I need some motor advice on a big red 250es

[scottcearlock]

Ok motor heads this is what I've got.... My inlaws 85 big red 250 developed an issue with the cam chain as it had stretched past the limit for the tensioner to keep it tight. It started making the racket in the motor where you could tell it was loose. So it was time to replace the chain. After tearing it down and inspecting everything, sliders, sprockets, and tensioner all looked good so I only replaced the chain. I lined everything back up, set the motor on the T mark on the compression stroke, set the cam by the cam marks with both lobes facing down and then adjusted the valves at .003. I fired it up and it purred like a kitten and runs out great. The problem I'm having is that at idle when you nail it to WOT, it trys to stall and if you don't let out on it, it will die out. If you take off in 1st and give it half throttle and then run through the gears WOT its fine. It's only at a standstill or taking off that the problem shows itself. I second guessed my self and pulled the valve cover back off to recheck all the timing marks and and cam position. Once again, everything lined up perfectly to the T. So my next thought was the carb which I had already went through about 3 weeks ago. I pulled the carb, went all though it, blew all the jets out, checked everything and it appears to be in perfect working order. Once again the stalling problem is still there. You can however choke it and it wont stall as bad which made me think it could be a carb issue. This problem did not come about until I replaced the cam chain. I thought I could have been a tooth off on the cam sprocket but with everything lining up perfectly and double checking it twice, I'm stumped. Anyone have any ideas?

[shortline10]

Did you try and adjust the fuel air mix screw on the bottom of the carb ? I noticed with the aftermarket carb kits for this model trike they dont run well at factory specs . Run the motor at a slightly high idle so the motor doesnt die out and turn the air screw all the way in and start backing it out till it runs the best . Could be anywere from a half turn to up two three or four turns out . Re adjust the idle and see how it runs . Also make sure the motor is at running temps when doing this .

[RubberSalt]

Yup, this is defiantly a carburetor problem. If the main jet is the stock jet and the engine doesn't have any performance modifications, then leave the main jet alone. You'll need to adjust the fuel mixture screw as shortline10 suggested. This screw is mostly seen from an idle to 1\4 throttle, if you crack the throttle to about 1\4 and it bogs, adjust that screw.

After that is tuned in about right, you need to adjust your needle clip position. This is the needle going through the slide. Raise the clip(lower the needle) but 1 notch and see if that helps. It sounds to rich if it's wanting to die like that. Lean usually hesitates and the takes off.

[scottcearlock]

Well thats kind of what I was thinking. This thing has never seen a honda dealer except for when it was new. The carb settings from the factory are untouched which had me wondering. The 3 wheeler was on its side while I was removing the right side cover and the possibility of trash floating around the carb and getting into the jets is what got me thinking to check the carb to begin with. I did check the plug after letting it idle for about 10 minutes and it was really black so I did lean out the air/fuel screw which helped a little bit. 2/3 throttle was right on the money according to the plug, and actually maybe a bit leaner that I like to see so I left it. 2/3 throttle left me with a black plug with a slight visible touch of gray. I never checked the plug at WOT so I don't know if the main jet is causing the motor to get flooded or not. Once your moving along and the RPM's are above idle, the power band is better than ever. I'm thinking I better check the plug at WOT and see if I need to drop a size or two on the main jet. I just hate tampering with a factory set carb when there has never been any issues with it in the past. But for the life of me, I just cannot figure out what would cause the jetting issues when all I did was change the cam chain. It ran great and the valves were sloppy, I tightened them up to the spec and guess that could have cause an issue with the valve staying open a touch longer. Beats me, any other ideas?

[tri again]

You are right about the chain timing.
They can stretch quite a bit and maybe the carb
was adjusted over the years to compensate for the late valve timing.

There is also a hidden emulsion tube under one of the
jets that I've missed before and is usually full of muck.

It's about an inch long and the diameter of a pencil lead
with a bunch of holes in it.

Any chance the gas tank screen is clogged?
or gas tank vent?

[mrmello]

I had a BR a few years ago that did that too. Had to constantly play with the choke.

Replaced the Pilot Jet and was perfect after that. I would suspect that is your issue as well.

At least thats what it sounds like to me. Good luck!

[atc007]

VERY often as a mechanic,,you fix one thing and something else,completely unrelated goes wrong! NOT uncommon at all!. Clean your carb,adjust, and she'll just purrr!!

[scottcearlock]

Well after checking the jet sizes and part numbers, I cross match the honda jets and actually had a brand new #130 jet which is what was in the big red. Just for shits and giggles I replaced the factory 130 main jet with a brand new 130 main jet and in my opinion, the problem resolved itself. I got a call this evening that my inlaws wanted to go back to the original jet because it ran better. Who knows........It's ridden by a stubborn 81 year old man who runs it as hard as us younger folks, but he gets what he wants. I guess he'll have to live with the hesitation. Thanks to everyone for all your help!