New to the list and have spent a few hours now trying to find a similar issue, was not having luck. I recently completley overhauled from the seat back. Bought the 250 with a hole in the piston so knew there were issues but knew I would go through everything anyway.

Issue: warm it up for about a minute in small loops around a circle drive and then open the throttle wide open down my 3/4 mile gravel drive, about 1/4 mile into the run and runnig very strong!, I get a hollow sound from the exhaust with a complete loss in power. I release the throttle and it idles fine never stalling, has power for a turn, then on the return to the garage it tries to zoom, then loses power again and again cycling every few seconds...dispite every effort to feather the throttle to get somethign better. I have bursts of full throttle on the return but it can never sustain, I've let it idle for a minute for the fuel bowl to recover, if that was the problem, but no help. If I shut it down for 5-10 minutes I can get the same original 1/4 mile run and repeat symptoms.

Rebuilt original fuel pump, new fuel line, clean tank,fuel return/bypass valve, new fuel filter, fresh 93 octane 20:1 mix, and a rebuilt carb completley dissasembeled, solvent cleaned, and air blown.
New Wiseco piston bored 20 thosandths over and cyl surface scuffed
New crankshaft oil seals (bearings solvent cleaned and all spatter from old piston removed form bottom half)
Reassebled with SAE 30 oil as an assebley lube in the bottom half
All new gaskets, head, cyl to crank, crank half, exhaust and inlet port and biscuit to pipe.
I was very careful to clean all the gasket surfaces, this was done right.
Stock pipe cleaned and blown out.


This is driving me crazy...is there any chance this is the CDI (Capacitor Discharge Ignition) or coil???? It is around freezing here in Illinois for temperature..Is this carb? is it jets?

I've replaced so much stuff I can only start to think it is the stuff I've not yet touched in the ignition... Everything is stock OEM except the oversized piston (only oversized to fix scratches from the last failed piston).. It runs so well then falls apart and can't recover. I did use a Keister whatever carb kit, saw some complained about that, but the thing runs sooo well for the 1/4 mile before problems. Help and Experience please!

Things done already to try to diagnose:

I trimmed the ends on the plug wire, checkd resistance it was good and reassembeled..
Tried 2 new sparkplugs no change
Have moved the clip on the main needle all over the 5 settings settling on the middle notch (gives some smoke from the pipe)
Checked and adjusted the float level on the tight side incase it was the bowl emptying, float seems ok.
bought a new $18 (I felt ripped off) fuel bypass valve thinking the original may have been bad
adjusted the air screw on the carb at idle incase that had impacts on this...but kinda knew that was not it.
Have not checked compression but I get tired after a few pulls, this thing is strong.

out of ideas....

Thanks!

What year is the fl250? How did you do the break in on the Engine? Did you just let it idle or did you drive it slow for many cycles? Hows your plug? Hows the air filter is it heavelly oiled?

Vapor lock? Crack gas cap and try again.

Slightly plugged exhaust could do similar things.

Regulator tee in backwards or just plain wrong.

Thanks guys for the thoughts,

The FL250 is a 1982 model, I did the breakin by running it slowly around the yard varying the throttle between idle and half for about 20-30 minutes, then tried the 1/4 mile test and keep running into problems, but have done that test maybe 15 times now. After assembly I did let it idle and it smoked like crazy burning out the 30 wt. oil assebly oil from the bearings.

The aircleaner is new and thoroughly oil soaked and has the stock snorkel installed and cleaned.

The plugs are new NGK out of a box (BR8ES with an itallic "R" under the NGK), but I did not gap them as the honda service manual I have does not list a gap spec.

The regulator Tee was a new Honda part and the correct part number, just double checked....I am considering visegripping the return hose closed for a run to see if there is a change, saw on the list some complaining about even the new ones not working correctly.

I'll try cracking the gas cap on a run too to see what happens. and i'll take off the pipe as well and bang it around some to see if somethign else broke lose in there after I cleaned it last week. I beadblasted the spart arestor and repainted it so I know that is not the issue.

folks don't think this is an overheating coil or CDI (Capacitor Discharge Ignition)?

I know I rebuilt the fuel pump right, I put the machine up on jack stands and opened it wide up, removed the fuel cap, and a big stream of gas was returning to the tank...part of the reason I bought the new regulator Tee, but also what I guess I would expect to see when the pump is working like crazy and the fuel demand is low, so I can only assume that under load the carb is getting all the fuel it needs.

Any other thoughts? I'll try these suggestions and write back later today. Thanks!

Ok I took a pair of vice grips to the return fuel line side of the Tee and it ran at full throttle all day long no issues.

Now what the heck do I do to fix that? does someone know of a Tee that trips out at a higher pressure? or any other rigs anyone has found to work?

I'm fairly sure I have the Tee installed correctly, the two clean sides are supply from pump and out to carb, with the bulged side contianing the valve towards the tank return line.

Thanks for any thoughts.

I have had the same issue several times on my 350s tees. The best cheap fix for me has been to add a large main jet in the return to tank line. That has been enough to keep good fuel flow down to the carb. I also add a large glass fuel filter between the tee and the carb so I know for sure that there is fuel going to the carb. Hope that helps,
Gary

Oh, welcome to the board! any pics? We all like lots of pictures.

i don't run a return T on my 250. i left the line from the take as a vent line and ran the line from the fuel pump straight to the carb. i have had no problems - runs real good - you will need to make sure a have a new or nearly new float needle and seat and change out every year or so.

OMO

Thanks for the help guys, I called Randy and he is sending me some things to try. I'll send pictures once it is warm enough for my wife to snap a few, it is wicked cold here right now ...not even sure the camera would work!