View Full Version : 70cc Oliver City 50 now 70 but won't stay running

08-21-2006, 09:51 PM
I put a 70cc kit on my Oliver City 50, then put on an Arreche 19mm carb. The carb came with a #95 main jet installed and a 105 in the box. Per the instructions on this site, I installed the 105, attached the carb and fired it up. It ran well although the top end seemed a tad sluggish More importantly, when it was flying down the road it purred like a kitten but when it idled, it sounded really harsh....bang bang bang bang bang. I played with the a/f screw and idle screw but if I turned it up enough to eliminate that harsh noise, the clutch would engage and spin the back tire. Finally, tonight, I fired up the bike and it blew out a large plume of smoke, then settled down. I never saw it do that before. But since it settled, I took it out and it performed REALLY well. Then I hit a traffic light and when it turned green and I hit the gas, the poor scooter died. I was able to start it again but it wouldn't stay running and it sounded "slushy". I assumed the worst and took the cylinder head off and it's filthy in there, caked with carbon, but it looked basically ok otherwise. The compression guage read 130 so I didn't bother taking apart the rest of the cylinder. If I shoot a little starter fluid in there, it'll start and if I immediately rev it up, it'll run great. Let go of the throttle and it'll start banging again, then get that slushy sound and die. I'm real open for ideas!

Edit: Prior to this, for a few days I'd had difficulty starting the bike. It turned over alright but wouldn't start. If it had been running relatively recently, it would start right up again but otherwise it would require a shot of starter fluid. I pulled the vacuum line and started the bike while sucking on it and it started weakly. Could it be the fuel valve?

08-21-2006, 11:20 PM
That main is gonna be too big most likely. I would be surprised if you needed more than the 95. If you throw the 95 in I'm guessing it will run great.

08-22-2006, 12:34 AM
I was kind of suspicious about that main jet size. From my reading on this site, it seemed like the 90's was about right. But since the instructions said use the one in the box, I thought I'd give it a shot. Thanks for the info fellas, I'll switch 'em around in the morning before the driveway asphalt hits the melting point of skin.

One related thing if you see this again before morning...would it make any difference if I got at least the bulk of the carbon off the head and piston while I have everything hanging open or would that just burn off with a leaner jet?

Thanks again for the info!

08-22-2006, 09:50 AM
Well, I swapped out the 105 for the 95, put it all back together and it exhibits the same problem except that it's blowing a LOT of smoke, relatively speaking. From everything I've read so far, it looks like, at idle, it's barely getting any air. Still, crank the throttle and it starts running just fine. I wouldn't say it's blowing huge clouds of smoke but it is blowing considerably more than it did before all this started. Could it be that it's not getting enough air at idle?

08-22-2006, 10:04 AM
List the full setup that you have. Its easier to say which jets to put in with the full setup.

08-22-2006, 02:34 PM
Oliver City 50, 70cc kit (unknown make, ebay item #320013251044 if you're interested), Arreche 19mm carb (#95 main jet at the moment), stock exhaust (CPI "performance kit" pipe, not the original restricted pipe) and stock airbox with several holes added.

It still doesn't really want to start and when I try, it putts with the starter and blows out a lot of smoke like it's not getting any air. I had the cylinder off and the piston looks ok, the rings look ok and the inside of the cylinder also looks ok. No noticable scratches or anything.

As always, any help will be greatly appreciated.

08-22-2006, 02:39 PM
Ok, now that we know your setup we can help some more.

With that cylinder, your not getting total performance so I would drop the main jet for that cylinder alone. Then, the CPI's new head that you have got on there is nothing in comparison to an expansion chamber. Since your using the stock airbox too, I would cover up those holes with some duct tape then put in an 80 mainjet, its gonna run better.

08-22-2006, 03:09 PM
"your not getting total performance"...what would you recommend to get total performance relative to the fact that I don't want to sound like an angry chainsaw? :-) That is, if I don't want to replace the pipe to a Next R or whatnot and don't want to replace the airbox, is there a point to doing an aluminum (or higher performance) cylinder?

Right now, I'll be happy if I can get it to run on it's own. One thing I omitted above is that I'm using an autolite equiv of a BR9HS as the local auto parts store didn't have any. I have a couple on order but they haven't arrived yet.

Again, thanks much for your time and input. I'm learning fast but still trying to fill in the gaps.

08-22-2006, 03:50 PM
I know how you want to keep the noise down and thats fine but by putting those holes in the stock airbox, you created noise not performance. And keeping the stock pipe is fine, you just need to set everything else up accordingly. And i would suggest getting a better cylinder such as an Airsal.

08-23-2006, 09:58 AM
One thing I omitted above is that I'm using an autolite equiv of a BR9HS

am i understanding this ? you need a cooler plug (BR9HS)
for a 70cc than a 49cc(BPR6HS) if so thats news to me :spiny:

08-23-2006, 10:11 AM
I usually use a BR8HS for cast 70's and 90's and a BR9HS for the Airsal, and then full race use a BR10EIX usually.

And I dont know which bike your using but a BPR6HS is real hot. The CPI's and Ventos should use a BR8HSA stock.

