I have a fl250 Engine out of an early model that seems like it’s been rebuilt. I’ve been working on it for about a week now and it just won’t idle. It starts with a little persuasion and starting fluid, but it just won’t idle. The Engine is on a 1981 Odyssey that has all the ignition components that an 81 Engine needs. The stator has been swapped from points to a different stator that was on the original 81 Engine that blew up due to an incorrect fuel mixture, the stator and magneto were both swapped. There wasn’t any information on timing between the two generations of engines so I bolted it all up anyway and luckily it ran. The carburetor is the stock one from the 81 that ran perfectly fine before it blew up.

The symptoms I have right now are it’ll start but it isn’t easy. The Engine will idle for a while and then it will bog and it cannot be revived by giving it throttle. After it starts and finds idle it can be revved up and sounds perfect at high RPM, but once I release the throttle and attempt to return to idle it bogs and again, cannot be revived. This is in a time frame of maybe 20-30 seconds. The Engine will start right back up with more starting fluid after it dies.

As stated previously the Engine must’ve been rebuilt before as I found form-a-gasket in the spark plug between the insulator and the threads. Another sign was a compression test was performed and it came up at 150psi, which seemed unlikely for a 40+ year old Engine, especially since stock is 128psi. Some more info on the Engine is that the stock exhaust does not have the greatest seal against the exhaust flange on the jug of the Engine. The spark plug is a NGK BR8ES that tends to have unburnt fuel on it that came from the 81 Engine, the gap is set to 0.26. The fuel filter is a little dirty and the fuel pump is the stock pump that worked just fine with the last Engine. The ‘T’ connector that goes between the carburetor and fuel pump to the gas tank is not there and the pump just goes straight to the carburetor. The last item is that the air screw is set 2 full turns out and the air/fuel screw is out 3/4 of a turn.

I think it could be one of the following: the spark plug as it’s supposed to be a BR7ES for an early model Engine, the ‘T’ connector could be effecting fuel delivery, the fuel filter may be clogged causing poor fuel delivery due to the vacuum to not be strong enough at low RPM, or the idle jet or slow speed jet may have something wrong. Any information as to why the Engine will not idle would be awesome! I feel like I’m on the verge of getting this thing running and tearing up my backyard again. Thanks!

Welcome aboard!

One thing, I would not use starting fluid at all if possible on a 2 stroke. I know it's tempting.


The fuel T is absolutely essential for operation. If the fuel pump is properly operating, it will overwhelm the float needle. Since you say wet gas on the spark plug I'm guessing that's the case. You should verify fuel pump flow, get a fuel T, and set the carb back to factory specs in terms of adjustment.


Someone with a bigger brain than me will help you shortly, hang in there.

I didn’t even consider the fact that starting fluid doesn’t have lubricant in it for a two stroke Engine! Tho ask for the info as I may have ruined this Engine as well, haha! I read in another forum that WD-40 works well as a starting fluid for a two stroke. Come to think of it, that’s probably why the last motor (( Internal Combustion Engine ? )) blew. I ran 32:1 mixture that many people swear by for these engines but it was started every time with starting fluid. I did a little more research on that little ‘T’ and found it’s a check valve. Does anyone have any information on this check valve? And also can anyone verify that WD-40 would do no harm to these engines as a starting fluid? Thanks!

OH MY.
There is lots wrong here.
Do you have a manual ?? You can get a free pdf download here: https://oddatv.com/wp-content/uploads/2 ... Manual.pdf

Welcome new guy.
There can be many things wrong so lets take these one at a time.
1) Make sure the gas tank is clean and the pick up tube is not plugged.
2) Ditch the fuel filter and get a new one.
3) Your fuel pump must put out 4.5 oz in 10 seconds -- use a stop watch. Your machine must have electric start for this test. If you don't have that then you are screwed for now until you get it running. If the pump puts out something like 1 oz or 2 oz then the pump is probably shot.
Why did I make these my first three suggestions ?? Poor fuel flow is deadly to a two stroke. It's probably the #1 cause of Engine failures. The #2 reason for Engine failure is an air leak. If at ANY TIME your Engine runs away and revs to the moon you got an air leak. Don't even start it again. Fix it. You need to pressure test your Engine to do this. NEVER use more than 7 psi (but I have got away with 10 psi) or you can blow seals out.
4) Most likely your problem here is a very dirty carb -- the pilot circuit. You are going to have to pull the carb and clean all passages and jets. If the jets are plugged and you can't clean it with compressed air then buy new ones. NO you can't drill it out.
5) Once you know for sure the carb is clean and the floats are set right and screws at factory recommended turns then it will most likely start up and you can tune the carb for best idle.
Garemie is right -- DON'T USE STARTING FLUID. If you need that shyte then something is seriously wrong.
CO

I bought a Clymer manual for the Odyssey when the first Engine blew since I’m new to the two stroke scene and don’t know too much about these engines. I’ve had a few two strokes and have worked on a few. There’s a lot of vagueness I’ve seen in this manual but all around it’s great. But of course more resources is always a good thing. Thanks for the link and I’ll check it out!!

