I just bought a 81 fl250 and it runs good and starts easy after the first start of the day and overall is in great shape but wont idle with the choke off.
I have checked:
Checked valve is installed correctly
Carb and pump rebuilt by honda
gas is 20:1 and fresh
tank is rust free and clean
new fuel filter and clear fuel lines
new plug and blue spark when checked
clean the exhaust and checked the carb intake, no air leaks

It came with a new belt and it looks like it is the right one when I search the part number. But it seems like the belt drags, can this cause the Engine not to idle? I was going to remove the belt and see if it idles. How tight should it be?

If i leave the choke on it will idle fine, even when I get the choke lever half way back it will idle fine. This tells me at idle its not getting enough fuel or the belt is to tight and putting a load on the Engine.

My next step is to remove the carb and check it myself and do a compression test.

Runs great otherwise, these are fun

The 20 to 1 ratio is what was recommended back in the day, new 2 cycle oil is much better than what was available back in the day.

I think you will know more after your compression check. Some symptoms of low compression are, difficult cold starts and crappy idle.

If you're lucky, a 32/1 mix, new plug, and a carb clean might just fix your issues.

I can't really answer your belt tension question, but the clutch shouldn't start to squeeze the belt at idle. The clutch should start to close when you rev the Engine. Note the position of the clutch with the Engine off.

Check the idle jet/low speed jet in the carb. I know it says it was just gone through but they are small enough if it picked up a piece of debris it could keep it from idling. I’ve had to pull them and put a bic lighter to them to burn out old/bad fuel. It would flare up when the bad fuel finally burned off. Then just hit it with an air compressor to blow and debris out.

My guess is the slow circuit is clogged requiring a higher then usual idle which in turn is causing the clutch to start closing. I think it's all connected.
It is not getting enough fuel through the idle circuit and the choke is compensating for it.
Clean the carb then clean it two more times. I like the burn out technique mentioned above. Set it to factory settings and go from there. A compression test don't hurt either but I'm leaning in the carb direction.

Thanks everyone, I'm going to try and take it apart this weekend. I 'll post an update after I clean the carb and see how its running.

I had time tonight to take the carb apart. It was very clean inside and I didn't see any obstruction in the jets or orifices. I sprayed all the jets and holes with brake clean and nothing was clogged. I took it all apart and put it in the sonic bath anyway.

The jets are 120 main, 58 idle and the float orifice is marked 2.0

While I had it apart I looked at how the choke works. When it was running if I had the choke on just a bit it would idle. I could see why, when the choke is on just a bit the choke rod lets fuel into the carb.

So I'm thinking either something was in the idle jet, or the idle jet is too small or maybe just a guess here, the float is out of adjustment and the idle jet wasn't submerged in fuel and could not pick up fuel? Does the down stroke of the Engine pull air through the carb and pull the fuel up through the idle jet?

One last thing it looks like the air filter or part of it is missing. When I removed the air cleaner lid all that is in there is the metal filter screen but no pre filter soaked in oil. This might be my problem too, to much air at idle leaning out the mixture. Whats the recommended air filter for the stock air box?

Tim

No air filter will definatly cause you trouble.

This is what I use.

https://www.ebay.com/itm/Uni-Air-Filter ... -1&vxp=mtr

No filter and too much oil in the gas could definitely be an issue. 32/1 and a new plug is the way to go. IMHO

That's assuming the compression is good and the belt isn't too short.

I ordered the filter you have in the link plus some Bel Ray MC1 oil and I will mix new gas and oil at 32:1 and give it a try. I assembled the carb last night and checked the float height and it was 20mm from the base of the card to the top of the float. The picture in the online free manual is a little difficult to see so I think I did that right. The only thing I saw was the jet holder (looks like a tear drop) was upside down, I flipped it over when I assembled the carb per the shop manual.

After I get the new oil and air filter I'll post back on how its running. I'm also going to check and measure the belt and do a compression test while I'm waiting for the parts.

Thanks

I got the air filter today, oiled it and installed it but it still will not idle. I removed the belt and that made no difference, I did measure the belt and it is 15/16 wide. I also checked the compression when the Engine was warm, throttle full open, 120 psi. The throttle stop screw is all of the way in and the pilot jet E clip is in the middle position.

I did not get the oil yet to mix fresh gas at 32:1, it should be here Tuesday.

I tried adjusting the air jet in and out from the two turns out I set it to after cleaning the carb. It didn't seem to make a difference if I turned it in or out.

