Gilera DNA 50 - 70cc Full rebuild help and advice needed

[supra3turbo]

Hi There,

As you know my little brother got this gilera as his first bike, advertised as needing crank seals and will start...

I admit i went a bit overboard, but on stripping the engine down, and finding it had a 70cc kit on it, and one of the crank bearings was noisy, i went about a full engine rebuild

Its got a HPC racing crankshaft in it, new bearings, everything is brand new, other than the 70cc kit that was new on the bike when bought.

The bike is back together and starts first press and sounds great (The fact im even posting this on here is beyond me, but the pressures of a 16 year old and his first bike are getting to me)

Basically its still not fully completed, but it has been heat cycled and ran in, but if i give it full throttle it revs to about 7k then just bogs to nothing, 3/4 throttle and under is fine, but full throttle and it sounds like youve just put your hand right over the carb intake, flat as a pancake.

I have thrown a 68 jet in it, and an aftermarket ait filter.... thats it, i did originally say this project woudld take me 2 weeks, but for some reason he passed his cbt in a day of buying this bike so he wants it NOW!!!! as you can immagine

Has anyone experienced this, or like i said, am i just being a bellend? Knowing i have a full jet kit to go through, Carb settings, needle position, 2 stroke pump setting might have gone off, just a thought if anyone could help me that would be greatly appreciated

Joe
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Hoda CBR 600 FX stolen from stalybridge 2017/2018 black
Current Project Suzuki RG125 Cafe Racer

[supra3turbo]

Can i also just say, ive built probably 15+ 2 stroke engines of all variations, taking my time and doing things slowly and methodically as you should, but never have i had the entire engine in bits on the bench friday night, and running and riding sunday and not spending a single FULL day, so its basically been a day or 2, and the whole bike is back together, i know its the carb settings, ive touched nothing other than throw that jet in it, it did have a 60 jet in it.... Im tired now, worked all day, spent all night in the workshop with a 16 year old.....

Just tell me im being a massive bell and being too soft, and that i need to say "STFU, IT WILL BE READY WHEN ITS READY, I CANT BUILD AND FULLY TUNE A 2 STROKE IN 3 DAYS" LOL
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Hoda CBR 600 FX stolen from stalybridge 2017/2018 black
Current Project Suzuki RG125 Cafe Racer

[jeffyjeff]

If this looks like I cut and paste from the ER5 posting... Sounds to me like your engine is demanding more fuel than is available.

Check the fuel supply to the carburetor. Make sure that the petcock flows fuel freely and that there are no restrictions, debris, fuel filter issues, etc. restricting fuel flow.
Does that bike have a vacuum operated fuel tap on it? If so, a vacuum leak could be causing the tap to partially restrict fuel flow (in addition to the suggestions listed above).
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History shows again and again how nature points out the folly of men - BOC

[supra3turbo]

It is a vacuum operated fuel pump, if i take the fuel pipe off the carb and put it right into the fuel filler and start the engine, it squirts out fine, really nice flow
____________________
Hoda CBR 600 FX stolen from stalybridge 2017/2018 black
Current Project Suzuki RG125 Cafe Racer

[jeffyjeff]

[stinkwheel]

Was it running properly on full throttle before?

Brand new bigbore kit fitted then up for sale immediately after with a running issue rings alarm bells to me.

Maybe they couldn't get it to run right and assumed it was a crank seal and punted it on so it could be someone elses problem?

I'd set the carb to stock-standard and work from there. It should at least run at that and give you a basis for setting it up properly.... A larger capacity doesn't necessarily mean you need a bigger jet. Maybe worth checking float height too?

Then there is the old true-ism that 90% of carb faults are electrical. I presume the flywheel is keyed and it's a CDI ignition but checking it's got a new plug of the correct grade is always a good start with any 2t. As well as a fully charged battery.
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“Rule one: Always stick around for one more drink. That's when things happen. That's when you find out everything you want to know.”
I did the 2010 Round Britain Rally on my 350 Bullet. 89 landmarks, 3 months, 9,500 miles.

[supra3turbo]

Thank you all for your input i really appreciate it, when i got home from an 8 hour work shift i went straight back into the workshop and went straight to the carburettor.....

Some 16 year old in the past must have gone "ye m8, needle clip at the bottom, for bare fuel init, that will make it start"....

So with the upjet, and the needle as high as it would go, it was just slavering the poor thing with fuel, now thats set, the mixture screw is set, the carburetttor has stopped leaking (Thanks to it having a plastic bowl, gently honed the face down on some 400 grit to allow the rubber gasket to seal, as i could not get a carb rebuild kit in under a week delivery)

THE BIKE NOW RUNS GREAT!! Im 14 stone, and i got 42mph and ran out of private tarmaced lane

So the bike now has the 70cc kit, (Gently honed by me, with a 3 stone drill honer, it had never ran with this kit on, and had tried to be started MANY times) I ported the exhaust port with a de buring tool as it was pathetically small, and just touched the intake port to smooth out the flow, The piston had VERY minor scoring which i polished out with autosol and a microfiber cloth, New bearings, seals, HPC full circle racing crank shaft (For longevity mainly, due to the increased stress of the 70cc kit, need this thing to last for him)

Also i reconditioned the brakes, new brake pads (The brake fluid was just rust water black garbage) new suspension seals and fluid, new gearbox oil, all the engine cases and gearbox casings went in the dishwasher before re assembly and i used the Official Loctite 510 as crankcase sealant (FU***NG Expensive that stuff!!!

But now the bike is right, running great, and i really hope it lasts for a long time!!

Thanks again!
____________________
Hoda CBR 600 FX stolen from stalybridge 2017/2018 black
Current Project Suzuki RG125 Cafe Racer