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Hot starting trouble

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Hi, I'm pretty new to MX, but not new to bikes... I've recently bought an '08 Honda CRF250R, which starts ok I guess, but when its really hot, eg. after 10 mins use, it doesnt start well, and will need to rest for 5 mins. I'll use the hot start, and when it eventually does start again, the hot start does help, so I don't think thats completely knackered. Does the hot start just lean it out?

 

So I'm going to look at the valves/shims, and make sure the carb seems ok, but which way would help the bike start when hot: bigger or smaller shims? Or is it just a case of experimenting?

 

 

Thanks

Edited by Bufort

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Cold start procedure:

 

gas on / choke on / NO THROTTLE / kick slowly a few times / KICK HARD

 

If it's under 65 degrees F, it might take a pull on the thrrotte once or twice before kicking.

 

Hot start procedure:

 

NO THROTTLE OF ANY KIND / KICK EASY TILL IT STARTS

 

- try the choke again if needed.

 

If you can't start it this way, you have a valve clearance problem

 

...you also have to get an R&D remote fuel screw so once it's hot, you can properly adjust the fuel screw for the best running

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To add.... many people excessively richen the pilot circuit in the mistaken belief 'all bikes are too lean', that the pilot circuit will richen everything significantly and because they put on an open pipe and now it backfires.

I you can close the fuel screw and the bikes stalls, the pilot jet is not too rich. If it still runs, carefully remove it and check the size, it should be a 42 or a 45, no larger.

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What choke? I thought these bikes were set up for starting cold and therefore have the hot start to lean it when hot - opposite to a road bike where it's set up to start hot and therefore have the choke to richen it when cold.

It had a 42 jet but changed it to a 40 but had no effect. The bike doesn't have issues starting cold, doesn't backfire, and runs really well on the track.

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No.....there is a choke (Enricher) for cold start (black knob) and a hot start (red knob on the carb or a lever on the bars.) Sounds like your choke is either removed and in the 'open' position or you just do not realize how it works

 

Looks like someone failed to read the manual..................

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No.....there is a choke (Enricher) for cold start (black knob) and a hot start (red knob on the carb or a lever on the bars.) Sounds like your choke is either removed and in the 'open' position or you just do not realize how it works

 

Looks like someone failed to read the manual..................

 

I know exactly how a carb works, I've rebuilt many, and I was actually reading the manual last night before I posted here; the choke must've been removed then.

 

Can anyone answer my question then of which way I should adjust the shims, smaller or bigger, to help with a hot start? Or is it a case of it just has to be correct, to help with starting hot?

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Reinstall the choke.

Shims? What shims? There are no shims with a hot start.

If you are unsure what you are doing, have a pro look it over. It sounds like someone who had no idea what they were doing messed with it and no telling what else is wrong that can cause tail chasing. You need someone who knows what they are looking at to check your bike.

 

Fix what is known to be broken. Read the manual some more.

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What choke? I thought these bikes were set up for starting cold and therefore have the hot start to lean it when hot - opposite to a road bike where it's set up to start hot and therefore have the choke to richen it when cold.

It had a 42 jet but changed it to a 40 but had no effect. The bike doesn't have issues starting cold, doesn't backfire, and runs really well on the track.

 

What?

 

That statement is not rooted in truth or reality.

 

You should be running a 45 pilot jet, with the fuel screw adjusted for highest idle, then drop the idle with the idle screw.

 

You have a choke knob, and idle knob, a fuel screw and a hot start remote lever on the bars

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Hi Aidan,

 

This used to be my old race bike before I went over seas for a few years.  I came home. Serviced it and rode it a few times while my overseas bike was in transit. Just to clear a few things up:

 

  • the choke is present and nothing has been particularly messed with although I have installed an R&D float bowl, pilot adjustment screw and loud mouth air filter for him.
  • the hot start plunger was a little rough (but seemingly acceptable).  As was the hot start cable
  • by shims I think he's referring to valve shims.

 

The bike used to run strong and was a good starter.  Only thing I can think of is that the jetting is out of spec for time of year and/or passageways are partially blocked with fluff & debris?

 

I also used to run the exhaust valve clearances on the tighter side of allowable tolerances for less pounding (tuner recommendation who installed the ss intake valves).

 

What do you guys think about the possibility of over heating and dropping the bike fairly frequently?  He's not new to bikes but quite green to mx and the tracks he's been to have been tight and relatively slow going for beginners (1st / 2nd I might imagine).  I personally never discount the valves on these bike either as they can "move" anytime, although I would be very surprised. given the little time the reconditioned head has been ran for.

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Hi Aidan,

 

This used to be my old race bike before I went over seas for a few years.  I came home. Serviced it and rode it a few times while my overseas bike was in transit. Just to clear a few things up:

 

  • the choke is present and nothing has been particularly messed with although I have installed an R&D float bowl, pilot adjustment screw and loud mouth air filter for him.
  • the hot start plunger was a little rough (but seemingly acceptable).  As was the hot start cable
  • by shims I think he's referring to valve shims.