I noticed that where the idle screw touches the carb slide it is a little grooved from closing on the screw. Does this cause any issues or can the screw turn in enough to compensate?

What else can I check?

Something doesn't sound right here when I read all this.
You said: "I did not get the oil yet to mix fresh gas at 32:1, it should be here Tuesday"
Then I read that you just bought this thing. So now I am thinking that not only is the oil mix wrong but the fuel could be from 1978. You are wasting your time right now. You need new fuel with the proper mix. That 20/1 is just drowning the combustion in oil. Just my opinion.
Next you say that the idle screw is all the way in. That gives it away right there. Your pilot jet is wrong or it could be all the oil in old fuel. You need to start fresh.
Next you say you turned the air screw in and out and it made no difference. That's right, it didn't. Well maybe it did but you didn't have a tach hooked up did you ?? There is no way in hell you can hear a few hundred rpm change in a two stoke. That's all an air screw adjustment will make -- a few hundred rpm. You need a tach.
Start over.

Edit: Anytime you have to add choke to get your machine to idle that just screams pilot jet or plugged pilot jet circuit.

You can get a free pdf manual here: viewtopic.php?f=2&t=17268&hilit=manuals

Check your baseline jetting based on the manual.

120 psi is low. I wouldn't be surprised if that didn't have something to do with cold starts, and weak idle. I would confirm it with another gauge and consider a top end rebuild.

Thanks for the responses.

I'm going to try and do a leak down test possibly this weekend, I found a post describing the process. I'll also try another compression test gauge and check compression again. Everything I search said factory compression was 128psi so I would think 120psi is pretty good still. If this isn't correct please let me know.

The intake looks a little dried up possibly some cracks so I'm searching for a new intake and intake gasket.

I'm also searching for the electronic start while I do my research. Is there anything I need to watch out for when buying a used kit, gear wear or a part that breaks often? Canadian oddy I saw your post on the goki starter and printed that pdf, thanks

Goki went out of business. The owner apparently died.
Here is some more info on it: viewtopic.php?f=1&t=16706

128? My bad, I thought it was supposed to be around 135. I must be thinking of something else.

I've coated a cracked intake with liquid electric tape for a temporary fix before..lol

Actually 129 per the manual, not 128 like I said.

I did a leak test on the Engine and found that the intake and intake gasket were leaking pretty bad. I bought a new intake and gasket and now they no longer leak but it still failed a leak down test.

I put 6 psi in the Engine through the crank case line that pulses the fuel pump and I plugged the intake and exhaust ports. At 6 psi I would turn off the air flow and the needle would slowly drop to about 3 psi in about a minute then slowly drop to 1.5 psi after a few more minutes and then stay at 1.5psi for a while.

I found another leak by the crank shaft output seal. So it looks like I need to pull the Engine and re-seal/gasket it, I'm going to replace the crank bearings too. So I started searching for the parts and the tools I need to split the case.

I haven't started it after replacing the intake and intake gasket but from the way they leaked air this was probably the biggest problem with the Engine not idling. After I get the new oil, which should have been here last week, I'll mix up some gas/oil at 32:1 and see how it runs.

I started it today, still will not idle but it almost wants to, getting better but still not there. Looks like Ill have to pull the Engine apart and re-seal it.

Besides a spanner to take the clutch off what other special tools are needed to split the case?

So I found a flywheel puller for 15
gasket set for 20
crank bearings and seals for 44
all of this is off ebay btw.

Is there a particular brand of bearing I should be using or one to stay away from? I'm looking for best quality not price.

I plan on measuring the bore when I get the head off to see if I need to bore it out or if its good can I hone it and replace just the rings?

Thanks

If your compression is good it would seem a waste to bore the cylinder.

Ya I'm hoping to maybe just do a hone and rings.

Should I just leave the top end and just change crank seals and bearings?

If you got the whole thing apart I would do rings. Assuming it doesn't run fine when you gas it up.

So any better source for parts then ebay?

I'm worried about the ebay crank bearings being junk

Any recommendations for where to buy parts or which brands to buy?

Thanks

if you want OEM - I see 3 on ebay. just search for 91030-950-003.

I would make this guy an offer for the 2 he shows on ebay.

https://www.ebay.com/itm/Honda-NOS-cran ... RM&vxp=mtr

I'd offer him 35 plus shipping - and go from there.

Oil seals are still available from Honda. Looks like you can get new bolts for .21 each - I would replace them as well as the dowel pins.