Hornet CB250 starting issues

[mnishi]

Hello everyone!

Picked up a cb250 hornet recently and it ran ok. Recently however, after about riding for 5mins, it turns off. Then after a while, it’ll go again but then starts to bog off and loses power and turns off. Then goes again..

So I’ve changed the spark plugs, yes there is spark. I’ve changed the fuel, old fuel was not the best, in doing that I also opened the carbs, jets were clogged, and just cleaned the carbs. Brand new battery, and air filter looks ok.

I read a thread which said the fuel air mixture should be about 2-2.5 turns from lightly tight so I adjusted that too.

Now, it’s still the same. I can’t seem to start it without choke.

And if I take the choke off, it shuts off and even with choke on - and if I give it gas, it’ll also shut.

What’s the issue here? What else shall I eliminate?

Thanks

[OddDuck]

Sounds like its worth having a look at the petcock and the fuel filter - the carb bowls may not be getting refilled fast enough.

Other possibilities... charging system OK, you're getting 14V at the battery terminals with the bike revving? For that matter, how old is the battery?

[FJRider]

Check the air filter isn't full of crap. It needs fuel AND air to run properly.

Check for kinks and blockages in the fuel line.

[Bonez]

Sounds like the carbs are gungrd up like my XF650. Injector/Carb cleanerv in a tank full of fresh fuel and a decent run( around 200 or more kms at varying speeds. should ) sorted it out if it is gumbed up carbs.

FJriders an OldDucks suggestions are valid as well.

[mnishi]

Sounds like its worth having a look at the petcock and the fuel filter - the carb bowls may not be getting refilled fast enough.

Other possibilities... charging system OK, you're getting 14V at the battery terminals with the bike revving? For that matter, how old is the battery?

Battery is brand spanking new.

Fuel filter is ok too, I’ve opened it and cleaned it also.

[mnishi]

Check the air filter isn't full of crap. It needs fuel AND air to run properly.

Check for kinks and blockages in the fuel line.

Ordered a new air filter.. so will wait for that. Old air filter does look pretty bad. But I didn’t think this would be the cause? Let’s see,,,

[pete376403]

Ordered a new air filter.. so will wait for that. Old air filter does look pretty bad. But I didn’t think this would be the cause? Let’s see,,,

I would imagine any blockage of the air system would increase the effect of choke, but you say taking the choke off and the engine dies immediately?
The "choke" system is probably a plunger that lifts and opens another passage for fuel to get into the intake, which would suggest to me that there is a blockage in the main fueling circuit of the carbs and as soon as the choke is "off", there goes the fuel that the engine was running on.

A more thorough carb clean may be required. Each carb feeding a 65cc cylinder - there are some very tiny passages in there.

[FJRider]

I would imagine any blockage of the air system would increase the effect of choke, but you say taking the choke off and the engine dies immediately?
The "choke" system is probably a plunger that lifts and opens another passage for fuel to get into the intake, which would suggest to me that there is a blockage in the main fueling circuit of the carbs and as soon as the choke is "off", there goes the fuel that the engine was running on.

A more thorough carb clean may be required. Each carb feeding a 65cc cylinder - there are some very tiny passages in there.

The Choke is reduce air-flow through the carb. Increasing the amount of fuel in the fuel-air mixture that is going into the carb.

If it dies when the choke is off ... that indicates not enough fuel is getting to (or through) the carb.

The Petcock may be the issue. If the normal ON setting is being used ... try the reserve or Run setting so fuel should flow all the time. This can be checked by turning it to OFF. Then pull the line off the carb and trying both on and the run/reserve setting and see how good the fuel flows. If it has a vacuum line ... with no off setting ... you might need to suck on the vacuum line to get the fuel to flow. If it has a vacuum line ... THAT in itself may be the issue if the line is not attached (or blocked. or attached at the wrong place) to the carb.

This will/might confirm if the issue is in the carb or Petcock/tank area. Unless you know what you are doing ... pulling the carb apart can go badly.

Old adage with old bikes ... try the simple things first and hope ...