Thanks for the info here! I have a new filter I’ll install and I figured there was something wrong with the pump in the first place as it was hard to get fuel to the carburetor when first trying to start it, which lead me to use starting fluid. Sadly I don’t have an electric start, but on the bright side it has led to my forearms getting a nice workout! I’ll purchase a new pump since I do not want to have a track record of blowing up engines and I’d rather be on the safe side. The pressure test I’ve heard of, but I’ve never done one so I’ll look up some videos and see what I can find regarding the procedures of performing the test. As for the high rev it only happened when I first started it for the very first time. I adjusted the air screw and it didn’t happen again so I don’t believe I have an air leak, but I could be mistaken. And ah yes, I feared a carb rebuild but it is probably for the best regardless since the previous owner didn’t even have an air filter on the Odyssey when I bought it, and let me tell you, the gunk I pulled out of the blown engines crankcase was ridiculous! I’m surprised that Engine could take the beating it did when it ran! Again, thanks for the tips here and I’ll report back with any findings after I clean the carb, replace that ‘T’, run a pressure test, replace the fuel filter, replace the fuel pump and clean the tank. Again, thanks!

Thanks for the info here! I have a new filter I’ll install and I figured there was something wrong with the pump in the first place as it was hard to get fuel to the carburetor when first trying to start it, which lead me to use starting fluid. Sadly I don’t have an electric start, but on the bright side it has led to my forearms getting a nice workout! I’ll purchase a new pump since I do not want to have a track record of blowing up engines and I’d rather be on the safe side. The pressure test I’ve heard of, but I’ve never done one so I’ll look up some videos and see what I can find regarding the procedures of performing the test. As for the high rev it only happened when I first started it for the very first time. I adjusted the air screw and it didn’t happen again so I don’t believe I have an air leak, but I could be mistaken. And ah yes, I feared a carb rebuild but it is probably for the best regardless since the previous owner didn’t even have an air filter on the Odyssey when I bought it, and let me tell you, the gunk I pulled out of the blown engines crankcase was ridiculous! I’m surprised that Engine could take the beating it did when it ran! Again, thanks for the tips here and I’ll report back with any findings after I clean the carb, replace that ‘T’, run a pressure test, replace the fuel filter, replace the fuel pump and clean the tank. Again, thanks!

Here is some more info and PDF's:

The serial numbers are:
FL250 A (77) FL MODELS, JPN, VIN# FL250-1000001 TO FL250-1011921
FL250 A (78) FL MODELS, JPN, VIN# FL250-1100001 TO FL250-1112345
FL250 A (79) FL MODELS, JPN, VIN# FL250-2000001 TO FL250-2012620
FL250 A (80) FL MODELS, JPN, VIN# TB04-2000001 TO TB04-2006315
FL250 A (81) FL MODELS, JPN, VIN# JH3TB040-BC400001 TO JH3TB040-BC406324
FL250 A (82) FL MODELS, JPN, VIN# JH3TB040-CC500001 TO JH3TB040-CC514700
FL250 A (83) FL MODELS, JPN, VIN# JH3TB040-DC600001 TO JH3TB040-DC617555
FL250 A (84) FL MODELS, JPN, VIN# JH3TB040-EC700051 TO JH3TB040-EC703225
FL350R A (85) FL MODELS, JPN, VIN# JH3TE020-FC100015
FL400R A (89) FL MODELS, JPN, VIN# JH3TE160-KK000044 TO JH3TE160-KK004102
FL400R A (90) FL MODELS, JPN, VIN# JH3TE160-LK100001

11921 1977 fl 250s produced
12345 1978 fl250s
12620 1979 fl250s
6315 1980 fl250s
6324 1981 fl250s
14700 1982 fl250s
17555 1983 fl250s
3175 1984 fl250s
no ending vin for 1985 fl350s
4059 1989 fl400s
no ending vin for 1990 fl400s

Here is how you pressure test a two stroke: (PDF below)

I don't want to bury you with to much info but that stuff should keep you busy.
That's the key stuff you must know.
CO

If you fear taking that carb apart then you are just fearing the old "monsters under the bed" thing.
It's not that tuff. Lay out a clean white towel on the bench and lay out each piece in order. Then clean one piece at a time and put it back on the towel. You need a magnifying glass, welders tip cleaner, brake cleaner, compressed air (bonus) and a flashlight.
Every homo has a phone with a camera ------- take pictures if you are not sure.
CO

WOW! Thank you so much for all the information! Thank goodness for the internet because I would be at a complete loss here with an Engine that blew up and another that won’t run! I’m going to take a crack at everything I can tomorrow and see what I can get my hands on. Hopefully ODDATV and eBay has everything I might need. I’ll check my local motorsport shops and see what they might have to get my odyssey going again.

