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Older BF100, BF75, or 8HP Carb Jet and Fuel Pump Questions

J

jduck1

Contributing Member
Honda BF100, BF75 (7.5hp), or 8 hp motor carburetors? According to the manual #88 is the main jetsize.
Why all the other size jets listed?
Any HP upgrade by using a different # jet?

On the older models that have a fuel pump metal cover (Coverattaches to the valve cover and is chrome). Older models are the only ones whohave the cover. Is it necessary to have the cover or what is the purpose of thecover?
There are 2 styles of fuel pumps. Can either style be usedon the late 70’s early 80’s motor (Points or CDI)?
 
I don't know specifically for the motors you have but I do know that jet options exist for other motors for the purpose of tuning the carbies to run at high altitudes or possibly very hot/cold environments.
 
OK. So is there any guide that tells what jet for what situation? I am in the Sierra Nevadas near Tahoe and often run my motors at 5,000-8,000 ft elevation. They seems to run fine at that altitude but could I get better performance for a jet change?
 
I don't know for your engine. It may be in the service manual or someone with access to that info may be able to tell you on this forum. For thinner air (higher altitude) the jets get smaller to keep stoichiometric mixture. I don't believe that the numbers on the Jets have a proportional relationship to the size of the jets for honda though so be careful. Ie. A #88 is not necessarily larger than a #75.
 
Between 5000 and 8000 ft, if your standard main jet is #88, you should change it to #85.
Needless to say, the engine will not have the same amount of power as running the standard main jet below 5000 ft......but the air fuel mixture will be better and keep it from running too lean.

In some cases, you may have to change the prop to a lower pitch (if it is available) to keep the rpm's up....depending on the boat size.

Mike
 
Thanks Mike. Would #85 work on both a BF100 and BF75? I have read posts that some think the jet is different size on the 10hp and 7.5hp and besides the cam is the reason for extra hp on the 10hp compared to the 7.5hp.

Also any help on necessary to have the fuel pump cover on these motors? What is the real purpose of the cover as no new models even came with them?

Thanks again for all the help.
 
If your either motor standard main jet is #88, then #85 is what you use between 5000 and 8000 ft. I understood from your post that the standard for both was #88. If not, let me know. That one will need a different size..

As for the cover on the fuel pump...I do not know. I would only guess that in the early days, Honda thought the fuel pump had to be protected, but learned over time that they do not (and it eliminates a part and cost to not have it).

Mike
 
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