Yamaha Jog R low top speed

[geoffh]

errmkk,it might be better if you started a post in 2stroke trouble shooting section of the forum,before you do here,s a few questions you,ll be asked

stock air box .in good codition
belt size,condition
rollers all ok
plug color /condition
it,s hard to help without the full picture

geoff

[paydem]

Update on this thing.

Still has some carb issues on cold starts. Besides that, I found out that the belt is still OEM.



I measured it and the current width is 14.5mm, instead of the 16.5mm. The service manual says the limit is around 1.5mm of wear, so no wonder why it has such a low top speed.



In the winter I'll be fitting a sports exhaust Gianelli Extra V2 and the rollers that will come with the set. I'll be replacing the OEM belt with the Malossi X-Special one. (745x16.5)

That should take me to 80 km/h range, if it does 75 km/h - I'm happy. After that, I'll be working on acceleration mods, and do a little bit of stunting.

[paydem]

Not sure if anyone reads the stuff I write here, but if anyone has simiral problems and doesn't find the answer, hopefully it helps you.

After switching over to 12mm carb, the engine sometimes ran very lean, the other day it ran very rich, it was impossible to tune it properly. I raised the needle one position over from the middle and stayed with it. I had a lot of cold start problems and bogging on acceleration. I took off the air filter and found out that the gas was spitting back to the air filter box. I took off the intake manifold. The gasket was cracked and definitely was sucking in excessive air. Then I checked reed valves, and it definitely needed to be replaced too. One reed valve was stuck open, and from what I understand, that's why the fuel have been spitting back to the air filter box! I measured the fuel I used up and the MPG's are terrible, I got 6l/100km, which is equivalent to 47 mpg. After fixing all that stuff the scooter should run much richer, after tuning it I hope to get smaller fuel consumption as well as improved power.

[geoffh]

errmkk,glad to hear your making progress and making plans to improve your scoot,it sounds like your engine has never been looked after,before you make any changes get it running at factory settings and a full CVT check is in order.That OE belt has had a hard life IMO I,d replace it with a OE spec belt and some 6gram rollers so that you can bench mark the engine before you make the changes to the pipe and CVT.

400 views to date and your English is fine

geoff

[paydem]

Nov 25, 2017 10:21:33 GMT -5 geoffh said:

errmkk,glad to hear your making progress and making plans to improve your scoot,it sounds like your engine has never been looked after,before you make any changes get it running at factory settings and a full CVT check is in order.That OE belt has had a hard life IMO I,d replace it with a OE spec belt and some 6gram rollers so that you can bench mark the engine before you make the changes to the pipe and CVT.

400 views to date and your English is fine

geoff

Yes, the scooter is in a bad shape. I took out the spark plug and found out that it's hotter than it needs to be, 7 instead of 8. Only if I knew that it was that bad, I wouldn't had bought it. The belt I'm planning to put it has the same specs so it won't affect anything. The CVT is absolutely stock too. After I get the engine running in a good condition then I'll be screwing around for more power.

[joeesquire]

Amazing! Simply amazing coincidence!
Been trying to chase down a no-start, then a no-idle problem for days on my 95 jog. It has been suffering for a while with poorer and poorer performance, lately unable to get up my insanely-steep hill to get home. I had done all the usual things....again, wracking my brain trying to trouble-shoot this problem(s).

Just today I was able to get it started and keep it running (barely), by removing the auto enrichener power, so it was running, albeit slowly...very slowly, and did respond to nearly full rich needle setting and throttle screw increases. Re-plugging in the enrichener always killed it.
From this result, I am assuming that there is a massive air leak(s) somewhere. I had suspected and dreaded this for some time, so yesterday just finished replacing both crankshaft seals. I believe they were both originals. The variator side seal was a right bastard, both to remove, AND to install! I have done this type of work most of my career, but I pretty nearly buggered-up this one. I was paranoid enough to buy two seal sets a while ago.

So....for quite some time, I have noticed that, with the air cleaner removed, there was ALWAYS fuel spitting out of the carb mouth. I assumed that this was normal, and that it showed why you needed your air cleaner in place, since it would run badly with it off, because you were losing part of your fuel charge. Isn't that what that reverse pressure wave does? It blows back through the main jet? Isn't that why folks try to sell us those cute little anti-reversionary chambers? Boost bottles?

Well, Hell! If I had not seen your post, I would be out there tomorrow, with my propane torch, going over every millimeter of the motor, trying to find an air leak. The jog intake is so far under my storage that it seems a right pain to access, without dropping the motor. So, it'll be motor-dropping time tomorrow....thanks to your comment! Even though my odometer has gone around 3 times, I did not want to believe that my OEM Yamaha could suffer parts wear! I have never seen this reed valve, but do have a new assembly, made in Taiwan, with a set of fiberglass petals. I do remember someone saying "When your steel reeds break, they destroy everything downstream from them!" Yikes! You might have warned me just in time! Thank You!

I should shut up here. Just was wondering if you had snow yet in Lithuania? Am in Kalifornia, so all we get are earthquakes, surf and taxes. The earthquakes are free.

Thanks again, and regards

[paydem]

Nov 27, 2017 22:27:43 GMT -5 joeesquire said:

Amazing! Simply amazing coincidence!
Been trying to chase down a no-start, then a no-idle problem for days on my 95 jog. It has been suffering for a while with poorer and poorer performance, lately unable to get up my insanely-steep hill to get home. I had done all the usual things....again, wracking my brain trying to trouble-shoot this problem(s).

