GT250 Engine rebuild, but not starting

[Micron]

Hi all,

A newby, from the UK.

I have recently rebuilt a GT250 engine, it have the crank seals and bearing replaced, then all the other seals and gaskets replaced as it was rebuilt.

I didn't put the engine back in straight away, but once I did, and put everything back, I put a new battery on it, new fuel, connected up the electronic ignition, and gave it a go.

But nothing , it's like it doesn't want to even try, it has a spark, and fuel appears to be getting in to the ports, but no joy?

So I'm after ideas of what could be the issue?

Thanking you all in advance

Trev

[rngdng]

Squirt some gas down the spark-plug holes and kick it over. If it fires, you know it's a carb issue. The choke and pilot circuits are very small and can be clogged.



Lane

[sportston]

Swap the plug leads over? Sometimes they get connected the wrong way round after a rebuild
Check it is not being flooded with too much fuel. Are the floats in the carbs set to the right level?

[Micron]

I did swap the plug leads round, as someone on the RD owners club suggested ( I own one of those too), and it fired up, but would not tick over, then it stopped and hasn't really been running since.

I did notice that the left hand back was oiling up a lot, and I noticed that fuel was leaking out of the same carb.
I took the carb off, and removed the bowl, as I had looked at this one before, and I wasn't sure if I had put the floats back correctly, I need to take the other off to make sure? The fuel isn't leaking anymore, but who knows why?

So any ideas as to why one plug oils up and the other doesn't, i'm getting a spark on both plugs?

Thanks for the replies, much appreciated

Trev

[sportston]

I did swap the plug leads round, as someone on the RD owners club suggested ( I own one of those too), and it fired up, but would not tick over, then it stopped and hasn't really been running since.

I did notice that the left hand back was oiling up a lot, and I noticed that fuel was leaking out of the same carb.
I took the carb off, and removed the bowl, as I had looked at this one before, and I wasn't sure if I had put the floats back correctly, I need to take the other off to make sure? The fuel isn't leaking anymore, but who knows why?

So any ideas as to why one plug oils up and the other doesn't, i'm getting a spark on both plugs?

Thanks for the replies, much appreciated

Trev

aha. So it is a combination of things. Sounds like you have carb problems now you have fixed the ignition problem. If fuel is leaking out of the carb, your float valve is not closing. Either you have dirt in the valve, it is badly adjusted or you have a damaged float.
Solution:-
Strip the carb
Inspect the float needle. Does the end cone have a ridge on it due to wear? If so you need a new one.
Is there a chunk of debris stopping it from closing?
If the needle and seat appear clean and undamaged, inspect the float. Does it have any fluid inside it, indicating a hole? Is it bent?
If nothing appears damaged, dirty, bent or worn, strip the entire carb removing every jet, adjuster and needle and blow it all out on a high-pressure airline making sure you do it thoroughly, blowing air through every hole and aperture (this is to save you finding out later that you have a blockage due to disturbing a small piece of dirt whilst working on it. Trust me, this is not a waste of time).
Then rebuild the carb leaving the float assembly until last.
Now assemble the float assembly and set the float height by carefully bending the tang on the float that presses against the float needle to the exact level your workshop manual specifies (even 1mm out of spec can cause you serious hassle). On some carbs you have to set the level with the carb upside down on the bench. On others you do it with the carb on its side. Your Haynes manual should tell you which is right for your model.
Before you connect your clean and correctly adjusted carb to the fuel supply again. Make sure you have an inline fuel filter installed. This is an essential item on any classic bike if you want to avoid running problems and recurring headaches.
Balance your carbs by checking that they both open equally at idle and when you open the throttle.
Adjust the pilot air screw by turning it out about 1.5-1.75 turns (you can fiddle with it more later once you have it running, if necessary. Your Haynes manual may tell you how many turns it should be for your particular model, but it is only ever a rough guess for DIY mechanics. The best way to set it is using a gas analyser, but most folks don't have that).

Good luck
Tom

[Micron]

Wow thanks Tom, I'll need to plan that in as I've a busy few weeks coming up so please don't think I've ignored your advice etc.

Also thanks for the PM, and hopefully you can save me a lot of headaches

Trev

[sportston]

P.S. I have a gas analyser. Its not portable though, it is built in to my Crypton machine, which is way too big to put into the boot of my Celica. If you wanted me to check the carb settings for you, bring the bike over to my place and I'll have a look and make sure they are well balanced. I also have a compressor for blowing out carbs with. Non-starting and tuning is my forte. I used to do it for a living. So if you get stuck, you've got my number.

[Micron]

Hi Tom,

Thanks for the offer, I may take you up on some of that, although I do own a compressor. I will have to work out how to get it to you?

I did reply to your PM, but you have not looked at it as yet?

[jabcb]

What model year is your motor?

The ignition timing varied depending on the model year. Things got screwy in 1976 when they updated the motor & changed the timing.
See this service bulletin if you’ve got an affected motor: http://www.ozebook.com/compendium/techb ... 027-33.pdf
Some years ago I bought a sweet 76 GT250 that had new crank seals. Was F***x# hard to kickstart because the timing was too advanced but was fine after I set the timing.

Check the carb sides to make sure you don’t have them switched & in backwards. (A common mistake.)

I had a problem with an ignition wire on a GT750 this spring. The affected plug was barely getting wet so I was thinking the worst.
But when I fixed the problem, that cylinder ran fine & the bike turned into a smoke signal generator till it cleared out the excess oil. My driveway was actually getting cloudy.
Similarly, your right cylinder might just has way too much oil/gas in the bottom end for the pumping action to be effective.

