Honda Monkey Clone YX 150cc Electric Start w/ 184cc BBK problems galore.

[rjensen]

So I bought my baby over a year ago its a Chinese retro 125 clone of a Honda Monkey. I have put over 2k miles on it in a year. So when it started leaking oil I decided it was time to get some HP for it. I love the electric start and didn't want to lose that. So I went with the YX 150cc from T-Bolt, and the 184cc BBK, a VM26 (190 main jet), and have got everything working (not really).

So I noticed when I got the motor a week ago that it looked like it had a few nicks on the head I didn't pay much attention to it as its a Chinese motor, and I can't complain about a 7 year old in china. Immediately when I got the motor I installed the BBK. (Easier to do everything on a bench) After installing it I can not for the life of me get this thing to rev past about 2-3k it just slows rpm and then tries again. I have noticed gas spraying out of the carb occasionally especially if I try to rev it. I thought for sure that I had everything perfect (I have rebuilt around 20-30 motors). I have made sure my valve clearance is perfect .004 and .003 for intake and exhaust.

Any thoughts?

Other info.

Using Tbolts easy start cdi
I have excellent compression at tdc with slight wiggle room on both valves.

I have the cam sprocket pointing at 9 while the factory T is at TDC

off the stator I have 1 of the yellows grounded to the frame per t bolt.

Also my intake valve rocker arm does not line up with the top of the valve they are off like this much...

.O = center of valve
O = center of rocker tappet

 

[rjensen]

So I pulled the head off tonight, and noticed that the exhaust rocker slightly ticks up because it was riding on an adjacent part of the cam. I rotated that part of the cam and put it all back together. Oh and I poured wd40 down the intake to check for leaks... none, same with exhaust, and no problem there either. Still does the same thing revs to about 2-3k and then its like it has a rev limiter keeping it from going higher. I am so damn tired of this thing. I have over 40 hours into trying to do a 6 hour job.

 

[motorman]

I know this might sound silly but by what you are describing it appears to be a simple jetting issue.

I think your looking into it too much. What pilot jet are you running? How many turns is the mixture screw out?

Also make sure the carb is connected properly to the engine and there are no leaks. Start motor and spray some WD40 around seal and see if engine rev's change. If they do you got a leak.

I would also go back to stock CDI to make sure it's nothing crazy there.

Put a pic up as well.

 

[rjensen]

I think you're onto something, I just ordered a V2 head, and a 28mm carb, and a whole set of top end gaskets, as mine are hammered from all this messing around with it. This is a picture of the bike, since this picture I have swapped the motor, and moved the seat back about 2.5 inches.

 

[rjensen]

So its been almost a month... Here is what I learned. My setup probably would have worked fine had I put more effort into finding the right jets for the carb. Instead I bought the v2 head roller rocker, cam etc, and 28mm carb. Same problem replaced the CDI, the Coil, same problem continued.

Finally after ordering several different jets... the problem ended up being that I was at a 190 for my main jet and I needed 100 or 105, I was at a 35 for my pilot, and I need a 30. Thanks for pointing to the jets, I assumed that T-Bolt wouldn't ship a carb with a head, knowing what it was going on with jets that were so off. (My bad)

I have in it right now a 100 and a 25 pilot. Its almost dialed in, but the pilot is not big enough.

All that said, this bike is one scary beast. It pull so hard, its almost not fun to ride. I am going to be ordering a smaller rear sprocket and installing a longer swing arm to compensate for the increased torque.

 

[gottagetacheaperhobby]

What 28mm carb did you get? I have heard some nasty storys about the tb carbs...... my old v2 184 engine ran a keihin 28mm carb (genuine) and i ended up with a 42 pilot jet with a 115 main jet. Keihin jet sizes are different to mikuni and mikuni copy jets though so if your carb is running round jets then my jetting baseline would be way different...

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[rjensen]

It is a VM28-49, the short round slide. I don't think it was a TB problem, although they should recommend different jets seeing they are selling "kits" and telling people "oh this is the carb you need". Jetting isn't rocket science they should be more proactive about recommending jets and selling them with their "kits". But to tBolts credit, they are nice and willing to help. You say my "old" what happened to it, did it die? What wore out first. This is going to be my daily cruiser around town so I want this engine to last as long as possible.

 

[gottagetacheaperhobby]

The bottom end started having issues, the crank bearings spun in the cases, timing chain was shot, guides were shot and the clutch needed replacing. All fixeable, but i wanted to go to a 201 kit which required case boring so i started fresh. I got that engine second hand however, and put a lot of hours on it after i got it.


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[rjensen]

So how many hours would you estimate you got out of it?