Just today I was able to get it started and keep it running (barely), by removing the auto enrichener power, so it was running, albeit slowly...very slowly, and did respond to nearly full rich needle setting and throttle screw increases. Re-plugging in the enrichener always killed it.
From this result, I am assuming that there is a massive air leak(s) somewhere. I had suspected and dreaded this for some time, so yesterday just finished replacing both crankshaft seals. I believe they were both originals. The variator side seal was a right bastard, both to remove, AND to install! I have done this type of work most of my career, but I pretty nearly buggered-up this one. I was paranoid enough to buy two seal sets a while ago.

So....for quite some time, I have noticed that, with the air cleaner removed, there was ALWAYS fuel spitting out of the carb mouth. I assumed that this was normal, and that it showed why you needed your air cleaner in place, since it would run badly with it off, because you were losing part of your fuel charge. Isn't that what that reverse pressure wave does? It blows back through the main jet? Isn't that why folks try to sell us those cute little anti-reversionary chambers? Boost bottles?

Well, Hell! If I had not seen your post, I would be out there tomorrow, with my propane torch, going over every millimeter of the motor, trying to find an air leak. The jog intake is so far under my storage that it seems a right pain to access, without dropping the motor. So, it'll be motor-dropping time tomorrow....thanks to your comment! Even though my odometer has gone around 3 times, I did not want to believe that my OEM Yamaha could suffer parts wear! I have never seen this reed valve, but do have a new assembly, made in Taiwan, with a set of fiberglass petals. I do remember someone saying "When your steel reeds break, they destroy everything downstream from them!" Yikes! You might have warned me just in time! Thank You!

I should shut up here. Just was wondering if you had snow yet in Lithuania? Am in Kalifornia, so all we get are earthquakes, surf and taxes. The earthquakes are free.

Thanks again, and regards

Good to hear that! Yes, in Lithuania here it have been snowing non-stop for two days already. Can't wait to fix my Jog up and try it out in the snow.

[paydem]

I installed new Dayco belt (747mm lenght, 16.5mm width). The situation did not get any better at all. Without the spacer on the variator, the take off was depressingly bad. I put 1mm spacer on the variator and the acceleration was better than ever, now it does wheelies but still, the situation is pretty bad. I extended drive ramps in order for longer belt travel, but even without spacer, the belt doesn't reach outer edge of the variator (5-6mm left). On the rear pulley, the belt still sits ~6mm low on the outer edge, even with 1mm spacer. The belt is just too short and in tension even without variator added. I contacted the seller and he doesn't want to replace it, not sure what I'm going to do, I don't want to throw away money for things that probably won't even work out.

I saw 16.5mm belt with 796mm lenght but it looks like it will be too long for me. Any recommendations?

[ThaiGyro]

Sounds to me like you have multiple issues to look after. My suggestion:

Tune your top end: carb/plug/plug wire maybe?/ensure clean air filter

Then, clean your exhaust inside...you must remove it and choose a method that causes the least harm to get the goo out.

Then tune your carb...

Then tune your CVT.

You will waste less time...though it takes some time...and spend less money.

It would help others to know...what conditions are you currently trying to run your scoot monster? It makes a huge difference! If it ran well in warm-to-hot weather, it won't in cold.  If you have huge humidity swings, as I do, you need to tune more often. If set up originally near sea level and now in mountains...same issue.

[geoffh]

errmkk,don,t waste your cash on "will fit" parts that will fit but don,t work.the correct belt for your engine is 738x16.5 the Naraku part number is NK900.12 fit one and use it judge any improvments you make,

geoff

[paydem]

Jan 9, 2018 16:06:06 GMT -5 geoffh said:

errmkk,don,t waste your cash on "will fit" parts that will fit but don,t work.the correct belt for your engine is 738x16.5 the Naraku part number is NK900.12 fit one and use it judge any improvments you make,

geoff

I already said I have 747x16,5 belt and it's too short.

[paydem]

So, I watched a lot of videos, read a lot of opinions regarding this topic and decided to buy a new variator to bring the belt up. Some people claim the belt is perfect for a sports variator like Polini Hi-Speed or Malossi Multivar, but in my opinion people who tune CVT's don't pay a lot of attention to belt travel, etc. If the belt will still sit too low, I'll buy a belt that is ment to be used on Minarelli short case engine, Malossi 6112741 I think the code is. The lenght is 792mm and width 16,5mm, it's not like a overrange belt or anything so it still would cost me like 16-17 euro.

[AtariGuy]

You can option a 17 belt and that should open up some additional options. A 788x17x28 may be a good fit and its a common size as well so should be friendly to your wallet

[repherence2]

Jan 15, 2018 10:56:30 GMT -5 paydem said:

So, I watched a lot of videos, read a lot of opinions regarding this topic and decided to buy a new variator to bring the belt up. Some people claim the belt is perfect for a sports variator like Polini Hi-Speed or Malossi Multivar, but in my opinion people who tune CVT's don't pay a lot of attention to belt travel, etc. If the belt will still sit too low, I'll buy a belt that is ment to be used on Minarelli short case engine, Malossi 6112741 I think the code is. The lenght is 792mm and width 16,5mm, it's not like a overrange belt or anything so it still would cost me like 16-17 euro.

My Ningbo GTX (Chinese minarelli clone) came with a 788 belt. The jog90 block that I have currently installed came with a 792 x 16.5mm. I tried the 788 belt on the jog90 because I was accustomed to CVT tuning with the 788. I got higher top speed from the 792 belt. Personal preference, I'm happier with the results of the 792. The problem that I face here on Oahu, Hawaii is that all the moped shops stock the 788 and no one stocks 792 belts. By the way, I use Keli (brand) variators on all of my builds because that all the local shops sell. The GTX stock block came with large splines large taper 12 pin crank so all of my 50cc CVT parts crossover to the jog90 block.