stored in the battery and some goes to the ignition and accessories on the bike.

Either the generating system has failed and fried the battery or the battery has expired due to neglect, ie not checking fluid.

Simply replacing the fried battery may result in having two fried batteries.

[mattycoops43]

Totally agree, you need to find out what is actually not working before spending lots of money, But you need a battery, so I would get one, then check what its charging at before you run it much, A dead battery will draw all the current from the generator, so even a fully working charging system will not run the spark, a faulty charging system will not run the spark and cause a dead battery.

Put the battery on, if it's a 6v I am not an expert in these, but I would guess you want 7.5-8v while running. A 12v system should be 13.4 up when running and fully charged.

[jasper090]

Okay I see, well i hope to get the battery tomorrow and i shall report back my results. by the way, the bike runs without the battery and still bogs down - which indicates that it might not be a battery fault as everything is the same when i am bypassing the battery... (battery wasnt completely dry, the electrodes were still wet, there jsut wasnt excess fluid...

Thanks again.

[Tango]

If the battery is fried due to insufficient electrolyte it can go low resistance and drag the voltage down from the Reg/Rec, charging circuit. Of course the opposite could be true in that the charging circuit has been pumping too much voltage into the battery and boiled it dry. Personally, the battery is dead so will need replacing anyway....but when the new one is fitted to the bike you need to check the charging voltage to make sure it is in the right area as suggested above. If it's too high then you run the risk of boiling the battery. I think for a 6v system you'd need to see 7 - 7.5v at the battery....any more and it'll boil the battery...any less and it just won't charge it.....

[jasper090]

Right well it works... And is running jsut fine - I just took it apart and gave it a good clean again and its decided to work however because this is what happened previously and then it died again would it be a good idea still to get a new battery?

Tango, the manual says its a 12v (4 amp hours).

Thanks

[eastanglianbiker]

if its 12v battery and you say you was only getting a reading of 3 volts and then 4 with engine running i would start checking alternator and reg/rectifier

[Tango]

If the battery is stuffed it could be dragging the voltage from the Reg/Rec down. I'd be inclined to replace the battery and check the voltage again. It should be approx 13.4v with the engine running.....12v ish without the engine running.

[jasper090]

Well I got a new battery its doing exactly as it should be doing which is great! Hopefully the problem will go away now however i suspect that it will rear its head again soon!

Thanks everyone for their help and advice!

[Tango]

So.....13.4v with the engine running and 12ish without? If so, I don't think you have a problem with the charging circuit.....which is good news.....

[Colin the Bear]

Have a little faith and keep an eye on the fluid.

However with a high performance (relitively speaking) small 2Stroke another problem will be along shortly.