Oil pump

[hazza]

Well I installed the clutch back onto the bike and it is no better or maybe a bit worse. Swapped the 4.5 rollers back to the 3.5s and it revs a bit better but won't take off. There is next to no acceleration and it builds speed slowly. Maintains speed up hills slightly better but if it is a long drag it will slow eventually.
It just doesn't seem to be revving like it did with the 50cc barrel. Revs OK on the stand but not when I'm on it, and I only weigh 150 pounds.
It bogs slightly at about half throttle so I recon thats the carb but I'm not sure what to change. Any suggestions anyone.
On another note, it sounds nice and throaty, I may just leave it out front ticking over so I can listen to it.

Harry

[90GTVert]

I would think 3.5g rollers would be plenty light for a 70cc, but maybe getting the revs up with a stiffer contra spring or lighter rollers would help. I'm starting to wonder if something is up with the BBK. You should be seeing a big power increase going from 50-70cc. It should accelerate stronger without even having to change weights. More power usually means you'll need heavier weights, unless you are using a big bore kit that needs to rev high like a race or high end kit.

[hazza]

Just found out that the carb that I am running is 12.5mm. Do you think that this is what is holding it back?
Also would a multivar variator help?
As far as I know the big bore kit is pretty much bog standard, cast iron with 2 rings.
cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&item=230617887299

I just rode a workmates Aprillia with a 70 kit on and it kicked hard and accelaration was excellent. He gets over 60mph out of it no problem.

Found this carb for a good price, is it any good?
www.adrenalin-pedstop.co.uk/p-21mm_racing_carburettor_from_TNT_for_2T_scooters-4361.aspx

We are away for a few days from tomorrow and won't be back untill Monday so I will have to try and figure it out when I get back.
Thanks for all the advice

Harry

[90GTVert]

Yeah, that's a sport kit so it shouldn't need rev too high. I can't imagine the 12.5mm carb is doing you much justice. 17.5-21mm are good choices for 70cc kits. I'm not familiar with that exact carb. Reminds me of a DellOrto.

[hazza]

Thanks Brent, I will pick up the carb when I get back, but will be Tuesday now. I will also need to fit a cable as it doesn't have auto choke, shouldn't be a problem, I just need to decide where to put the pull switch so it is accessible but not in the way.
No wonder the one I have now only takes small size jets when everyone else reccomends bigger ones.
Cheers
Harry

[lshigham]

That carb's a 21mm dellorto PHBG clone, I've been using one for a while now.

[hazza]

Hi Ishigham, Did you need to alter anything on the carb or did it fit straight on? I may need to go a bit bigger on the main jet as it will be going on a 70cc. I will also need to accommodate a cable choke as the mikuni is auto choke.

Harry

[lshigham]

They've got a choke built into the top of the carb, if you don't mind reaching in. You should be looking at 90's for the main with an open filter, and you will probably need to decrease the pilot jet to a 35-40. It should fit right in to your stock manifold, the difficulty is in finding an air filter that'll fit if you don't use the airbox.

[hazza]

Thanks for that, I am hoping to use the stock airbox as I don't want it to be too noisy.
I will try a 90 first and see what that does then take it from there. I was hoping that the pilot that is in would be OK.
I will need to fit a cable as there is no direct access to the carb once the seat box is fitted. Thats just a case of finding a suitable location for the pull.

Harry

[lshigham]

If I can find my bag of dellorto Pilot's I'll post a suitable size to you FOC if you need one.

Start at 80 and work down with the air box

[hazza]

Thanks Ishigham, I will let you know how I get on.
It will be Tuesday pm before I can get the carb 'cos I'm working in the morning but will go straight after and pick it up.
I will ask about the pilots when I get the carb and see what they recommend. They are very helpful and don't mind spending a bit of time answering questions. I will probably stick to the oil pump for now as well.
Cheers

Harry

[hazza]

I can't get hold of a carb until the end of the w eek so I have been fiddling around with the one I have got.
I can't get the damn thing to run at all now. It revs ok on the stand but just bogs when I sit on it. I tested the compression and I get 110psi, does this sound about right or is it on the low side? Not sure what it's suppose to be on a 70 kit.
Looks like I'm gonna have to wait for the new carb to come in.

Harry

[90GTVert]

110psi is low, but I don't think that's your issue with the bog right now. I think you are on the right track with the carb/tuning.

[hazza]

I just knew you were going to say that so I checked it again and got 115psi. The engine was cold when I did the tests so could go up a little when its warmed up. I just can't get it to run well enough to get it warm up. What did it ought to be, roughly.
I also checked the variator in case something had come loose but everything was tight. Well, everything except the drive shaft that the clutch slides onto which has a fair bit of play in it. It was always like this though since I got it.

That will need an overhaul when I get round to it, seems like the bearing has seen better days, not looking forward to stripping this out but if I do then I might as well fit an gear up kit while it is in bits.

Harry

[90GTVert]

One bit of good news for you, it's actually normal for that drive shaft to have play in it. That worried me too when I first started messing with scoots.

I dunno for sure on a 70cc, I've got so used to 90cc stuff and even than it can vary. I'd liek to see 125psi as a minimum for a decent running engine.