[pete376403]

The Choke is reduce air-flow through the carb. Increasing the amount of fuel in the fuel-air mixture that is going into the carb..
Is the choke on this model another butterfly in the mouth of the carb? The diagram I am looking at shows a "valve set, starter" which looks more like a normal plunger. However given that there are probaly a hundred different models of 250 hornet...

https://www.bike-parts-honda.com/honda-motorcycle/250-MOTO/HORNET/2006/CB250F6/Engine/CARBURETOR-COMPONENT-PARTS-/90051/E_17_1/1/22978

[FJRider]

Is the choke on this model another butterfly in the mouth of the carb? The diagram I am looking at shows a "valve set, starter" which looks more like a normal plunger. However given that there are probaly a hundred different models of 250 hornet...



Methods may vary. But the end result achieved is the same. Increased fuel amount in the fuel / air mixture.

No actual model mentioned by the OP.

[spanner spinner]

check the things got compression, use to work on these and cbr250's (same base engine) & this is showing classic low compression problems. If the compression is low they will still run but will not create enough vacuum to carburate properly, they give the symptoms you have described IE will have to use excessive choke to get them to keep running. If the compression is low check the valve clearance as most leaners that use to own these could not afford to get the valve clearance maintenance done as they are as expensive as a 1000cc bike to set as there are 16 valves to set.

[F5 Dave]

Check the air filter isn't full of crap. It needs fuel AND air to run properly.

Check for kinks and blockages in the fuel line.
Post above is interesting, but to quote this one and the OP reply 2 down. . .fuel filter? The one in the tank? Or has someone fitted an inline filter? These just Love to cause a kink in the line and it doesn't seem apparent. Replace with straight hose and clean tank out if there is a silting problem.

Be interested to hear about compression reading.

[FJRider]

Post above is interesting, but to quote this one and the OP reply 2 down. . .fuel filter? The one in the tank? Or has someone fitted an inline filter? These just Love to cause a kink in the line and it doesn't seem apparent. Replace with straight hose and clean tank out if there is a silting problem.

Be interested to hear about compression reading.

If an inline filter WAS installed ... it is another thing that largely gets ignored for many years. Not even looked at. Thus then becomes an issue of it's own.

Replacing fuel lines with clear lines helps see issues with bikes having fuel issues.

I'm curious about the km's done. A good idea then of those sorts of issues being involved. Compression doesn't need to be down much on the small bikes to make a big difference.


But the bike was probably cheap.

[Bonez]

If an inline filter WAS installed ... it is another thing that largely gets ignored for many years. Not even looked at. Thus then becomes an issue of it's own.

Replacing fuel lines with clear lines helps see issues with bikes having fuel issues.
.This was a known issue with XF650 and was one of the first thing I check as one is in the OEM main fuel. Felling the outside of the fuel indidicated one was there but when I pul the line out to chck a PO, I assume the original that did over 50,000kms on it, had clearly drilled the inards pout and flusked it properly. Obvious no fuel line issue.

Next tried to undo the carb flote boul drain screws. Got one out after just over an hour. The second one just wouldn't budge. Two carbs on the XF659 single. Look at what came out of the right hand card and the drain screws being difcult to omposible to remove isurmise gumped up laguer was the issue.

Ran the the bike totally out of fuel then putting the conten of the 5ltr fuel container I had in my man bag them filling up at my usual petrol station a few blocks away I put 1/2 a botle of injector/carb cleaner in with the fresh fuel. Doned my long distance riding and did a Palmiy-Havelock North return trip mostlyon back country roads so I woulkdn't affect traffic on the major route.

Apon ariving home the bike felt tolally different. Not random cutouts amost stall or stall then come back to life after a a minute or two.

I was very very sceptacle on the injecter/carb cleaner and aditives in general at first but now I am sold on the stuff.:niceone:

[mnishi]

If an inline filter WAS installed ... it is another thing that largely gets ignored for many years. Not even looked at. Thus then becomes an issue of it's own.

Replacing fuel lines with clear lines helps see issues with bikes having fuel issues.

I'm curious about the km's done. A good idea then of those sorts of issues being involved. Compression doesn't need to be down much on the small bikes to make a big difference.


But the bike was probably cheap.

The bikes done 29,000kms and is a 1997 model.

As an update, still waiting on the air filter today - but I've been starting the bike with choke and it goes ok, if I hold the revs and take the choke off, it also goes ok, it doesn't just die easily. If I keep giving it some gas, it runs, but of course as soon as I let throttle go, it turns off.

