high speed miss - non GS

[kamesama980]

I'm asking on behalf of y girlfriends dad. he has a 08 johnny pag (aka chinese junk) police cruiser with maybe 1200 miles. seems to have a 270cc honda knockoff engine, 5 speed, chain drive. the problem is that it has some issues over 50-55 mph. acceleration is fine in all gears for the low-mid revs. WOT in the first few gears gets a tiny bit of bucking right before redline. 4th and 5th will buck starting about 50-55 and holding the throttle you can get to maybe 60, like it's got a bad miss. you can hold throttle and it keeps going the same, bucking no more, no less (IE doesn't seem like it's running out of gas).
-it has an electronic tach (ie hooked up to the coil) which is not tripping out (I've seen tachs with an ignition miss....all over the place) when the miss is happening so I don't think it's in the ignition (unless it's hooked to the primary side and the problem is in the secondary side)
-I did a plug chop while it was bucking. plugs are unmarked at all, look like they're fresh out of the box.
-I checked the valves myself and they're perfectly in spec. .003" intake, .004" exhaust.
-The exhaust did have a bolt or 2 that was loose, he tightened them and it took care of some vibration/noise but it runs the same.
-the plugs have been changed, going hotter and colder, took the carbs apart half a dozen times (new jets, cleaned everything, adjusted everything till it stalls, both ways, and back), cleaned out the petcock sediment bowl, chain adjusted, valves checked, wiring all looks excellent, battery is fully charged, charging system works. I'm not sure what to check next.

the reason the bikes chinese junk is that it broke the rear engine mount bolt multiple times. first replaced with an OE bolt, then a non-rated, grade 5 lasted 500 miles lol. the oil cap popped off once while driving, whole thing just feels cheap. riding it around it almost wants to fall over. the brakes are spongy and vague at best (bled, new fluid, stainless lines, f+r disk) shifter has about a 5" throw and if you don't use it all it just slips between gears. etc etc etc.

 

[kamesama980]

nothin huh? need to fix it to sell it!

 

[GregT]

The symptoms you describe are similar to what we found on speed restricted imports made for the Jap home market.
Try disconnecting the speedo cable & give it a run.
If it pulls right through ok like this it's a case of tracing the sender wire from the speedo and inserting a resistance to fool it into thinking it's going slow.

 

[kamesama980]

nope, it's a somethings broken kind of problem. on the ride home from the dealer it did 75+ and one weekend in the midst of the troubles it was fine.

 

[GregT]

Pull the fuel line off the carb and check that fuel will run free for at least a minute - with the tank cap on.
If it won't run, try without the cap.

 

[FormerBMWguy]

You're a braver man than I if you would ride that Chinese junkbox at 75!

 

[kamesama980]

did the fuel line thing. it was a problem for a bit, but the seal has already been cut to alleviate it. plenty of fuel flows. Analogueing to fuel injection I'd say it's more like a throttle position/mechanical airflow meter problem in that it's there as soon as you demand enough of the engine, it's not like a fuel supply problem that you can go for a short while at WOT till the bowl empties.

As it often goes, I didn't realize how bad it was till later lol.... I'm only getting into bikes in the last year or 2 and as with all things: you keep learning as you keep at them. when it was fresh from the dealer the only problem was a badly designed engine vibrating like a mofo to the point your feet go numb on the pegs even with cushy rubber bushings and the shifter with 4" throw each way (yes 8" travel total, I kid you not). amazing how the thing works perfectly but within 1000 miles it barely runs.

strangely enough he's trying to take over my girlfriends bike ('77 suzuki GT185). she said he was asking her if we were taking the bikes to school right away or if it would be sitting around up here for a while yet and if he could use it in that time. lol. even if he did buy all the parts, it's registered to us and she put in all the time making it shiny and putting on parts. all I've done on it is fiddle with the carbs/tuning and I'm doing the brake hydraulics just because neither are exactly newb work.

 

[SqDancerLynn1]

I would try cleaning the carb, It may have an air leak or it is just jetted too lean from the factory

 

[kamesama980]

carbs were cleaned, new jets, tried setting the needles in all 5 positions (CV type units). it's not a factory problem since it ran great for several hundred miles. anyway, new carbs are ordered, we'll see how that goes.

 

[kamesama980]

well, the miss is no longer a mystery: one of the spade connectors on the primary side of one coil was loose and just sitting against the terminal. either by vibration or by resistance it didn't have enough oomph. the bike runs fine. new problem is the clutch cable let go, the end frayed because the bracket was misaligned from the factory. looks like the mechanism inside might have a problem since it moves awful freely and jerks and dies when you kick it into gear no matter how tight the cable is. it's gone as soon as it's working ok lol