If and when you do the pressure test you can make your own test rig.
You need some inner tube and a plate (aluminum or steel). You drill three holes in it for the exhaust bolts to fit through. Drill a hole in the center of the plate so that you can attach a low pressure gauge. Drill another hole next it and install a shrader valve that bolts on. You can get these at an auto supply store. Cut a piece of inner tube to use as a seal. Bolt it on. Exhaust is now sealed. Put a bolt into the vacuum line and use a clamp. Vacuum line is now sealed. Remove the carb -- this is the tough part -- you need something to fit in the rubber intake hole and then tighten down the clamp on it.
Pic below of my test rig. I use a small air tank that I can pump up to 10 psi or just set your air regulator on your compressor if you have one.
I don't know what kind of tools you got so I am just guessing here.
If you do have an air leak you try to find it with a bottle of soap water. Most of the time the leak is the intake boot or one of the crank seals.
CO

I told ya a bigger brain would come help.


Just FYI there's stock size fuel filters available listed as a 1978 Honda Civic fuel filter at your auto parts stores.


Good luck and don't get discouraged!

Good news! All that information was incredibly helpful! I bought and installed a new fuel filter, new air filter, new and correct spark plug and I added the fuel check valve. Engine started on the first pull after getting fuel to the carburetor. It idled just fine and the Engine sounds very strong. Now here is the catch, it won’t drive under load. When the back wheels are off the ground it will reach full throttle just fine and the Engine sounds very healthy. Once I put the Oddy on the ground and drive, it was fine in the lower RPMs and pulled hard. Then full throttle was applied and it sputtered out and died. It’ll start right up with one pull after it dies but it just won’t take a load and get to full throttle. I got about 1000 feet before it stopped. If anyone has some info on why this is happening I’d greatly appreciate it because it sounds like I’m so close to getting this thing out in the yard again! I think it might be the air/fuel mixture but I wanted to check here since everything else was doing just fine until I hit high RPM.

Last thing I’d like to bring up is the form-a-gasket I found in the spark plug again. The Engine had to have been rebuilt, but is there a break in process before I can rip the Engine to its full potential? Thanks!

They had just the parts I needed! They even had the check valve ‘T’ also! Thank you for the tips and hopefully I can solve the next issue with running under load!

I bet the rent money you are running out of fuel because the fuel pump is junk.
You are going to blow it up if there isn't enough fuel.
What was your fuel flow rate again when you tested it ??
CO

I do not have an electric start to test the pump with sadly, do you have any other methods of testing? I know it has to be a fuel delivery issue due to the fact it holds pressure and it starts and idles just fine. I know a fuel pump isn’t a hard thing to get a hold of. Could it also be the high speed jet? Thanks! I’ll also keep fiddling with the air/fuel screw to see if anything changes.

Yes there is another way.
I didn't want to mention it because of fire hazard !!
Honda says to test the pump with the Engine at idle but this is risky due to fire. If you do want to test it that way (which is your only choice right now) you WILL HAVE A FIRE EXTINGISHER HANDY.
This is how it works:
1) Start your machine and make sure it idles (without you having to throttle it LOL)
2) Shut the Engine down and remove the hose that goes to the carb. If it is to short then put a longer hose on it.
3) Put the hose into a measuring beaker or something that has oz marked on it.
4) DON'T TOUCH THE THROTTLE and start the machine.
5) Immediately after the Engine starts you start a stop watch.
6) Immediately shut the Engine off AT 10 seconds. (NOT 9 SEC AND NOT 11 SEC) That's cheating.
7) You need 4.5 oz in 10 sec APPROX. I say approx because it's only a 250cc so if you are getting 3.5 or more you're good in my opinion. If you are getting less than that give it up pal, the pump is shot and you WILL hole a piston or melt it down.
CO

Sounds good! I’ll give that a shot and hope for the best with a good pump and NO fires! Haha! Thanks

One more query here on a possible problem, could it be the exhaust? On the last Engine I ran an aftermarket exhaust that was a little quieter if I remember correctly. But I know it was a performance exhaust. The exhaust wouldn’t fit on this new Engine and I’m not for sure why. But the exhaust on there now is stock and has been sitting for years. I know the older exhausts are known to not help with peak performance. I thought this could be a factor as well. Thanks

Stock exhaust should be fine for a stock setup. One thing to consider, people often change carburetor jetting when they change exhaust systems. So it could be that the buggy is jetted for the other exhaust.

What was the fuel flow rate after the test ??
CO

The exhaust needs to be checked and make sure it is not blocked by build up or mouse nests or anything else......just say’n