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Motor starter has probs after rebuilding engine

This is a discussion on Motor starter has probs after rebuilding engine within the Technical forums, part of the Caferacer.net Forums category; I managed to get him to run again! First I checked in the cilinders with a flashlight if the valves were popping in and out ...

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Thread: Motor starter has probs after rebuilding engine

  1. #11
    Junior Member daansteegmans's Avatar
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    I managed to get him to run again! First I checked in the cilinders with a flashlight if the valves were popping in and out at the right times, which they did. After that I put some oil in the cilinders and gave it some turns which made him run but only when putting some fuel directly IN the cilinders. he seems to not pull in fuel on his own.. I did change to K&N pod filters instead of the airbox and just ordered a main jet size of 137.5. What other reason could cause it not to pull in fuel on his own? Hope it's ok to change the issue here

  2. #12
    Senior Member TrialsRider's Avatar
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    Is your thread, do whatever you want!

    Don't go chasing carburetor jet sizes thinking that will make the difference of sucking fuel or not, it don't work that way, your engine draws in fuel and air mix as the result of the vacuum that is produced during the intake stroke of the piston.

    The carburetor is little more then a toilet tank (that's your float bowl) and a spray bottle (that's the part that atomizes the correct amount of fuel into the intake path) if your motor is producing vacuum at the correct time (intake valve timing) then one of those other 2 things is still a problem.

  3. #13
    Senior Member scramblermike's Avatar
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    When you had the carbs off the bike did you plug the intakes with a cloth and when you reinstall the cards forget to take them out? Seen that a few times over the past couple years the people in a rush to get their bikes up and running and leaving them in

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  5. #14
    Junior Member daansteegmans's Avatar
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    @scramblermike I took the cloths out, would have been funny tho hehe
    @trialsrider apparently they do suggest to change the main jet after switching to pod filters from an airbox? and 137.5 should be a good size to get they say?
    maybe cleaning my carbs out could fix this issue.. i'll keep you guys posted!
    Thanks again

  6. #15
    Senior Member TrialsRider's Avatar
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    Good, hurry up I want to see pictures of it jumping over shit.

    oh wait, you probably don't jump over shit with that bike, I just want to see it ...
    what are you going to do with it again? do you do wheelies?
    Last edited by TrialsRider; 09-29-2019 at 05:21 PM.

  7. #16
    Junior Member daansteegmans's Avatar
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    Hahah yea I might go into trial biking and otherwise i'll try moto gp with it

  8. #17
    Junior Member daansteegmans's Avatar
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    Quote Originally Posted by TrialsRider View Post
    Good, hurry up I want to see pictures of it jumping over shit.

    oh wait, you probably don't jump over shit with that bike, I just want to see it ...
    what are you going to do with it again? do you do wheelies?
    Hi guys, I started working on the bike again last weekend. I cleaned out the carbs and mounted my nice pair of k&n filters on it. Still when trying to start it now it doesn't run without the choke. Apparently this means my pilot/idle jet is clogged but I'm sure I cleaned that jet and the whole passage with some compressed air.. Is there another reason why this could be happening? Pilot jet is unchanged from the standard, main jet is 137.5 now.

    Cheerios!

  9. #18
    Senior Member TrialsRider's Avatar
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    Quote Originally Posted by daansteegmans View Post
    Hi guys, I started working on the bike again last weekend. I cleaned out the carbs and mounted my nice pair of k&n filters on it. Still when trying to start it now it doesn't run without the choke. Apparently this means my pilot/idle jet is clogged but I'm sure I cleaned that jet and the whole passage with some compressed air.. Is there another reason why this could be happening? Pilot jet is unchanged from the standard, main jet is 137.5 now.

    Cheerios!
    I found a copy of the owner manual, that says there is only 2 things you can set on the carburetor, idle and throttle cable slack.
    Found a writeup on cleaning those POS CV carbs: GS450_Carb_Rebuild_Guide

    Symptom you described suggests a plugged pilot jet. ... you have 2 carbs,
    is there anything such as heat coming off the motor or out both exhausts to confirm that it is operating on both cylinders but carburating equally poorly?

    Odds of that are slim unless you are not cleaning either of them sufficiently. There are a slew of videos out there on the subject,
    here is one picked at relative random, is not great but not bad either. https://www.howtomotorcyclerepair.com/onlyrunsonchoke/
    in the video he has the advantage of only 1 carb to deal with.


    "
    nice pair of k&n filters on it"
    Pod filters? no airbox? no velocity stacks? no intake plenum? Still trying to make that work on constant velocity carburetors and a free flow exhaust?
    :/ you are probably still spinning your wheels, I doubt it has ever been made to work well given those parameters. Your vacuum operated carburetors might not even be moving the slides yet if it is running only on the choke circuit.

    When it is running on the choke I assume only at idle and you slowly apply some throttle, what happens?
    Last edited by TrialsRider; 10-19-2019 at 09:03 PM.

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