Apollo 250 rough under load

[Rcsup1]

Hi All,


My bike was running perfect and all of the sudden develop a bad miss/ hesitation under load, popping and banging from 1/2 throttle on. I took the carb out a mikuni vm26 rep cleaned it thoroughly and put in new jets since it was slightly lean before after the filter install.

20 pilot to 25
115 main to 125
I'm at sea level

The bike has full intake with K&N cone filter.. the cat has been eliminated along with all the emissions components and I installed a cdi with adjustable timing which is advanced.

Any ideas as to what could be causing it to run so poorly all of the sudden?

It will idle and free rev with no hesitation. Under load not so much.

[Its_not_a_honda]

Spark-plug?

Mine did almost the same thing and it was the plug.

[Douglass]

I am at sea level, and have the stock airbox/exhaust. Currently I have the Mikuni vm26 Carb installed with a 30 pilot, air/fuel screw is 2 1/2 turns out, and a 120 main, with the needle clip in the middle. I am running an NKG iridium plug, and burn looks real good. Assuming the plug is not bad, I would start with the adjustable CDI/Timing component that was added. Might want to try an adjustment, or swap the stock ignition parts in to rule it out as a possible problem.

[Rcsup1]

Thanks for the reply guy's. The spark plug is a new (maybe 2hours of use) ngk irdium. I swapped in the stock CDI and had no change. I'm going to try a new coil next I guess

[Its_not_a_honda]

I would still do a new plug. I have seen the porcelain crack and do weird things to engines. Never pass on doing the simple things.

[Douglass]

I would still do a new plug. I have seen the porcelain crack and do weird things to engines. Never pass on doing the simple things.

this is a good idea too. If you have the old spark plug swap it in. If not buy a cheap copper NGK plug. Another thing to check are the connections. Check for loose, bad or corroded.

Did the problem start while you where riding?

[Weldangrind]

I suspect that a 125 main is a little much, even at sea level. Maybe put the 115 back in and see how it behaves with a 25/115 combo. I'm betting that it's going to want jetting closer to what Douglass is using.

[ChrisWNY]

Where is the clip on the needle in your Mikuni VM26? Is it centered or closer to the bottom (rich) or top (lean)? Thinking your needle may be running either too rich or too lean based on the fact that your issues are surfacing by 1/2 throttle. If your spark plug is black and has a lot of fouling, you're running rich (raise the clip on the needle up 1 notch)...if the plug is clean or has white residue on the electrode, you're running too lean (lower the clip down 1 notch on the needle to richen things at 25%-70% throttle). You'll likely be running too rich at full throttle if you're running a main jet larger than a #115. I found that a #120 main jet was too rich, and that was after an air box and exhaust mod which allows much more airflow through the engine. YMMV though depending on temp, humidity, etc.

[Rcsup1]

The issue started gradually and got worst quickly. This all started prior to any changes made to the carb/jetting. The bike was running perfect, then the issues began with no changes made to the bike.

I initially thought it could be debris in the carb. This is why I took it apart to clean it and install fatter jetting as I felt it was a slightly lean after air filter mod. It had a slight lean spot when whacking the throttle.

The clip was and remains all the way on bottom last notch (rich). It only stumbles under load and mid to high rpm. I can free rev the bike all the way from idle to WOT with no hesitation.

The plug was burning almost perfectly. I'll try to put in the old plug to see if that makes any difference.

Thanks again for your reply's!

[JerryHawk250]

Have you checked and adjusted the valves lately?

[ChrisWNY]

I would move the clip up a notch or two, set it back toward the middle just to rule it out. I ran my needle setting rich for awhile and found it was definitely too rich 25%-70% throttle. No hesitation but the spark plug was fouled up pretty good upon inspection. Definitely adjust the valves if you haven't done so already. If those valves are too tight they can overheat which can wear the valves prematurely or burn them out and cause engine performance to suffer. 0.003" intake and 0.004" exhaust is typically a good place to start for valve gap adjustment.

[Rcsup1]

I pulled the plug and it is definitely a lean condition issue. It was white as can be, where before when I pulled it was a light'ish grey. I ordered a new fuel filter even though the one on it looks new. It definitely appears to be a fueling issue. The valves where adjusted by the previous owner but I can check them.

I kinda of at loss, is there anything else I should be looking for with regards to the carb? I took it apart completely cleaned it with brake cleaner and compressed air. I checked the float height and it was right in the middle. I don't see any points of an air leak but I may be missing something.

[JerryHawk250]

Check for cracks or bad gasket causing intake air leaks. this will make it run lean.

[Rcsup1]

Previously I changed the jets back to what it had 20/115 and the issue persisted.

This last weekend I did the coil on plug conversion as described in this thread http://chinariders.net/showthread.php?t=21066&page=2 and the bike is running like a million bucks. Apparently it was a bad coil the entire time!

Ironically as I was wrapping up the coil install the pumper carb arrived at my door. I originally thought it was a carb related issue.

The bike is running so good now it may be a while before I try it out. I cant imagine it would make that big a difference at this point. Throttle is instantaneous and it pulls great through the entire power band.

[JerryHawk250]

Previously I changed the jets back to what it had 20/115 and the issue persisted.

This last weekend I did the coil on plug conversion as described in this thread http://chinariders.net/showthread.php?t=21066&page=2 and the bike is running like a million bucks. Apparently it was a bad coil the entire time!

Ironically as I was wrapping up the coil install the pumper carb arrived at my door. I originally thought it was a carb related issue.

The bike is running so good now it may be a while before I try it out. I cant imagine it would make that big a difference at this point. Throttle is instantaneous and it pulls great through the entire power band.

Awesome :tup: One of the best mods I've done to my Hawk.
I would install the pumper carb. I think it will perform better on the low end.

[Rcsup1]

Here some pics of the coil conversion. I'll come up with a better mounting bracket but it is holding steady for now.

[JerryHawk250]

I made a bracket from the coil to valve cover bolt.