Another AFP vs. Precision Question

I like the idea of the AFP FI system because of the purge valve, an option that is designed to facilitate hot starts. However, I've been told by someone who I would consider to be knowledgable on the subject, who said that hotstarts with the Precision are not really an issue, due to the state of the art, and the quality of the entire system. Also that the Precision system is much more common and would be more familiar to your average A&P. I'm interested in what the real world experience has been. Are hot starts a problem with the Precision FI system? If you've put in a Precision, would you go with the AFP if you had it to do over again? Finally, any comments good or bad on each company's customer service?

Thanks

I have the Precision FI and have no problems at all with hot starting here in Georgia in three summers of flying. I would not let the existence of a purge valve be a deciding factor in your decision.

My Superior manual contained the following hot start procedure that works like a charm.

1) NO prime.
2) Throttle full open.
3) Mixture full rich.
4) Throttle closed.
5) Mixture ICO
6) Throttle cracked 1/4 of an inch.
7) Engage starter.
8) When engine fires, bring in mixture.

I never sweat having to hot start my RV. I have yet to see a need for a purge valve. I understand the concept and the theory but for me it's just another potential failure point the fuel system.

No regrets at all with my decision. I would install a PA FI system on my next RV.

Hope that helps,
Jamie

Not to sway your decision - but in the (granted, relatively unlikely, but extremely ugly) chance of a vapor lock scenario on approach, you have the additional tool of the purge valve to flush fuel through the pump, delivery lines, and injector body for a few seconds to purge the vapor bubble and regain power.

I'll be using wing-root electric pumps so that won't be an issue. Just sayin'...

I don't have the purge system and once I learned the right procedure I've not had any trouble in almost 200 hours of flying.

I DO prime the engine a little when hot, then move the mixture control to idle cut-off and leave the throttle wide open. Crank it over and when it fires move the throttle back to about 1/3 throttle and then slowly move the mixture control back to rich.

If I had a Bendix or Precision system and it needed service, I'd send it to Airflow.

As for the purge valve, Don just announced the availability of a new no-purge AFP system.

Service !!!

Yea, I bet Precision won't flow test your air box designs for free

BTW Dan, 2nd design A OK. Report on the way.

Don

Don at Airflow said:

Yea, I bet Precision won't flow test your air box designs for free

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That's for sure, but I was thinking more about the new Precision carb I pulled apart for leaking at the body joint. Significant machining error; it went back to them and came back uncorrected. 'Nuff said.

Until someone from Precision Airmotive finds this site and logs on, the outcome of any debate re AFP versus Precision, will inevitably be somewhat biased in favour of AFP.

Dogtail2 said:

Until someone from Precision Airmotive finds this site and logs on, the outcome of any debate re AFP versus Precision, will inevitably be somewhat biased in favour of AFP.

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Both good products, but yes the balance will tilt in favor for the company that has better customer service.

Don at Airflow has always been helpful by phone and email and always quick to provide information. I'm very satisfied with their product too. I have not dealt with the other guys so cannot comment, but I don't see how they could be any better than Airflow.

The value of good customer service cannot be calculated.

When I was trying to figure out what to do for my fuel delivery system Don was kind enough to stay late while myself and two other RV friends (Is there any other kind of friend?) met him at his shop.

Don was very gracious and spent a lot of time talking about the different types of fuel injection, carburetors, accessories, etc.

When I change my carburetor to FI, you can bet it will be one of Don's!

AFP

airguy said:

Not to sway your decision - but in the (granted, relatively unlikely, but extremely ugly) chance of a vapor lock scenario on approach, you have the additional tool of the purge valve to flush fuel through the pump, delivery lines, and injector body for a few seconds to purge the vapor bubble and regain power.

Click to expand...

Uh... not a good idea to pull the purge valve in flight unless you want ad hoc glider lessons... Use the electric boost pump during takeoff and landing phases to prevent any unlikely vapor lock conditions and to provide redundant pump operations.

AFP recommends engine shutdown be done using the purge valve as it kills system flow and pressure immediatly. By design, this saves wear and tear on the servo mixture plates/mechanism, as there is always a small bit of fuel flow there to lubricate the parts. So use of the mixture control for engine shutdown is not all that effective.

I would also second that AFP has excellant customer service. Don is always accessable to discuss any issues or make recommendataions. The only other recommendation is to add a return spring to the purge valve, so that an in flight purge valve control cable breakage doesn't cause engine shutdown.

After flying both AFP and Bendix/RSA/Silverhawk injected machines, they all have their own slight idiosynchrasies for cold and hot starts. Both are easily learned with a little procedure review and instruction.