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Hi all, 

Have a problem here that I need sorted by tomorrow night. Let me just say that the bike (2010 kx250f) was running like a dream (well, maybe a little lean) before any of this happened. Recently the throttle cable snapped which prompted me to replace it, no biggie. I had been running without a hotstart since I had bought the bike last year so I decided to replace it along side the throttle repair.

The bike came with no lever for the hotstart and I presumed that the cable was snapped (which it was). I bought a replacement cable and lever, no hassle. I pulled the tank off the bike to access the carb to replace the cable. I unscrewed the plastic screw that sits over the hotstart. There was no little brass cylinder (not sure if this is the plunger) or spring on the end of the cable or in this screw. There was no point in replacing the cable since I hadn't got the brass cylinder or spring so I left it while i fixed the throttle cables. I have now seemingly lost the black plastic screw leaving a little nipple like rubbery thing sticking out of hotstart port in the carb. I am presuming that this is the plunger which should be pushed into itself rather than sticking out. I didn't think of it as much of an issue at the time, but now with the bike back together, the carb is pissing out fuel, from what I think is the float overflow tube, every time I turn the fuel flow valve to open. I can now not get the bike started.. The only reason I can think of this happening is because the little rubber nipple is sticking out of the carb.

Can anyone confirm this or have any quick fixes that I can use? I cannot for the life of me find the plastic screw and will not be able to get one by Sunday

Below on the right, is a picture of the black plastic screw I was talking about.

 

hot start screw.jpg

Edited by Dylan Kilbride

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Nothing you described doing should of caused the float to stick or debris become lodged in the float needle seat unless you neglected to tell us you also removed the float bowl. In any case, you need to now and clean/check/service it.

The hot start is supposed to have a brass plunger (with a rubber insert in the bottom to seal when fully in), then a spring, then the 'nut -in your picture) and a boot and the cable. With nothing to hold the hot start plunger down, you are SOL. If you can source a spare choke assy, you can install it in the hot start cavity (same plunger and nut threads!)

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@William1 I haven't touched the carb other than pulling the plastic casing off the opposite side to swap out the throttle cables. The brass plunger and spring were never there when i pulled the nut off. The rubber nipple thing sticking out is the only thing that is different. I am assuming that it was pushed inwards before I took the nut off..

Are you saying that if I can source another choke lever, I can install it in the hotstart port? will that remove the need for a hotstart lever of is it just a 'quick fix'

Edited by Dylan Kilbride

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If.... the hot start plunger and related parts were 'never there' your bike should never of idled properly and dirt should been able to enter the carb (those are air passage ways). Some owners, in a ham fisted attempt at 'making do' have jammed crap in the hole to plug it up, perhaps that is what is going on with your bike.

If... you can ensure the hot start passage is clean, yeah, a choke assy will replace it fine (assuming you have the clearance). Some bikes use a knob instead of the cable/lever, the only difference between the choke assy and the hot start one is the knob color, the hot start ones are red. Dimensional wise, they are identical (though knob diameters vary some, but that s nit-picky).

If you never needed the hot start, yup, you are done if you replace with a knob. Keep in mind, your previous owner may of compensated (again, a ham fisted thing to do) by putting in a huge pilot jet, which now would be way too rich. Correct pilot for your bike, IIRC, is a #42.

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Okay I will have a look for a new choke knob then. I don't want to pull this rubbery thing out as I feel like I'm forcing it and do not want to break it incase it is important. Here is a pic of it. You might know what it is. It is sticking out of the hole just in near the centre of the picture. 

I doubt he changed any of the jets because the bike was running a tad lean since I bought it. Presumably because of the hot start being broken

14982463842901517829839.jpg

Edited by Dylan Kilbride

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24 minutes ago, Dylan Kilbride said:

 

Okay I will have a look for a new choke knob then. I don't want to pull this rubbery thing out as I feel like I'm forcing it and do not want to break it incase it is important. Here is a pic of it. You might know what it is. It is sticking out of the hole just in near the centre of the picture. 

I doubt he changed any of the jets because the bike was running a tad lean since I bought it. Presumably because of the hot start being broken

14982463842901517829839.jpg

Ugh!

I'll wager the plunger is in there and the previous owner jury rigged it in with globs of RTV or something. If it seems 'stuck', I am sure it will stay stuck until you fix it correctly. You can use a knob (hot start or choke) oinstead of the cable assy, only difference is color and the hot start knob only comes in 'large', IIRC

Getting the plunger out can be a pain, typical method is to scrap out the crap, being careful of the threads in the carb body. Then tiny vice grips in the shaft of the plunger and a firm straight pull. If the shaft snaps off, then you will need to use a slide hammer, probably wise to use PB Blaster for a few days to try and lube it up.

