Ran great, died idleling.

[maxman]

Freshly rebuilt top end. .020 over. Valves reseated. Lifter gaps are correct. Ran great after rebuild. Then would not start. It just died while idling. Has compression. Has gas. Has spark. Tore down carb and discovered pilot jet was missing o-ring and washer. Bought new and replaced. Will "fire" a sec and cranking for awhile, but dies immediately. Starting fluid spray makes it back fire, but no run. Correct valve timing was confirmed. There is spark, just will not start. Noticed spark was not at center of electrode, it appeared around the perimeter of the electrode, kinda strange. I put in another not-so-old plug, spark appears in the center, but still no start. Does look like the best spark, so I am going to buy another plug and try. Any other ideas?

[honda400ex2003]

what pilot are you running? does it help with 4-5 pumps of the throttle or using the choke to get it fired up or does that make it worse? what is the rest of the jetting? steve

[maxman]

Do not know exactly what jets, but I am sure they are according to OEM specs in the service manual I have. The main jet was confirmed and the pilot jet was ordered new per OEM part number from Honda. Pumping the throttle or choking does not matter. If I crank it for 30 seconds, with the choke, it may fire a few times then dead. Stops running by the time I release the start button.

[honda400ex2003]

verify the jets and make sure they are not a 148 main. that will not be enough to get it running good. a bigger pilot is probably neccessary also. I would say a 42 would be better since i am assuming it is a 38 now. I would at least like to find out what you have in it for sure before recommending anything further though. I would be willing to bet that it is fuel related. steve

[maxman]

By the way, it is a 1999 TRX400EX. The machine ran great with the jetting that is in it. 148 main rings a bell as I did check this. New OEM pilot jet. Did not know of other sizes available. I am referring to the brass adjustment screw located external to the bowl, on the outside of the carburetor at the intake, on the bottom of the carb. It has one large o-ring at the larger diameter and one smaller o-ring and washer located at the smaller end.

I am going to try a new plug. I do not disagree that it could be a fuel problem. But if it ran great, for quite awhile with the current set-up, for a few days, nothing changing, why would the jetting be suspect? Same fuel in tank. Maybe bad jetting has caused the plug to foul/fail prematurely? I will start there and reply tomorrow night.

Normally, a blast of starting fluid in a carburetor will make anything fire up if there is a spark.

[honda400ex2003]

did you turn your f/a screw back out to the correct setting? 2.25 is stock setting for it. that is the brass flat head screw that you are referring to. most of the time when it is bored it will be a bit more fuel. It could def have something to do with your plug but it will not wear out that fast. Is the plug white? Black? white is too lean, black too rich. the stock jetting is 148 main, 38 pilot, 3rd needle clip position from the top, and 2.25 turns out on the f/a screw. unless you just did the bore, without any performance adders it will require different jetting 99% of the time. there is still alot to be answered here possibly. Even boring by itself usually does need a bit more mixture to get it correct again depending on the setup.

do you have any other mods? If not then you may be closer than i first suspected. I assumed that you probably had at least a new aftermarket filter or exhaust when i started thinking of which jetting you would require.

steve

[maxman]

New plug got it running. Running rich for sure. Very cold outside in the barn. Prior plugs were black and wet.

f/a screw is turned out 2-1/4 times per the service manual. The main jet is a 148. The online parts breakdown now calls out a 140 main (it was 148).

I'll have to tear the carb back apart to make sure that the pilot jet is a #38. Web breakdown of the carb refers to this as a "slow jet". Also, I am not sure where the needle clip is set at.

I bought this beast for $400 with no compression. Piston melt down. Word is that it was run low on oil. The cylinder was bored .02 over and valves were reseated. After market top end gasket kit but with a OEM head gasket. It ran great until the plug fouled.

K&N filter. Yashimura pipe. I do not think that the pipe is an extreme one.

With the given information, what is your recommended set-up. I do not want to drop a bunch of cash into this.

Feedback is greatly appreciated.

[honda400ex2003]

a yoshi is a very nice exhaust along with t-4 from pro circuit and fmf q4 is also a great quiet alternative. the filter is also a good addition while doing the exhaust.

i would recommend doing some plug chops to see how the plug is on the main jet first. then you will have to your pilot circuit the same way along with your needle.

check out this thread,

http://www.exriders.com/vbb/showthread.php?s=&threadid=445695&highlight=jetting+placement

it shows the procedures that will need to be done to check your jetting and get it dialed in.

with only a 85.5mm piston you wont need to change a whole lot. but i would be willing to bet that you will have to go to at least a 150 main with 3-3.5 turns out on the f/a screw with the needle on the 3rd position.

it is hard to say though.

steve

[maxman]

OK. Thanks a bunch! I'll run through it.