So I forgot to mention, off the carbs there's these two hoses that are coming down. When I removed the air box thing, it was just hanging there. Do these two hoses connect to anything?

Also, there's another pipe that runs from the right side of the tank, and also goes no where. Where is this meant to go?

Added photos!

Thank you

[mnishi]

Is the choke on this model another butterfly in the mouth of the carb? The diagram I am looking at shows a "valve set, starter" which looks more like a normal plunger. However given that there are probaly a hundred different models of 250 hornet...

https://www.bike-parts-honda.com/honda-motorcycle/250-MOTO/HORNET/2006/CB250F6/Engine/CARBURETOR-COMPONENT-PARTS-/90051/E_17_1/1/22978

Here's the correct one.

https://www.bike-parts-honda.com/honda-motorcycle/250-MOTO/HORNET/1997/CB250FV/Engine/CARBURETOR-ASSY-/90061/E_17/1/909

[mnishi]

The Choke is reduce air-flow through the carb. Increasing the amount of fuel in the fuel-air mixture that is going into the carb.

If it dies when the choke is off ... that indicates not enough fuel is getting to (or through) the carb.

The Petcock may be the issue. If the normal ON setting is being used ... try the reserve or Run setting so fuel should flow all the time. This can be checked by turning it to OFF. Then pull the line off the carb and trying both on and the run/reserve setting and see how good the fuel flows. If it has a vacuum line ... with no off setting ... you might need to suck on the vacuum line to get the fuel to flow. If it has a vacuum line ... THAT in itself may be the issue if the line is not attached (or blocked. or attached at the wrong place) to the carb.

This will/might confirm if the issue is in the carb or Petcock/tank area. Unless you know what you are doing ... pulling the carb apart can go badly.

Old adage with old bikes ... try the simple things first and hope ...

it does start on both res and on, but with the choke on. I'll pull the fuel line off - then see how it runs on both 'on' and 'res'. Thank you.

[FJRider]

The bikes done 29,000kms and is a 1997 model.

As an update, still waiting on the air filter today - but I've been starting the bike with choke and it goes ok, if I hold the revs and take the choke off, it also goes ok, it doesn't just die easily. If I keep giving it some gas, it runs, but of course as soon as I let throttle go, it turns off.

So I forgot to mention, off the carbs there's these two hoses that are coming down. When I removed the air box thing, it was just hanging there. Do these two hoses connect to anything?

Also, there's another pipe that runs from the right side of the tank, and also goes no where. Where is this meant to go?

Added photos!

Thank you

The one off the tank might be an overflow drain for around the filler cap on the tank that drains it to the ground.

Is the one in image two connected at the other end from your finger to the carb .. ??? Is there a spare "Outlet" on the petcock .. ??

With the age of the bike ... I would have thought a vacuum line would be fitted.

And at 29,000 km's ... unless the bike has been SERIOUSLY abused ... I doubt that compression issues are the problem.

[FJRider]

Here's the correct one.

https://www.bike-parts-honda.com/honda-motorcycle/250-MOTO/HORNET/1997/CB250FV/Engine/CARBURETOR-ASSY-/90061/E_17/1/909

Diagram's list parts numbers 38 and 39 (listed as Tube for both) are suspiciously similar to fuel line and vacuum line.

[mnishi]

The one off the tank might be an overflow drain for around the filler cap on the tank that drains it to the ground.

Is the one in image two connected at the other end from your finger to the carb .. ??? Is there a spare "Outlet" on the petcock .. ??

With the age of the bike ... I would have thought a vacuum line would be fitted.

And at 29,000 km's ... unless the bike has been SERIOUSLY abused ... I doubt that compression issues are the problem.

Yes, it does go to the carb.

There is just two lines from the petcock - vacuum line and a fuel line.

So the vacuum like goes to the centre of the head it seems (image 1). You can just make out where its going.

The fuel lines goes to the centre of the carb.

(image 1 showing vacuum line connected the head)
(image 2 showing fuel line connected to carb)
(image 3 showing petcock)

[mnishi]

Diagram's list parts numbers 38 and 39 (listed as Tube for both) are suspiciously similar to fuel line and vacuum line.

That looks about right... they're currently just dangling off, any idea where they should be connected?

Thanks

[FJRider]

Yes, it does go to the carb.

There is just two lines from the petcock - vacuum line and a fuel line.

