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post #1 of 25 (permalink) Old 01-16-2016, 03:15 PM Thread Starter
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Fuel injectors

I have a 58mm throttle body on my bike i was running 4.22 injectors the bike was not smooth up to 30 mph i put 5.3 injectors in the bike now it runs smoother i was wondering if the 4.22 were not letting enough fuel in at low speeds


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post #2 of 25 (permalink) Old 01-17-2016, 01:15 AM
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Low speed shouldn't be the issue and the stock injectors should be sufficient up to all but the peak power. Larger injectors are needed at higher throttle openings when the injectors can't flow enough to support the airflow and power created by the motor. Injector duty cycle can be measured on a dyno. Generally if you are breaking 80% duty cycle on an injector you should bump up to the next larger size. Since you are running the ThunderMax the issue may be that the base tune has been designed with the larger injector in mind.

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post #3 of 25 (permalink) Old 01-17-2016, 10:54 AM
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I used the stock injectors on my 58mm TB and didn't have any issues so I would think it would be in your base map. I had to use a base map for stock injectors.


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post #4 of 25 (permalink) Old 01-17-2016, 11:23 AM
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HD recommends to upgrade your injectors when you surpass the 100HP threshold.


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post #5 of 25 (permalink) Old 01-17-2016, 12:19 PM
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Yes they do but any build that HD has also states for "RACE APPLICATION ONLY" so that means you are running full throttle more often than not.
The stock injectors work just fine with a 58mm TB if you use the right EFI map and the only thing it would affect would be the top end performance.
In all reality the 50mm TB works just fine on any 103 stage 4 build.


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post #6 of 25 (permalink) Old 01-17-2016, 03:02 PM
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Quote:
Originally Posted by ironmark View Post
Yes they do but any build that HD has also states for "RACE APPLICATION ONLY" so that means you are running full throttle more often than not.

The stock injectors work just fine with a 58mm TB if you use the right EFI map and the only thing it would affect would be the top end performance.

In all reality the 50mm TB works just fine on any 103 stage 4 build.

That makes sense. HD's guidance is kind of misleading in that both pre-2014 103 stage IV kits come with the 58mm TB. Both are expected to produce upwards of 100hp, but only the race application comes with the bigger injectors.


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post #7 of 25 (permalink) Old 01-17-2016, 06:03 PM
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I have stock injectors with a 54mm TB in my 107 , runs awesome


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post #8 of 25 (permalink) Old 01-17-2016, 06:32 PM
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Fuel injectors

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Originally Posted by Nordic Berserker View Post
I have stock injectors with a 54mm TB in my 107 , runs awesome

Same here, injectors that is. I have the street legal version of the 103" stage IV. It came with the 58mm TB. My stock injectors have worked fine for me. Makes 110hp.

Looking to move up to 120 soon. I assume I'll need to upgrade injectors then.


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post #9 of 25 (permalink) Old 01-17-2016, 06:51 PM Thread Starter
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My bike makes over 100 hp i didn't notice a gain when i changed my injectors just ran better a lower speeds might be because of the cam 585 with higher compression


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post #10 of 25 (permalink) Old 01-18-2016, 12:17 AM
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Have you dyno'd the bike yet?

The only difference that you will find from the larger injectors is a slight change in peak HP. Low speed manners are tune related. The stock injectors are more than sufficient to feed enough fuel for the lower RPMs.

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