08-23-2006, 12:46 PM
So the idea is that almost everything I've done was done incorrectly with mismatched parts and this is more like 90% magic and 10% logic. Given my level of frustration at this point, if it was a horse, I'd have shot it. Maybe I should just nip this attempt at a hobby in the bud right now before I waste any more time and money on it. Thanks anyway.

08-23-2006, 02:51 PM
I noticed the Arreche and Mikuni main jets are not interchangable so to downjet I had to replace the Arreche with the Mikuni, which I did. Lo and behold, the thing fired right up. So yeah, it appears to be grossly overjetted. The larger carb was a definate plus so I guess I need to find smaller jets for the Arreche. Second big plus...I finally did something right so I must not be completely stupid. :)

08-23-2006, 08:00 PM
I usually use a BR8HS for cast 70's and 90's and a BR9HS for the Airsal, and then full race use a BR10EIX usually.

And I dont know which bike your using but a BPR6HS is real hot. The CPI's and Ventos should use a BR8HSA stock.

type o ment to hait the 7 or it could be my spazzy finger
but thanks for the info
what would the plug gap be on the BR8HS ? in a 70cc that is

08-23-2006, 08:04 PM
I keep it between .026"-.028".

08-27-2006, 08:27 PM
Oliver City 50, 70cc kit (unknown make, ebay item #320013251044 if you're interested)

Thats a CPI bike just FYI.. Its the same motor that comes on the UM Xpeed and the Vento RX8i strada...

09-17-2006, 06:08 PM
Well it's running again...finally. I got the aluminum 70cc kit sold here and slapped that on, the 19mm carb and a Malossi variator kit and it ran great...for about 3 miles. At that point the little star shaped washer that holds the variator together disintegrated and parts of variator scattered in all directions. That was a quick $100. I have another one on the way along with some misc other parts from Yamaha and that should take care of it. The washer was in bad shape and I knew it, but forgot in the excitment of actually getting the thing on the road. The Malossi variator itself worked beautifully.

Two things I noticed:
First, there was a problem with some oil leaking from the where the cylinder meets the casing. Not a lot, just a little bit. The engine was WAY loud and the plug was white no matter what I did. I replaced the gasket that came with the 70cc kit with the original gasket from the 49cc engine. It's rubberish (as opposed to what feels like paper with the 70cc gasket) and about three times thicker. I fired it up again and it was MUCH quieter and the plug was a nice brown color, at last.
Second, the 70cc kit gave me FITS when I went to install it and torqued one of the cylinder stud bolts past the threads on the stud. Further inspection showed that the 70cc cylinder is a little smaller than the original 49cc cylinder (the pistons are the same length, however). So I ordered 4 Yamaha Zuma studs and bolts and slapped one on and they're about 1/2 an inch shorter than the original CPI studs. More, the threads are about 1/4 of an inch longer on each end, so these are far superior to those that came on the CPI and they screwed right into the casing without a problem. Seems the CPI Oliver City 50 is pretty much the same as the Yamaha Zuma. I only trashed one stud so there's only one Yamaha stud on the engine right now, but there are three more here in case I trash any or all of the other three. Just FYI, I have each bolt torqued at 16 foot pounds. I've never seen anything that specified a ballpark of how tight they should be, so there ya go. I've heard "snug" and "until they squeek" but the last time I tried snug, the bolt went past the threads. Bullwinkle not knowing his own strength came to mind.

So there's Mark's excellent adventure into scooter modification. Hopefully the transmission parts will get here in time to let me get it out on the road and break the engine in before cold weather sets in and I have to put it away.

A BIG thanks to Jered for his patience with my questions.

11-25-2006, 04:30 PM
Thought I fried the 70cc engine. Fortunately, I did not so I cleaned things up, put it back together and it ran quite well. I took the scoot out on the road and *that's* when I noticed what my problem was....I never replaced the clutch springs with the red ones that came with the updated variator. So I took the clutch unit off and that sucker would not come apart. I tried a vise and strap wrench, chisel and hammer, heat from a torch...tried everything, that nut wasn't coming off. So I couldn't replace the torque spring but I was able to replace the clutch springs using a needle nosed pliers and, eventually, it made a huge difference at initial take-off. After I put the new springs in, I put the clutch unit back on, put half the variator on, put the belt on, put the other half of the variator on, put on the nut that holds the variator together and tightened it down a little by hand, then took an impact wrench to it. God knows how, but it got a little crooked at some point which trashed the "official CPI nut" and stripped the bolt. So back to the hardware store for a tap and die set which I used to create new threads that would match a 10 cent bolt you could get at any hardware store in the country. With the addition of an extra washer to save me another hour of making threads, it all went together and using a strap wrench and socket set (heh), it was nice and tight and ready for the road. I took it out and it ran like a champ for (so far) 23 miles, the most I've been able to put on the bike since June, and I think I'll put on more tomorrow as it's supposed to be in the 60's again. o_o

I'm thinking at this point I should consider opening a scooter repair shop. I've got all the tools and have nearly every screw, bolt and part, and where each goes, memorized. :)