 

The bike used to run strong and was a good starter.  Only thing I can think of is that the jetting is out of spec for time of year and/or passageways are partially blocked with fluff & debris?

 

I also used to run the exhaust valve clearances on the tighter side of allowable tolerances for less pounding (tuner recommendation who installed the ss intake valves).

 

What do you guys think about the possibility of over heating and dropping the bike fairly frequently?  He's not new to bikes but quite green to mx and the tracks he's been to have been tight and relatively slow going for beginners (1st / 2nd I might imagine).  I personally never discount the valves on these bike either as they can "move" anytime, although I would be very surprised. given the little time the reconditioned head has been ran for.

Not valves. Valves closing up manifest as hard to start cold.

Based on his lack of valid information, we are shooting in the dark. Further attempts at helping are somewhat pointless as it is guessing and advising a person who has nary a clue. No offense as everyone is a beginner some time but this is a situation where he would be best served by visiting a local pro wrench and having someone who knows what he is looking at.

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Reinstall the choke.

Shims? What shims? There are no shims with a hot start.

If you are unsure what you are doing, have a pro look it over. It sounds like someone who had no idea what they were doing messed with it and no telling what else is wrong that can cause tail chasing. You need someone who knows what they are looking at to check your bike.

 

Fix what is known to be broken. Read the manual some more.

 

*shims for the valves, to help with starting it when hot - not the 'hot start' lever.

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I came home. Serviced it and rode it a few times while my overseas bike was in transit.

 

The bike used to run strong and was a good starter.  Only thing I can think of is that the jetting is out of spec for time of year and/or passageways are partially blocked with fluff & debris?

 

 

Hey Maxy Mouse, what's changed then between you using it and giving it to me? (other than my slightly lower use of throttle than you probably) Because don't forget, it's been like this since the first time I used it, so I hadn't damaged, dirtied, dropped or fiddled with it when it.

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There is no 'hot shim size' 

You are either in spec or you are not.

I know. I'm asking if making it tighter, or looser, would help when starting it hot.

 

Just like Max said he ran the exhaust valves tighter to help with something, perhaps running the inlet valves looser might help with starting it hot.

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I know. I'm asking if making it tighter, or looser, would help when starting it hot.

 

Just like Max said he ran the exhaust valves tighter to help with something, perhaps running the inlet valves looser might help with starting it hot.

 

I'm not sure where you are getting all this terrible information, because it is erroneous and pointless to follow up on.

They are not 'set up for cold or hot'. They don't have a 'hot starting vavle spec'.

 

You don't need to worry if they are in spec.

 

Your bike is easly as hell to start hot if the carb is maintained correctly.

In fact, you should never need the hot start at all unless you have stalled the bike under full engine load....

 

You are chasing a magic bullet....

 

We keep giving advice and asking you questions, but you don't respond.

 

I'm done

Edited by KRANNIE

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I'm not sure where you are getting all this terrible information

 

Nowhere, I didn't quote anyone. It was a simple suggestion, a thought.

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We keep giving advice and asking you questions, but you don't respond.

 

I'm sorry if I missed a question. Which question haven't I answered?

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Not valves. Valves closing up manifest as hard to start cold.

Based on his lack of valid information, we are shooting in the dark. Further attempts at helping are somewhat pointless as it is guessing and advising a person who has nary a clue. No offense as everyone is a beginner some time but this is a situation where he would be best served by visiting a local pro wrench and having someone who knows what he is looking at.

 

Good point about the valves / hot cold starting.  And i generally agree with the rest

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Hey Maxy Mouse, what's changed then between you using it and giving it to me? (other than my slightly lower use of throttle than you probably) Because don't forget, it's been like this since the first time I used it, so I hadn't damaged, dirtied, dropped or fiddled with it when it.

 

Thing is when i tuned the carb and used the bike i never needed (or ever used) the hot start.  Only using the choke on cold mornings/first start of the day.  Hot starting was simply a non issue.

 

I would warm the bike up.  Set a high idle.  Adjust the fuel screw until the idle was at it highest "sweet" spot (swapping pilots if the fuel screw would fall out of range).  Return idle back.  Do a wee ride.  High/top end plug chop inspection. Then that would be it generally.

 

I have had no troubles operating the bike during my ownership.....and since selling it on its started ok for me all those months ago?  I also rarely crashed and then immediately tried to start a downed and hot machine.

 

  • Hows your starting technique?  Have you researched how to start a hot carburetor equipped thumper?  For instance: Sometimes holding the throttle wide open for a few seconds can help get cooler air to the engine (not blipping the throttle, that'll chuck loads of fuel via the accelerator pump into the inlet manifold).  Are you actually doing TDC based nice long steady strokes and not touching that throttle.  Have you got the "feel" yet?  Trying to start it while tired?
  • Does the throttle have a wee bit of play in it with bars locked left and right?
  • Have you dropped the hot bike that was under load/throttle and tried immediately starting?
  • Have you had the carb apart?
  • Seeing as this is apparently a hot start issue have you looked into the hot start mechanism, how it works and its operation?
  • Start the bike on the stand and let it warm up.  Hit the kill switch and then try to start.  How does that work out?

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