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That sounds about right alright... I've spent the last 10 mins scraping rubbery sh**e out of the carb and getting nowhere. I removed the choke to get a look at what the port should look like. I'm far from them looking similar.. going to remove the carb now and have a proper go at it. 

Thanks for the help! Will let you know how I get on or if I spot any more anomalies..

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After cleaning the bulk of the rubber out of it, this is what I'm left with. The port doesn't look in good shape. There is something mangled and bent inside.20170623_215408_001.jpg.37537de5f811f1789ae4caf88b3a508b.jpg

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Hard to tell but (hopefully) it is the remains of the old hot start plunger. It might be worth the $20 to have a machine shop remove it for you to prevent damage to the hot start bore.

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Possibly.. I'm not sure if the hole is supposed to be nearly identical to the choke port. If it is then it looks messy, if not, if the hole is a bit tighter and the hot start plunger is a smaller diameter then it is probably okay, just needs a clean. I'm collecting a choke assembly later today to just block the port. 

What, if any, implicatioms will it have on the bike if I block the port completely just temporarily?

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40 minutes ago, Dylan Kilbride said:

Possibly.. I'm not sure if the hole is supposed to be nearly identical to the choke port. If it is then it looks messy, if not, if the hole is a bit tighter and the hot start plunger is a smaller diameter then it is probably okay, just needs a clean. I'm collecting a choke assembly later today to just block the port. 

What, if any, implicatioms will it have on the bike if I block the port completely just temporarily?

It is supposed to look identical to the choke port. The last thing you want to happen is to damage the carb body. While you could probably re-block the hot start opening, that would be part of the birth of a frankenbike. I'd never be able to sleep at night! Blocked simply would mean you'd never have the use of the hot start. A hot day and a stall could leave you sitting for an hour waiting for it to cool enough to restart. With it working, you will restart in seconds.

The plunger is brass, and hollow, once the stem is removed/broken off, inside is a rubber plug - you've seen it on your choke. A lot of times, the brass plunger gets seized in the carb body from lack of use/poor servicing. It can be removed with skill and the bore burnished. But you have to be careful not to damage the carb body or those threads and especially be careful not to damage the port openings on the bottom.

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A Frankenbike haha! I like the sound of that funny enough:cool:. As I won't be able to get the choke plunger to fit by tomorrow, I'm going to just remove the plunger and spring and then screw in the plastic casing to block the port temporarily. I believe that since it was blocked before, if I block it again it should run as it was.. (open to correction). It was running a bit lean before so can I just adjust the fuel/air screw to richen the bike out? I can't see any flaws in this logic although I'm sure the seasoned mechanic is kicking himself:goofy:

How many turns should I go CCW to even the mixture back out?

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The fuel screw is just a very fine adjustment on the idle mix. 'Normal' settign on a fuel screw is about 1/75 turns from gently closed. Once past 2.5 turns, the screw is fully open and further opening does nothing.

 

C/P

Fuel Screw/Pilot Jet
Fuel screw settings in the 'book' are recommended starting points. Every bike is different, as is the temp and altitude. Set the screw according to this method. Do it with the bike fully heated up.
Gently turn the fuel screw all the way in. Now back it out two turns. Start the bike and fully warm it up, go for a 10 minute ride. Set the idle knob to speed to 1,500~1,800 RPM as best you can (I know, without a tach this is tough, just set it to were it idles relatively smoothly).  Once warmed, slow the idle speed (knob) to the lowest possible speed.
*** When turning the fuel screw, keep an accurate 'count' of the amount you are turning it and record it in case you have to reset it for some reason. Makes life easier when you can just set it from notes Vs. going through the procedure again.***
Turn the fuel screw in until the idle becomes rough or the bike stalls.
if it stalled, open the screw about 1/4 more turn. Restart it and slowly screw it in till you can just perceive a change.
If the screw can be turned all the way in and the bike still idles perfectly and does not stall, then you need to go down a size in pilot jet.
Now very slowly, open the fuel screw till the idle is smooth. Blip the throttle, let the bike return to an idle, wait say ten seconds. Confirm it is the same smooth idle.
If the screw has to be opened more than 3 turns to get a smooth idle, you need to go up a size in pilot jet.
If you find it does not stall with the larger jet but has to be open more than three turns with the smaller pilot jet, put the larger one in and set the fuel screw at 1/2 turn.
If the idle speed increased, adjust the idle speed knob to return the bike to a real slow idle speed. You must then re-visit the fuel screw. Keep doing this till the fuel screw is opened just enough to provide a nice steady idle at the lowest possible RPM. Once this is done, increase the idle speed to the normal one for your bike, typically about 1,850 rpm, but go by the spec in your manual.

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