Honda BF75L 7.5 HP 4 stroke hard to restart when hot

Andreea

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May 26, 2018
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Hi
I just purchased a Honda BF 75 L 4 stroke. Changed the oil , replaced t-stat and impeller, cleaned up the carburetor , replaced the spark plugs all basic stuff. I will start the motor , no problem , it will run with no problem , idles ok but if I kill it after running and getting hot up it is extremely hard to restart it. Not sure if this is related but I've noticed that if I run it at hi RPM and QUICKLY throttle it down to idle it will die on me. If I throttle it SLOWLY to idle it will not die and will idle perfectly
Any idea what could be the cause of such a hard start when hot?
Regards
D
 

Andreea

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Thanks a lot for the response. Mine has the CDI system , i am fairly new at this, i don't think has points and condenser.
Thanks a lot
D
 

Sea Rider

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What's the idle rpm with engine sufficiently warmed up of when throttling down after running at high rpms for some minutes?

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Andreea

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Thank you all . I don't have a tachometer (yet) so I am not sure what the RPM is. However I start the motor in " start" position , let it run for a few minutes then I turn it down to "shift" ( idle) with no problem maintaining the RPM . I I keep running there is no issue . Only i I shut it off and I try to restart I run into issues as the motor is extremely hard to restart.
racerone : I am sorry but what valves should I check for clearance?
thanks a lot gentlemen
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Andreea

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racerone Thanks a lot for your patience, As you can see I am pretty green at this : how do I check the clearance and what am I looking for ? Thanks a lot
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Sea Rider

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racerone Thanks a lot for your patience, As you can see I am pretty green at this : how do I check the clearance and what am I looking for ? Thanks a lot
D

If wanting DIY work along being tech inclined will need a service manual to start with. If motor runs fine and has only restart issues it's not a valve related problem.

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Andreea

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Thank you SeaRider. Totally agree that having a service manual would help a lot. The motor is old and to be honest I don't know where to get a manual ( according to my research is a '85). As you stated the issue is when I try to restart it. I have used the same spark plugs i have found in it. Is it possible that due to intense heat in the combustion chamber the gap to change or maybe the motor runs too rich ,un burnt gas to make the spark plugs wet ? It is probably something not very complicated but I need a start point. I will clean the carb again and give it another try. Just in case, what is the procedure to check the valves clearance and what values am I looking for? Thanks a lot for your help
Happy holidays everybody
D
 

pvanv

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I have checked valve clearances on tons of small 4-strokes, but have never needed to adjust them. Try opening the throttle for more air when hot restarting.
 

Sea Rider

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That's a 7.5 HP-OB, right ? Try what Paul suggested, if doesn't work...

Without a tach it's impossible to know at which rpm the OB is idling at. Try this : With OB sufficiently warmed up after a cold start adjust idle rpm carb screw bit higher say + 25-30 degrees to a point that when gearing forward will still hear a soft gear box clak sound. Go for a water test, report your findings....

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Andreea

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Thanks a lot gentlemen
i will follow your advice .
Priority #1- Service manual
Priority #2- tachometer.
Happy holidays
D
 

Sea Rider

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My priority would be to get a high quality Tiny Tach or Hardline hour/tach in first place, could be that that OB is way low on idle rpms and it's as simple as to increase idle rpm a bit, a tach will tell...

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Andreea

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searider Thanks a lot. You are probably right on point , my confusion comes from the fact that the OB , once started runs without hiccups in idle ( I assumed that the idle RPM are in the correct range ) also please correct me if I am wrong , i'm still pretty new at this, but when I start the OB the throttle is in " Start" position which , once the OB starts gives me higher RPM. Please don't get me wrong , I really appreciate your and everybody else's help , just trying to get familiar with this little "beast"
Best regards
D
 

Sea Rider

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It's quite normal for any outboard to increase its idle rpm to at least 2000 rpm specially if set at the starting position, there the carb is opened more than at idle position which works at ralenti at around 800 revs. If the higher rpm bothers you, let engine stabilize its rpm when at the starting position for say 20 seconds, then move throttle to idle position and let OB warm up for at least 3 minutes before normal forward operation.

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