Stalls when warmed up

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Stalls when warmed up

This is a discussion on Stalls when warmed up within the Honda CRF70 forums, part of the General Talk category; Background: Having an issue with my bike. I recently picked it up and know it had been sitting for awhile. I could start it but ...

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  1. #1
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    jamesfl's Avatar

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    Stalls when warmed up

    Background:

    Having an issue with my bike. I recently picked it up and know it had been sitting for awhile. I could start it but it was running rough so I cleaned the carb including the jets and set the valve lash to 0.05mm. The needle is set at 3rd notch from the top and the air filter is clean.

    Once I did all this I was able to start the bike in 1 or 2 kicks with the choke off. It's 80+ degrees here in Florida. I adjusted the air/fuel screw and set the idle. I do occasionally get a little puff of white smoke coming back out of the air filter when starting but I am running rec gas with Sea Foam.

    Now the issues:

    While riding the bike, it will sputter like it wants to back fire when you let off the throttle.

    The main issue though is that once the engine warming up it dies. I can only get it started again with the choke on. If I try closing the choke, even slowly, I can hear it sucking in air a then it dies.

    Any idea what the issue/s might be?

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    kirrbby's Avatar

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    Try opening the vale lash a smidge. As if thermal expansion is causing the valves to leak when the stems get hot. Especially the exhaust valve.

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    dirtbkr188's Avatar
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    Popping on decel is usually indicative of a lean condition, quite possibly your carb passageways are partially blocked, and/or you have an air leak in the head/manifold area or the carb/manifold area. While maintaining a steady idle, spray some brake or contact cleaner in the above mentioned areas, and see if there is an increase/decrease in RPM level, then a return to steady idle. If that happens, you usually have an air leak
    - dirtbkr188 -



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    Thanks for the suggestions guys. I would try them both now, but getting ready to take my son to the Mini Motor track for the 1st time!

    Dirtbkr you might be on to something about the leak. I thought I could hear a sucking sound but could not isolate where it was coming from. Even tried removing carb from the intake manifold to check the condition of the heat spacer.

    I will update after checking things tomorrow.

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    dirtbkr188's Avatar
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    Just an FYI, a light coating of engine oil or wheel bearing grease on all of the gaskets and/or o-rings in both of those areas will help make a seal and eliminate them as the source of the leak.
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    Awesome thanks for the tip

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    We missed practice day due to a change in scheduling so...

    Tried spraying brake cleaner in both areas dirtbkr recommended with no apparent change in idle. Figured I would try that before loosening the valve lash a tad as kirrbby recommended.

    The bike is now smoking with smoke also coming out from between the crankcase and cylinder head and the values tapping seems louder than yesterday. I am guessing I need new piston rings but as I said I am learning as I go and need your expertise. Tried to upload a video but keep getting an error. I can try PM'ing the video if someone can help.

    Please tell me what you guys think.

    BTW, I do have a new pz20 carb and petcock being delivered tomorrow to try and address fuel leak issues.

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    Is it a leak where the pipe goes into the head? Possibly the pipe flange isn't seated flush with the gasket, and you have an exhaust leak?
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    Stalls when warmed up

    I only checked both sides of the intake manifold. I will pull the exhaust and reinstall it as well as loosen the valve lash today.

    Still can't post the video. Says can post due to a network error.
    Last edited by jamesfl; 04-02-2017 at 08:14 PM.

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    Stalls when warmed up

    Think I may have found the potential problem.

    Went to install the new carb (20mm).


    Removed the intake spacer to apply some grease as dirtbiker recommended to make sure it isn't leaking. That's when I noticed this.


    It appears the spacer is a 17mm spacer.


    On top of that the intake manifold looks to be either a 25 or 26mm intake.

    I have a 22mm Takegawa intake manifold I was going to try but unfortunately it is straight and not angled so I would not be able to fit the carb.

    Do you think this could be causing the issues I described?
    Last edited by jamesfl; 04-30-2017 at 10:21 PM.

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    You can do one of two things here, IMO...

    1. Use one of these to enlarge the hole in the insulator, or

    2. Bolt the carb right up to the manifold without the insulator, just put a little grease on the carb o-ring before bolting it up.
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    That or order a 20mm insulator and gasket off of eBay or Amazon.

    Do you think that the insulator was mostly likely culprit then?

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    Quote Originally Posted by jamesfl View Post
    Do you think that the insulator was mostly likely culprit then?
    That's hard to say, but, if you try it without the insulator and it works alright, then you would know it was the culprit.
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  16. #15
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    I haven't had a chance to ride the bike again since replacing the intake spacer, carb, and tank but I did noticed a spot of oil under the front of the motor yesterday. The bike has been on a stand with the front tire on the ground so the engine is tilted slightly forward.

    It appears the drop of oil came from the exhaust port on the head.

    Would this be normal when an engine is stored in this position or is a sign I may need new piston rings?

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