If you bought new floats or had to make big float level adjustments to get them is spec, then your fuel levels may be way off.
See: viewtopic.php?f=9&t=13045
And see: viewtopic.php?f=2&t=11656&hilit=float&start=6

Also check to see if your petcock is leaking. A leaking petcock can flood a GT250 to the point that gas is dripping out the exhaust.

[Micron]

Jabcb, I'm not 100% sure what model it is, as based on another post of mine, it might be a L or M, but with an A engine, as it has the paintwork for a L or M, but an A engine, no Ram-air?

I have printed off the relevant pages and will take a look as soon as I can.

I have to say that everyone is most helpful, thank you

[Micron]

Well, it now runs , my mate and me took the crabs apart and gave them a clean ( maybe not the full works, but better than they were ) we then tried it, and it started, but it was only running on one? Tried each plug for spark, and one wasn't working, it has an electronic ignition on it ( Newtronic ), so I did the paper test, and both sparked, then I looked at the rotor plate, and it seemed that one wasn't being covered as much as the other, so I swapped them around, tried it again and it was firing on both, happy days

BUT, that is where the happy pills wear off, because when it is under load it just goes blah! ( technical term ) it really seems to suffer, but will tick over fine, and you can rev it up ok whilst stationery?

I don't claim to have everything set up as it should be, so I am looking for some more expert advice

Thanks

Trev

[sportston]

when it is under load it just goes blah! ( technical term ) it really seems to suffer, but will tick over fine, and you can rev it up ok whilst stationery?
Trev

Could be a number of things. Most likely, but not definitely, by the sound of your symptoms, is fuel starvation.
Did you set the float height correctly?
Are the needles set to the correct height?
Is the air filter installed, clean and oiled?
Are there any inlet air leaks? (check by spraying Easy Start around the intake flanges and any vacuum pipes while the engine is running. If you have a leak, the engine note will change when you spray)
What colour are the plugs? If they have been oiled up or are sooty they may be misfiring.
Is the timing correctly set?
Are the plug caps a nice tight fit at both ends and have no cracks or signs of corrosion?
I suggest checking all of these. When diagnosing and tuning it doesn't pay to skip these checks. You cannot tune carbs if the ignition is bad and you cannot tune the ignition if the fueling is bad. One fault in any of these things buggers up other things. e.g. An over-fueling carb can permanently kill your nice new spark plug quite rapidly.

[Micron]

when it is under load it just goes blah! ( technical term ) it really seems to suffer, but will tick over fine, and you can rev it up ok whilst stationery?
Trev

Could be a number of things. Most likely, but not definitely, by the sound of your symptoms, is fuel starvation.
Did you set the float height correctly? yes we did
Are the needles set to the correct height? don't know, not sure how to check that one, but we did set the float height correctly, so they move together, balanced shall we say
Is the air filter installed, clean and oiled? yes it is fitted, but no not oiled, so I will do that
Are there any inlet air leaks? (check by spraying Easy Start around the intake flanges and any vacuum pipes while the engine is running. If you have a leak, the engine note will change when you spray) not sure, will have to check, ok daft question, where are the vacuum pipes
What colour are the plugs? If they have been oiled up or are sooty they may be misfiring. plugs appear to be ok,
however I will check them again after giving it a little run
Is the timing correctly set? Apparently I need to check it with a strobe light?
Are the plug caps a nice tight fit at both ends and have no cracks or signs of corrosion? I will double check, but I believe they are ok
I suggest checking all of these. When diagnosing and tuning it doesn't pay to skip these checks. You cannot tune carbs if the ignition is bad and you cannot tune the ignition if the fueling is bad. One fault in any of these things buggers up other things. e.g. An over-fueling carb can permanently kill your nice new spark plug quite rapidly.

Answers above, so still a bit of work to do!!!

As I've never done it before, i have one question about timing and electronic ignition, it it done in the same way, as it would be if it still had contacts?

[sportston]

1. You often can set electronic ignition timing static like you may have done with points before, that would get you close enough. Doing it with a strobe light whilst the engine is running is slightly more accurate.
2. Vacuum pipe may be used to connect your petrol tap to the inlet port between the carb and the barrel.

3. To check needle height, (i didn't mean the float needle) do this one carb at a time;
a. remove the slide from the carb
b. disconnect throttle cable and remove carb top and spring from slide
c. remove retaining clip from inside the bottom of slide
d. remove needle.
e. on many bikes, on the needle you will see three grooves at the top with a c-clip inserted into one of them. Depending on the model the c-clip must be placed in the correct groove. Check your workshop manual to tell you which groove is right for your bike.

4. When you double check plug caps, unscrew them from the HT lead and check for corrosion or signs of arcing (blackening) on the end of the lead and in the cap. If it is bad, replace the cap and shorten lead until you get to fresh clean copper

[Micron]

I would just like to start by saying Aaaaaaaarrrrrrrrgggggghhhhhh!

So we did everything except the timing, as my strobe light didn't seem to work?

But, the bike is no better, and We are loosing the will to live as they say, I know I shouldn't give up that quick, but it is a bit argh!

So where do we go from here?

I am assuming that the carbs ( see pics below) are from a 250A. If they are then is there anything in particular that I need to look at? And what carbs are they?

Tom, I think I need your help!