So the vacuum like goes to the centre of the head it seems (image 1). You can just make out where its going.

The fuel lines goes to the centre of the carb.

(image 1 showing vacuum line connected the head)
(image 2 showing fuel line connected to carb)
(image 3 showing petcock)

The vacuum line should go to the CARB (from the petcock).

The hose attached to the center of the Head should be a breather hose for the top of the engine to go down below the engine to drain out to the ground. Usually gasses and a few spotty bits of oil (at worst) come out. This is so the top end of the engine (camshafts and top of the valves) does not pressurize.

Connect the vacuum line to the carb and the line from the top of the head down and behind/below the engine. Preferably to the side and away from the rear wheel centerline.

Then see how it goes.

[pete376403]

Look at this diagram https://www.bike-parts-honda.com/honda-motorcycle/250-MOTO/HORNET/1997/CB250FV/Frame/FUEL-TANK-CB250FT-V-X-/90061/F_14/2/909
Item #10 is the main fuel supply to the carbs. refer to diagram E-17 to where that connects. All carbs will connect together with a pipe, one of which will have a T for the fuel pipe to connect to
Item #19 is the vacuum line to opens the fuel when the engine is running. Refer to E-2 to see where that connects. This will be a connector on the inlet manifold, between a carb and the cylinder head. When the engine cranks and creates vacuum in the intake, the diaphragm valve on the fuel tap open and allow flow to the carb bowls

There will also be an overflow pipe from the carb, as stated keep this out of direct line of the tyre

[mnishi]

The vacuum line should go to the CARB (from the petcock).

The hose attached to the center of the Head should be a breather hose for the top of the engine to go down below the engine to drain out to the ground. Usually gasses and a few spotty bits of oil (at worst) come out. This is so the top end of the engine (camshafts and top of the valves) does not pressurize.

Connect the vacuum line to the carb and the line from the top of the head down and behind/below the engine. Preferably to the side and away from the rear wheel centerline.

Then see how it goes.

Ok, so I didn’t really understand that diagram a whole lot..

So I’ll connect the vacuum pipe from the petcock to the carb, I’ll search for where this might connect...

As for the breather pipe, I’ll search for this also.

Will update some time tomorrow!

[mnishi]

Look at this diagram https://www.bike-parts-honda.com/honda-motorcycle/250-MOTO/HORNET/1997/CB250FV/Frame/FUEL-TANK-CB250FT-V-X-/90061/F_14/2/909
Item #10 is the main fuel supply to the carbs. refer to diagram E-17 to where that connects. All carbs will connect together with a pipe, one of which will have a T for the fuel pipe to connect to
Item #19 is the vacuum line to opens the fuel when the engine is running. Refer to E-2 to see where that connects. This will be a connector on the inlet manifold, between a carb and the cylinder head. When the engine cranks and creates vacuum in the intake, the diaphragm valve on the fuel tap open and allow flow to the carb bowls

There will also be an overflow pipe from the carb, as stated keep this out of direct line of the tyre

How do I know where E-2 connects?

[FJRider]

So I’ll connect the vacuum pipe from the petcock to the carb, I’ll search for where this might connect...

As for the breather pipe, I’ll search for this also.

Will update some time tomorrow!

The vacuum hose and breather hoses (and fuel hose) are usually different diameters, So there should be little (no) confusion about which is which.

However ... the unknowing can often MAKE them fit. Resulting in having problems similar to yours.

[pete376403]

How do I know where E-2 connects?

In diagram E14, there are 4 T pieces (item 5, 7, 9 & 10) which hoses could connect to. If the diagram is to scale, 9 looks bigger so thats *probably* the crankcase breather, if it is the same diameter as the breather attachment on the top of the cam cover (diagram E1, arrow out going out to F17).
I think 7 is the fuel inlet because its going to diagram f14, the fuel tank. 5 looks like it attaches to a hose pointing downward so *probably* a carb float bowl overflow drain, which leave 10 as the vacuum source to the fuel tap. You've probably worked this out already, but diagrams Exxx refer to engine, Fxxx refer to frame, ie everything else


Hold up! Another look. the crankcase vent in the top of the cam cover goes to the air filter case diagram F17, and the T connector 9 in the carbs as above goes to another breather valve in the air cleaner (also diagram F17.)

Disclaimer I have never been close to a hornet 250 :-)